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• Cell body – nucleus and other organelles • Dendrites – branched, short and receive incoming messages from other cells or the environment • Axon – long, single fiber, conducts signal toward another neuron or effector • Supporting cells – protect, insulate and reinforce neurons • Myelin sheath – chain of beadlike supporting cells • Nodes of Ranvier – spaces in myelin, only points where the impulse can be transmitted – Signals can travel >150 m/sec (330 mi/hr) • Synaptic knob – relays signals to another neuron or effector Motor Neuron • Resting Potential – voltage (potential difference) across the plasma membrane of a resting neuron – Negative charge inside, positive charge outside • Stimulus – anything that causes a nerve signal to start • Action potential – selfpropagating change in the voltage across the plasma membrane How an impulse move through a neuron 1. Resting potential – negative on inside / positive on the outside 2. Stimulus allows a few positive ions to enter neuron. • • 3. 4. If strong enough stimulus then action potential Threshold potential – minimum change in membrane’s voltage to reach action potential Inside becomes positive and outside becomes negative Membrane returns to resting potential by allowing positive ions to diffuse back outside neuron • The action potential must be propagated (travel along the neuron) Propagation • Starts near the cell body and moves toward the axon terminals 1. In the 1st section of the neuron positive ions diffuse inward to generate an action potential 2. The 1st section allows positive ions to diffuse out of the neuron and prevents more positive ions from entering 3. 1st section then returns to resting potential