Part 2 book “Pocket companion to guyton and hall textbook of medical physiology” has contents: Cardiac arrhythmias and their electrocardiographic interpretation, rhythmical excitation of the heart, the normal electrocardiogram, overview of the circulation; biophysics of pressure, flow, and resistance,. and other contents. | IX The Nervous System: A. General Principles and Sensory Physiology 45. Organization of the Nervous System, Basic Functions of Synapses, and Neurotransmitters 46. Sensory Receptors, Neuronal Circuits for Processing Information 47. Somatic Sensations: I. General Organization, the Tactile and Position Senses 48. Somatic Sensations: II. Pain, Headache, and Thermal Sensations This page intentionally left blank CHAPT ER 45 Organization of the Nervous System, Basic Functions of Synapses, and Neurotransmitters General Design of the Nervous System (p. 543) The Nervous System Includes Both Sensory (Input) and Motor (Output) Systems Interconnected by Complex Integrative Mechanisms. The fundamental unit of oper- ation is the neuron, which typically consists of a cell body (soma), several dendrites, and a single axon. Although most neurons exhibit the same three components, there is enormous variability in the morphology of individual neurons throughout the brain. It is estimated that the nervous system is composed of more than 100 billion neurons. Much of the activity in the nervous system arises from mechanisms that stimulate sensory receptors located at the distal termination of a sensory neuron. Signals travel over peripheral nerves to reach the spinal cord and are then transmitted throughout the brain. Incoming sensory messages are processed and integrated with information stored in various pools of neurons such that the resulting signals can be used to generate an appropriate motor response. The motor division of the nervous system is responsible for controlling a variety of bodily activities such as contraction of striated and smooth muscles and secretion by exocrine and endocrine glands. Actually, only a relatively small proportion of the sensory input received by the brain is used to generate an immediate motor response. Much of it is discarded as irrelevant to the function at hand. Sensory input can be stored in the form of memory. Information stored as memory
