Prepared by I Gede Purnawinadi, S.Kep., M.Kes. The Nervous System Prepared by I Gede Purnawinadi, S.Kep., M.Kes.
Overview of the Nervous System The nervous system is the master controlling and communicating system of the body. Every thought, action, and emotion reflects its activity. Its cells communicate by electrical and chemical signals, which are rapid and specific, and usually cause almost immediate responses. The nervous system has three overlapping functions: The gathered information is called sensory input It processes and interprets sensory input and decides what should be done at each moment—a process called integration. It causes a response, called motor output, by activating effector organs.
Overview of the Nervous System The basic functions of the nervous system are as follows: Recognizing changes in the internal and external environments. Processing and integrating the environmental changes that are perceived. Reacting to the environmental changes by producing an action or response.
For information to be transmitted throughout the nervous system, neurons must communicate with one another and with muscles and glands. In the autonomic nervous system this communication involves the connection of two neurons in series. As the action potential travels along the first nerve, it encounters the first synapse, or juncture.
The nervous system’s functions
Organization of the Nervous System The central nervous system (CNS) consists of the brain and spinal cord, which occupy the dorsal body cavity. The CNS is the integrating and command center of the nervous system. It interprets sensory input and dictates motor responses based on past experience, reflexes, and current conditions. The peripheral nervous system (PNS), the part of the nervous system outside the CNS, consists mainly of the nerves (bundles of axons) that extend from the brain and spinal cord. Spinal nerves carry impulses to and from the spinal cord; cranial nerves carry impulses to and from the brain. These peripheral nerves serve as the communication lines that link all parts of the body to the CNS.
Types of Circuits
Basic Principles of Electricity The human body is electrically neutral; it has the same number of positive and negative charges. However, there are areas where one type of charge predominates, making such regions positively or negatively charged. Because opposite charges attract each other, energy must be used (work must be done) to separate them. Information Transfer Across Chemical Synapses, when a nerve impulse reaches the axon terminal, it sets into motion a chain of events that triggers neurotransmitter release. Neurotransmitter binds to postsynaptic receptors, the neurotransmitter diffuses across the synaptic cleft and binds reversibly to specific protein receptors clustered on the postsynaptic membrane.
The Synapse A synapse is a functional junction between neurons. The information-transmitting neuron is the presynaptic neuron; the information-receiving neuron is the postsynaptic neuron. Electrical synapses allow ions to flow directly from one neuron to another; the cells are electrically coupled. The major classes of neurotransmitters based on chemical structure are acetylcholine, biogenic amines, amino acids, peptides, purines, and dissolved gases.
Related Clinical Terms Neuroblastoma (nu″ro-blas-to′mah; oma = tumor) A malignant tumor in children; arises from cells that retain a neuroblast-like structure. These tumors sometimes arise in the brain, but most occur in the peripheral nervous system.
Related Clinical Terms Neuropathy (nu-rop′ah-the) Any disease of nervous tissue, but particularly degenerative disease of nerves.
Related Clinical Terms Neurotoxin Substance that is poisonous or destructive to nervous tissue, e.g., botulinum and tetanus toxins.
Related Clinical Terms Rabies (rabies = madness) A viral infection of the nervous system transmitted by the bite of an infected mammal (such as a dog, bat, or skunk). After entry, the virus travels via axonal transport in peripheral nerve axons to the CNS, where it causes brain inflammation, delirium, and death.
Related Clinical Terms Shingles (herpes zoster) A viral infection of sensory neurons serving the skin. Characterized by scaly, painful blisters usually confined to a narrow strip of skin, often on one side of the body trunk.