Unit 4.pdf - NERVOUS SYSTEM Nervous system receives and processes sensory information from external and the internal environments \u2022 Two major

Unit 4.pdf - NERVOUS SYSTEM Nervous system receives and...

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NERVOUS SYSTEM - Nervous system: receives and processes sensory information from external and the internal environments Two major divisions: - Central nervous system (CNS): consists of the brain and spinal cord Spinal cord provides a means of communication between brain and PNS Process information and initiate commands - Peripheral nervous system (PNS): consists of nerves, which lie outside the CNS Bring information to CNS and commands from the CNS - Two types of cells found in the nervous system: Neurons: cells that transmit information within the nervous system Neuroglia: cells that support and nourish the neurons NEURONS - Three types of neurons: Sensory (afferent)—found in PNS: detects changes in environment, signals to inform the CNS Interneuron—found in CNS: receives/integrates information from multiple neurons, initiates a response Motor (efferent)—found in PNS: relays commands from the CNS to an effector (ex. gland or muscle fiber); executes a response to the change in the environment NEURON STRUCTURE - Cell body: nucleus and organelles - Dendrites: receive signals from the environment or other neurons Have specialized receptors: proteins embedded in their membrane which detect stimuli in the environment. Dendrite receptors exist that detect heat, cold, pressure, chemicals (released from other neurons, or from tissue injury—pain), etc. - Axon: single, long extension that carries signals, in the form of a nerve impulse, towards another neuron or target tissue Nerve: a bundle of axons from multiple neurons - Myelin sheath: cover the axon of many neurons Made of neuroglia that wrap their lipid membrane around the axon Myelin covers only a portion of the axon, leaving gaps in between (Nodes of Ranvier) The presence of myelin increases the speed of nerve impulse conducting and permits rapid communication within and between neurons DEMYELINATION - Multiple sclerosis: a progressive autoimmune disease whereby the body attacks and destroys oligodendrocytes that form myelin in the CNS “Demyelination” of CNS axons results. Ultimately neurons function as if they had no myelin NEURONS - Communication is crucial function of neurons Nerve impulses: electrochemical changes used by neurons to convey information along their axon, and to neighboring neurons - Electro: neurons use electrical changes to transmit a signal down the length of their axon - Chemical: when the electrical signal reaches the end of the axon, neurons use a chemical signal to communicate with the next cell “RESTING” NEURONS - What’s happening when a neuron has not detected any changes, and does not have anything to communicate?
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  • Fall '07
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