Question

The term ‘innervation ratio’ refers to the average number of muscle fibres that

are innervated by a single motor neuron. Describe the relationship between this ratio and the body’s skeletal muscles.

Answer 1

MOTOR UNIT- motor unit comprises of a motor neuron and muscle fiber

INNERVATION RATION is defined as the number of muscle fiber innervated by a single motor unit.

Normally motor neuron ( Nerve supplying the muscle for the action of the muscle) will innervate more than one muscle fiber .But a Muscle fiber is only supplied by a single Motor neuron.

Skeletal muscle are of two type

1)Bulk or coarse muscle : Coarse muscle are the muscles with more number of muscle fiber that help in the movement of the body.Eg: MUSCLES IN THE THIGH , LEG

This type of muscles have HIGH INNERVATION RATE , that is a single motor unit will supply more number of Muscle fibers. It i because this type of muscle doesnt need more coordination between the muscle fiber.

2) FINE SKELETAL MUSCLE :This type of muscle are used for the fine movement like muscles in the hand and fingers. This type of muscle have a lowINNERVATION RATIO, that is a single motor unit supply only few number of muscle fiber . This type of muscle need more coordination between the fibers because they are used in the fine movements.So, muscle fibers of the muscle are innervated by more number of motor unit.