THE NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM BRAIN PERIPHERAL NERVOUS SYSTEM SPINAL CORD AUTONOMIC SYMPATHETIC SOMATIC PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM 1 Sympathetic Nervous System High energy usage Prepares for fight or flight Pupils open Pulse quickens Adrenaline released 2 Parasympathetic Nervous System Conserves energy Prepares for rest Pupils constrict Pulse slows STRUCTURE OF NEURONS Three main parts DENDRITES CELL BODY AXON Saltatory Conduction Myelin Sheath Nodes of Ranvier HOW A NEURON FIRES Impulse reaches the axon terminal the end of an axon from which the axon releases its message The axon terminal has within it several synaptic vesicles containing a neurotransmitter Action Potential 40 Na in Depolarizatio n K out Repolarizatio n 0 70 Resting Potential K keeps leaving Hyperpolarizati on Na K pump AP STEPS 1 Resting potential 70 mv sodium potassium pump keeps Na outside and K inside the cell 2 Depolarization sodium gates open and Na enters 3 Threshold 55mv reached with influx of Na 4 Action Potential peak 40 mv 5 Repolarization sodium gates shut potassium gates open Na stops coming in and K leaves 6 Refractory periodoverreaction 90 7 Resting state Na K pump regains balance 70
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