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Unit 1 Opener

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Video 1: multi-electrode recording onan oscilloscope

Video 2: multi-electrode recordings of motor cortex during tracking task

Video 3: implications for rehabilitationfor stroke and spinal cord injury

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Mo to r C o rtex, Spike Rec o rdings, Cyberkinetics

July 2006

http://www.cyberkineticsinc.c om /c o ntent/index.jsp

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Intr o ducti o n t o Electrical Signaling of Nerve Cells

A m icr o electr o de m ade of glass and f illedwith a salt s o lutio n (c o nductive) can rec o rd

the transm

em

brane vo

ltageof

a nerve cell

The f irst event that happens when them icr o electr o de is inserted is that a verys m all negative v o ltage is rec o rded, calledthe resting m e m brane p o tential

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Intr o ducti o n t o Electrical Signaling of Nerve Cells

Neur o ns generate a negative p o tential at rest,called the resting m e m brane p o tential Can be rec o rded inside and o utside of nerve cells T ypically between -40 t o -90 mV

Neur o ns generate electrical signals based o nthe f lo w of io ns acr o ss their plas m a m e m brane

Recept o r p o tentials are due t o activati o n of sens o ry neur o ns by external sti m uli Light, heat, s o und

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Electrical Signals C o ntinued

Synaptic p o tentials the electrical p o tentialgenerated f r om comm unicati o n f r om o ne neur o nto an o ther Used in central and peripheral nerv o us syste m

W hen neur o ns send signals acr o ss a l o ngdistance d o wn the ax o n, acti o n p o tentials aregenerated.

Are the ax o ns g oo d c o nduct o rs of electricity? Ho w d o es the nerv o us syste m acc ommo date?

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F igure 2.1 T ypes of neur o nal electrical signals (Part 1)

P acinian Corpuscle

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F igure 2.1 T ypes of neur o nal electrical signals (Part 2)

Hippocampal P yramidal neuron

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F igure 2.1 T ypes of neur o nal electrical signals (Part 3)

S pinal motor neuron

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H yperp o larizati o n and Dep o larizati o n

Hyperp o larizati o n is when the m e m branepo tential bec om es mo re negative

Dep o larizati o n is when the restingm e m brane p o tential bec om es mo repo sitive A ctio n p o tential o ccurs when the thresh o ld

po tential is reached

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F igure 2.2 Rec o rding passive and active electrical signals in a nerve cell (Part 1)

Micr o leo ctr o de

co nnected t o battery

Negative current

applied, what w o uld

happen?

P o sitive currentapplied, what w o uld

happen?

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F igure 2.2 Rec o rding passive and active electrical signals in a nerve cell (Part 2)

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Speci f ics of acti o n p o tentials

Speci f ics of acti o n p o tentials Independent of current used t o ev o ke it

A

llo

r no

ne M ultiple acti o n p o tentials can o ccur i f thecurrent intensities are su ff iciently l o ng anda m plitude is great en o ugh

Leads t o f requency enc o ding Am plitude of synaptic p o tentials and recept o r

po tentials can be graded

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Io nic Mo ve m ents Pr o duce Electrical Signals

Electrical signals generated acr o ssm e m branes

Diff

erences in co

ncentratio

ns M e m branes are selectively per m eable Exchange of io ns acr o ss io nic channels

Pr o teins that all o w o nly certain kinds of io ns t o

cr o ss the m e m brane in the directi o n of their co ncentrati o n gradient

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F igure 2.3 T ransp o rters and channels mo ve i o ns acr o ss neur o nal m e m branes

- F riends at the Bears ga m e getsyo u t o a seat that is n o t yo ur ticket.

- T icket checker at Bears ga m eallo wing pe o ple t o go where theyare supp o sed t o go .

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Io n transp o rters and Io n channelsbasically w o rk against each o ther

To gether, they help t o generate the restingm e m brane p o tential, acti o n p o tentials,synaptic p o tentials, recept o r p o tentials

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F igure 2.4 Electr o che m ical equilibriu m (Part 1)

No electricalpo tential

F loo d le f t side with K+, and i o ns will f lo w d o wn c o ncentrati o n gradient

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F igure 2.4 Electr o che m ical equilibriu m (Part 2)

Greater the c o ncentrati o n ino ne side of the m e m brane of K+, then the mo re negative them e m brane p o tential

T his is part of theNernst equati o n

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Basic F eatures of the A ctio n P o tential

Nernst equati o n describes a m e m brane p o tentialper m eable t o o nly o ne i o nIf yo u wanted t o calculate the equilibriu m po tentials fo r an i o n use Nernst

Ho wever, David G o ldm an rec o gnized thatm e m branes are per m eable t o mo re than o ne i o n

Go ldm an equati o n describes h o w changingper m eability f r om o ne i o n t o an o ther generatesacti o n p o tentials

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T hree Im po rtant Io ns

S o diu m : Na +P o tassiu m : K+Chl o ride: Cl -

Equilibriu m po tentials fo r each i o n are devel o ped byusing the Nernst equati o nEx = R T /zF * ln [X1]/[X2] R is the gas c o nstant T is the abs o lute

te m perature

z is the valence F is the F araday c o nstantS o diu m -po tassiu m pu m p Receives energy f r om AT P

st o red in m ito ch o ndria Breaks AT P d o wn t o A DP

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Sh o w Resting P o tential A nim ati o n

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F igure 2.6 Resting and acti o n p o tentials arise f r om diff erential per m eability t o io ns

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Na resp o nds quickly playing an i m po rtant r o le in acti o n p o tential generati o n

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Na increases quickly but K changes mo re sl o wly during an acti o n p o tential

Rec o very ti m eneeded fo r Na to rec o ver Called re f ract o ry

peri o d

Na takes ti m e t o rec o ver but there isno re f ract o ry peri o dfo r p o tassiu mchannels

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F igure 2.7 Resting m e m brane p o tential is deter m ined by the K + co ncentrati o n gradient

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F igure 2.8 T he r o le of Na + in the generati o n of an acti o n p o tential in a squid giant ax o n (Part 1)

a) A n acti o n p o tential ev o ked under

no r m al c o nditi o ns

b) Na reduced by 1/3 n o tice that

rate of rise and a m plitude of acti o n

po tential is reduced

Na rest o red t o no r m al levels

acti o n p o tential shape is rest o red

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F igure 2.8 T he r o le of Na + in the generati o n of an acti o n p o tential in a squid giant ax o n (Part 2)

(D) Na is important in action potential generation

(E) Na is not that important for the resting membrane potential

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Sh o w A ctio n P o tential A nim ati o n

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Assign m ent fo r W eek 2Read

V ilis 7. To uch GO T Ohttp://www.physphar m .fm d.uw o .ca/undergrad/sensesweb/ W atch M acr om edia F lash Player

Print o ut PD F fo r class fo r T uesday.

Read Chapter 9 of Purves