Motor Control - Reflexes Flashcards
Placing reaction and hopping reaction are examples of
cortical reflexes
Stretch (myotactic), golgi tendon, and crossed extensor ar examples of
spinal reflexes
vestibular, righting, suckle, yawn, eye/head movements are examples of
Brainstem/midbrain reflexes
Reflexes in oder to be effective must be very precise. This “precision” can
make reflexes look like volitional movement
difference between reflex and volitional movement
a reflex movement occurs faster than the fastest voluntary motion
reflex activity characteristics
precis motions in response to afferent stimuli
mediated at all levels of the CNS
rapid initiation
many elicited even during unconsciousneess
volitional activity characteristics
originates in cortical areas associated with judgement, initiative, and motor control
longer onset, latency due to processing
require conscious awareness
myotactic reflex (stretch) - appearance
shortening/contraction of a stretched muscle
myotactic reflex - purpose
protect mm from tearing due to strain
myotactic reflex - characteristics
initiated by muscle spindle
monosynaptic, segmental reflex
the muscle spindle is ____ to extra fusel fibers
parallel
There are ______ types of fibers with in the muscle____
several
spindle
muscle contains _____ and _____ parts
afferent (sensory)
efferent (muscle)
intrafual fibers of the muscle spindle have _______ components
both motor and sensory
Characeristics of the sensory fiber of a muscle spindle
not contractile it's the portion sensitive to length two sensors with different afferents 1. nuclear bag fiber 2. nuclear chain fiber
Primary afferent of myotactic reflex
1a fiber
characteristics of 1a fiber
large, myelinated
sensitive to both length of mm and how fast that length is changing
1a fiber innervates
nuclear bag and nuclear change
at resting lenth, the 1a fiber fires
less frequently
with stretch, the 1a fiber fires
more frequently
with fast stretch, the 1a fiber fires
most frequently
The secondary afferent is a ____ fiber
Group II fiber
secondary afferent characteristics
smaller, myelinated,
sensitive only to the length of the muscle
the secondary afferent innervates
only the nuclear chain
Primary Afferent associated with the muscle spindle - summary
large 1a fiber (heavily myelinated, fast velocity, low threshold)
innervates both nuclear bag and nuclear chain fiber
detects length and speed of change of length
Secondary Afferent associated with the muscle spindle - summary
group II fiber (smaller, less myelin, still pretty fast)
innervates nuclear chain only
detects only lenth
Motor portion of the muscle spindle consists of
intrafusal contractile elements
characteristics of motor portion of muscle spindle
same as skeletal muscle
control length of the sensory portion
motor portion of the muscle spindle innervated by
gamma motor neuron
By contracting intrafual muscles, we
stretch the sensory portion
this renders the sensory portion more sensitive to a superimposed stretch
gamma motor neurons are important in
controlling sensitivity
alpa motor neurons - summary
large, heavily myelinated fiber
innervates via NMJ the skeletal muscle
responsible for activating muscle
activity directly leads to motion
Gamma motor neuron - summary
slightly smaller, slower than alpha, still fast overall
innervates the contractile component of the muscle spindle via nmj
activity causes contraction - controls sensitivity of muscle spindle , does NOT directly lead to motion
path of myotactic reflex at spinal level
motor neuron is excited by activation of Ia afferent ==> contraction releives the stretch, returning the Ia discharge rate back to normal
stretch reflex - we contract the agonist muscle, what happens to the antagonist muscle? why
it gets stretched
there;s more than just a single synapse, the Ia afferent can also act on interneurons
with the stretch reflex, there is a ______ in the activity of the _____ innervating the antagonist allowing____
decrease
alpha motorneuron
relax and lenthen
Golgi tendon reflex - aka
invers myotactic, autogenic inhibition
Golgi tendon reflex - appearance
sudden relaxation of a contracted muscle
Golgi tendon reflex - purpose
to protect muscle from damage due to excessive force
Golgi tendon reflex - characteristics
initiated by golgi tendon organ
polysynaptic, segmental reflez
Golgi tendon organs
innervate tendon
bare nerve ending with lots of branches
action potentials increase with tension
golgi tendon organs use ___ fibers
Ib
Golgi tendon reflex - mechanism
Ib afferent is + on the interneurin, which inhibits the motor neuron
result = abrupt relaxation of the muscle occurs, returning golgi tendon organ discharge rate back to normal
Myotatic reflex - summary
initiated by muscle spindle
passive stretch of muscle
monosynaptic reflex
contraction of stretched muscle back to normal leng
Golgi tendon reflex - summary
reverse myotactic
active contraction of muscle
polysynaptic refles
abrupt relaxation of contracted muscle to prevent damage
Motor control - modification of reflexes (general types)
spinal shock
decerebrate posturing
spasticity
Spinal shock
even though neurons producing the reflex are below the level of transection, (therefore intact) the reflex fails to occur
spinal shock - recovery
results from axonal sprouting below the level of transection
expression of receptor phenotypes that are self activating (5HT-C)
Decerebrate posturing results from
loss of all structures rostral to the pons
Rigidity
resists motion in all directions
results from maintained mm contraction
continual activation of alpha motor neurons - not due to reflexes, brainstem is activating alpha motor neurons, but why is not clear
Spasticity
resists motion in a given direction
myotatic reflex hyperactive
continual activation of gamma motor neurons - contracts nitrafual muscle, lenthens nuclear bag/chain fibers,
brainstem
spasticity - brainstem facilitory region
by actuating the gamma motror neurons, makes muscle spindle more sensitive,
this region is spontaneously active
Spasticity - brainstem inhibitory region
inhibits gamma motor neurons, making muscle spindle les sensitive
this region requires activation from cortical regions.
Spasticity- why the loss the the cortex, the _____ region is not activated, leaving the _____ region to dominate
brainstem inhibitory
brainstem facilitory
the end result of the uncontrolled brainstem facility region is stretch reflexes that fight any passive motion - spasticity
patient resists a passive stretch of their muscles
the contraction doesn’t start until the stretch occurs
hyperactie myotactic reflex due to increased gamma motor neuron firing
spasticity
cause of spasticity
damage to cortex that abolishes activation of the brainstem inhibitory region (brain arousal systems0
contraction of muscle in the absence of other stimuli
alpha motor neurons continually active
rigidity
cause of rigidity
loss of cortical influence that inhibits a medullary input to the alpha motor neurons.
decorticate posturing =
rigidity
decorticate posturing - pt position
flexion of upper limb joints
extension of lower limbs
dependant on head position
unlike the decerebrate posturing, decorticate posturing is dependent on
head position and while change as the head is moved passively
you are extremely likely to see its with unilateral ____ posturing, which commonly results from
decorticate
strokes in the vicinity of the internal capsule
Transection of the spinal cord
all reflexes abolished, even if circuit is intact.
Cause>
spinal shock
hyper polarization of spinal neurons due to loss of excitatory input from cortex
internal rotation of legs in extended position, flexion of arms, dependent on head position
may be unilateral or bilateral
cause?
Decorticate posturing
loss of cortical inputs - most commonly caused by lesion of internal capsule
contraction of all antigravity mm (arms in extension)
usually bilateral and indicative of severe brain injury
cause?
Decerebrate Posture
loss of input from all structures rostral to the pons.
