THALAMUS AND HYPOTHALAMUSEpithalamus Thalamus Hypothalamus and Subthalamus Thalamus is most important sensory relay station . Ascending fibers synapse in thalamus and are then It also

THALAMUS AND HYPOTHALAMUS

Prof.Sangeeta SinghalDepartment of Physiology

JNMC ALIGARH

INTRODUCTION:- The term thalamus derives from a Greek word that

means “ inner chamber” or meeting place.

Paired ,oval ,nuclear mass of 30×20×20 mm

The largest component 80% of the diencephalon

The term diencephalon includes the following structures:-

Epithalamus

Thalamus

Hypothalamus and

Subthalamus

Thalamus is most important sensory relay station .

Ascending fibers synapse in thalamus and are then projected to the cortical sensory areas.

It also receives impulses from the ascending Reticular formation which it relays to cerebral cortex.

The two thalami form the floor and lateral walls of the third ventricle of brain.

Separated from hypothalamus by hypothalamic sulcus.

CLASSIFICATION OF THALAMIC NUCLEI:-

1-NEUROANATOMIC CLASSIFICATION:- Divided by internal medullary lamina into three

nuclear groups:-

Lateral group of nucleiMedial group of nuclei Anterior group of nuclei

Lateral group of nuclei2 types :- dorsal and ventral group of nucleiVentral group:- 1-Ventral anterior nucleus

2-Ventral posterior nucleus3-Ventral lateral nucleus

Dorsal group:- 1-Lateral dorsal nucleus2-Lateral posterior nucleus 3-Pulvinar nuclei

MEDIAL GROUP OF NUCLEI:-1- DORSOMEDIAL NUCLEUS

Anterior group of nuclei:-Anterior thalamic nuclei

• OTHER NUCLEI:-1-MIDLINE NUCLEI

2-Intralaminar nuclei

3-Reticular nucleus

4-Medial and lateral geniculate bodies

PHYSIOLOGICAL CLASSIFICATION:-On the basis of functions nuclei are classified into:-1-Specific sensory relay nuclei

2-Specific motor nuclei

3-Association nuclei

4-Limbic system nuclei

CONNECTIONS OF THALAMUS

NEUROTRANSMITTERS AND NEUROPEPTIDES INTHALAMUS:-

GABA is the inhibitory NT in local circuit neurons ,reticular nucleus and lateral geniculate nucleus

Glutamate and Aspartate are the excitatory NT in corticothalamic and thalamocortical projection neurons

Many neuropeptides, like substance P, Somatostatin and Enkephalin

FUNCTIONS OF THALAMUS:-1-RELAY CENTER:- impulses of almost all the

sensations reach the thalamic nuclei, after being processed in the thalamus the impulses are carried to cerebral cortex

2-CENTER FOR PROCESSING OF SENSORY INFORMATION

3- Role IN AROUSAL and ALERTNESS REACTIONS

4-CENTER FOR REFLEX ACTIVITY

5-CENTER FOR INTIGRATION OF MOTOR ACTIVITY:- through the connections with cerebellum and basal ganglia.

APPLIED PHYSIOLOGYTHALAMIC SYNDROME :- also known as

“Dejerine-Roussy disease”.Caused due to infarct in geniculothalamic artery , a

branch of posterior cerebral artery.The clinical hallmark is a pan sensory loss

contralateral to the lesion, paraesthesia, and thalamic pain.

Transient hemiparesis, homonymous hemianopia, hemi ataxia, tremor and spatial neglect, all contralateral to the lesion in the thalamus.

Thalamic hand:- the contralateral hand is fixed and pronated at the wrist and metacarpo-phalangeal joints and extended at inter phalangeal joints. (due to involvement of posterolateral nucleus)

Thalamic phantom limb:- when eyes are closed , the patient finds it difficult to locate the limb and he catches it in the air as if it is lost.(due to involvement of posteroventral nucleus)

HYPOTHALAMUS

Hypothalamus is described as “The Head ganglion of the autonomic nervous system” by Sherrington.

It is a small bilateral structure extends from the region of optic chiasma to the caudal border of the mammillary bodies.

It is below the Thalamus ,very small in size (wt 4 gmonly )

PARTS OF THE HYPOTHALAMUS

The hypothalamus is subdivided into optic, tuberaland mammillary parts . The nuclei present in each part are as follows:

OPTIC PART:- 1- Preoptic and supraoptic nuclei2-Paraventricular nucleus3-Suprachiasmatic nucleus

Tuberal part:- 1-Ventromedial nucleus2-Dorsomedial nucleus3-Tuberal nucleus4-Arcuate nucleus

Mammillary part:- 1-Posterior nucleus2-Lateral nucleus3-Mammillary body

FUNCTIONS OF HYPOTHALAMUS

1-Endocrine control2-General autonomic effect3-Temperature regulation4-Food intake5-Thirst –fluid regulation6-Sleep and wakefulness7-Circadian rhythm8-Sexual behaviour and reproduction9-Emotion, fear, rage, aversion , pleasure and reward