Transmission of Nerve Impulses

1. Transmission of Nerve Impulses

2. Nerve Impulse • An electrical current, travels along dendrites or axons • Ions move through voltage-gated channels • Channels open/close in response to changes in electrical charge around them

3. Resting Membrane Potential • Polarized = charge difference between inside and outside of cell membrane • At rest, net negative charge on inside of cell

4. Resting Membrane Potential • Selectively permeable ion channels • Maintained by sodium potassium pumps (active transport) • let Potassium (K+) in easily • weak permeability to Sodium (Na+)

5. Resting Membrane Potential • Net Result: • more Potassium (K+) inside neuron • more Sodium (Na+) outside neuron

6. Stimulated Neuron • Stimulated neuron: (Example: light, sound, pressure) • Nerve Impulse begins when stimulus disturbs dendrite • Result: Membrane permeability changes

7. Stimulated Neuron • Sodium channels open andsodium ions flow into neuron • Lessens charge difference • Net charge inside neuron more positive • Called Depolarization

8. Depolarization • Local region inside the neuron has net positive charge and outside is net negative • Neighboring voltage-gated sodium channels open • If depolarization above threshold, there is complete reversal of membrane potential

9. Action Potential • Depolarization moves along the membrane = action potential • Called Action potential or nerve impulse

10. Action Potential • “All-or-none” response – either conducted over entire axon, or doesn’t happen at all

11. Repolarization • Sodium channels close & potassium channels open • Potassium (K+) floods out of the cell • Result: restores internal negative charge

12. Hyperpolarization • If K+ channels stay open after reaching resting potential • MorePotassium (K+) outsidecell than necessary • Result: Leaves greater negative charge inside cell

13. Refractory period • Potassium and Sodium on wrong sides of membrane • ‘Recovery period’ • Action: Sodium and Potassium channels restore them