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 McGrawHill narrated animation & quiz:
• http://highered.mcgrawhill.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 postsynaptic neuron
• acetylcholine (excitatory) causes Na+
channels to open, propagating the
action potential
Animations
• Quick McGraw-Hill narrated animation
with quiz:
• http://highered.mcgrawhill.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