Brain
Brainstem
Keeper of vital life functions
Overview
The brainstem connects the cerebrum to the spinal cord and cerebellum. It comprises three sections—the midbrain, pons, and medulla oblongata—and is responsible for basic life-sustaining functions: breathing, heart rate, blood pressure, and sleep-wake regulation. Ten of the twelve cranial nerves originate here.
Function
- Regulates breathing, heart rate, and blood pressure
- Controls swallowing, coughing, and vomiting reflexes
- Routes sensory and motor signals between brain and body
- Regulates alertness and the sleep-wake cycle via the reticular formation
- Origin of most cranial nerves
Key Facts
- Brainstem death is the legal and medical definition of death in most countries
- The reticular activating system (RAS) in the brainstem controls wakefulness
- A fingertip-sized lesion here can be fatal
- The medulla is the oldest brain structure evolutionarily
Key Substructures
- Medulla oblongata: cardiac, respiratory, and vomiting centers; junction with spinal cord
- Pons: facial sensory/motor nuclei, REM sleep circuitry, pontine respiratory group
- Midbrain: superior/inferior colliculi, substantia nigra, dopaminergic VTA
- Reticular formation: controls arousal, alertness, and pain modulation across all three regions
- Cranial nerve nuclei III–XII: nearly all cranial nerves originate within the brainstem
Clinical Notes
- Brainstem death is the legal and medical definition of death in most countries
- Locked-in syndrome: consciousness fully intact but the patient cannot move except the eyes
- Lateral medullary syndrome (Wallenberg): crossed sensory loss and swallowing difficulty after PICA stroke
- Small strokes can be catastrophic: major tracts are densely packed in a tiny volume