Structure of the Motor Unit Flashcards
What is the motor unit?
Is the motor neuron and all muscle fibres with which it connects to and stimulates.
What does a small motor unit do?
Will stimulate a small number of muscle fibres. They are not strong and are used for producing subtle and precise control.
What does a large motor unit do?
Will stimulate a large number of muscle fibres. They are strong to produce little fine control.
Draw a diagram of the motor unit.
Did you include -
1. Nucleus.
2. Cell body.
3. Dendrites.
4. Myelin sheath.
5. Axon.
6. Arrow outlining the direction of the nerve impulse.
7. Muscle fibre.
What is the function of dendrites (dendrites of sensory neurons)?
Pass information from the sensory receptors to the cell body of the sensory neuron.
What is the function of axons (Axons of motor neurons)?
Transmit electrical information or signals away from the cell body to the muscle fibres.
What is the function of the spinal cord?
Transmit electrical messages from the brain to parts pf the body.
What is the function of neurons?
A cell within the nervous system that transmits impulses to other nerve cells and muscles.
What is the function of the motor unit?
Causes contraction of associated muscle fibres to create movement.
Outline the 9-step process of how a message is transported through a motor unit/neuron.
- Brain receives a signal from the sensory nerve.
- Message travels via motor neurons.
- Arrives at the neuromuscular junction and has to cross the synapse.
- Arrive of action potential opens calcium channels so calcium ions enter.
- Influx of calcium triggers a biochemical cascade.
- This causes the neurotransmitter, acetylcholine into the synapse.
- This signal on the end plate then transmits nerve signals to the muscle fibre.
- This signal releases the calcium from the sarcoplasmic reticulum causing the sliding filament theory.
- Nerve cells extend across the length of the myofibril but only stimulate portions of the muscle belly.
Define the ‘all or nothing’ response.
Is the process of an electrical threshold of the motor neuron being reached, causing all muscle fibres connected to the motor unit to contract. All muscle fibres of the motor unit contract with the same maximal force at the same time.
What happens if a motor unit does not receive sufficient impulses/the threshold is not met?
None of the fibres will be activated to contract.
What are the 3 ways more force can be produced?
- Greater number of motor units are used.
- Activating larger motor units.
- Rectruits appropriate muscle type II (fast twitch)
Describe the relationship between muscle contractions and nerve functions.
The arrival of an action potential at the neuromuscular junction triggers calcium channels to open, releasing calcium ions. This initiates the release of the neurotransmitter acetylcholine into the synaptic cleft. This transmits nerve signals onward to the muscle fibre.
