Motor Unit: Definition And Diagram
Question 1. Write a short note on motor unit.
Answer. It is a functional unit of muscle. It consists of a single alpha motor neuron and all the muscle fibres which it innervates.
“The Role Of Motor Neurons In Controlling Muscle Fibers”
“What Is A Motor Unit In Anatomy”
About 150 muscle fibres are innervated by a single alpha motor neuron. The motor units are of two types: large and small.
The large motor units supply large number of muscle fibres, i.e. 2000–3000. These units supply muscles responsible for coarse but powerful actions,
Example: Gluteus maximus, gastrocnemius and deltoid.
Motor Unit Definition and Diagram
“Functions Of A Motor Unit In The Body”
The small motor units supply small number of muscle fibres, i.e. 10–20. These units supply muscles responsible for fine and precise movements, e.g. muscles causing eye movements, finger movements and vocal cord movements.
Question 2. Write a short note on neuromuscular junction (or motor end plate).
Answer.
It is a junction between the nerve terminal and cell membrane (sarcolemma) of a muscle fibre. At neuromuscular junction, the axon loses its myelin sheath and breaks up into number of branches to supply the individual muscle fibres. Each branch becomes distended to form synaptic knob .
which contains large number of vesicles containing acetylcholine. The muscle fibre at this site also becomes specialized into a sole plate . Here the muscle membrane, i.e. sarcolemma, is thrown into folds and contain receptors for acetylcholine.
Motor Unit in Anatomy
“Early Signs Of Problems With Motor Units”
“Risk Factors For Motor Unit Dysfunction”
The narrow space between the two plates – the synaptic cleft – is filled by a chemical substance called acetylcholine (a neurotransmitter). At the time of passage of impulse, the acetylcholine is broken down by an enzyme called acetylcholinesterase.
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