Three Types of Muscle Tissue

Skeletal

Cardiac

Smooth

SKELETAL MUSCLE

Attached to bone, skin or fascia

Striated (light and dark bands visible)

Voluntary control of contraction and relaxation

Cardiac Muscle

-Striated in appearance

-Involuntary control

- Autorhythmic because of built in pacemaker

Anatomy of Cardiac Muscle

- Striated, branching fibers

- Single centrally located nucleus

- Cells are connected by intercalated discs with gap junctions

- Same arrangement of thick and thin filaments as skeletal.

Smooth Muscle

- Attached to hair follicles in skin

- In walls of hollow organs: blood vessels & GI

- Nonstriated in appearance (looks smooth)

- Involuntary

Anatomy of Smooth Muscle

- Lacks sarcomeres bc lacking orderly arranged thick and thin filaments.

- Sliding of the thick and thing filaments creates tension.

- Transferred to intermediate filaments & dense bodies attached to sarcolemma

- Muscle fiber contracts and twists into a helix as it shortens, and relaxes by untwisting.

Regeneration of Muscle

- SKELETAL muscle cannot divide after 1st year: growth is enlargement of existing cells.

- For repair: satellite cells and bone marrow produce some new cells, but if not enough, fibrosis occurs most often.

- CARDIAC muscle cannot divide or regenerate

- For repair: all is done by fibrosis (scar formation)

- SMOOTH muscle are able to regenerate

- Cells can grow in size (hypertrophy)

- Some cells (uterus) can divide (hyperplasia)

- new fibers can form in walls of BVs called pericytes

Functions of Muscle Tissue

- Producing Body movements

- Movement and storage of substances within the body

- Maintenance of body position

- Producing heat

Properties of Muscle Tissue

- Excitability

- Contractility

- Extensibility

- Elasticity

Skeletal Muscle's CT Coverings

- Epimysium

- Perimysium

- Endomysium

Dense fascia is dense irregular CT around muscle

- Epimysium: surrounds the whole muscle

- Perimysium: surrounds bundles (fascicles) of 10-100 muscle cells

- Endomysium: separates individual muscle cells

Muscle Cells

Sarcolemma

Sarcoplasm

Muscle Cells are long, cylindrical, & multinucleated

Sarcolemma is the muscle cell membrane

Sarcoplasm is filled with tiny threads called myofibrils & myoglobin (red-colored, O2 binding protein)

Myofibrils & Myofilaments

- Muscle fibers are filled with threads called myofibrils separated by SR (sarcoplasmic reticulum).

- Myofilaments (thick and thin filaments) are the contractile proteins of muscle.

Sarcoplasmic Reticulum (SR)

- System of tubular sacs similar to smooth ER in nonmuscle cells

- Stores Ca+2 in a relaxed muscle

- Release of Ca+2 triggers muscle contraction

Transverse Tubules

T (transverse) tubules are invaginations of the sarcolemma into the center of the cell.

- filled with the extracellular fluid

- carry muscle action potentials down into cell

(Note: mitochondria lie in rows throughout the cell; near the muscle proteins that use ATP during contractions).

Development of Skeletal Muscles

- Every mature muscle cell developed from 100 myoblasts that fused together in the fetus.

- Cannot divide

- Satellite cells retain the abillity to regenerate new cells.

Filaments and the Sarcomere

- Thick (MYOSIN) and Thin (ACTIN) filaments overlap each other in pattern that creates striations

- They are arranged in compartments called sarcomeres, separated by Z discs.

- Myosin cross bridges pull the thin actin filaments toward the center of the sarcomere, which shortens the muscle fiber.

- This event requires the release of calcium ions from the SR into the the cytosol and energy ATP from the mitochondria.

Sarcomere

A Band: Anistropic band is rich in thick filaments, Myosin & other proteins.

I Band: Isotropic band is poor in thick filaments, contains numerous thin filaments, actin.

H Band: Helle Zone is myosin-bare zone

M Line: middle of H band

Z disk: marks ends of sarcomere

Sliding Filament Mechanism of Contraction

- Myosin cross bridges pull on thin filaments

- Thin filaments slide inward

- Z discs come toward each other

- Sarcomeres shorten --> Muscle fiber shortens --> Muscle shortens.

- Thick and thin filaments do not change in length.

Nerve and Blood Supply

Each skeletal muscle is supplied by a nerve, artery and vein.

Each motor neuron supplies muscle cells (neuromuscular junction)

- Nerve fibers and capillaries are found in the endomysium between individual cells.

- More number of neurons means you have moree control in those muscles. Hand muscles vs Back Muscles.

Structures of the Neuromuscular Junction Region

- Synaptic end bulbs contain vesicles filled with ACh

- Motor end plate membrane contains 30 million ACh receptors

Variations in Skeletal Muscle Fibers

- Myoglobin, MitC, and Capillaries

- RED muscle fibers have more myoglobin which is an O2 storing reddish pigment, and have more capillaires and MitC.

- WHITE muscle fibers have less myoglobin, and less capillaries.

- Contraction and relaxation speeds vary (how fast myosin ATPase hydrolyzes ATP).

- Resistance to fatigue (different metabolic rxns used to generate ATP).

Red Slow Twitch

- RED in colors (lots/abundant amounts of of MitC, Myoglobin, & BVs.)

- Small/thin muscle fibers and least powerful muscle type

- Prolonged, sustained contractions for maintaining posture.

- Use ATP at a slow rate.

- Produce slow, weak, but long lasting contracions that are essential for postural muscles of the back.

WHITE FAST TWITCH

- White, little myoglobin and few BVs

- Large/thick muscle fibers, most powerful but short contractions

- Contractions last for short duration;

used for weight-lifting, found in the muscles of the upper limbs.

- Split ATP fast but fatigue quickly

Intermediate Fast Twitch

- Intermediate in thickness; gives strength of contraction

- RED, moderate amounts of mitc, myo, and bvs.

- Good source of energy, and ability to split ATP at fast rate, used for walking and sprinting.

- Contract quickly with more power than red fibers but contain moderate amounts of myoglobin so are somewhat fatigue resistant

dominant in lower limbs for posture, endurance and acceleration

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Atrophy

Hypertropy

Atrophy is the wasitng away of muscles and caused by the disuse (disuse atrophy) or severing of the nerve supply (denervation atrophy)

Hypertrophy is the increase in the diameter of muscle fibers. Results from very forceful, repetitive muscular activity and an increase in myofibrils, SR & mitC.

Rigor Mortis

- Muscular rigidity that begins 3-4 hours after death and lasts about 24 hours.

- After death, Ca2+ ions leak out of the SR and allow myosin heads to bind to actin.

- Since ATP synthesis has ceased crossbridges cannot detach from actin proteolytic enzymes begin to digest the decomposing cells.