Neuromuscular Physiology II

Question 1

What is a muscle twitch?

Answer 1

Contractile response of a muscle fiber to a single muscle AP

Question 2

What happens if all muscle fibers within a muscle were activated?

Answer 2

Whole muscle twitch

Question 3

Latent Period

Answer 3

delay between the arrival of the AP and initiation of contraction

Question 4

Contraction period

Answer 4

When CA2+ binds to troponin and the actin-myosin cross-bridges are formed

Question 5

Relaxation period

Answer 5

When Ca2+ is actively pumped back into the SR, myosin head detaches from actin and muscle tension decreases

Question 6

Refractory period

Answer 6

the period of time when the muscle tissue is unable to respond to a subsequent AP

Question 7

Wave summation

Answer 7

occurs when a second AP triggers muscle contraction before the first contraction has finished

Question 8

Wave summation - result

Answer 8

stronger contraction; b/c the muscle fiber hasn’t had enough time to completely reset its self

Question 9

What is tetanus

Answer 9

when repeated stimuli are sent in short durations that they can lead to an even greater summation of contraction force

Question 10

Unfused (incomplete) tetanus

Answer 10

occurs when muscle fibers are stimulated at a rate where they don’t completely relax between stimuli

Question 11

Fused (complete) tetanus

Answer 11

occurs when muscle fibers are stimulated at a rate where they don’t relax AT ALL between stimuli

Question 12

Henneman’s size prinicple

Answer 12

• not all MN have same excitability threshold
• smaller, fatigue-resistant MU’s recruited first

Question 13

What is fatigue?

Answer 13

reduction in the force output (or capacity) of a muscle in response to a voluntary effort

Question 14

Where does peripheral fatigue occur?

Answer 14

at or below the level of the NMJ

Question 15

Where does central fatigue occur?

Answer 15

above the level of the NMJ; motor cortex, spinal cord

Question 16

Motor unit rotation

Answer 16

some MU’s deactivate and others become active, maintaining contraction strength

Question 17

Muscle and tendon proprioceptor role

Answer 17

send info to CNS about changes in length, tension, and joint angles

Question 18

Muscle spindle location

Answer 18

within muscle body

Question 19

golgi tendon organ location

Answer 19

within the tendon

Question 20

Names of muscle and tendon proprioceptors

Answer 20

• muscle spindles
• golgi tendons

Question 21

What affects the force produced by a muscle?

Answer 21

sarcomere length

Question 22

Passive tension

Answer 22

as you stretch the muscle beyond resting length it produces a force (non-contracting)

Question 23

Active tension

Answer 23

force produced by contractile mechanisms

Question 24

Optimum length (Lo)

Answer 24

maximum active force
- optimal overlap of actin-myosin cross-bridge produces greatest tension development

Question 25

Force-velocity relationship - concentric

Answer 25

as velocity of a concentric muscle action is increased, less force is capable of being generated

Question 26

Force-velocity relationship - eccentric

Answer 26

as the velocity of an eccentric muscle action is increases, more force is capable of being generated during that contraction

Question 27

Force-velocity relationship - eccentric - why?

Answer 27

greater strain placed on the myosin heads, facilitates the attatchment of the second head more frequently

Question 28

Force-velocity relationship - concentric - why?

Answer 28

takes time for cross-bridges to attach/detach - number of total cross-bridges becomes limited as contraction velocity increases

Question 29

Ways to improve maximal power output of a muscle

Answer 29

- increasing the maximal force we can move - increasing our movement velocity

Question 30

What dictates the amount of force generated by a muscle?

Answer 30

the number of attached cross-bridges

Question 31

Does force production increase or decrease when contraction velocity increases?

Answer 31

Force production decrease

Question 32

equation: power =

Answer 32

Power = force x velocity

Question 33

What is power maximized at?

Answer 33

maximized at a combination of submaximal force and velocity values

Question 34

What affects the force-velocity properties of a muscle?

Answer 34

affected by the fibre type contribution to the whole muscle area

Question 35

What muscle fiber has the fastest velocity?

Answer 35

Type IIx; 5.6 fiber lengths/second

Question 36

Power and velocity continuum of muscle fiber types

Answer 36

IIx > IIa > I