Part Six: Muscle Physiology Concepts

Question 1

Can a muscle fiber (cell) contract “halfway” or incompletely?

Answer 1

No, muscle cells can’t contract halfway or do a lazy contraction
(unlike people, they don’t have the choice to be lazy!)

Question 2

B.What is the name of this concept?

Answer 2

This is known as the ALL OR NONE PRINCIPLE.

Question 3

c.What does this mean about the way sarcomeres act during a
contraction?

Answer 3

This means that when actin slides in the sarcomere, it slides as
far as it can. The sarcomeres always shorten to their fullest
possible extent, which is what creates the strongest possible
contraction of the cell.

Question 4

Muscles are made up of many motor units. What is a motor unit?

Answer 4

A motor unit is a group of muscle cells (fibers) that are under
the control of one nerve. (The nerve controls the contraction of
the muscle cells). For example, in the leg a typical motor unit
is made of 1,000 muscle cells all controlled by one nerve. The
motor unit is similar to a unit/group of soldiers that are led by
one commander. Instead of a group of soldiers, the motor unit is
a group of cells that contract together. The “leader” of the
unit is the nerve.

Question 5

If the electrical voltage (stimulus/shock) applied to a muscle is
gradually increased, what happens to the number of motor units which
contract? What does this mean happens to the muscle contraction?

Answer 5

The number of motor units (groups of cells) contracting increases
as the voltage (electrical current) is increased. This causes
the muscle contraction to get stronger.

Question 6

a. If a subthreshold stimulus (shock) is used on a muscle,
how many motor units in the muscle will contract?
b. If a threshold stimulus is used on a muscle, how many motor units
in the muscle will contract?
c. If a maximal stimulus is used, what happens?

Answer 6

Motor Unit Summation
a. A subthreshold stimulus will not cause any motor units to
contract because it is too weak to cause cells to contract.
b. Threshold stimulus: Only one motor unit (group of cells) will
contract out of the many motor units in the muscle.
c. Maximal stimulus: Causes ALL motor units in the muscle to
contract, producing the strongest contraction possible.

Question 7

. A maximal stimulus is one that is strong enough to cause ________
motor units in a muscle to contract.

Answer 7

A maximal stimulus is one that is strong enough to cause ALL
motor units in a muscle to contract.

Question 8

b. Motor Unit Summation means that as the stimulus (electrical voltage)
is _______________, the ______________ of a muscle
contraction increases.

Answer 8

b. Motor Unit Summation means that as the stimulus (electrical
voltage) is increased, the strength of a muscle contraction
increases.

Question 9

c. Motor Unit Summation explains how one muscle can have
contractions of varying or different _________________–like a
pat, slap, or punch done by the same muscle.

Answer 9

Motor Unit Summation explains how one muscle can have
contractions of varying or different strengths.

Question 10

Motor Unit Summation is also called ______________.

Answer 10

Recruitment [Because as you increase the electrical current, you 
are recruiting (getting) more and more cells to contract.]

Question 11

Sometimes, after a period of rest, when a muscle first contracts, not
all of its calcium is released from the sarcoplasmic reticuli.

Answer 11

The Treppe Effect/ Staircase Phenomenon
In this graph the stimulus (voltage) is NOT being increased
but remains constant.

page 17 graph

Question 12

. Since only some of the calcium is released, will the muscle contract
fully the first few times it contracts?

Answer 12

No, the contraction will not be as strong as it should be if all
of the calcium is not released by the SR.

Question 13

What is this concept known as?

Answer 13

The Treppe Effect.

Question 14

What do these contractions look like? Because of this, what is this
concept also called?

Answer 14

The Treppe Effect is a series of contractions that gradually get
stronger. The contractions look like steps going up because they
increase in size, so this concept is also called the Staircase
Phenomenon.

Question 15

. What kind of stimuli (shocks) are used to produce this and how many
are given per second?

Answer 15

The shocks should be maximal (normally they would cause a full
muscle contraction) and be given at low frequency, or 10-20
shocks per second.

Question 16

Wave Summation means that several individual muscle contractions
can be ___________ together so that they create a contraction that
is _________________ than a single contraction

Answer 16

Wave Summation, Incomplete and Complete Tetanus

view graph

Wave Summation means that several individual muscle contractions
can be added (summated) together so that they create a
contraction that is stronger than a single contraction.

Question 17

How is Wave Summation created in a muscle?

Answer 17

Wave Summation is created when electrical shocks are applied to
to the muscle while it is already contracting
(mid-contraction), using 20-40 stimuli (shocks) per second.

Question 18

When many contractions are summated, this leads to a type of Wave
Summation called tetanus.
In Complete Tetanus many contractions fuse together, producing one
long, powerful contraction

Answer 18

Complete Tetanus)

Question 19

How is Complete Tetanus created in a muscle?

Answer 19

a. The muscle is not allowed to relax between stimuli (shocks) by
applying the stimuli at a high frequency—using 40-50 stimuli
per second.

Question 20

What specifically happens in muscle cells that causes Complete
Tetanus?

Answer 20

Calcium cannot be returned to the sarcoplasmic reticulum between
shocks because they occur too rapidly. Calcium has to be returned
to the SR to end any contraction. When calcium remains in the
sarcomeres this creates a single, long, strong contraction—
complete tetanus.

Question 21

Why is Complete Tetanus NOT a regular event in the body?

Answer 21

Complete tetanus occurs when the muscle is stimulated at 40-50
shocks/sec., but the typical firing of nerves in the body is
around 25 stim/second. *(However, incomplete tetanus, where the
contractions do not all fuse together, does happen regularly in
the body. In incomplete tetanus the muscle does relax slightly
between contractions—which looks like a long, quivering
contraction). See  in above diagram.

Question 22

How fast does a nerve have to fire action potentials onto a muscle to
cause the Treppe Effect?

Answer 22

. (Treppe Effect)
a. At 10-20 shocks per second——low frequency.

Question 23

Overall, what causes the Treppe Effect to occur? (What is the main
thing that causes the contractions to get stronger?)

Answer 23

The main cause is a gradual release of calcium by the SR. It
takes several contractions for all of the calcium to be released.

Question 24

WHY does the amount of calcium released by the sarcoplasmic reticuli
affect the strength of muscle contractions?

Answer 24

The amount of calcium determines the number of active sites that
will be uncovered and thus, the number of myosin heads that can
attach to actin. The more myosin heads that attach, the stronger
the contraction.

Question 25

Muscle Tone can be described as a ________________ contraction
because only a _____________ number of motor units are
contracting at any one time.

Answer 25

Muscle Tone can be described as a partial contraction
because only a limited number of motor units are contracting at
any one time.

Question 26

What term describes the type of contraction that Muscle Tone is?

Answer 26

Isometric contraction.

Question 27

Can the Sliding Filament Theory be used to explain Muscle Tone?

Answer 27

No, because actin doesn’t slide in a Muscle Tone contraction.

Question 28

What is happening in Muscle Tone?

Answer 28

There is an increase in tension (the ‘tone’) in the muscle
because myosin heads attach to actin. (Myosin heads do NOT swing
and pull on actin however—so actin doesn’t slide).

Question 29

e. Can a Muscle Tone contraction be used to move your arms and legs?

Answer 29

e. No, Muscle Tone contractions can’t move arms or legs.

Question 30

f. What two things are Muscle Tone contractions used for?

Answer 30

f. Muscle Tone contractions: 1) Keep postural muscles taunt/tight
to keep head upright, torso and calf muscles tight
2) Are use to hold limbs in position (stabilize them) after they
have already been moved

Question 31

a. There is an energy-production system used in skeletal muscle known as
the Phosphagen System. What is creatine phosphate?

Answer 31

a. Creatine phosphate (CP) is an energy source that is stored in
skeletal muscle to prevent muscle from totally running out of
ATP. Each CP is a “backup energy supply” that is rapidly turned
into 1 ATP when ATP levels are low.

Question 32

b. At what point during physical exercise is creatine phosphate used?

Answer 32

b. At the very beginning of intense, short-term exercise. It
provides energy for the first 15 seconds of exercise.

Question 33

c. Why is creatine phosphate used at this point in physical exercise?

Answer 33

c. It quickly provides energy for contraction while the slower
processes that create energy from food (aerobic and anaerobic
metabolism) are not yet producing ATP.

Question 34

59.
a. What is Fatigue?

Answer 34

59. (Fatigue)
    a. The deterioration (decline) of muscle contraction, leading to the
    total loss of the muscle’s ability to contract.

Question 35

b. What are the main causes of Fatigue?

Answer 35

b. Insufficient energy (ATP) production, often due to lack of oxygen
and lack of sugar in the muscle.

Question 36

c. What specifically happens in the muscle when Fatigue occurs?

Answer 36

c. Without ATP, the sarcoplasmic reticulum is unable to store
calcium. Calcium leaks out of the SR, causing myosin to attach
to actin, producing tetanus. Eventually, collapse of the
contraction occurs. The tetanus that occurs with fatigue is seen
in rigor mortis, when muscles stiffen a few hours after death.

Question 37

d. How are cramps or contractures related to Fatigue?

Answer 37

d. Contractures are a type of cramping in muscle that is the start
of fatigue, a temporary state of tetanus that often occurs in the
hands (as with Writer’s Cramp).

Question 38

a. How much ATP is created from 1 glucose by this method?

Answer 38

Aerobic metabolism creates 36 ATP from each molecule of glucose.
*Other foods besides sugar, like protein and fat, are also turned
into ATP using the aerobic process.

Question 39

60. There are two methods the body uses to make energy (ATP) from
    food sources. The method called aerobic metabolism creates the
    most energy from food of the two methods.

Question 40

b. What makes this process so good at producing energy?

Answer 40

b. The use of oxygen allows the greatest amount of energy to be
made from foods. The word “aerobic” means that oxygen is used.

Question 41

c. What type of skeletal muscle cells are best at producing energy, and
thus, use this method?

Answer 41

c. Slow twitch or slow oxidative cells

Question 42

d. What does this mean about how long these cells can contract before
fatiguing (tiring out)?

Answer 42

d. Able to contract for long periods of time (fatigue-resistant).

Question 43

e. What special molecule do these cells contain and how does it help in
the energy-making process?

Answer 43

e. Slow twitch cells contain myoglobin, a molecule that allows them
to store oxygen. It is also is responsible for the dark color of
the cells (which we call “dark meat” in chicken or turkey).

Question 44

a. What is the alternate method of producing energy?

Answer 44

a. Anaerobic metabolism (or fermentation).

Question 45

b. Why is it less efficient at making energy?

Answer 45

b. It is less efficient at making energy from food because it
does not use oxygen.

Question 46

c. What are the major drawbacks to a muscle cell using this method?

Answer 46

c. Only a limited amount of energy is produced, 2 ATP per glucose.
This only allows the cell to contract for brief periods of time
before tiring out. Anaerobic metabolism also produces lactic
acid which contributes to the poor ability to make ATP and
creates a burning, painful sensation in muscle.

Question 47

d. What one advantage does it have over aerobic metabolism?

Answer 47

d. The process of producing ATP by anaerobic respiration is 2 ½
times faster than producing it by aerobic respiration. Thus, it
is a process that provides energy for muscle contraction during
the first minute of any type of exercise. It also is the process
used during on and off bursts of exercise like tennis, soccer, or
a short swim.

Question 48

e. What type of skeletal muscle cells use this method?

Answer 48

e. Fast twitch or fast glycolytic.

Question 49

f. Even though these cells are not designed for endurance, what are
they designed for?

Answer 49

f. Quick, powerful contractions that give speed in a short activity
like sprinting and weight lifting.

Question 50

g. In some people endurance training can cause fast twitch to turn into
intermediate fibers. What does this mean happens to these fibers?

Answer 50

g. When fast twitch turn into intermediate fibers, they have the
endurance of slow twitch fibers. This means the intermediate
fiber is a type of fast twitch that is not only good for speed
but also for endurance (doesn’t tire out quickly).