Muscle physiology is the study of muscle function. A muscle is a bundle of fibers that contract to

produce heat, posture, and motion, either of internal organs or of the organism itself. Muscle physiology studies the physical, mechanical, and biochemical aspects of muscles in development, fiber structure,

muscle structure, contraction, and strength-building. (1)

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How do skeletal muscles provide

movement, heat, and posture.

Are all of these functions unique

to muscles? Since skeletal muscles are attached to the

bones of the body and they are under

voluntary control. The provide movement of

the joints by contracting, also they prevent

from unwanted movement. To cause the

skeletal muscles to contract, impulses are

transmitted by a nerve signal, called a motor

neuron, which sends the impulse throughout

multiple muscle cells to contract that muscle

to produce movement.

The chemical reactions that cause muscle

contraction generate heat - energy

conversion always generates "useless"

energy; entropy increases (2)

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fiber shortens as contraction occurs. (4)

The characteristics are shared with the nervous

system. The muscle impulse reaches the

sarcoplasmic reticulum, which releases calcium

ions into the sarcoplasm of the muscle

fiber;Calcium binds to troponin, moving

tropomyosin and exposing myosin binding sites on

actin filament; Cross-bridges (linkages) form

between actin and myosin; Actin filaments are

pulled inward by myosin cross-bridges;The muscle

fiber shortens as contraction occurs. (4)

Muscle contractions occur every time we move. The muscle must contract in order to move the bone that it is attached to or to provide resistance against a force. Isometric contractions occur when the muscle contracts but there is no movement. Muscle contractions which result in movement are known as isotonic contractions. There are two types of isotonic muscle contraction �Concentric and Eccentric. Concentric muscle contractions are the most common form of contraction. These occur when the muscle shortens in length in order to make the bone move. These contractions occur when the body is working against gravity. Eccentric contractions are the opposite of concentric contractions. The muscle contracts but increases in length. This type of contraction occurs usually in the direction of gravity, to control a movement. (5)

More muscle

info!

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Myofilament is a term that the chains of (primarily) actin and myosin that pack a

muscle fiber. These are the force generating structures. Although there are still

gaps in what we know of the structure and functional significance of the

myofilament lattice, some of the key proteins includes myosin, actin, troponin,

titin, and nebulin. a myofilament shows several distict bands, each of which has

been given a special letter. The lightest (least electron dense) band is known as the

I band and consists mostly of actin. The wide, dark band, known as the A band, is

composed primarily of myosin. In the center of the I band is an electron dense line,

known as the Z-line. In the middle of the A band is another dense line known as

the M line. (6)

function.

3)Explain how the structure of the

myofilaments is related to their

function.

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In cross section, under very high magnification, both A

and I bands can be seen to be hexagonal networks.

These networks are apparently ordered and fixed at the

M- and Z-lines. In the region where the A and I bands

overlap (sometimes known as the H band) the two

hexagonal networks intermesh so that each myosin

filament is surrounded by six actin filaments. These

networks appear to be anchored to (and through) the

cell membrane in two ways. At the ends of fibrils, special

structures anchor the terminal actin filaments to the

membrane. There also appear to be connections

between the Z and M lines and the cell membrane. (7)

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8)

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5)Explain how the sliding filament theory

allows for the shortening of a muscle fiber.

Sliding filament theory in its simplest

form states that muscle fibers shorten

when actin filaments slide inward on

myosin filaments - pulling the z-lines

closer together. Actin filaments (the

light bands in the diagram above) slide

over myosin filaments (the dark bands)

the H-zone and I-band decrease.

Myosin filaments contain tiny globular

heads, called cross bridges at regular

intervals. These cross bridges attach to

the actin filaments pulling on them to

create movement. Each flexion of a

cross bridge produces only a very

small movement in the actin filament

so many cross bridges throughout the

muscle must flex repeatedly and

rapidly for any measurable movement

to occur. (9)

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6. Compare and contrast the role of Ca++ in

excitation, contraction, and relaxation of a

muscle cell.

An action potential in the muscle cell is what

triggers muscle cell contraction. We have seen

that calcium ions regulate whether or not

contraction can occur. The action of Ca++ and

is generated by for removal and the relaxation

is taken up in 24th plate. A muscle contraction

in response to a single nerve action potential is

called a twitch contraction. A myogram, a

graph of muscle strength (tension) with time.

The latent period is the time required for the

release of Ca2+. The contraction period

represents the time during actual muscle

contraction. The relaxation period is the time

during which Ca2+ are returned to the

sarcoplasmic reticulum by active transport.

10) explain the meaning of unit of

combined cells

Cardiac muscle combines as a syncytium, which is a

unit of combined cells. They are self exciting which

means they don’t need nerve impulses to contract.

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11)What is rigor mortis

Atp binds to the myosin heads releasing it from actin

and making the muscle pliable. If no atp is available,

myosin heads remain stuck to actin and the muscle

becomes stiff. This is the rigidity of rigor mortis

following death. (13)

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13)What are the phases of a twitch contraction? What molecular events occur during each of

these phases.

muscle contraction in response to a single nerve action potential is called a twitch

contraction.

1.The latent period is the time required for the release of Ca2+.

2.The contraction period represents the time during actual muscle contraction.

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12)What are the 4 factors

that influence the

strength of muscle

contractions?

1. The number of muscle

fibers stimulated

2. The relative size of the

fibers

3. Frequency of

stimulation

4. The degree of muscle

strength(14)

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3. The relaxation period is the time during

which Ca2+ are returned to the sarcoplasmic

reticulum by active transport.

4. The refractory period is the time

immediately following a stimulus. This is the

time period when a muscle is contracting and

therefore will not respond to a second

stimulus. Since this is occurring at the same

time as the contraction, it does not appear on

the myogram as a separate event. (15)

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14)How does the treppe effect relate to the warm-up exercises of athletes?

The concept or phenomenon of "Treppe" occurs when a muscle contracts more forcefully after it has contracted a few times than when it first contracts. This is due to the fact that active muscles require decreasing degrees of succeeding stimuli to elicit maximal contractions. Returning to our example of the second set of squats feeling easier than the first, during the first set there was insufficient warm-up, and the second set felt easier because the first set actually served as a warm-up. The phenomenon in which the contraction strength of a muscle increases, due to increased Ca2+ availability and enzyme efficiency during the warm-up. (15)

Muscles of the

face include:

deppresor,

temporalis,

and levators

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