Muscle Tissue

Types (of muscle tissue): Skeletal –Attached to bone, moves skeleton –striated – alternating light & dark bands –Voluntary –Limited capacity for regeneration Cardiac –Only in heart –Striated –Involuntary –Cannot regenerate Smooth –Wall of internal structures –Non-striated –Involuntary –regenerates

Functions (of muscle tissue): Produce body movement Stabilize body positions Regulate organ volume Move substances w/in body Produce heat

Characteristics (of muscle tissue): Excitability: –Ability of muscle tissue (& nerve tissue) to receive & respond to stimuli by producing electrical signals (action potential) Contractility: –Ability of muscle tissue to contract (shorten & thicken) when stimulated by action potential Extensibility: –Ability of muscle tissue to stretch (extend) w/out being damaged Elasticity: –Ability of muscle tissue to return to its original shape after contraction or extension

Muscle cells are called muscle fibers because of their elongated shape Fascia: sheet or broad band of fibrous connective tissue –2 types: Superficial fascia (subcutaneous layer) –Immediately under skin –Composed of areolar CT & adipose Deep fascia –Composed of dense irregular –Holds muscles together & separates them into functional grps

CT that extend from deep fascia: Epimysium: –Wraps entire muscle Perimysium: –Covers bundles of muscle fibers called fascicles Endomysium: –Wraps each individual muscle fiber All 3 extend beyond muscle as a tendon which attaches muscle to bone

Muscle fiber/cell: Sarcolemma –Plasma membrane Transverse tubules(T-tubules) –Tunnel-like extensions of sarcolemma, pass through muscle fiber from side to side Sarcoplasm –Muscle fiber’s cytoplasm, contains many mitochondria Sarcoplasmic reticulum –Network of membrane enclosed tubules, stores calcium ions needed for muscle contraction

Myoglobin –Reddish pigment similar to hemoglobin in blood; stores oxygen needed by mitochondria to generate ATP Myofibrils –Cylindrical structures that extend along entire length of muscle fiber –Each myofibril consists of 2 types of protein filaments Thin filaments= actin Thick filaments= myosin

Filaments over lap in specific patterns & form compartments called sarcomeres –Basic functional unit of striated muscle fibers

Sarcomeres: Z discs: –Zig zagging zones of dense material A band: –Darker area extends entire length of thick filaments (myosin) H zone: –Center of A band containing only thick filaments I band: –Lighter area composed of thin filaments (actin) –Extends into 2 sarcomeres, divided in half by Z disc

Alternating A bands and I bands give striated appearance

Sliding filament mechanisms: Myosin heads of thick filaments pull on thin filaments (actin) Causing them to slide toward the center of sarcomere Max contraction: I bands and H zones disappear Both calcium ions & energy (ATP) are needed for muscle contraction

Types of skeletal muscle fibers: Slow oxidative (SO fibers)Type I: –Small in diameter –Dark red (dark meat); large amount of myoglobin –Generate ATP by aerobic cellular respiration –Contraction cycle proceeds at a slower pace –Resistant to fatigue, capable of prolonged sustained contractions

Type II a Fast oxidative-glycolytic (FOG) fibers: –Intermediate in diameter –Dark red (dark meat); large amt of myoglobin –Can generate ATP by aerobic respiration –Glycogen content is high; can also generate ATP by glycolysis –“fast”; they can contract & relax more quickly than SO fibers

Type II b Fast glycolytic (FG) fibers: –Largest in diameter –Contain most myofibrils –Generate the most powerful & most rapid contractions –Low myoglobin content (white meat); few mitochondria –Contain large amts of glycogen & generate ATP by glycolysis –Used for intense movements of short duration –Fatigue quickly –Strength training programs requiring great strength for short period produce increase in size, strength & glycogen content of FG fibers

Believed that we all have all types of fibers Genetically some of us may have more of one type then the other Training can help develop which ever fibers

Muscular atrophy: wasting away of muscles –Disuse atrophy: Bedridden/cast –Denervation atrophy: Nerve impulse ceases in motor neuron 6 months-2yrs =muscle fibers replaced by fibrous CT; when complete can’t reverse Spinal cord injury