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13.1 The Nervous System -- Part 1
The major tools for the study of life processes have been provided by this technology.
Many life processes involve electrical phenomena.
The nervous system of animals and the control of muscle movement are governed by electrical interactions.
In Chapter 14 we will discuss the applications of electrical technology in biology and medicine, and in this chapter we will describe some of the electrical phenomena in living organisms.
There is a brief review of electricity in Appendix B.
Animals have the most remarkable use of electrical phenomena in their nervous system.
The brain is located in the center of the network and has the ability to store and analyze information.
The nervous system is in charge of various parts of the body.
The human nervous system is very complex.
It is not known how information is stored and processed by the nervous system.
Some aspects of the nervous system are well known.
The method of signal propagation through the nervous system has been firmly established over the past 40 years.
The messages are sent by the brain.
When a neuron is stimulated, it produces electrical impulses that travel along its cablelike structure.
The pulse is constant in magnitude and duration.
The number of pulse produced is a good indicator of the strength of theStimulus.
When the pulse reaches the end of the cable, other cells are activated.
The internal and external environment of the body are monitored by the sensory organs.
Depending on the function of the sensory neurons, they convey messages about factors such as heat, light, pressure, muscle tension, and odor to higher centers in the nervous system.
The motor neurons communicate with the muscle cells.
The central nervous system located in the brain provides information to these messages.
The interneurons communicate.
Nerve endings at the far end of the axon transmit signals to other cells.
Nerve impulses from a muscle travel to the spine.
The signal is sent to a motor neuron, which sends impulses to control the muscle.
Simple circuits are associated with actions.
The axon conducts electrical impulses away from the cell body.
The axons connecting the spine with the fingers and toes are more than a meter in length.
The myelin sheath increases the speed of pulse propagation.
Many axons share a common path within the body.
These axons are usually grouped together.
The special elec trical characteristics of the axon allow the neuron to transmit messages.
The data about the electrical and chemical properties of the axon can be obtained by injecting small needlelike probes into the axon.
It is possible to measure currents flowing in the axon with probes.
The diameter of most axons is very small.
Experiments with the squid axon yielded a lot of information about signal transmission in the nervous system.
Salt and other substances are positive and negative in the body.
Body fluids are good conductors of electricity.
The fluids' resistivity is 100 million times greater than that of copper.
The inside of the axon has an ionic fluid that is separated from the surrounding body fluid.
The axon membrane is not a perfect electrical insulator.
The electrical resistivities of the internal and external fluids are the same.
Its ionic solutes are mostly positive.
The axon has positive and negative ion concentrations.
There is a large concentration of sodium ion outside the axon and a large concentration of potassium ion inside the axon.
The answer is in the properties of the axon.
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