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Nervous system is composed of three major parts: the sensory input portion, the central nervous system) or integrated portion), and the motor output portion

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Introduction

Anatomy and Physiology The term homeostasis is used to mean maintenance of static or constant conditions in the internal environment in the organism. Essentially all of the organs and tissues of the body perform functions that help to maintain these constant conditions. For instance, the lungs provide oxygen to the extra cellular fluid to replenish oxygen that is being used by the cells; the kidneys maintain constant ion concentrations and the gastrointestinal system provides nutrients. Not all substances absorbed from the gastrointestinal tract can be used in their absorbed form by the cells. The liver changes the chemical compositions of many of these substances to more useable forms and other tissues of the body - fat cells, gastrointestinal mucosa, kidneys, and endocrine glands - help to modify the absorbed substances or store them until they are needed. Nervous system is composed of three major parts: the sensory input portion, the central nervous system) or integrated portion), and the motor output portion. Sensory receptors detect the state of the body or the state of the surrounding. ...read more.

Middle

In a typical neuron dendrites respond to stimuli through input to the neuron cell body. When the stimulus is large enough the cell body sends a one way electrochemical impulse through the axon to the next neuron or to some effector such as a muscle. The most important part of a neuron is its cell membrane. Using active transport and special Na+/K+ ion pumps in the membrane of the axon a neuron creates a resting potential of -70 millivolts. The cell essentially becomes a tiny battery ready for action. The action is the action potential -- a wave of electro-chemical activity which sweeps down the axon in one direction, changing its polarity. Depolarization leads to further depolarization as special electrically sensitive protein gates swing open allowing Na+ ions to enter the cell and K+ ions to escape. Once depolarized the Na+/K+ pumps quickly re-polarize the axon by using ATP to transfer 3 Na+ ions back out of the cell while simultaneously ushering 2 K+ ions into the cell. ...read more.

Conclusion

An action potential is a very rapid change in membrane potential that occurs when a nerve cell membrane is stimulated. Specifically, the membrane potential goes from the resting potential (typically -70 mV) to some positive value (typically about +30 mV) in a very short period of time (just a few milliseconds). There are two types of neurotransmitters: Excitatory - neurotransmitters that make membrane potential less negative (via increased permeability of the membrane to sodium) therefore, tend to 'excite' or stimulate the postsynaptic membrane and Inhibitory - neurotransmitters that make membrane potential more negative (via increased permeability of the membrane to potassium), therefore, tend to 'inhibit' (or make less likely) the transmission of an impulse. Located in the body there are eight major endocrine glands that secrete chemical substances called hormones. Hormones are transported in the extra cellular fluid to all parts of the body to help regulate cellular function. For instance thyroid hormone increases the rates of most chemical reactions in all cells. In this way, thyroid hormone helps to set the tempo of body activity. Insulin controls glucose metabolism; hormonal system mainly controls metabolic functions. ...read more.

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