Electrochemical Impulse
9.2
Nerve Impulses(Image on previous slide: http://scientopia.org/blogs/scicurious/2011/05/04/science-101-the-neuron/)
• there are about 100 billion neurons in the human brain
• neurons can transmit 1000 nerve impulses per second
(Source: http://virtuallabs.stanford.edu/tech/images/ReactionTime.SU-Tech.pdf)
(Image from:http://www.thenutritionpost.com/tag/brain-scans)
Potential Difference(Image from: http://people.eku.edu/ritchisong/301notes2.htm)
• caused by relative concentrations of positive ions (Na+ and K+) on either side of the membrane
Neuron Membrane(Image from: http://www.columbia.edu/cu/psychology/courses/1010/mangels/neuro/neurosignaling/neurosignaling.html)
Resting Potential -70mV
• the resting membrane is about 50 times more permeable to K+ ions than Na+
• more K+ out than Na+ in
• polarized membrane
Excitation of Neuron
depolarization
+ repolarization
+ restoration of resting potential
= action potential
Depolarization (+40 mV)(Image from: http://www.lionden.com/nerve_animations.htm)
• Na+ channels open
• Na+ ions enter, causing charge reversal (depolarization)
Repolarization (-70+ mV)(Image from: http://elysium.wustl.edu/LingleLab/general.htm)
• Na+ channels shut
• K+ channels open
• K+ moves out of cell
Repolarization (-70 mV)(Image from: http://student.ccbcmd.edu/~gkaiser/biotutorials/eustruct/sppump.html)
Action Potential(Image from: http://jacobsussmanpsych100.blogspot.com)
Animation…
• Neat interactive animation of action potential; worth spending the time to go through:
• http://outreach.mcb.harvard.edu/animations/actionpotential.swf
• The dry but informative McGraw-Hill narrated animation & quiz:
• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html
From: http://commons.wikimedia.org/wiki/File:Action_potential_propagation_animation.gif
Action Potential(Image from: http://jacobsussmanpsych100.blogspot.com)
• refractory period (1-10 ms)
• threshold level
• all-or-none response
What happens when the action potential reaches the axon
terminals?
Synaptic Transmission(Image from: http://cwx.prenhall.com/bookbind/pubbooks/morris5/chapter2/custom1/deluxe-content.html)
Synaptic Transmission
• nerve impulse in presynaptic neuron causes calcium channels to open
• Ca2+ ions flow in and cause the release of neurotransmitters (such as acetylcholine) into the synaptic cleft
Synaptic Transmission 2
• neurotransmitter (e.g. acetylcholine) binds to receptors in dendrites of post-synaptic neuron
• acetylcholine (excitatory) causes Na+ channels to open, propagating the action potential
Animations
• Quick McGraw-Hill narrated animation with quiz:
• http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter8/animation__chemical_synapse__quiz_1_.html
• Narrated animation with quiz (a bit more detailed):
• http://bcs.whfreeman.com/thelifewire/content/chp44/4403s.swf
Other Neurotransmitters
• dopamine - regulates motor skills, emotional response, ability to express pleasure and pain
• serotonin - helps with sleep, calms anxiety, relieves depression
• histamine - allergic reactions• norepinephrine (noradrenaline)• epinephrine (adrenaline)
some related material from 9.4…
Anti-anxiety drugs(Image from: http://www.mxmcreation.com/medicine/generic-forms-of-valium.html)
• depressants such as diazepam (Valium) act by increasing the amount of inhibitory neurotransmitters at synapses
Pain
• substantia gelatinosa (SG) in the spinal cord interprets pain signals
• produces neurotransmitter that transmits pain information to injured tissue or organ
• more neurotransmitter = more pain
Natural Painkillers
• endorphins and enkephalins are produced by the pituitary and hypothalamus
• released in times of pain (and also during exercise, etc.)
• bind to receptors on SG cells so that neurotransmitter is not produced
Endorphins
endorphin= endogenous
morphine
(http://dictionary.reference.com/browse/endorphin)
Artificial Painkillers(Image from: http://www.drugrehabscalifornia.org/about-the-drugs/opiates)
• opiates such as heroin, codeine, morphine mimic the action of endorphins
• depressants don’t act on SG cells exclusively, but cause inhibitory