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
motor cortex
-3 areas- primary motor cortex, supplementary motor cortex, and premotor cortex
-voluntary movement
-first organized in associative areas of cerebral cortex
-transmitted to supplementary and premotor cortices for develop of motor plan -> you are going to contract this and relax that
-planned
-plan is transmitted to upper motoneurons in primary motor cortex -> Sent down to lower motoneurons in the spinal cord -> execute plan
-primary motor cortex is topographically organized and is described as motor homunculus -> know exactly where we are sending signals
-supplementary and premotor cortices (area 6)- plan
-primary motor cortex (area 4)- execution
electroencephalogram
-record electrical activity in brain -> on cerebral cortex
-sleep study
-awake- eyes closed -> alpha waves
-beta waves- eyes open
-stage 1- on and off alpha waves and theta
-stage 2- high frequency bursts (sleep spindle) and slow potential (K complexes)
-stage 3- very low frequency delta waves and occasional sleep spindles
-stage 4- large delta waves
-REM sleep (paradoxyl)- desynchronized beta, low and high frequency, resembles awake, every 90 minutes, deep sleep
jacksonian seizures
-epileptic events originating in primary motor cortex
-begins in fingers of one hand and progresses to hand and arms
-eventually spreads over entire body
-jacksonian march
cerebellum dysfunction
-ataxia
-delayed onset of movement or poor execution
-overshooting or undershooting targets
-dysdiadochokinesia- unable to perform rapid alternating movements
-intention tremors- occur perpendicular to direction of a voluntary movement, increasing near the end of movement
-rebound phenomenon- inability to stop movement- ex. unable to stop flexion when resistance is removed
REM sleep
-loss of temperature regulation
-pupillary constriction
-penile erection
-fluctuations in HR, BP, respiration
-dreams
-slow wave sleep varies over life
learning
-neural mechanism by which a person changes their behavior as a result of their experiences
-non-associative-habituation, repeated stimulus -> response that gradually diminishes as it is learned to be unimportant OR sensitization- greater probability of response when it is learned to be important
-associative- consistent relationship in timing of stimuli - classic -> Repetition
-operant condition- response to stimulus is reinforced (+ or -) -> causing response to change
memories
synaptic plasticity
–potentiation- repeated activation of neuronal pathway leads to increased responsiveness of postsynaptic neurons in the pathway
-can be long term or short
-use it or lose it
-synaptic strength
-in habituation -> increased synaptic activity causes decreased responsiveness of postsynaptic neuron
CSF
-fluid that surrounds brain
-contained in ventricles within brain
-nourish brain
-being produced by choroid plexus and reabsorbed at a constant rate
-flows into ventricles and subarachnoid spaces -> surrounds brain and spinal cord
-fluid is transferred from CSF to venous blood by one way bulk flow and returned to systemic circulation
-sample via LP - inflammatory cells
-administer anesthesia by blocking nerves
-Na, Cl<, HCO3, osmolarity- same as blood
-K, Ca, glucose, amino acids, pH, cholesterol, protein- less than blood
-Mg and creatinine- more than blood
-these concentrations are due to barriers being permeable to specific substances
-no large molecules in CSF so it can flow freely (pr0tein, cholesterol)
choroid plexus
-choroid plexus- barrier between arterial blood and CSF
-BBB- barrier between arteries and interstitial fluid and brain cells
-CSF, interstitial fluid, and brain cells drain into cerebral venous blood
-only allow lipid substances to get through -> very selective
-
blood brain barrier
-barrier between arteries and interstitial fluid and brain cells
-3 layer system
-capillary endothelial cells and basement membrane, neuroglial membrane, and glial end feet
-junctions between endothelial cells in brain are so tight that few substances can cross
-only few substances can pass-> lipid soluble (O2, CO2)
-water soluble is excluded
-keeps bacteria and drugs out
-inflammation, chemo, antibiotics, radiolabeled markers, cancer -> breaking BBB -> more permeable -> increase affects from drugs
-lipids= non ionized
