Physio Lecture 10 Questions (Exam 2)

Front 1

What is atrophy?

Back 1

Loss of muscle mass.

Front 2

How is the muscle structure changed?

Back 2

There is a
breakdown of actin and myosin

Front 3

What causes atrophy?

Back 3

Atrophy results when the muscle fibers do not receive neuronal stimulation.

Front 4

What is hypertrophy?

Back 4

Increase in muscle mass

Front 5

How is the muscle structure changed?

Back 5

More actin and myosin filaments are created within the muscle fiber.

Front 6

What causes hypertrophy?

Back 6

Excessive neuronal stimulation, as occurs with extensive muscular activity.

Front 7

What effect does aging have on muscle mass past middle age?

Back 7

Past middle age - mass slowly
decreases, this is due to a gradual loss of neurons -> gradual loss of activation by ACh. And muscle loss is replaced by fibrous tissue and adipose tissue.

Front 8

What is the effect of Botulinum toxin (Botox) on the NMJ?

Back 8

It prevents the exocytosis (release) of ACh.

Front 9

What does Black Widow venom do?

Back 9

Causes an explosive release of ACh

Front 10

How does Curare (IntocostrinTm) work?

Back 10

It is an antagonist and binds to ACh receptors, so blocks the
activity of ACh.

Front 11

What is a motor unit?

Back 11

Any somatic motor neuron and all of the muscle fibers innervated by it.

Front 12

If a motor neuron reaches threshold do all of the fibers it innervates form action potentials?

Back 12

yes

Front 13

Do all the fibers in a motor unit fire in unison?

Back 13

yes

Front 14

Does a muscle have > 1 motor unit?

Back 14

yes

Front 15

Are all the motor units in a muscle the same size?

Back 15

no

Front 16

Do all the motor units in a muscle have the same threshold?

Back 16

no

Front 17

Is there a relationship between motor unit size and threshold?

Back 17

Yes, small motor units have lower
thresholds than larger motor units.

Front 18

Is there a relationship between motor unit size and function?

Back 18

Yes, small motor units give you a fine degree of control i.e. your hands have many small motor units to control the fine moments of the hand.

Front 19

Does activating different #s of motor units give different levels of contraction strength?

Back 19

Yes, this is referred to as recruitment (just like with neurons).

Front 20

How is it determined by you how many motor units should be activated?

Back 20

The brain estimates
how many motor units you will need… more and more are activated until you get the desired effect.

Front 21

What part of your brain do you use to activate motor units?

Back 21

Motor cortex - the precentral
gyrus.

Front 22

Can different fibers within a single motor unit be activated independently (asynchronously)?

Back 22

no

Front 23

Can different motor units within a single muscle be activated independently?

Back 23

yes

Front 24

What is the difference between isotonic and isometric contractions?

Back 24

In isotonic contraction, the
force/tension remains the same as the muscle shortens in length. In isometric contraction, there is no shortening, but more and more force/tension is generated.

Front 25

Why is the lag time between stimulus and actual muscle shortening greater when lifting a rock than when lifting a feather?

Back 25

In both, there is an equal lag time in which the series elastic
components need to be "tightened", however, when lifting the rock, more force/tension (isometric
contraction) needs to be produced to be able to lift the rock before the isotonic contractions (shortening) will occur.

Front 26

Can muscle cells generate ATP via aerobic and/or anaerobic metabolism?

Back 26

both

Front 27

Which is a more efficient use of fuel?

Back 27

Aerobic, uses oxidative phosphorylation pathway and can generate ~36-38 ATP molecules/ glucose.

Front 28

Which generates ATP faster?

Back 28

Anaerobic, which is the process
of glycolysis, will quickly generate 2 net ATP without O2.)

Front 29

Under what circumstances does a muscle use anaerobic metabolism and can it continue after its glycogen stores are used up?

Back 29

Anaerobic metabolism actually includes two different processes; glycolysis and fermentation. Anaerobic metabolism is used in the first 45 to 90 seconds of moderate to heavy exercise, because
with these levels of exercise even the amount of oxygen stored in myoglobin is not enough to convert all the pyruvate to ATP (so you are producing ATP from glycolysis and converting lactic acid to pyruvate which is sent back to the liver via the bloodstream). Anaerobic metabolism also occurs when you are at about 60% of the total maximum oxygen uptake, in other
words when a person reaches their “lactate threshold” (our definition of heavy exercise).
Anaerobic metabolism can continue after glycogen is used up because the lactic acid (lactate) being sent back to the liver will be converted to glucose and sent back to the tissues to be used in
glycolysis.
Furthermore, most muscles are made up of a combination of fast glycolytic, fast oxidative and slow oxidative fiber types (note that in a motor unit, all the muscle fibers will only be one type). It is not unusual for the fast glycolytic fibers to be activated/recruited first in light exercise (recall that these use primarily glycolysis and fatigue quickly) then as exercise proceeds in duration and
intensity, you will activate the fast oxidative and finally the slow oxidative fibers. As these later fiber types use up their glycogen stores, lactate will be produced by them and fermentation will also occur.

Front 30

What is the role of creatine-P in muscle metabolism?

Back 30

It is a fast way to create new ATP molecules from ADP, in which the phosphate group from creatine-P is transferred directely to the ADP molecule.

Front 31

What are some of the suspected causes of muscle fatigue?

Back 31

1. An increase in extracellular
potassium.
2. A change in the membrane potential which decreases the amount of Ca++ released from the SR.
3. Depletion of ACh at the neuromuscular junction.
4. CNS control - the brain decides that it is time to quit using the muscles, before all ATP is consumed.

Front 32

Are all the fibers within a muscle alike?

Back 32

no

Front 33

What are the three types of fibers?

Back 33

Slow twitch (Type I) AKA Slow oxidative
fast-twitch (Type IIA) AKA fast oxidative
(Type IIX) AKA fast glycolytic.

Front 34

What is the main difference between fast and slow fibers?

Back 34

Resistance to fatigue and
method of ATP production.

Front 35

What are the differences between the two types of fast fibers?

Back 35

Type IIA (fast oxidative) uses oxidative phosphorylation pathway and appear very white to pinkish in color. Type IIX (fast glycolytic) uses glycolysis and appears VERY white in color.

Front 36

Why does one fiber appear red and the other white?

Back 36

The red (or pinkish) color is due the myoglobin in the fibers, that is a pigment, like hemoglobin, and stores oxygen for fibers to use in the oxidative phosphorylation pathway. The Type IIX rarely uses the oxidative phosphorylation pathway, and therefore contains virtually no myoglobin, thus giving it the white appearance.

Front 37

Which fiber type fatigues the fastest?

Back 37

The fast-twitch, with Type IIX fatiguing the fastest

Front 38

Which fiber type can generate ATP the fastest?

Back 38

The Type IIX fibers.

Front 39

What is the relationship between
predominant fiber type in a muscle and its function?

Back 39

Slow twitch is for endurance, fast twitch is for a lot of force quickly.

Front 40

Can a single motor unit have > 1 fiber type?

Back 40

No - all the fibers of a particular motor unit are believed to be composed of the same fiber type.

Front 41

What 9 variables can you think of that can affect skeletal muscle contraction?

Back 41

1. # of motor units
2. Frequency of stimulation
3. Length of muscle at beginning of contraction
4. Use of muscle - state of atropy
5. Age
6. Weight of load
7. Size of muscle
8. State of fatigue
9. Motor neuron damage.

Front 42

Atrophy

Back 42

Muscles that are not innervated by neurons loose muscle mass, this is due to the break down of actin and myosin

Front 43

Hypertrophy

Back 43

An increased amount of neural stimulation will cause an increase in the size of the cells by creating more myofibrils (actin and myosin) within the cells

Front 44

Hyperplasia

Back 44

An increase in the actual number of muscle cells (a general term for division of cells in any tissue) – not generally a normal condition for adult muscles as the cell # increases (cancers throughout the cell)

Front 45

Series Elastic Components

Back 45

Tendons and connective tissue are elastic and absorb tension as muscle contracts, they recoil as muscle relaxes and spring back to resting length, elasticity brings muscle back to resting & normal length

Front 46

Recruitment

Back 46

Using multiple fibers to create a desired strength, Brain estimated number of motor units required and stimulates them to contract, it keeps recruiting more units until desired movement is accomplished in smooth fasion, more and larger motor units activated to produce greater strength

Front 47

Summation

Back 47

If the second stimulus occurs before muscles relaxes from the first then the second twitch will be greater

Front 48

Twitch

Back 48

A single rapid contraction and relaxation of muscle fibers

Front 49

Tetanus

Back 49

If frequency is so fast that no relaxation occurs then a smooth sustained contraction results, this is the normal way a muscle works

Front 50

Isometric Contraction

Back 50

A muscle contraction in which the development of tension occurs at constant muscle length, the exerted force does not cause load to move and length of fibers remains constant

Front 51

Isotonic Contraction

Back 51

A muscle contraction in which muscle tension remains constant as the muscle fiber changes length, force remain constant throughout shortening process

Front 52

Motor Unit

Back 52

One motor neuron plus all the muscle fibers it innervates, when a motor neuron is activated – all muscle fibers in its motor unit contract, # of muscle fibers in motor unit varies according to degree of fine control capability of the muslce

Front 53

Length-Tension Relationship

Back 53

The relationship between the length of a muscle fiber at the onset of contraction and the tension of the fiber can achieve on a subsequent tetanic contraction

Front 54

V02 Max

Back 54

Maximum oxygen uptake (aerobic capacity) is maximum rate of oxygen consumption determined by age, gender, and size

Front 55

Lactate Threshold

Back 55

Is the % of max O2 uptake at which there is significant rise in blood lactate levels, when lactic acid appear in blood stream = lactate threshold

Front 56

Oxygen Debt

Back 56

When exercise stops, rate of oxygen uptake does not immediately return to pre-exercise levels as all oxygen debt accumulated during exercise, all oxygen is taken from myoglobin and hemoglobin and after exercise oxygen needs to be refilled into myoglobin so heavy breathing continues until debt is replenished

Front 57

Phosphocreatine/Creatine

Back 57

During exercise, creatine is turned into phosphocreatine which can be used to make ATP from ADP (ADP + Pi) since not enough regular phosphatecan be produced to be used for ATP, source of high energy Ps to regenerate ATP from ADP

Front 58

Slow Twitch/Type I/Slow Oxidative

Back 58

Adaptive fibers to contract slowly without fatiguing, uses mostly aerobic respiration, has rich capillary supply, many mitochondria, and aerobic enzymes, has lots of myoglobin (O2 storage molecule), red color fiber, small motor neurons with small motor units

Front 59

Fast Twitch/Type IIA/Fast Oxidative

Back 59

Adapted to contract fast using aerobic metabolism, intermediate between Type I and Type IIX, have large motor neurons with large motor units, found in large muscles such as legs

Front 60

Fast Twitch/Type IIX/Fast Glycolytic

Back 60

Adapted to contract fast using anaerobic metabolism, has large stores of glycogen, few capillaries, few mitochondria, little myoglobin,

Front 61

Myoglobin

Back 61

O2 storage molecule, four per one hemoglobin

Front 62

Fatigue

Back 62

Inability to maintain muscle tension at a given level despite sustained stimulation, competition for available ATP becomes limited, brain is less able to activate muscles (central fatigue), exercise induced reduction in ability of muscle to generate force

Front 63

CPK – Creatine Phosphokinase

Back 63

Enzyme that converts creatine to phosphocreatine

Front 64

Curare

Back 64

Binds to Ach receptor site instead of the actual Ach (bind of ach allows channel to open for Na/K to initiate AP) which does not activate them (used in surgeries involving hands to prevent random contractions)

Front 65

Botox

Back 65

Ach doesn’t get exocytosized/exited into cleft so calcium isn’t released and muscles don’t contract

Front 66

Black Widows Venom

Back 66

Ach is released to cause muscles to contract but ACH is explosively exocytosized so muscles aren’t allowed to relax and they stay contracted and this spreads throughout entire body