Spinal Reflexes

Question 1

what is a motor unit?

Answer 1

single motor neuron and the muscle fiber it innervates

Question 2

what is the size principal for motor units?

Answer 2

more units involved means more tension generated

Question 3

what is a type I muscle fiber?

Answer 3

slow twitch (higher fatigue resistance, many mitochondria, posture maintenance)

Question 4

what is a type IIb

Answer 4

fast twitch fatigue able (abundant glycogen, larger fiber diameter, fast contraction, high tension but low endurance)

Question 5

with exercise which muscle fibers can switch?

Answer 5

IIb can switch to IIa
(aging or stopping training with revert the fibers)

Question 6

which fiber type is darker in appearance?

Answer 6

slow twitch is darker, fast is lighter

Question 7

how does the primary motor cortex and other brain centers command movement in the body?

Answer 7

No specific muscle motor units in a bundle that can be ordered to contract by the primary motor
cortex. It can only modulate the
contraction in controlling the
execution of the movement.

contraction of whole muscle proceeded by size principal

Question 8

according to the size principal what fires first?

Answer 8

slow twitch and small motor units first, as more needed bigger/faster become recruited

Question 9

what are S motor units?

Answer 9

fibers that are small in size and generate ow tension, require little ATP, good for waking or jogging

Question 10

which fiber type generates lactic acid?

Answer 10

fast twitch

Question 11

what is the common nerve muscle ratio for motor units?

Answer 11

1:600 (ocular muscles are 1:3)

Question 12

what determines movement within specific parameters?

Answer 12

feedback

Question 13

If the motor action is not within the required parameters, what happens?

Answer 13

the number and activation of motor units involved will be adjusted to correct the movement (i.e., learning and memory is involved with this as well)

Question 14

during sustained activity how do the motor units react?

Answer 14

can rotate through which units are firing to hep resist fatigue it will eventually fatigue (we become less and less precise with time preforming the activity)

Question 15

what are characteristics of reflexes?

Answer 15

repeatable, directed and purposeful, rapid

Question 16

by definition reflexes are:

Answer 16

involuntary`

Question 17

what are Renshaw cells?

Answer 17

inhibitory cells that control surrounding neurons

Question 18

what are A ang G motor fibers?

Answer 18

a for extrafusal muscle fibers
g for intrafusal

Question 19

what do extrafusal fibers do?

Answer 19

generate force

Question 20

does g fibers generate force?

Answer 20

no they are too small to generate force
(they adjust sensitivity in the muscle spindle)

Question 21

what does the muscle spindle do?

Answer 21

sense muscle length and rate of change (dynamic)

Question 22

what does co-activation of a and g allow?

Answer 22

muscle spindle remains sensitive to change in length even as the muscle shortens (helps keep spindle from opposing the skeletal muscle and helps smoothen out movement)

Question 23

what are the two types of length receptors in muscle?

Answer 23

intrafusal (nuclear bag) and nuclear chain fiber

Question 24

what are intrafusal fibers?

Answer 24

-high compliance and can rapidly
adapt to prolonged stretch.

• Intrafusal fibers mediate the phasic or “dynamic” response. Group Ia afferents detect the velocity of
  length change. These are phasic receptors

Question 25

what happens when the muscle is stretched?

Answer 25

When the muscle is stretched, the mechanoreceptors open on the Ia afferent and open sodium channels (i.e., depolarization).

Question 26

Nuclear chain fibers are innervated by ______ and are involved in what type of response?

Answer 26

Group II afferents These fibers are involved in static response

Question 27

what kind of endings to DYNAMIC gamma motor neurons have? what do they innervate?

Answer 27

flower spray that innervate mainly nuclear bag

Question 28

what kind of endings to STATIC gamma motor neurons have? what do they innervate?

Answer 28

flower spray also but innervate nuclear chain fibers instead

Question 29

group II afferents are what kind of receptor?

Answer 29

tonic, give info on where limb is whether it is moving or not

Question 30

what effect does dampening or smoothing out the movement have?

Answer 30

prevents oscillation or jerky movements

Question 31

monosynaptic (jerk reflex) reflex responds to change in_____

Answer 31

muscle length (rapid stretch of muscle triggers the reflex)

Question 32

reflex establishes _____

Answer 32

tone (in resting muscle to oppose gravity)

Question 33

what three circuits can modulate the monosynaptic reflex?

Answer 33

reciprocal innervation Renshaw arc gamma efferent

Question 34

what is reciprocal innervation?

Answer 34

afferent Ia can stimulate the interneuron, enhance action of agonist and inhibit antagonist muscles increasing the efficiency of the contraction for the agonist muscle because less energy will be needed to move it (because it will NOT be opposed by antagonist)

Question 35

renshaw arc do what?

Answer 35

group of interneurons that cause inhibition of a motor neurons preventing too much response or response from unwanted muscle groups (feedback inhibition)

Question 36

baclofen is used to _______

Answer 36

treat muscle spasticity

Question 37

what is the primary function of the Golgi tendon organ?

Answer 37

equalize muscle tension between antagonist and agonist to help reduce tension in each muscle preventing damage

Question 38

what is the seocndary function of the golgi tendon organ?

Answer 38

prevent so much tension that the tendon rips off the bone

Question 39

what types of responses can be generated from the golgi tendon organ?

Answer 39

dynamic and static responses, meaning it will respond to rate of change in muscle tension and constant tension imposed by the muscle

Question 40

The _________ will activate an inhibitory interneuron. This will inhibit the anterior motor neuron. This local circuit will not affect adjacent muscles the above is an example of what?

Answer 40

sensory afferent (Type Ib) feedforward inhibition

Question 41

are antagonist muses activated by golgi?

Answer 41

yes they become activated by interneurons during the Golgi tendon reflex

Question 42

why does the golgi activate the agonist muscles?

Answer 42

helps to relieve stress from the stretched tendon

Question 43

what is the flexor withdraw reflex?

Answer 43

motor response to protopathic stimuli that cause perception of pain

Question 44

on the ipsilateral side of the pain, what happens to the muscles?

Answer 44

the flexors are activated to move you away from the pain stimulus the extensors are inhibited to reduce them resisting the movement

Question 45

on the contralateral side of the pain what is happening to the muscle groups?

Answer 45

the flexors are inhibited and extensors are activated but ultimate you do not want much movement on this side so that this side can act as a stabilizer

Question 46

what is another name for the pain reflex?

Answer 46

crossed extensor reflex

Question 47

what do divergence circuits allow for?

Answer 47

spread reflex to the necessary muscles

Question 48

what is after discharge?

Answer 48

continued rate of flexor contraction due to recurrent pathways (protects the flexors because it allows the tension to be released more slowly)

Question 49

what determines the after discharge?

Answer 49

intensity of the sensory stimulus, pain has high AD (reflex will fatigue as it runs out of NT)

Question 50

what does the after discharge of extensors look like?

Answer 50

even longer latency after discharge (helping to hold the pained area away from the stimulus)

Question 50

what are central pattern generators?

Answer 50

makes patterns of repetitive and alternating activity, chewing, doggy paddle

Question 51

what parts of the brain are involved in the CPG?

Answer 51

-motor cortex for initiation -BG for maintaining repetitive movement -CPG control centers

Question 52

what is a motor unit?

Answer 52

A motor unit is where a single motor neuron innervates the skeletal muscle. The force of the contraction is graded by recruitment of motor units

Question 53

what are some energy differences in sow and fast fibers?

Answer 53

Slow fibers have myoglobin and many mitochondria. Fast will have abundant glycogen

Question 54

what does the size principal do?

Answer 54

allows for the recruitment of slow, then fast fatigue resistant, and finally fast fatigable skeletal muscle

Question 55

when would you have a hyperactivity reflex vs absent?

Answer 55

hyperactive would be in the upper motor neuron absent would be the result of a compression or lower motor neuron lesion