Physiology-Spinal Reflexes Flashcards
What muscles are involved in the reflex arc?
Extrafusal muscle fibers (efferent only) and intrafusal fibers (contain muscle spindle, afferent and effernt fibers)
What muscle receptors are associated with the reflex arc?
Muscle spindle (senses length, velocity and gives location) and Golgi tendon (senses muscle force)
What are the different types of fibers located in the muscle spindle? What sensory neuron innervates these fibers and takes it toward the reflex arc?
Chain fibers and bag fibers. 1a fibers inncervate all bag and all chain fibers. Group II fibers innervate all chain fibers and only some bag fibers.
Which sensory fiber is the major player in the reflexes you test clinically?
Group Ia fibers
What motor fibers innervate the muscle spindle fibers involved in the reflex arc?
Gamma-motor neurons innervate the fibers in the muscle spindle
What is the purpose of gamma-motor neuron stimulation of the muscle spindle?
It hypersensitizes the muscle spindle to changes in velocity and length. These are used when signing your name or concentrating on a balance beam
How does the CNS receive sensory input when a muscle is passively stretched?
Stretching of the muscle spindle fibers stimulates the group Ia afferent neuron at increasing frequency proportional to velocity of stretch. Once stretch has stopped, there is a new steady rate proportional to the new muscle length.
How does the CNS receive sensory input when a muscle is actively stretched by an alpha and gamma motor neuron?
The CNS needs to calculate gamma-motor activity sent to the muscle fibers AND coordinate that with group Ia signals coming back to determine how much and how fast stretch is occurring in the muscle.
What are golgi tendon organs made up of?
Finely braided collagen fibers and a single Ib sensory fiber.
What stimuli triggers Ib sensory fiber signal transmission in golgi tendons?
Passive stretch (very slight response) or muscle contraction (very strong response). The golgi tendon primarily senses force.
What are the two components of the myotatic reflex?
Phasic (change in muscle length triggered by Ia stimulus, like the knee jerk reflex) and tonic (when muscle is under a constant load, group II fibers)
Label the different players of the myotatic reflex circuitry seen below:
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How does the myotatic reflex proceed when the muscle is stretched as seen in the image below?
Muscle stretch -> Ia afferent fiber -> alpha-motor neuron in homonymous, synergist and inhibitory interneuron in antagonist -> contraction of homonymous and synergist and relaxation of antagonist -> Muscle returns to standing position
How does the golgi tendon organ reflex proceed when someone is trying to hold a heavy piano up while situating the rug beneath it?
Golgi tendon organ fires faster -> Ib afferent neuron fires -> flexor inhibitory interneuron activated and extensor excitatory interneuron activated -> flexor alpha-motor neuron inhibited and extensor alpha-motor neuron excited -> flexor muscle tension decreased and extensor tension increased -> negative feedback to golgi tendon
What are the different working parts of the golgi tendon organ reflex seen below:
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What different inputs go into the Ib inhibitory neuron?
Cutaneous skin receptors, muscle spindles, joint receptors and excitatory/inhibitory descending pathways.
You want to touch your nose without crushing it. How does the body prevent you from crushing your nose once you find it?
CNS brings Ib inhibitory interneuron near threshold -> You touch your nose -> Cutaneous sensory neuron stimulated -> Ib inhibitory interneuron stimulated and fires -> alpha-motor neuron turned off and you don’t smash your nose
How does the body know you are crushing your nose when you decide to crush your own nose?
CNS hyperpolarizes Ib inhibitory interneuron away from threshold -> you touch your nose -> cutaneous signals fire to interneuron -> hyperpolarization prevents alpha-motor inhibition by interneuron -> nose gets crushed.
How does your body pull your finger away from a burning stove without even thinking about it?
Stimulation of cutaneous receptor -> A-delta group (III) stimulated -> polysynaptic reflex in spinal cord -> stimulation of excitatory and inhibitor interneurons -> stimulation of flexor or extensor and inhibition of extensor or flexor. At the same time, the signal travels to the other limb and does the same thing to support the reflex on the contralateral side.
