2 Functional Properties of Neurons 1. Irritability Ability to respond to stimuli 2. Conductivity Ability to transmit an impulse

How neurons communicate Action Potential electrical signal that travels on the membrane of a neuron based on movements of ions between the outside and inside of the cell

If the stimulus reaches threshold then an action potential is started in the neuron and will travel down the membrane (This is called a nerve impulse) This is the ALL or NONE PRINCIPLE.

Steps to a Nerve Impulse Polarized: Resting neuron Inside membrane is slightly – Outside membrane is slightly + Most membrane channels are closed, there is some normal diffusion of K+ or Na+ between cell and the environment through the sodium/potassium pump (active transport) Stimulus Occurs: Depolarization: Active Neuron Sodium (Na+) channels open allowing Na+ to diffuse into the cell quickly This causes the inside to become + (outside -) Repolarize: Normalizing K+ gates open in order to allow K+ to diffuse out of the cell – this restores the membrane (+ outside, - inside)

Nerve Impulses Refractory Period K+ must be moved back to the inside of the cell and NA+ must be pumped out of the cell in order to prepare for the next impulse The sodium-potassium pump ( a membrane channel), using ATP, restores the original configuration

Nerve Impulses another way Figure 7.9a–b

Nerve Impulses Figure 7.9c–d

Nerve Impulses Figure 7.9e–f

Simple Video showing Action Potential http://video.google.com/videoplay?docid=-6890770586678681705&ei=3qb9SqPxO5_arQKQp-inBA&hl=en# http://outreach.mcb.harvard.edu/animations/actionpotential.swf http://video.google.com/videoplay?docid=-6890770586678681705&ei=3qb9SqPxO5_arQKQp-inBA&hl=en#docid=-4821246047499143591

Transmission of a Signal at Synapses Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a presynaptic nerve’s axon terminal http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis%20and%20Exocytosis The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter An action potential is started in the post-synaptic dendrite

Name the phase and describe what is happening in each step.