is important to understand the microscopic
structure of skeletal muscle and how these structures
assist with creating movement.
create movement by pulling on the bone to
which they attach. In order to do this, messages are
sent from the brain to the muscles to initiate
coordinate in pairs to produce coordinated
A motor unit
A motor unit consists of one
motor neuron and the muscle fibre
it stimulates (Each neuron may
stimulate a number of muscle
Depending on the size and function
of a muscle will depend on the
number of motor units it has
The quadriceps is responsible for
gross movement such as kicking
and jumping. It has a very large
number of motor units
The muscles that control
movements like writing and typing
have only a small number of motor
The ‘all or nothing’ principle
The nerve impulse will not stimulate the muscle fibres until it
reaches a certain threshold level. Once the nerve impulse
reaches this threshold, all fibres of the motor unit will contract
at the same time and maximally. If the impulse is too weak, no
fibres will contract.
Therefore depending on the force required for a movement will
impact the number and speed of nerve impulses sent.
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