Transcript Nerve Impulse Notes

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
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
Figure 7.9a–b
• 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.
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
Figure 7.9e–f
Nerve Impulses
Figure 7.9c–d
Simple Video showing Action Potential
• https://www.youtube.com/watch?v=ifD1YG07fB8
• https://www.youtube.com/watch?v=7EyhsOewnH4
• http://outreach.mcb.harvard.edu/animations/actionpotenti
al_short.swf
Long, but good explanation of Action Potential
• https://www.youtube.com/watch?v=-6t_n6kTj1A
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::535::/sites/dl/free/00
72437316/120068/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