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