skeletal muscle contraction Flashcards
what is a motor neuron
- a nerve cell which conducts a nerve impulse to a group of muscle fibres
- specialised cells which transmit nerve
impulses rapidly to a group of muscles. - Cell body in the brain or spinal cord with an extending axon which
branches to connect motor end plates to a group of muscles fibres.
what is a motor unit
a motor neuron and the muscle fibre stimulated by its axon
what is a motor units function
to carry nerve impulses from the brain + spinal cord to the muscle fibres, initiating muscular contraction
what is a neurotransmitter
a chemical (acetylcholine) produced and secreted by a neuron which transmits the nerve impulse across the synaptic cleft to the muscle fibre
what is the all-or-none-law
- depending on whether the stimulus (action potential) is above a threshold, all muscle fibres will give a comply contraction or no contraction at all
- in order for a contraction to occur, all the muscle fibres must be ready to contract or no contraction will happen
what is the process of the motor unit + skeletal muscle contraction
- skeletal muscle can only contract when stimulated by an electrical impulse sent from the CNS
- Motor neurons are the specialised cells which transmit nerve impulses rapidly to a group of muscles
- Cell body in the brain or spinal cord with an extending axon which branches to connect motor end plates to a group of muscles fibres
- Sending the nerve impulse to the muscle fibres is an electrochemical process which relies on a nerve action potential to conduct the nerve impulse as an action potential cannot cross the synaptic cleft without a neurotransmitter
- If enough neurotransmitter is secreted, electrical charge will surpass the threshold, muscle action potential is created
- This action potential creates a wave of contraction down the muscle fire - all muscle fibres will contract at the same time with maximum force
what is the process of the motor unit + skeletal muscle contraction (shorter/condensed)
- Nerve impulse initiated in the motor neuron cell body
- Nerve impulse conducted down the axon of the motor neuron by a nerve action potential to the synaptic cleft
- Neurotransmitter called acetylcholine is secreted into the synaptic cleft to conduct the nerve impulse across the gap
- If the electrical charge is above a threshold, the muscle fibre will contract
- This is an ‘all or none’ fashion
What is the effect of stimulating more motor units?
Increased strength / force of contraction
small motor neurons features
- Stimulate few small muscle fibres
- Small & slow amount of force
- Fatigue resistant
large motor neurons features
- Stimulate many large muscle fibres
- Large amounts & rapid forces
- Fatigue quickly