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Unit Three Nervous System Lisa Michelek Regulation • Regulation is the life process by which cells and organisms respond to changes in and around them. • The actions of the nervous and endocrine systems control and regulate the body. • These two systems allow us to adjust to internal as well as external environmental changes. Nerve Regulation • There are three parts to nerve regulation: – The stimulus – The impulse – The response • A stimulus is a specific change in the environment that affects the nervous system. • A response is a reaction to this stimulus. Nerve Regulation • Many organs and glands of the body receive stimuli that are translated into impulses. • An impulse is an electrical or chemical message that is carried by nerve cells. • The impulses are then transferred to the central nervous system (brain and spinal cord). • The central nervous system then sorts out and interprets the incoming impulses. • The impulse is then sent to organs or glands. • These organs and glands provide responses to these impulses. Human Nervous System • The human nervous system includes the brain, spinal cord, and nerves that lie outside of the brain and spinal cord. • Nerve cells receive impulses and send them to various body parts. Nerve Cells • Nerve cells are also called neurons. • A nerve cell is made up of a – Cell body – containing the nucleus and cytoplasm – Dendrites – branched parts that receive impulses from other neurons or sense organs – Axon – a single, long fiber that carries impulses away from the cell body Nerve Cells • Between the dendrites of one neuron and the axon of another is a space called a synapse. • Impulses cross the synapse by means of chemical neurotransmitters. Nerves • A nerve is a bundle of neurons or parts of neurons. • Nerves can be classified as – Sensory – carry impulses to the brain and spinal cord – Motor – carry impulses from the brain and spinal cord to the various body parts such as muscles or glands – Mixed – contain both sensory and motor fibers • A nerve fiber is like a telephone line carrying messages to and from your home. The Brain • The brain is the major control center of the body. • The bones of the skull surround and protect the brain. • The cerebrum, cerebellum, and medulla are three parts of the brain. The Brain - Cerebrum • The cerebrum is the center of thinking, memory, emotions, sensory impulse interpretation, and all voluntary activity. • It is the largest part of the brain. • When you take a test, you are using your cerebrum. The Brain - Cerebellum • The cerebellum is responsible for coordination of muscles and is the center of balance. • When you bounce a basketball, you are using your cerebellum. • Alcohol reduces the ability of the cerebellum to coordinate muscle activity. – This results in slurred speech and unbalanced walking. The Brain - Medulla • The medulla or brain stem is the center of respiration, heartbeat, and other involuntary activities. • Your medulla is controlling all the activities of your body that you cannot control such as breathing and peristalsis. The Spinal Cord • The spinal cord is the tubular mass of nerve cells that extends from the brain stem downward through the center of the spinal column. • It is surrounded and protected by the vertebrae of the spinal column (backbone). • The spinal cord relays impulses to and from the brain and is the center of some reflex actions. Receptors • Receptors are special structures that are sensitive to stimuli. • Receptors receive messages. External Receptors • External receptors, called sense organs include – – – – – Eyes Ears Nose Tongue Skin. Internal Receptors • Internal receptors are located in the internal organs • They allow the brain to detect – – – – Hunger Thirst Muscle position Carbon dioxide levels in the blood. Involuntary Behavior • The total response of an organism to stimuli is known as behavior. • The response may be inborn or learned, voluntary or involuntary. • Examples of Involuntary behaviors that occur automatically without conscious control include: – Contraction of heart and diaphragm muscles – Secretion of glands – Simple reflexes ( knee jerk and iris movement) Involuntary Behavior • Examples of Involuntary actions that are acquired by the individual through repetition include: – Writing one’s name – Riding a bike – Playing a musical instrument The Reflex • The reflex is an example of involuntary behavior. • A reflex action does not require thought; it is an automatic action. • Blinking and the knee jerk are examples of a reflex. Voluntary Behavior • Voluntary behaviors require thinking. • The impulses start in the brain and are carried by nerve cells to muscles or glands. • The muscles or glands respond in a certain way. • Voluntary actions include – Measuring with a meter stick – Picking up a book – Building a model airplane. Nervous System Disorders • Paralysis is caused by severe damage to the spinal cord. – It results in the loss of feeling and muscle function in the lower parts of the body. – Paralysis occurs because impulses to and from the lower body muscles cannot be transmitted to the brain. Nervous System Disorders • Meningitis is an inflammation of the membranes that surround the brain and spinal cord. – The disease is caused by bacteria. – The symptoms include severe headache and stiffness of the neck. – Meningitis can be fatal. – Antibiotics are used to treat meningitis. Nervous System Disorders • Polio is a viral disease of the central nervous system that can cause paralysis. – It can be prevented by immunization. Drugs and the Nervous System • Drugs affect the nervous system in many different ways. • Some drugs create a feeling of euphoria (well-being). • Other drugs cause a decrease in inhibitions, or an inability to stop doing something that a person would not normally do. • Using some drugs results in tolerance when they are taken continually for a few weeks. – This means that increasingly larger amounts are needed to get the desired effect. Drugs and the Nervous System • There are some drugs that cause stimulation (excitement) and feelings of high energy. • Physical dependence, or addiction, can result from using drugs. • When the drug is withheld, the addict suffers physical illness and withdrawal symptoms. Nervous System Overview • http://www.youtube.com/watch?v=x4PPZC LnVkA