4. Neurophysiology I Flashcards
Small Changes in Ko have big impact on EK
Increasing Ko by 4.5 mM depolarizes EK by ____ mV
Decreasing Ki by 10 mM depolarizes EK by ____ mV
Increasing Nai by 14 mM hyperpolarizes ENa by ____ mV
Decreasing Nao by 22 mM hyperpolarizes ENa by ____ mV
It’s all in the ratio
of ____ to ____ concentrations
19
3
18
4
Adding only 4.5 mM K+ to the extracellular solution depolarized the membrane by ____ mV
Removing 22 mM Na from the extracellular solution hyperpolarized the membrane by ____ mV
Increasing the permeability of Na to = K depolarized the membrane by ____ mV
This increase in ____ puts the “Action” in action potential
8.1
2.4
62
PNa
Take home messages from homework
- Changes in ____ have a big impact on EK and on Vm because Ko usually low and because relative permeability high.
- Increases in the relative permeability of the membrane to ____ have a big impact on Vm because ENa very depolarized
The greater the ____, the more influence an ion has on the membrane potential
Ko
Na+
permeability
So, we know
1) there is a electrical potential where ions at a given concentration are in balance (____)
2) the more permeable a membrane is to a particular ion X, the closer the membrane potential gets to ____
How do electrochemical gradients and changing permeability signal along a nerve membrane?
Nernst potential, Ex
Ex
Lidocaine
• Lidocaine reduces pain by blocking ____ channels in the nerves
• Why does this matter?
sodium
The membrane potential can be measured using electrodes
* Traditionally used with electrodes, connected to \_\_\_\_, measure difference in potential from ref electrode to inside cell * Electrode filled with \_\_\_\_, \_\_\_\_ to move * And translate solutional signal into \_\_\_\_ signal with \_\_\_\_ electrode > measure changes in membrane potential
volt-meter potassium chloride free electrical silver chloride
Optical measurements of membrane potential enable location information
Action potential signals from axons and dendrites loaded with membrane- potential sensitive ____ - great for studying neurons where ____ signal across regions
* Voltage sensitive dyes > advantage: can look at changes in membrane potential in diff parts of \_\_\_\_ (dendrites, soma, axon, etc.) * \_\_\_\_ of signal > sub 3 mV changes are weak, but the \_\_\_\_ information is astounding
styryl
heterogeneous
neurons
accuracy
spatial
Graded potentials
• Amplitude ∝ ____, few mV to 10 mV
• ____ electrical spread to neighboring membrane
• Amplitude ____ with distance from initial site
____ diffusion of charge runs out
* \_\_\_\_ neurons - the larger you poke the arger the amplitude * Further from intial site, the smaller the amplitude of the singal
stimuli strength passive decreases passive sensory
Action potentials
• Amplitude ____ – all or none, >____ mV
• ____ spread to neighboring membrane
• Amplitude ____ with distance from initial site
Active propagation perpetuates
constant
50
active
constant
The action potential -
all or none once reach threshold
* Rapid response, whole thing is over in \_\_\_\_ msec * RMP > depolarization from adj parts of membrane > \_\_\_\_ (point of no return) > continue all the way, depolarize into the positive portion > \_\_\_\_, rapidly the repolarization begins > hyperpolarization > brief period, you are more negative than resting potential > \_\_\_\_, \_\_\_\_ period
1.5 threshold overshoot undershoot refractory
Action potential 1: Membrane potential
- Resting potential very negative, close to EK: K+ ____ dominates
- Peak potential very positive and close to ENa: ____ permeability dominates
- Rapid repolarization: less
influence from ____ as inactivation
• Reduction in permeability to sodium, and increase with potassium - Brief undershoot: relative permeability to ____ greater than at rest
permeability
Na+
PNa
K+
____ changes in the permeability to Na+ and K+ underlie the action potentia
time-dependent
The Action Potential 2: Changes in relative conductance
Looking at the changes in conductance over the course of action potential:
The conductance is a term that’s analog to ____ and is the inverse of ____.
The lower your resistance, the higher your ____ analogous to
your increased ____ to the ions.
This is a ____ scale on the y axis **
permeability
resistance
conductance
permeability
log
Action potential due to changes in relative permeability to K+ and Na+
- To begin with, (and at the end) the “resting” membrane potential, conductance to ____»_space;Na+
- Na+ channels open as membrane ____ – voltage gated but as they open, membrane depolarizes further: ____ feedback-key to rapid
depolarization. As long as depolarize past a given threshold voltage, this positive feedback continues all the way until the ____ of an action potential
• Speed at which sodium permeability increase (speed at which channels open) is much greater - K+ channels also
open as membrane depolarizes but with ____ – slow rise and stop peak getting to ENa - Na+ channels ____ with time – shut closed so
influence of ENa is ____- lived.
• Within few hundreths of a ms, Na channels inactivate
• Domination of Na on potential is very rapid, very short
• As Na inactivate, rise in ____ of K channels - K+ channels shut more ____ as membrane gets more negative
• As they open, they bring the potential to Ek - very negative
• K are ____ dependent, but they’re slower to open, as the membrane becomes more negative, the ____ of K decreases, but slower
K+
depolarizes
positive
peak
delay
inactivate
short
permeability
slowly
voltage
conductance
Changes in conductance determine changes in membrane potential
Sodium channel activating and we go rapidly from
-90 to +10. We see the K+ channel conductance is
____ as the Na is ____. As we get
hyperpolarized, the K+ channels shut down. The
+10 mV is a much shorter period than the diagram
is showing but this is just another way to look at it
increasing
inactivating
Absolute and relative refractory periods
• Absolute refractory period – impossible to initiate another ____ because Na+ channel ____ or soon to be inactivated.
• Relative refractory period – ____ to initiate action potential because voltage- dependent ____ channels
open, pulling V
towards ____.
action potential
inactivated
harder
K+
Positive and negative feedback cycles in an action potential
- Opening of Na+ channels lets Na+ enter cell, which ____ membrane and further opens ____ channels
- Opening of K+ channels lets ____ exit cell, which hyperpolarizes membrane, decreasing the number of ____ channels that open
depolarizes
voltage-dependent Na+
K+
voltage-dependent K+
Gating of ion channels: how do they open and close
• Changes in voltage can gate the membrane > \_\_\_\_ changes in voltage sensitive ion channels
allosteric
Action potential due to changes in relative permeability to K+ and Na+
____ the membrane
____ channels open first, then inactivate ~1 msec
K channels open with ____, close when potential hyperpolarized
• A voltage sensor in both channels, a series of AA with \_\_\_\_ charges that can move easily through the channels • Both start in closed configuration, when MP is depol, the more + on inside, the voltage sensor of Na, physically moves towards the \_\_\_\_ of the channel > opens up the Na channel (\_\_\_\_) > Na rapidly drives in (large electrochemical gradient) • As soon as Na opens, inactivating \_\_\_\_ it snaps the channels shut again, Na+ has access to \_\_\_\_, but cannot access other side > inactivated state for as long as membrane is depolarized [voltage sensor is \_\_\_\_, but \_\_\_\_ is blocking from cytoplasmic side] • When membrane is hyperpolarized, the \_\_\_\_ moves back tdown and \_\_\_\_ moves out the way, which is closed ○ \_\_\_\_ GATES • Do same with K, start with volt sensor closed when mem is hyperpolazied, then depol and voltage sensor takes \_\_\_\_ to move through ○ At same time as \_\_\_\_ of Na • K flow out of the channels, and hyperpolarizes the cell, unlike Na, they don't \_\_\_\_, as long as depolarize K will flow through, but when you hyperpolarize, the voltage sensor moves back down and closed ○ \_\_\_\_ GATE
depolarize
Na
delay
positive
outside
allosterically
ball-and-chain
pore
open
ball-and-chain
voltage sensor
ball-and-chain
two
longer
inactivation
inactivate
one
Changes in conductance relate to physical changes in channels
When we talk about the ball
and chain: ____-
____-____
(IFM) is the inactivating ball
and is what moves to border the blocking once they have access when the Na+ channel opens.
isoleucine
phenylalanine
methionine
