muscles Flashcards
(4 cards)
fibers being stimulated for contraction
In skeletal muscles, the “all-or-none” law of muscle physiology applies to the muscle fiber, not to the whole muscle. It states that a muscle fiber will contract to its fullest extent when it is stimulated adequately; it never partially contracts. However, the whole muscle reacts to stimuli with graded responses, or different degrees of shortening, which generate different amounts of force. In general, graded muscle contractions can be produced two ways: (1) by changing the frequency of muscle stimulation and (2) by changing the number of muscle fibers being stimulated at one time. Next, let’s describe a muscle’s response to each of these.
Muscle Response to Increasingly Rapid Stimulation
Single Twitch (muscle twitch)
This is just one quick signal.
The muscle contracts briefly and then relaxes right away.
It’s like a quick jerk.
Not how your muscles normally work when you’re moving around.
- Unfused Tetanus (Incomplete Tetanus)
This happens when signals come more rapidly, before the muscle fully relaxes.
The next signal “builds on” the last one.
The contractions start to add up and become smoother and stronger, but there are still tiny relaxations between them.
Think of it like a stuttering but growing contraction.
- Fused Tetanus (Complete Tetanus or Tetanic Contraction)
Now the signals are coming super fast, with no time at all for the muscle to relax between them.
The muscle stays fully contracted—smooth, strong, and sustained.
This is how muscles work during most voluntary movement when you’re holding or lifting something steadily.
Tetanus (the sustained firing of impulses) gives your muscles smooth control.
The number of muscle fibers activated controls how strong the contraction is.
So your body can fine-tune every movement — from gentle to powerful — using a combo of stimulation frequency (tetanus) and fiber recruitment. Pretty amazing, right?
atp regenerating for muscles
Surprisingly, muscles store very limited supplies of ATP—only a few seconds’ worth, just enough to get you going. Because ATP is the only energy source that can be used directly to power muscle activity, ATP must be regenerated continuously if contraction is to continue.
Creatine phosphate (CP) making ATP is anaerobic because it requires no oxygen. ATP is made when CP donates its phosphate to ADP, turning it into ATP. This is the fastest way to get ATP, but it only lasts about 15 seconds. It’s usually used during short, explosive activities like sprinting.
Aerobic means that oxygen is required to make ATP.
In this process, glucose or fats are broken down in the presence of oxygen inside the mitochondria of cells.
This breakdown releases energy, which is used to form a lot of ATP (about 32 per glucose).
It’s a slow process, but it can keep producing ATP for a long time — even for minutes to hours — as long as oxygen and fuel are available.
It’s used during light to moderate exercise, like walking, jogging, or biking — activities where you’re breathing steadily.
Anaerobic glycolysis breaks down glucose (which can come from glycogen stored in muscles) without oxygen.
It’s faster than aerobic respiration but produces less ATP overall.
It usually lasts about 30 seconds to 1 minute during intense activity.
It’s used during heavy lifting, sprinting, or other short bursts of high-intensity exercise when oxygen can’t keep up.
Anaerobic glycolysis is a fast way to make ATP without oxygen.
It produces ATP about 2.5 times faster than aerobic respiration.
But it only makes about 5% as much ATP from each glucose molecule.
It can provide energy for about 30 to 40 seconds of intense activity (like sprinting or heavy lifting).
