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CA (650,000)
UTSC (30,000)
NROB60H3 (100)
Lecture

NROB60H3 Lecture Notes - Voltage-Gated Potassium Channel, Resting Potential, Oscilloscope


Department
Neuroscience
Course Code
NROB60H3
Professor
Janelle Leboutillier

Page:
of 19
NROB60 - LEC06
NROB60 - LEC06
key SYMBOLS
RMP - resting membrane potential
MP - membrane potential
AP - action potentials
VG - voltage-gated
ANNOUNCEMENTS
- lecture test is NOT cumulative
- final exam
>- 4,5,6, all of 7 and appendix
- keep e-mail questions v.brief if close to examinations
- developmental section is excluded from C7
[?] What page range is this?
- some figures will be excluded (see slides)
[1]
LECTURE OVERVIEW
LECTURE OVERVIEW
OUTLINE OF LECTURE
1. BRIEF REVIEW
2. THE AP
- In Theory
- In Reality
- do NOT need to know Box 4.2 (The Patch-Clamp Method)
[2]
BRIEF REVIEW FIRST
1. What is RP (resting membrane potential) the consequence of?
a) difference in [ion]'s inside vs. outside of neuron
b) membrane's semipermeable nature
2. Membrane mainly permeable to K+ ions
- RP is in range of -60 to -70mV when (eq) is reached b/ween:
a) diffusion P forcing K+ out of cell, and
b) electrostatic P forcing K+ into cell
=> that is why its called "potassium membrane" at rest
- inside of memb is primarily [K+], as a result of it being mainly perm. to K+
- v.close to (eq) pot. of K+ at rest
3. Na/K pump (sodium potassium pump) used to main ion balance b/c
there is gradual leakage of ions across membrane
- what maintains pot. is using sodium-potassium pumps
- some K+ channels leaky (not a total seal), so need to constantly
maintaining this balance
[3]
PROPERTIES OF ACTION POTENTIAL
Now we are looking at: what happens when RP is altered, to the extent that an
action potential may fire?
THE UPS AND DOWNS OF AN ACTION POTENTIAL
- oscilloscope is used to visualize the AP
- 4 main phases of AP
- RISING
- OVERSHOOT
- MP goes above 0 (becomes +ve)
- FALLING
- MP dropping back to RP
- UNDERSHOOT
- MP falling below RMP
Questions we are going to be answering
- going to look at what happens at each particular phase of AP
- what is going on wrt ion channels?
- as potential is changing, what is changing on membrane?
ANIMATION OF AP BY VOLTAGE-GATED Na CHANNEL
- To measure elec current, one technique is to insert 2 electrodes into neuron
- one for recording MP
- other to inject current, or divert current away
=> can either depolarize (make cell more +ve) or hyperpolarize
(make cell more -ve)
- elec. current gen'ed has to be large enough to gen. AP
- hyperpolarization: drives MP in -ve dir.
- makes MP more and more -ve
- voltage response dir. prop to magnitude of current
- ie. the extent of alteration in voltage is prop to amt of current
affecting it
How is AP gen'ed?
- if stimulus is sufficient to push it (MP) further than firing threshold, then AP is
gen'ed
- depolarization of memb past threshold sets changes in memb conductances,
which ultimately leads to gen'ion of AP
NOTE:
[!] AP is an all-or-none event
- amplitude doesn't change with size of stimulus
- once AP gen'ed, it doesn't vary when related to size of stimulus by its amplitude
and duration
=> will prod. similar amplitude and duration, regardless of size (aka str.) of
stimulus, or mag. of current incoming
RESTING PHASE (aka "steady state")