10.2 Local Control of Motor Neurons

Alpha-Gamma Coactivation

Simultaneous firing of action potentials along alpha motor neurons to extrafusal fibers of a muscle and along gamma motor neurons to the contractile ends of intrafusal fibers within that muscle

Alpha Motor Neurons

Somatic efferent neurons, which innervate skeletal muscle

Crossed-Extensor Reflex

Increased activation of extensor muscles contralateral to limb flexion

Extrafusal Fibers

Primary muscle fibers in skeletal muscle, as opposed to modified (intrafusal) fibers in muscle spindle

Gamma Motor Neurons

Small motor neurons that control intrafusal muscle fibers in muscle spindles

Golgi Tendon Organs

Tension-sensitive mechanoreceptor endings of afferent neuron; wrapped around collagen bundles in tendon

Intrafusal Fibers

Modified skeletal muscle fibers

Knee-Jerk Reflex

Often used in clinical assessment of nerve and muscle function; striking the tendon just below the kneecap causes reflex contraction of anterior thigh muscles, which extends the knee

Monosynaptic Reflex

Reflex in which the afferent neuron directly activates motor neurons

Muscle Spindle

A receptor organ, made up of specialized muscle fibers, that detects stretch of skeletal muscles

Muscle-Spindle Stretch Receptors

Capsule-enclosed arrangements of afferent neuron endings around specialized skeletal muscle fibers; sensitive to stretch

Polysynaptic Reflexes

A neuronal pathway such as occurs in some reflexes in which two or more synapses are present

Reciprocal Innervation

Inhibition of motor neurons activating muscles whose contraction would oppose an intended movement

Stretch Reflex

Monosynaptic reflex, mediated by muscle-spindle stretch receptor, in which muscle stretch causes contraction of that muscle

Synergistic Muscles

Muscles that exert force to aid intended motion

Withdrawal Reflex

Bending of those joints that withdraw an injured part away from a painful stimulus.