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The Neuron __________________________ - the long extension of a neuron that carries nerve impulses away from the body of the cell. __________________________ - the hair-like ends of the axon __________________________ - the cell body of the neuron; it contains the nucleus (also called the soma) __________________________ - the branching structure of a neuron that receives messages (attached to the cell body) __________________________ - the fatty substance that surrounds and protects some nerve fibers node of Ranvier - one of the many gaps in the myelin sheath - this is where the action potential occurs during saltatory conduction along the axon Nucleus - the organelle in the cell body of the neuron that contains the genetic material of the cell Schwann Cell - cells that produce myelin - they are located within the myelin sheath. I. Nervous System Notes 1. General information: passage of information occurs in two ways: Nerves - process and send information fast (eg. stepping on a tack) Hormones - process and send information slowly (eg. growth hormone etc) 2. Major components of the nervous system: Two major divisions The central nervous system (CNS) - made up of the spinal cord and brain The peripheral nervous system (PNS) - made up of the cranial and spinal nerves Central Nervous System Peripheral Nervous System axon - the long extension of a neuron that carries nerve impulses away from the body of the cell. myelin sheath - the fatty substance that surrounds and protects some nerve fibers node of Ranvier - one of the many gaps in the axon terminals - the hair-like ends myelin sheath - this is where the action potential of the axon occurs during saltatory conduction along the axon cell body - the cell body of the nucleus - the organelle in the cell body of the neuron; it contains the nucleus (also neuron that contains the genetic material of the cell called the soma) Schwann's cells - cells that produce myelin - they dendrites - the branching structure are located within the myelin sheath. of a neuron that receives messages (attached to the cell body) The Neuron Very Special(ized) Cells Your nervous system is composed of specialized cells called neurons. The structure of a neuron can give you a clue to its function. Each has a compact cell body and long, slender processes - a little like antennae. The processes that pick up messages are called dendrites. Those that conduct messages to the next cell are called axons. Let's see how a message travels down an axon. The neuron has the special ability to build up a charge - much like a battery - across its membrane. More sodium ions (Na+) and potassium ions (K+) build up outside the membrane, so the inside of the cell is more negative. If you could put a microscopic meter on each side of the membrane, you could measure the potential energy (about -70 millivolts), like a tiny battery. When the neuron is stimulated, sodium ions can enter the cell. The potential energy (voltage) across the membrane drops. Even though the cell membrane quickly begins to restore the ions to their proper position, this change, in turn, affects the membrane next to it. Like fire along a fuse, the electrical change moves down the axon. By the time the membrane restores the charge across the membrane at one point, the signal is moving ahead. Axons are the longest parts of any cell. A single axon can be only a few micrometers or as long as a meter. But eventually the electrical signal reaches the end. The axon of one neuron doesn't touch the dendrites of the next neuron. Instead there is a tiny gap called a synapse. A chemical neurotransmitter is released from the end of the axon, which jumps the gap and starts the process all over again, stimulating the next nerve cell. How fast does this occur? Don't be confused by the word "electric." Unlike electrons in a conductor (which move at nearly the speed of light) the messages that are sent by movement of charged ions move at about 100 m/second. How the Neuron Works Vocabulary Action potential Synapse Neurotransmitter Terminal endings