L5 Locomotion

Question 1

What are the three types of motor units?

Answer 1

small
intermediate
large

Question 2

What is a motor unit?

Answer 2

one motor neuron and the muscle fibers it innervates

Question 3

What is the motor neuron pool?

Answer 3

all motor neurons innervating a given muscle

Question 4

Which motor units have high myoglobin content?

Answer 4

small and intermediate

Question 5

Which motor units are recruited first?

Answer 5

small

Question 6

Which motor units are recruited last?

Answer 6

large

Question 7

What is a muscle spindle?

Answer 7

CT sheath that contains muscle fibers

Question 8

How are muscle spindles arranged?

Answer 8

In parallel

Question 9

What innervates intrafusal muscle fibers?

Answer 9

sensory nerve endings

Question 10

How do sensory nerves enter the spinal cord?

Answer 10

Via dorsal roots

Question 11

What do Ia fibers measure?

Answer 11

muscle length and rate of length change

Question 12

What do group II fibers measure?

Answer 12

length

Question 13

Which fiber group has a faster conduction speed?

Answer 13

Ia

Question 14

What is reciprocal inhibition?

Answer 14

an inhibitory interneuron between Ia afferent and motor neurons

Question 15

What do interneurons innervate?

Answer 15

Unstretched muscle

Question 16

What is a stretch reflex?

Answer 16

a muscle is stretched, spindle afferents excite alpha motor neurons

Question 17

What does the stretch reflex regulate?

Answer 17

muscle length via negative feedback

Question 18

What is proprioception?

Answer 18

sense of relative position

Question 19

What type of afferents provide proprioceptive information?

Answer 19

Ia afferents

Question 20

What causes contraction of the two end of muscle fibers?

Answer 20

gamma motor neurons

Question 21

What is the effect of gamma motoneuron activation?

Answer 21

contraction at the end of the muscle
stretches the middle
promotes Ia activity

Question 22

What are the two classes of descending alpha motoneuron activation?

Answer 22

direct activation
indirect activation

Question 23

What facilitates indirect activation of alpha motoneurons?

Answer 23

gamma loop

Question 24

Describe the gamma loop?

Answer 24

gamma excited –> intrafusal fiber contract –> Ia stretches –> activates alpha motoneuron

Question 25

what does alpha-gamma co-activation produce?

Answer 25

movement

Question 26

What is the effect of alpha-gamma co-activation?

Answer 26

Ia spindles afferents remain active for load increase

Question 27

Where are Ib nerve ending found?

Answer 27

small tendon fascicles

Question 28

How are Ib fibers activated?

Answer 28

by tension produced by muscle contraction

Question 29

What is the inverse myotatic reflex (tendon organ reflex)?

Answer 29

di-synaptic reflex arc - synergistic muscles are inhibited - antagonistic muscles are excited

Question 30

What does the tendon organ reflex regulate?

Answer 30

muscle force via negative feedback

Question 31

Why do we have the tendon organ reflex?

Answer 31

to reduce muscle force

Question 32

T/F the stretch rflx and tendon organ rflx can work together

Answer 32

TRUE

Question 33

What is muscle stiffness?

Answer 33

change in force / change in length

Question 34

What the relationship b/n stretch rflx and muscle stiffness?

Answer 34

it increases muscle stiffness

Question 35

What the relationship b/n tendon organ rflx and muscle stiffness?

Answer 35

it decrease muscle stiffness

Question 36

What is the main effect of reflexes?

Answer 36

balancing support and shock absorption in anti gravity muscles

Question 37

What the the flexor rflx a response to?

Answer 37

noxious stimulation of muscle or skin

Question 38

What influence spinal cord motor units?

Answer 38

descending ptwys from the brain

Question 39

What are upper motor neurons?

Answer 39

neurons in the brain

Question 40

What changes occur in motor tone when upper motor neurons are damaged?

Answer 40

spinal shock (hypotonia) spasticity (hypertonia)

Question 41

What contributes to spasticity after spinal cord injury?

Answer 41

down-regulation of K-NA cotransporter KCC2

Question 42

T/F BDNF can up regulate the transporter after spinal cord injury

Answer 42

True

Question 43

What are the phases of step cycling?

Answer 43

extensor phase flexor phase

Question 44

What does reflex feedback influence?

Answer 44

phase duration and pattern but is not necessary for rhythm generation

Question 45

What can Dysfunctions in brainstem circuits cause?

Answer 45

REM sleep disorder (sleep walking)

Question 46

What are the two classes of mechanism for Central pattern generator?

Answer 46

1. cell have intrinsic burts of APs 2. Emergent network property

Question 47

What is the emergent network property?

Answer 47

reciprocal inhibition and adaption account for alternating activity in flexors and extensors