Functions:

Thalamus is primarily concerned with somatic functions and it plays little role in the visceral functions. The various functions of thalamus are:

RELAY CENTER

The impulses of almost all the sensations (except olfactory) reach the thalamic nuclei, particularly in the ventral posterolateral nucleus. After being processed in the thalamus, the impulses are carried to cerebral cortex through thalamocortical fibers. Thus, thalamus forms the relay center for sensations.

In fact, very little information about the somatosensory function is sent to cerebral cortex directly without being processed by the thalamic nuclei. Because of this, thalamus is usually called a "Functional gateway" for cerebral cortex.

CENTER FOR INTEGRATION OF SENSORY IMPULSES

Thalamus forms the major center for the integration and modification of peripheral sensory impulses before the impulses are projected to specific areas of cerebral cortex. Generally, this function of thalamus is called the processing of sensory information.

Thalamus is also the center determining the quality of sensations.

Usually the sensations have two qualities:

a). The discriminative nature: ability to recognize the type, location and other details of the sensations - the function of cerebral cortex.

b). The affective nature: capacity to determine whether asensation is pleasant or unpleasant and agreeable or disagreeable - the function of thalamus.

CENTER FOR SEXUAL SENSATIONS

Thalamus forms the center for perception of sexual sensations.

ROLE IN AROUSAL AND ALERTNESS REACTIONS

Because of its connections with nuclei of reticular formation, thalamus plays an important role in arousal and alertness reactions.

CENTER FOR REFLEX ACTIVITY

Since the sensory fibers relay here, thalamus forms the center for many reflex activities.

CENTER FOR INTEGRATION OF MOTOR FUNCTIONS

Through the connections with cerebellum and basal ganglia, thalamus serves as a center for integration of motor functions.

Fig.23. Connections of thalamus.

EPITHALAMUS PHYSIOLOGY

3 regions:

1) frenulum;

2) brain anterior comissure;

3) epiphysis.

Epiphysis is endocrine gland secreting hormone melatonin. It provides regulation of:

1. biological rhythms;

2. endocrine function;

3. metabolism.

Shortly, melatonin is necessary for organism adaptation to different conditions of enlighting and organism biorhythms. Its main effect is gonadotropine secretion decreasing by adenohypophysis. Enlighting decreasing reducel sympathetic influencings activity breaking cavn to epiphysis and thus melatonin synthesis decreasing.

HYPOTHALAMUS PHYSIOLOGY

Hypothalamus is a diencephalic structure. It is situated just below thalamus in the ventral part of diencephalon. It is formed by groups of nuclei scattered in the walls and floor of third ventricle. It extends from optic chiasma to mamillary body.

Hypothalamus consists of scattered nuclei, which are divided into three groups, anterior or supraoptic group, middle or tuberal group and posterior or mamillary group.

Anterior or supraoptic group	Middle or tuberal group	Posterior or mamillary group
1. Preoptic nucleus 2. Paraventricular nucleus 3. Anterior nucleus 4. Supraoptic nucleus	1. Dorsomedial nucleus 2. Ventomedial nucleus 3. Lateral nucleus 4. Tuberal nucleus	1.Posterior nucleus 2. Mamillary body

Afferent connections to hypothalamus:

1)Medial forebrain bundle: From rhinencephalon (limbic cortex) to preoptic nucleus, lateral nucleus and mamillary body.

2) Fornix: From hippocampus to mamillary body.

Efferent connections from hypothalamus:

1. Mamillothalamic tract: From mamillary body to anterior thalamic nuclei.

2. Mamillotegmental tract: From mamillary body to the tegmental nuclei of midbrain.

3. Periventricular fibers: Fibers from posterior, supraoptic and tuberal nuclei of hypothalamus pass through periventricular gray matter and reach the following:

a. Reticular formation in brainstem and spinal cord,

b. Dorsomedial nucleus of thalamus and

c. Frontal lobe of cerebral cortex.

4. Hypothalamo-hypophyseal tract: From supraoptic and paraventricular nuclei of hypothalamus to posterior pituitary.