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6

To answer the numbered questions: In general, neurons never divide by mitosis. However, I believe you may have unintentionally misphrased your question; there are functional neural stem cells in the adult human brain as well, and these are believed to give rise to new neurons throughout the lifespan of an individual. They have only been found in specific ...


4

One of the physical limits to biological flight is muscle physiology. Muscle force output is proportional to muscle physiological cross sectional area (PCSA) multiplied by its specific tension (Gans, 1982): $$F = \text{PCSA} \times \text{Specific Tension}$$ PCSA is basically just the cross-sectional area of a muscle adjusted for its architecture. Pennate ...


3

This is because of the difference in mitochondrial protein expression of red and white muscle fibres. There is difference in posttranslational modification, which leads to functional difference as red muscle contraction is slow, and white muscle contraction is rapid. Metabolic control in mitochondria contributes in speed of activity and cellular energy ...


3

A major determiner of blood flow redirection among muscles is increased oxygen demand in the working muscles. When a muscle works, it uses oxygen, so the partial pressure of oxygen (PO2) in the muscle falls, which signals small arteries (arterioles) to dilate, which results in increased blood flow and hence oxygen and nutrients delivery to the muscle (...


3

A myotube is a type of cell which will develop into a muscle fiber. It is formed by the fusion of multiple myoblasts, and thereby acquires multiple cell nuclei. The nuclei are in the middle of the myotube cell, unlike the mature muscle fiber where the nuclei are at the periphery of the cell. A myotube has a tubular form instead of the more typical rounded ...


2

Calcium ($\ce{Ca^{2+}}$) is a signalling molecule and it acts like a chemical switch that tells other chemicals in the cell to enact the contraction. It's not accurate to think of the cell "filling up" with $\ce{Ca^{2+}}$ since $\ce{Ca^{2+}}$ wouldn't significantly change the volume of the cell alone *. Also, during contraction, the muscle cells contract in ...


2

Breathing is controlled by both the Autonomic nervous system and the voluntary nervous system. You see this in instances where our breath rate increases in flight or fight situations glide to the secretion of Adrenaline and also when we intentionally increase the breathing rate when undergoing high levels of activity. This is due to the fact that the ...


2

Your body in this case is generating more "power" by having something to push against. When flicking your finger, your finger is pushing against your thumb and that pressure you feel is the force of both your finger against your thumb and your thumb against your finger. This is important as you can only apply so much force to a mass before it gives out and ...


1

Skeletal muscle cells are excitable, like neurons. Enough summation of end-plate potentials causes the cell to reach threshold and fire an action potential (which then spreads throughout the cell membrane through positive feedback, just like a neuronal action potential). There are some differences between skeletal muscle and typical neurons, like greater ...


1

The tendon and muscle attachment are not the same. In your example, both are affected, so they are described separately. A muscle extends into a tendon and this into an enthesis - an actual attachment site where the muscle is attached to the bone (PubMed).


1

{1} greatly answers the question. Regarding the insertion location (lateral view): Note that unlike the gluteus minimus insertion, the gluteus medius insertion can also be viewed anterolaterally: Table 2 contains more detailed insertion location data: Regarding the insertion area: Gluteus maximus: Average Area, mm^2 (95% CI): 473.4 (381.0, 565.8). ...


1

Maybe it isn't. The standard theory: muscle cramps are caused by loss of fluids and electrolytes, which alters fluid balance in the body and increases the excitability of nerves. The "new" theory: muscles cramps result from "altered neuromuscular control," which can be triggered by a variety of factors, including genetic predisposition, damaged or ...


1

Yes, muscles do work as brakes; it's a process called eccentric contraction. The energy balance of an eccentric contraction is a pretty difficult question. Some fairly recent research (Linari et al., 2003) found that a low velocities more energy is consumed (i.e. released as heat) even during eccentric contraction, while at high velocities, the muscle does ...


1

Though neurons do not possess the ability to divide in adult humans, glial cells do, and in case of injury or disease, tend to fill up the gaps created by loss of neurons. Most muscle cells lose their ability to divide after maturation. There are a few cases however, like those in disease or damage, when cells that are lost may be replaced. These are ...


1

this depends on largely how you define it, what we normally measure is efficiency including how much energy is used on metabolic upkeep and heating the body in addition to muscle output. we use oxygen consumption to know exactly how many calories we have "burned" when doing this. In this study we get between 18-26% efficiency, thats calories ingested to ...


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