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The organization of the mammalian nervous system can be described anatomically and functionally. In anatomical terms, all vertebrate nervous systems consist of three parts: a brain, a spinal cord, and a set of peripheral nerves that reach all parts of the body. As discussed in Key Concept 44.4, the brain and spinal cord are the central nervous system, or CNS, and the neurons that connect the CNS to all the tissues and sensors of the body are the peripheral nervous system, or PNS. An additional division of the nervous system exists in the gut; we will discuss this enteric nervous system in Chapter 50.
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Conscious sensory and unconscious physiological information flow to the central nervous system via afferent neurons, resulting in efferent outputs to voluntary muscles (i.e., movement) and in involuntary commands over autonomic responses.
From anterior to posterior, the embryonic neural tube gives rise to the cerebrum, thalamus/hypothalamus, midbrain structures, and cerebellum/pons/medulla, respectively.
Specific areas within the five lobes of the cerebral cortex have sensory, motor, and associative functions.
Humans are called the “big-
Recall from Key Concept 45.1 that a neuron is an electrically excitable cell that communicates via an axon. When used in the context of a nervous system, the term nerve refers to a bundle of axons in the PNS that carry information about many things simultaneously. Some axons in a nerve may be carrying information to the CNS while other axons in the same nerve are carrying information from the CNS to the body’s organs. A discussion of the functional organization of the nervous system refers to these paths of information flow. In this chapter we will divide the anatomy of the mammalian brain, spinal cord, and PNS into smaller, discrete functional units.