anatomy -- ch. 10
thin filaments
- actin protein (8 nm diameter)
H band
- area within A band with only thick filaments
myosin head
- binds ATP and actin
what is myoglobin?
- binds O2 that diffuses into muscle fiber
myofibrils
- contractile organelles in skeletal muscle fibers - thread-like structures within sarcoplasm - extend the entire length of muscle fiber - striation in myofibrils is source of muscle fiber striation
what is sarcoplasm?
- cytoplasm of muscle fibers
A band
- darker middle part of sarcomere - entire length of thick filaments
Z discs
- dense protein separating sarcomeres - passes through center of I band
microscopic anatomy of skeletal muscle fiber
- diameter: 10 to 100 nanometers - length: 10 cm (4 inches) - multinucleated due to fusion of myoblasts during development - mature muscle fibers (myocytes) do not undergo cell division
what is terminal cisterns?
- dilated end sacs found on both sides of a T tubule
nerve and blood supply
- each skeletal muscle penetrated by a nerve, artery, 1-2 veins - somatic motor neurons axons extend from brain or spinal cord to group of muscle fibers - each muscle fibers is close to 1+ blood capillaries - active muscle fibers require oxygen, glucose, fatty acids - blood removes heat and metabolic waste products
muscular tissue properties
- electrical excitability - contractility - extensibility - elasticity
3 layers of connective tissue
- epimysium - perimysium - endomysium
sarcoplasmic reticulum
- fluid filled membranous sacs surrounding each myofibril - stores Ca2+ in resting muscle fiber - release of Ca2+ triggers muscle contraction - terminal cisterns - triad
what is a triad?
- formation of T tubules on either side of terminal cistern
sarcomere
- functional unit of myofibril - A band - H band - M line - Z discs - I band
endomysium
- inner layer - separates individual muscle fibers - mostly reticular fibers
connective tissue components of muscle
- lines body wall and limbs - supports and surrounds muscles and organs - holds muscles with similar functions together - carries nerves, blood vessels, and lymphatic vessels
sarcoplasm
- lots of glycogen, used in ATP synthesis - myoglobin - mitochondria
what is glycogen?
- macromolecule made of glucose
Myosin: contractile muscle protein
- main component of thick filaments - motor protein in all 3 types of muscle tissue - converts ATP chemical energy into mechanical energy - myosin tail - myosin head - ATP binding site hydrolyzes ATP to generate energy
more connective tissue components of muscle
- may extend to form tendons to attach muscle to bone - may extend as flat sheets (aponeuroses)
perimysium
- middle layer - surrounds muscle fascicles (bundles of 10-100+ muscle fibers) - dense irregular connective tissue
M line
- midline - proteins hold thick filaments together at center of H band
muscular tissue function?
- movement: through interaction of skeletal muscles, bones, and joints - posture: stabilize body positions - storage: cardiac muscle contractions - thermogenesis: generation of heat
thick filaments
- myosin protein (16 nm diameter)
epimysium
- outer layer - encircles entire muscle - dense irregular connective tissue
sarcolemma
- plasma membrane of muscle fibers (cells) - nuclei are located next to sarcolemma - transverse tubules - filled with interstitial fluid - allows fast spread of action potential along sarcolemma throughout fiber
what is mitochondria?
- produce ATP to provide energy for muscle fibers
I band
- remaining thin filaments, no thick filaments
sarcomeres
- smaller component of myofilaments
myofilaments
- smaller filaments within myofibrils - muscle contraction occurs as filaments slide past each other - do not extend whole length of myofibril - thin filaments - thick filaments
transverse tubules (T tubules)
- tunnels of sarcolemma toward center of muscle fibers
contractility
ability to contract when stimulated by nerve impulse
electrical excitability
ability to produce muscle action impulses in response to certain stimuli (chemical stimuli, autorythmic response to electrical signals)
elasticity
ability to return to original length and shape after contraction or extension
extensibility
ability to stretch without being damaged
fascia
dense sheet of irregular connective tissue
myosin tail
points toward the M line in center of sarcomere
sphincters
rings of smooth muscles at exit of hollow organs