Characteristics of skeletal muscle contraction

Question 1

A  single  action  potential
in  a  single  muscle
fiber  causes  a  brief
contraction  followed
by relaxation.
Is?

Answer 1

muscle twitch.

Question 2

Types of Contraction of Skeletal Muscle : ?

Answer 2

1- Isotonic contraction: This occurs when the muscle shortens but the muscle
tension remains constant.
3- Isokinetic contraction: The velocity of shortening remain constant as muscle
changes length
2- Isometric contraction: Refers to a contraction in which the external length of the
muscle does not change through the tension is highly
increased.

Question 3

This occurs when the muscle shortens but the muscle

tension remains constant.

Answer 3

Isotonic contraction:

Question 4

Refers to a contraction in which the external length of the
muscle does not change through the tension is highly
increased.
?

Answer 4

Isometric contraction:

Question 5

The velocity of shortening remain constant as muscle
changes length
?

Answer 5

Isokinetic contraction:

Question 6

The skeletal muscles contain which elements ?

Answer 6

contractile  element (CE), elastic and viscous elements  in  series  with the  contractile  element and  present  mainly  in the  tendons,  the   series elastic  component
(SEC).

Question 7

The “ CE” shortens & the “ SEC” is greatly stretched “ because the load is not
moved “
What happens ? And what type of contraction ?

Answer 7

the whole muscle is not shortened & its tension is markedly
increased.
/ isometric Contraction

Question 8

important for
maintaining posture and support object in a fixed position.
?

Answer 8

sub- maximal isometric contractions

Question 9

The “CE” shortens and the “SEC” is not markedly stretched “because the load
is moved “.
What is the result ? What time of contraction?

Answer 9

whole muscle is shortened & its tension remains constant.

/ isotonic contraction

Question 10

Do not take place normally but can be achieved using special
exercise machine that can be set up to require muscle
contraction at a constant velocity through out the entire
range in motion.

Answer 10

Isokinetic contractions :

Question 11

Advantage of Isokinetic contractions :

Answer 11

Advantages: more rapid development of muscle strength

Question 12

contractions the muscle shortens in?

Answer 12

concentric

Question 13

contractions the muscle lengthens in?

Answer 13

eccentric

Question 14

W = L x D ?

Answer 14

W is the work output ( mechanical efficiency ) & L is the load & D is the
distance of movement

Question 15

W is the work output ( mechanical efficiency ) & L is the load & D is the
distance of movement
What type of contraction ? What iOS the mechanical efficiency ?

Answer 15

Isotonic contraction / mechanical efficiency (the percentage of energy input
that is converted into work instead of heat) is about 20-25%.

Question 16

since load distance is zero , no external
work is done by the muscle
What type of contraction? What is the mechanical efficiency ?

Answer 16

isometric contraction / the mechanical efficiency is zero
and the all the energy consumed by the muscle during contraction is converted to heat.

Question 17

evokes movement of part of the body or the
body as a whole.
What type of contraction ?

Answer 17

Isotonic contraction

Question 18

tenses a part of the body and
maintains the posture against gravity.
What type of contraction?

Answer 18

Isometric contraction

Question 19

Muscles can contract both isometrically and isotonically in the body, but most contractions are actually

Answer 19

mixture of the two.

Question 20

When standing, person tenses the quadriceps muscles to
stiffen the knee joints and to keep the leg stiff
Type of contraction?

Answer 20

isometric

contraction

Question 21

During running, contractions of leg muscles are a mixture of? [when the legs hit the ground] and to move the limbs ?

Answer 21

isometric / isotonic

Question 22

When a person lifts a heavy weight using the biceps, the
contraction starts? and completes ?

Answer 22

isometrically and completed isotonically.

Question 23

With heavier loads: The duration of ? Is prolonged ?

Answer 23

isometric contraction

phase is longer.

Question 24

Isotonic
Muscle length ? Muscle tension? Energy of contraction ? Sliding of myosin and actin ? Duration of contraction ? O2 and nutrients? Heat products?

Answer 24

Decreased
Remain constant
Converted to external work and waste heat
Occurs 
Long
Great
Less

Question 25

Isometric Muscle length ? Muscle tension? Energy of contraction ? Sliding of myosin and actin ? Duration of contraction ? O2 and nutrients? Heat products?

Answer 25

``` Remain Constant Increase Converted to waste heat occur short less Great ```

Question 26

All the muscle fibers innervated by a single nerve fiber are called a?

Answer 26

motor unit.

Question 27

``` Each motor neuron that leaves the spinal cord innervates? ```

Answer 27

multiple | muscle fibers,

Question 28

each muscle fiber is | supplied by only?

Answer 28

only | one motor neuron.

Question 29

The All or None Law obeyed by?

Answer 29

A single skeletal muscle fiber obeys the all or none law. | Single nerve fiber • Cardiac muscle as a whole

Question 30

do not obey the all or non law | ?

Answer 30

whole skeletal muscle or the nerve trunk

Question 31

The skeletal muscle fiber contracts maximally if stimulated by threshold or does not contract at all if the stimulus is?

Answer 31

sub-threshold.

Question 32

increase the intensity of overall muscle contraction in two ways: ?

Answer 32

recruitment tetanization

Question 33

by increasing the number of motor units | contracting simultaneously,

Answer 33

multiple fiber summation (recruitment

Question 34

by increasing the frequency of contraction, which | is called

Answer 34

frequency summation and can lead to | tetanization.

Question 35

The greater the number of fibers contracting, | ?

Answer 35

the greater the | total muscle tension.

Question 36

For weak contraction of the whole muscle ? of its motor | units are ?

Answer 36

Few / activated

Question 37

for stronger contraction more and ? motor units are recruited (stimulated) to contract simultaneously

Answer 37

More

Question 38

For weak contraction of the whole muscle few of its motor units are activated, for stronger contraction more and more motor units are recruited (stimulated) to contract simultaneously, this is called?

Answer 38

Motor Unit Recruitment.

Question 39

This recruitment allows lifting of objects of varying weights. ?

Answer 39

Motor Unit Recruitment.

Question 40

strength of the signal increases,

Answer 40

larger and larger | motor units begin to be excited as well.

Question 41

that is the number of muscle | fibers controlled by a single motor neuron.

Answer 41

size principle

Question 42

it allows the gradations of muscle force during weak contraction to occur in small steps, whereas the steps become progressively greater when large amounts of force are required. ?

Answer 42

size principle:

Question 43

important feature of ? asynchronous recruitment)

Answer 43

multiple fiber summation

Question 44

different motor units are driven asynchronously by the spinal cord ?

Answer 44

asynchronous recruitment

Question 45

contraction alternates among motor units one after the other, thus providing smooth non jerky contraction also it is important to delay fatigue. By?

Answer 45

asynchronous recruitment

Question 46

is possible only for submaximal | contraction ?

Answer 46

Asynchronous recruitment

Question 47

During ? it is impossible to alternate motor unit activity to prevent fatigue.

Answer 47

maximal contraction

Question 48

The force of contraction can be increased by? Because?

Answer 48

The force of contraction can be increased by increasing the frequency of muscle stimulation because more Ca2+ is released from the SR each time the muscle is stimulated.

Question 49

activation of the contractile mechanism occurs repeatedly before any relaxation has occurred, with?

Answer 49

rapidly repeated stimulation,

Question 50

individual responses fuse | into one continuous contraction called a?

Answer 50

tetanus

Question 51

when there is no relaxation between | stimuli ?

Answer 51

complete tetanus

Question 52

when there are periods of incomplete relaxation between the gathered stimuli. ?

Answer 52

incomplete tetanus

Question 53

progressive increase in the magnitude of separate twitch contraction of skeletal muscle to a plateau value during repetitive stimulation after a period of rest.

Answer 53

Treppe "The Stair Case Phenomenon”:

Question 54

Treppe "The Stair Case Phenomenon”: is explained by the ?

Answer 54

persistent elevated | levels of free Ca 2+ in the cytoplasm.