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The Nerve Impulse

The Nerve Impulse. Voltage is the measure of the electrical potential difference between 2 points. The 2 points of the neuron refer to the inside of the axon and the outside of the axon. Resting Potential.

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The Nerve Impulse

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  1. The Nerve Impulse Voltage is the measure of the electrical potential difference between 2 points. The 2 points of the neuron refer to the inside of the axon and the outside of the axon.

  2. Resting Potential • When the axon is NOT conducting an impulse, the inside of the axon is negative compared to the outside, -65 mV. • The concentration of Na+ is greater outside the axon and the concentration of K+ is greater inside the axon. • The unequal distribution of these ions creates this resting potential of – 65 mV. • The sodium-potassium pump, an integral membrane protein, actively transports Na+ out and K+ into the axon to maintain this unequal distribution. • The pump is always working because the membrane ion channels are somewhat permeable to these ions and are continually diffusing down their concentration gradients. • The membrane is more permeable to K+ than Na+, creating more positive ions outside the axon. Additional negatively charged organic ions inside the axon helps combine to create the resting potential.

  3. Motor Neuron Axon – resting potential of -65mV.

  4. Integral Membrane Proteins

  5. Action Potential • A rapid change in polarity across an axon membrane as the nerve impulse occurs. -65mV to +40 mV to -65 mV. • All- or -none phenomenon. • If a stimulus reaches the threshold, -40 mV, an action potential occurs.

  6. Action Potential • Depolarization - sodium gates open, Na+ flow down concentration gradient and enter the axon. • The membrane potential changes from -65 mV to +40 mV. • Repolarization – potassium gates open, K+ flow down concentration gradient and exit the axon. • The membrane potential changes from +40 mV back to -65mV. • This occurs in 2 ms!

  7. Myelinatedvs Non-myelinated • Myelinated axons conduct the impulse more quickly as the impulse jumps from node of Ranvier to nodeRanvier. • The action potential can travel up to 200 m/s! (450mph) • Nonmyelinated axons, carry the action potential down the axon one small section at a time. • As soon as the action potential has moved on the previous axon section undergoes a refractory period.

  8. Refractory Period • The sodium gates are unable to open. • The nerve impulse cannot conduct backwards. • This makes the action potential always move toward the axon terminals – the axon bulbs.

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