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Physiology > Characteristics of skeletal muscle contraction > Flashcards

Characteristics of skeletal muscle contraction Flashcards

1
Q 
A  single  action  potential
in  a  single  muscle
fiber  causes  a  brief
contraction  followed
by relaxation.
Is?
A

muscle twitch.

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2
Q

Types of Contraction of Skeletal Muscle : ?

A

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.

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3
Q

This occurs when the muscle shortens but the muscle

tension remains constant.

A

Isotonic contraction:

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4
Q

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

A

Isometric contraction:

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5
Q

The velocity of shortening remain constant as muscle
changes length
?

A

Isokinetic contraction:

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6
Q

The skeletal muscles contain which elements ?

A 
contractile  element (CE), elastic and viscous elements  in  series  with the  contractile  element and  present  mainly  in the  tendons,  the   series elastic  component
(SEC).
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7
Q

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

A

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

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8
Q

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

A

sub- maximal isometric contractions

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9
Q

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

A

whole muscle is shortened & its tension remains constant.

/ isotonic contraction

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10
Q

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.

A

Isokinetic contractions :

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11
Q

Advantage of Isokinetic contractions :

A

Advantages: more rapid development of muscle strength

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12
Q

contractions the muscle shortens in?

A

concentric

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13
Q

contractions the muscle lengthens in?

A

eccentric

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14
Q

W = L x D ?

A

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

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15
Q

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 ?

A

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

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16
Q

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

A

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

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17
Q

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

A

Isotonic contraction

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18
Q

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

A

Isometric contraction

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19
Q

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

A

mixture of the two.

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20
Q

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

A

isometric

contraction

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21
Q

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

A

isometric / isotonic

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22
Q

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

A

isometrically and completed isotonically.

23
Q

With heavier loads: The duration of ? Is prolonged ?

A

isometric contraction

phase is longer.

24
Q

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

A 
Decreased
Remain constant
Converted to external work and waste heat
Occurs 
Long
Great
Less
25
Q

Isometric

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

A 
Remain Constant
Increase
Converted to waste heat
occur
short
less
Great
26
Q

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

A

motor unit.

27
Q 
Each  motor  neuron
that  leaves  the
spinal
 cord
innervates?
A

multiple

muscle fibers,

28
Q

each muscle fiber is

supplied by only?

A

only

one motor neuron.

29
Q

The All or None Law obeyed by?

A

A single skeletal muscle fiber obeys the all or none law.

Single nerve fiber • Cardiac muscle as a whole

30
Q

do not obey the all or non law

?

A

whole skeletal muscle or the nerve trunk

31
Q

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

A

sub-threshold.

32
Q

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

A

recruitment

tetanization

33
Q

by increasing the number of motor units

contracting simultaneously,

A

multiple fiber summation (recruitment

34
Q

by increasing the frequency of contraction, which

is called

A

frequency summation and can lead to

tetanization.

35
Q

The greater the number of fibers contracting,

?

A

the greater the

total muscle tension.

36
Q

For weak contraction of the whole muscle ? of its motor

units are ?

A

Few / activated

37
Q

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

A

More

38
Q

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?

A

Motor Unit Recruitment.

39
Q

This recruitment allows lifting of
objects of varying weights.
?

A

Motor Unit Recruitment.

40
Q

strength of the signal increases,

A

larger and larger

motor units begin to be excited as well.

41
Q

that is the number of muscle

fibers controlled by a single motor neuron.

A

size principle

42
Q

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.
?

A

size principle:

43
Q

important feature of ?

asynchronous recruitment)

A

multiple fiber summation

44
Q

different motor units are driven asynchronously by the
spinal cord ?

A

asynchronous recruitment

45
Q

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

A

asynchronous recruitment

46
Q

is possible only for submaximal

contraction ?

A

Asynchronous recruitment

47
Q

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

A

maximal contraction

48
Q

The force of contraction can be increased by? Because?

A

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.

49
Q

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

A

rapidly repeated stimulation,

50
Q

individual responses fuse

into one continuous contraction called a?

A

tetanus

51
Q

when there is no relaxation between

stimuli ?

A

complete tetanus

52
Q

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

A

incomplete tetanus

53
Q

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

A

Treppe “The Stair Case Phenomenon”:

54
Q

Treppe “The Stair Case Phenomenon”:

is explained by the ?

A

persistent elevated

levels of free Ca 2+ in the cytoplasm.

Physiology (2 decks)

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