Muscle innervation and motor unit

Question 1

1A muscle fiber receptor

Answer 1

primary spindle endings, measures length and rate of change length

Question 2

1b muscle fiber receptor

Answer 2

receptor is on golgi tendon organ measures tension

Question 3

II muscel fiber receptor

Answer 3

receptor on secondary spindle endings measures length receptor on non-spindle endings measures deep pressure

Question 4

III and IV(unmyelinated) muscle fiber receptor

Answer 4

free nerve ending that measures pain, chemicals and temp.

Question 5

changes in muscle length are related to

Answer 5

changes of the angle of the joint(joint position)

Question 6

muscle spindles emit axons that serve as

Answer 6

afferent components of muscle stretch reflexes

Question 7

motor innervation of muscle spindle organs

Answer 7

gamma neurons that adjust sensitivity of the spindle stretch

Question 8

components of spindle

Answer 8

small group of fine intrfusal muscle fibers -myelinated sensory axons with receptive endings on the central regions of intrafusal fibers -myelinated motor axons that innervate the contractile regions adjacent to the central regions of the intrafusal fibers.

Question 9

intrafusal fibers lie

Answer 9

within the spindle which is attached to connective tissue running parralle to and between the extrafusal fibers

Question 10

each spindle indrectly connects to

Answer 10

the tendons

Question 11

when muscles are stretched the spindle

Answer 11

also is stretched with an increase of firing rate of muscle spindle afferents.

Question 12

types of itnrafusal fibers

Answer 12

dynamic nuclear bag- change in length and rate of change nuclear chain- changes in length static nuclear bag- changes in length

Question 13

dynamic nuclear bag innervated by

Answer 13

Group 1a afferent dynamic and static Dynamic A gamma motor neurons- end on contractile portions

Question 14

nuclear chain and static nuclear bag innervated by

Answer 14

group II afferent Static A gamma neurons ends on contractile portions.

Question 15

extrafusal innervation of extrafusal fibers

Answer 15

large A Alpha (myelinated with large diameter.

Question 16

role of muscle spindle

Answer 16

stretch reflex, proprioceptive info regarding movement and position of body parts, regulating muscle contraction under influence of descending motor pathways and afferent feedback.

Question 17

role of muscle spindle in stretch reflex

Answer 17

1a fibers conduct action potentials towards excitator alpha motor neurons . these muscles contract while collaterals of the excited 1a fibers excite interneurons that inhibit firing of alpha neurons on antagonist muscle

Question 18

muscle spindle activity during sustained stretch

Answer 18

some spindles fire tonically instead of phasically

Question 19

muscle spindle activity during alpha motor stimulation

Answer 19

the spindle becomes inactive and the afferent discharge ceases leading to reduced activity of alpha motor neurons.

Question 20

coactivation of alpha and gamma motor neurons

Answer 20

both extrafusal and intrafusal fibers contract, the spindles remain loaded and sensitive to stretch. enables muscle spindle to measure muscle length continuously

Question 21

role of gamma motor activity on spindle performance.

Answer 21

stimulation of effernet fibers sensitizes the spindle to changes in muscle length. ( contraction of the ends of the intrafusal fibers exerts tension on the sensory components of these fibers. at any length of the spindle the firing rates are enhanced during periods of gamma motor neuron stimulation and the spindle remains sensitive to further increases in length

Question 22

golgi is innervated by

Answer 22

a single large 1B fibers, within the organ it looses it’s myelin sheath. leaving naked nerve endings to interweave among the collagen fibers.

Question 23

when golgi organ is deformed during muscle contraction

Answer 23

the ner ve endings undergo distortion which opens the membrane spanning stretch sensitive vation channels and the rate of action potential firing thus increases in the 1b fibers.

Question 24

golgi organ monitors

Answer 24

tension

Question 25

at great tensions the golgi organ mediates

Answer 25

inhibition of over active alpha motor neurons (inverse myotatic reflex) that relaxes teh muscles and excites the antagonist muscle

Question 26

Renshaw cells

Answer 26

inhibitory interneurons that connect to the alpha motor neurons

Question 27

the major collateral of the lower motor neurons leaves

Answer 27

the CNS and runs to the skeletal muscle branching extensively to innervate the multiple muscle fibers distributed within a muscle belly.

Question 28

motor neuron pools

Answer 28

lower motor neurons that control individual muscle troups. are located in the columns sometimes bridging several cord segments and are scattered along the derivatives of the basal plate of the brainstem.

Question 29

large populations of motor neurons on the ventral horns of the cervical and lumbar segements serve

Answer 29

the muscles of the upper and lower limbs. with fewer motor neurons located in the thoracic segments of the cord.

Question 30

input to motor neurons

Answer 30

muscle spindle afferents, interneurons, upper motor neurons.

Question 31

neuromuscular junction is located in

Answer 31

the middle of the muscle fiber.

Question 32

hypotonia

Answer 32

detectable by palpation. caused by damage to 1a fibers or alapha motor neurons . can also arise from lesions in other parts of the motor system like the cerebellum.