Skeletal muscle via ventral root, peripheral nerve and neuromuscular junction
Cortex or muscle · effector
The lower motor neurone axon releases acetylcholine at the neuromuscular junction onto nicotinic receptors of the motor end plate; one motor neurone with all the fibres it supplies is a motor unit. Weakness must be localised along this chain to UMN, anterior horn, root, nerve, junction or muscle.
Traced from the start
- Primary motor cortex (precentral gyrus, Brodmann area 4)
- Upper motor neurone axon: corona radiata, posterior limb of internal capsule, crus cerebri, basis pontis and medullary pyramid
- Pyramidal (motor) decussation at the cervicomedullary junction
- Proprioceptors (muscle spindle, Golgi tendon organ, joint receptors)
- Lateral corticospinal tractAnterior corticospinal tract (uncrossed 10-15%)Ia afferent monosynaptic collateral (stretch reflex arc)
- Anterior horn cell (alpha motor neurone, lower motor neurone)
- Skeletal muscle via ventral root, peripheral nerve and neuromuscular junction
Detail
- Transmitter
- Acetylcholine on nicotinic receptors
- Motor unit
- One alpha motor neurone plus every muscle fibre it supplies
When it goes wrong
Neuromuscular junction disease (myasthenia gravis)
Fatigable weakness of ocular, bulbar and proximal muscles with normal reflexes and no sensory loss
Primary myopathy (inflammatory, dystrophy)
Symmetrical proximal weakness with reflexes preserved until late, no fasciculations and no sensory loss
Practise this structure
1 question in the bank tagged Neuromuscular Transmission.