Neural Considerations for Movement

Question 1

a motor unit includes

Answer 1

a cell body
an axon
dendrites
all muscle fibers it innervates

Question 2

all fibers act as one unit according to the _______ principle

Answer 2

all or nothing

Question 3

T or F? fibers of a motor unit are bunched together

Answer 3

false, they are spread throughout the muscle

Question 4

innervation ratio determines?

Answer 4

motor unit role

Question 5

low innervation ratios

Answer 5

-many neurons that each control a small portion of the total muscle
- cns can modulate force more precisely

Question 6

high innervation ratios

Answer 6

• have fewer neurons that each control a large portion of the total muscle
• cns can modulate force less precisely but can activate many fibers at once for high force production

Question 7

Type 1

Answer 7

• SO
• smallest neurons
• slowest velocity
• lowest threshold for excitability

Question 8

type 2a

Answer 8

• FO
• moderate size neurons
• moderate velocity

Question 9

type 2b

Answer 9

• FG
• largest neurons
• highest velocity

Question 10

cns modulates muscle force through 3 primary mechanisms

Answer 10

1 - number of MU recruited
2 - MU activation frequency
3 - synchronization of MU

Question 11

length of an AP

Answer 11

3-4 msec

Question 12

length of a fiber twitch

Answer 12

40-300 msec

Question 13

spatial summation

Answer 13

recruit the necessary number of motor units to produce the desired force - determined by size principle

Question 14

temporal summation (rate coding)

Answer 14

modulation of the frequency of action potentials reaching the muscle fibers - higher frequency produces higher force from each motor unit

Question 15

unfused tetanus

Answer 15

twitches are overlapping resulting in summation

Question 16

fused tetanus is

Answer 16

tetanization

Question 17

the frequency of unfused and fused tetanus is dependent on the

Answer 17

MU type

Question 18

tetanus occurs in type one when you recruit more than ______ MU (type one) and _______ (type 2) times/sec

Answer 18

30, 50

Question 19

synchronization

Answer 19

all MU activated at once

Question 20

what is the exception to the size principle

Answer 20

synchronization

Question 21

synchronization results in:

Answer 21

greater and more rapid generation of muscle force and joint acceleration
observed during ballistic movements

Question 22

CNS allows _______ control and PNS allows _________ control

Answer 22

voluntary
automatic

Question 23

extra-fusal fibers

Answer 23

main contractile component

Question 24

which fiber has the alpha motor neuron? gamma?

Answer 24

extra-fusal
intra-fusal

Question 25

intra-fusal fibers

Answer 25

contractile component of the muscle spindle