1.5 Neural control of muscles Flashcards
(10 cards)
Movement and messages
Muscles create movement by pulling on the bones to which they attach. In order to do this, messages are sent from the brain to the muscles to initiate movement.
Nervous control of muscular movement
The brain must send electrical nervous messages to the muscles.
These messages/signals travel down the spinal cord to the motor nerves that branch from the spinal cord to the relevant muscles
Leaving the spinal cord, the motor nerve separates into smaller motor neurons that then divide a number of times to attach to individual muscles.
Where the nerves meet the muscle fibres, there is a gap across which the nerve impulse has to travel.
A neurotransmitter, which is a chemical compound called acetylcholine, helps the nerve impulse make this jump
The muscle will continue to contract for as long as the brain sends messages and the relevant energy sources last
Motor units
Motor unit consists of one motor neuron and the muscle fibre it stimulates.
Each neuron may stimulate a number of muscle fibres
The ‘all or nothing’ principle
‘all or nothing’ principle states that if the nerve impulse meets a certain threshold, maximal action occurs in the muscle fibre.
If the stimulation is less than threshold, no muscle action occurs in the muscle fibre.
Intensity can vary on the number of motor units stimulated
Not all the motor units within a muscle need to be recruited at one time for a muscle contraction.
If you require a large degree of strength, then more nerve impulses are sent, activating more motor units and therefore contracting more muscle fibres.
If you require a minimal degree of strength, then fewer impulses are sent, contracting fewer fibres.
Intensity can vary on the frequency at which the impulses arrive at the motor unit
The greater the frequency of nerve impulses, the greater the contractions in the muscle.
If you require a large degree of strength, then impulses will be sent at a faster rate to the muscles involved.
Size principle
The size principle, also known as the Henneman principle states that the recruitment of motor units in skeletal muscles starts with small motor units to large motor units
Small motor units
Slow contracting
Easily excitable and recruited
Fatigue resistant
Used for prolonged activities (e.g walking, posture control)
Large motor units
Fast contracting
Less easily excitable and recruited
Rapidly fatigable
Used for high force activities (e.g. sprinting, hitting, jumping)
Development of muscle force factors:
The number and type of motor units activated
The size of the muscle
The initial length of muscle that is being activated
The angle of the joint
The muscle’s speed of action
