diencephalon dr. zeenat zaidi diencephalon paired structure located between the brain stem and the...
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DIENCEPHALONDIENCEPHALON
Dr. Zeenat Zaidi
DiencephalonDiencephalon Paired structure Located between the
brain stem and the cerebral hemisphere
Continuous with the rostral part of the midbrain
Forms the lateral wall of the 3rd ventricle
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Almost entirely surrounded by the cerebral hemispheres
A little part seen externally on the base of the brain caudal to optic chiasma, includes:• Infundibulum• Tuber cinerium• Mamillary bodies
Other parts seen on sagittal & coronal sections
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On the medial surface, the diencephalon is subdivided, by hypothalamic sulcus (indicated by black line) into: Dorsal part Ventral part
Cerebral aqueduct
Dorsal
Fornix
Optic chiasma
Ventral
Midbrain
CC
Dorsal partDorsal part Thalamus & Epithalamus
Subthalamus & HypothalamusVentral partVentral part H
RelationsRelations
Lateral: Internal capsule
Medial: 3rd ventricle
Dorsal: Lateral ventricle
Ventral: Exposed on the base of the brain
EPITHALAMUSEPITHALAMUS
EpithalamusEpithalamusRelatively small
part, located in most caudal and dorsal region
Lies immediately rostral to superior colliculus
Consists of: Pineal gland & Habenular nuclei
Pineal GlandPineal GlandAn endocrine organSynthesizes
melatoninControls:
Sleep/awake cycle
Regulation of onset of puberty
Habenular nucleiHabenular nucleiLocated in habenular
triangle (area in the posterior part of the diencephalon, just anterior to pineal gland)
Have connections with limbic system
Serves autonomic function and emotional drives
THALAMUSTHALAMUS
ThalamusThalamus Large mass of grey matter, in shape and size, resembles
small hen’s egg Forms the lateral wall of the 3rd ventricle Separated from hypothalamus by hypothalamic sulcus May be connected to opposite thalamus by interthalamic
adhesion (massa intermedia)
thalamus
Interthalamic adhesion
Hypothalamic sulcus
Thalamus: In horizontal sections of brainThalamus: In horizontal sections of brain
Higher level
Lower level
Thalamus has a narrow anterior end called tubercle of thalamustubercle of thalamus, that lies in the posterior boundary of the interventricular foramen
The expanded posterior end, called pulvinar, lies above the superior colliculi
RelationsRelations
MedialMedial: 3rd ventricle
DorsalDorsal: lateral ventricle
Ventral: Subthalamus & Hypothalamus
LateralLateral: Internal capsule
CaudalCaudal: midbrain
AnteriorAnterior: interventricular foramen
SurfacesSurfaces
4 Surfaces:• Superior• Inferior• Medial• Lateral
S
l
ML
Superior SurfaceSuperior Surface Bounded laterally by
caudate nucleus, thalamostriate vein and a nerve fiber bundle called stria terminalis
Lateral part lies in the floor of the lateral ventricle & is covered by ependymaependyma
Medial part is related to the choroid plexus choroid plexus of the 3rd ventricle
caudate nucleus
LVLV
ependymachoroid plexus
thalamo-thalamo-striate veinstriate vein
stria terminalis
Lateral SurfaceRelated to the
internal capsuleinternal capsule
Inferior SurfaceRests on the
subthalamus & hypothalamus
Medial SurfaceMedial Surface Stria medullaris thalami Stria medullaris thalami
(a fascicle of nerve fibers) courses along its dorsomedial margin
Below is limited by hypothalamic sulcus
Forms the upper part of the lateral wall of the 3rd ventricle
Covered by ependyma
Stria medullaris thalami
Hypothalamic sulcus
Internal OrganizationInternal Organization Thalamus is composed
of grey mattergrey matter, interrupted by two two vertical sheaths of white vertical sheaths of white matter called matter called medullary medullary laminae. laminae.
External medullary External medullary laminalamina: :
Located laterally, separates reticular reticular nucleus nucleus from the rest of the thalamic mass
Contains thalamocorticalthalamocortical & corticothalamiccorticothalamic fibers
Internal medullary Internal medullary laminalamina
Y- shaped bandY- shaped band, , divides divides thalamusthalamus into Anterior, Medial & Lateral nuclear groups
Contains: Fibers connecting
thalamic nuclei with one another
Neuronal collections called intralaminar intralaminar nucleinuclei
Nuclear GroupsNuclear Groups AnteriorAnterior nuclear group Lateral Lateral nuclear group:
Divided into: dorsal & dorsal & ventral tiersventral tiers
MedialMedial nuclear group IntralaminarIntralaminar nuclei Reticular Reticular nucleus MidlineMidline nuclei
Functional OrganizationFunctional Organization All the nuclei of the
thalamus except reticular nucleus, project to ipsilateral ipsilateral cerebral cortexcerebral cortex
The whole of the cerebral cortex receives input from the thalamus
All thalamic nuclei receive corticofugal fibersfibers in a basically reciprocal fashion
Based on their connection with the cerebral cortex, the thalamic nuclei are divided into:Specific nucleiSpecific nucleiNonspecific nucleiNonspecific nuclei
Specific nucleiSpecific nuclei:: Have well-defined
sensory and motor functions
Have highly organized point-to-point connection with sensory & motor regions of cerebral cortex
Lie within the ventral group of the lateral nuclear group
Non-specific Nuclei: Receive less functionally
distinct afferent input Connect with wider area
of cortex, including associative and limbic regions
Include nuclei of the dorsal tier of lateral group, and whole of the anterior and medial group
Lateral Nuclear GroupLateral Nuclear GroupVentral TierVentral Tier
• Ventral anterior• Ventral lateral• Ventral posterior:
• (VPL)• (VPM)
• Lateral geniculate • Medial geniculate
Ventral Anterior NucleusVentral Anterior Nucleus
Influences motor activity
Premotor & supplementary motor cortex
Ipsilateral globus pallidus & substantia nigraMotor cortex
Ventral Lateral NucleusVentral Lateral Nucleus
Influences motor activity
Ipsilateral globus pallidus &substantia nigraContralateral dentate nucleusPrimary motor cortex
Primary motor cortex
Ventral Posterior NucleusVentral Posterior Nucleus Chief sensory relay station
General sensory afferents from the contralateral half of the Head & neck (VPM) and Body (VPL)
Primary somatosensory cortex
Lateral Geniculate BodyLateral Geniculate Body
Part of the Visual Pathway
Ipsilateral temporal hemiretinaContralateral nasal hemiretina
Optic radiation to the primary visual cortex
Medial Geniculate BodyMedial Geniculate Body
Part of the Auditory Pathway
Inferior colliculus
Auditory radiation to the primary auditory cortex
Lateral Nuclear GroupLateral Nuclear Group Dorsal TierDorsal Tier
• Lateral Dorsal• Lateral Posterior• Pulvinar
Pulvinar:Pulvinar: Sensory association cortices of parietal, temporal & occipital lobes
Lateral posterior nucleussensory association cortex of parietal lobe
Lateral dorsal Lateral dorsal nucleusnucleus Part of Limbic Part of Limbic SystemSystem Hippocamus
Cingulate gyrus
Medial Nuclear GroupMedial Nuclear Group
Integrates emotion, thought, and judgmentIntegrates emotion, thought, and judgment
Hypothalamus, amygdala, other thalamic nuclei, prefrontal cortex
Prefrontal cortex & limbic structures
Mediodorsal nucleus Mediodorsal nucleus & Nucleus reuniens& Nucleus reuniens
Anterior Nuclear GroupsAnterior Nuclear Groups
3 parts: Anteroventral Anteromedial Anterodorsal•
Functionally part of the limbic system. Involved in control of instinctive drives, emotional aspect of behaviour and in memory
Mammillary body of hypothalamus via mammillothalamic tract
cingulate gyrus
Midline NucleiMidline Nuclei Located
between medial nuclear group and the ependyma of 3rd ventricle
Important in visceral functions
Brainstem reticular formation
Cingulate gyrus and hypothalamus
Intralaminar NucleiIntralaminar Nuclei Located within the
internal medullary lamina
Main nuclei: Centromedian & Parafascicular
Function as activator of the cerebral cortical mantle
Lesions reduce the perception of pain and level of conciousness
Widespread regions of cerebral cortex, caudate & putamen of the basal ganglia
Reticular formation, spinothalamic & trigeminothalamic systems
Reticular NucleusReticular Nucleus
Located between the external medullary lamina & the internal capsule
Regulates the activity of thalamus
Collaterals of both Thalamocortical & Corticothalamic fibers
Other thalamic nuclei
Functions of the thalamusFunctions of the thalamus Receives and analyses all the sensory information
(except olfactory) from the body Having extensive connections with the basal ganglia and
the motor cortices, it plays a pivot role in voluntary motor activity. Thalamotomy (VA, VL) was once used to treat basal ganglia disorders
Connections with the limbic system makes it important in the control of mood, emotional and sexual behavior, and memory
Thalamic LesionsThalamic Lesions Cerebrovascular lesions or tumors of thalamus lead to: Loss of sensation in the contralateral side of face and
body followed by distressing discomfort, & burning and diffuse pain in the anaesthetic areas (thalamic pain)
Thalamic syndrome: Abnormal voluntary movements (chorea or hemiballismus) with hemisensory disturbance
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