spinal reflexes

Question 1

what is the only afferent in the CNS that receives a nerve supply?

Answer 1

muscle spindle

Question 2

which fibers are the true force-producing fiber?

Answer 2

extrafusal fibers

Question 3

what do intrafusal fibers do?

Answer 3

CHANGE INTERNAL STIFFNESS:
when the muscle is stretched, tension placed on the intrafusal fibers activates mechanically gated ion channels in the nerve endings, triggering action potentials.

Question 4

what do group Ia afferents do?

Answer 4

(group Ia afferents) and have rapidly adapting responses to changes in muscle length

Question 5

what do group II afferents do?

Answer 5

group II afferents) produce sustained responses to constant muscle lengths.

they provide information about the static position of limbs.

Question 6

describe the firing pattern of group Ia afferents in response to spinal stretch

Answer 6

it is dynamic; intense firing w/ stretch onset , then slows down ( non- linear)

Question 7

describe the firing pattern of group II afferents in response to spinal stretch

Answer 7

static; steady firing, increasing with increasing stretch ( linear)

Question 8

what are the sensory zones included in an intrafusal fibe?

Answer 8

central region: group Ia receptors
and
distal regions: group II receptors

Question 9

what innervates intrafusal fibers?

Answer 9

gamma motor neurons

Question 10

explain the stretch reflex circuitry

Answer 10

Stretching a muscle spindle leads to increased activity in Ia afferents and an increase in the activity of alpha motor neurons that innervate the same muscle. Ia afferents also excite the motor neurons that innervate synergistic muscles. and inhibit indirectly the motor neurons that innervate antagonists. The stretch reflex operates as a negative feedback loop to regulate muscle length.

Question 11

what is reciprocal innervation ( AKA the way stretch reflex works) ?

Answer 11

when a Ia neuron forms a monosynaptic excitatory connection with the alpha motor neurons in the ventral hom of the spinal cord that innervate the same (homonymous) muscle and, via local circuit neurons, forms inhibitory connections with the a motor neurons of antagonistic (heteronymous) muscles

Question 12

are antagonistic muscles always in opposition of each other?

Answer 12

no they can work as agonist , it just depends on the task. e.g. the queen of England’s wave - muscles that are normally antagonist act as agonist

Question 13

when muscle fibers contract ( extrafusal fibers the muscle shortens and the ability to signal further changes in muscle length are eliminated. Given this how can the muscles remain sensitive to further changes in muscle length?

Answer 13

the gamma motor neurons fire to shorten intrafusal fibers when an alpha motor neurons fire so that the spindle contracts and maintains sensitivity

Question 14

what is the difference between golgi tendon organs and muscle spindles ( list 3 things) #1 listed in the answer is the major difference ?

Answer 14

Golgi tendon organs are 1.exquisitely sensitive to increases in muscle tension that arise from muscle contraction ( not sensitive to passive stretch), 2. organized in series with muscle extrafusal fibers 3, are located at the junction of muscle and tendon

SPindles are 1.sensitive to Passive stretch 2. organized in Parallel with extrafusal fibers 3. not located at jnc of muscle and fiber

Question 15

what type of afferents are active in golgi tendon organs?

Answer 15

group Ib

Question 16

describe the overall difference between the golgi tendon organ and muscles spindle?

Answer 16

muscLe spindLe system is a feedback system that monitors and maintains muscle Length, and the Golgi tendon system is a feedback system that monitors and maintains muscle force.

Question 17

the Ib afferent inhibitory interneuron fires __________ pathway

Answer 17

fires disynaptic pathway

Question 18

explain the flexion crossed extension reflex

Answer 18

stimulation of cutaneous receptors in the foot (by stepping on a tack. in this example) leads to activation of spinal cord local circuits that seNe to withdraw (flex) the stimulated extremity and extend the other extremity to provide compensatory support. ( see purves pg 415 or notes pg. 708)

Question 19

what does a central pattern generator do?

Answer 19

control the coordinated movements associated with locomotion ( e.g walking, swimming or scratching)

Question 20

where does central pattern generator system reside?

Answer 20

entirely in the spinal cord

Question 21

what evidence is there for plasticity of the spinal cord?

Answer 21

if you train a cat to walk on a treadmill then transect the spinal cord, after a few weeks the cat will still walk on a moving treadmill whereas a cat that could walk prior but wasn’t trained on a treadmill won’t be able to walk on the moving treadmill.

Question 22

the more selective an electromyorgram the more?

Answer 22

the more noise

Question 23

what is commonly diagnosed with use of an electromyorgram?

Answer 23

neuromuscular disorders

Question 24

why is an electromyorgram easy to record?

Answer 24

because the muscle unit of a motor unit serves as a natural biologic amplifier of a nerve action potential

Question 25

an electromyorgram electrode design can influence what 4 aspects of a recording?

Answer 25

volume of muscle recorded from
signal characteristics
frequency response
sensitivity to noise

Question 26

electromyorgrams can be _________ or __________ and __________ or __________

Answer 26

electromyorgrams can be non-selective or selective and surface or needle.

Question 27

what can a non-selective surface EMG be used for?

Answer 27

stimulation

Question 28

what can a non-selective sub-dermal ( needle) EMG be used for?

Answer 28

use in the operating room

Question 29

for selective EMG why is use of a concentric bipolar needle standardization important ?

Answer 29

because it allows for comparison between labs and across subjects

Question 30

what is a hollow cannula insulated along it’s length ecept at the tip used for?

Answer 30

botox injections so you can electrically stimulate until you get the desired twitch.

Question 31

what are 2 ways to modulate muscle force?

Answer 31

recruitment of a previously silent motor unit

and

rate-coding( increasing the firing/discharging) of an already-firing motor unit

Question 32

what does a needle EMG allow you to do?

Answer 32

look at the activity ( and timing) of a single cell within the CNS

Question 33

what is the sound you hear in an EMG?

Answer 33

the interference of motor neurons that are firing and being recruited