Motor Systems Flashcards
motor systems
-movement and posture
-involuntary reflex- spinal cord
-voluntary- higher brain center
recruitment
-generate a lot of force by innervating smaller motor units first (lower threshold) -> over time if stimulus is strong enough -> recruit more larger motoneurons -> greater tension
alpha motoneurons
-innervate skeletal muscle (extrafusal fibers)
gamma motoneurons
-innervate intrafusal muscle fibers (component of muscle spindles)
-spindles dont contract they sense muscle length -> Reflex
-intrafusal fibers are too small to generate significant force
-identify when a muscle is moving and how stretched it is
-keep body aligned
-2 types:
-nuclear chain fiber -> innervated by static gamma motoneuron- receptors are one after another like a chain
-nuclear bag fiber-> innervated by dynamic gamma motoneuron- receptors are grouped like a bag
intrafusal muscle fiber structure
-runs parallel to extrafusal skeletal muscle
-intrafusal muscles lengthen when the skeletal muscle lengthens
-shorten when skeletal muscles shorten
-gets sensed by group 1 afferent a nerve fibers - run in middle of the spindles -> sense velocity of muscle change
-group1a are the largest and fastest neurons
-group 2 efferent- only on the bottom of the nucleus chain fiber-> length of muscle fiber
stretch reflex aka 1 synapse reflex
-by sensing the length and stretch of muscles via the intrafusal muscle fibers -> it reinnervates alpha motoneurons to contract -> keeps muscle stable
-contract muscles being stretched
-1 synapse
-ex. - hit knee with hammer -> stretches fibers -> group 1a afferent senses this -> goes through spinal cord -> alpha motoneuron -> reciprocal contraction of quadricep muscle -> Stability
golgi tendon 2 fiber reflex
-clasp knife
-sense contraction and shortening of the muscle itself -> goes up spinal cord via group 1b afferent -> innervation to multiple synapse
-2 synapses
-1. inhibits contracting muscle -> lengthening muscle
-2. innervates antagonist muscles to contract
polymodal synapse: flexor withdrawal reflex
-touch a hot stove -> stimulate nociceptors -> spinal cord -> contraction of ipsilateral flexor muscles and inhibit extensor muscles -> also contraction of extensor muscles and relaxation of flexor muscles on contralateral side (maintain balance)
-multiple synapses
-groups 2, 3, 4 afferent fibers
-cross extension reflex- opposite side reflex
-afterdischarge- after removed arm away from painful stimuli still an action potential and contraction to make sure you avoid the stimuli
decerebrate rigidity
-lesions of brain stem above pontine reticular formation and lateral vestibular nucleus but below midbrain -> increase in extensor tone -> decerebrate rigidity
-extensor inhibition is above this and below are extensor activators -> if you have a lesion here -> excessive extension
-lesions above midbrain do not cause decerebrate rigidity
-localizes lesions
cerebellum
-coordination
-controls, rate, range, force, and direction of movement
-lesions here -> ataxia -> uncoordinated
-3 divisions:
-vestibulcerebellum (input from vestibular system)
-spinocerebellum (input from spinal cord)- reflex
-pontocerebellum (input from pontine nuclei) -> preplanned coordinated voluntary movement
3 layers of cerebellum
-base
-granular layer- cell bodies and glomerulus (meeting points for cells)
-purkinje cell layer- purkinje cells
-molecular layer- dendrites, axons, cells, parallel fibers
-top outer surface
-molecular layer has parallel (horizontal) transmission of information
input and output in cerebellum
-2 inputs-
-1. climbing fiber innervates onto ONLY purkinje cell -> action potentials through complex spikes
-2. mossy fiber- signals through simple spikes into the glomerulus and from there other cells
-output- ONLY output is purkinje cell -> inhibitory -> prevents overreaction to a movement (smoothes)
-purkinje only has gamma neurotranmitters
-input through mossy fibers -> spread -> purkinje fiber picks up -> output -> climbing cell modules the output
basal ganglia
-deep nuclei of telencephalon: caudate nucleus, putamen, globus pallidus, and amygdala
-regulate movement coming from cortex
-signals from cortex have to go through basal nuclei first before leaving to thalamus
-modulate and smooth movements
-2 pathways:
-direct- excitatory -> stimulate motor movement
-indirect-inhibitory- cortex -> striatum -> globus pallidus -> subthalamic nuclei -> globus pallidus -> substantia nigra -> thalamus
parkinsons disease
-loss of substantia nigra -> reduces inhibition of indirect and excitation of direct
-loss of indirect and indirect pathway
-reduction in modulation of movements
-tremors
-slow
-treatment- replacement of dopamine by treatment with I -dopa or administration of dopamine agonists (bromocriptine)
huntingtons disease
-loss of striatal and cortical cholinergic neurons and inhibitory GABAergic neurons
-losing ability to make movements from the cortex
-neurologic symptoms- choreic (writhing) movements and dementia
-no cure
