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Neuro- Reflexes

Reflexes, Upper Motor Neurons and Lower Motor Neurons

Alpha Motor Neuron Convey all commands for movements (reflexive and voluntary); considered the "final common pathway" for movement
Location of Alpha Motor Neuron cell body Ventral Horn of Spinal Cord
Motor neuron pool All motor neurons invervated a single muscle
Topigraphical Relationship of motor pools in the spinal cord Proximal motor pools are located most medial, distal motor pools are located most laterally
Motor Unit Muscle fibers innervated by a single alpha motor neuron
Motor Unit Size Variation Motor unit size is dependent upon the size of the muscle
Henneman Size Principle Smaller motor units are recrited preferentially to large motor units, the first excited are the last to relax
Functional impact of Henneman Size Prinicple Provides for production of a graded force
Reflex Stereotyped repsonse to a specific sensory stimulus
Purpose of stretch reflex Resist muscle lengthening and tearing
Muscle spindle afferent nerve Large diameter, Ia afferent
Monosynaptic reflex Allows direct excitation fo the homonymous muscle
Polysnyaptic reflex Inhibits antagonict (heteronymous) muscle via interneurons in the spinal cord
Reciprial innervation Connection of excitatory relex of one muscle to the inhibitory reflex of its antagonist
Open loop system For both the GTO and the muscle spindles, there is more than just the afferent information action on the motor neuron, there is input from upper neural centers as well
Upper motor neuron function plan, initiate and direct voluntary movements and coordianation of skilled movements
Places upper motor neurons project from Primary motor cortex, lateral premotor cortex, medial premotor cortex
Upper Motor neurons procject to Alpha motor neurons, interneurons, and presynapic terminals of afferent fibers
3 Functions of Upper Motor Neurons located in the brain stem 1. Regulate musle tone 2. Orient eyes, head, and body with respect to the vestibular, somatic, auditory and visual sensory input 3. Contribute to control of posture
Upper Motor Neuron use of reflexes Reflexes may be used by the CNS to simpify desceding commands
Spastsicity Velocity-dependent reaction to stretch
Hyperreflexia Hyperactive stretch reflex
Results of Upper Motor Neuron Injury Decreased inhibition of reflexes by higher CNS centers = spasticity
Muscle tone steady level of muscle tension
2 things that contribute to Muscle tone stretch reflex (gamma neurons) and uppor motor neurons in brainstem
Purpose of muscle spindles detect musle stretch
Purpose of gamma-motor neurons Set muscle spindle to appropriate length
Purpose of alpha-gamma coactivation Allows muscle spindles to signal length changes throughout the full ROM
Gamma gain level of gamma activity
When gain is high: a small stimulus can cause a large contraction force- good for precise movments
When gain is low: a large stimulus is needed to cause contraction force - good support on an unsteady surface (riding a bus standing up)
Golgi tendon organ location muscle-tendon junction
GTO innervation a single Ib afferent nerve
GTO arrangement with extrafusal muscle fibers In series
GTOs ungergo _________ during muscle contraction compression
GTOs are relatively __________ to passive stretch insensitive
GTO's Ib axons synapse with inhbitory interneurons
The Ib inhibitory interneurons of the GTO system synapse with alpha motor neurongs of the homonymous muslce
When excessive force is detected the GTO will _____________ muscle activity decrease
Both GTOs and muscle spindles are ________, ______________ feedback loops open, negative
Monitor and maintain muscle length Musle spindles
Monitor and maintain muscle force Golgi tendon organ
Withdrawl of a limb from a painful stimuls causes excitation of the ipsilateral ________ flexor
Crossed-extenson flexor withdrawl reflex A polysnaptic reflext to remove a limb from a painful stimulus
Withdrawl of a limb from a painful stimuls causes inhibition the ipsilateral ________ extensor
Withdrawl of a limb from a painful stimuls causes excitation of the contralateral ________ extensor
Withdrawl of a limb from a painful stimuls causes excitation of the contralateral ________ flexor
Central pattern generator neural network of interneurons capable of generating a rythmic pattern of motor activity in the absense of sensory input from peripheral receptors
2 phases of single limb movement stance and swing
Central Pattern generators are more ____________ in humans or have less ____________ complex, control
Results of Upper Motor Neuron Injury loss of voluntary movements, increased reflexes, spasticity, increased musle tone, and positve babinski sign
Positive Babinski sign toes extend instead of curl upon plantar surface stimulus
Results of a lower motor neuron injury paralysis or paresis, areflexia, loss of muscle tone, musle atrophy, muscle fibrillations/fasiculations
Created by: aglade