1/28
Looks like no tags are added yet.
Name | Mastery | Learn | Test | Matching | Spaced |
---|
No study sessions yet.
STEPS for Full Muscle Contraction-Relaxation Cycle
Pre-
a) motor nueron fires Ach released to neuromuscular junction, action potential starts in muscle fiber and travels down t-tubules, triggers release of Ca2+ into SR.
Ca2+ levels increase in cytosol.
Ca2+ bind to troponin C, changing shape of actin/ troponin complex.
Changing of the troponin complex specifically changes the way tropomyosin binds to the thin filament. Tropomyosin is now releasing it’s grip, unveiling the myosin binding sites.
Myosin head (cocked aka loaded with ATP energy from hydrolysis) can now strongly bind to actin, releasing Pi (what’s holding this energy and allowing myosin head to be in this cocked position), pulling actin toward the center of the sarcomere. The power stroke is initiated.
Actin filament moves due to the power stroke with the sarcomere shortening, causing muscle contractions, and the release of ADP from myosin head.
ATP binds to myosin. Myosin completely detaches from actin filament, breaking the cross-bridge.
Myosin hydrolyzes ATP into ADP and Pi, resetting/re-cocking the myosin head physically (returning it to it’s “cocked” high energy statae, like resetting a mouse trap, preparing for the next cycle).
Power stroke begins again. If Ca2+ was still present and attached to actin, the myosin binding sites are still exposed, the re-cocked myosin binds to a new (usually adjacent) site on actin. This binding creates the next power stroke, continuing the power-stroke cycle (hence, why it’s called a cycle.)
Ca2+ ATPase pumps Ca2+ from cytosol back into —> SR. Once the motor neuron/nerve stops firing action potentials, no more Ca2+ is released. This low release of Ca2+ causes the pump to use ATP to actively transport Ca2+ back into the SR, lowing it’s concentration in the cytosol. This pump works because they want to stop muscle contraction and instead allow the muscle to relax. (Muscle Relaxation)
Decrease in Ca2+ in cytosol causes Ca2+ to unbind from troponin which causes troponin to return to it’s inactive resting state.
Tropomyosin recovers myosin-binding sites on actin, now myosin can no longer bind, cross-bridge cycling stops.
Removal of Ca2+ ions cause elastic elements to pull filaments back to their relaxed position (due to stop in sliding). With no active force (no tension) holding the shortening sarcomere, elastic elements like titin and external forces recoil the muscle fiber causing the muscle to relax and everything (including the sarcomere) to return to it’s normal length. (Final Stage of Muscle Relaxation)
What does 1 muscle action ALWAYS equal?
One contraction
What is a motor unit?
A motor unit is ONE motorneuron and ALL the muscle fibers it controls simutaneously.
Muscle vs. Motor Units vs. Fibers vs. Neurons
Muscles contain many motor units which can contain different types of muscle fibers (Type I, Type IIA, Type IIB), which allow for both varied control and strong movements. Each muscle fiber is innervated/controlled by only one motor neuron at a time, while a single neuron can control many fibers.
Analogy: one worker can only have one boss at a time while boss can manage many workers.
What are muscle contractions and what are they caused by?
Muscle contractions are a process where muscles generate force by shortening, lengthening, or remaining the same length under tension It is powered by the sliding of actin + myosin filament aka the power stroke within the muscle fibers. These contractions can ONLY PULL a bone and CANNOT push a bone away.
What are antagonist pairs and what do they consist of?
Antagonist pairs are muscles that work together to perform opposite functions/directions at a joint. They usually consist of extensors and flexors.
What are extensors and flexors and how do they differ?
Extensors contract to INCREASE the angle of a joint causing it to STRAIGHTEN. It functions to bring two body parts together. Ex: Triceps, Quadriceps
Flexors contract to DECREASE the angle of a joint causing it to bend. It functions to bring two body parts together. Ex: hamstring, hips
What is peristalsis?
Peristalsis is the muscular process where you alternate circular + longitudinal contractions in order to create a wave to propel food through the digestive track. Also used to help earthworms move through soil.
What are circular and Longitudinal Muscles and how do they work antagonistally to propel?
Circular and longitudinal muscles work together antagonistically during peristalsis by creasing a wave-like movement The circular muscles contract behind the food, narrowing the tube and pushing the contents forward. The longitudinal muscles contract ahead of the food, shortening and widening that segmnet to recieve the food. By alternating contractions (one contracts while the other one relaxes), these two muscles work together to move contents efficiently and in one direction.
Give 2 ex of how circular + longitudinal muscles work antagonistically to propel.
Ex 1 of Peristalsis: Earthworms
Peristalsis in earthworms is a travelling wave of alternating circular + longitudinal muscle contractions. The wave starts at the head and moves backward, allowing the worm to extend forward, anchor its body using body hair called setae, and then pull its body forward to move
Ex 2 of Peristalsis: Human stomach
Peristalsis in the stomach are waves of alternating circular + longitudinal muscle contractions that travel from top-> bottom, mixing food and pushing it forward the small intestine.
Antagonist muscles/pairs
Extensors + flexors (limb movement). Circular + Longitudinal (worms/digestive tract peristalsis)
How do muscle fibers generate tension?
By shortening the sarcomere during contraction + relaxed states.
What factors affect the tension a muscle generates?
Sarcomere legnth within a muscle fiber
Summation of twitches within a muscle fiber
Recruitment of additional motor units
The properties of recruited motor units
How does sarcomere length in a muscle fiber affect the tension a muscle generates?
If the sarcomere is too long or too short in a muscle fiber than there will be less tension produced. We want to aim for a sarcomere length that’s just right (not too long, not too short) that would produce MAXIMUM tension in a muscle fiber. This tension is determined by the number of crossbridges (myosin heads attached to actin in sarcomere) during RESTING- this resting length influences amount of tension generated.
How does summation of twitches in a muscle fiber affect the tension a muscle generates?
One muscle twitch is defined as ONE contraction of ONE muscle fiber in response to stimulation by ONE motor neuron (aka the unit of contraction). There will be a latent period between the action potential in the fiber and the start of contraction due to the wait for Ca2+ concentrations to accumulate in SR to bind to troponin and form cross bridges. This latency is a good thing as it acts as a short delay before the muscle fiber’s full contraction allows for stronger, more continuous muscle movements through a process called “wave summations.” There are 4 different types of wave summations: 1) single twitch 2) summation/temporal 3) summation leading to unfused tetanus 4) summation leading to complete tetanus.
What are the 4 different types of summations and their tension scenarios?
1) Single Twitch
2) Summation (temporal)
3) Summation leading to unfused tetanusyo
4) Summation leading to complete tetanus
What is muscle fatigue?
Muscle fatigue is the decline in the muscle’s ability to maintain tension during periods of sustained, or repeated activation. Fatigue is more pronounced(more likely to occur in and occurs quicker) in fast glycotic fibers Type IIB which rely eavily on anaerobic glycolysis. Caused by ATP depletion, lactic acid buildup, and other metabolic limits.
How does recruitment of additional motor units affect the tension a muscle generates?
When more force is needed, the nervous system recruits additional motor units (groups of muscle fibers+ their motor neuron). Recruitment follows the size principle which states that smaller fibers get recruited first, then comes the larger fibers. Distribution of fiber types also depends upon the muscle function: slow fibers for endurance, fast fibers for strength/power (Type I, TYpe IIA, Type IIB).
What’s the difference between aerobic and anaerobic respiration when it comes to how much tension a muscle generates?
Anaerobic Respiration is glycolysis only. It occurs in the mitochondria and uses substrate-level phosphorylation to produce 2 ATP per glucose + Lactic Acid (as byproduct). This is mainly used by Type IIB and sometimes by Type IIA.
Aerobic Respiration is citric acid cycle or oxidative phosphorylation. It occurs in the mitochondria and produces a lot of ATP but requires O2. This is mainly used by Type I and Type IIA fibers.
Why does the distribution of fiber types depend on the muscle’s function?
Distribution of fiber types also depends upon the muscle function: slow fibers for endurance, fast fibers for strength/power (Type I, TYpe IIA, Type IIB).
What are the diff types of muscle fibers
Slow Twitch Type I -slow weak contractions, high fatigue for long duration activities like posture, walking
Fast Twitch Oxidative Glycotic Type IIA-fast, moderate contraction, moderate fatigue resistance for routine movements like jogging, cycling.
Fast Twitch Glycotic Type IIB-fast, strongest contractions, rapidly fatigued for short strength excercises like weightlifting, sprinting
How do the properties of recruited motor units in a muscle fiber affect the tension a muscle generates?
The motor size determines how many muscle fibers it can innervate/control.
Small motor units=innervates few muscle fibers
Large motor units= innervates many muscle fibers
The size/diameter of muscle fibers determine the amount of tension generated and fatigue.
Small muscle fibers= small diameter muscle fibers (Type I)
Large muscle fibers = large diameter muscle fibers (Type IIB)
Single Twitch Summation
spaced apart stimuli, each twitch occurs on its own. between each AP/contrraction, the muscles relax COMPLETELY and tension is low. Graph looks like up and down spikes
Temporal Summation
stimuli come close together, the new contraction builds upon the previous one causing higher total tension + no complete relaxation. Tension rises higher with each stimulus.
Unfused/ Incomplete Tetanus Summation
stimuli are frequent but not the fastest possible/not max frequency. Muscles stay at high tension but show small up-and-down fluctuations (partial relaxation).
Fused/ Complete Summation
stimuli are so rapid that there’s no relaxation at all. The muscle stays at maximum steady tension. Over time, when fatigue sets in, the tension drops even if stimulation continues (ex: when ur holding something for too long, the grip loosens even if your brain is still telling ur muscles to squeeze).
What is asynchronous recruitment and how does it allow for longer contractions?
Asynchronous recruitment is the alternating activation and firing motor units within a muscle, where some units contract and others relax, allowing them to alternate and rest. This prevents rapid fatigue and enables sustained, smooth, and prolonged contractions that geenrate a consistent level of tension over time.
What is Hypertrophy vs. Hyperplasia and how are they different?
Hypertrophy is when existing muscle cells INCREASE in size (more proteins, storage, and strength). Usually muscle training causes this and results in larger muscles.
Hyperplasia is when the body makes NEW muscle fibers- usually very rare in hmans and not the main way we get bigger muscles. There are two types of hyperplasia:
Sarcoplasmic Hypertrophy: increased glycogen + storage space inside cell (makes muscles look bigger but doesn’t add much strength)→ common in body building
Myofibrillar Hypertrophy: increase actin+ myosin production which make fibers denser and stronger→ common in strength training
Knowing the definitions of hypertrophy and hyperplasia, answer the following questions. Does an increase in muscle size signify that new muscle cells grew? Why or why not?
No, because increase in muscle size is Hypertrophy whereas new muscle cells is Hyperplasia which are two different things.