general muscular

8/8/2019 General Muscular

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Over 600 skeletal muscles function for body movement through

contraction and relaxation of voluntary, striated muscle fibers.

These muscles are attached to bones, and are typically underconscious control for locomotion, facial expressions, posture, and

other body movements.



Muscles account for almost 40% of the body¶s weight. The

metabolism that occurs in this large mass produces heat

essential for the maintenance of body temperature.

Do you think Marge is

hot? Uh ± never mind.



Cardiac muscle is found only in the heart and makes up the atria

and ventricles. Like skeletal muscle, cardiac muscle contains

striated fibers. Cardiac muscle is called involuntary musclebecause conscious thought does not control its contractions.

Specialized cardiac muscle cells maintain a consistent heart rate.

Notice in the picture to

the left: the Z band is

made of a thin filament

(actin) and the A band is

made of a thick filament

(myosin). Overlap of

thick & thin filaments

gives cardiac muscle its

characteristic striations.



Cells of the heart can be separated with an enzyme called

trypsin. The individual cell is called a myocyte (myo ± means

muscle). A single cell beats when a series of channelproteins opens and closes.

As long as the cells do NOT touch one another

they beat independently; some fast and some

slow. BUT, if they are allowed contact within 2-3

days they form gap junctions between each other(joining their cytoplasm) and the cells begin to

beat as one. If an adult¶s cells do not beat as one,

an arrythmia (uneven heart beat) will occur.

Pacemakers (electronic) are sometimes used for

this problem.



Smooth muscle is found throughout the body, including in

visceral (internal) organs, blood vessels, and glands. Like

cardiac muscle, smooth muscle is involuntary. Unlike skeletaland cardiac muscle, smooth muscle is nonstriated (not banded).

Smooth muscle, which is extensively within the walls of digestive

tract organs, causes peristalsis (wave-like contractions) that aids

in food digestion and transport.



Except the heart, any action that the body performs without

conscious thought is done by smooth muscle contractions. This

includes activities such as constricting (closing) the bronchioles(air passages) of the lungs or pupils of the eye or causing

goosebumps in cold conditions.



The epimysium surrounds a group of fascicles. The perimysium

surrounds an individual fascicle. The endomysium surrounds

& separates the individual muscle fibers that make up the

fascicle.



A skeletal muscle has regular, ordered groups of fascicles,

muscle fibers, myofibrils, and myofilaments.

Muscle Structure - nice animation of parts

As you can see a muscle fiber divides into smaller and smaller

parts. Within the fiber is the myofibril, these are subdivided

into myofilaments.Myofilaments are made of actin andmyosin and are responsible for the striations you see.

This is a single myofibril dissected from a muscle fiber.

(1micrometer)



The actin and myosin myofilaments align evenly, producing

dark and light bands on the myofibril. Each dark band

depicts an area where the myofilaments overlap, causing thestriated appearance of skeletal muscles.

Using a special stain the banding is evident.

All dark and light bands of the myofilaments have names.



At the Z line, actin strands interweave. The region between 2 Z

lines is a sarcomere, the functional unit of skeletal muscle.Muscle contraction occurs when overlapping actin and myosin

myofilaments overlap further and shorten the muscle cell. The

myofilaments keep their length. The overlapping of

myofilaments is the basis for the sliding filament theory of

contraction. (Sliding filament theory will be another unit.)



Skeletal muscle is a system of pairs

that relax and contract to move a

joint. For example, when front leg

muscles contract, the knee extends(straightens) while back leg muscles

relax.Conversely, to flex (bend) the

knee, back leg muscles contract

while front leg muscles relax.



Some muscles are named for their ability to extend or flex a

joint; for example, extensor carpiradialis longus muscle and

flexor digitorum brevis muscle.



Tendons attach most

skeletal muscles to bones.

Tendons are strong sheets

of connective tissue that are

identical with ligaments.

Tendons and ligaments

differ in function only.

Physical exercise

strengthens the attachmentof tendons to bones.



Skeletal muscles have muscle tone (remain partly contracted),

which helps maintain body posture. Ongoing signals from the

nervous system to the muscle cells help maintain tone andreadiness for physical activity.

What Diseases ISMDA Striving to Defeat?

Animated Exercise Instruction forMuscle Toning,Bodybuilding, Fitness, Dieting and Losing Weight



Skeletal muscles have two types of musclefibers: fast-twitch and slow-twitch. Anaerobic

exercise uses fast-twitch fibers. Such exercise

includes activities that are fleeting and require

brief high energy expenditure. Weightlifting,

sprinting, and push-ups are examples of anaerobic exercise. Because all cells require

oxygen to produce energy, anaerobic exercise

depletes oxygen reserves in the muscle cells

very quickly.



Slow twitch muscles contain large numbers of mitochondria (the "powerhouse" of the muscle).

They have high concentrations of the red pigmentcalled myoglobin, which "shuttles" oxygen betweenthe mitochondria and the circulating blood. Slowmuscles also have a highly developed blood supply.

These unique features provide slow twitch muscleswith a high capacity for aerobic metabolism and ahigh resistance to fatigue.

Interestingly, very little is known about how drugsand hormones change the function of slow-twitchmuscles.



Fast-twitch fibers predominantly burn sugar. Slow-twitch

fibers predominantly burn fatty acids.

An average person's total musculature is about 50percent fast-twitch and 50 percent slow-twitch. Athletes

tend to have more of one or the other depending on their

sport. A sprinter will usually have more fast-twitch

muscles while a marathoner may have more slow-twitch.

The type of muscles we have are not changed by

exercise. We are born with them. If we are born with a

slight predominance of fast-twitch muscles then thepower type sports will seem easier to us. And the

reverse is true; people with slightly more slow twitch

muscles gravitate to the endurance sports.



Is it better to do power sports or

endurance sports? Since most of us

have an equal amount of fast- and

slow-twitch fibers, it's good to do

both kinds of sports to keep ALL of our muscles in prime condition.

However, it's the slow-twitch muscles

that use fat for fuel so if losing fat is

your primary concern, do the long

slow endurance sports that require

slow twitch locomotion.



Because all cells require oxygen to produce energy, anaerobic

exercise depletes oxygen reserves in the muscle cells quickly. The

result is an oxygen debt. To repay the debt, you breathe deeply and

quickly. When oxygen is depleted, the body goes to anotherpathway, ³anaerobic respiration.´ This pathway results in lactic

acid. By increasing oxygen intake, the liver cells can convert the

excess lactic acid into glucose, the primary food molecule used in

cellular metabolism.

24-28 ATP are made 2 ATP are made



Aerobic exercise uses slow-twitch muscle fibers. Such

exercise includes activities that are prolonged and

require constant energy. Long distance running and

cycling are examples of aerobic exercise. In aerobic

exercise, the muscle cell requires the same amount of

oxygen that the body supplies. The oxygen debt is

slashed and lactic acid is not formed.

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