Motor Control: From Intention to Muscle
Movement is produced by a hierarchy: the cord holds reflex circuits and pattern generators, the brainstem handles posture, and the cortex specifies what to do rather than which muscle to use. Errors are corrected by loops through the cerebellum and basal ganglia, which is why damage there degrades movement without paralysing it.
What a learner can do afterwards
- Distinguish the roles of spinal, brainstem and cortical levels in a single reaching movement
- Explain what a motor unit is and how force is graded by recruitment
- Contrast the movement disorder caused by cerebellar damage with the one caused by basal ganglia damage
1 · Read
Movement is produced by a hierarchy of levels. The cord holds reflex circuits and pattern generators for fast local loops, the brainstem handles posture and gain, and the cortex specifies what to do rather than which muscle to use. Errors are corrected by loops through the cerebellum and basal ganglia.
Reach for a cup: your cortex selects the target and the plan, your brainstem tunes posture so you do not topple, and spinal circuits adjust the arm within milliseconds. Damage to the cerebellum or basal ganglia degrades this reach without paralyzing it.
Force itself is graded at the motor unit: one motor neuron plus all the fibres it drives. Small units join first for delicate jobs, bigger ones join as demand rises, and firing faster adds more. Recruitment order plus firing rate sets the force.
Tell the two corrector faults apart by their signature. Cerebellar damage brings overshoot, bad timing, and wobbly balance with normal strength. Basal ganglia damage brings stiffness, slowness, rest tremor, or unwanted extra motions. Clumsy but willing points one way, reluctant or excessive the other.
Cortex plans, brainstem steadies, cord executes, and two correctors keep the motion clean.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.