SN3
SHORT NOTE
5M
★ High-yield
Enumerate the functions of the hypothalamus. Add a note on temperature regulation.
Introduction
The hypothalamus weighs only about 4 g, yet it is the chief integrating centre for the autonomic nervous system, endocrine function and homeostasis. It is often called the "head ganglion of the autonomic nervous system".
Functions and Their Nuclei
| Function | Nucleus / centre | Effect of lesion |
|---|---|---|
| Temperature regulation | Anterior — heat loss; Posterior — heat conservation | Anterior lesion → hyperthermia; posterior → poikilothermia |
| Food intake | Ventromedial — satiety centre; Lateral — feeding (hunger) centre | VMN lesion → hyperphagia and obesity; lateral lesion → anorexia |
| Water balance and thirst | Supraoptic and paraventricular (ADH); osmoreceptors | Diabetes insipidus |
| Endocrine control | Releasing and inhibiting hormones to the pituitary | Pituitary failure |
| Autonomic control | Anterior — parasympathetic; Posterior — sympathetic | — |
| Circadian rhythm | Suprachiasmatic nucleus | Loss of sleep–wake rhythm |
| Emotion and behaviour | Part of the limbic system | Sham rage |
| Sexual behaviour | Preoptic, ventromedial | Loss of libido |
Temperature Regulation in Detail
↑ Core temperature → Anterior hypothalamic thermoreceptors → Heat loss centre → Cutaneous vasodilatation + sweating → Temperature falls
- Fever — pyrogens (IL-1, IL-6, TNF) → prostaglandin E2 in the hypothalamus → the set point is raised. The patient feels cold and shivers until the new set point is reached
- Antipyretics (paracetamol, aspirin) act by inhibiting prostaglandin synthesis and resetting the set point — they do not lower normal temperature
- Heat stroke differs — the set point is normal but the mechanisms are overwhelmed
Connections
- Afferents — from the limbic system, thalamus, retina (retinohypothalamic tract), and visceral afferents
- Efferents — to the pituitary (hypophyseal portal system and supraopticohypophyseal tract), brainstem and cord
- Hypophyseal portal system carries the releasing hormones directly to the anterior pituitary — a very short, high-concentration route
Applied Aspects
- Craniopharyngioma — the commonest hypothalamic tumour of childhood; growth failure, diabetes insipidus, visual field defect
- Fröhlich syndrome — obesity with hypogonadism from a hypothalamic lesion
- Narcolepsy — loss of orexin (hypocretin) neurones
- Malignant hyperthermia and neuroleptic malignant syndrome involve disordered central temperature control
All questions in Nervous System (neurophysiology)
- Q1Define synapse. Classify synapses and describe the mechanism and properties of synaptic transmission. Add a note on synaptic inhibition. ★
- Q2Describe the ascending tracts of the spinal cord. Trace the pathway for pain, temperature and fine touch from the periphery to the cortex. ★
- Q3Describe the pyramidal tract with its origin, course and functions. Differentiate between upper and lower motor neurone lesions. ★
- Q4Describe the functional divisions and connections of the cerebellum. Enumerate the signs of cerebellar lesion and explain why they are ipsilateral. ★
- Q5Define reflex action. Classify reflexes and describe their properties. Describe the stretch reflex and the inverse stretch reflex. ★
- SN1Describe the structure and functions of the muscle spindle. Add a note on the gamma loop. ★
- SN2Enumerate the components and functions of the basal ganglia. Describe the features of Parkinson disease. ★
- SN3Enumerate the functions of the hypothalamus. Add a note on temperature regulation. ★
- SN4Describe the formation, circulation and functions of cerebrospinal fluid. Give its normal values. ★
- SN5Define referred pain. Explain its mechanism and give common examples. Add a note on the gate control theory. ★
- SN6Describe the features of Brown–Séquard syndrome and explain their basis. ★
- SN7Describe the normal electroencephalogram and the stages of sleep.