Motor Control (Intro) Flashcards
what controls posture and balance?
brainstem nuclei (by controlling and integrating spinal reflexes into higher order reflexes)
from what do brainstem nuclei receive input?
higher brain centres:
> cerebral cortex
> basal ganglia
> cerebellum
what four systems control muscle movement?
> descending control pathways
basal ganglia
cerebellum
local spinal cord and brainstem circuits
a lesion in which motor neuron would cause flaccid paralysis and muscle atrophy?
lower motor neurons
lesions in which motor neurons would cause spasticity and some paralysis, which may be transient?
upper motor neurons
what do lesions in posture regulating pathways cause?
spastic paralysis
what will corticospinal lesions cause?
weakness
where are proximal shoulder muscle mapped to?
medial motorneurones
where are finger muscles mapped to?
lateral motorneurones
how does the spinal cord receive descending input?
via neurons in the brainstem
how does the spinal cord receive direct cortical input?
via corticospinal/pyramidal tract
at what levels does sensory input enter the spinal cord?
at all levels
in the brainstem what does the vestibular system inform about?
balance
what is the effect of damaged sensory inputs?
paralysis similar to if the motor neurones themselves have been damaged
describe the stretch reflex
the muscle spindle is stretched and the action potential is fired synapsing in the spinal cord on an excitatory motor neuron which will innervate the same muscle.
at the same time the sensory neuron synapses on an interneuron which releases inhibitory neurotransmitter quieting any action potential of the alphamotor neuron supplying the antagonist muscle (flexor)
what spinal cord segment is tested in bicep reflex?
C6
what spinal cord segment is tested in tricep reflex?
c7
what spinal cord segment is tested in patellar tendon reflex?
L4
what spinal cord segment is tested in Achilles tendon reflex?
s1
is the flexor/withdrawal reflex monosynaptic and protective?
no it is polysynaptic and protective
describe the limb is withdrawn in the flexor/withdrawal reflex
increased activity in the flexor muscles of the affected part via a number of excitatory interneurons.
at the same time through excitatory and inhibitory interneurons the antagonistic extensors are inhibited.
what is the effect of the branching of the sensory neuron carrying pain in the flexor withdrawal reflex?
interneurons in several spinal segments are activated which in turn activate alpha motor neurones controlling all the flexor muscles of the affected limb
describe how the contralateral limb extends in the flexor withdrawal reflex
> excitatory interneurons cross the spinal cord and excite the contralateral extensors
via interneurons there is inhibition of the contralateral flexors
sensory information ascends the brain in the contralateral spinothalamic tract to help maintain upright posture
which is slower the stretch reflex or the flexor reflex?
the flexor reflex
how are reflexes overridden voluntarily?
descending voluntary excitation of alpha motorneurones can override the inhibition from the GTOs and maintain contraction
what is the effect on muscles of high gamma motorneurone activation of muscles spindles?
muscles become extremely resistant to stretch and are spastic
what does the activation of gamma motor neurons depend on?
descending pathways
what is facilitation?
increased effects due to an increased sensory input
how do pain fibres facilitate the action of muscle spindles?
by maintaining the aloha motor neurons in a more depolarised state.
what is babinski’s sign?
extension and not flexion of the toes when stimulating the lateral aspect of the sole due to damage or disruption of the CS tract
are reflexes seen in limbs after spinal shock?
yes after a period of time there is a gradual return of reflexes which are exaggerated. (clonus) though there limbs are still functionally useless.
