Module 7: Muscle Physiology Set 2

What is muscle tension

force exerted by a muscle

What is the opposing force called

the load

What is isometric contraction

muscle contracts but doesn't shorten

Isotonic contraction

muscle contracts and shortens

Concentric contraction

muscle contracts and shortens

What happens in concentric contraction

force exceeds load

What happens in eccentric contraction

load exceeds force

Eccentric contraction

muscle contracts but lengths

Can isometric contraction move a load

no because the muscle contracts but doesn't shorten

Can isotonic contraction move a load

yep bc the muscle contracts and shortens which creates the force needed

How many nerves does a muscle have

1 (but each nerve has multiple neurons)

What does each neuron innervate with

multiple myofibers of a given muscle

What determines how many myofibers are activated

which neurons send APs

An increase in # of myofibers activated...

increases force of contraction

What causes you to shake during a strong forcible contraction

motor units oscillating to reduce fatigue

Subthreshold stimulus

stimulus sent to muscle but no observable contraction

Threshold stimulus

stimulus sent to muscle and results in observable contraction

Maximal stimulus

all motor units recruited resulting in maximal tension

Muscle twitch

a motor units response to a single AP

What are the 3 phases of a muscle twitch

latent period, period of contraction, relaxation

What does an increase in frequency of APs casues

an increase in twitches

Wave summation

muscle tension increases due to increased stimulus frequency

Unfused tetanus

sustained but "quivering" contraction

What happens between stimuli in unfused tetanus

result of partial relaxation in between stimuli

What happens between stimuli in fused tetanus

result of no relaxation between stimulus

Fused tetanus

maximal tension sustained

What happens in a single stimulus

a single stimuli is delivered and the muscle contracts once before relaxing

Are muscles ever fully relaxed

NO! They are ALWAYS slightly contracted

What causes muscles to always be slightly contracted

due to a feedback mechanism that involves stretch receptors

How many twitches are supported by free ATP alone

10

How many twitches are supported by CP alone

70

How many twitches are supported by Glycogen alone in glycolysis

670

How many twitches are supported by glycogen alone in aerobic metabolism

12,000!

What phosphorylates ADP directly to make ATP

creatine phosphate

How many ATP per CP molecule

1

What is the duration of energy that comes from creatine phosphate phosphorylating ADP

15 seconds

What happens in lactic acid fermentation

ATP from glucose via glycolysis produces pyruvic acid and in absence of oxygen pyruvic acid converted to lactic acid

How many ATP comes from one molecule of glucose in lactic acid fermentation

2

What is the duration of energy from lactic acid fermentation

30 seconds

What happens in aerobic respiration

ATP from glucose via glycolysis and aerobic respiration

What is the aerobic respiration cycle aka

TCA/Citric acid cycle

How many ATP are produced from one glucose molecule

28

How much time is given from aerobic respiration

hours

What is the energy source for aerobic respiration

glucose, pyruvic acid, free fatty acids from adipose tissue; amino acids from protein catabolism

What is muscle fatigue

physiological inability to contract in the presence of a stimulus, hence decreased "work"

What is the most likely cause of muscle fatigue

lack of ATP

Physiological contracture

state of fatigue where, due to lack of ATP, neither contraction or relaxation can occur

Rigor

muscle state in which muscles are "locked" in the contracted state

What causes rigor

lack of ATP to operate the Ca2+/ATPase and inability of Ca2+ to be cleared from the sarcoplasm

What is rigor mortis

Ca/ATPase breaks down and Ca2+ leaks from SR occurs in death

EPOC

Excessive post-exercise oxygen consumption

What happens in EPOC

oxygen reserves in myoglobin are depleted and need replenish; glycogen stores also need replenished, ATP and creatine phosphate stores need replenished

What must lactic acid be converted to in EPOC

pyruvic acid

What is involved in muscle contraction force

-number of muscle fibers recruited

-size of muscle fibers

-frequency of stimulation

-degree of muscle stretch (greatest force with slight stretch prior to contraction)

Speed of contraction

how fast myosin ATPase splits ATP

Slow fibers

slow twitch, more fatigue resistant

Fast fibers

fast twitch, fatigues more readily

Oxidative fibers

use aerobic respiration

Glycolytic fibers

use anaerobic respiration

Slow-twitch oxidative muscle fibers

smaller diameter, darker color due to myoglobin, fatigue resistant

Fast-twitch glycolic muscle fibers

larger diameter, pale color, easily fatigued

What is the capillary supply like in fast fibers

scarce

What is the capillary supply like in slow fibers

dense

What is time to peak tension like in fast fibers

rapid

What is time to peak tension like in slow fibers

prolonged

What is the glycolytic enzyme concentration in cytosol like in fast fibers

high

What is the glycolytic enzyme concentration in cytosol like in intermediate fibers

high

What is the glycolytic enzyme concentration in cytosol like in slow fibers

low

What substrates for ATP are used in fast fibers

carbs (anearobic)

What substrates for ATP are used in slow fibers

lipids, carbs, amino acids (aerobic)

What substrates for ATP are used for intermediate fibers

primarily carbohydrates (anaerobic)

What's the alt. name for intermediate fibers

Type II-A, fast twitch oxidative

What's the alt. name for slow fibers

Type I, S, red, SO, slow-twitch oxidative

What's the alt. name for fast fibers

Type II-B, white, FF, fast-twitch glycolytic

What is contraction speed of intermediate fibers

fast

What is the color of intermediate fibers

pink

What's the C.T. components of skeletal muscle

epimysium, perimysium, and endomysium

What's the C.T. components of smooth muscle

endomysium

What's the C.T. components of cardiac muscle

endomysium attached to fibrous skeleton of heart

Does smooth muscle have myofibers with sarcomeres

no, but actin and myosin filaments are present throughout; dense bodies anchor actin filaments

How many T-Tubules are in skeletal muscle

Two per sarcomere at the A-I junctions

How many T-Tubules are in cardiac muscle

one per sarcomere at the Z disc (larger in diameter than in skeletal muscle)

How many T-Tubules are in smooth muscle

none, just caveolae

Do cells exhibit individual neuromuscular junctions in skeletal muscle?

yes

Do cells exhibit individual neuromuscular junctions in cardiac muscle?

no

Do cells exhibit individual neuromuscular junctions in smooth muscle?

not in the unitary muscle but in the multi unit muscle

Are there gap junctions in skeletal muscle

no

Are there gap junctions in cardiac muscle

yes at intercalated discs

Are there gap junctions in smooth muscle

yes in unitary muscle

What is the regulation of contraction in skeletal muscle

voluntary via axon terminals of the somatic nervous system

What is the regulation of contraction in smooth muscle

involuntary; autonomic. nerves, hormones, local chemicals, stretch

What is the regulation of contraction in cardiac muscle

involuntary; intrinsic system regulation; also autonomic nervous system controls; hormones; stretch