SABIHA M. HAQIIMC

Learning objectivesDescribe the location and

boundaries of DiencephalonEnumerate parts of Diencephalon

and describe each one brieflyIdentify the location of these parts

on diagrams/modelsBriefly describe the clinical effects

of the lesions of diencephalon

INTRODUCTION/LOCATIONIt is the area which surrounds third ventricle

It has two walls, a roof, ant wall and floor

Posteriorly the roof and floor converge. This is the point where third ventricle meets the cerebral aqueduct

Anterior wallFormed by lamina terminalis which is a thin

layer of grey matterIts lower end meets the optic chiasma in an

angle called the optic recessBehind its upper end is ant commissure

(connects the two temporal lobes, olfactory tracts and amygdala)

Behind ant commissure are ant columns of fornix

Behind each ant column is interventricular foramen connecting third and lat ventricles

FloorIt is actually the

floor of third ventricle

It extends across optic chiasma, tuber cinerium, infundibulum and mamillary bodies to posterior perforated substance

Side wallsThese are the

lateral walls of third ventricle

Formed by thalamus, hypothalamic groove or sulcus and hypothalamus itself

RoofRoof is formed

by pia mater and choroid plexus

of third ventricle

Parts of DiencephalonThalamusHypothalamusEpithalamusSubthalamus

ThalamusLargest partWedge shaped

ThalamusIt has four surfaces, lateral, medial, superior

and inferior and two ends, anterior and posterior

Medial surface forms the lateral wall of third ventricle & is lined by ependymaIt has an interthalamic connectionPosteriorly it diverges from the midline & ends

in a large convexity, the pulvinarLateral & medial geniculate bodies bulge out

from pulvinar

ThalamusLateral surface lies in contact with the internal

capsuleThe ascending fibres from various tracts

pass through thalamic nuclei and leave the lateral surface to join the internal capsule on their way to the cortex

Superior surface is convex & triangular & tapers anteriorlyA band of white matter called medullary

stria meets the stria from the other thalamus to form U shaped habenular commissure

(The habenular nuclei are involved in pain processing, reproductive behavior, nutrition, sleep-wake cycles, stress responses, and learning )

ThalamusInferior surface is narrow and joins

the hypothalamus mediallyPosterolaterally it receives the lemnisci from the midbrain

All four surfaces converge to the narrow anterior pole which forms the posterior boundary of interventricular foramen

Thalamic nucleiA, Y shaped sheet of

white matter int medullary lamina divides the thalamus into three parts

AnteriorMedial LateralEach part contains

several nuclei

Thalamic nucleiAnterior thalamic nuclei are

concerned with the emotional tone and recent memory

Medial thalamic nuclei are concerned with the behavior and expression

Lateral thalamic nuclei are connected to sensory and motor pathways including sense of taste and balance

Other thalamic nucleiMedial geniculate

body concerned with auditory relay through inf colliculi

Lateral geniculate body concerned with visual relay through superior colliculi

Functions of thalamusPlays an important part in the

integration of sensory and motor systemsRecieves precortical sensory input from

all the sensory systems except the olfactory system

Centre for Visual reflexesCentre for Auditory reflexesTaste pathways

HypothalamusThe floor of diencephalon is called

hypothalamusIt maintains the internal

environment of the body through 3 systemsAutonomic NSEndocrine systemLimbic system

Hypothalamus Parts of hypothalamus visible from the

ventral surfaceInfundibulumMamillary bodiesTuber cinereumMedian eminence which is responsible for

the production of neurosecretory substances which control the ant pitutary

Posterior perforated substanceThis is one of the few parts of brain which

has no blood brain barrier

Functions of hypothalamusThirst and water balance (supraoptic &

paraventricular nuclei)Production of releasing factors for

AdenohypophysisPrecursors of ADH & OxytocinHunger centreAutonomic regulation centreTemperature regulation centre

SubthalamusThis is the caudal part of thalamus,

containsSubthalamic nucleusCranial part of red nucleusCranial part of substantia nigra It is a part of basal ganglia and the reticular activating system of brain (RAS)

Epithalamus It consists of Fornix Habenular nuclei and commissurePineal glandPosterior commissure (concerned with bilateral

pupillary reflex)

The pineal gland secretes Melatonin which sets the day and night clock of the body

It becomes calcified in old age

Lesions of diencephalon cause:Poor temperature controlAbnormal appetiteLack of ADH causing polyuria and polydypsia

These lesions rarely ever occur alone. Usually they occur in conjunction with cerebral lesions.

THE END