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40 Cards in this Set

  • Front
  • Back

motor control is a major task in the nervous system

•Defined as the generationof signals to coordinatecontraction of the musculature of the bodyand head

physical energy->sensory systems->neural signals->motor systems-> muscle contractions->movement

How the system works

motor responses can be both _______ and________

voluntary(cerebral cortex) and involuntary(sensory input)

lowest system of motor control is

spinal cord. then brain stem. then cerebral cortex.

Most reflexes are SPINAL CORD

higher complex bx are higher motor area of CNS

cerebellum and basal ganglia

planning, refining, and coordinating signals


•is a series of neurons whose axons run upand down the spinal cord to connect the different levels of the cord to oneanother . Allows coordination of activity at different levels--voluntary movement, and muscle tone

Alpha motor neurons



axons leave spinal cord through ventral roots and brainstem from a few cranial nerve

motor unit

alpha motor neuron and all of the skeletal muscle fibers its axons supply.

lower ratio in eye (ex 1:1) vs 1:1000 in quads

gamma motor neurons is smaller than alpha

theyre located in the same motor nucleus as the alpha.

synapse on intrafusal muscle fibers found within muscle spindles

orderly recruitment of motor units occurs _____

in the order of the motor neuron axon size

•same size EPSC will generate a larger potential change at the axon hillock of a small motor neuron than it will at a largermotor neuron

•Smaller motor neurons have a highermembrane resistance than the large motor neurons (V =IR)

reflex arc

basic circuit that underlies a reflex

(afferent, synapse, efferent)

knee jerk. Hammer hits patella, , causes stretch of quad. afferent signal, synapse, efferent, quad contracts, hamstrings relax

group 1a fibers in muscle spindels (Afferent)

•Each spinal reflex is elicited by the activationof one or more classes of sensory receptors

muscle spindles and GTO.

These are also important for proprioception

muscle spindles lie in PARALLEL with regular muscle fiber. Detect changes in muscle length

muscle fibers within the spindle are called intrafusal fibers.

spindles are sensed by mechanoreceptors of the group1a and group II spindle afferents

intrafusal fibers

narrower than extrafusal

dont run the length of the muscle

dont contribute significantly to muscle tension or cause changes in length by contracting

intrafusal fiber types (2)

nuclear bag fibers (larger, nuclei are bunched)

BAG1 and BAG2

nuclear chain fibers (smaller, nuclei in a row)

bag2fibers are functionally similar to nuclear chain fibers

Extrafusal vs intrafusal

•Extrafusal fiber is innervated by a single alpha motorneuron

•Intrafusal fibers are multiply innervated and receive bothsensory and motor innervation

group 1a afferent fiber forms a primary ending consisting of a spiral-shapedterminal composed of branches of the group 1a fiber oneach of the intrafusal muscle fibers

•primary endings are found on both bag1 and bag2and on nuclear chain fibers

Group II afferent fiber forms a secondary ending, which is found on the nuclearchain and bag2 fibers but not on bag1 fibers

•Group II fibers are intermediate in sizeand conduct at 36-72 m/sec

•The primary and secondary endings have mechaosensitive channels

•sensitive to the levelof tension on the intrafusal muscle fibers

•The motor supply to a muscle spindleconsists of two types of gamma motor neuron axons

•Dynamicgamma motorneuron axons end on bag1 fibers

•Staticgamma motorneuron axons end on bag2 and nuclear chain fibers

Responseof afferent 1a and II fiber endings of a muscle spindle to changes in musclelength

Group1a: sensitive to both the amount of muscle stretch and to the rateof stretch (think reflex hammer)

GroupII: respond chiefly to the amount ofmuscle stretch. They fire proportionally to the amount of stretch

muscle stretch dynamic response

Dynamicresponses: activity overshoots during musclestretch and undershootsor ceases during muscle shortening

gamma Motorneurons adjust the Sensitivity of the Spindle

Whenmuscle relaxes and thus elongates, Aconcurrent ↓ gamma motor neuron activity will allow the intrafusalfibers to relax as well

Gamma motor neuron system allows the muscle spindle to operate over a wide range of muscle lengths whileretaining high sensitivity to small changes in length


•alpha and gamma motor neurons simultaneously activated

causes synchronous contraction of extrafusal and intrafusal muscle fibers

roleof gamma motor neurons-

keep spindle always active so it cansense change in muscle

Golgi Tendon Organs

Innervatedfrom the terminals of group 1b afferent fibers

Group 1b conduct in the same velocity as 1a

•Terminals of a 1b fiber are wrappedaround bundlesof collagen fibers in the tendon of a muscle

•Sensory endings are arranged in SERIES with the muscle

GTO signal FORCE

Spindles signal LENGTH

•Group 1b firing correlates with forcelevel during isometriccontraction even though muscle length, and therefore1a activity, are unchanged

propriospinal system- (think proprioception)

important for locomotion.

ascending sensory, decending motor paths for VOLUNTARY movement

alpha motor neurons are in the

ventral horn,

and travel via peripheral nerves

gamma motor neuron

synapse on intrafusal muscle fibers within the muscle spindle

afferent limb of reflex. Sign is carried by 1a fibers

efferent- motor neurons

muscle spindles lie PARALLEL with muscle fibers


intrafusal fibers (bag and chain) are multiply innervated

receive both sensory and motor innervation

(sensory- 1a afferent, II afferent)

extrafusal fibers are innervated by a SINGLE

alpha motor neuron

group 1a have primary endings (bag1,2 and chain fibers)

group II, found on Bag 2 and chain