Chapter 3: In Review Each neuron has dendrites which receive nerve impulses from other neurons; a cell body (soma) which controls the vital processes of the cell; and an axon which conducts nerve impulses to adjacent neurons, muscles and glands Neural transmission is an electrochemical process. The nerve impulse, or action potential is a brief reversal in the electrical potential of a membrane as sodium ions from the surrounding fluid flow into the cell through sodium ion channels, depolarizing the axon's membrane. Grader potentials are proportional to the amount of stimulation being received, whereas action potentials obey the all-or-none law, occurring at full intensity if the action potential threshold is reached. The myelin sheath increases the speed of neural transmission. Passage of the impulse occurs across the synapse is mediated by chemical transmitter substances. Neurons are selective in the NTs that can stimulate them. Some neurotransmitters excite neurons, whereas others inhibit firing of the postsynaptic neuron. The nervous system is composed of sensory neurons, motor neurons, and interneurons (associative neurons). Its two major divisions are the central nervous system, consisting of the brain and the spinal cord, and the peripheral nervous system. The latter is divided into the somatic nervous system, which has sensory and motor functions, and the autonomic nervous system, which directs the activity of the body's internal organs and glands. The spinal cord contains sensory neurons and motor neurons. Interneurons inside the spinal cord serve a connective function bw the two. Simple stimulus-response connections can occur as spinal reflexes. The autonomic nervous system consists of sympathetic and parasympathetic divisions. The sympathetic system has an arousal function and tends to act as a unit. The parasympathetic system slows down body processes and is more specific in its actions. Together, the two divisions maintain a state of internal balance, or homeostasis. Discoveries about brain-behaviour relations are made by using techniques such as neuropsychological tests, electrical and chemical stimulation of the
brain, electrical recording, and brain-imaging techniques. Recently, developed methods for producing computer-generated pictures of structures and processes within the living brain include CT and PET scans and MRI. The human brain consists of the hindbrain, the midbrain, and the forebrain, and organization that reflects the evolution of increasingly more complex structures related to behavioural capabilities.
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- Spring '09