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Sherrington is best known for...
importance of role of reflexes in patterning of muscle activity
proposed skin and muscle receptors elicit activation of movement
demonstrated that sensory input was required to elecit the stretch reflex
first person to use the term "synapse"
quick stretch involves which afferent axon
flexion - withdrawal reflex
pain that makes you withdraw from a stim
it's a protective reflex involving multi-joint actions
concurrent inhibition of motor neruons that innervate extensor muscles of the limb
who talked about it?
Sherrington (right, bc it's a reflex)
He called it the excitation/inhibition (either) of antagonistic muscles on the ipsilateral limb
flex yr right knee and hip to get off a tack, and the left knee and hip will extend
crossed extensor reflex
flexors of one leg contrac as extension/weight acceptance occurs in the other leg
reciprocal innnervation according to Sherrington
He tried to passively flex the extended (rigid) hind leg of a decerebate cat, and the stretch led to increased contraction of the extensor muscles.
decerebrate vs decorticate
- Decerebrate - losing cerebral reflex control, as in an
- intracranial catastrophe, causing stiffened extension in legs, arms, back, and pronation of arms
Decorticate - loss at the level of the midbrain: causing flexed arms and extended legs
stim's impact on reflex
greater stim intensity causes more forceful reflex
spindle main job
they're used by the CNS to keep the brain and cerebellum informed on relative position of body segments and even slight changes in muscle tone
alpha motor neurons provide innervation to...?
alpha motor neurons are excited by...?
extrafusal muscle fibers
corticospinal neurons (and 1a neurons?)
where are intrafusal muscle fibers non-contractile?
in the center
where are afferent sensory fiber endings found in a muscle spindle
these large diameter myelinated fibers are in the center
contraction of interfusal fibers pulls on...
the central regions from both ends, changing the sensitivity of the sensory fiber endings to stretch
gamma efferent fibers
- cause the ends of intrafusal fibers to contract.
- this stretches the central region and sustains sensory affernt output
output to primary sensory ending in the spindle effectively resets the sensitivity of the spindle
gamma effernt fibers to the end of muscle spindle fibers adjust spindle fiber stretch to the spinle is responsive thru the physiological range of musle lengths
keep a level of muscle tone even when at rest so yr ready for movement
collateral fibers from muscle spindle synapse on...?
Spindles send messages to spinocerebellar tracts. From the cerebellum this info on body segment location goes to...?
what happens there?
red nucleus and thalamus
their input is coordinated w info from motor cortex and basal ganglia
happens due to CNS injury or pathology
can lead to overactivation of gamma system
(under normal conditions, intrafusal spindle fibers are partially contracted. Greater firing rate of gamma efferents causes greater intrafusal contraction and greater sensitivity of spindle)
if supraspinal structures influence the intrafusal fibers to contract to a length shorter than the surrounding extrafusals, what happens?
- the sensory endings (type 2 afferent fibers on chain fibers) continue to fire,
- which will stim the alpha motor nerves
- to stim contraction of extrafusal fibers
CNS can independantly adjust what about the affernt fibers from muscle spindles?
their dynamic and static sensitivity
effect of supraspinal structures on efferent motor control impulses are...?
facilitatory and inhibitory
Spindle take-away message:
Movement is produced via: a normal postural set and motor pattern synergy, normal sensory info which is correctly processed, and complete interaction withn the CNS regarding expectations of movement and monitoring actual outcomes. So, injury or disruption anywhere in the PNS or CNS can produce deficits in movement and functions.
peripheral input which increases excitability of anterior horn cell
peripheral input which decreases excitability of anterior horn cell
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