2 Functional Properties of Neurons 1 Irritability Ability

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. 9 a–b

Nerve Impulses Figure 7. 9 c–d

Nerve Impulses Figure 7. 9 e–f

Simple Video showing Action Potential • http: //video. google. com/videoplay? docid=- 6890770586678681705&ei=3 qb 9 Sq. Px. O 5_ar. QKQpin. BA&hl=en# • http: //outreach. mcb. harvard. edu/animations/actionpotentia l. swf • http: //video. google. com/videoplay? docid=6890770586678681705&ei=3 qb 9 Sq. Px. O 5_ar. QKQpin. BA&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. mcgrawhill. com/olcweb/cgi/pluginpop. cgi? it=swf: : 535: : /sites/dl/free/00 72437316/120068/bio 02. swf: : Endocytosis%20 and%20 Exocytosis • 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.