The Electromyogram — Interfacing the Neuromuscular System
Prof. Dr. Alessandro Del Vecchio, Daniel Fenzel, Annika Ritter, Atharva Pall · 8 concepts · 6 questions
Concept 1 / 8
The Motor Unit — Neural Command to Muscle
A motor unit is the fundamental functional unit of motor control: one alpha motor neuron plus all the muscle fibres it innervates through neuromuscular junctions (NMJs). When the motor neuron fires, every fibre in the unit contracts simultaneously (all-or-nothing principle).
Neural pathway from brain to muscle:
1. Descending corticospinal tract — voluntary motor commands from motor cortex
2. Spinal cord integration — inputs converge at the alpha motor neuron
3. Proprioceptive feedback — muscle spindles (Group Ia/Ib) report length and tension
4. Renshaw cell inhibition — recurrent inhibition prevents over-excitation
5. Neuromuscular junction — action potential triggers muscle contraction
Why this matters for neural interfacing:
| Disease | What breaks | Effect |
|---|---|---|
| ALS (e.g., Stephen Hawking) | Alpha motor neurons die | Paralysis with intact cognition |
| Spinal cord injury (e.g., Christopher Reeve) | Descending drive is severed | Motor neurons intact but unreachable |
| Peripheral neuropathy | NMJ or axon damaged | Partial or full denervation |
Recording and decoding the electrical signals produced by motor units is the core technical challenge this course addresses.