Muscle Physiology

Question 1

What are the 4 mechanics of skeletal muscle contraction?

Answer 1

• twitch
• force
• length
• velocity

Question 2

What is a twitch?

Answer 2

contraction produced in a muscle fibre in response to a single AP

Question 3

What is the all-or-none principle?

Answer 3

• the principle that the strength by which a nerve or muscle fiber responds to a stimulus is independent of the strength of the stimulus
• If that stimulus exceeds the threshold potential, the nerve or muscle fiber will give a complete response; otherwise, there is no response

Question 4

A twitch can happen for a ______, _______ or ______.

Answer 4

• muscle fibre
• motor unit
• whole muscle level

Question 5

What are the 3 phases of a twitch?

Answer 5

• latent period
• contraction phase
• relaxation phase

Question 6

What happens during the latent period?

Answer 6

• AP in cell –> onset of contraction (2-3 ms)

- excitation-contraction coupling

Question 7

What happens during the contraction phase?

Answer 7

• 10-100 msec, tension development peaks

- crossbridge cycling

Question 8

What happens during the relaxation phase?

Answer 8

• peak - end of contraction (longest)

- Ca2+ reuptake, crossbridges decrease

Question 9

What is the cause of summation and tetanus?

Answer 9

• tension depends on Ca2+ bound to troponin
• high frequencies = release exceeds reuptake
• saturation

Question 10

In summation, action potential lasts ___ msec.

Answer 10

2 msec.

Question 11

In summation, how long does contraction last?

Answer 11

10-200 msec.

Question 12

In summation, contractions can ____ and _____.

Answer 12

overlap and sum

Question 13

In summation, high frequencies = ______ exceeds _____.

Answer 13

release exceeds reuptake

Question 14

In summation, Ca2+ increases in cytosol –>

Answer 14

saturation

Question 15

Describe saturation in summation.

Answer 15

• all troponin has Ca2+ bound to it
• cross bridge cycling maxed out
• maximum tetanic contraction

Question 16

What are the 2 types of twitches?

Answer 16

• isometric

- isotonic

Question 17

Contractile elements =

Answer 17

sacromeres

Question 18

Series elastic elements =

Answer 18

connective tissue, tendons

Question 19

Force exerted by contracting muscle =

Answer 19

tension

Question 20

Force opposing contraction (ie. weight to be moved) =

Answer 20

load

Question 21

In isometric twitch contraction, the length is _______.

Answer 21

constant

Question 22

In isometric twitch contraction, _____ _____ contract, generating ______.

Answer 22

• contractile elements

- tension

Question 23

Isometric twitch contraction occurs when:

Answer 23

load > tension

Question 24

What happens when load > tension in isometric twitch contraction?

Answer 24

• stretches series of elastic elements

- muscle does not shorten, load not lifted

Question 25

Isotonic twitch contraction is _____ tension.

Answer 25

constant

Question 26

Isotonic twitch contraction occurs when:

Answer 26

tension > load

Question 27

What happens when tension > load in isotonic twitch contraction?

Answer 27

load is lifted as muscle shortens

Question 28

In normal muscle activity, some purely _______ contractions occur.

Answer 28

- isometric | - postural

Question 29

In normal muscle activity, purely ______ contractions are rare.

Answer 29

isotonic

Question 30

In normal muscle activity, load generally _____ constant.

Answer 30

not

Question 31

In normal muscle activity, load changes as ____ ____ changes.

Answer 31

limb position

Question 32

Graded muscle contractions depend on 2 factors:

Answer 32

- tension produced by each fibre | - number of fibres contracting

Question 33

What consists of tension produced by each fibre?

Answer 33

- number of active cross bridges that bind to actin | - more crossbridges that bind --> more force

Question 34

Force generating capacity =

Answer 34

inherent ability of muscle to generate force

Question 35

Force generating capacity depends on:

Answer 35

- the number of crossbridges in each sarcomere | - the genetic arrangement of sarcomeres

Question 36

More crossbridges/sarcomere =

Answer 36

more force

Question 37

More sarcomeres in parallel =

Answer 37

more force

Question 38

Number of thick and thin filaments/area =

Answer 38

constant

Question 39

Is fibre diameter constant?

Answer 39

no, it varies

Question 40

Large diameter =

Answer 40

more filaments = more force

Question 41

Length of fibre at the _____ of contraction affects:

Answer 41

- onset | - force generated

Question 42

What is optimal length?

Answer 42

- resting length of muscle at which the fibre can develop the greatest amount of tension - due to maximum overlap of thick filament crossbridges and thin filaments

Question 43

Most muscles are at _____ length.

Answer 43

optimal

Question 44

If a muscle is at greater than optimum length ...

Answer 44

decrease crossbridge overlap

Question 45

If muscle is at less than optimum length...

Answer 45

- thin filaments overlap each other | - Z lines contact thick filaments

Question 46

More fibres contracting =

Answer 46

greater tension

Question 47

Recruitment:

Answer 47

stimulating more muscle fibres to contract

Question 48

Recruitment occurs at level of...

Answer 48

motor unit (MU)

Question 49

Activation of the motor neuron activates:

Answer 49

all muscle fibres in the motor unit

Question 50

Increases in tension occur in steps proportional to...

Answer 50

the size of the motor unit

Question 51

What motor units are used in muscles for delicate movements?

Answer 51

small motor units

Question 52

What motor units are used in muscles for strength?

Answer 52

large motor units

Question 53

Number of motor units varies in _____ ______.

Answer 53

different muscles

Question 54

Small fibre diameter in motor units are used for what movements?

Answer 54

weaker

Question 55

Large fibre diameter in motor units are used for what movements?

Answer 55

stronger

Question 56

Small motor units =

Answer 56

- small fibres - small motor neuron cell bodies - small axon diameters

Question 57

Large motor units =

Answer 57

- large fibres - large motor neuron cell bodies - large axon diameters

Question 58

The size principle:

Answer 58

order of muscle unit recruitment related to the size of muscle units

Question 59

The size principle says ____ excited first, _____ last.

Answer 59

- small | - large

Question 60

Why are large motor units excited last?

Answer 60

- difficult to depolarize to threshold | - greater synaptic input

Question 61

When muscle contracts isotonically, _____ period of shortening _____ with increasing load.

Answer 61

- latent | - increases

Question 62

When muscle contracts isotonically, duration of shortening with _______ load.

Answer 62

- decreases | - increasing

Question 63

When muscle contracts isotonically, velocity of shortening ______ with _____ load.

Answer 63

- decreases | - increasing

Question 64

When muscle contracts isotonically, the rate of change of the distance is _____.

Answer 64

shortened

Question 65

Velocity of shortening reaches 0 when...

Answer 65

load > or equal to max tension

Question 66

Velocity of shortening is greatest when...

Answer 66

no load on muscle

Question 67

As the angle of pennation increases, there is...

Answer 67

greater force development (not power)

Question 68

Greater mechanical advantage with a _____ angle of insertion (_____ to force arm) = _____ force development, but a _____ in the rate at which that force is developed (power)

Answer 68

- greater - closer - greater - reduction

Question 69

Potassium is thought to contribute to fatigue due to...

Answer 69

- increased efflux out of the cell into the tissue space (Na+/K+ pump activity) - impairs membrane excitability