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Transcript
Ch. 35.2 THE NERVOUS SYSTEM Nearly all multicellular organisms have communication systems Specialized cells carry messages from one cell to another. NERVOUS SYSTEM CONTROLS AND COORDINATES FUNCTIONS THROUGHOUT THE BODY AND RESPONDS TO INTERNAL AND EXTERNAL STIMULI Neurons Electrical signals are called impulses NEURONS cells that transmit the electrical impulses SENSORY: impulses from sense organs to spinal cord and brain INTERNEURONS: connect sensory ad motor neurons Neuron Structure Largest part is the CELL BODY contains the nucleus and cytoplasm Metabolic activity takes place in the cell body Short, branched extensions DENDRITES carry impulses from the environment or other neurons TOWARD the cell body Long fibers AXON carry impulses AWAY from the cell body Neurons may have many dendrites by only one axon Form NERVES when axons and dendrites are clustered together Some neurons are surrounded by an insulated layer MYELIN SHEATH The Nerve Impulse Nerve impulse is like electricity through a wire Sodium/potassium pump ions diffuse across the cell membrane Builds up charges and creates a RESTING POTENTIAL Moving Impulse Nerve impulse begins when a neuron is stimulated by another neuron or by its environment The protein channels help ions pass in and out of the cell When positive ions flow in, gains a positive charge an then switches to a negative charge ACTION POTENTIAL One impulse causes another impulse at the next point on the membrane Threshold Strength of impulse is always the same Minimum level of a stimulus that is required to activate a neuron is THRESHOLD The Synapse Neurons make contact with other cells at the axon terminal Neuron transfer impulses to another cell is a SYNAPSE NEUROTRASMITTERS chemicals used by a neuron to transmit an impulse across a synapse to another cell
