skeletal muscle contraction

Question 1

what is a motor neuron

Answer 1

• 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.

Question 2

what is a motor unit

Answer 2

a motor neuron and the muscle fibre stimulated by its axon

Question 3

what is a motor units function

Answer 3

to carry nerve impulses from the brain + spinal cord to the muscle fibres, initiating muscular contraction

Question 4

what is a neurotransmitter

Answer 4

a chemical (acetylcholine) produced and secreted by a neuron which transmits the nerve impulse across the synaptic cleft to the muscle fibre

Question 5

what is the all-or-none-law

Answer 5

• 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

Question 6

what is the process of the motor unit + skeletal muscle contraction

Answer 6

• 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

Question 7

what is the process of the motor unit + skeletal muscle contraction (shorter/condensed)

Answer 7

• 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

Question 8

What is the effect of stimulating more motor units?

Answer 8

Increased strength / force of contraction

Question 9

small motor neurons features

Answer 9

• Stimulate few small muscle fibres
• Small & slow amount of force
• Fatigue resistant

Question 10

large motor neurons features

Answer 10

• Stimulate many large muscle fibres
• Large amounts & rapid forces
• Fatigue quickly