Notes on Thalamus

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THALAMUS

Relay station for sensory impulses.

The thalamus is part of the diencephalon. Other components of the diencephalon include the hypothalamus, subthalamus and epithalamus.

Two wedge-shaped or ovoid (egg) structures composed of grey matter and joined together by the interthalamic adhesion. Form the lateral walls of 3rd ventricle.

The internal medullary Y-shaped lamina consisting of white matter divides the thalamus into three portions and 25 nuclei (thalamic organization).

a. Lateral nuclear mass.

b. Mediodorsal nuclear mass.

c. Anterior nuclear mass.

The reticular nucleus is also separated from the thalamus by the external medullary lamina.

Identifiable Macro Components:

1. Interthalamic adhesion (joins two thalami).

2. Pulvinar (posterior surface).

3. Lateral (i.e. for vision) and medial geniculate bodies (latter for auditory impulses).

4. Lateral surface beveled by internal capsule.

5. Various nuclei and internal medullary Y-shaped lamina.

6. Ventral posterior nucleus (associated with taste, touch, pressure, vibration, heat, cold, pain).

Function of Thalamic Nuclei:

Major synaptic relay station.

1. Specific or relay nuclei:

Have specific connections with the motory or sensory areas of the cerebral cortex. (Ventral anterior nucleus, ventral lateral nucleus, ventral posterior nucleus, medial and lateral geniculate nucleus). Crude appreciation of subconscious sensation. Vague awareness of sleep and level of consciousness.

2. Association nuclei:

Reciprocally connected to the association areas of the cerebral cortex.

3. Non-specific nuclei:

Intralaminar and reticular nuclei.

4. Principal somatosensory relay nuclei (ventrobasal complex of nuclei):

These are concerned with taste sensation, vestibular relay, auditory, visual, motory and limbic relay. Initial autonomic response to pain.

Summary:

Principal relay station for sensory impulses that reach the cerebral cortex from the spinal cord, brainstem, cerebellum and cerebrum. Crude appreciation of pain, temperature and pressure. Essential role in the acquisition of knowledge (= cognition).

Nuclear Connections:

1. Afferent: To motor and prefrontal cortex, sensory cortex, visual and auditory cortex.

2. Efferent: From globus pallidus, cerebellum, spinal lemnisci and optic tracts.

3. Cerebral connections: Are via fanlike thelamic projections to the anterior, superior, posterior and inferior peduncles.

Dysfunction:

Tumour infiltration or ischaemia due to thrombosis may result in the thalamic syndrome which is characterized by a lowered threshold to pain, temperature and touch.

Location of Primary Sensory and Association Areas of the Human Cerebral Cortex:

• Primary sensory area (posterior to central sulcus).

• Sensory association area (behind the primary area).

• Visual association area.

• Primary visual area.

• Wernicke's area.

• Primary auditory area.

• Broca's area (motor, speech): Area 44. Left cerebral hemisphere.

Epithalamus:

Consists of the pineal gland, habenula and stria medullaris. (Latter are part of the limbic system).

Further Topics on Subcortical Grey Matter:

1. Notes on Thalamus
2. Notes on Pineal Gland
3. Notes on Hypothalamus
4. Notes on Limbic System
5. Notes on Pituitary Gland
6. Notes on Basal Nuclei
7. Amygdaloid Body and Temporal Lobe

Additional Reading:

Basic Neurology

1. Peripheral Nervous System
2. Central Nervous System
3. The Ventricular System
4. The Spinal Cord
5. The Brain Stem
6. The Cerebellum
7. Visual Pathways
8. Diencephalon
9. Basal Ganglia
10. Cerebral Cortex
11. Sleep Disorders
12. Autonomic Nervous System
13. Cranial Nerves and Parasympathetic Ganglia
14. Cells of the Nervous System
15. Cerebrospinal fluid
16. Additional short notes on Cerebrum
17. Functions and Diseases of Cerebrum
18. Subcortical Grey Matter
19. Notes on The Spinal Cord
20. Regulation of Heart Rate by Autonomic Nervous System
21. Action Potentials, Axon Conduction, and Neuromuscular Junction
22. Types of Seizures
23. What is a Cough Reflex?
24. Notes on Congenital Prosopagnosia
25. Findings in Parkinson's Disease
26. Types of Heat Strokes
27. Types of Strokes
28. What is Benign Intracranial Hypertension?
29. What is Cauda Equina Syndrome?
30. Cranial Nerve Locations in Brain Stem
31. What is a Cluster Headache?
32. What is a Subarachnoid Hemorrhage?
33. What is a Tension Headache?

Neurology Videos

1. Video of Neurology Examination in a Clinical Setting

Medical Images

Useful Medical Images & Diagrams (link opens in a new window)

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1. Nervous System Disorders
2. Histology of Nervous Tissue
3. Cranial Nerve Reflexes
4. Motor System Examination

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