THALAMUS

Thalamus in Greek means “Ante chamber” or “Inner chamber“. It was discovered way back in the 2nd Century AD, when Galen traced the optic-nerve fibers to an oval mass closely associated with the ventricles.

It is considered as head ganglion of all sensory systems.It integrates & processes all sensory impulses. All sensory pathways (EXCEPTION – Olfactory pathway) that proceeds to the cortex first relays in the thalamus before reaching its destination.

THALAMIC NUCLEI

FUNCTIONAL CLASSIFICATION

NON-SPECIFIC N– RECEIVE IMPULSES FOR DIFFUSE SECONDARY RESPONSES FROM THE RETICULAR ACTIVATING SYSTEM & PROJECT DIFFUSELY TO NEOCORTEX. SPECIFIC NUCLEI – RECEIVE SPECIFIC SENSATION & PROJECT TO SPECIFIC PORTION OF NEOCORTEX & LIMBIC SYSTEM
DEPENDING UPON THE TYPE OF SENSATION, THE SPECIFIC PROJECTION NUCLEI CAN BE DIVIDED INTO 4 GROUPS

CONNECTIONS OF THALAMUS

Afferent & efferent connections of various thalamic nuclei is based on the functional classification:

SPECIFIC NUCLEI OF THALAMUS

  1. PRINCIPAL RELAY
PRINCIPAL RELAY

VENTRAL POSTERIOR NUCLEUS (VPN) It has 2 divisions : VPL( Ventro posterior Lateral) & VPM (Ventro Postero Medial) {sensory relay Nuclei}

MEDIAL GENICULATE BODY – Receive topically organised projection of auditory fibers. {sensory relay Nuclei}

LATERAL GENICULATE BODY – Show an orderly organized representation of the retina {sensory relay Nuclei} AFFERENT: OPTIC TRACT, SUPERIOR COLLICULUS EFFERENT : VISUAL CORTEX (17,18,19) FUNCTION : VISION

VENTRAL LATERAL NUCLEUS (VLN) : Chief motor nucleus of Thalamus . Acts as a relay centre for cerebellar impulses. {Motor Control Nuclei}

VLN OF THALAMUS

VENTRAL ANTERIOR NUCLEUS : Involved in the programming of movements controlled by the basal Ganglia. {Motor Control Nuclei}

VENTRAL ANTERIOR NUCLEUS

ANTERIOR NUCLEUS : Belongs to Papez Circuit of Limbic system. Concerned with recent memory & emotions {Visceral Efferent Control Nuclei}

ANTERIOR NUCLEUS OF THALAMUS

2. ASSOCIATION NUCLEUS

LATERAL NUCLEUS : AFFERENT : Parietal lobe of cortex, Sup colliculus, principal relay N. EFFERENT : Parietal association area (language), Cingulate Gyrus. FUNCTION : Language comprehension, speech, other integrated function

DORSOMEDIAL NUCLEUS: AFFERENT : Relay N, Hypothalamus, Amygdala, Pre-frontal Cortex, Olfactory information. EEFERENT : Pre-frontal Cortex (area- 8,9,10,11), Newer olfactory pathway to orbito-frontal cortex. FUNCTION : Processing of Crude somatic, visceral sensation, perception of olfaction, elaboration of thought, word formation.

PULVINAR : AFFERENT : Relay N, Parietal, Temporal, Occipital Cortex, Sup Colliculus. EFFERENT : Visual association area (lateral part) & Auditory association area (medial part) FUNCTION : Integration of visual, auditory & Somasthetic information.

NON-SPECIFIC THALAMIC NUCLEI

NON-SPECIFIC THALAMIC NUCLEI

FUNCTIONS OF THALAMUS

FUNCTIONS OF THALAMUS

THALAMIC SYNDROME

Dejerine (1906) – Described , Roussy (1907) – Named

Occlusion of Thalamo-geniculate branch Post cerebral artery damages VPL Nucleus (Sparing VPM Nucleus)

APPLIED

THALAMIC SYNDROME

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