Muscular System Flashcards
Skeletal Muscle
Single, very long, cylindrical, multinucleate cells with striations
Smooth Muscle
Single, fusiform, uninucleate; no striations
Cardiac Muscle
Brancing chains of cells; uninucleate; striations; intercalated discs
What is Neuromuscular Junction
Synaptic connection between terminal end of a motor nerve and a muscle
Neuromuscular Junction Steps
1) Nerve impulse reaches axon terminal of motor neuron
2) Calcium channels open, calcium enters the axon terminal
3) Synaptic vesicles to release the neurotransmitter acetylcholine by exocytosis
4) Acetylcholine diffuses across synaptic cleft and binds to receptors in sacrolemma
5) ACh opens channels that allow simultaneous passage of Na+ into the muscle fiber and K+ out of the muscle fiber. More Na+ ions enter than K+ ion leave, producing a local change in the electrical conditions of the membrane (depolarization). This eventually leads to an action potential
6) The enzyme acetylcholineterase breaks down ACh in synaptic clever, ending the process
Sliding Filament Model
1) ATP is split when myosin head is unattached
2) ADP and P are bound to myosin as cross-bridge forms between the myosin head and actin
3) Upon ADP and P release, power strike occurs; head bends and pulls actin
4) Binding of fresh ATP causes myosin head to return to resting position
Sarcolemma
Plasma membrane in muscle fibers
Sarcoplasm
The cytoplasm of a muscle cell
Sarcoplasmic
reticulum
A specialized smooth endoplasmic reticulum
T tubules
Consists of sarcolemma penetrating into the myocyte interior, allows transmission of the action potential
Myofibrils
A cylindrical bundle of sacromeres within the skeletal muscle cell
Sarcomeres
A functional unit of muscle fiber
Myofilaments: Actin
Thin filaments made of actin,
Myofilaments: Myosin
Thick filaments made of myosin
Endomysium
Connective tissue sheath wrapped around muscle fiber
Perimysium
Fibrous membrane wrapped around fascicles (bundle of muscle fiber)
Epimysium
Connective tissue that covers the muscle
Tendon
Indirectly attaches muscle to bone
Isotonic
Same tension, changing length
Myofilaments slide, muscle shortens and movement occurs
E.g., bending knees, lighting weights
Isometric
Same length, changing tension
Myosin filaments are ‘spinning their wheels’, trying to slide but muscle is pitted against some more or less immovable object
E.g., pushing the palms together in front of you causes arm and chest muscles to contract isometrically
Origin
Attached to the immovable/less-moveable bone, anchor/leverage point
Insertion
Attached to the moveable bone, when contraction occurs insertion moves towards origin
Prime Mover
Major responsibility for causing a particular movement
Antagonist
Muscles that oppose or reverse a movement, are stretched and relaxed when prime mover is active
