Test #3 Flashcards
All muscles produce
Heat during contraction
Cells of muscles (skeletal)
Sarcolemma - muscle fiber plasma membrane
Sarcoplasm - muscle fiber cytoplasm
Glycosomes - glycogen storage
Myoglobin - O2 storage
Organelles
–Myofibrils - contractile unit; densely patched rodlike elements; contains striations, sarcomeres, 1000’s of myofilaments; account for 80% of muscle cell volume
–Sarcomere - unit of myofibril; z-disc to z-disc
–Sarcoplasmic reticulum - stores and releases Ca+
–T tubules - protrusion of sarcolemma into cell to reach each muscle fiber
Cells of muscles (smooth)
Uninucleated, no striations, no sacromeres, no protective sheaths (endomysium only)
Varicosities of nerve fibers instead of neuromascular junctions
Diffuse junction - wide synaptic cleft
No troponin; calmodulin binds Ca2+
Tropomyosin serves same function as in skeletal,
Caveola - sarcolemma of smooth muscle contains pouch-like infoldings
Myosin heads across the whole length (as opposed to skeletal which is only at the ends)
Where are ACh receptors found?
Junctional folds of the sarcolemma/motor end plate
Steps from nerve stimulation to muscle contraction (skeletal; steps/summary)
— A. Neuromuscular junction
— B. Muscle fiber excitation
— C. Excitation-Contracting coupling (activities of the triad)
— D. Cross bridge cycling occurs via the sliding of myofilaments
Summary of steps from nerve stimulation to muscle contraction
1) Motor neuron AP
2) N/T release
3) Muscle cell AP
4) Release of Ca2+ from SR
5) ATP-driven power stroke
6) Sliding of myofilaments
What is an axon terminal?
The bulbous distal endings of the terminal branches of an axon where neurotransmitters are released. Takes in Ca2+, releases ACh
What causes action potential?
Depolarization of the sarcolemma - the rising membrane voltage crosses a threshold value, and an AP is generated
Three parts of the motor neural junction
- Axon terminal
- Synaptic cleft
- Muscle/motor end plate
Troponin vs calmodulin
Troponin - skeletal muscle; Ca2+ binds to troponin which causes tropomyosin to expose myosin-binding sites
Calmodulin - smooth muscle; Ca2+ binds to Calmodulin which activates it (which activates MLCK enzymes, which then phosphorylyse heads of the myosin)
MLCK
Enzyme (myosin light chain kinase) this activates myosin heads in smooth muscle; causes activation of ATPase
MLCP
Enzyme (myosin light chain phosphates) that dephosphorolyses myosin heads in smooth muscle; causes deactivation of ATPase
ATPase
Enzyme that hydrolyzes ATP, providing the energy for the power stroke
Three ways to create ATP in the muscles
1) Direct phosphorylation of ADP by creatine phosphate (CP)
–Creatine phosphate in the muscle cell stores energy that will be transferred to ADP to recreate ATP
–No oxygen use, 1 ATP per CP, 15 seconds energy
2) Anaerobic pathway: glycolysis and lactic acid formation
–No oxygen use, 2 ATP per glucose & 2 pyruvic acid, 30-40 seconds energy
3) Aerobic pathway - glucose plus three acids AND OXYGEN aerobically respirate in mitochondria
–OXYGEN USE, 32 ATP per glucose, hours of energy
EPOC
Excess post-exercise oxygen consumption; EPOC is the amount of oxygen our body consumes following an exercise session that is above and beyond the pre-exercise oxygen consumption baseline
Structural and functional characteristics of the three types of muscle fibers
Muscle twitch phases
Latent - events of excitation-contraction coupling - no muscle tension
Contraction - cross-bridge formation - tension increases
Relaxation - Ca+ reentry into sarcoplasmic reticulum - tension decreases to zero
Treppe
Warming up; enhances availability of Ca and efficiency of enzymes
Hypertrophy vs hyperplasia
Hypertrophy - increase in size; hyperplasia - increase in number
Latch-bridge
A cross-bridge connection that happens in smooth muscle where the connection can hold indefinitely without ATP resulting in a low energy contraction
Isometric contraction vs isotonic contraction
Isometric contraction - no muscle length change; muscle tension increases but does not exceed load; e.g., pushing against a wall
Isotonic contraction - muscle length changes because muscle tension exceeds load
A) Eccentric contractions - muscle lengthens
B) Concentric contractions - muscle shortens
Triad
Triad is a T tubule & two terminal cisterns (sarcoplasmic reticulum - releases and reabsorbs calcium)
Motor end plate
Junctional folds of the sarcolemma
Disuse atrophy
Degeneration and loss of mass due to immobilization or loss of neural stimulation - can begin almost immediately