cerebellum
Meaning of cerebellum: Damage on one side shows on the same side of the body, the opposite of what the rest of the brain does.
Definition of cerebellum
The cerebellum is the tightly folded structure tucked beneath the back of the cerebrum and behind the brain stem, and its name means little brain. It does not start movement. It compares the movement that was intended against the movement actually being made and corrects the difference, which is what makes an action smooth, accurate and well timed.
What does it actually do?
The cerebellum receives two streams at once: a copy of the movement commands leaving the cerebrum, and a continuous report of what the body is really doing, gathered from muscles, joints, the balance organs of the inner ear and the eyes. Comparing the two reveals the gap between intention and execution, and the cerebellum sends corrections back through the brain stem and the thalamus while the movement is still under way. That is why practiced actions become smooth and eventually automatic. It stores the learning too, which is what improves with repetition when a skill such as riding a bicycle is acquired. Its influence reaches beyond the limbs. It times the muscles of speech, holds the eyes steady on a target, and adjusts posture continuously during standing and walking. Its rear portions have also been linked to attention, language and the regulation of emotion, so the older description of a purely motor structure is now regarded as incomplete.
How is it organized?
| Region | What it governs |
|---|---|
| The midline strip, called the vermis | Posture, trunk stability and walking |
| The zone on either side of the midline | Ongoing correction of arm and leg movement |
| The lateral hemispheres | Planning and timing of skilled, practiced movement |
| The lower flap at the back | Balance and steady eye movement, working with the inner ear |
What does damage look like?
The pattern has a name, ataxia. Walking becomes unsteady with the feet set wide apart, reaching overshoots or falls short of the target, a tremor appears as the hand nears an object rather than at rest, rapid alternating movements turn clumsy, speech breaks into uneven syllables, and the eyes drift and jerk. Strength, sensation and alertness are ordinarily preserved, which separates this picture from a stroke in the cerebrum. One feature is distinctive: because the correcting signals cross the midline twice on their way out and back, damage to one half of the cerebellum shows itself on the same side of the body rather than the opposite one. Stroke, tumors, multiple sclerosis, long term heavy alcohol use, thiamine deficiency and inherited degenerative conditions are among the causes.
Used in a sentence
Imaging identified a lesion within the cerebellum consistent with the patient's reported balance difficulties.
Good to know
Cerebellar damage typically leaves strength and sensation intact while disrupting coordination, balance and the timing of movement, and damage to one side produces signs on the same side of the body rather than the opposite side.
Word origin
Where “cerebellum” comes from
From Latin cerebellum, a diminutive of cerebrum, meaning brain, translating literally as little brain.