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Download Chapter 31: Nervous System Nervous System – processes
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Chapter 31: Nervous System Nervous System – processes information for the body and responds Neuron: a cell that carries messages throughout the nervous system Parts of a Neuron Cell Body (Soma): largest part of a typical neuron; contains the nucleus and much of the cytoplasm Dendrites: extension of the cell body of a neuron that carries impulses from the environment or from other neurons TOWARD the cell body Axon: long fiber that carries impulses AWAY from the cell body of an neuron Schwann Cells: cells that grow around an axon and wrap it in layers of their own cell membrane Myelin Sheath: insulating membrane surrounding the axon in some neurons made by Schwann cells Nodes of Ranvier: gaps in the axon where there is no myelin sheath Axon terminal: the end of an axon Nerves: clusters of neurons into bundles of fibers 3 Types of Neurons: Sensory neurons – carry impulses from sense organs to brain & spinal cord. Motor neurons – carry impulses from brain or spinal cord to muscles or other organs Interneurons – carry impulses between sensory & motor neurons Nerve Impulse Messages are sent by nerve impulses that travel rapidly from cell body down the axon and then to the next neuron. Resting potential is the electrical charge held when a neuron is NOT carrying an impulse. As an impulse is sent along neurons, the neuron develops an action potential: a difference in electrical charge across cell membrane that allows the impulse to travel down the neuron similar to a row of dominoes. The myelin sheath protects and insulates the nerve just like electrical wires are insulated by a protective coating. Prevents short circuiting. Impulses jump from node to node in myelinated nerves to move faster Synapse Synapse: small space between nerves, where axon of one nerve meets dendrite of the next nerve Nuerotransmitters: chemical signals sent by one neuron to another across synapse gap Drugs and Neurotransmitters Stimulants like cocaine increase release of neurotransmitters, particularly the neurotransmitter dopamine, speeds up nervous system giving feeling of energy, well-being, and pleasure. Depressants, like alcohol, enhance effects of neurotransmitters that prevent some nerve cells from firing, calming parts of the brain. Depressant drugs reduce effects of natural processes of relaxation. Opiates: mimic natural chemicals in the brain called endorphins, which help overcome sensations of pain. After using opiates the body gets used to higher levels of endorphins and cannot naturally produce enough endorphins for the body. Organization of Nervous System Central Nervous System (CNS): brain and spinal cord - Brain is protected by skull, spinal cord by the vertebrae - Meninges: 3 layers of tough tissue that protects brain and cord - Cerebrospinal fluid: fluid between meninges that cushions brain and spinal cord Cerebrum: largest part of brain, responsible for learning, intelligence, judgement. Divided into a left and a right hemisphere. Cerebral Cortex: surface of the cerebrum. It is deeply creased and processes information from the senses, controls body movements. Cerebellum: Second-largest part of brain. Coordinates and balances the actions of muscles so the body moves gracefully and efficiently. Brain Stem: connects brain to the spinal cord. Includes medulla oblongata, pons. Controls blood pressure, heart rate, breathing Spinal Cord: links brain and rest of the body Reflex – quick automatic response to stimulus. Travels from sensory neuron to spinal cord then to a motor neuron response. Peripheral Nervous System Includes all the nerves and associated cells that connect the brain and spinal cord to the rest of the body 2 Divisions of Peripheral Nervous System Sensory division: carries information from the sense organs to the CNS Motor division: transmits info from the CNS to the rest of the body - Somatic Nervous System: Controls voluntary (conscious) movements. Some are also part of reflexes and act with or without conscious control. - Autonomic Nervous System: Regulates activities that are not under conscious control; heart beat, digestive system muscles. 1. What do you see happening in this picture? 2. What part of the nerve is damaged? 3. How do you think this damage would affect the Nervous System? 4. How will it affect traveling impulses? 5. How might this disorder affect a person’s life?
