Neuro Flashcards
Dendrites
-signal reception
Soma (cell body)
-signal reception
Axon hillock
- signal integration
- sense change in membrane pot and initiates AP
Axon
- signal conduction
- APs conducted down to axon terminal
Pre-syn terminal
- Signal transmission
- NT released into synapse and transmits a signal to the target cell
Permeability
-incr P, incr # leak channels
current
= P + ions
ex- Na moving through a Na channel is Na current
Resting membrane pot (Vm)
- the voltage difference across the cell membrane AT REST
- inside is -70 mV
leak channels
- channels that are always open (not gated)– ion channels so they are selective
- permit unregulated flow of ions down their electrochem gradient until they are in equil
- they disrupt the conc gradient made by Na/K ATPase
Na/K ATPase
- actively transports N out and K in
- helps maintain conc gradients in order to do work. so it counters the effect of leak channels
- electrogenic pump
electrogenic pump
pumping ions in opposite directions in unequal numbers
Resting membrane pot reqs:
- electrical gradient
- chem gradient
- leak channels
- Na/K ATPase
Driving force =
= Vm - Ex
[K+] is higher on the
inside
[Na+] is higher on the
outside
[Cl-] is higher on the
outside
[A-] is higher on the
inside
-there is none outside so there is no permeability
Nernst equil pot (definition)
the membrane pot that will balance the conc for a particular ion. Conc bw the inside and outside will be balanced
Nernst equil pot =
RT/ZF ln [X]o / [X]in
(T/F) when an ion is in equil, it can still flow through a leak channel
T, it will just have no great flux
1 ion sets the membrane pot for the cell when
the cell only has leak channels for that particular ion
Why is Ca2+ very low in the inside of the cell? And describe the DF
- cell wants to tightly regulate Ca2+ bc it’s a second messenger
- DF is huge to go inside
Goldman-Hodgkin Katz eqn (definition) and why is everything normalized to K?
allows more accurate prediction of Vm bc P reflects pop of leak channels
-Normalized to K bc more K leak channels
Goldman-Hodgkin Katz eqn =
and ratios of ions
Vm = RT/F ln (pK [K]o + pNa [Na]o + pCl [Cl]i ) / (pK [K]i + pNa [Na]i pCl [Cl]o )
pK : pNa : pCl = 1.0 : 0.04 : 0.45
Vm prediction for cell that is only permeable to Na and K?
bw the two but closer to K
AP
short lived change in membrane pot
nerve cell AP vs cardiac myocyte AP
nerve cell faster and different shape
Voltage gated Na channel cycle
closed (resting) then it gets activated (which is depolarized) to an open state. This is pos feedback (hodgkin cycle).
channel open for a short time and then gets inactivated. in inactive state channel open, but loop swings shut. Then channel recovers by removing the loop and closing the channel. Channel can recover from inactive state until cell is repolarized back to resting membrane pot
6 characteristics of an AP
1- triggered by depolarization of resting membrane pot- something has to disturb the cell at rest
2-threshold - no threshold reached, no AP
3-Reverse polarity
4-All or none
5-Propagates without decrement down the axon
6-Refractory period - can’t fire another AP
Hodgkin cycle
- pos feel back cycle once we reach threshold
- this is responsible for the rapid depolarization we see during AP
- As more Na enter, membrane gets more pos (depolarization), so incr P more voltage gated channels open and more Na enters.
What happens during rising phase of AP?
-permeability of Na is greatly increased (was 0.04 now 20) this means during depolarization, were driving the membrane pot toward nernst equil potential for Na
During the rising phase of AP, why don’t we reach the nernst equil pot for Na?
1- inactivation of Na channels
2-activation of voltage gated K cannels
conductance
relative permeability for different ions
incr membrane pot incr conductance
Relative refractory period
either cell can’t fire another AP or it’s very difficult.
- a stronger stimulus might support an AP.
- long period
- proportional to population recovery of activation
Absolute refractory period
can’t fire another AP until Na channels recover from inactivation
Propagation of AP
- wave of depolarization followed by wave of hyperpolarization. Activation of Na channels followed by inactivation, so you can’t fire another AP in the same area
- can only move in one direction, cell body –> pre syn terminal
Myelin functions
1-provides insulation and decr change of current leaking out of axon so it incr change of successful conduction
2-proteins interact with myelin and axon plasma membrane and help stabilize.
3-speed up date of conduction
Where are Na and K channels located on the axon?
-nodes and nowhere else!`
schwann cells
- in PNS
- cells themselves wrap the axon
- looks like black electron dense ring
- it squeezes out its cytoplasm creating thin bands which is mostly plasma membrane and wraps axon over and over
oligodendrocytes
- in CNS
- cells extend processes that wrap around the axon
Saltatory conduction
APs are only discharged at nodes but waves of depolarization continue through the cytoplasm of the axon.
-inside of cell is ions and water so good conductor
MS
desease where myelin is destroyed
-causes slow and failure of conduction –> muscle weakness and paralysis
synapse
specialized point of contact bw two neurons where info is transmitted from one neuron to the other
electrical synapse
- prevalent in invertebrates
- mediated by gap junctions (by conexons)- allows current and 2nd messengers to flow
- advantages: very fast- depolarization in one cell causes instantaneous depolarization in the other
- disadvantages: largely unregulated, not good at information processing
- in humans located in cardiac and smooth muscle bc we req a lot of connectivity and coordination very wast.
Chemical synapse
-majority of the synapses in our CNS
-electrical sig –> chem sig –> electrical sig
via release of NT from pre to post syn
How can you tell if pre or post syn terminal? and what is electron dense dark region?
- pre has many vesicles
- electron dense dark region is the post syn density where lots of cytoskeletal elements. help anchor Rs to post syn cell
Are synapses unifrom?
no some release small amt of vesicles some large, so can make small or large signal
NT
chemical signal released by presyn teminal to the syn cleft and effects another cell
–chemical that supports the transition of info bw 2 cells (including 2 neurons)
NT criteria
1-must be present in pre syn term
2-must be released in Ca2+ dependent way
3-must have post syn receptors it can interact with
4-needs deactivation mech
Small molecule NTs
- class I- Ach (at NMJ)
- Class II- amines (epi, norepi, dopamine, serotonin, histamine)
- Class III - AA (GABA, gly, glutamate, aspartate)
- Class IV - NO (gases)- don’t fit all criteria, not lipophilic so can’t be released by vesicles so can’t be Ca 2+ dependent
Neuropeptide NTs
string of AA (3 - 100 AA long)
inh NTs
- cause hyperpolarization
- make post syn cell less likely to fire AP
excitatory NTs
- cause depolarization
- make post syn cell more likely to fire AP
(T/F) one NT can be inh or exc depending on the R it interacts with and second messenger system
T, so exc and inh NTs are not an absolutely classification
lifecycle of NT
1-synthesis 2-packaging into vesicles 3-release 4-binding to R 5-decomission (diffusion, destruction, reuptake)
Which 2 steps of the NT lifecycle differ if NT is small molecule or neuropeptide, and how?
small molecule: synthesized and packaged in per syn terminal
Neuropeptides: they are proteins so they are synthesized and packaged through protein synthesis machinery in cell body. they need to be transported down the axon after to pre syn terminal
presyn vesicles composition
-have lipid bilayer and tons of membrane proteins.
why are membrane proteins impt in pre syn vesciles
they help pump NT into vesicle and anchor vesicle to pre syn term and mediate exocytosis.
(T/F) vesicle as an organelle is not very complex
F, vesicles are very complex as an organelle
How to tell if a neuropeptide or small molecule NT from picture
neuropeptide = dense
small molecule = clear
readily releasable pool
fastest population to be released into syn cleft
-vesicles are sitting at the active zone
recycling pool
-larger than the readily releasable pool, but not at active zone. therefore slower time course to be released. not vertical line like RRP but larger response bc larger population
reserve pool
majority of the vesicles in the pre syn terminal
-slowest to be released bc furthest from active zone
Which pools of syn vesicles do we use are physiological levels
RRP and recycling
where does synaptic transmission take place?
active zone
Mixing bw the vesicle pools
the RRP is refreshed with vesicles from the recycling pool. Recycling pool is replenished with vesicles from reserve pool but this replenishment is slower.
synaptic vesicle cycle
1-docking at active zone (RRP)
2-priming- req ATP. once priming takes place the vesicles are sensitive to Ca2+
3-Voltage gated Ca2+ channels open and increase intracellular Ca2+
4-Fusion -vesicle fuses to pre syn membrane and contents of vesicles are emptied into syn cleft
kiss and stay
-if we want to reuse the vesicle after contents released
-we don’t undock, we just refill it and reprime it so it never leaves the active zone
FAST
kiss and run
-if we want to reuse the vesicle after contents released
-vesicle is endocytosed and joins recycling pool- where it is refilled using proton pump mech. it has to come dock again at active zone .so we have mixing with recycling pool
FAST
endocytosmal recycling
-after contents of vesicle are released
-vesicle goes all the way back to reserve pool.
-fuses with lipid endosome and it is completely decomissioned.
-budding off of the endosome are brand new vesicles with no proteins assoc with them. then another pumping and filling mech takes place
SLOW
graded potentials
- vary in magnitude and duration depending on strength of stim
- everyting that leads up to an AP (depolarization Na, Ca and hyperpolarization K, Cl)
- travel short distances
How graded pots travel short distances
1-NT binds to ligand gated Na channels
2- Na enters through open channel (depolarization) so right around R it’s very depolarized
3-current spreads through the cell (diffuse)
4-strength of the signal decreases with dist
so incr membrane pot, NT is closer to R
EPSP
raises membrane pot above resting membrane pot
-happens with influx of cations in post syn cell– produces transient depolarization (Na)
IPSP
lets in ions that will cause hyperpolarizationof post syn cell like Cl, (and K if they can leave)
temoral summation
when the same impulse is activated in close proximity that the 2 impulses add together
spatial summation
2 diff impulses add close together they sum
EPSP-IPSP cancellation
exh and inh impulse applied close enough together they cancel out
separated electrical charges of the opposite sign have the potential to do work. This potential is called the _______. It is determined by the different in the amount of charge bw the two points.
electrical potential
Charges in biological systems are often separated by________, which acts as insulators
membranes
the movement of electrical charge is called a _______
current
All cells, under resting conditions have an electrical potential across their plasma membranes, with the inside of the cell ______ charged with respect to the outside. This potential across the plasma membrane is called the _______
negatively, resting membrane pot
What does the Nernst eqn tell you
- the equilibrium pot for an given ion
- which is the electrical gradient that will balance the chem gradient
What does the goldman-hodgkin katz eqn tell you?
-extended version of the nernst eqn that allows us to consider multiple ions and their relative permeabilities so that we can calculate membrane potential.
contrast graded pots and APs
graded pots:
- changes in membrane pot confined to a small region of the plasma membrane
- variable amplitude
- include receptor potentials, synaptic pots and postsyn pots
- conducted decrementally
APs:
- brief excitatory depolarization of the membrane pot
- large, all or non, constant amplitude
- reverses polarity in neurons (ex- neuron becomes momentarily pos with respect to the outside)
- conducted non-decremantally
