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
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