MUSCLE PHYSIOLOGY Flashcards
Requirements for skeletal muscle contraction (2)
- Neuromuscular junction (site where motor neuron’s axon terminal meets muscle fiber)
- Excitation-contraction coupling
Neuromuscular junction
Action potential at motor neuron terminal triggers Ca2+ influx, releasing acetylcholine into synaptic cleft. Acetylcholine binds to sarcolemma, opening channels for positive ions, initiating depolarization and action potential propagation.
Propagation of Action Potential
Action potential prompts Ca2+ release from SR, T tubules transmit it, leading to Ca2+ diffusion and muscle fiber contraction.
T tubules
Extensions of the cell membrane that penetrate into the center of skeletal and cardiac muscle cells.
Skeletal Muscle and Contraction & Relaxation PART 1 - SKELETAL MUSCLE CONTRACTION INITIATION (3):
- Action potential triggers Ca2+ release from SR
- Ca2+ binds to troponin, exposing myosin-binding sites on actin
- ATP sustains muscle contraction
Skeletal Muscle and Contraction & Relaxation PART 2 - MUSCLE CONTRACTION PROCESS (3)
- Myosin heads pull actin, causing shortening of sarcomeres
- Cross bridge cycle involves myosin binding, power stroke and detachment
- ATP essential for myosin detachment and recocking
Skeletal Muscle and Contraction & Relaxation PART 3 - MUSCLE CONTRACTION REGULATION (3)
- Troponin and tropomyosin regulate actin-myosin interaction
- Ca2+ presence allows crossbridge formation; absence blocks it
- Rigor mortis occurs due to ATP depletion, leading to sustained cross bridges
Tropomyosin
Long rod like molecule that blocks muscle contraction
Troponin
Promotes muscle contraction
Cross bridge formation
The attachment of myosin with actin within the muscle cell
Power stroke
Movement of when actin is pulled
Creatine phosphate
Main high-energy, phosphate-storage molecule of muscle
Glycolysis
Process which glucose is broken down to produce energy. Muscles turn to glycolysis as an ATP source once the ATP produced by creatine phosphate is depleted
Aerobic cellular respiration
Breakdown of glucose or other nutrients in PRESENCE OF OXYGEN to produce carbon dioxide, water and ATP. 95% of ATP required for resting or moderately active muscles are provided by this
Anaerobic respiration
Takes place in the absence of oxygen
Skeletal muscle relaxation
Motor neuron stops releasing acetylcholine, muscle fibers repolarize and close gates, remove calcium ions from sarcoplasm via active transport and tropomyosin blocks myosin binding sites = no crossbridge formation
Cardiac muscle
Only found in the heart, responsible for pumping blood throughout circulatory system. Cardiac muscle is not consciously controlled, but the pacemaker cells respond to signals from the ANS
Cardiac muscle structure (3):
- Shorter branched shape that connect at ends to one another by intercalated discs
- Striated, organized into sarcomeres and posses many mitochondria
- One nucleus
Intercalated disc
Part of sarcolemma and contain 2 structures important in cardiac muscle contractions; gap junctions and desmosomes
Gap junction
AAllow the exchange of ions, second messengers, and small metabolites between adjacent cells
Electric coupling
The joining formed by gap junction that allows quick transmission of action potentials and coordinated contraction of entire heart
Syncytium
Functional unit of contraction
Desmosomes
Anchor ends of cardiac muscle fibers together so that cells do not pull apart during stress
Pace maker cells
Specialized cardiac muscle cells that directly control heart rate and are self excitable (set action potentials on their own; autorhythmicity). Connected to gap junctions so it can transfer depolarization to other cardiac muscle fibers in a coordinated manner
Smooth muscle
Arranged in layers and the triggers include hormones, neural stimulation by ANS, and pH factors, etc. Found around hollow organs that produce slow and steady contractions known as peristalis, such as moving food in digestive tract. It is an involuntary muscle
Smooth muscle structure (4)
- Spindle shaped
- No striations
- Single nucleus
- Thin (actin) and thick (myosin) filaments present
Thin filaments of smooth muscle
Attached to sarcolemma by dense bodies
Caveolae
Membrane indentations of smooth muscle where calcium ions are supplied by the SR
Calmodulin
Regulatory protein in smooth muscle cells instead of tropon-tropomyosin complex
Smooth muscle contraction mechanism (6):
- Calcium ions from SR and extracellular fluid bind to calmodulin
- Calmodulin activates enzyme that activates myosin heads
- Myosin heads attach to actin binding sites and pull thin filaments
- Thin filaments slide past thick filaments pulling dense bodies
- Dense bodies pull on intermediate filaments causing muscle fiber contraction
- Muscle fiber contracts with ends pulled towards the center causing midsection bulging inward
Where do thin filaments get pulled towards during contraction
M-line
Myoblast
Immature muscle cell
