Chapter 4: Neuronal Physiology Flashcards
Depolarization
a change in polarization that makes the membrane less polarized than at resting potential (closer to 0)
hyperpolarization
change in potential that makes the membrane more polarized than resting potential.
patch clamping
using a micropipette to isolate a single ion channel or receptor protein and measuring its electrical properties.
2 main types of membrane channels involved in neuronal physiology
1) leak: nongated channels, open all the time
2) gated: open and close in response to specific stimuli, typically to voltage or ligand binding.
graded potentials are ____, and serves as a ____ distance signal
graded potentials are PRIMITIVE, and serves as a SHORT distance signal
____ signal over longer distances without decay
action potential
chemically gated channels change confomation ____
allosterically
the magnitude of a triggering effects can be seen by a graded potential’s ____
size(amplitude) and duration. the stronger a triggering event, the more Na+ channesl open, and the more + charge enters the cell, resulting in a larger graded potential.
in terms of graded potentials, the longer the triggering even, the ____ the graded potential
longer the graded potential.
T/F: GPs are only depolarizing
false. they are depolarizing or hyper polarizing.
graded potentials spread by ____ current flow and are ____ by resistances
graded potentials spread by PASSIVE current flow and are IMPEDED BY resistances
directionality in terms of graded potentials
a graded potential occurs in one segment where the channel opens, and the initial active area moves to adjacent segments in BOTH DIRECTIONSS until it decrementally fades away.
graded potential depolarization is caused by:
Na+ influx.
orthodromic conduction
movement of AP from dendrite to terminals
Antidromic conduction. When is this seen?
reverse movement of AP from terminal to dendrite. seen in nerve bundles that carry both afferent and efferent neurons/
Why are graded potentials decremental?
GPs involve PASSIVE current flow. NOthing is maintaining or helping to propagate the current. over distance, current leaks out through uninsulated parts of the membrane, reducing current avaible to flow down the membrane.
decremental graded potentials can be explained by ___
ohms law
what types of neurons utilize graded potentials?
nonspiking neurons: neurons that use graded potentials for communication.
examples of a graded potential
pacemaker potentials, slow wave potentials.
Graded potentials are seen in post synaptic potentials that ____ to trigger an ____
Graded potentials are seen in post synaptic potentials that SUMMATE to trigger an ACTION POTENTIAL
Define action potential
a rapid, self propagating electrical signal along the membrane that temporarily reverses the negative resting potential.
T/F: Action potentials are decremental
false. they are propagated and do not fade down while moving
Briedly explain the temporary potential reversal
1) EPSPs/GPs summate to cause slight depolarizations at the axon hillock
2) the axon hillock reaches membrane threshold (-50mv), triggering the opening of voltage gated Na+ channels
3) the opening of VG channels causes net Na+ influx, resulting in depolarization to positive potential (potential reversal)
4) just as rapidly, membrane repolarizes and drops to resting potential (initially hyper polarizes)
changes in ____ _____ triggers the action potentials
changes in ion permeability
the most rapid changes in ion permeability is due to ____
positive feedback of sodium influx.
2 main gates of the voltage gated sodium channel
1) activation gate: guards the channel by opening and closing
2) inactivation gates: ball and chain AA’s face the ICF and plug the opening by preventing any Na+ from entering
describe the 3 conformations of the voltage gated sodium channel
1) Closed but CAPABLE of opening: activation gate is closed, but the inactivation gate is open
2) Active: both activation gate and inactivation gates are open
3) Closed and cannot open: activation gate is OPEN , but the inactivation gate is CLOSED.
What is the conformation of the sodium voltage gated channel when the membrane is in resting potential?
closed but capable of opening: activation gate is closed, but the inactivation gate is open.
explain the positive feedback system of sodium
the passive spread of current from adjacent depolarized sites (GPs, EPSPs) cause depolarization of membrane, opening SOME Na+ channels. the opening of these channels brings the membrane to THRESHOLD potential, opening a multitude of Na+ channels and triggering an explosive influx of Na+, resulting in further depolarization.
how many gates does a voltage-gated potassium channel have?
1.
what is the conformation of the potassium voltage gated channel when the membrane is at resting potential?
closed. it wants to open when the membrane reaches threshold potential, but it is so slow that it opens much later than the voltage gated sodium channels, which also opens in response to threshold potential being reached.
at threshold, the na+ VG channel is in ____ state, and the K+ channel is ____
at threshold, the na+ VG channel is in ACTIVE state, and the K+ channel is CLOSED
at peak of the depolarization, the Na+ VG Channel is in _____ state, and the K+ channel is _____
at peak of the depolarization, the Na+ VG Channel is in CLOSED AND CANNOT OPEN state, and the K+ channel is OPEN
no more Na+ influx, rapid K+ efflux. Na+ Channel cannot open at all, the axon is in absolute refraction.
at hyperpolarization, the Na+ VG Channel is in _____ state, and the K+ channel is _____
at hyperpolarization, the Na+ VG Channel is in CLOSED BUT CAPABLE OF OPENING state, and the K+ channel is OPEN
efflux of K+ still occuring, causes cell to get increasingly negative. the Na+ channel is capable of opening in the EPSP/GP is strong enough to bring the membrane from hyperpolarization to threshold, so an AP can be triggered while hyperpolarized, its just harder to do so. the membrane is thus in RELATIVE refractory period.
T/F: The body waits for the Na+/K+ Atpase pump to re-equilbrate and reset the membrane to resting potential before another AP can be triggered
false. the body has a large enough ion surplus to fire many APs without Na+/K+ maintaining the gradient. At some point however, ion concentration would deplete though, so it is still important to have a functioning pump.
compare APs and GPs in terms of triggering event
AP: triggered by summation of depolarization at the axon hillock or by passive spread of depolarization from adjeacent node of ranvier
GP: specific stimulus
compare Aps and GPs in terms of ion movements that changes potentials
AP: depolarization caused by Na+ influx
GP: can be a depolarization of hyperpolarization event. Therefore, could be Na+ influx or other ion influx (Cl-, K+ efflux or Ca2+ influx)
compare Aps and GPs in terms of magnitude
AP: all or none law. Aps are all the same size and duration as long as threshold is reached
GP: differ in magnitude and duration depending on stimulus.
compare AP and GP in terms of duration
AP: all last the same length, and are very short
GP: can last a long time depending on magnitude of stimulus. the more VG Channels open, the longer the GP.
Compare AP and GP in terms of magnitude with distance from initial site
AP: non decremental propagation
GP: decremental. Current is lost as current escapes through uninsulated portions of the membrane. passive current flow.
Compare AP and GP in terms of refractory period.
AP: has an absolute and relative refractory period
GP: no refractory period
Compare AP and GP in terms of summation
AP: cannot be summated
GPs: can be summated spatially or temporally
Compare Ap and GP in terms of how they change membrane potential
AP: always depolarizes
GP: can be depolarizing or hyper polarizing
Compare Ap and GP in terms of location
AP: occurs in regions with sufficient number of voltage gated Na+ channels (nodes of ranvier and axon hillock of axon)
GP: occurs in cell bodies and dendrites
NOTE: when comparing graded potentials to APs, remember;
IMPREST (LTD) like its a company:
I: Ion (type of ion)
M: magnitude
P: Propagated or decremental?
RE: Refractory period
S: Summation (how are aps and gps summated)
T: poTential change (depolarizing or hyperpolarizing)?
L: locatoin
T: Triggering event
D: Duration.
Nerve
a bundle of axons Inside the PNS
Fiber tract
bundle of axons INSIDE the CNS
Ganglion
a group of cell bodies in the PNS with a similar function
Collaterals
branching off the main axon that can terminate at other regions
Axon Hillock
the trigger zone of Aps. Site of Ap initiation if GPs at the dendrite are of significant magnitude to bring the membrane to threshold. Connects axon to the cell body
T/F: GPs and Aps overlap. Why or why not?
False. Gp and Ap sites do not overlap beacuse Aps only occur where there are significant numbers of voltage gated Na+ ion channels. Gps occur where there aren’t many VGNa+ channels (Dendrites and cell body), but they can be summated to elicit an AP in an adjacent region with VG na+ channels.
the site where an electrical AP signal turns to chemical neurotransmitter signal
axon terminals.
the ___ limits the frequency of Aps
the refractory period. Ensures one-way propagation with no backflow of APs.
Absolute refractory period
completely refractory membrane. no AP can occur when membrane is absolutely refractory. This is because the Na+ VG Channels are in “closed and cannot open state”
Relative refractory period
when the membrane is hyperpolarized. It is capable of triggering another AP because the VG Na channel is in closed but capable of opening state, but it needs a stronger trigerring event.
multicellular organism that does not use APs
sponges
name toxins that inhibit voltage gated Na+ channels
1) tetrodoxin (puffer fish)
2) Saxitoxin (dinoflagellates)
toxins that prolongs the activation of K+ channels and prevents APs
dendroxin (black mamba): prolongs K+ channel activation
All or none law
an excitable membrane either responds to a triggering event with a maximal AP that spreads non-decrementally throughout the membrane, or it doesn’t happen at all.
strength of stimulus is Encoded by
the number of APs per unit time to be propagated along the fiber. a stronger stimulus resultsin more neurons reaching threshold and thus total info sent to the CNS is also increased.
define Contiguous conduction. Where does this happen? Drawbacks?
AP spreads along every patch of membrane down the length of an axon.
Occurs in unmyelinated axon, and the AP waveform triggers new AP at adjacent sites like a wave.
Drawbacks: can only occur in short distances. depolarization to threshold takes time. AP must be regenerated at each point along the axon.
Define saltatory conduction. Where does this happen? Why is this method of propagation better than contiguous?
the leaping of APs from each node of ranview to the next. it occurs in mylenated fibers. All the VG Na+ channels are located in smaller areas (nodes)
It is better because it does not take as long for the area to depolarize, since the area of depolarization is confined to small notes rather than the entire axon.
Takes less ENERGY as well, because na+ k+ atpase pump only needs to maintain potential at the nodes rather than the entire axon.
