Unit 2 Notes:

Nerve Impulses

Wednesday 2-24-2010

(1) Nerve Impulses

• Nerve Impulse = Electrical Current– Comes from the flow of positively charged ions– Ions move across the neuron’s membrane

(2) Neuron Membranes & Ions

• Neurons have Na+ and K+ pumps within their membranes.– Na+ gets pumped out of the neuron– K+ gets pumped into the neuron

• Na+ and K+ ions can only move across the membrane through these “pumps”.

(3) Neuron Resting Potential

• K+ channel a little “loose”:– Some K+ leaks OUT of the neuron– Build up of MORE positive ions outside of the

membrane

• Neuron Inside = More Negative

• Neuron Outside = More positive

• Neuron membrane = Polarized

(4) Ion & Charge Imbalance

• K+ ions leak out:– More (+) charges outside than in– Change in Charges

• Change = No more Homeostasis = AHHHH!

(5) Depolarization & Repolarization

• Depolarization:– Na+ ions need to flow in– Na+ pump opens Na+ flows inward– Depolarization Temporary Balance– Now more (+) on the inside than outside!

• Repolarization:– K+ ions need to leave– K+ pump opens TONS of K+ flows outward– Repolarization

http://upload.wikimedia.org/wikipedia/commons/2/2f/Action_potential_propagation_animation.gif

(6) Action Potential• Action Potential = Movement of Na+ and K+

ions in and out (across) the neuron membrane.

• Process: – Cycle of depolarization + repolarization– Stimulus Opening of Na+ Pumps

Movement Inward of Na+ Depolarization & Shutting of Na+ Pumps

– Depolarization Opening of K+ Pumps Movement Outward of K+ Repolarization & Shutting of K+ Pumps

http://www.youtube.com/watch?v=90cj4NX87Yk&NR=1

(7) Regaining Resting Potential• Action Potential caused imbalance of Na+

and K+ ions down axon membrane

• Change = NOT NORMAL

• Na+ and K+ Pumps Actively Transport (using ATP) Na+ and K+ back out/in of the axon– Na+ pushes out– K+ pushes in– More negative inside + Pumps Close

(8) Myelin & Action Potential

• Myelin = Insulation along axon

• Creates “gaps” between Na+ and K+ pumps in membrane…– “Gaps” electrical jumping– Ions fly down to the next set of pumps– Increases Speed of Current / Impulse