Motor Units

What do motor units consist of?

a single motor unit and all the muscle fibers it stimulates

What are motor neurons?

nerve cells

What do these nerve cells send?

electrical signals from the brain or spinal chord to muscle fibers

What these electrical signals initiate the process of?

muscle contraction

All or nothing principle

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What must a signal sent by a motor neuron reach?

a certain level (threshold) to activate the muscle fibers

What will happen if the signal manages to reach this threshold?

all the muscle fibers in the motor unit contract fully

What will happen if the signal doesn't reach the threshold?

none of the fibers contract

How is more force produced?

by recruiting more motor units

How is more force not produced?

by making fibers contract harder

What do muscle contractions require?

energy provided by ATP

ATP

adenosine triphosphate

Usage of ATP when the motor unit contracts

.

What is released from actin?

mysoin

What does ATP allow myosin heads to do?

let go of actin after the muscle has contracted

What does ATP pump calcium back into?

storage to help the muscle relax

What does ATP prepare myosin for?

the next contraction

What does ATP do to the myosin heads?

resets them for the next contraction

What does the principle of orderly recruitment refer to?

how motor units are activated in a predictable sequence when muscles contract

What happens when a motor unit is activated?

all the muscle fibers in the unit contract

What happens when all the muscle fibers in the unit contract?

developes force

What needs to be activated to produce more force?

more motor units

What is recruited first?

smaller motor units

What do smaller motor units have?

smaller muscle fibers

What are smaller motor units responsible for?

fine, precise movements (writing)

When are larger motor units recruited?

when the demand for forces increases

What do larger movements help with?

more powerful movements (lifting heavy weights)

What does it ensure the body uses the appropriate amounts of?

force for each task

Types of motor units

type 1, type IIa, type IIx

Type 1

slow nerve transmission speeds (cross country race)

Type IIa

fast transmission times and stronger contraction force (400m)

Type IIx

fastest transmission times and strongest contraction forces (100m)

What do IIx motor units do the quickest?

fatigue

Motor Units