Thalamus

Thalamus- Dr. Chintan

Thalamus• The thalamus is a midline symmetrical structure of two

halves, situated between the cerebral cortex and the midbrain.

• Some of its functions are the relaying of sensory and motor signals to the cerebral cortex and the regulation of consciousness, sleep and alertness.

• All sensory pathways, except olfactory, relay in the thalamus before reaching the cortex

• Medially borders the third ventricle and laterally borders the internal capsule

• It is the main product of the embryonic diencephalon.

Thalamic nuclei• anterior nuclear of thalamus

• medial nuclear group (or dorsomedial nucleus)

• Intralaminar nuclear group (Intralaminar nuclei)• anterior (rostral) group• paracentral nucleus• central lateral nucleus• central medial nucleus• posterior (caudal) intralaminar group• centromedian nucleus

Thalamic nuclei• posterior region• pulvinar• lateral posterior nucleus • lateral dorsal nucleus

• ventral nuclear group• ventral anterior nucleus• ventral lateral nucleus• ventral posterior nucleus• ----------------ventral posterolateral• ----------------ventral posteromedial

• medial geniculate body• lateral geniculate body

Connections

Connections

Connections

Functions• [I] SENSORY FUNCTIONS• 1. Relay Station for Sensory Impulses• Somatic Sensation – • In Ventral-Posterior part of Lateral Nuclei via• - Medial Lemniscus: Kinesthetic, Fine Touch and

Vibration.• - Spinal Lemniscus: Crude Touch, Pain and

Temperature.• - Trigeminal Lemniscus: From Face.

• Auditory Sensation – • In Medial Geniculate Body via Lat. Lemniscus.• Visual Sensation – • In Lateral Geniculate Body via Optic Tract

Functions• 2. Crude Sensory Center• - Partial Perception of Pain

• 3. Relay Station for Non-specific Impulses

• As a part of Reticular Activating System (R.A.S.) it contributes in control of different states of consciousness, e.g. Waking, Sleep, Meditative.

Functions• [II] MOTOR FUNCTIONS• Contributes in Planning and Smooth Performance of

Voluntary Movements through Its connections with

• - Neocortex - Neocerebellum and - Basal ganglia.

• [III] MOTIVATIONAL / EMOTIONAL FUNCTIONS

• Forms a part of Limbic System contributing in• - Subjective Feeling of Emotions and• - Personality.

LESIONS OF THE THALAMUS• Sensory Loss

• These lesions usually result from thrombosis or hemorrhage of one of the arteries that supply the thalamus.

• Since the thalamus receives sensory impulses from the opposite side of the body, the disability resulting from a lesion within it will be confined to the contralateral side of the body.

• There may be a major impairment of all forms of sensation, which include light touch, tactile localization and discrimination, and loss of appreciation of joint movements.

LESIONS OF THE THALAMUS• Thalamic Syndrome

• Dejerine – Roussy syndrome or thalamic pain syndrome

• This syndrome may occur as the patient is recovering from a thalamic infarct – blockage of thalamogeniculate branch of PCA – Posteroventral & posterolateral

• Spontaneous pain, which is often excessive (thalamic overreaction), occurs on the opposite side of the body.

• The painful sensation may be aroused by light touch or by cold, and may fail to respond to powerful analgesic drugs.

LESIONS OF THE THALAMUS• Thalamic Syndrome

• Initial lack of sensation and tingling in the opposite side of the body.

• Weeks to months later, numbness can develop into severe and chronic pain that is not proportional to an environmental stimulus, called dysaesthesia or allodynia

• Astereognosis, thalamic phantom limb

• Ataxia, hypotonia, muscle weakness, involuntary movements, thalamic hand (athetoid hand – flexion of wrist, hyperextended fingers)

THANQ…