14. Myostatic Reflexes & Golgi Tendon Organ

Question 1

what reflexes are controled in the cortex

Answer 1

placing reaction (brush babies feet)

hopping reaction

Question 2

what reflexes are controlled in the brainstem/midbrain

Answer 2

vestibular

right reflex

suckle

yawn

eye/head movement

Question 3

what are the spinal reflexes

Answer 3

stretch (myotatic)

golgi tendon reflex

cross extensor

Question 4

what is the purpose of a reflex

Answer 4

protect

create movement thats required w/o voluntary control

= fast

Question 5

what is the key to being an effective reflex

Answer 5

must be very PRECISE

Question 6

how do you tell the different btn volitional movement & normal reflexes

Answer 6

normal reflexes = faster than fastest volitional movement

Question 7

what are the characteristics of a myotatic reflex

Answer 7

-initated by M spindles to contract (shorten) a stretched M

= protection from tearing due to over stretching

= monosynaptic & segmental (stay in same seg of sp cord)

Question 8

what is a muscle spindle

Answer 8

w/i sk. muscle - embedded in fusiform capsule

= parallel to M fibers

-contain afferent & efferent components

Question 9

compare intrafusal vs extrafusal fibers

Answer 9

intrafusal: fibers w/i capsule
extrafusal: bulk of the M (the M you see)

Question 10

what are characteristics of intrafusal fibers

Answer 10

contain BOTH motor/sensory components

Question 11

what are characteristics of the sensory portion of a M spindle

Answer 11

= sensitive to length

• 2 sensors : nuclear bag afferent & nuclear chain afferent

not contractile

Question 12

what does the 1a fibers do

Answer 12

innervate nuclear bag & nuclear chain structures

Large & myelinated

sensitive to BOTH: length & how faxt its changing

increase firing with stretch

Question 13

what do Group II fibers do

Answer 13

innervate ONLY nuclear chain

small & myelinated (still pretty fast)

sensitive to ONLY length of M

Question 14

what does the motor portion of the m. spindle contain

Answer 14

similar histo as sk. M

inneraved by GAMMA MNs

control the length of the sensory portion

=contractile

Question 15

what is the role of gamma MNs

Answer 15

control length of sensory part of M spindle

control sensitivity / cause contraction

does NOT directly lead to motion

–> contract intrafusal fibers stretch the sensory part –> increase the sensitivity of 1a & II fibers

(slighty smaller/slower than alpha MNs)

Question 16

describe the stretch reflex (myotatic)

Answer 16

M stretched –> 1a activated –> synapse DIRECTLY w/ alpha MN –> activate alpha MN by releasing EAA –> alpha MN contract the M to shorten (decrease the stretch)

Question 17

how does the antagonist M come into play in the stretch reflex

Answer 17

when 1a stimulated it synapse with alpha MN

AND an interneuron (stimulates interneuron with EAA –> interneuron release GABA and inhibit alpha MN of antagoinst M –> fewer APs to anagonist –> relax)

==> the originally stretched M is no longer opposed

Question 18

what is the Golgi Tendon reflex

aka inverse myotatic

aka autogenic inhibition

Answer 18

initiated by golgi tendon organ

= polysynaptic, segmental reflex

= sudden relaxation of contracted M –> protects M from damage from excess force

Question 19

what is the golgi tendon organ

Answer 19

tendon with bare N endings w lots of branches

APs increase w/ tension

–> 1b fibers

must have LARGE contracting force to activate GTO (passive stretch initiates M. spindles not GTO)

Question 20

what are the steps to the golgi tendon reflex

Answer 20

strong contraction of golgi tendon –> 1b afferent activated –> release EAA & activate interneuron –> interneuron inhibits (hyperpolarizes) alpha MN of contracting M –> decrease APs = sudden relaxation

Question 21

do higher regions of the brain stimulate or inhibit reflexes?

Answer 21

often = inhibitory

by some regions provide excitation

Question 22

what happens to a reflex below a transection

Answer 22

fail to occur, even if they’re intact

Question 23

how doe recovery of reflexes occur

Answer 23

axons sprouting below levels on transection

expression of self activating receptor phenotypes (5HTC receptor)

Question 24

what occurs in decerebrate posturing

Answer 24

loss of all structures above red nucleus

–> rigidity (motion restricted in all directions); maintained M contrction & continual activation of alpha MNs (activated by Br.st)

—> spasticity: resist motion in a direction; hyperactive myotatic reflex & continual activation of gamma MNs (make m spindles more sensitive –> spontanously active)

Question 25

explain spasticity in decerebate posture

Answer 25

resist motion in a direction; hyperactive myotatic reflex & continual activation of gamma MNs (make m spindles more sensitive –> spontanously active)

-loss of cortex –> br.st not activated –> leaves the brainstem faciliatory region in charge

==> uncontrolled brainstem faciliatroy region –> stretch reflexes that fight any passive motion ==> spasiticity

Question 26

what is decorticate postureing

Answer 26

-rigidity; flexion of Upper limbs (disinhibition of red nucleus)

;extension of lower limbs (disinhibition of reticulospinal and vestibulospinal paths

=dep on head position

=strokes in vicinity of IC