JLPascual Brainstem Version 2

THE BRAINSTEM

J. Leonard Pascual MD FPNAAssociate Professor, Department of Anatomy, College of Medicine, UP ManilaDepartment of Neurosciences, Philippine General Hospital

OBJECTIVES

FORM: identify the different structures in the brainstem External anatomy

Subdivisions (diencephalon, midbrain, pons, medulla) Fissures and sulci Cranial nerves Peduncles Relationships to surrounding structures and cisterns

Cross-sectional anatomy Subdivisions (tectum, tegmentum) Grey matter (cranial nerve nuclei, other nuclei) White matter (fiber tracts)

FUNCTION: know the significance of each structure of the brainstem in the normal human being

Neuroanatomy at a Glance



The diencephalon is actually the most rostral end of the brainstem

Subdivisions of the Brainstem

DiencephalonMidbrainPonsMedulla

Hypothalamus

Infundibulum

Mammillary body

Internal capsule

Internal capsule

Basal ganglia

Internal capsule

Basal ganglia

Optic nerve

Internal capsule

Basal ganglia

Optic nerve

Optic chiasm

Internal capsule

Basal ganglia

Optic nerve

Optic chiasm

Optic tract

Mammillary body

Hypothalamus

Third ventricle

Putamen

Putamen

Nucleus accumbens

Putamen

Nucleus accumbens

Anterior limb, internal capsule

Putamen

Nucleus accumbens

Anterior limb, internal capsule

Posterior limb, internal capsule

Hypothalamus

Thalamus

Pineal body

Habenula

Third ventricle

Internal capsule

Internal capsule

Caudate nucleus

Internal capsule

Caudate nucleusPutamen

Third ventricle

Thalamus

Subthalamus

Infundibulum

Hypothalamus

Anterior commissure Posterior commissure

Third ventricle

Mammillary body

Thalamus

Thalamus

Hypothalamus

Third ventricle

Interthalamic adhesion

Thalamus

The thalami are paired symmetrical bulb-shaped masses obliquely and lateral to the 3rd ventricle

Thalamus

The thalami are paired symmetrical bulb-shaped masses located obliquely and lateral to the 3rd ventricle

Thalamus

Lies medial to the posterior limb of the internal capsule

Thalamus

Between 70-80% of humans will have an interthalamic adhesion (massa intermedia) connecting both thalami










Subdivisions of the Brainstem (lateral view)

Subdivisions of the Brainstem (dorsal view)

Subdivisions of the Brainstem (ventral view)

Midbrain (cerebral peduncles)

Pons (basis pontis)

Medulla oblongata

Interpeduncular fossa

Cerebellopontine angle

Pontomedullary sulcus

Anterior median sulcus

Anterolateral sulcus

Pyramid

Olive


Anterior median sulcus

Anteriorolateral sulcus

Posterolateral sulcus

Pyramid

Pyramid

CP angle

Medulla

Pons

Midbrain

Thalamus

Posterior commissure

Cerebral peduncle

Superior cerebellar peduncle

Superior colliculus

Inferior colliculus

Middle cerebellar peduncle


Pons

Latin for “bridge” (ventral pons appears like a bridge between cerebellar hemispheres)Cerebellar peduncles

(brachium conjunctivum) (brachium pontis)

Superior cerebellar peduncle


Floor of the 4th ventricle

*Obex

*Obex

Open medulla

Closed medulla

*Obex

Open medulla

Closed medulla

*

Inferior cerebellar peduncle

The Cranial Nerves

Olfactory nerve

Optic nerve, chiasm, and

tract

Interpeduncular fossa

Midbrain

The oculomotor nerve exits from the ventral surface of the midbrain into the space between the two cerebral peduncles (interpeduncular fossa)

Oculomotor nerve

Oculomotor nerve

Uncus

Midbrain

The trochlear nerve exits dorsally at the junction between the caudal midbrain and pons

Trochlear nerve


Trochlear nerve

Trochlear nerve

Parahippocampal gyrus

Pons

The trigeminal nerve enters the brainstem at mid-ponsTri – Gemini (3 twins): ophthalmic, maxillary, and mandibular nerves

Trigeminal nerve

Trigeminal nerve Middle cerebellar peduncle

Pons

3 other cranial nerves enter / leave along groove between pons and medulla (pontomedullary sulcus)

Pons

The abducens nerve is the smallest and most medial of the 3 cranial nerves that enter / leave at the pontomedullary junction

Pons

The facial nerve is further lateralConsists of a larger medial root and a smaller sensory root (nervus intermedius)

Pons

The vestibulocochlear nerve is slightly lateral to the facial nerve

Consists of a vestibular division and a more lateral cochlear division

Abducens nerve

Abducens nerve


Facial nerve

Vestibulocochlear nerve

Vagus nerve

Vagus nerve

Olive

Hypoglossal nerve

Hypoglossal nerve

Pyramid

Abducens nerve

Facial nerve

Vestibulo-cochlear nerve

Posterolateral sulcus

Glossopharyngeal nerve

Vagus nerve

Anterolateral sulcus

Hypoglossal nerve

Spinal accessory nerve

Spinal accessory nerve

The Brain “Stem”: Nuclei

Organizational Set-Up of the Nervous System

ROSTRAL CAUDAL


DORSAL

VENTRAL


DORSAL

VENTRAL

Neurons specialized for receiving information (SENSORY) from the environment and their axons are located dorsally


DORSAL

VENTRAL

Neurons specialized for receiving information (SENSORY) from the environment and their axons are located dorsally

Neurons that control movements (MOTOR) are located ventrally




Curling of the neural tube results in rotation of structures in the telencephalonVentral structures come to lie anteriorly (MOTOR)Dorsal structures come to lie posteriorly (SENSORY)

anterior

posterior

ventral dorsal

dorsal

ventral

anterior posterior


The dorsal:sensory / ventral:motor orientation remains the same within the brainstem and spinal cord

anterior

posterior

ventral dorsal

dorsal

ventral

anterior posterior

Embryology and the Architecture of the Brainstem

4th Ventricle

Somatic afferent column

Sensory inputsLocated dorsally and laterally


4th Ventricle


Sensory inputsLocated dorsally and laterally

Somatic efferent column

Motor output for muscles

Located ventrally and medially


4th Ventricle

SENSORY

MOTOR

Sulcus limitans


4th Ventricle


Somatic afferents

Visceral afferents

Unlike the spinal cord which innervates only skeletal muscles (somites), the brainstem also innervates muscles in the face derived from the branchial arches


Somatic efferent

Visceral efferent


4th Ventricle


Somatic afferents

GSA

SSA

Visceral afferentsGVA

SVA

Additional components in cranial nerves are innervations for special functions


Somatic efferentGSE

Visceral efferent

GVE

SVE



Somatic afferents

GSA

SSA


SSA: afferents to the special senses


Somatic efferentGSE

Visceral efferent

GVE

Vision

Hearing and balance



Somatic afferents

GSA

SSA


SVA

SVA's are sensory nerves that develop in association with the gastrointestinal system


Somatic efferentGSE

Visceral efferent

GVE

Olfaction Taste

Choking



Somatic afferents

GSA

SSA


SVA

SVE's innervate muscles derived from the branchial arches (branchiomotor nerves)


Somatic efferentGSE

Visceral efferent

GVE

SVESwallowing and digesting

Chewing

Smiling and facial movements


4th Ventricle


SSAGSA

GVA

SVA


4th Ventricle



GVE

SVE

GSE


Somatic afferents

GSA

SSA


SVA


Somatic efferentGSE

Visceral efferent

GVE

SVE

Columnar arrangement of cranial nerve nuclei

Cranial nerve fibers will proceed to / arise from cranial nerve nuclei

III

Cranial Nerve Nuclei in the Midbrain

Oculomotor nerve nuclei complex

III


Oculomotor nerve nuclei complexEdinger-Westphal nucleus

EW

III


Oculomotor nerve nuclei complexEdinger-Westphal nucleusTrochlear nerve nucleus

IV

EW

III


Oculomotor nerve nuclei complexEdinger-Westphal nucleusTrochlear nerve nucleusMesencephalic nucleus of CN V

IV

EW

V

III


Oculomotor nerve nuclei complexEdinger-Westphal nucleusTrochlear nerve nucleusMesencephalic nucleus of CN V

IV

EW

V

345 MB

Cranial Nerve Nuclei in the Pons

Motor nucleus of CN V

V


Motor nucleus of CN VAbducens nucleus

V

VI


Motor nucleus of CN VAbducens nucleusFacial nucleus

V

VI

VII


Motor nucleus of CN VAbducens nucleusFacial nucleusSuperior salivatory nucleus (CN X)

V

VI

VII

X


Main sensory nucleus of CN V

V

VI

VII

X

V


Main sensory nucleus of CN VSpinal nucleus of CN V

V

VI

VII

X

V

V


Main sensory nucleus of CN VSpinal nucleus of CN VVestibular nucleus (CN VIII)

V

VI

VII

X

V

VVII


Main sensory nucleus of CN VSpinal nucleus of CN VVestibular nucleus (CN VIII)Cochlear nucleus (CN VIII)

V

VI

VII

X

V

VVIII

VIII


V

VI

VII

X

V

VVIII

VIII

Motor nuclei


V

VI

VII

X

V

VVIII

VIII

Motor nuclei

Sensory nuclei

Cranial Nerve Nuclei in the Rostral Medulla

Hypoglossal nucleus

XII


Hypoglossal nucleusAmbiguous nucleus (CN's IX and X)

XII X

IX


Hypoglossal nucleusAmbiguous nucleus (CN's IX and X)Inferior salivatory nucleus (CN IX)

XII X

IX

IX


Hypoglossal nucleusAmbiguous nucleus (CN's IX and X)Inferior salivatory nucleus (CN IX)Dorsal motor nucleus of CN X

XII X

IX

IX

X


Solitary nucleus (CN X)

XII X

IX

IX

X

X


Solitary nucleus (CN X)Continuation of Spinal nucleus of CN V

XII X

IX

IX

X

X V


Solitary nucleus (CN X)Continuation of Spinal nucleus of CN VContinuation of Vestibular nucleus

XII X

IX

IX

X

X V

VIII

Cranial Nerve Nuclei in the Caudal Medulla

Accessory nucleus

XI

Cranial Nerve Nuclei in the Caudal Medulla

Accessory nucleusSpinal nucleus of CN V (continuation)

XI

V

The Brain “Stem”: Long Tracts


DESCENDING

ASCENDING


DECUSSATION


LAMINATION

The Brainstem and its contents

Grey matter on the insideWhite matter on the outside


Grey matter on the insideCranial nerve nucleiReticular formationPontine nuclei

White matter on the outside



White matter on the outsideAscendingDescendingMixed ascending and descending



White matter on the outsideAscending

Reticular activating system Spinothalamic tract Spinocerebellar tract Medial lemniscal – dorsal column pathway Auditory pathway Gustatory pathway

DescendingMixed ascending and descending

ASCENDING RETICULAR ACTIVATING SYSTEM

ASCENDING RETICULAR ACTIVATING SYSTEM

Portion of the reticular formation concerned with arousalEnsures that thalamocortical impulses are fired to “awaken” the cerebral hemispheresDamage leads to comaAffected by psychotropic drugs and anestheticsOveractivity (imbalance of norepinephrine) has been linked to ADHD (attention deficit hyperactivity disorder)



White matter on the outsideAscendingDescending

Corticospinal tract Corticobulbar tract

Mixed ascending and descending



White matter on the outsideAscendingDescendingMixed ascending and descending

Medial longitudinal fasciculus

Corticospinal tract

Spinothalamic tract

Medial longitudinal fasciculus

Cross-sectional Anatomy of the

Brainstem


EXTRA-AXIAL

INTRA-AXIAL


EXTRAMEDULLARY

MEDULLARY

Architecture of the Brainstem

General morphology of the brainstem:

Tectum: roof of ventricular cavityTegmentum: floor of ventricular cavity:

Dorsolateral: sensory fibers / nucleiVentromedial: motor cranial nucleiIn between: reticular formation

Base: mainly motor fibers



Cerebral aqueduct


Cerebral peduncle

Midbrain

Large cerebral peduncles on its anterior surface


Substantia nigra




Thalamus


Thalamus

3rd ventricle


Red nucleus


Red nucleus

Pinkish color is attributed to iron content


Red nucleus

Pinkish color is attributed to iron content

Mainly responsible for movement in animals without corticospinal tracts (controls large muscle groups)


Red nucleus

Crawling of babies and arm swing is controlled by this nucleus

Midbrain (Internal Structure)

Rostral midbrain: contains the superior colliculiExtends from the intercollicular groove to the posterior commissure

Rostral Midbrain

Superior colliculus: paired bumps in the midbrain tectumIts neurons respond to visual, auditory, and somatosensory stimuliTogether with the inferior colliculus = corpora quadrigemina

Rostral Midbrain

Superior colliculus: involved in saccades (fast eye movements)

Helps orient the head and the eyes towards something seen or heard

Rostral Midbrain

Substantia nigra: pale on myelin-stained brain tissue, dark on unstained brain tissue

produces dopamineReceives and sends fibers to the putamen (striatum) and caudate nucleus

Rostral Midbrain

Ventral tegmental area: lies close to the substantia nigra and red nucleus

Provides dopaminergic innervation to the frontal cortex and limbic systemActivities that elicit pleasure activates this area (including psychostimulants like cocaine)

Reward / addiction Fear / avoidance behavior

Ventral tegmental area of the midbrain

Rostral Midbrain

Oculomotor nucleus: in the floor of the cerebral aqueductActually a complex of 2 groups of smaller subnuclei that innervate individual muscles

Rostral Midbrain

Oculomotor nuclei complex: the subnucleus for the levator palpebrae superioris (upper eyelid) is shared by both oculomotor nuclei

Rostral Midbrain

Oculomotor nuclei complex: the nucleus for the superior rectus (SR) muscle travels in the contralateral oculomotor nerve (similar to CN IV) to innervate the contralateral muscle.

SR

Rostral Midbrain

Oculomotor nuclei complex: the nucleus for the medial rectus (MR), inferior oblique (IO), and inferior rectus (IR) muscles travel in the ipsilateral CN III to the eyeball

MR IO

IR

Rostral Midbrain

Edinger-Westphal nucleus:Lies in close proximity to CN III nucleusSends GVE's to the ipsilateral ciliary ganglion

Ciliary ganglion innervates the sphincter pupillae (iris) and ciliary muscle

Midbrain (Internal Structure)

Caudal midbrain: contains the inferior colliculiExtends from where the trochlear nerve emerges to the intercollicular groove

Caudal midbrain

The 4th ventricle has narrowed into the cerebral aqueductThe periaqueductal gray matter encircles the aqueduct

Cerebral aqueduct

Periaqueductal gray

Caudal midbrain

Periaqueductal gray:Role in defensive behavior in animals (freezing, jumping, rapid heart beat, high blood pressure)Role in female copulatory behavior (lordosis behavior) via pathway from the hypothalamusExcited by endorphins and by opiate analgesics

Caudal midbrain

The inferior colliculus: principal nucleus of the auditory pathway in the midbrain

Relays auditory input from the contralateral ear to the thalamus (medial geniculate body)

Inferior colliculus

Caudal midbrain

The MLF continues its course in the midline below the floor of the cerebral aqueduct

MLF

Caudal midbrain

The tiny trochlear nucleus lies lateral to the MLF

Trochlear nucleus

Caudal midbrain

Trochlear nucleus: fibers decussate in the superior medullary velum of the tectum and exit dorsally.

Superior medullary velum

Caudal midbrain

Trochlear nucleus: innervates the contralateral superior oblique muscle of the eyeball


Pons (Internal Structure)

Rostral pons: from the point of attachment of the trigeminal nerve to the beginning of the cerebral aqueduct / at the point of emergence of the trochlear nerve

Rostral Pons

The median longitudinal fasciculus (MLF) lies near the midline beneath the 4th ventricle

Rostral Pons

The superior cerebellar peduncle appears in the lateral walls of the 4th ventricle

Major outflow from the cerebellum (efferent) to the thalamus

Rostral Pons

Locus ceruleus: contains norepinephrine, innervates virtually the entire CNS, from spinal cord to cerebral cortex

Increased firing rate of neurons during arousal, decreases with drowsiness, and abolished during sleepReceives afferents from hypothalamus, cingulate cortex, and amygdalaActivated during stress, neurons seen to be depleted in posttraumatic stress disorder patients

Pons (Internal Structure)

Caudal pons: bottom half of the pons from the point of attachment of CN V to the lateral wall of the 4th ventricle

Caudal Pons

Caudal pons: bottom half of the pons from the point of attachment of CN V to the lateral wall of the 4th ventricle

Caudal Pons

The pyramidal tract is broken up by pontine nuclei and their decussating fibers, which form the middle cerebellar peduncle


Motor nucleus of CN VAbducens nucleusFacial nucleusSuperior salivatory nucleus (CN X)

V

VI

VII

X


Main sensory nucleus of CN VSpinal nucleus of CN VVestibular nucleus (CN VIII)Cochlear nucleus (CN VIII)

V

VI

VII

X

V

VVIII

VIII

Caudal Pons

The facial colliculus is formed by fascicles from the facial nucleus which loop around the abducens nucleus which lies on the floor of the 4th ventricle

CN VI

CN VII

Caudal Pons

CN VI

CN VII

The facial colliculus is formed by fascicles from the facial nucleus which loop around the abducens nucleus which lies on the floor of the 4th ventricle

Caudal Pons

The abducens innervates the lateral rectus muscle of the eyeball (GSE)

Due to the long distance it travels en route to the eyeball, it is most frequently compressed / stretched by space-occupying lesions in the cranial cavityUsually stretched / compressed against the clivus

Caudal Pons

The abducens lies in close proximity to the parapontine reticular formation (PPRF) which is the horizontal gaze center in the pons

Caudal Pons

The MLF is nearby (yokes / synchronizes the movements of the eyeballs)

Connects the abducens to the contralateral oculomotor nucleus in the midbrain





Medulla (Internal Structure)

Rostral medulla: from the obex to the lateral recess where the inferior cerebellar peduncle enters the cerebellum

Rostral Medulla

The rostral medulla no longer looks like the spinal cord due to the presence of the 4th ventricle dorsally

Rostral Medulla

The inferior olivary nucleus is a prominent feature of the rostral medulla, forms the swelling called the olive.

Fibers from each nucleus arch across the midline to enter the contralateral inferior cerebellar peduncle


Hypoglossal nucleusAmbiguous nucleus (CN's IX and X)Inferior salivatory nucleus (CN IX)Dorsal motor nucleus of CN X

XII X

IX

IX

X


Solitary nucleus (CN X)Continuation of Spinal nucleus of CN VContinuation of Vestibular nucleus

XII X

IX

IX

X

X V

VIII

Rostral Medulla

Fascicles of the hypoglossal nerve exit between the pyramid and the inferior olivary nucleus

Rostral Medulla

Fascicles of the hypoglossal nerve exit between the pyramid and the inferior olivary nucleus

Innervates the muscles of the tongue (general visceral efferent)

Rostral Medulla

A pair of medial longitudinal fasciculi (MLF) lie beneath the floor of the 4th ventricle posterior to the medial lemniscus, can be traced all the way to the midbrain

involved in yoking eye movements as well as vestibular functions

Rostral Medulla

The dorsal motor nucleus of the vagus lies in the floor of the 4th ventricle, dorsolateral to the hypoglossal nucleus

Main parasympathetic nucleusSends GVE to the thoracic and abdominal viscera

Rostral Medulla

The solitary tract and nucleus of the vagus lies in the floor of the 4th ventricle, lateral to the dorsal nucleus of X

Taste impulses from the CN VII, IX, X, and XI (gustatory / rostral half of the solitary nucleus)

Rostral Medulla

The solitary tract and nucleus of the vagus:The caudal half of the solitary nucleus receives cranial afferent inputs related to cardiovascular, respiratory, and gastrointestinal receptors

Rostral Medulla

The solitary tract and nucleus of the vagus:Mediates the cough reflex, baroceptor reflex, gag reflex, baroceptor and chemoreceptor reflexes, among others

Rostral Medulla

The solitary tract and nucleus of the vagus:Projects efferent output to the hypothalamus, cingulate gyrus, and other brainstem nuclei (heart beat, breathing)

Rostral Medulla

The ambiguous nucleus:Cannot be distinguished in myelin stained brain tissueLocated dorsal to the inferior olivary nucleus, within the ventrolateral tegmentum, embedded within the reticular formation

Nucleus ambiguus

Rostral Medulla

The ambiguous nucleus:Gives rise to SVE's that travel within the glossopharyngeal nerve to innervate the stylopharyngeus muscle, and within the vagus nerve to innervate the rest of the pharyngeal muscles (swallowing)

Rostral Medulla

The vestibular and cochlear nuclei are found dorsolaterally

The Pontomedullary Junction

Lateral recess of the 4th ventricle

The vestibular and cochlear nuclei occupy the ventricular floor at the pontomedullary junction


Medulla (Ventral aspect)

Pyramids contain the descending fibers of the corticospinal tract

Crossing over of the fibers to the other side (decussation)

Medulla (Dorsal aspect)

The dorsal columns of the spinal cord continue into the medulla

The cuneate fasciculus ends in a swelling called the cuneate tubercle (overlying the nucleus cuneatus)

Medulla (Dorsal aspect)

The dorsal columns of the spinal cord continue into the medulla

The fasciculus gracilis near the midline ends in a similar small bump called the gracile tubercle (or clava) overlying the nucleus gracilis.

Medulla (Internal Structure)

Caudal medulla: from pyramidal decussation to the obexSimilar appearance to the spinal cord

Caudal Medulla

The pyramids of the corticospinal tract lie most anteriorly

Fibers will decussate and travel to the contralateral anterior horn of the spinal cord

External Relationships of the Brainstem

External Anatomical Relationships of the Brainstem

The ventral brainstem is bathed in cerebrospinal fluid within the subarachnoid space

Contains blood vessels and cranial nerves


Interpeduncular cistern = the space between (and around) the two cerebral peduncles in the midbrain


Interpeduncular cistern = the space between (and around) the two cerebral peduncles in the midbrain


The basilar artery runs across the midline of the pons within the pontine cistern


Medullary cistern


The cerebral peduncles of the midbrain must pass through the incisura of the tentorium cerebelli


Clivus is a sloping shallow depression of the sphenoid bone of the base of the skull which supports the pons


The sphenoid sinus is one of the paranasal sinuses that lies beneath the sella turcica (where the pituitary gland sits) and anterior to the clivus


Pontocerebellar cistern over the cerebellopontine angleThe facial and vestibulocochlear nerves as well as the trigeminal nerve lie close to the cerebellum

CN V

CN VII

CN VIII


Foramen magnum is the largest opening of the skull through which the medulla passes to become the spinal cord

Pons (Dorsal Aspect)

Cerebellar peduncles The superior cerebellar peduncles form the roof of diamond-shaped cavity of the 4th ventricle

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JLPascual Brainstem Version 2