Part Six: Muscle Physiology Concepts Flashcards Preview

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Flashcards in Part Six: Muscle Physiology Concepts Deck (50)
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Can a muscle fiber (cell) contract “halfway” or incompletely? 

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


B.What is the name of this concept?

This is known as the ALL OR NONE PRINCIPLE.



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


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.



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

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. 


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?

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.


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?


 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. 


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

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



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

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



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.

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



Motor Unit Summation is also called ______________. 


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



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

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



page 17 graph


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


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



What is this concept known as?

The Treppe Effect.


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

 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 


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

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.



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

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.


How is Wave Summation created in a muscle?

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.



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

Complete Tetanus)


How is Complete Tetanus created in a muscle?

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.



What specifically happens in muscle cells that causes Complete 

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.



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

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.


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


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


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


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



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

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.



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

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



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

Isometric contraction.


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

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


What is happening in Muscle Tone? 

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).



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

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


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


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



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

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. 


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

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


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


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.



a. What is Fatigue?

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



b. What are the main causes of Fatigue?


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



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

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. 


d. How are cramps or contractures related to Fatigue?


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).


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

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.



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.


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


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


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


c. Slow twitch or slow oxidative cells


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


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


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

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).



a. What is the alternate method of producing energy?

a. Anaerobic metabolism (or fermentation).



b. Why is it less efficient at making energy?

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


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

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.



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

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.



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


e. Fast twitch or fast glycolytic.


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

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


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


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).