CH. 28 and 30 - I Structure and Functions of the Nervous...

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I. Structure and Functions of the Nervous System A. they all have specialized structures that enable them to convey electrical signals I I. central nervous system (CNS) - the brain and the spinal cord 1. the body's main information processing center B. makes up the peripheral nervous system (PNS) - nervous tissue outside the CNS 1. delivers information to the CNS 2. carries messages from the CNS to other organs through nerves C. nerve - consists of one or more bundles of neuron fibers surrounded by connective tissue. 1. Sensory Input a) PNS receives information about an environmental change, or stimulus b) Neurons that carry info about stimuli to the CNS are called sensory neurons (1) Some sensory neurons detect stimuli directly (2) most stimuli are received by sensory receptors . 2. Integration a) CNS interprets the information b) neurons located entirely within the CNS, which are called interneurons 3. Motor Output a) CNS orders a response b) Neurons that carry responses away from the CNS: motor neurons . D. The Knee-Jerk Reflex: An Example
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1. a rapid, automatic response known as a reflex 2. The nervous system pathway that regulates a reflex is called a reflex arc III. Structure of a Neuron A. cell body- houses the neuron's nucleus and most of the organelles B. dendrites - receive signals & carry them to the neuron's cell body C. axon - carry elect. impulses away from cell body& to other cells 1. end of axon forms a clump of knobbed branches; play a role in transmitting messages to another neuron or other cell 2. Some neurons have very long axons 3. insulated by a thick coat of myelin sheath (chain of oblong beads0 4. Between the "beads" are uninsulated spaces called nodes 5. Electrical signals jump from node to node IV. A Neuron at Rest A. Resting Potential 1. A resting neuron stores electrical energy 2. plasma membrane, which separates ions located inside and outside the cell. 3. B/c opposite charges attract, separating them is a form of potential energy 4. holding opp. charges apart produces an electrical "pressure" called voltage 5. Voltage is measured in units called volts 6. voltage of -70 mV (The - indicates that the inside of the nerve cell is negative) 7. voltage across the membrane of a resting neuron: resting potential B. Ion Channels
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1. Na + - concentrated outside the neuron &K + -concentrated inside 2. channels allow the ions to diffuse from high to low concentration 3. more K + ion channels than Na + ion channels 4. unbalanced diffusion cause of the outside of the cell being positive C. Ion Pumps 1. Pumping chemicals in a direction opposite to diffusion requires energy D. resting potential & concentration diff of Na + & K + make it sensitive to stimulation. V. How a Nerve Signal Travels A. Triggering the Nerve Signal 1. When stimulation occurs, the voltage changes at the point of stimulation.
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