AsturiaNOTES Lecture 6&7: Brainstem · PDF fileLecture 6&7: Brainstem Neuroscience1: Entire 2nd shift: Midbrain, Pons, Medulla, CNs ... Cranial Nerves 3-12 (the last 10 cranial nerves)

Lecture 6&7: Brainstem Neuroscience1: Entire 2nd shift: Midbrain, Pons, Medulla, CNs

AsturiaNOTES by RAsturiano UST-FMS A-2019: #TheElusiveDoktora 9/24/15 & 10/01/15 By Dra. Lumitao/Dra. Bautista—downloadable (for free!) at: www.elusivedoktora.wordpress.com

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Brainstem

A stalk-like structure The following compose the “brainstem”:

o Medulla (Rhombencephalon, Myelen) o Pons (Rhombencephalon, Meten) o Midbrain (Mesencephalon)

The brainstem extends from the pyramidal decussation to the posterior commissure

Blood supply: received from the Ventrobasilar System—from the branches of the vertebral and basilar arteries

Connects the Spinal Cord (SC) with the Forebrain including Diencephalon +

Cerebral Hemispheres Derived from: Rhombencephalon and Mesencephalon Spatial relations:

o Lies below the tentorium cerebelli making it the INFRATENTORIAL BRAIN

Note: Infratentorial Brain—Brainstem + Cerebellum

Supratentorial Brain--Cerebrum o Anterior to Cerebellum o Within the Posterior Cranial Fossa o Separated from cerebrum above by the Transverse Fissure

In the Transverse Fissure is where the fold of dura (a meningeal layer) inserts

Functions:

o Conduit for ascending and descending fiber tracts so that impulses from periphery is delivered to spinal cord brainstem brain (higher center)

o It is an important reflex center

For respiratory processes For cardiovascular dynamics For consciousness

o Contains important nuclei of (except for the spinal part of CN11): Cranial Nerves 3-12 (the last 10 cranial nerves)

1 Cranial Nerves listed with their function (S=Sensory, M=Motor,

B=Both) a 1—Olfactory—S b 2—Optic—S

c 3—Oculomotor—M d 4—Trochlear—M e 5—Trigeminal—B f 6—Abducent/Abducens—M

g 7—Facial—B h 8—Auditory/Vestibulocochlear—S i 9—Glossopharyngeal—B



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j 10—Vagus—B

k 11—Accessory (Spinal)—M l 12—Hypoglossal—M

2 Mnemonic for Cranial Nerves: Oh! Oh! Oh! To Touch And Feel A Gurl’s Vagina? Ah, Heaven!

3 Mnemonic for Cranial Nerve Function: Stefani Said Masarap Muscles But My Bekifriend Said Big Bananas ayyy!!! Masarap na Masarap

Cranial Nerve (CN) EXIT: 1 CNs that exit from the brainstem as elaborated by the following:

a Midbrain—3, 4 (2 CNs)

b Pons—5, 6, 7, 8 (4 CNs) c Medulla—9, 10, 11, 12 (4 CNs)

The cerebellum is NOT part of the brainstem, however, the cerebellum is joined

to the brainstem via the 3 CEREBELLAR PEDUNCLES (CP) o CP1: Cerebello-medullary connection via the INFERIOR CEREBELLAR

PEDUNCLE

o CP2: Pons (basilar part) to the cerebellum via the MIDDLE CEREBELLAR PEDUNCLE/BRACHIUM PONTIS

o CP3: Midbrain-Cerebellum connection via the SUPERIOR CEREBELLAR PEDUNCLE/BRACHIUM CONJUNCTIVUM

Foramen Magnum o Marks the commencement of the SC below it o Demarcates the junction between the superior medulla and the inferior

SC—the spinomedullary junction From the SC is where the 31 pairs (62 in total) of spinal nerves

emerge

The brainstem is the site where efferent nerves emerge and afferent nerves enter

DIAGRAMATIC REPRESENTATION OF THE BRAINSTEM Figure 1. The DORSAL SURFACE of the brainstem.

The three cerebellar peduncles are removed to expose the rhomboid fossa. The Trochlear Nerve (CN 4) is the

ONLY cranial nerve that exits from the brainstem in the dorsal aspect. The facial colliculus

surmounts the genu of the Facial Nerve (CN 7) and the Abducent Nucleus (CN 6).



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Figure 2. The VENTRAL SURFACE of the brainstem and the attached cranial nerves.

DIVISIONS OF THE BRAINSTEM Ventral Division:

o Superior Pontine Sulcus

Separates the midbrain from the pons o Inferior Pontine Sulcus

Separates the pons from the medulla

Dorsal Division: o Here, the divisions are only dictated by landmarks. The pontine sulci are

NOT present

Pontomidbrain junction/Pontomesencephalic junction 1 This is where the Basilar Artery terminates to give 2

Posterior Cerebral Arteries (PCA)

2 This is where Trochlear Nerve (CN 4) exits 3 This is where the Superior Pontine Sulcus is located 4 This is the rostral peak of the 4th ventricle

Pontomedullary junction

1 Demarcated by line between the Fastigium and the Inferior Pontine Sulcus

2 This is where the Basilar Artery commences from the 2

Posterior Cerebral Arteries (PCA) 3 This is the specific area of the pons where the LAST 3

pontine cranial nerves exit:



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a CN 6

b CN 7 c CN 8

4 This is the plane of tallest point/peak and widest diameter of the 4th ventricle—the Fastigium

5 The rostral edge of the stria medullaris of the 4th ventricle is the pontomedullary junction—demarcates the pons and medulla

COMPONENTS OF THE BRAINSTEM—THE TRANSVERSE SECTION FEATURES Again, the brainstem is composed of the following in rostrocaudal order:

Midbrain—most rostral/cephalic/superior/pinaka-nasa taas Pons—nasa gitna ng midbrain at ng medulla Medulla—most caudal/inferior/pinaka-nasa baba

A. MIDBRAIN From the mesencephalon and can also be referred to as the mesencephalon

Extends rostrally from the pons-midbrain junction to join the diencephalon (thalamus)

2cm in length Less than 1% of brain weight

Among the three, it is the closest to the tentorium cerebelli Blood Supply:

o Paramedian branch of the basilar artery

Occlusion of the paramedian branch of basilar artery can result to: Benedikt Syndrome

1 Affects:

a Medial Lemniscus b Red nucleus

2 Signs:

a Ipsilateral oculomotor paralysis b Contralateral hemianesthesia c Contralateral cerebellar dystaxia with intention

tremor o Superior cerebellar artery o Posterior cerebral artery (PCA)

Occlusion of posterior cerebral artery results to: Weber Syndrome

1 Signs: a Necrosis of brain tissue involving the oculomotor

nerve and the crus cerebri

i Ipsilateral ophthalmoplegia ii Contralateral paralysis of the:

lower half of face



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arm

leg tongue

iii Eyeball is deviated medially

iv Ptosis v Dilated pupils

b Contralateral spastic hemiparesis (corticospinal

tract) c Weakness of contralateral lower face, tongue,

and palate

Boundaries: o Caudal Boundaries:

Superior Pontine Sulcus

Sites of exit of CN 4 o Rostral Boundaries:

Imaginary line from mammillary bodies to posterior commissure It is above the pons

Cranial Nerve exit: o At the dorsal/posterior aspect of the midbrain is where the Trochlear nerve

(CN4) exits

o At the ventral/anterior aspect of the midbrain is where the Oculomotor nerve (CN 3) exits

Midbrain halves:

o Lower ½ Level of:

1 IC

2 Trochlear Nerve 3 Decussation of Superior Cerebellar Peduncle

o Upper ½--characterized by wider interpeduncular fossa

Level of: 1 SC (Superior Colliculus) 2 Oculomotor Nerve 3 Red Nucleus

Midbrain External Structures: o Posterior/Dorsal aspect contains the:

Corpora quadrigemina—4 rounded bodies, 2 pairs of each of the

following: 1 Superior colliculi

a For visual reflexes and visual orientation

b Linked to the lateral geniculate body (LGB) via the superior quadrigeminal brachium (SQB)

i SQB runs from superior colliculus to LGB

2 Inferior colliculi



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a For hearing

b Midline below the IC, the trochlear nerves emerge after decussating completely within the superior medullary velum—important dorsal landmark of the pontomidbrain junction

c The Inferior Quadrigeminal Brachium (IQB) i IQB connects the ICMedial Geniculate

Body (MGB, the thalamic nucleus for

hearing) Trochlear nerve

1 Lateral to crus cerebri

2 Only CN that exits dorsally and decussates completely Thalami

1 Egg-shaped, ovoid mass with small appendages

2 Lateral Geniculate Body—where optic tract terminates 3 Medial Geniculate Body

Superor Cerebeller Peduncle

1 Not ascending parallel, but ascending superiorly and medially

2 Bound to cross when it reaches the midbrain

o Anterior/Ventral aspect contains the: Crus cerebri Interpeduncular fossa

1 Space between the 2 crura

2 Houses hypothalamic structures 3 Marks the exit of CN 3 medially 4 CN 4 winds at the lateral borders

5 The roof is penetrated by numerous blood vessels, this area is called posterior perforated substance

6 Within the interpeduncular fossa is the Tuberum cinereum—

the pituitary base—and the infundibulum—the pituitary stalk Posterior Communicating Artery

1 Branch of the internal carotid artery

2 At the point where they anastomose with the posterior cerebellar artery, an aneurysm can develop that can compress CN 3

a CN 3 hooks under the posterior cerebellar artery o Lateral aspect contains the:

Brachia/Arms of the colliculi Lateral Mesencephalic Sulcus

1 Shallow groove or sulcus that marks the plane of separation of the tegmentum and the basis externally

2 This is where the substantia nigra is located internally



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Superior Cerebellar Peduncle

1 AKA brachium conjunctivum 2 Conveys cerebellar efferents (cerebellorubrothalamic

pathway) 3 Enters the mibrain at the tegmentum

Tentorium cerebelli 1 If this is displaced, results to a head trauma where the

trochlear nerve is the one to be compressed first

o Midsagittal aspect contains the: Midbrain-diencephalic junction containing the following structures:

1 Pretectal nuclei

a Lies above superior colliculus b Photosensitive c Center for pupillary light reflex

i Shine light to one eye, there is pupillary constriction to both by virtue of the Edinger-Westphal Nucleus (EWN)

2 Posterior Commissure a Landmark of midbrain-diencephalic junction dorsally b Fibers from the pretectal area of one side

projecting to EWN at the contralateral side

(crossed) i Fibers for upward vertical gaze

c Diencephalon:

i Thalamus ii Hypothalamus iii Epithalamus—contains the pineal gland

which is held in place by the pineal stalk (inferior wall formed by posterior commissure)

d Horizontal conjugate gaze

i Directed by the parapontine reticular formation (PPRF)—coordinatin center for horizontal conjugate gaze

ii MLF (Medial Longitudinal Fasciculus)—pathway that connects CN 3 and CN 4

e Vertical conjugate gaze i Rostral interstitial nucleus of MLF

Found in midbrain Coordinating center for vertical

conjugate gaze ii Pineal Gland tumor

This compresses the posterior

commissuretendency is for it to go



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downParinaud’s syndrome

(hallmark is: paralysis of upward vertical gaze)

f Posterior commissure contains crossed fibers

i Fibers from pretectal area cross contralateral to the opposite EWN

ii Upward vertical gaze pathways CROSS at the posterior commissure

iii Downward vertical gaze does NOT cross the posterior commissure

3 Cerebral Aqueduct

a Separates the corpora quadrigemina from the tegmentum

b IC,SupC

Contains the Sylvian Aqueduct o AKA: Cerebral Aqueduct, Iter o A very narrow cavity: 1-3mm in diameter

o Connects the 3rd (which is more superior, the diencephalic cavity) and 4th ventricles (which is more inferior, the rhombencephalic cavity)

o Does NOT contain choroid plexus

o The walls are made up of periaqueductal gray (PAG) o Roof/Superior Border: Tectum, specific part of the tectum: Corpora

Quadrigemina

B. PONS Boundaries:

o Rostral Boundaries:

Cerebral peduncles Superior pontine sulcus

o Caudal Boundaries:

Inferior pontine sulcus o Lateral Boundaries:

Middle cerebellar peduncles

One of the two derivatives of the metencephalon o The other one is the cerebellum

The cerebellum developed by the rapid proliferation of cells at the

dorsal wall of the brain vesicle to become a protuberance devoid of any neural cavity—NOT part of the “brainstem”

Evolved by the process of invagination with retention of the 4th ventricle 1.3% of total brain weight

Holds important sensory and motor nuclei essential for life Blood supply:

o The Basilar artery



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Three branches of the basilar artery that supply the pons

1 Paramedian branch a Supplies medial pons

i The corticospinal tracts ii The pontine nuclei

iii Fibers passing to the cerebellum through middle cerebellar peduncle

b Occlusion? Medial Inferior Pontine Syndrome

i Signs: Corticospinal tract—Contralateral

spastic hemiparesis

Medial lemniscus—Contralateral loss of tactile sensation from trunk and extremities

Abducent nerve roots—Ipsilateral lateral rectus paralysis

2 Short circumferential branch a Supplies lateral pons

i Trigeminal nerve ii Medial lemniscus

iii Middle cerebellar peduncle 3 Long circumferential branch

a Supplies posterior pons (most of the pontine

tegmentum of rostral and caudal pons) o The Superior Cerebellar Artery

Supplies rostral pons

o The Anterior Inferior Cerebellar Artery (AICA) Lesion? Lateral inferior pontine syndrome

1 Signs:

a Facial nucleus and intraaxial fibers—Ipsilateral facial nerve deficits such as:

i Ipsilateral facial nerve paralysis

ii Ipsilateral loss of taste from anterior 2/3 of tongue

iii Ipsilateral loss of lacrimation

iv Ipsilateral reduced salivation v Loss of corneal reflexes

b Cochlear nuclei—unilateral central deafness c Vestibular nuclei—Nystagmus, nausea, vomiting,

vertigo d Spinal nucleus of the trigeminal—Ipsilateral facial

hemianesthesia



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e Mid/Inferior cerebellar peduncles—Ipsilateral limb

and gait dystaxia f Spinothalamic tract—Contralateral loss of

pain/thermal sense from limb+extremities g Descending sympathetic tract—Ipsilateral Horner’s

Syndrome i Characterized by:

Miosis

Ptosis Non-sweating at ipsilateral face

External Features: o Mid-Sagittal Aspect:

From pontomidbrain junction rostrally to pontomedullary junction

caudally Cortico-pontocerebellar Tract

1 Cortex to pontine nucleus to cerebellum via the middle cerebellar peduncle

Contains some part of the medullary pyramidal tract o Ventral Aspect:

Bulbous, represents the globularly enlarged basis that appears as a

broad band of transversely coursing fibers, which on either side coalesce to form the middle cerebellar peduncles

Boundaries are the pontine sulci

Basilar sulcus—runs along the midline and lodges the basilar artery

CN 5

1 Emerges from the ventrolateral surface at the point of transition of the pontine basis to its middle cerebellar peduncle

2 Roots: a Large sensory root b Small motor root

i Therefore, CN 5 is more of a sensory nerve

especially to the face CN 6, 7, and 8

1 Exit along the inferior pontine sulcus in ventrodorsal order

a The site of exit dermacate the pontomedullary junction ventrally

2 Cerebellopontine angle—the specific site of exit of CN 7/8

CN 7 1 Roots:

a Large motor root



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b Small sensory root (Intermediate nerve of

Wrisberg or Nervus Intermdius i Carries BOTH sensory + parasympathetic

preganglionic efferents 2 CN 7 is MAJOR motor innervation of face EXCEPT:

a Masticatory muscles that are supplied by CN 5 i Lateral Pterygoid ii Medial Pterygoid

iii Masseter iv Temporalis

b Extraocular muscles which are supplied by:

i CN 3 ii CN 4 iii CN 6

CN 8 (Auditory/Vestibulocochlear) 1 Vestibular nerve—for equilibrium 2 Cochlear nerve—for hearing

o Lateral aspect: 3 cerebellar peduncles that attach the cerebellum to the dorsal

surface of the pons, contain fiber tracts that functionally connect the cerebellum with other parts of the nervous system:

1 Superior Cerebellar Peduncle—Brachium Conjunctivum a Primarily transmit fibers that link the cerebellum

with the midbrain and eventually the thalamus and

cerebral cortex (cerebellar efferents) b Small group of fibers from spinal cord and

brainstem for unconscious proprioception

(cerebellar Afferents) i Ventral spinocerebellar tract (VSCT) ii Trigeminocerebellar tract

2 Middle Cerebellar Peduncle a From pons to cerebellum—pontocerebellar tract b Purely Afferent

3 Inferior Cerebellar Peduncle a Connects spinal cord + medulla to cerebellum b MOSTLY afferent (but not purely) c Restiform Body (Afferent)

i Cuneatocerebellar tract (CCT) ii Dorsal Spinocerebellar tract (DSCT)

d Juxtarestiform Body (Afferent + Efferent)

i Vestibulocerebellar tract (from vestibular nuclei to cerebellum)



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ii Efferent from cerebellum to vestibular

nuclei and reticular formation Cerebellopontine angle

1 At the caudal border of the middle cerebellar peduncles close to the lateral recess of the 4th ventricle—an angular

space formed on either side with the upper parts of the medulla and adjoining cerebellum dorsally

2 Delineates the sites of exit of Facial and Vestibulocochlear

nerves 3 Acoustic neuroma—tumor involving the CN 8

(Vestibulocochlear Nerve), producing a lesion at this angle

o Dorsal Aspect: Only visible after detaching the cerebellum and the superior medullary

velum

Forms the superior half of the rhomboid fossa which floors the 4th ventricle

Laterally, it is bounded by cut sections of the cerebellar peduncles

Median sulcus—continues upwards from the caudal or medullary portion of the 4th ventricular floor to divide it into two asymmetrical halves

Sulcus limitans (SL)—further subdivides the each half into:

1 Median eminence—medially located 2 Facial colliculus

a Medial, below the median eminence

b Overlies the abducens nucleus and the genu of the motor root of the facial nerve

3 Area vestibularis

a Overlies the vestibular nuclei b Tuberculum acousticum—lateral to the area

vestibularis, a rounded elevation, beneath it lies the

dorsal cochlear nucleus Locus ceruleus

1 A bluish-gray discoloration close to the

pontomesencephalic junction beneath the SL 2 Group of cells within the tegmentum 3 Norepinephrinergic

Contains the upper ½ of the 4th ventricle

o Continuous with the cerebral aqueduct Contains the upper ½ of the Rhomboid Fossa Lower ½ of pons—at the level of the facial colliculus

o Level where 4th ventricle is widest Upper ½ of pons—at the level of the Trigeminal Nerve



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C. MEDULLA

Lies just above the SC 3 cm in length 0.5% of total brain weight Located here are the central connections concerned with respiration and heart

rate From rhombencephalonmyelencephalonthen becomes the medulla Blood supply:

o Arterial supply Medullary branch of the vertebral artery

1 Supplies the anterolateral medulla

Medullary branch of the basilar artery Posterior Inferior Cerebellar Artery (PICA)

1 Supplies the posterolateral medulla

2 Lesion at PICA produces lateral medullary syndrome a AKA Wallenberg/PICA syndrome

i Signs:

Contralateral loss of pain and thermal sense from the body

Ipsilateral loss of pain and thermal

sense from the face Hoarseness + Dysphagia

o Dysphagia—difficulty in

swallowing Vertigo + Nystagmus

o Vertigo—a feeling of dizziness

o Nystagmus—a rapid involuntary oscillation of the eyeballs

Anterior Spinal Artery (ASA) 1 Supplies the anteromedial medulla 2 Lesion at ASA produces medial medullary syndrome

a AKA Dejerine’s syndrome i Signs:

Contralateral hemiparesis

o Hemiparesis—weakness of one side of body

o Hemiplegia—paralysis of one

side of body Contralateral loss of proprioception

and vibratory sense

Deviation of tongue to the ipsilateral side



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Posterior Spinal Artery (PSA)

1 Supplies the posterior medulla 2 Lesion at PSA produces:

a Ipsilateral loss of proprioception and vibratory sense

b Ipsilateral loss of pain and thermal sense from the face

o Venous supply

Basilar venous plexus Inferior petrosal sinus Occipital sinus

Boundaries: o Rostral boundaries:

Inferior pontine sulcus

Stria medullaris of 4th ventricle o Caudal boundaries:

Foramen magnum

Highest ventral rootlets of C1 Lowest decussating fibers of pyramidal tract

External Features o Presents more or less parallel longitudinal grooves that divide the medulla

into ventral, dorsal, and lateral areas by the following: Anterior Median Fissure (AMF) Posterior Median Sulcus (PMS)

Posterolateral sulci (PLS) (paired) Anterolateral sulci (ALS) (paired) Posterior Intermediate sulci (PIS) (paired)

o Ventral aspect: Between AMF and ALS

1 The AMF is partially interrupted at caudal border by the

crossing fibers of the pyramidal decussation 2 The rostral ends of the ALS allow exit of Hypoglossal Nerve

(CN 12) rootlets

Spinomedullary junction 1 This is where the ventral roots emerge

o Mid-sagittal aspect: Made up of the pyramidal tracts=corticobulbar+corticospinal tracts

90% of the corticospinal fibers cross o Lateral aspect:

Between ALS and LS

1 ALS AKA the preolivary sulci—lie anterior to olives 2 PLS AKA the postolivary sulci—lie posterior to olives

a CNs 9, 10, 11 exit posterolaterally to the olives



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Arcuate fibers

1 Fibers unique to medulla, perpendicular to the long axis 2 Types:

a Ventral External Arcuate Fibers i Course the lateral surface, most conspicuous

on the olivary surface ii From ventral aspect, go posteriorly to enter

Inferior Cerebellar Peduncle

b Internal Arcuate Fibers i Internally located within the medullary

tegmentum

Inferior Cerebellar Peduncle 1 Connects the cerebellum to medulla+spinal cord 2 Restiform Body—larger, from spinal cord and medulla to

cerebellum (cerebellar afferents) 3 Juxtarestiform Body—from vestibular nuclei to

cerebellum (afferent); from cerebellum to vestibular nuclei

+ reticular formation (efferent) o Dorsal Aspect (CLOSED MEDULLA)

Between PMS and PLS Fasciculus cuneatus (FC)

1 Laterally located 2 Ends as expanded oval enlargement—the tuberculum

cuneatus

Fasciculus gracilis (FG) 1 Medially located 2 Ends as expanded oval enlargement—the tuberculum

gracilis (clava) PIS separates the FC and FG Tuberculum cinereum—lateral to the FC and overlies the

descending or spinal nucleus and tract of the trigeminal PLS—exit of CNs 9-11

1 CNs that exit at medulla

a 9, 10, 11—posterolateral to the olives at posterolateral sulci

b 12—medial to the olives, exit at anterolateral sulci (ALS)

o Dorsal Aspect (OPEN MEDULLA) Lower ½ of the floor of the 4th ventricle (rhomboid fossa) Partially covered by the inferior medullary velum

Inferior Cerebellar Peduncles (restiform bodies) at the lateral boundaries on either side

Divided into two halves by the medial sulcus



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1 Each half is further divided into three paired trigones

a Hypoglossal Trigone--medially b Vagal Trigone--intermediately c Area Vestibularis—laterally

Area postrema—caudal end of vagal rigone

1 No blood-brain barrier 2 Considered to be the chemoreceptor trigger zone for vomiting

which stimulates the vomiting center located deep within the

medullary tegmentum Tuberculum cinereum

1 Prominent only at the middle third because it is covered by

the inferior cerebellar peduncle 2 Overlies the descending spinal nucleus

Internal Features

o In cross section, the medulla has 3 levels: Upper 1/3

1 Where the open medulla is found

a Where the 4th ventricle is found Middle 1/3 Lower 1/3

1 Middle 1/3 + Lower 1/3 = Lower 2/3

a Where the closed medulla is found i Where the central canal is found enclosed

within the medullary substance

o Lower 1/3 of the Medulla—Level of the Motor or Pyramidal Decussation

Nuclear masses on posterior white column:

1 Nucleus cuneatus a Laterally located b For the following sensory modalities of upper

extremities/trunk: i Conscious proprioception

2 Nucleus gracilis

a Medially located b For the following sensory modalities of the lower

extremities/trunk: i Conscious proprioception

Lateral to the fasciculus and nucleus cuneatus on each side: 1 Descending or spinal nucleus of the Trigeminal

a Replaces the substantia gelatinosa of the spinal

cord b Mediates the following sensory modalities of the face:

i Pain sense



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ii Thermal sense

2 Descending or spinal tract of the Trigeminal a Replaces the Lizzauer’s Zone of the spinal cord

Corticospinal tract 1 Pyramidal decussation (or motor decussation)

a 90% of the fibers that cross the midline to enter the opposite side

b Cuts the anterior gray horn from the rest of the

gray matter c Descends as the Lateral Corticospinal Tract that

synapse with the spinal motor neurons that control

movements of muscles of the extremities 2 The other 10%

a Did NOT cross

b Will descend uncrossed as the Anterior Corticospinal Tract that will terminate on the spinal motor neurons directed to the trunk and

girdle muscles i 8% of the 10=Tract of Turke ii 2% of the 10=Tract of Barnes

Lesions

1 Upper motor neuron lesions are of the corticospinal tract from origin or termination above or below the decussation leading to loss of motor function

a If lesion is above the pyramidal decussation—contralateral motor function loss/weakness

b If lesion is below the pyramidal decussation—

ipsilateral motor function loss/weakness 2 Lower motor neuron lesions are lesions on the cell body or

axon—the motor weakness is ipsilateral ONLY because the

fibers has already decussated Medial Longitudinal Fasciculus (MLF)/Ascending and Descending

Pathways

1 MLF is pushed laterally by the crossing fibers of the pyramidal decussation

2 Other ascending and descending tracts that course through the medulla from and to the spinal cord are also seen in the

ventrolateral portions of the closed medulla 3 Anterolateral System (Ascending pathway) is composed of

fiber tracts:

a Lateral and ventral spinothalamic b Spinoreticular c Spinomesencephalic



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Central Canal

1 Within the medullary core 2 Surrounded by the scattered cells of the central gray/PAG 3 Projection neurons—cross and project p as part of the

ascending tract

Reticular formation 1 Rest of the gray matter between the gelatinous substance

and the cut ventral horn composed of intermingling of cells

and fiber bundles ***The Law of Lamination by Level of Entry—fibers that enter first occupy the medial position while the fibers that enter last occupy the lateral position

First to enter? Medially located Last to enter? Laterally located

o Middle 1/3 of Medulla—Level of the Sensory Decussation

2 Tuberculae on the dorsal surface of the medulla 1 Tuberculum gracilis

a Oval, enlarged size of the nucleus gracilis

b When the nucleus gracilis reaches its greatest extent, all fibers have terminated already

2 Tuberculum cuneatus

a Enlarged size of the nucleus cuneatus b Nucleus cuneatus also increases in size although a

considerable number of fibers of the fasciculus

cuneatus still remain dorsal to the nucleus Unconscious proprioception

1 Accessory or Lateral Cuneate Nucleus a It is lateral to the nucleus cuneatus

b It sends fibers to the cerebellum as the cuneocerebellar tract (dorsal external arcuate fibers)—upper extremities

2 Dorsal Nucleus of Clarke a Found in the spinal cord b Counterpart of the accessory cuneate nucleus

c It sends fibers to the cerebellum as dorsal spinocerebellar tract—lower extremities

Descending or Spinal Nucleus and Tract of the Trigeminal

1 Increases in size as the level of the trigeminal neve in the pons is reached

2 Externally, it is seen as the tuberculum cinereum (overlaps

the descending nucleus of trigeminal nerve) Medial Lemniscus



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1 Formed by the axons of NC and NG that sweep

ventromedially as the internal arcuate fibers crossing the median raphe and ascend contralaterally

2 Contains well-defined bundle of fibers 3 Constitutes the sensory decussation

a The point at which a major ascending sensory pathway crosses the midline

4 Dorsal Column-Medial Lemniscal Pathway

a Specifically involved in the mediation of conscious proprioception from the trunk + limbs

The MLF is pushed further (dorsolaterally), other fiber tracts coursing

within the central core of the medulla are likewise spread ventrolaterally

Central Canal

1 Surrounded by the Central Gray/PAG 2 Houses the caudal beginning of the:

a Hypoglossal nuclei

b Vagal nuclei c Solitary nuclei

Nucleus ambiguous 1 Deeply placed within the medullary reticular formation

Inferior olivary nuclei 1 Begin to emerge laterally

Pyramids

1 Descending uncrossed corticospinal and remaining corticobulbar tracts

2 From the distinct oval structures at the most ventral

aspect Medullary Reticular Formation

1 It is interspersed with the more compact nuclei and tracts

within the tegmentum 2 Arranged mediolaterally

a Raphe group—most medial

b Medial group—gitna c Lateral group—most lateral

o Upper 1/3 of medulla—at the level of the open medulla Open Medulla

1 Central canal opens up to become the 4th ventricle a 4th ventricle is widest at the pontomedullary

junction

2 Lateral recess of the 4th ventricle or foramina of Luschka a Laterally located b Horn-shaped aperture of the 4th ventricle



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c Opens into the cerebellomedullary

cistern/cisterna magna 4th ventricular floor

1 Cranial nerve nuclei is distinctly seen 2 Hypoglossal Trigone—hypoglossal nucleus is beneath HT

3 Vagal Trigone (or Ala cinerea)—Dorsal motor nucleus of the vagus and nucleus of tractus solitaries are beneath VT

4 Area Vestibularis—Caudal poles of the medial and inferior

vestibular nuclei are beneath AV Inferior Cerebellar Peduncles or The Restiform Bodies

1 At the posterolateral aspect of the medulla

2 Its prominent fibers push the accessory nucleus (CN11) dorsally and the spinal nucleus (CN11) and tract of the trigeminal medially

3 Convey fibers from the spinal cord and medulla to the cerebellum

4 Fibers that run through the ICP

a Cuneocerebellar b Olivocerebellar c Arcuatocerebellar d Stria medullaris

e Dorsal spinocerebellar tract (from spinal cord) Nucleus ambiguous

1 Placed ventromedially to the descending or spinal nucleus

and tract of the trigeminal 2 Parts:

a Rostral cardioinhibitory portion

i Gives rise to preganglionic parasympathetic efferents that supply the heart

ii Slows heart rate b Branchiomotor

i Larger

ii Supplies the branchiomeric muscles Pharyngeal Laryngeal

Palatal Inferior olivary nuclei

1 Lies beneath the prominent olivary eminences on the

lateral surface of the medulla 2 Appear as convoluted groups of cells occupying the lateral

parts

3 Each complex is composed of:



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AsturiaNOTES

a Principal or main inferior olivary nucleus

i This is the origin of the olivocerebellar tract that crosses to enter the cerebellum via the opposite inferior cerebellar peduncle

Forms the internal arcuate fibers of

the inferior olivary body 4 Amiculum olivae

a Densely myelinated fibers surrounding the inferior

olivary nucleus b Consists of axons projecting to the ION from higher

brain structures (red nucleus of midbrain) via a

composite bundle known as central tegmental tract

***Sources of internal arcuate fibers in the medulla

Nucleus Gracilis Nucleus Cuneatus Inferior Olivary Nucleus

Medial lemnisci 1 Triangular areas on both side of the median raphe 2 MLF lies dorsal to the medial lemniscus

3 Pyramids lie ventral to the medial lemniscus Arcuate nuclei

1 Ventral to the pyramids 2 Displaced pontine nuclei

3 Project to the cerebellum via the inferior cerebellar peduncle (ICP)

4 The axons of the arcuate nuclei course on the ventrolateral

surface of the medulla as the ventral external arcuate fibers to enter the ipsilateral ICP

a The axons may run dorsomedially within the

medullary substance to emerge on the dorsal surface as the stria medullaris of the 4th ventricle to enter the contralateral ICP (Inferor cerebellar

peduncle) Other ascending and descending tracts including the autonomic fiber

projections remain at the same positions at the ventrolateral aspect of

the medulla Respiratory Centers

1 Located in the medullary tegmentum 2 Dorsal Respiratory Group—primary source of the

inspiratory drive a Located within the middle 1/3 of the nucleus of

tractus solitaries



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AsturiaNOTES

3 Ventral Respiratory Group—both inspiratory and

expiratory a Located within the nucleus ambiguous and

retroambiguus Medullary Reticular Formation

1 Nucleus Raphe Magnus (NRM) a Receives inputs from the PAG of midbrain b Sends descending serotonergic projections to

the dorsal horn of the spinal cord as the raphespinal tract—has an important role in the suppression of CNS pain transmission

2 Medial Medullary Reticular Formation a Gigantocellular nucleus

i Gives rise to one of the descending

subcortical motor tracts—the medullary reticulospinal tract

ii Considered as the efferent nucleus of the

reticular activating system (RAS) 3 Lateral Medullary Reticular Formation

a Parvocellular nucleus—efferent nucleus of the RAS

b Dorsolateral medullary reticular formation i The vomiting center ii Receives afferent impulses from area

postrema and nucleus tractus solitaries c Ventrolateral medullary reticular formation

i Adrenergic neurons that send descending

projections to the sympathetic preganglionic neurons of the spinal cord making it the sympathetic vasomotor

center Hypoglossal Nerve (CN 12)

1 Arises from its nucleus at the floor of the 4th ventricle

2 Runs ventrally, exits laterally to the pyramids but medial to the olives

3 Innervates the tongue muscles Spinal Accessory Nerve (CN 11)

1 The cranial root from the nucleus ambiguous: a Exits posterolateral to the olives b Supplies the laryngeal muscles

2 The spinal root from the ventral horn cells of the upper cervical spinal cord

a Enters the skull via the foramen magnum



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AsturiaNOTES

b Supplies the trapezius and SCM

Glossopharyngeal Nerve (CN 9) 1 Posterolateral to the olives 2 Associated with more than one function, thus the CN 9 has

more than 1 nucleus

Vagus Nerve (CN 10) 1 Emerges posterolaterally from the postolivary sulci

posterolateral to the olives together with CN 9 and 11

2 Associated with more than 1 function and therefore has more than 1 nucleus

Table 1. Functions of the Vagus Nerve

Function Nucleus Ganglion Area Supplied

Branchiomotor The branchiomotor

division of the nucleus

ambiguus

1. Pharyngeal muscles

2. Laryngeal muscles

3. Palatal muscles

Parasympathetic The rostral

cardioinhibitory division

of the nucleus ambiguus

1. Heart (slows heart rate)

Dorsal motor nucleus of the

vagus

1. Lungs—

bronchoconstriction

2. GIT—Smooth muscle

contraction, sphincter

relaxation

Taste Upper 1/3 of Nucleus

Tractus Solitarius

Nodose 1. Epiglottal taste buds

General Visceral Sensation

Lower 1/3 of Nucleus

Tractus Solitarius

Nodose

Baroreceptor Middle 1/3 (medially) of

Nucleus Tractus Solitarius

Nodose 1. Aortic Sinus

Chemoreceptor (O2 and CO2 tension)

Middle 1/3 (laterally) of


Nodose 1. Aortic Body

General Somatic Sensation

Descending nucleus of the

Trigeminal

Superior

Ganglion of

the

vagus/Jugular

1. Ear

2. Dura

Table 2. Functions of the Glossopharyngeal Nerve

Function Nucleus Ganglion Area Supplied

Branchiomotor The branchiomotor

division of the nucleus

ambiguous

1. Stylopharyngeus (for

swallowing)

Parasympathetic Inferior Salivary Nucleus Otic 1. Parotid Glad (for

secretion of saliva)

Taste Upper 1/3 of Nucleus

Tractus Solitarius

Petrosal 1. Posterior 1/3 of

Tongue

General Visceral Lower 1/3 of Nucleus Petrosal 1. Posterior 1/3 of



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AsturiaNOTES

Sensation Tractus Solitarius Tongue

2. Tonsils

Baroreceptor Middle 1/3 (medially) of


Petrosal 1. Carotid Sinus

Chemoreceptor (O2 & CO2 tension)

Middle 1/3 (laterally) of


Petrosal 1. Carotid Body

General Somatic Sensation

Descending nucleus of

the trigeminal

Superior

Ganglion of the

Glossopharyngeal

1. Ear

Contains the lower ½ of the 4th ventricle o Specifically in the “open medulla”

Contains the lower ½ of the Rhomboid Fossa

Contains the Central Canal o Specifically in the “closed medulla”

VENTRICULAR SYSTEMS The 4th ventricle The triangular cavity of the Rhombencephalon

Its rostral portion lies between the pons and cerebellum Its caudal portion is located in the medulla Fastigium—the structure that denotes the tallest/peak point of the 4th ventricle

Continuous with the following ventricles/ducts: o Rostrally—Cerebral Aqueduct o Caudally—Central Canal of the caudal medulla and cervical spinal

cord o Laterally—The communication with the subarachnoid space for CSF flow

Via the three openings: 1 Foramen of Magendie (medially)

a Located in the caudal roof of the 4th ventricle b Opens into:

i Dorsal Cerebellomedullary

Cistern/Cisterna Magna c It punctures/perfortes the inferior medullary

velum

2 Foramina of Luschka (laterally) a Paired structure b AKA lateral aperture of the 4th ventricle

c Located at the ends of the lateral recesses of the 4th ventricle and open into the subarachnoid space at the cerebellopontine angle

i Lateral recesses Funnel-shaped portions of the 4th

ventricle that extend around the



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AsturiaNOTES

brainstem at the ponto-medullary

junction d Opens into:

i Pontocerebellar cistern at the cerebellopontine angle

Roof/Superior Wall is part of the upper ½ of the 4th ventricle and is composed of: o Anterior/Superior Medullary Velum--rostrally o Some portion of the cerebellum—in the middle

o Tela Choroidea—a thin membranous structure caudally Floor/Inferior Wall is composed of:

o Rhomboid Fossa (RF)

RF is part of the open medulla, lower part of the 4th ventricle The deep median sulcus divides the RF into two symmetrical

halves

1 The two symmetrical halves is divided even further by the sulcus limitans creating depressions:

a Superior Fovea—the rostral depression

i Laterally adjacent to the Facial Colliculus b Inferior Fovea—the caudal depression

i Laterally adjacent to the: Vagal Trigone

Hypoglossal Trigone 2 Sulcus Limitans (SL)

a SL is an embryological landmark that persists and separates the alar plate and basal plate derivatives

i Motor nuclei of cranial nerves arise from basal plate neurons

ii Sensory nuclei of cranial nerves arise from alar plate neurons

b Cranial nerve nuclei between the deep median

sulcus and the SL are = MOTOR c Cranial nerve nuclei lateral to the SL are =

SENSORY

d Triangular structures that are present on medial to the SL (paired structures):

i Vagal Trigone

AKA Ala Cinerea Overlies Vagal Nuclei

o Vagal nuclei include (1) Dorsal

motor nucleus of vagus (DMNV) and (2) Nucleus of Tractus Solitarius (Solitary

Nucleus)



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AsturiaNOTES

Caudal end of vagal trigone is the

Area Postrema (AP) o AP is the chemoreceptor

trigger zone for vomiting—it is

the vomiting center o The vomiting can be triggered

by: 1. toxins

2. hepatopathy 3. nephropathy 4. chemotherapy

5. opioid drug use o AP is devoid of blood-brain

barrier

ii Hypoglossal Trigone Overlies the Hypoglossal Nuclei

iii Facial Colliculus—at the caudal pontine

region Abducens motor nucleus Internal genu of facial nerve

e Structures present lateral to the SL, in the medulla and caudal pons is a flattened structure called the area vestibularis

i Overlies the Vestibular Nuclei The Stria Medullaris of the 4th ventricle

o Series of fiber bundles running from midline to laterally into the lateral

recess o The rostral edge of the 4th ventricular stria medullaris is =

pontomedullary junction

The halves: o Upper half—contained in the pons o Lower half—contained in the “open” medulla

Table 3. Summary of Brainstem Components:Generalities

Brainstem Part Cranial Nerves that exit from it Neural Cavities/Ventricular Spaces

Midbrain 3—Oculomotor

4—Trochlear Cerebral/Sylvian Aqueduct

Pons

5—Trigeminal

6—Abducens

7—Facial

8—Vesitbulocochlear

Upper ½ of the 4th ventricle

Upper ½ of the Rhomboid Fossa

Medulla

9—Glossopharyngeal

10—Vagus

11—Accesory

12—Hypoglossal

Lower ½ of the 4th ventricle

Lower ½ of the Rhomboid Fossa

Central Canal



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AsturiaNOTES

BRAINSTEM FEATURES AT THE MIDSAGITTAL SECTION

Figure 3. Midsagittal cut showing demarcation lines

The demarcation lines for important anatomic structures: Mammillary Body to Posterior Commissure

o Separates the Diencephalon from the Midbrain o Mammillary Body—Anteriorly o Posterior Commissure—Posteriorly

The posterior commissure holds the: 1 Pineal Stalk 2 Pineal Gland—A pea-sized conical mass of tissue behind the

3rd ventricle. It produces the sleep hormone—melatonin a Specific location is at the epithalamus near the

center of the brain between the two hemispheres

Pontomesencephalic Junction/Ponto-midbrain Junction Pontomedullary Junction Spinomedullary Junction

o Demarcated by the foramen magnum o Separates the SC from the medulla



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AsturiaNOTES

BRAINSTEM FEATURES AT THE LONGITUDINAL SECTION PER BRAINSTEM

PART

Figure 4. Longitudinal cut of the brainstem showing basic divisions. 1. Tectum

Only place in the brainstem that contains substantial neural tissue Most dorsal among the three longitudinal segments of the midbrain

o Other two: Tegmentum

Basis Plane of brainstem that is dorsal to the plane of the cerebral aqueduct

o From tallest rostral tip of 4th ventricle to the lower boundary of the 4th

ventricle At midbrain:

o Consists of 4 rounded elevations collectively known as the Corpora

Quadrigemina Roofs the cerebral aqueduct of midbrain Consists of a pair of:

1 Superior Colliculi (SC) a SC contains nuclei for visual pathway b Mediates visual reflexes and visual orientation

(tracking, searching, scanning) c Receives visual inputs from:

i Retina ii Frontal and Occipital eye fields

d Mostly concerned with the detection of motion in the visual fields

e Receives auditory inputs from the IC that are

important for audiovisual reflexes f Sends descending projections to the:

i Brainstem



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AsturiaNOTES

ii Spinal Cord

g Terminates at the Red Nucleus (RN) h Each colliculus connects the lateral geniculate

body via the superior quadrigeminal brachium (SQB)

i SQB conducts retinal and corticotectal fibers

ii Mediates visual reflexes

2 Inferior Colliculi (IC) a IC contains nuclei for auditory pathway b IC projects to the medial geniculate body (MGB)

i MGB is part of the auditory thalamus and represents the thalamic relay between the IC and the auditory cortex

Relay is via inferior quadrigeminal brachium (IQB)

o IQB is a fiber bundle passing

from the inferior colliculus on both sides of the brainstem along the lateral border of the SC to

the posterior part of the thalamus where it pierces the MGB

o IQB forms part of the major ascending auditory pathway

ii Also sends projections to the SC c In the midbrain: there are auditory relay nuclei

i However, in the pons, there are superior

olives d It is the principal ascending pathway

i The lateral lemniscus ends at the crus cerebri

in midbrain o The medial longitudinal groove running vertically between the colliculi

will expand superiorly to form the Pineal Trigone where the pineal

gland rests and attaches inferiorly to frenulum veli of the superior medullary velum

o The trochlear neve (CN 4) emerges below the IC after decussating

within the superior medullary velum CN 4 is lateral to the crus cerebri As CN 4 goes out, it crosses the opposite side (decussates), curve

laterally and pass ventrolateral to the midbrain

It is the only cranial nerve that: 1 Exits dorsally 2 Decussates completely



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AsturiaNOTES

o The tectospinal tract

Descending from superior colliculus to spinal cord Crosses at dorsomedial aspect of midbrain tegmentum

1 Which is why it can be called the Dorsal tegmental decussation

Terminates at the ventral funiculus of spinal cord at the cervical segment

Supplies neck muscles

1 Reflex movement of head, neck, and eyes in response to audiovisual stimulus

o The Red Nucleus

Termination of superior cerebellar peduncle that decussated at lower half is partly RN

Tracts:

1 Rubroolivary Tract a RNInferior Olives b Descending, uncrossed

2 Rubrospinal Tract a RNSpinal Cord b Descending, crossed

c For the correction of errors of movement of distal limb

At pons:

o Characterized by the presence of Superior Medullary Velum which roofs the 4th ventricle

At medulla:

o Characterized by the presence of the Inferior Medullary Velum which also roofs the 4th ventricle

o Perforated by the median foramen of Magendie that opens into the

cisterna magna 2. Tegmentum

Contains a mixture of neurons and fiber tracts (gray matter=neurons, white matter=fiber tracts)

It is the “brainstem core”—the area between tectum and basis

o Most complicated part because it contains a conglomeration of nuclei interspersed with fiber tracts

It is ventral to the neural cavities

Contains: o CN nuclei o Ascending sensory tracts o Nuclei with distinctive neurotransmitter



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AsturiaNOTES

o Ascending and descending autonomic fibers

o Reticular nuclei At midbrain:

o In between the tectum and basis: Separated from the tectum by the cerebral aqueduct

Separated from the basis by the substantia nigra o It contains cranial nerve nuclei o Contains the following:

A. Substantia Nigra (SN) 1 Largest nucleus of midbrain, most voluminous structure 2 Most centrally placed, lies at the most ventral aspect

3 Does not absorb any stain 4 Functionally associated with basal nuclei/ganglia, and dorsal

striatum

5 Functions for the regulation and modulation of movement 6 Lateral mesencephalic sulcus—shallow groove on the

surface of SN

a Dorsal part: Substantia nigra pars compacta i Rich in dopaminergic neurons ii Projects to the dorsal striatum iii Major source of striatal dopamine

iv The dopaminergic pathway: AKA the nigrostriatal pathway SNDorsal striatum

v Loss of nigral/dopaminergic neurons reduces striatal dopamine leading to Parkinson’s

Dse b Ventral part: Substantia nigra pars reticulata

i Rich in GABAnergic neurons ii Projects to the thalamus

iii The GABAnergic pathway: AKA the nigrothalamic pathway

SNThalamus 7 The Dorsal Striatum

a Also rich in GABAnergic neurons

b Projcts to the SN pars reticulate c The striato-nigral pathway:

i DSSN pars reticulata

B. Ventral Tegmental Area of Tsai (VTAT) 1 Rich in dopaminergic neurons 2 Projects to the nucleus accumbens

a Nucleus accumbens: i Is part of the ventral striatum (VS)



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AsturiaNOTES

ii Functions as a reward/pleasure and

motivation center 3 Close to midbrain-diencephalic junction 4 Pathway used is the mesolimbic pathway:

a VTATVS

b AKA the pleasure/reward pathway c The pathway is used during pleasurable experiences:

i Food (Chocolate, etc)

ii Alcohol iii Drugs iv Sex

5 Check point! Summary: a Dopamine: Mesolimbic, nirgrostriatal b GABA: striatonigral, nigrothalamic

C. Periaqueductal Gray (PAG) 1 AKA central gray 2 Does NOT absorb stain

3 Rich in nuclei a Mesencephalic nucleus of the Trigeminal

i Located at the lateral aspect of PAG

ii Its fiber passes downwards to the pons to synapse with the motor root of trigeminal

iii For the unconscious proprioception of the face

iv Works together with the upper ½ of pons b Midbrain Reticular Formation

i Consists of:

ii Dorsal Raphe Nucleus Serotonergic

o The serotonergic projects are

sent to a widespread area of the cerebral cortex where they modulate neuronal activity

involved in sleep/dream cycles iii Cuneiform and Subcuneiform Nuclei

Participate in the ascending

activating system that maintains state of alertness/wakefulness

c Locus ceruleus

i At lower ½ of midbrain + upper ½ of pons ii Norepinephrinergic

d Dorsal Tegmental Nucleus

i Rich in Enkephalins



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AsturiaNOTES

ii For pain modulation and suppression

e Trochlear nuclei i Nucleus mismo ng trochlear nerve ii Located at the most ventral part of the PAG,

immediately dorsal to the Medial

Longitudinal Fasciculus (MLF) iii Course:

Its nerve fibers curve dorsally and

caudally along the outer margin of the PAG, crosses, runs laterally, goes ventrally, and then laterally to the crus

cerebri It then decussates completely at the

frenulum veli of the superior

medullary velum It emerges at the dorsal surface of the

brainstem caudal to the inferior

colliculi iv It supplies the superior oblique eye muscle

(Remember: Superior Oblique = SO is CN4 =

SO4) Action: Moves the eyeball down when

turned inwards (downward-inward

gaze) CN4 of one side supply the

contralateral SO muscle

v Lesion of CN4: Weakness of SO, express difficulty in

looking down and inward (ex, going

down the stairs) If lesion occurs before

crossing/decussation: weakness in

contralateral SO If lesion occurs after

crossing/decussation:weakness in

ipsilateral SO f At upper ½ of midbrain, the same nuclei are seen

in the PAG as mentioned above EXCEPT:

i Locus ceruleus ii Trochlear nuclei

4 The PAG is a prominent collection of nuclei (as evidenced

above) that surround the cerebral aqueduct 5 The PAG has high levels of opiate receptors



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AsturiaNOTES

6 The PAG receives spinomesencephalic inputs via the

anterolateral system 7 The PAG sends descending projections to the nucleus

raphe magnus (NRM) a NRM gives rise to the descending raphespinal

tract that inhibit the transmission of pain i Therefore, PAG has a role in the descending

modulation of pain transmission

D. Medial Longitudinal Fasciculus (MLF) 1 Lies immediately ventral to the PAG 2 It connects the nuclei of the following CNs to integrate

movements directed by the gaze centers: a 3 b 4

c 6 3 For conjugate gaze—motion of both eyes towards the same

direction at the same time

4 Ends at upper ½ of midbrain o The midbrain tegmentum also contains the following tracts:

A. Central Tegmental Tracts 1 It lies ventral to the MLF

2 Composed of: a Ascending reticulothalamic tract b Descending rubroolivary tract

Decussation of the Brachium Conjunctivum (BC) (LM) o BC AKA Superior Cerebellar Peduncles o Located in the ventromedial aspect of midbrain tegmentum

o Stains well o Consist of crossed fibers from the deep cerebellar nuclei as they ascend

towards the red nucleus/thalamus

o At the upper ½ of midbrain: The BC/SCP is complete and the large red nucleus becomes visible

on each side

1 The large RN occupies the bulk of the ventral aspect of the midbrain tegmentum

2 The large RN receives descending projections from the ipsilateral cerebral cortex (corticorubral tract)

3 The large RN receives ascending projections from the contralateral deep cerebellar nuclei via the BC

In the BC is a pathway used wherein one side of the cerebellar

hemisphere communicates with the opposite side of the cerebellar hemisphere (cerebellar communication)



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AsturiaNOTES

Although some cerebellar fibers end in the RN, most continue up to

the thalamus as the cerebello-rubro-thalamic nucleus (CRTN) 1 The CRTN sends descending fibers to the ipsilateral

inferior olvies via the rubroolivary tract 2 The CRTN sends descending fibers to the contralateral

spinal motor neurons via the rubrospinal tract 3 Cerebellorubrothalamic pathway is a pathway used so that

one side of cerebellum communicates with the opposite side

of the cerebral hemisphere Olivocerebellar tract

1 Crosses the opposite cerebellar hemisphere

2 Inf.O. Inf. Cerebellar Peduncle a Right inferior olives receives info from L.

cerebellar hemisphere via the Right RN, answers

back via olivocerebellar tract which crosses the opposite side

Corticopontocerebellar tract

1 Cortexpontine nucleicerebellar hemisphere (ex, left cortex to right cerebellum)

Rostral parvicellular portion

1 Origin of the rubroolivary (uncrossed) fibers that course through the central tegmental tract

Caudal magnocellular portion

1 Origin/Source of the rubrospinal fibers that cross and descend on the contralateral side of spinal cord

a Influence the activity of the motor neurons innervating skeletal muscles

Cerebellar relay (UM) o Makes use of 2 relay nuclei:

RN

Inferior Olivary Nucleus o If cerebellum influences a side of the body—it is always IPSILATERAL

because there are 2 decussations (from leftright (1st decussation)left

(2nd decussation)) o If cerebrum influences a side of the body—it is always CONTRALATERAL

because there is only 1 decussation

Ventromedial aspect of the midbrain tegmentum (UM) o The Ventromedial Tegmental Decussation of Forel (VTDF)

Consists of the crossed axons of the RN that descend to the spinal

cord as the rubrospinal tract o The Dorsal Tegmental Decussation of Meynert (DTDM)

Consists of crossed projections of the superior colliculi that

descend to a variety of brainstem areas:



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AsturiaNOTES

1 Tectoreticular

2 Tectoolivary 3 Cervical spinal cord (tectospinal)

Medial lemniscus & accompanying fibers of the anterolateral system (LM) o Lemniscal crescent

Formed by grouping together the different ascending tracts at the lateral portion of the midbrain tegmentum

Made up of various lemniscal pathways (ascending)

1 Lateral lemniscus a Terminates at the inferior colliculus b Driven dorsolaterally next to the inferior colliculus

where its fibers terminates c Receives auditory information from both ears

(through IC)

i Cross and uncrossed auditory 2 Trigeminal lemniscus

a Ventral and dorsal trigeminothalamic tracts are

displaced dorsally b Axons of primary sensory nucleus

i For conscious proprioception of contralateral ½ of face

c Descending nucleus of the trigeminal is for: i Pain ii Temperature

iii Crude Touch d Lesions in the trigeminothalamic tract:

i Hemisensory loss to face that is contralateral

Hemisensory—loss of sensation at one side of body, either right or left

3 Medial lemniscus

a For the following sensory modalities of limbs/trunk: i Conscious proprioception ii Vibration

iii Fine touch b Lesions of medial lemniscus at level of midbrain:

i Contralateral loss of sensation of limbs and

trunk 4 Spinal lemniscus

a Lateral Spinothalamic Trunk i For pain and temperature

b Ventral Spinothalamic Trunk i For crude touch

c a and b are both sensory for trunk/limbs



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AsturiaNOTES

d Both are above decussation (decussate at SC)

Major Ascending Fibers (UM) o Lemniscal crescent seen at the LM (lower midbrain) are present in more or

less at the same positions in the UM EXCEPT: Lateral Lemniscus (LL)

1 Here, LL fibers have already terminated in the IC below o The Spinomesencephalic Fibers

Part of the anterolateral system

Terminates in the: 1 PAG 2 Adjacent regions of the midbrain reticular formation

3 Superior Colliculus The OCULOMOTOR NUCLEAR COMPLEX (SUBNUCLEI) (UM)

o Location: Ventral aspect of PAG close to the median place where it forms

a V-shaped region dorsal to the MLF o Composed of many subnuclei where each nuclei innervates a specific

muscle—PURELY MOTOR

Levator palpebra 1 Action: Lifts eyelids (opens eyes) 2 Lesion involving the CN 3 and levator palpebral muscle will

result to ptosis (drooping of eyelids)

Extraocular muscles 1 Inferior oblique—supplied ipsilaterally 2 Inferior rectus—supplied ipsilaterally

3 Medial rectus—supplied ipsilaterally 4 Super rectus—supplied contralaterally 5 Upward Gaze

a Muscles needed: Inferior oblique (IO) and superior rectus (SR)

b Process:

i The left and right rostral interstitial nucleus of MLF cross at posterior commissure

If posterior commissure is

compressed, upward gaze is imposible

ii Right SR and left IO = up and right eyeball

movement The rostral interstitial nucleus of MLF

stimulates left CN3 to stimulate left

IO and right SR 6 Downward Gaze

a Muscles needed: Inferior rectus (IR) and Superior Oblique (SO)



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AsturiaNOTES

b Process:

i The rostral interstitial nuclei do NOT cross ii They relay impulses to CN4 and CN3

ipsilaterally CN4=for SO

CN3=for IR iii Right IR + Left SO = down and right

eyeball movement iv An aneurysm that compresses CN3, affects

downward gaze Edwinger-Westphal Nucleus (EWN)

1 Is an accessory nucleus of CN3 2 Innervates:

a Iris sphincter muscle

b Ciliary muscle 3 Supplies pareganglionic parasympathetic fibers to the eye:

a For pupillary constriction

b Lens accommodation c Convergence of Eyes

4 EWN is composed of:

a Central nucleus of Perlia that supplies the ciliary muscle for convergence + accommodation

b A lateral somatic cell column

c A midline dorsal somatic cell column d A midline dorsal visceral cell column e B-D (somatic cell columns) innervate all the

extraocular muscles except:

i Lateral Rectus=CN6 ii Superior Oblique=CN4

5 The EWN include:

a Interstitial nucleus of Cajal b Nucleus of Darkschewitsch c Nucleus of the posterior commissure

d Rostral interstitial nucleus of the MLF 6 Lesions at EWN:

a External compression = dilated pupil

Oculomotor nerve o Passes ventromedially in bundles to emerge from within the

interpeduncular fossa medial to the crus cerebri

o Parasympathetic fibers are more superficially located than the somatic fibers

However, the parasympathetic fibers are the first ones to be affected in compression injury



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AsturiaNOTES

Table 4. Summary of important midbrain tegmental nuclei

Nuclear Group Location Neurotransmitter

Raphe Nuclei Within the brainstem tegmentum (buong

brainstem)

Serotonin

Interpeduncular Nucleus Midbrain

Tegmentum

Acetylcholine

Substantia Nigra Pars Compacta

Dopamine

VTA Tsai (Ventral

Tegmental Area of Tsai)

Dopamine

At pons:

o The pontine tegmentum is separated from the tectum by the 4th

ventricle o The pontine tegmentum is separated from the basis by the trapezoid

body—The trapezoid body is the most ventrally located part of the

tegmentum o Trapezoid Body

Made up of transversely crossing auditory fibers that ascend as the lateral lemniscus

Contains crossed auditory fibers from ventral cochlear nucleus and superior olivary nucleus

In the upper ½ of the pons, the trapezoid body is NOT as

prominent o Medial Lemniscus

Flattened, elliptical disc on each side of the medial raphe near the

dorsal border of the basis Crossed fibers only

o Anterolateral System—upper ½ of the pons

Lies very near the dorsolateral aspect of the medial lemniscus Lateral Spinothalamic Tract—for pain and temperature sense

from the trunk and limbs

Ventral Spinothalamic Tract—for touch sense from the trunk and limbs

o Ventral Trigeminothalamic Tract—upper ½ of pons 1 Lies adjacent to the dorsal border of the medial lemniscus

2 Sensory modalities carried from the face: a Pain b Temperature

c Crude and Fine touch d Conscious proprioception e Vibratory sensations



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o Central Tegmental Tract

Dorsolateral to the medial lemniscus Rubroolivary tract (descending)

1 RN of midbrain to inferior olives Reticulothalamic tract (ascending)

1 Reticular formationthalamus In the upper ½ of the pons, the CTT becomes more dorsal

o Superior Olivary Nucleus (SON)

It is a relay nucleus for the auditory pathway Lateral to both the medial lemniscus and central tegmental

tract

Gives rise to axons that cross the opposite side or ascend to the same side

o Trigeminal (CN 5) Nuclei—upper ½ of pons

Nuclei: 1 Motor nuclei of the Trigeminal

a Lie along a groove between MCP and SCP (Middle

and Superior Cerebellar Peduncles) b Gives rise to the small motor root of the

trigeminal that exits the ventrolateral surface of

pons to supply: masticatory muscles 2 Mesencephalic Nucleus of the Trigeminal

a Located more dorsally at the floor of the 4th ventricle medial to the SCP

b Does NOT ascend to the cerebrum c Made up of pseudounipolar neurons that directly

transmit to the trigeminal motor nucleus

i Proprioceptive impulses from the muscle spindles in the jaw

ii Mechanoreceptors in the periodontal

membrane d Concerned with the mechanisms that control the

force of bite

e Has a role in jaw jerk reflex i AKA trigeminotrigeminal reflex ii Afferent limb: Mesencephalic Nucleus of

CN 5 iii Efferent limb: Motor Nucleus of CN 5

3 Principal nucleus of the Trigeminal a AKA Main Sensory Nucleus of the Trigeminal

b Lies along a groove between MCP and SCP c Receives in part, the central processes of the

Trigeminal/Gasserian/Semilunar Ganglion that



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enter the pons as the large sensory root of the

trigeminal d Carries the following sensory modalities (“facial

touch”) from the face: i Conscious proprioception

ii Vibration sense iii Fine touch

e Other touch afferents join the pain and

temperature afferents i And together, they descend and terminate in

the descending or spinal nucleus at the caudal

level f Contributes fibers to the:

i Dorsal trigeminothalamic tract—

uncrossed ii Ventral trigeminothalamic tract—crossed

4 Descending nucleus of the trigeminal

a Location: Lower ½ pons + medulla b Carries the following sensory modalities:

i Pain ii Temperature

iii Crude Touch c Part of the Gasserian Ganglion d It sends collateral connections to the:

i Lacrimal nucleus ii Facial motor nucleus

The trigeminofacial collateral

connection is responsible for corneal reflex/BLINKING

o Afferent limb: Descending

nucleus of CN 5 o Efferent limb: Motor nucleus of

CN 7

5 1, 2, and 3 mentioned above are at the upper ½ of pons occupying the dorsolateral aspect of the pontine tegmentum

o Lateral Lemniscus Lateral to the superior olives Principal ascending auditory pathway Carry sensory fibers from both ears (bilateral) but bulk of info is

from the opposite ear 1 Thus, lesion at this site results in partial deafness only

Crossed fibers, sources:



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1 Dorsal cochlear nucleus

2 Ventral cochlear nucleus 3 Superior Olivary nucleus

Uncrossed fibers: 1 SON of same side

In the upper ½ of pons, the lateral lemniscus is lateral to the anterolateral system

o Medial Lemniscal Fasciculus (MLF)

Most dorsal position on each side of the midline Primary brainstem pathway for conjugate gaze

1 Both eyes look left:

a Lateral rectus of left eye contracts b Medial rectus of right eye contracts

2 Both eyes look right:

a Lateral rectus of right eye contracts b Medial rectus of left eye contracts

Abducens nucleus supplying the lateral rectus and also send

ascending fibers to the contralateral oculomotor nerve that supply the medial rectus

The medial vestibulospinal tract contained here is descending o Descending or Spinal Nucleus and Tract of the Trigeminal

Internally located, receives sensory inputs largely from the trigeminal nerve that enters the pons at a more rostral level

Gives rise to the crossed ventral trigeminothalamic tract that

ascends the pons close to the medial lemniscus Conveys facial pain and thermal sense as well as crude touch

o Other ascending and descending fiber tracts that course through the pontine

tegmentum from and to the spinal cord are situated more laterally o Abducens nucleus

Medial aspect of the floor of the 4th ventricle

Gives rise to the abducens nerve that course: 1 Runs ventrally through the tegmentum, passes adjacent to the

pyramidal tracts in the basis and emerges at the ventral surface

along the inferior pontine sulcus Supplies:

1 The lateral rectus a As the name of the muscle implies, it moves the

eyeball laterally Lesion:

1 Deviates the eyeball medially

o Motor nucleus of the Facial Nerve Dorsal to the superior olives Course:



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1 Its motor root emerges from its dorsal surface, proceeds

dorsomedially towards the floor of the 4th ventricle and then makes a sharp curve (genu) over the abducens nucleus, forming an expanded elevation referred to as the facial colliculus

a It will continue its ventrolateral course within the pontine tegmentum and will exit along the inferior pontine sulcus at the cerebellopontine

angle Supplies MOST of facial muscles, again, EXCEPT for:

1 Masticatory muscles

2 Extraocular muscles such as the: a Orbicularis oculi which is innervated by CN 7 to

close the eye

3 Levator palpebrae a Innervated by CN3 to open the eye

o Lacrimal & Superior Salivary Nuclei

Ventrolateral to the abducens nucleus and dorsomedial to the facial nucleus

Gives rise to the parasympathetic preganglionic efferents of the facial neve that supply the lacrimal and salivary glands

Both exit as part of the smaller intermediate nerve of Wrisberg (nervus intermedius) of the facial nerve

1 The nervus intermedius contains:

a Taste fibers from the anterior 2/3 of the tongue (viscerosensory fibers)

b General sensory afferents from the external ear

(somatic sensory fibers) c Parasympathetic preganglionic efferents from

the lacrimal and superior salivary nucleus

o Vestibular Nuclei The Superior Vestibular Nucleus

1 AKA Bechterew’s Nucleus

The Medial Vestibular Nucleus 1 AKA Principal Vestibular Nucleus

The Lateral Vestibular Nucleus 1 AKA Deiter’s Nucleus

ALL vestibular nuclei lie beneath the area vestibularis at the lateral aspect of the floor of the 4th ventricle medial to the inferior cerebellar peduncle

Together with the inferior vestibular nucleus (found at the open medulla), they receive afferent fibers of the vestibular nerve that come from their cell bodies in the Scarpa’s Ganglion



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The Vestibular division of CN 8 mediates sense of balance and

equilibrium o 2 Descending Tracts of the Vestibular Nuclei

Lateral Vestibulospinal Tract 1 Uncrossed

2 For upright position Medial Vestibulospinal Tract

1 Crossed and uncrossed

2 For head position and head movement by way of influence to the neck muscles (until cervical spinal cord ONLY)

o Cochlear Nucleus

The Dorsal Cochlear Nucleus lies beneath the tuberculum acousticum and ventral cochlear nucleus is anterior to it

1 It hugs the lateral aspect of the ICP at the floor of the 4th

ventricle Sites of synapse of auditory fibers of the cochlear nerve whose cell

bodies lie at the SPIRAL GANGLION

Axons run ventromedially within the pontine tegmentum and may either:

1 synapse at the ipsilateral superior olives 2 cross the midline as part of the trapezoid body to ascend

and synapse in the contralateral lateral lemniscus Lesion in cochlear nucleus/nerve?COMPLETE DEAFNESS that is

ipsilateral

o The Auditory Pathway Components:

1 Cochlear division of CN 8

2 Cochlear Nuclei 3 Superior Olives 4 Trapezoid Body

5 Lateral Lemniscus Lesions:

1 Lesion at the spiral ganglion/peripheral nerve/peripheral

auditory pathway—complete deafness on the ipsilateral side

2 Lesion at the central auditory pathway (lateral

lemniscus)—bilateral partial deafness a The deafness is more prominent on the

contralateral side because bulk of the fibers of the lateral lemniscus are from the opposite ear

o Pontine Reticular Formation Organized into 3 nuclear groups (from medial to lateral

sequence):



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1 Raphe group

2 Medial group 3 Lateral group

Seen at the caudal pontine level 1 Rostral extensions of the nucleus raphe magnus of the

raphe group 2 Gigantocellular nucleus of the medial group 3 Parvocellular nucleus of the lateral group

o Locus Ceruleus—Upper ½ of pons Dorsolateral aspect of the pontine tegmentum close to the floor of the

4th ventricle

Largest collection of noradrenergic neurons in the CNS Major source of noradrenergic axons in the CNS Neurotransmitter: Norepinephrine

o Mesopontine Tegmentum Close and medial to the locus ceruleus Contains some amount of cholinergic neurons that are believed to

contribute to cortical arousal Neurotransmitter: Acetylcholine

o Pontine Reticular Formation Nucleus Raphe Pontis

Oral and Caudal Pontine Reticular Nuclei 1 Medially located 2 Gives rise to the pontine reticulospinal tracts

Parabrachial nuclear complex 1 Laterally located 2 Houses the pontine pneumotaxic and micturition centers

Paramedian Pontine Reticular Formation 1 Brainstem coordinating center for conjugate gaze

Table 5. Important pontine tegmental nuclei with their corresponding neurotransmitter

Nuclear Group Location Neurotransmitter

Locus Ceruleus Level of pons and lower midbrain

Norepinephrine

Pedunculopontine Pons Acetylcholine



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Table 6. Pathways facilitated by the NC and NG

Body Part Conscious Proprioception

Dorsal Unconscious

Ventral Proprioception

Face Principal Nucleus of

the Trigeminal

Trigemino-

Cerebellar Tract

Mesencephalic

Nucleus of the

Trigeminal

Upper Trunk and

Limbs

FCNC Medial

Lemniscus

The NC and

NG will

decussate to

form the

medial

lemniscal

pathway

CuneoCerebellar

TractAccesory/

Lateral Cuneate

Nucleus (ICP)

Cuneocerebellar

tract

Rostral

Spinocerebellar

Tract (ICP and SCP)

Lower Trunk

and Limbs

FGNG Dorsal

SpinoCerebellar

TractDorsal

nucleus of Clarke

(ICP)

VSCT (ICP)

Dorsal Column Medial Lemniscal Pathway For:

o Conscious proprioception of limbs and trunk

o Vibration sense o Fine, discriminative touch

At medulla:

o Central core of the medulla o Contains:

Motor and sensory nuclei of CN 9-12

Medullary reticular formation nuclei 1 Very important for cardiovascular and respiratory

functions!!!

Ascending sensory fiber tracts Autonomic fibers

1 That project to and from the hypothalamus

Descending subcortical motor tracts Medial longitudinal fasciculus

o Shows structural and functional similarities with the same areas in the pons

and midbrain, so that they form a rostrocaudal continuum o The Arcuate Fibers

Fibers that run perpendicular to axis of medulla ONLY medulla has arcuate fibers

1 Internal Arcuate Fibers 2 External Arcuate Fibers



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3. Basis Most ventral of the three longitudinal segments Contains the descending motor cortical tracts At midbrain:

o Contains 3 descending motor tracts Pyramidal tracts = corticospinal + corticobulbar

1 Occupies the intermediate 3/5 of each crus cerebri

Corticopontine fibers 1 Frontopontine Tract—AKA Arnold’s bundle

a Comes from the frontal cortex and lie at the

medial 1/5 of each crus cerebri 2 Occipitopontine/Peneopontine Tract—AKA Turck’s

bundle

a Comes from other parts of the cortex and lie at the lateral 1/5 of each crus cerebri

o The Crus Cerebri (or Crura Cerebri)

Refers to midbrain basis ALONE It shows 2 large fibers diverging like a pair of legs from the rostral

border of the pons and disappearing from view just beneath the optic chiasma and tracts

o The Cereberal Peduncle Refers to both midbrain basis PLUS midbrain tegmentum

At pons:

o Longitudinal Fiber Tracts (Descending Cortical Motor Tracts) Corticopontine Tract Corticospinal Tract

Corticobulbar Tract 1 Corticospinal + Corticobulbar Tracts are collectively known as

the pyramidal tract and are seen as rounded fascicles

o Transverse Fiber Tracts Pontocerebellar Tract

1 Axons of the pontine nuclei that cross (decussate at pontine

basis) the midline and enter the opposite cerebellar hemisphere via the contralateral middle cerebellar peduncle

Corticopontine-Pontocerebellar Pathway 1 One side of the cerebral cortex communicates with the

opposite cerebellar hemisphere a This linkage is one of the key elements in the overall

organization of the motor system

o Pontine Nuclei (scattered) Surrounds the pyramidal tracts Are the sites of termination of the corticopontine tract



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The upper ½ of the pontine basis is much larger

At medulla: o Ventrally located o Contains the pyramidal tracts:

Corticospinal tract

Corticobulbar tract 1 Both are descending cortical motor tracts that assume an oval

or pyramidal shape on cross-section

CRANIAL NERVE SUMMARY Table 7. Cranial Nerve Summary CN NAME COMPONENT SMB* FUNCTION LOCATION

1 Olfactory SVA S smell Cribriform plate

2 Optic SSA S Vision Optic canal

3 Oculomotor GSE, VSE M Eye movements Superior orbital

fissure

4 Trochlear GSE M Eye movements Superior orbital

fissure

5 Trigeminal

B

Ophthalmic GSA Sensory input from cornea,

skin of forehead scalp, eyelids

and nose, membranes of

paranasal sinuses and nasal

cavity

Superior orbital

fissure

Maxillary GSA Skin over maxilla, upper teeth,

membranes of nose, maxillary

sinus and palate

Foramen

rotundum

Mandibular SVE Skin of cheek, mandible and

side of head, lower teeth and

TMJ, membranes of mouth

and anterior tongue

Foramen ovale

6 Abducens SGE M Eye movements Superior orbital

fissure

7 Facial SVE B Muscles of face and scalp,

stapedius, posterior belly of

digastric and stylohyoid

Internal acoustic

meatus, facial

canal,

stylomastoid

foramen SVA Taste from anterior two-thirds

of tongue, floor of mouth and

palate

GVE Salivary glands, lacrimal

gland, glands of the nose and

palate

8 Vestibulocochlear S Internal acoustic

meatus Vestibular SSA Position and movement of

head

cochlear SSA Hearing

9 Glossopharyngeal SVE B Swallowing Jugular foramen



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GVE Parotid gland

GVA, SVA, GSA Taste from posterior third of

tongue, the carotid sinus and

carotid body

10 Vagus GVE, SVE B Heart, thoracic blood vessels,

larynx, trachea, bronchi,

lungs, GI tract, liver, kidneys,

pancreas

Jugular foramen

GVA, SVA, GSA

11 Accessory M Jugular foramen

Cranial root SVE Muscles of soft palate,

pharynx and larynx

Spinal root SVE Sternocleidomastoid and

trapezius

12 Hypoglossal GSE M Tongue shape and movement Hypoglossal canal

HERNIATION SYNDROMES RELATED TO THE BRAINSTEM Herniation—the protrusion of one anatomic structure into the territory of the

another

o Results in: Displacement Damage/Destruction

Neurologic deficits o Types:

Central Herniation/Transtentorial Herniation

1 Space-occupying lesion increases intracranial pressure and forces the diencephalon downward through the tentorial notch and into the brainstem

2 Changes in: a Respiration b Motor and sensory function

i There can be total loss

c Consciousness/Alertness Uncal Herniation

1 An expanding hemorrhagic lesion forces the uncus, the

most rostromedial edge of the temporal lobe, downward over the edge of the tentorium cerebelli and compresses midbrain

2 Results in: a Abnormal eye movement b Changes in respiration

c Abnormal reflexes Upward Cerebellar Herniation

1 A mass in the posterior fossa forces the cerebellum upward

through the tentorial notch and compresses the midbrain 2 Results in:



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a Cerebral infarctions

b Obstruction of the cerebral aqueduct leading to hydrocephalus

Tonsillar Herniation 1 Pressure in the posterior fossa may cause the brainstem to

herniate into the foramen magnum resulting in the compression of the medulla

2 Results in:

a Respiratory changes b Cardiac activity changes

-end- References 1. Lecture notes by RAsturiano (A-2019) from the lecturers 2. Midbrain notes by Aimee Rose C. Tan 3. Pons notes by Rica Adrienne R. Evangelista 4. Medulla notes by Rica Adrienne R. Evangelista 5. High-Yield Neuroanatomy (4th Edition) by James D. Fix 6. Brainstem Generalities notes by Laura Maniebo Downloadable for free at: www.theelusivedoktora.wordpress.com For any corrections you may find, content or otherwise, email me at: [email protected]

-THANKS-

AsturiaNOTES By RAsturiano

#TheElusiveDoktora

http://www.theelusivedoktora.wordpress.com/

mailto:[email protected]

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AsturiaNOTES Lecture 6&7: Brainstem · PDF fileLecture 6&7: Brainstem Neuroscience1: Entire 2nd shift: Midbrain, Pons, Medulla, CNs ... Cranial Nerves 3-12 (the last 10 cranial nerves)