Briefly compare/contrast the following terms: a.Homeostasis vs ba

Homeostasis is maintaining a constant, optimal internal environment.

The basal metabolic rate is the energy cost of maintaining metabolic homeostasis, nerve and muscle tone and circulation and breathing.

It is the energy expenditure measured when completely at rest, but awake, at a comfortable temperature (i.e. under conditions of thermal neutrality, so that the subject is not expending energy to keep warm or cool down), and several hours after the last meal, so that the subject is not expending energy on processing the products of digestion to synthesise body reserves of fat and glycogen.

The importance of being awake is that some people show an increase in metabolic activity when they are asleep, as a result of partial uncoupling of electron transport from ATP synthesis - this is a mechanism for regulating body weight as food intake varies. Other people show a fall in metabolic activity when they are asleep; such people are metabolically efficient, but are more likely to gain weight as a result of increased food intake.

Basal metabolic rate depends on metabolically active lean body tissue; mainly muscle, but all tissues make a contribution - although it is largely inert reserves of triacylglycerol, adipose tissue also makes a contribution to metabolic rate. Body weight is therefore an important factor in determining BMR, but gender and age are also important.

Women have a higher proportion of body weight as fat than do men. This means that a woman has a lower BMR than a man of the same body weight.

With increasing age, even if body weight does not change, lean muscle tissue is gradually replaced by fat, so that the proportion of fat in the body increases with age. This means that an older person has a lower BMR than a younger person of the same age.

In your body, nerve cells send and receive electrochemical messages called action potentials. Like any cell, the fluid inside is rich in potassium, but low in sodium. In contrast, the fluid outside is high in sodium, but low in potassium. Inside the cell, there are large negatively charged proteins that can't pass through the cell membrane, so the cell is negatively charged compared with the outside. The cell membrane is "leaky" to sodium and potassium; each ion can pass through specific channels or tunnels in the membrane, which are regulated (either open or closed).

An action potential works when a disturbance -- mechanical, electrical or chemical -- causes a few sodium channels in a small portion of the membrane to open. Sodium ions enter the cell through the open sodium channels. The positive charge that a sodium ion carries makes the inside of the cell slightly less negative, or depolarizes the cell. When the depolarization reaches a certain threshold value, more sodium channels in that area open, more sodium flows in and the local membrane becomes positive inside and negative outside. This is an action potential.

At some point, the sodium channels automatically close and no more sodium flows in. The positively charged membrane causes potassium channels to open and potassium leaves the cell. As potassium ions leave, the cell membrane returns to normal, which is negative on the inside and positive on the outside. Upon reaching the original state, the potassium channels shut down. A sodium-potassium pump restores the normal ion balance across the membrane.

This sequence of events occurs in a local area of the membrane. But these changes get passed on to the next area of membrane, then to the next area, and so on down the entire length of the axon. In this way, the action potential (nerve impulse or nerve signal) transmits, or propagates, down the nerve cell.

When the action potential reaches the end of one nerve cell, it causes the cell to secrete a chemical message that travels across the gap between cells and evokes an action potential in the next nerve cell in the pathway. This process is called synaptic transmission.

Through these processes, signals move through cellular circuits in your nervous system. These circuits transmit, process and store information such as sensations, thoughts, movements and reflexes. One example is a spinal reflex, the type that quickly withdraws your hand when it touches a hot pot.