muscle contraction step 1

activation of motor neuron

afferent division

sensory, to brain

efferent division

motor, from spinal cord

step 1

each muscle fiber is innervated by one neuron

step 2

each neuron innervates many muscle fibers (motor unit), the activation of neuron causes all fibers in motor unit to contract

small motor units

3-6 gibers, for fine motor skills, ex: hands, eyes

large motor units

100s-1000s fibers, for strength, ex: arms, legs