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