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
(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
(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