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