14. Myostatic Reflexes & Golgi Tendon Organ Flashcards
what reflexes are controled in the cortex
placing reaction (brush babies feet)
hopping reaction
what reflexes are controlled in the brainstem/midbrain
vestibular
right reflex
suckle
yawn
eye/head movement
what are the spinal reflexes
stretch (myotatic)
golgi tendon reflex
cross extensor
what is the purpose of a reflex
protect
create movement thats required w/o voluntary control
= fast
what is the key to being an effective reflex
must be very PRECISE
how do you tell the different btn volitional movement & normal reflexes
normal reflexes = faster than fastest volitional movement
what are the characteristics of a myotatic reflex
-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)
what is a muscle spindle
w/i sk. muscle - embedded in fusiform capsule
= parallel to M fibers
-contain afferent & efferent components
compare intrafusal vs extrafusal fibers
intrafusal: fibers w/i capsule
extrafusal: bulk of the M (the M you see)
what are characteristics of intrafusal fibers
contain BOTH motor/sensory components
what are characteristics of the sensory portion of a M spindle
= sensitive to length
- 2 sensors : nuclear bag afferent & nuclear chain afferent
not contractile
what does the 1a fibers do
innervate nuclear bag & nuclear chain structures
Large & myelinated
sensitive to BOTH: length & how faxt its changing
increase firing with stretch
what do Group II fibers do
innervate ONLY nuclear chain
small & myelinated (still pretty fast)
sensitive to ONLY length of M
what does the motor portion of the m. spindle contain
similar histo as sk. M
inneraved by GAMMA MNs
control the length of the sensory portion
=contractile
what is the role of gamma MNs
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)
describe the stretch reflex (myotatic)
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)
how does the antagonist M come into play in the stretch reflex
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
what is the Golgi Tendon reflex
aka inverse myotatic
aka autogenic inhibition
initiated by golgi tendon organ
= polysynaptic, segmental reflex
= sudden relaxation of contracted M –> protects M from damage from excess force
what is the golgi tendon organ
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)
what are the steps to the golgi tendon reflex
strong contraction of golgi tendon –> 1b afferent activated –> release EAA & activate interneuron –> interneuron inhibits (hyperpolarizes) alpha MN of contracting M –> decrease APs = sudden relaxation
do higher regions of the brain stimulate or inhibit reflexes?
often = inhibitory
by some regions provide excitation
what happens to a reflex below a transection
fail to occur, even if they’re intact
how doe recovery of reflexes occur
axons sprouting below levels on transection
expression of self activating receptor phenotypes (5HTC receptor)
what occurs in decerebrate posturing
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)
explain spasticity in decerebate posture
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
what is decorticate postureing
-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
