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Topic 3 & 4.docx

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York University
Kinesiology & Health Science
KINE 3020
Merv Mosher

Topic 3: Sensory – Motor. Systems 1: Control of Muscle/ Topic 4: Sensory – Motor. Systems 2: Proprioception 1. List the 3 main components of a muscle spindle?  (1) Specialized very small muscle fibers called intrafusal fibers, (2) sensory neuron endings (Group Ia and Group II afferents) that wrap around the central regions of these small intrafusal muscle fibers, (3) gamma motor neuron endings that activate the polar contractile regions of the intrafusal muscle fibers 2. Name two subtypes of intrafusal muscle fibres and differentiate between their ability to detect static and dynamic movement. Nuclear Bag (divided into both static and Nuclear Chain (static type) dynamic types) -fiber has many spherical nuclei in its -fiber has a single row of nuclei and being central noncontractile region (looking like less elastic stretches slowly an elastic bag of nuclei) which stretches quickly when lengthened because of its elasticity 3. Which afferent neurons are best able to respond quickly to stretching and sense the rate of change? Where can they be found?  The Ia fiber sensory endings wrap around the equatorial region (most elastic) of both the bag and chain intrafusal muscle fibers and thus respond quickly to stretching and sensing the rate of change (dynamic muscle length) of the muscle length. The afferent neuron endings can be found on cell bodies in the dorsal root ganglia of the spinal cord. 4. Which intrafusal muscle fibres do type II afferents mainly innervate and why are they less sensitive to dynamic change in muscle length when compared to type Ia afferents?  The group II endings wrap around the region next to the equator, which is less elastic and thus less responsive to stretching. Group II afferents go mainly to the chain fibers and are most responsive to steady-state or static muscle length 5. What is the main difference between alpha and gamma motor neuron function? Gamma motor neurons Alpha motor neurons (1) gamma dynamic: activate only -innervate extrafusal fibers (regular dynamic bag muscle fibers (enhance the skeletal muscle) dynamic responses of the Ia afferent neurons) (2) gamma static: innervate both static bag and chain muscle fibers (enhance the responses of the group II afferent neurons, signalling steady-state length of muscles) 6. The activation of __________ enhances dynamic response of Ia afferent neurons.  The activation of gamma dynamic motor neurons enhances the dynamic responses of the Ia afferent neurons 7. When John stretches his biceps muscle, what happens to his afferent neurons?  When a muscle is stretched, it stretches the muscle spindle, exciting the Ia afferent neurons. The spinal stretch reflex is activated by excitatory monosynaptic connections from the Ia afferent neurons to the alpha motor neurons, which activate their own muscle and synergistic muscles. The Ia afferents also excite Ia inhibitory interneurons, which then inhibit alpha motor neurons to the antagonist muscles 8. Where are Golgi tendon organs located and what are they sensitive to?  Golgi tendon organs are located at the muscle-tendon junction and are sensitive to tension changes that result from either stretch or contraction of the muscle 9. Which muscles have the highest concentration of spindles?  In humans the muscles with the highest spindle density (spindles per muscle) are extraocular, hand and neck muscles (this is because we use these muscles in head/eye coordination as we reach for obje
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