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Nervous System Nervous System - Function The basic functional units of the nervous system that transmit messages are cells called neurons. Signals travel through a neuron as electrical impulses. Neurons release chemical substances, known as neurotransmitters, to transmit information to other neurons, to muscles, or to glands. The chemical messages of the nervous system are transmitted over short distances, and their effects are short-lived. The nervous system allows for control and coordination of skeletal muscular movements that may be consciously predetermined, or may happen automatically, such as reflexes. Other parts of the nervous system control and coordinate subconscious body activities, including heart rate, gland secretions and smooth muscle movement in the digestive system. Some activities, such as breathing, can be controlled both subconsciously and consciously. The nervous system typically works quickly. It also allows us to integrate and store information, such as when you are learning. The nervous system transmits signals to different parts of the body to coordinate function. Electrochemical signals are processed in the brain and sent down the spinal cord, which runs the length of the back. From the spinal cord, peripheral nerves send signals out to the extremities. Return signals come in through sensory nerves and either return to the spinal cord for processing or back to the brain. The spinal cord processes reflexes and repeated patterns. Nervous System - Organs and Structures The nervous system is often divided into two functional parts: • • The central nervous system, which processes incoming information and initiates a response. The peripheral nervous system, which brings sensory information to, or carries motor output from, the central nervous system to initiate a reaction. Central Nervous System The major structures within the central nervous system are: • • Brain Spinal cord The brain has several lobes, each of which carries out specific functions and processes information associated with specific parts of the body. The spinal cord is located within the vertebral column and processes some reflexes but primarily transmits information to and from the brain along neurons. Specialized membranes called meninges cover the brain and the spinal cord to protect them. Additionally, a special fluid, called cerebrospinal fluid, chemically and mechanically protects the brain and spinal cord. Peripheral Nervous System The major structures within the peripheral nervous system are: • • Cranial nerves Spinal nerves The peripheral nervous system is composed of nerves outside the brain and spinal cord. Nerves are bundles of extensions from neurons that extend through the body in the peripheral nervous system. These nerves are categorized into the following functional groups: sensory nerves, which carry sensory input to the brain or spinal cord from the environment. • motor nerves, which carry motor impulses from the brain or spinal cord to muscles or glands. • mixed nerves, which have a combination of sensory and motor neurons in one nerve. The peripheral nervous system can be subdivided into two subdivisions: the somatic and autonomic divisions. The somatic nervous system includes sensory neurons that send sensory information from sensory receptors of the skeletal muscle, skin and special senses (including smell, taste, sight, hearing and equilibrium) to the central nervous system and motor neurons that control skeletal muscle. The autonomic nervous system monitors and regulates changes in the body's internal environment. These changes are not under voluntary control. Body processes controlled by the autonomic nervous system include the contractions of the stomach and other digestive organs, the heart rate, and contractions of blood vessels to control blood pressure and flow though the body. The autonomic nervous system is further divided into the sympathetic and parasympathetic divisions. The sympathetic nervous system controls functions that speed up the heart and increase energy usage during emergencies or times of stress. On the other hand, the parasympathetic nervous system controls functions that have the opposite effect—they reduce heart rate and decrease overall energy usage when the body is returning to normal after an emergency or during normal functioning. • Nervous System - Anatomy and Direction The brain is protected inside the skull. The spinal cord runs from the brain down through the bones of the spinal column. From the brain and spinal cord, nerves run throughout the body, including to the limbs.