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Muscles 2
| Term | Definition |
|---|---|
| Excitation | Step 1 of contraction, where the nerve action potentials lead to muscle action potentials |
| Excitation-Contraction Coupling | Step 2 of contraction, covering events that link the action potentials on the sarcolemma to activation of the myofilaments. Prepares for contraction |
| Contraction | Step 3 of contraction, where the muscle fiber develops tension and may shorten |
| Relaxation | Step 4 of contraction, where the muscle fiber relaxes and returns to its resting length |
| Excitation Step 1 | Nerve signal arrives at the synaptic knob, opening voltage gated calcium channels in the synaptic knob. |
| Excitation Step 2 | The calcium channels release calcium, which stimulates release of ACh into the synaptic cleft. |
| Excitation Step 3 | Two ACh molecules bind to each receptor protein to open the channels on the sarcolemma, diffusing Na and K ions across the membrane. |
| Excitation Step 4 | Na enters the inside of the membrane while K flows out of the membrane, shifting the resting potential from -90 mV to 75 mV. K then returns, RMP goes back to -90 mV. |
| Resting Membrane Potential (muscles) | -90 mV |
| End-Plate Potential (EPP) | A quick voltage shift experienced by the membrane in the muscles, which goes from -90 mV to 75 mV and back again |
| Excitation Step 5 | Action potential spreads down the muscle surface |
| Excitation-Contraction Coupling Step 1 | The action potential propagates down the T-tubules |
| Excitation-Contraction Coupling Step 2 | Voltage-gated calcium ion channels in T-tubules are opened and calcium channels are opened in the Sarcoplasmic Reticulum. Ca enters the cytosol |
| Excitation-Contraction Coupling Step 3 | Calcium binds to troponin on the thin filaments |
| Excitation-Contraction Coupling Step 4 | Troponin-tropomyosin complex changes shape as the result of the calcium, exposing the active sites on the actin |
| Contraction Step 1 | ATP molecule on myosin head is hydrolyzed by ATPase, creating ADP+Pi. Myosin head cocks back |
| Contraction Step 2 | Myosin head binds to actin active site, forming a myosin-actin cross bridge |
| Contraction Step 3 | Myosin head releases ADP and Pi, flexes and pulls thin filament past thick filament--power stroke |
| Contraction Step 4 | Myosin head binds to a new ATP molecule and breaks the cross-bridge with actin. |
| Relaxation Step 1 | Nerve stimulation and subsequent ACh release stops. |
| Relaxation Step 2 | Acetylcholinesterase (AChE) breaks down ACh and fragments are reabsorbed into the synaptic knob. |
| Relaxation Step 3 | Calcium ions are pumped back into SR by active transport, binding to calsequestrin while in storage. |
| Relaxation Step 4 | With the calcium ions gone, troponin stops binding to calcium and tropomyosin blocks the active sites again. Muscle fiber returns to resting length. |
| Rigor Mortis | Hardening of muscles and stiffening of the body beginning 3-4 hours after death. Deteriorating SR releases calcium ions, but no ATP molecules are present to relax the muscles. Peaks after 12 hours after death, then diminishes over 48-60 hours |
| Length-tension relationship | The amount of tension generated by a muscle and the force of contraction depends on how stretched or contracted it was before it was stimulated. |
| Optimum resting length | There is an ideal length that generates the maximum contraction. |
| Muscle tone | Central nervous system continually monitors and adjusts the length of the resting muscle, and maintains a state of partial contraction, making the muscles ideally ready for action |
| Isometric muscles contraction | Muscle develops tension, but does not shorten. There is no movement. |
| Isotonic concentric contraction | The muscle shortens, but tension remains constant. |
| Isotonic eccentric contraction | The muscle lengthens, but tension remains constant. |
| Isometric phase | At the beginning of contraction, the muscles tension rises but the muscles do not shorten |
| Isotonic phase | Tension overcomes the resistance of the load, and tension levels off. Muscle begins to shorten and move the load. |
| Myogram | A chart of the timing and strength of a muscle's contraction |
| Threshold | Minimum voltage necessary to generate an action potential in the muscle fiber and produce a contraction |
| Twich | A quick cycle of contraction when stimulus is at threshold or higher |
| Latent period | 2 ms delay between the onset of stimulus and the onset of twitch response. |
| Internal tension | Force generated during latent period; no shortening of the muscle occurs. |
| Contraction Phase | Phase in which filaments slide and the muscle shortens; muscle begins to produce external tension in muscle that moves a load. |
| Relaxation phase | SR quickly reabsorbs Ca. Myosin releases the thin filaments and tension declines. Muscle returns to resting length. |
| Twitch strength factors | How much the muscle was stretched before stimulation, temperature of muscles, state of hydration, stimulus frequency |
| Recruitment | The process of bringing more motor units into play |
| Treppe | Staircase phenomenon; 10-20 stimuli per second; Ca concentration in the cytosol rises higher and higher with each stimulus, causing subsequent twitches to become stronger. |
| Incomplete tetanus | 20-40 stimuli per second; each stimulus arrives before previous twitch is over, generating higher tension. |
| Temporal summation | Two stimuli arrives close together |
| Complete tetanus | Muscles have no time to relax before stimuli, producing a smooth, prolonged contraction. Rarely occurs in the body. |
Created by:
Rylyn27463
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