motor units Flashcards
what is a motor unit
A motor unit consists of a motor neuron AND a number of muscle fibres.
what is an axon
portion of a nerve cell (neuron) that carries nerve impulses away from the cell body
what are motor neurone
specialised cells which transmit nerve impulses to a group of muscle fibres
when can skeletal muscles contract
when stimulated by an electrical impulse, sent from the Central Nervous System which travels down the extending axon which connects to the motor end plates.
what is a neuromuscular junction
The point where the axon’s motor end plates meet the muscle fibre
what is action potential
refers to a positive electrical charge inside the motor unit, which conducts the nerve impulse down the neuron into the muscle fibre.
what happens when the action potential reaches or is above the threshold
ALL the muscle fibres within that motor unit will contract at the same time and with maximum force.
what happens when the action potential doesn’t hit the threshold
nothing happens
what is the gap between the motor end plates and the muscles fibres
synaptic cleft
what is the neurotransmitter
acetylcholine (Ach)
if enough neurotransmitter is secreted and the charge is enough what happens
muscle action potential is created
This creates a wave of contraction down the muscle fibre
what is the all or none law
When stimulated ALL the
Fibres within a motor unit
Contract completely or not
at all.
overview of the whole process
The central nervous system (CNS) sends an electrical Impulse to the motor neuron (specialised cells).
The neuron and its muscle fibres are termed the motor unit. The motor neuron transmits a nerve impulse. Depolarization - movement of sodium/ NA+ (ions) into the axon causes depolarisation An action potential conducts the nerve impulse as a wave of electrical charge down the axon to the motor end plates. The point where the axon meets the motor end plates is called the neuromuscular junction.
There is a small gap between the motor end plates and the muscle fibre called the synaptic cleft. A neurotransmitter is needed to carry the action potential across the synaptic cleft, called acetylcholine (Ach). If enough Ach is secreted and the electrical charge is above the threshold, a muscle action potential is created. This creates a wave of contraction down the muscle fibre.
When the motor unit receives an action potential that reaches the threshold charge, the muscles fibres will contract with maximum force. This is called the all or none law.
