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Neuro- Reflexes
Reflexes, Upper Motor Neurons and Lower Motor Neurons
| Question | Answer |
|---|---|
| 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
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