Download AHD The Telencephalon R. Altman 4-03

Overview of:
The Telencephalon
Haines Chapter 16
Neurology Academic Half-Day
Robert Altman PGY 2
March 4th 2009
Overview
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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
A= 4.75 wks
B= 6 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
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rapid enlargement of
forebrain regions:
telencephalon.
Ventricular spaces (dashed
lines, A-D) follow the shape
changes in the brain
The Telencephalon
Developmental Defects
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Largely a review of chapter 5
Improper migration of maturing neurons on radial glia
Structural +/- functional defects in cerebral cortex
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Lissencephaly
Pachygyria
Microgyria
Holoprosencephaly (pre-neurulation defect)
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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)
Corpus Striatum
• 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
Commisural bundles & hippocampus
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Medial aspects of hemispheres
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Origins of major commisural bundles & hippocampus
Develop in this order:
1. Anterior commisure
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Arises from lamina terminalis
From commisure to optic chiasm
2. Hippocampal commisure
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Along hippocampal primordium
Posteromedialtemporal
Crossing as growth occurs
3. Corpus callosum
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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
ORBITOFRONTAL
SURFACE
•Olfaction
•Medial and lateral
striae
•Olfactory trigone
•Anterior
perforated
substance
•Functionally
related to limbic
system
Together form: Primary
Frontal Lobe
Somatomotor Cortex
Contiunous with
anterior
paracentral
gyrus on medial
surface
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
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1.
2.
3.
4.
Below the interparietal sulcus,
particularly the angular gyrus or
subjacent WM of the L
hemisphere
Finger agnosia
Dyscalculia
Dysgraphia
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
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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
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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 Matter
3. 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.
2.
3.
the caudate and
lenticular nuclei
(together forming the
dorsal basal nuclei)
the nucleus accumbens
plus parts of the
adjacent olfactory
tubercle (the ventral
striatum), and
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
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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.
2.
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•
lenticular fasciculus
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.
A2
M1
P1
P2
P2
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 ???
FEF results in conjugate deviation of the eyes.
Inability to localize sounds in space /
• Damage to the auditory cortex may result in ???
altered perception of sound, not
deafness
• A small lesion in the genu of the internal capsule results in motor
deficits related primarily to which cranial nerves ???
VII, XI, XII
• This syndrome includes deficits reflecting damage to the internal
capsule and optic tract ???
Anterior choroidal artery syndrome
• The retrolenticular limb of the internal capsule contains ???
radiations. Lesions of these fibers result in ??? deficits on the
contralateral side
Optic / visual deficits
Bonus
• Huntington chorea is a neurodegenerative disease characterized by
loss of the ???
nucleus on magnetic resonance imaging.
Caudate
• A lesion of the subthalamic nucleus results in a contralateral ???
Hemiballismus
• A loss of the dopamine containing cells in the substantia nigra, the
pars ???
, results in the motor defects seen in Parkinson
compacta
disease.
Thank You
Questions?