ACTION POTENTIALS The neuron membrane Three major types

ACTION POTENTIALS

The neuron membrane Three major types of embedded proteins • Sodium (Na+) gated channels • Potassium (K+) gated channels • Sodium-Potassium Pump Gated channels opened/closed based on conditions, allow facilitated diffusion when open Pumps – use ATP to do active transport (move against the concentration gradient

IV. Nerve Impulses A. Resting potential – 1. Both the sodium and the potassium gated channels are closed 2. The sodium-potassium pump is moving sodium out of the cell and potassium into the cell, creating concentration gradients

https: //www. youtube. com/watch? v=90 cj 4 NX 87 Yk 3. the neuron cell membrane is polarized (more positive outside than inside) to -70 m. V

B. Depolarization – a stimulus causes sodium gated channels to open, sodium moves into the cell by facilitated diffusion 1. Cause charge inside the cell to increase 2. If the impulse is strong enough (reaches the threshold) an Action Potential is generated (goes down the length of the axon)

C. Repolarization – 1. When the charge in the cell reaches +40 m. V, the change in charge causes the sodium channels to close and the potassium channels to open 2. K+ ions move out of the cell by facilitated diffusion, causing the charge inside the cell to decrease

D. Hyperpolarization – so much potassium leaves the cell that the charge inside goes down to -80 m. V (even lower than the charge of a polarized cell) 1. 1. This prevents another action potential from starting before one is finished (called a refractory period)

4. Return to resting potential 1. When charge in the cell reaches -80 m. V, this causes the potassium channels to close 2. Na+/K+ Pump restores resting potential

Saltatory conduction – transmission of an impulse through myelination