BCMB 415 Final
how does the neural circuitry mediate the stretch reflex? 3 steps
1. group 1a afferents enter spinal cord 2. afferent axons branch 3. excitatory connections are made with either motor neurons or interneurons
how many nuclear bag fibers are in each muscle spindle?
2//one of each type
Which of the following is the most sensitive to an increase in muscle length? A. Group 1a afferents B. Group II afferents C. Group 1b afferents
A. Group 1a afferents
Which of the following mechanoreceptors ONLY provides information concerning dynamic changes in mechanical stimuli? A. Pacinian corpuscle B. Merkel disk C. Ruffini ending
A. Pacinian corpuscle
passively stretching a muscle also causes the __________ muscles to relax A. antagonistic B. synergistic C. homonymous
A. antagonistic
shortening/contracting of the muscle ________ the output of spindles and ________ the output of tendon organs. A. decreases; increases B. increases; decreases C. slows; fastens D. fastens; slows
A. decreases; increases
the myotatic reflex and the reverse myotatic reflex differ in that: A. excitation of motor neurons occur in the myotatic reflex B. inhibition of motor neurons occur in the myotatic reflex C. inhibitory interneurons are associated with the reverse myotatic reflex
A. excitation of motor neurons occur in the myotatic reflex
during production of the stretch reflex by the neural circuitry, muscle contraction is produced by group 1a afferents __________ motor neurons that innervate _________ muscles A. exciting; homonymous and synergistic B. inhibiting; homonymous and synergistic C. exciting; antagonistic
A. exciting; homonymous and synergistic
what type of muscles are associated with the reverse myotatic reflex? A. homonymous muscles B. synergistic muscles C. antagonistic muscles
A. homonymous muscles
what happens to the group 1b afferent fiber of the Golgi Tendon Organ when it enters the capsule? A. loses myelination and branches into many fine endings B. increases myelination and converges into one thick ending C. increases myelination and branches into many fine endings
A. loses myelination and branches into many fine endings
how does group 1a afferents enter the spinal cord during a stretch reflex? A. through the dorsal root B. through the dorsal horn C. through the ventral root
A. through the dorsal root
Which of the following areas of the primary somatosensory cortex receives input from muscle stretch receptors? A. 1 B. 3A C. 3B
B. 3B
Which of the following fiber types mediates the perception of prolonged pain? A. alpha-delta fibers B. c fibers C. alpha-beta fibers
B. c fibers
which afferent nerve fibers are associated with the reverse myotatic reflex? A. group 1a B. group 1b C. group II
B. group 1b
which of the following is not a component of muscle spindles? A. intafusal fibers B. group 1b axons C. gamma motor axons
B. group 1b axons
where does group 1a afferents branch in the spinal cord? A. in the dorsal root B. in the dorsal horn C. in the ventral root
B. in the dorsal horn
stretching/lengthening of the muscle __________ the output of spindles and __________ the output of tendon organs A. decreases; increases B. increases; decreases C. slows; fastens D. fastens; slows
B. increases; decreases
which of the following afferent nerve fiber innervates the Golgi Tendon Organ? A. single, myelinated group 1a afferent B. single, myelinated group 1b afferent C. single, myelinated group II afferent
B. single, myelinated group 1b afferent
the combined output of muscle spindles and tendon organs represents: A. relative position of limb segments B. muscle tension from motor acts C. Both A and B
C. Both A and B
(T/F) Cannibanoids modulate pain by influencing directly the output of which of the following cell types? A. Glutamatergic neurons in the spina cord B. Serotonergic neurons in the Raphe C. GABAergic neurons in the PAG
C. GABAergic neurons in the PAG
Which of the following fiber types, when activated, modulates the perception of pain at the level of the spinal cord? A. alpha-delta fibers B. c fibers C. alpha-beta fibers
C. alpha-beta fibers
which of the following is not an effect of the contraction of polar regions of intrafusal fibers? A. increased tension on the sensory endings B. non-contractile central regions are stretched C. decreased muscle spindle sensitivity
C. decreased muscle spindle sensitivity
the myotatic reflex and the reverse myotatic reflex differ in that: A. homonymous muscles are relaxed in the myotatic reflex whereas antagonistic muscles are relaxed in the reverse myotatic reflex B. a major component of the myotatic reflex are group 1b afferents whereas a major component of the reverse myotatic reflex are group 1a afferents C. during mediation, group 1b afferents enter the spinal cord via the dorsal horn whereas the group 1a afferents enter via the dorsal root
C. during mediation, group 1b afferents enter the spinal cord via the dorsal horn whereas the group 1a afferents enter via the dorsal root
during production of the stretch reflex by the neural circuitry, muscle relaxation is caused by ___________ of motor neurons that innervate _________ muscles. A. excitation; antagonistic B. inhibition; homonymous and synergistic C. inhibition; antagonistic
C. inhibition; antagonistic
which of the following is not a result of stretching the golgi tendon organ? A. afferent ending produces action potential B. collagen fibers are straightened C. nerve endings are expanded
C. nerve endings are expanded
which of the following is not an occurrence during fusimotor activation? A. muscle spindle sensitivity is increased B. tension is increased on sensory endings C. polar regions of extrafusal fibers are contracted
C. polar regions of extrafusal fibers are contracted
the effect of excitation of inhibitory interneurons differ from the excitation of motor neurons differ in that the first results in: A. contraction of antagonistic muscles B. contraction of homonymous + synergistic muscles C. relaxation of antagonistic muscles
C. relaxation of antagonistic muscles
who coined the term "myotatic reflex"?
Charles Sherrington
(T/F) The primary goal of the golgi tendon organs is to signal ongoing levels of muscle tension.
False
(T/F) Mechanoreceptors having the largest spatial receptive fields also exhibit the highest spatial resolution.
False.
encapsulated structures about 500 micrometers in length describe what proprioceptor?
Golgi Tendon Organ
(T/F) A somatotopic map exists in EACH of the four subdivisions of the primary somatosensory cortex.
True
(T/F) Noxious stimuli activate transient receptor potential channels.
True
(T/F) Per stretch reflex: excitation of the homonymous muscle involves a monosynaptic pathway while inhibition of the antagonist is disynaptic
True
(T/F) Release of prostaglandin E2 from damaged cells leads to phosphorylation of TRP channels resulting in hyperalgesia.
True
(T/F) Spacial discrimination is enhanced by lateral inhibition.
True
(T/F) The primary function of the fusimotor system is maintaining the sensitivity of muscle spindles at different muscle lengths.
True
define the somatosensory system
a diverse sensory system comprising the receptors and processing centers that produce sensory modalities
what helps maintain sensitivity of the muscle spindle with the muscle is at different lengths?
activation of gamma motor neurons (fusimotor system)
what effect from stretching the tendon organ causes the afferent ending to produce action potentials?
activation of stretch-activated ion channels
what mediates the reverse myotatic reflex?
activity of Golgi tendon organs
proprioception
awareness/perception of body position
characteristics of a phasic muscle contraction
brisk short-lasting
list the two major muscle contraction components of the stretch reflex
brisk, short-lasting phasic weak, long-lasting tonic
fascicles
bundle of structure
describe the structure of the Golgi Tendon Organ
collagen bundles within the capsule form a braided structure
muscle spindles and tendon organs provide what type of information about the mechanical state of a muscle?
complementary
how does shortening/contracting of muscle fibers affect the output of muscle spindles?
decreases
how does stretching/lengthening of muscle fibers affect the output of tendon organs?
decreases
what triggers a phasic muscle contraction?
dynamic change in muscle length
as group 1b afferent branches into many fine endings upon entering the capsule, how does it interact with the collagen?
each is intertwined among the braided collagen fascicles
what are the two outcomes after group 1a afferents are discharged during production of the stretch reflex?
excitation of motor neurons that innervate homonymous + synergistic muscles inhibition of motor neurons that innervate antagonistic muscles
gamma motor neurons constitute the _________ rather than the skeletomotor system
fusimotor
which group of afferent nerve fibers forms the primary sensory ending?
group 1a
which group of afferent nerve fibers terminate on all three types of intrafusal fiber?
group 1a
which afferent nerve fibers are associated with neural circuitry mediation/production of the stretch reflex?
group 1a afferents
which group of afferent nerve fibers innervate muscle spindles?
group 1a and group II
how does is the reverse myotatic reflex mediated? 4 steps
group 1b fibers synapse on inhibitory interneurons inhibitory interneurons synapse with motor neurons that innervate homonymous muscles motor neuron output is indirectly suppressed homonymous muscles are relaxed
which group of afferent nerve fibers forms the secondary sensory ending?
group II
which group of afferent nerve fibers terminate only on chain & static bag fibers?
group II
where do afferent axons branch in the process of mediating the stretch reflex?
in the dorsal horn of the spinal cord
how does shortening/contracting of muscle fibers affect the output of tendon organs?
increases
how does stretching/lengthening of muscle fibers affect the output of muscle spindles?
increases
during mediation of the reverse myotatic reflex, group 1b fibers synapse with ___________ which synapse with ___________ that innervate the homonymous muscles. A. alpha motorneurons; gamma motorneurons B. inhibitory interneurons; motor neurons C. motor neurons; inhibitory interneurons
inhibitory interneurons; motor neurons
list the three major components of muscle spindles
intrafusal fibers group Ia and II axons gamma motor axons
how does activation of gamma motor neurons affect intrafusal fibers?
it causes the polar regions to contract
what is the role of gamma motor neurons activity in muscle spindles?
it regulates the sensitivity of the muscle spindle
where is the Golgi Tendon Organ located?
junction of muscle and tendon
what kind of information do proprioceptors provide?
location of body parts in space
what are the primary functions of the reverse myotatic reflex?
mediate fine control of movement protect muscles from over-contraction
"myotatic", "stretch", or "resistance" reflex ALL refer to which type of phenomenon?
muscle contraction in response to passive stretching
elongated muscle spindles within fleshy portions of the muscle describe which proprioceptors?
muscle spindles
gamma motor neurons are an important component of which proprioceptor?
muscle spindles
intrafusal fibers are associated with what proprioceptor?
muscle spindles
name the two mechanosensitive proprioceptors
muscle spindles Golgi Tendon Organs
what is a synergistic muscle?
muscles that control the same joint & have a similar mechanical action
what is an antagonistic muscle?
muscles that opposes the action of another
what happens after activation of gamma motor neurons causes the polar regions of intrafusal fibers to contract?
non-contractile central regions are stretched tension is increased on sensory endings muscle spindle sensitivity is increased
list the two types of intrafusal fibers
nuclear bag nuclear chain
which type of intrafusal fiber is categorized in two types?
nuclear bag fibers: dynamic static
in which direction does muscle spindles run in relation to muscle fibers?
parallel
how does the neural circuitry produce the stretch reflex?
passive limb extension lengthens the flexor muscles -> increase in discharge rate of group 1a fibers group 1a afferents discharge, resulting in: excitation of motor neurons innervating homonymous + synergistic muscles -> contraction inhibition of motor neurons innervating the antagonistic muscles -> relaxation
how did Charles Sherrington discover the stretch reflex when working with decerebrate cats?
passively flexed, rigidly extended hind limb muscles showed increased contraction
what type of muscle contraction is triggered by the dynamic change in muscle length?
phasic
where do gamma motor neurons terminate?
polar/contractile ends of intrafusal fibers
fusimotor activation modulates spindle sensitivity by causing the _________ regions of intrafusal fibers to __________
polar; contract
stretch reflexes contribute to
postural adjustments
how do primary endings compare to secondary endings?
primary endings are much more sensitive to rate of change of muscle length
which characteristic of muscle lengthening are primary sensory endings most sensitive to?
rate of change of the muscle length
what reflex complements the myotatic reflex?
reverse myotatic reflex
what type of reflex results in the relaxation of homonymous muscles?
reverse myotatic reflex
nociception
sensory N.S response to pain
how many nuclear chain fibers are in each muscle spindle?
several (typically 5)
where do alpha motor neurons terminate?
skeletal muscle fibers (extrafusal)
where are mechanosensitive proprioceptors located?
skeletal muscles
what triggers a tonic muscle contraction?
static stretching of muscle at a new longer length
how does stretching of the tendon organ affect collagen fibers and nerve endings?
straightens the fibers compresses + elongates endings
what ultimately results in the relaxation of homonymous muscles in the reverse myotactic reflex?
suppression of motor neuron output
the firing rate of tendon organs are very sensitive to changes in what?
tension generated by muscle contraction
during production of the stretch reflex by the neural circuitry, what is increased as a result of the flexor muscles lengthening in response to a passive extension of the limb?
the discharge rate of group 1a fibers
during mediation of the reverse myotatic reflex, where do group 1b fibers enter?
the dorsal horn of the spinal cord
tension applied to afferent endings by lengthening/stretch of the muscle triggers what?
the opening of stretch-activated ion channels
define innervate
to supple an organ with nerves
what type of muscle contraction is triggered by the static stretching of the muscle at a new longer length?
tonic
________ contraction of the muscle is triggered by a static muscle stretching while __________ contraction of the muscle is triggered by a dynamic change
tonic; phasic
(T/F) Muscle spindle organs, but not golgi tendon organs are arranged in parallel with skeletal muscle fibers
true
during production of the stretch reflex by the neural circuitry, how do group 1a afferents inhibit motor neurons?
via excitation of inhibitory interneuron
characteristics of a tonic muscle contraction
weak long-lasting
list the three ways that afferent axons can make excitatory connections
with motor neurons that innervate homonymous muscles with motor neurons that innervate synergistic muscles with inhibitory interneurons that innervate antagonistic muscles