Overview of: Overview of: The TelencephalonThe Telencephalon

Haines Chapter 16Haines Chapter 16

Neurology Academic Half-DayNeurology Academic Half-Day

Robert Altman PGY 2Robert Altman PGY 2

March 4th 2009March 4th 2009

Overview

• Pre-Test• Development• Lobes of the Cerebral Cortex• WM of the Cerebral Hemispheres• Basal Nuclei• Hippocampus and Amygdala• Post-Test

Pre-Test

1. Destructive lesions to the frontal eye fields results in conjugate deviation of the eyes ipsilaterally or contrlaterally?

2. The retrolenticular limb of the internal capsule contains what type of fibers? Lesions to these cause what deficits?

3. Name the syndrome causing deficits reflecting damage to the internal capsule and optic tract ?

Before getting started

• Structure >>>> function

• Some functional anatomy and clinical pearls

• Lots of images and diagrams

B= 6 wks

A= 4.75 wks

Development

• Telencephalic flexure develops at 5 wks

• Cerebral vesicles enlarge• Pull on neural canal – lateral

ventricles• Interventricular foramina

(connections of lateral ventricles to 3rd) are initially large but become smaller as development progresses

C= 6.5 wks

D= 8.5 wks

• rapid enlargement of forebrain regions: telencephalon.

• Ventricular spaces (dashed lines, A-D) follow the shape changes in the brain

The Telencephalon

Developmental Defects

• Largely a review of chapter 5• Improper migration of maturing neurons on radial glia• Structural +/- functional defects in cerebral cortex

– Lissencephaly– Pachygyria– Microgyria– Holoprosencephaly (pre-neurulation defect)

• Alobar holoprosencephaly• Semilobar holoprosencephaly• Lobar holoprosencephaly

– Anencephaly– Agenesis of the corpus callosum

Failure of the anterior neuropore to close.

The lamina terminalis represents the adult position of the anterior neuropore

The Telencephalon

• 85% total brain weight

• Sensory, motor functions– Subcortical modulation

• Interrelating circuits / association areas

Overview

• Two large cerebral hemispheres– Cortex: outer layer(s) of cells– Gyri– Sulci

• Subcortical white matter• Basal Nuclei• Amygdala

*Subthalamic nucleus (diencephalon)

* Substanstia nigra (mesencephalon)

White Matter

1. Associtaion bundles– Connect adjacent or distant gyri in one

hemisphere

2. Commisural bundles– Connect the two hemispheres

3. Internal capsule– Corticofugal fibers (efferent)– Corticopetal fibers (afferent)

Hippocampal Complex and Amygdala

• In walls of temporal horn of lateral ventricle

• Axons coalesce:– Fornix (H)– StriaTerminalis (A)

• As development progresses, striatum is bisected by axons to and from the cerebral cortex– Internal capsule

• Medial caudate• Lateral putamen• Globus pallidus

– From diencephalon, migrates across internal capsule to be medial to putamen

• “Lenticular nucleus” = GP + P

Corpus Striatum

Commisural bundles & hippocampus

• Medial aspects of hemispheres– Origins of major commisural bundles & hippocampus– Develop in this order:

1. Anterior commisure– Arises from lamina terminalis– From commisure to optic chiasm

2. Hippocampal commisure– Along hippocampal primordium– Posteromedialtemporal– Crossing as growth occurs

3. Corpus callosum– From area of lamina terminalis– Initially composed of astrocytic processes– CC enlarges caudal direction

Lobes of Cerebral Cortex• 6 lobes

• Defined by sulci

• 5 exposed on surface of cerebral hemisphere– Insular located internal to lateral sulcus

• 4 named according to overlying bones

LATERAL

MEDIAL

VENTRAL

“Insular Lobe”

• Deep to Sylvian sulcus

• Satisfies definition as subdivision of cerebral cortex– Separated from adjoining cortical structures

by a named sulcus • Circular sulcus of the insula

Frontal Lobe

ORBITO-FRONTAL SURFACE

•Olfaction•Medial and lateral striae

•Olfactory trigone

•Anterior perforated substance

•Functionally related to limbic system

Frontal Lobe

Contiunous with anterior paracentral gyrus on medial surface

Together form: Primary Somatomotor Cortex

Frontal Function

• Primary somatomotor cortex (Brodmann 4)– Homonculus

• Frontal Eye Fields– Depths of precentral sulcus and in

cortex forming rostral bank of precentral sulcus

– Brodmann area 6 and extends to the transitional area between areas 6 and 8 in the most caudal portion

– projects to nuclei in the midbrain and pons (PPRF)

– Irritative vs. destructive lesions

• Inferior frontal gyrus in the dominant hemisphere called the Broca convolution – Brodmann area 44 – Expressive, non-fluent– Motor aphasia

Parietal Lobe

• Primary somatosensory cortex– Postcentral gyrus– Posterior paracentral lobule

• Somatosensory Cortex: Brodmann 3,1,2• Wernike’s Area: supramarginal (40) and

marginal = angular gyrus (39)– Clinically includes 21, 22 as well; extending into

temporal lobe– Fluent aphasia – Receptive

• Somatotopy similar to motor strip

LATERAL

*

*

* = inf. Parietal lobule

Parietal Lobe Anatomy

Parietal Lobe Anatomy

• Gertsmann’s Syndrome– Lesion located in inferior parietal

lobule• Below the interparietal sulcus,

particularly the angular gyrus or subjacent WM of the L hemisphere

1. Finger agnosia

2. Dyscalculia

3. Dysgraphia

4. Word alexia (and homonymous hemianopia, or lower quadrantopia, of which patient is unaware)

“Optic Ataxia”

• Defect in the superior parietal lobule of the dominant hemisphere– It represents a multi-modal sensory

integration center; cerebellar inputs, striate cortex inputs (areas 5 and 7)

– Outputs to 6,8 the visual components of movement (impaired judgement of depth)

Temporal Lobe

• Between the lateral and collateral sulcus• Superior, middle, inferior temporal gyri• Occipitotemporal gyri• Superior temporal sulcus• Inferior temporal sulcus• Transverse temporal gyri (of Heschl)

– Primary auditory cortex (Brodmann 41, 42)– Lesions result not in deafness, but in interpreting

sounds, localizing sound in space

Insular Lobe

• Oval region of cortex deep in lateral fissure– Gyri longi– Gyri breves– Central sulcus of insula

• Continuous at the circular sulcus of insula with adjacent frontal, parietal, temporal lobes

• “Lips” / opercula overlie insular region

• Exact function unclear, but nociceptive and viscerosensory input received here

Occipital Lobe

• Medial surface:– Parieto-occipital sulcus separates the cuneus

(occipital) from pre-cuneus (parietal)– Calcarine fissure/sulcus

• Separates the cuneus from the lingual gyrus

• Primary Visual Cortex– Brodmann 17, areas directly bordering

calcarine fissure

Limbic Lobe

• Limbic system– Very complex system– Chapter 31 dedicated to it– Includes lobe + afferent and efferent

connections to telencephalon, diencephalon, brainstem nuclei

• Linked to circuits that influence memory, learning and behaviour

Vasculature

Vasculature

•Details in Chp 8

•A1, A2

•M1, M2, M3, M4

•P1, P2, P3, P4

White Matter

1. Association Fibers– Connect adjacent or distant gyri in the same hemisphere– Short or long– Eg. Cingulum (CG-PHG), inferior longitundinal fasciculus

(T-O), uncinate fasciculus (F-T), Superior Longitundinal Fasciculus (F-P-O), arcuate (F-T), inferior fronto-occipital

– Claustrum: thin layer of neuron cell bodies in the insular cortex between two small association bundles

– Insular cortex - Extreme capsule - Claustrum - External capsule - putamen

White Matter

2. Commisural bundles– interconnect corresponding structures on either side

of the neuraxis• Corpus Callosum; rostrum, genu, body (trunk), splenium• Minor, major forceps• Tapetum (lateral wall of the atrium and posterior horn of the lateral ventricle)

• Anterior commissure and the hippocampal commissure• Posterior commissure and the habenular commissure

Commisures

White Matter3. Projection Fibers

– Corticopetal fibers (afferent: i.e. thalamocortical fibers ) Vs. Corticofugal fibers (efferent: i.e. corticospinal, corticopontine, and corticothalamic fibers)

– Internal capsule– Anterior limb:

– Thalamocortical/corticothalamic fibers (collectively called the anterior thalamic radiations) that interconnect the dorsomedial and anterior thalamic nuclei with areas of the frontal lobe and the cingulate gyrus.

– Frontopontine fibers, especially those from the prefrontal areas. • Genu:

– Corticonuclear (corticobulbar) fibers that arise in the frontal cortex just rostral to the precentral sulcus and from the precentral gyrus (primary motor cortex) and project to the motor nuclei of cranial nerves.

– Commonly facial and hypoglossal nerves • Posterior limb :

– It is sometimes divided into a: » thalamolenticular part » sublenticular part (ventral)» retrolenticular part (caudal)

Corona radiata ("radiating crown"), which contains converging corticofugal fibers, as well as diverging

corticopetal fibers

Vasculature of the Internal Capsule

• The anterior limb receives somewhat of a dual blood supply, lenticulostriate arteries, medial striate artery (usually a branch of A2)

• Genu and most of the posterior limb: Lenticulostriate arteries (M1)• Inferior region of the posterior limb, the optic tract, and the

immediately adjacent retrolenticular limb: Branches of the anterior choroidal artery

• Clinical Pearl:– Lesions of the posterior limb may result in a combination of

motor (corticospinal tract involvement) and sensory (thalamocortical fiber involvement) deficits that are seen on the side of the body contralateral to the lesion

– Lesions of the retrolenticular limb result in visual deficits (optic radiation fiber involvement)

Thalamic vasculature

Basal Nuclei

1. the caudate and lenticular nuclei (together forming the dorsal basal nuclei)

2. the nucleus accumbens plus parts of the adjacent olfactory tubercle (the ventral striatum), and

3. the substantia innominata (ventral pallidum)

Subthalamic nucleus and the substantia nigra are not components of the basal nuclei

Basal Nuclei

• Function of basal nuclei:– “function primarily in the motor sphere”

• Caudate and Lenticular Nuclei – caudate nucleus is characteristically located in the

lateral wall of the lateral ventricle and consists of three parts,

• head• body• tail

– "C" shape of the caudate nucleus faithfully follows the "C" shape of the lateral ventricle

Basal Nuclei

Basal Nuclei

Basal Nuclei

• Lenticular nucleus is located within the base of the hemisphere and is surrounded by WM

• The internal capsule borders the lenticular nucleus medially, and the external capsule separates it from the claustrum laterally

• Globus pallidus– medial (internal) and lateral (external) parts

• thin sheet of WM separates them

– The globus pallidus • also separated from the putamen by a thin lamina of WM

Nucleus Accumbens and Substantia Innominata

• N. Accumbens: – where the putamen is continuous with

the head of the caudate nucleus– closely apposed to the septal nuclei

and the nucleus of the diagonal band

• Substantia innominata (basal nucleus of Meynert)

– located internal to the anterior perforated substance in the area inferior to the anterior commissure

– Especially noticeable loss of larger neurons in the substantia innominata in

Alzheimer’s disease

Subthalamic Nucleus and Substantia Nigra

• Intimately allied with the basal nuclei based on their connections • The subthalamic nucleus = flattened, lens-shaped cell group located rostral

to the substantia nigra • It is medial to the internal capsule and is capped by a thin sheet of fibers

called the lenticular fasciculus

• Lesions of the subthalamic nucleus, which are commonly hemorrhagic in origin, result in a contralateral hemiballismus

• The substantia nigra, a part of the midbrain, is found internal to the crus cerebri and immediately caudal to the subthalamic nucleus

– pars reticulata – pars compacta

• numerous melanin-containing neuron cell bodies • utilize dopamine as their neurotransmitter• Integral in pathogenesis of PD

Major Connections of the Basal Nuclei

• Chp 26

• BN efferents:1. lenticular fasciculus

2. ansa lenticularis

• Subthalamic fasciculus

• Connections b/w substantia nigra and neostriatum

Bidirectional connections between the neostriatum and the substantia nigra course through the lateral aspect of the midbrain-diencephalic junction at the interface between the crus cerebri and the substantia nigra

Vasculature of the Basal Nuclei and Related Structures

• The blood supply to the caudate and putamen is provided by branches of the medial striate artery, lenticulostriate branches of the M1 segment, and the anterior choroidal artery.– The medial striate artery, usually a branch of A2, serves much of the

head of the caudate nucleus. – The tail of the caudate, adjacent portions of the lenticular nucleus, and

adjacent temporal lobe structures (hippocampus, choroid plexus) receive their blood supply via the anterior choroidal artery.

• It is important to remember that the anterior choroidal artery also serves the optic tract and inferior regions of the posterior limb of the internal capsule.

• The blood supply to the subthalamic nucleus and the substantia nigra arises from the posteromedial branches of the P1 segment and branches of the posterior communicating artery.

P2

P1

P2

A2

M1

Hippocampus and Amygdala

• The hippocampal formation and the amygdaloid complex are located in the temporal lobe.

– inferomedial floor of the temporal horn of the lateral ventricle – rostral end temporal horn of the lateral ventricle

• The hippocampal formation composed of the – subiculum, – hippocampus proper (also called Ammon horn), – dentate gyrus.

• Axons of hippocampal neurons converge to form a prominent bundle that arches around caudal, superior, and rostral aspects of the thalamus = fornix = major efferent path of the hippocampal formation.

– It is composed of a flattened caudal part, the crus; a compact superior portion, the body; and a part that arches around the rostral part of the thalamus and passes through the hypothalamus to terminate in the mammillary body-this is the column.

• Located along the edge of the dentate gyrus and continuing on the lateral edge of the crus and body of the fornix is a thin fringe of fibers called the fimbria.

• The amygdala (amygdaloid nuclear complex ) is located internal to the cortex of the uncus.

• Composed of several cell groups including caudomedial, basolateral, and central subdivisions.

• Two major efferent bundles are related to the amygdala. 1.stria terminalis

2.ventral amygdalofugal pathway

• The septal nuclei are medially adjacent to the nucleus accumbens and continuous with sheets of neuronal cell bodies that extend into the septum pellucidum. – extends, in general, from the fornix to

the inner surface of the corpus callosum.

– forms the medial wall of the anterior horns and a small part of the bodies of the lateral ventricles.

– In general, the septal nuclei have complex interconnections with hippocampal, amygdaloid, and other limbic structures.

Temporal Lobe Lesions

• Injury to the temporal lobe, especially bilateral damage, almost always involves the hippocampus and amygdala.

• Deficits include profound changes in eating and sexual behaviour, a decrease in aggression levels, and deficits in memory function.– Retro and antegrade– Long term intact

Vasculature of the Hippocampus and Amygdala

• The blood supply to the hippocampal formation and amygdaloid complex is primarily via the anterior choroidal artery. – arises from the internal carotid, passes along the medial edge of the

temporal horn, and sends branches into the hippocampus and amygdala.

– also serves the tail of the caudate, the choroid plexus of the temporal horn, and inferior regions of the lenticular nucleus.

• The cortex of the uncus and that of the parahippocampal gyrus are served by superficial branches of the middle cerebral and posterior

cerebral arteries, respectively.

The End

Post-Test Questions

• Damage to the ??? results in conjugate deviation of the eyes.

• Damage to the auditory cortex may result in ???

• A small lesion in the genu of the internal capsule results in motor deficits related primarily to which cranial nerves ???

• This syndrome includes deficits reflecting damage to the internal capsule and optic tract ???

• The retrolenticular limb of the internal capsule contains ??? radiations. Lesions of these fibers result in ??? deficits on the contralateral side

FEF

Inability to localize sounds in space / altered perception of sound, not deafness

VII, XI, XII

Anterior choroidal artery syndrome

Optic / visual deficits

Bonus

• Huntington chorea is a neurodegenerative disease characterized by loss of the ??? nucleus on magnetic resonance imaging.

• A lesion of the subthalamic nucleus results in a contralateral ???

• A loss of the dopamine containing cells in the substantia nigra, the pars ??? , results in the motor defects seen in Parkinson disease.

Caudate

Hemiballismus

compacta

Thank You

Questions?