0519 - Spinal reflex and muscle control - BX

Question 1

Classify the types of neurons that are responsible for muscle control?

Answer 1

-Upper: commanding neurons from cortex, commands lower motor neurons-lower: lower motor neurons control somatic muscles, from ventral horn -alpha motor neurons: innervates striated muscles -gamma motor neurons:innervation to contractile fibers in muscle spindle -contracts muscle spindle to remove slack

Question 2

Name the types of proprioceptive inputs to the spinal cord (hint: type of information and their carriers)

Answer 2

-proprioceptors: spindles, golgi tendon organs, mechanoreceptors -spindles: feedback of strength/stretch from muscle -golgi tendon: load/force on tendons, joint positions -mechanoreceptors: on joint capsules and ligaments, gives angle, velocity, and movement (dynamic input)-increased rate of fire = increased stretch, force and dynamic info

Question 3

name the 4 groups of neurons and identify what they innervate.

Answer 3

-4 Groups: I II III IV-group I: Ia and Ib, innervates muscle spindles (fast, myelinated, large) -Ia: all muscle spindles, detects rate of and degree of stretch (dynamic) -Ib: golgi tendon organs, detects muscle strain, decreases force-group II: mechanoreceptors from skin (myelinated, medium size + speed) -innervates bag2 + chain spindles, extra degree of stretch info (static)-group III: pain receptors, (small, myelinated, lowest of myelinated)-group IV: pain, temperature, itch (small, unmyelinated, persistent, slow)

Question 4

What are gamma motor neurons and their functions? what are the two different types responsible for?

Answer 4

-innervation to contractile fibers in muscle spindle-contracts muscle spindle to remove slack-allows detection at optimal range during muscle contraction-activated in parallel with alpha motor neurons-two types: gamma static, gamma dynamic -gamma static: increased sensitivity to I and II fibers -on Bag2 and chains (more static info than dynamic) -gamma dynamic: group Ia, on Bag1 fibers

Question 5

What is the organization of intrafusal fibers (name the types and their functions)

Answer 5

-two types: chain and bag fibers-all bag fibers are innervated by group Ia fibers -responds to degree and rate of stretch (dynamic information) -Bag2 and chain fibers innervated by group II fibres -responds to degree of stretch only (static/positional) -group II will not respond to fast stretch such as taps-Intrafusal fibers have gamma motor neuron innervation -keeps spindle working at optimal range -must contract at the same rate as extrafusal fibers (parallel) -maintains sensitivity-Bag1 fibers increase sensitivity to group Ia fibers -gamma dynamic fibre innervation-bag2 and chain increase sensitivity to group Ia and II fibres -gamma static fibre innervation

Question 6

What is the gamma loop? Describe its function.

Answer 6

-loop between muscle spindle afferents, gamma motor neurons, and alpha motor neurons -regulates tension during normal activity -causes involuntary contraction of muscle-during muscle contraction by alpha motor neurons, muscle spindles slack -causes gamma motor neurons to innervate spindles -brain perceives this as stretch -stimulates alpha motor neurons to contract

Question 7

Name the 4 types of reflexes, their organization, and their function.

Answer 7

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Question 8

What are central pattern generators?

Answer 8

structured motor programs that generated patterned movement -can produce rhythmic movement despite constant input from upper motor neurons -NMDA channels play a role -through calcium influx and potassium channel hyperpolarization of cells-done by pre-programed interneuron wiring-these inter-neurons can have pace-maker abilities or produce rhythmic movements by the nature of their circuitry-interneurons process several types of inputs: primary sensory, descending axons from brain and spinal cord, other interneurons, lower motor neurons