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.

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