The name means 'below the inner chamber': it lies beneath the brain's sensory relay
Hypothalamus — hypo (under) + thalamus.
Anatomy · Brain & nerves
Hypothalamus
About the size of an almond
Brain · diencephalon
A small but crucial region at the base of the brain, below the thalamus and above the pituitary gland, forming the floor and lower walls of the third ventricle. It keeps the body's internal conditions steady: temperature, thirst, hunger, sleep–wake cycles and hormone balance. Through its links to the pituitary it is the point where the nervous system commands the endocrine system.
How to spot them
- ▸A small area under the thalamus, on each side of the lower third ventricle, roughly the size of an almond
- ▸The optic chiasm lies just in front of it; the two round mammillary bodies bulge behind
- ▸A funnel-shaped stalk (the infundibulum) runs down from its floor to the pituitary gland
- ▸Its front-most nuclei sit just above the optic chiasm — the body's master clock
What to know
Roughly the size of an almond, yet it is the brain's master regulator of temperature, thirst, hunger and sleep
Hypothalamus — the body's thermostat and homeostatic controller.
Its neurosecretory cells make antidiuretic hormone and oxytocin, which are released from the back of the pituitary
Hypothalamus — supraoptic and paraventricular nuclei.
A tiny group of cells just above the optic chiasm keeps the body's 24-hour clock in step with daylight
Hypothalamus — the suprachiasmatic nucleus.
Two small round bumps behind it, on the base of the brain, are part of the circuit of memory described by James Papez
Hypothalamus — the mammillary bodies.
Releasing and inhibiting hormones from it reach the front of the pituitary through a special portal blood supply
Hypothalamus — the hypophyseal portal system.
In the classic animal experiments, lesions in its lateral part stopped feeding while lesions in its ventromedial part caused overeating
Hypothalamus — the old 'dual-centre' model of hunger and satiety.
Key ideas
- It is the link between nervous and endocrine systems: nerve signals in, hormones out via the pituitary.
- It works as a thermostat, comparing blood temperature with a set point and triggering sweating or shivering.
Quick-fire facts
- •About 4 g in weight, less than 1 per cent of the brain's mass
- •Forms the floor and lower walls of the third ventricle
- •Connected to the pituitary by the infundibulum (pituitary stalk)
- •Makes ADH and oxytocin, stored and released by the posterior pituitary
- •Releasing hormones such as TRH, CRH, GnRH and GHRH control the anterior pituitary
- •The suprachiasmatic nucleus is the body's main circadian pacemaker
- •The mammillary bodies belong to the Papez circuit, linked to memory
- •Damage can cause disorders of appetite, temperature, water balance and sleep
- •The 'four Fs' — feeding, fighting, fleeing and mating — are a classic shorthand for its behavioural roles
Drill it — 7 cards
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Sources
- Kenhub — Hypothalamus: Structure and functions
- Cleveland Clinic — Hypothalamus