Kinesiology : motor units

Motor unit

Comprised of cell body of alpha efferent neuron, axon, and all muscle fibers innervated by axon

Ventral side

Side of the spinal cord that efferent motor neurons exit

Fibers in a motor unit

Depends on how precise/powerful movements are that the muscle normally does

Fibers in quads, hamstrings, gastroc

More than 1500 fibers/mv

Fibers in hand

Less than 100 fibers/mv

How fibers are distributed throughout muscle

Some cover 1 cm and others spread throughout entire muscle

Twitch type

Respond to a single stimulus

Tonic type

Need multiple stimuli to contract

Twitch type examples

Most motor units

Tonic type examples

Eye

Summation

Building tension in an additive fashion in response to repeated stimulation

Tetanus/tetany

State of sustained max tension resulting from repetitive stimulation

• full bonding, recruited all sarcomeres

Effects of repeated stimulation in muscle force

1. Muscle is stimulated

2. myosin bonds with actin

3. Summation

4. Tetanus