Muscle Spindles and GTOs

Question 1

muscles spindles

• what are they
• location

Answer 1

specialized muscle fibers containing contractile elements
encased in a connective tissue sheath that is anchored to the endomysium and perimysium that surrounds the fascicles of the muscle

Question 2

intrafusal vs extrafusal muscle fibers

Answer 2

intrafusal
-contractile fibers within muscle spindle
extrafusal
-other muscle fibers

Question 3

where are the contractile elements located in muscle spindle fibers

Answer 3

at the poles or ends of each fiber

Question 4

what is the nuclei composition of a muscle spindle

Answer 4

multinucleated with all nuclei being located centrally (equatorially)

Question 5

nulcear arrangements of a muscle spindle

Answer 5

nuclear bag
-nuclei are clumped in the middle forming a “bag-like” enlargement of the sarcolemma
nuclear chain
-nuclei arranged linearly in a “chain-like” arrangement

Question 6

muscle spindle primary and secondary endings

Answer 6

all fibers have at least two sensory receptors located either centrally around the nuclear groups or peripherally near the contractile elements
primary
-centrally located
secondary
-peripherally located

Question 7

what causes the stimulus the muscle spindle receives

Answer 7

mechanical deformation of the afferent ending

Question 8

dynamic (phasic) sensory endings

• primary or secondary
• characteristic
• histological name

Answer 8

primary
highly responsive to the rate of change in the muscle length, encoding the velocity of the stretch
histological name
-annulospiral ring

Question 9

static (tonic) sensory endings

• primary or secondary
• responsive to what?
• histological name

Answer 9

secondary and some primary
responsive to static muscle length
histological name
-flower spray endings

Question 10

how is information carried to the CNS from

• primary endings
• secondary endings

Answer 10

primary
-Ia fibers
secondary
-type II fibers

Question 11

what controls the contraction of the muscle spindle

Answer 11

gamma motor neuron

Question 12

activation of the gamma motor neuron results in…

-can be used to…

Answer 12

contraction of the intrafusal fibers

can be used to adjust the sensitivity of each receptor within the muscle spindle

Question 13

is the adjustment of the sensitivity of each receptor in the muscle spindle combined or separate for the dynamic and static receptors

Answer 13

separate

Question 14

what is the purpose of the motor activation in the muscle spindle
-what is this called

Answer 14

to prevent “unloading” of the receptor during extrafusal muscle contraction
called alpha-gamma coactivation

Question 15

at the time of alpha motor neuron firing, what happens in the muscle spindle?
-this results in…

Answer 15

the appropriate gamma motor neurons are also activated

results in muscle spindle adjustment that parallels the contraction of the extrafusal muscle fiber

Question 16

stimulation of the gamma motor neurons that takes place in situations other than alpha-gamma coactivation results in…

• this stimulation can be influenced by…
• this allows for…

Answer 16

an increase in the sensitivity of both of the primary and secondary endings
can be influenced by CNS pathways or by cutaneous stimulation
allows for fine-tuning of the spindle as the difficulty of the motor task increases

Question 17

golgi tendon organs

• appearance
• location

Answer 17

slender capsule encased receptors

origin and insertion of skeletal muscles at musculo-tendinous junctions

Question 18

what are located on each end of the GTO capsule?

Answer 18

15-20 extrafusal fibers on one side

capsule attaches to tendon on other end

Question 19

the collagen fibers of the _____ become braided with the collagen of the recteptor capsule

Answer 19

collagen fibers of the epimysium and perimysium of the muscle

Question 20

GTO receptor capsule location in relation to nerve fibers

-how do they relate

Answer 20

located at the end of Ib nerve fibers

they intertwine

Question 21

contraction of the extrafusal fiber causes what to occur to the GTO

Answer 21

causes tension on the collagen bundles, which

• compresses the afferent nerve ending
• activates a receptor potential

Question 22

activation of a receptor potential in the GTO is followed by…

Answer 22

generation of an action potential if the stimulus is sufficient

Question 23

how sensitive is the GTO

Answer 23

highly sensitive to small changes in muscle tension, providing continuous feedback to regulate muscle tension

Question 24

what is autogenic inhibition

Answer 24

GTO has a high threshold to tension (resisted muscle stretch) that plays a protective role by inhibiting alpha motor neuron activation of the contracting muscle when extremes of range are reached