The brainstem connects the brain to the spinal cord and keeps us alive by controlling breathing, heart rate and consciousness. The cerebellum sits behind it and fine-tunes movement and balance.
Midbrain
The midbrain controls eye movements and pupil reflexes through cranial nerves III and IV. It also relays signals for hearing, vision and movement.
Pons
The pons links the cerebrum to the cerebellum, helps set the breathing rhythm and holds the nuclei of cranial nerves V to VIII.
Medulla
The medulla contains the centers for breathing, heart rate and blood pressure, plus reflexes like swallowing, coughing and gagging. The main motor pathways cross to the other side here.
Reticular activating system
A network running through the brainstem keeps the cortex awake. Damage to it, or to both hemispheres, lowers the level of consciousness.
Cerebellum
The cerebellum compares planned movement with actual movement and corrects errors. Damage causes problems on the same side of the body: unsteady gait, tremor when reaching and slurred speech.
At the bedside
Pupils, eye movements, the gag reflex and the breathing pattern test the brainstem, and the Glasgow Coma Scale tracks consciousness. Finger-to-nose, heel-to-shin and gait testing check the cerebellum.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).