The motor unit
- Created by: Megan66
- Created on: 26-10-16 21:24
View mindmap
- The motor unit
- Definitions
- Motor unit - a motor neurone and its muscle fibres
- Motor neurones- Nerve cells which transmit the brain's instructions as electrical impulses to the muscles
- Neuromuscular junciton - where the motorneurone and the msclefibre meet
- All or none law - where a sequence of impulses has to have sufficient intensity to stimulate all of the muscle fibres in a motor unit for them to contract or none of them contract
- Wave summation - where there is a repeated nerve impulse with no time to relax as a smooth, sustained contraction occurs, rather than twitches
- Tetanic contraction - A sustained muscle contraction caused by a series of fast repeating stimuli
- Spatial summation - When the strength of a contraction changes by altering the number and size of the muscle's motor units
- About the Motor unit
- Muscle fibres are grouped into motor units.
- A motor unit consists of a motor neurone and its muscle fibres.
- Only one type of muscle fibre can be found in one particular motor unit.
- Muscle fibres work with the nervous system so that a contraction can occur.
- The motor neurone transits the nerve impulse to the muscle fibre
- Each motor neurone has branches that end in the neuromascular junction on the muscle fbre
- Good to know
- Motor = Movement
- Each muscle is made up of many motor units and they vary in size.
- A small muscle that is used for fine motor control, for example eye movement will have motor units that have only a few fibres per motor neurone.
- A large muscle used for gross motor control such as the quadriceps when the leg is extended, will have motor units with a motor neurone feeding hundreds of fibres.
- The all or none law
- Once the motor neurone stimulates the muscle fibres, either all or none of them contract.
- It is not possible for a motor to partially contract, this is called the all or none law.
- A minimum amount of stimulation called the 'threshold' is required in start the contraction
- If the sequence of impulses is equal to or more than the threshold then all the muscle fibres will contract if not then no muscle action will occur.
- Slow twitch and fast twitch motor units
- Motor units contain the same type of muscle fibre so they are either slow twitch or fast twitch motor units.
- The brain will recruit slow twitch motor units for low intensity activity such as jogging or long-distance swimming.
- if a greater force of contraction is needed, the brain will recruit fast twitch motor units for activities such as sprinting or power lifting.
- How to increase the strength of contraction
- Wave summation
- The greater force of stimuli, the greater the tension developed by them muscle.
- Where a repeated activation of a motor neurone stimulating a given muscle fibre results in a greater force of contraction
- Each time the nerve impulse reaches the muscle cell, calcium is released.
- Calcium needs to be present for muscles to contract.
- If there are repeated nerve impulses with no time to relax,calcium will build up within the muscle cell.
- This produces a forceful, sustained, smooth contraction which is referred to as a tetanic contraction.
- Spatial summation
- This occurs when impulses are received at the same time at different places on the neurone which add up to fire the neurone.
- It is the recruitment of additional and bigger motor units within a muscle to develop more force.
- Wave summation
- Definitions
Comments
No comments have yet been made