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Portrait of Brainstem

Anatomy · Brain & nerves

Brainstem

Midbrain, pons and medulla oblongata

Brain · stalk connecting brain and spinal cord

The stalk of the brain, made up of the midbrain, pons and medulla oblongata stacked from top to bottom. It links the cerebrum and cerebellum to the spinal cord, carries almost every ascending and descending pathway, and houses the centres that keep us breathing, keep the heart beating and keep us awake. Ten of the twelve pairs of cranial nerves emerge from it.

How to spot them

  • ▸A stalk running down from the base of the forebrain to the foramen magnum, in three stacked parts
  • ▸The bulging middle part is the pons, with the little brain wrapped over its back
  • ▸The lowest part narrows into the spinal cord as it passes through the hole in the base of the skull
  • ▸Its front surface rests on the sloping clivus; the cranial nerves sprout from its sides and front

What to know

Midbrain, pons and medulla oblongata stacked one above another

Brainstem — the three-part stalk of the brain.

The point of origin of cranial nerves III to XII

Brainstem — nerves I and II attach to the forebrain instead.

The region whose irreversible failure is the legal basis for diagnosing death in the United Kingdom

Brainstem — 'brain-stem death' is the UK criterion.

Home to the reticular formation, a diffuse network that keeps the cortex awake

Brainstem — the reticular activating system regulates arousal.

The part of the central nervous system that passes through the foramen magnum to become the spinal cord

Brainstem — the medulla is continuous with the cord at the foramen magnum.

Carries the motor fibres of the pyramidal tracts on their way down, and the sensory tracts on their way up

Brainstem — nearly every long tract between brain and body passes through it.

Key ideas

  • From top to bottom the parts are midbrain, pons, medulla; each has its own group of cranial nerve nuclei and its own reflex centres.
  • Cranial nerves III and IV emerge at midbrain level, V–VIII at the pons, and IX–XII at the medulla.

Quick-fire facts

  • •The three parts are the midbrain, the pons and the medulla oblongata
  • •Cranial nerves III–XII arise from it: III and IV from the midbrain, V–VIII from the pons, IX–XII from the medulla
  • •Contains centres for breathing and cardiovascular control, chiefly in the medulla and pons
  • •Contains the reticular formation, important in arousal, sleep and consciousness
  • •In the UK, death is diagnosed by irreversible loss of brainstem function ('brain-stem death'), with tests of the cranial nerve reflexes
  • •Damage to the pons can cause locked-in syndrome, with awareness intact but almost all movement lost
  • •Some authors include the diencephalon as well; the standard textbook definition uses the three lower parts
  • •It lies in the posterior cranial fossa, on the clivus, in front of the cerebellum and the fourth ventricle

Drill it — 6 cards

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Sources