Spinal Mechanisms of Motor Control Flashcards
sensory receptor
trasduces physical stimuli into neural signal
sensory input
afferent to CNS
phasic stretch reflex
very brief stretch usually elicited by tapping on a tendon
tonic stretch reflex
longer lasting stretch casued by stretching a muscle and holding it at its new longer legth
what is the fasters refelx
monosynaptic stretch reflex
where is muscle spindle
parallel to extrafusal muscle fibers
what are the intrafusal muscle fibers
dynamic nuclear bag
static nuclear bag
nuclear chain
what is the pirmary ending of sensory innervation of muscle spindle
group Ia fiber
Group Ia fier
usually innervates all intrafusal fibers in a muscle spindle
what is firing pattern of group Ia afferent related to
how fast the muscle length is changing and the current length of muscle
what is the seoncdary ending of sensory innervation of muscle spindle
group II fiber
what does firing rate of Group II fiber tell you
muscle length but NOT how fast muscle length is changing
gamma efferent fibers
provide fusimotor drive to muscle spindles
skeletofusimotor fibers
innervate both extrafusal and intrafusal fibers (sometimes called beta innervation)
muscle spindle function
sensory input for stretch reflexes
sensory input to cerebullum
output related to cerebral cortex for conscious proprioception
what is phasic stretch reflex eleicited by
primary ending of muscle spindle
what does group Ia fiber from muscle spindle synapse directly one
alpha motor neuron of its muscle
what does tonic stretch reflex depend on
primary and secondary endings
function of tonic stretch reflex
measure muscle tone
who would have exaggerated tonic stretch reflex
parkinsons
co-contraction
simultaneous activation of agonist and antagonists at a joint
when do we use co=contraction
first learning skilled movements
inappropriate coactivation conributes to motor control problems found in children with what
cerebral pasly
gain of stretch reflex
how large a response you get or a stretch of a certain amount
what is gain of stretch reflex depend on
level of acitivty in gamma motor neurons
background inhibition/excitation of alpha motor neurons
how is stretch reflex modified by
presynpathic inhibition of Ia afferent onto motor neurons
what is GTO innervated by
single group Ib fiber
GTO info goes to what
spinal cord
cerebellum
cerebral cortex
what can GTO reflex cause
disynaptic inhibitory reflex, causes inhibition of GTO’s muscle and exitation of its antagonist
what is the result of increase tenson on muscle
increases firing in Ib fiber
Ib fiber synpases on Ib inhibitory interneuron which inhibits alpha motoneuron of homonymous muscle
muscle is inhibited
what else does Ib inhibitory neurons releve input from
cutaneous receptor, joint receptor, muscle spindle, descending apthway
what do flexion flex afferents include
group II muscle spindle afferent
group III and group IV muscle afferents and skin afferents
what do renshaw cells produce
recurrent inhibitor in alpha motor neurons of agonist muscle
functions of renshaw cells
inhibit synergistic alpha motor neurons and gamma motor enurons to homonynmous and synergistic muscles
inhbit Ia inhibitory interneurons to agtagonist muscle
disinhibition
inhibiting a inhibitor
what are the 2 phases of maintained muscle stretch
dynamic phase and static or steady phase
static/steady phase
muscle has stabilized at new length
Ia fibers
big, fast myelinated
II fibers
less bi and fast compared to Ia
where are Ia fibers going
every intrafusal muscle fibers
what do II fibers carry
static information
what sets the sensitivity of the muscle spindle
gamma celsl
is Ia fiber firing during muscle contraction
no
how does co-contraction affect joint
stiffens
where are GTOs found
between muscle and tendon, in series with muscle
what else is Ib reflex known as
inverse myotactic reflex
glycine
most common inhibitory neurotransmitter in spinal cord
how are renshaw cells involved in spasticity
if spaciticy results from cutting descending tracts we are having disordered regulation of renshaw cells
