ch13saladinIM - Chapter 13: Nervous Tissue Chapter Overview...

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Chapter 13: Nervous Tissue Chapter Overview Humans are large organisms with trillions of cells. Cellular activity must be coordinated so that a person can function as an integrated whole and interact in a meaningful way with a complex environment. Two systems of communication prevent physiological chaos—the nervous system and the endocrine system. These systems detect changes and modify the activity of cells, organs, and the individual. They play a central role in maintaining homeostasis. The nervous system in particular is the focus of exciting current research; many questions about its function remain unanswered. Overview of the Nervous System The nervous system 1) receives information about the internal and external environment, 2) processes information and determines a response, and 3) issues commands to cells to carry out the response. The nervous system has two main divisions—the central nervous system (CNS), and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord, while the PNS consists of nerves and ganglia. Nerves are organs that contain bundles of nerve fibers (axons) that carry information to and from the CNS. Ganglia are collections of nerve cell bodies that lie outside the CNS. The PNS is further divided into the sensory and motor divisions. The sensory (afferent) division carries signals from sensory receptors through afferent nerve fibers to the brain or spinal cord. The visceral sensory division carries signals from viscera of the thoracic and abdominal cavities. The somatic sensory division carries signals from receptors in the skin, muscles, bones, and joints. The motor (efferent) division carries signals from the CNS through efferent nerve fibers to effectors (cells or organs that carry 83
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out responses). The visceral motor division, or autonomic nervous system, carries messages to glands, cardiac muscle, and smooth muscle. The autonomic nervous system is divided into sympathetic and parasympathetic portions. The sympathetic nervous system prepares the body for action required in extraordinary circumstances. The parasympathetic division carries on “business as usual” when the body is in a state of rest. The somatic motor division sends signals to skeletal muscles, many of which are under voluntary control. Nerve Cells (Neurons) The functional unit of the nervous system is the neuron because it carries out the system’s communication role. Universal Properties of Neurons Excitability (Irritability) Neurons are highly responsive to stimuli. Conductivity Neurons respond to stimuli by producing electrical signals. Secretion Neurons secrete a neurotransmitter when an electrical signal reaches the end of the nerve fiber that passes a message to other cells. Functional Classes of Neurons
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ch13saladinIM - Chapter 13: Nervous Tissue Chapter Overview...

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