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28 Cards in this Set
- Front
- Back
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Upper or lower motor neurons all body movements generated by stimulation of skeletal muscle fibres |
lower motor neurons |
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Upper or lower motor neurons complex movements |
coordination of LMN activity by UMN originating in the cerebral cortex & brainstem |
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What regulates upper motor neurons? |
cerebellum basal ganglia |
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Motor programs in the spinal cord occur without input from ?? and are modified by ?? |
occur without input from brain modified by descending commands from brain |
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What is the smallest component of the motor system? |
motor unit |
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What does the motor unit consist of? |
lower motor neurones muscle fibres it innervates |
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What do alpha motor neurons innervate? |
striated extrafusal muscle fibres that generate forces required for movement and postural balance |
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What are the different types of motor units? |
slow motor units fast motor units--fatigue resistant and fast fatigable |
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what do the slow motor units consist of and what do they do? |
most numerous red fibers a lot of mitochondria slow to contract sustain contraction without fatigue postural control |
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What do the fast motor units consist of and what do they do? |
pale fibers fewer mitochondria contract rapidly and powerfully fatigue more quickly arm muscles, jumping/sprinting muscles |
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What are fatigue resistant fast motor units? |
moderately strong fast contraction relatively resistant to fatique |
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What are fast fatiguable fast motor units? |
strongest, fastest contractons fatigue rapidly |
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How many different types of fibres can a muscle have? a motor unit? |
muscle--al three motor unit--one |
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What are muscle spindles? |
parallel muscle fibers specialised sensory receptors--stretch receptors sense changes in muscle length |
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What is the pathway of muscle spindles? |
Ia sensory axons wrap around fibres in the spindle --> enter dorsal horn and form excitatory synapses on interneurons and alpha motor neurons in ventral horns |
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What are intrafusal fibres? |
skeletal muscle fibres inside the muscle spindle |
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What innervation do intrafusal muscle spindle fibers recieve? |
lower motor neurone--gamma motor neurons |
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What is the golgi tendon organs? |
proprioceptors monitor muscle tension |
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Where are the golgi tendon organs located and what are they innervated by? |
located at junction of muscle and tendon innervated by Ib sensory neurons |
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How are golgi tendon organ fibres arranged? |
in series with muscle fibres to sense muscle tension |
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What is the pathway from the golgi tendon organs in muscle tension regulation? |
Ib axons synpase on inhibitory interneurons in spinal cord synapse onto alpha motor neurons of the same muscle to prevent further increases in tension |
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What do interneurons receive synaptic input from? |
primary sensory axons descending axons from brain collaterals of lower motor neurone axons |
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What do inhibitory interneurons do and why are they important? |
limit activity of other neurons important for reciprocal inhibition--when a muscle is contracted, the antagonist muscle must relax |
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What do excitatory interneurons do and why are they important? |
excite other neurones important for excitation of all flexor muscles of affected limb in flexor reflex |
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Reciprocal inhibition during stretch reflex Describe what happens when stretching of the biceps activates muscle spindles. |
monosynaptic Ia sensory axons excite alpha motor neurons acivating the muscle and synergistic flexors polysynaptic Ia sensory axons stimulate inhibitory interneurons to inhibit alpha motor neurons supplying the antagonistic extensor muscle |
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What is the flexor withdrawal reflex? |
polysnaptic reflex to withdraw limb from aversive stimulus |
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What is the pathway of the flexor withdrawal reflex? |
activated by small, myelinated Aδ nociceptive fibres (pain) sensory axons branch in spinal cord activating interneurons in several spinal segments excitatory interneurons excite alpha motor neurons that control flexor muscle of affected limb inhibitory interneurons recruited to inhibit alpha motor neurons controlling the opposing extensor muscles |
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What is the cross extensor reflex? |
when flexor reflex is activated there is activation of extensor muscles and inhibitor of flexor muscles on the opposite side stops us from falling compensates for extra load caused by limb withdrawal on the antigravity extensor muscles of opposite leg |
