GLOSSARY

The branches of motor neurons are the terminal ramifications of a motor neuron’s axon that divide after entering the muscle, with each branch reaching one muscle fibre.

Characteristics

• One branch, one fibre: each muscle fibre is normally innervated by a single branch of one motor neuron, but one neuron can innervate tens to thousands of fibres.
• Scattered fibres: a neuron’s fibres are not clustered together but scattered in a mosaic across part of the muscle, giving even force distribution.
• Terminals: each branch ends in synaptic boutons that release acetylcholine at the neuromuscular junction.

Sprouting

If some motor neurons die, neighbouring healthy neurons produce collateral sprouts and reinnervate the denervated fibres, forming larger motor units.

Clinical Application and Relevance to Sport

• Ageing: with loss of motor neurons and sprouting, motor units become fewer but larger, reducing fine motor control and speed.
• Polio and nerve injury: sprouting helps recover some strength.
• Exercise: regular training in older age helps preserve nerve–muscle connections.