Muscle spindles and stretch reflexes Flashcards
(19 cards)
What do muscle spindles detect primarily?
muscle stretch
What do golgi tendon organs detect primarily?
muscle contraction
Where do we find muscle spindles
all locomotor muscles and most motor cranial nerve muscles
higher density in muscles with finer movements
only associated with fatigue-resistant red fibers (slow acting fibers)
What is the morphology of the muscle spindle? How do they relate to extrafusal fibers?
cluid filled ct capsule. long and linked to both ends of the muscle. made of intrafusal contractile fibers (bulk of muscle = extrafusal fibers). parallel to muscle.
all have equatorial region with cell nuclei and polar regions with contractile elements.
What are the 2 classes of intrafusal fibers and how are morphologically different?
nuclear chain: smaller with single row of cell nuclei in equatorial region
nuclear bag cells with many cell nuclei in a bag (bag 1 and bag 2)
What is the afferent innervation to nuclear chain cells?
primary afferents (Ia) wrapped around the equatorial regionand secondary afferents, which send collateral branches to nuclear chain as flower sprays
What is the afferent innervation to nuclear bag cells?
primary afferents.(Ia) wraped around the equatorial region
What is the difference between primary and secondary afferents
primary afferents are large and mylinated. they go to both nuclear chain and nuclear bag fibers
secondary afferents are smaller but still myelinated. they go to nuclear chain cells –> flower sprays
Where do primary and secondary afferents of the muscle spindle give collaterals? What about for the Golgi tendon organ?
- cerebellum for unconscious proprioception
- spinal cord for spinal reflex circuits
- dorsal columns to medial lemniscus for conscious proprioception
What is the efferent innervation to the muscle spindle?
gamma motor neurons from ventral horn.
Gamma 1 to plate endings on the polar ends of nuclear bag fibers
gamma 2 to trail endings to the polar ends of nuclear chain fibers
What is the main difference in function btw nuclear bag and nuclear chain fibers?
nuclear bag and IA afferents detect dynamic changes in the rate and velocity of muscle lengthening
nuclear chain fibers and II afferents detect static conditions and moniter muscle length
What is the purpose of gamma neuron innervation to the muscle spindle fibers?
the keep them taut over the range of muscle fiber lengths- important since signals transduce muscle stretch
What is the purpose of Ia stimulation? What happens if you loose inhibition to the muscle spindle system?
purpose is muscle tone
if you loose inhibition, you see spacticity
What does the Golgi tendon organ detect?
contraction: pulls on tendon. as more muscles are recruited, more golgi organs respond. tells about the force of contraction
What is the morphology of the Golgi tendon organ
Large myelinated sensory axon Ib fibers that terminate with fine nerve endings intertwined among bundles of collagen fibers. run IN SERIES with the extrafusal fibers.
How does the stretch reflex work?
monosynaptic connection between Ia afferents of the golgi spindle and alpha motor neurons
On what cells to Ia afferents terminate in the spinal cord?
alpha motor neurons of the homonymous cells (motor neurons for the muscles that they came from), alpha motor neurons for synergist muscles (muscles that have the same function as the homonomous cells), and on inhibitory interneurons to the antagonist muscles. this means that they can contract homonymous muscles and relax opposing muscles.
What is the function of the stretch reflex? What helps monitor it?
negative feedback to maintain muscle length CNS helps modulate the “gain” of this stretch response.
What happens in spinal shock?
temporary hypoactive reflexes for things below the level of a spinal or CNS lesion. then, you see brisk reflexes, and possibly spasticity from upper motor neuron problems
