Neurobio Exam 1 Class notes Flashcards
How are ion channels studied?
bc ion channels are too small to be visible under a light microscope, an electron microscope must be used
How does an electron microscope work?
electrons are shined through electromagnets and looked through at a sample through an electron detector.
How is the cell membrane structured?
it’s structured in the phospholipid-bilayer. this is structured in hydrophilic heads on the outside and hydrophobic tails on the inside. This allows the cell membrane to be selective with what it allows in and out of the cell.
Why are ion channels needed?
ions don’t permeate cell membranes. ions channels allows ions to pass through the membrane by creating a link
a positive ion
cation
a negative ion
anion
how does the ion channel work?
it can be activated to open or close its gate by plugging or blocking it.
Draw an open gate
what two ways can channels be activated?
they can be activated through physical changes in the cell membrane (voltage-activated or mechanically-activated) or they can be activated by ligands
draw a voltage-activated channel
draw a closed gate
draw the phospholipid-bilayer
what channels can be physically opened?
mechanic-activated
how does a ligands activated channel work?
a ligand will either attach to the outside of the cell for extracellular activation or the inside of the cell for intracellular activation.
what 2 channels are activated by physical changes?
voltage-activated and mechanically-activated channels
draw an intracellular activated ligand channel
draw an extracellular activated ligand channel
How are ion channels structured?
they are made of strings of amino acids with patterns of hydrophobic and hydrophilic molecules to allow to filter out. (ex a string of phobic,philic,phobic,philic,phobic,philic) when the strings are looped, it creates one side that is hydrophilic and the other side that is hydrophobic.
How does an ion channel open?
through molecular tremors
what are molecular tremors?
a dynamic shaking that results in the letting ions in and out of the ion channel
what is voltage in terms of ions?
the force/pressure that pushes ions out
what is amps in terms of ions?
how many ions are moving across channels
Patch Clamping recording
an electrode tip is applied to the cell and forms a gigaohm seal
inside out patch in patch clamping exp
you can tear/pull off the pipette
what patch clamping exp allows access/control to different sides of the channels
inside out cells, outside out patch, and whole-cell recording
whole-cell recording patch clamp exp
if more suction is applied, cell ruptures inside the pipette and cell becomes one with the pipette
outside-out patch in patch clamp exp
pulling/tearing after whole-cell recording phase
Gigaohm seal
cell-attached patch
How can we approach the complexity of the NS system?
we can look at the “simple” systems. Ex. visual system, anatomy
we can classify components of the NS
ex cell types : motion neurons, glial cells
we can classify connection types:
divergent signals, convergent signals, feedback loops, synchronized
we can measure things and do experiments
ex. imaging, electroimaging
because neurons are still cells…
they require certain components to function
father of neuroscience
Santiago Ramon y Cajal
how was Santiago Ramon y Cajal able to draw pictures of the cell?
using the golgi stainging method. Because the staining wasn’t perfect, he was able to see the networks
how does the photoreceptor work in basic terms
light hits the photoreceptor which in turn sends a message by releasing ions and stimulating the bipolar cell
electrical recording techniques
extracellular recording: measures firing from outside the cell
intracellular recording: measures specifically what one neuron is doing
whole cell patch recording: sucks cell into a capillary and gives access to control and measures the cell
what do intracellular recording and patch recording have in common?
-they use a capillary
-both, the cells die once capillary is removed
what is the currency of the NS?
electricity
resting potential is always…
negative
depolarization
brings the cell to a positive voltage
hyperpolarization
brings the cell to an even lower negative voltage
local graded potential
has a gradient response
what happens if local graded potential meets threshold?
an action potential
action potential is considered all-….
all or nothing. it is not a gradient
how is action potential measured?
by frequency
inhibitory signals happen when a cell is
hyperpolarized
excitatory signals happen when a cell is
depolarized
equilibrium potential
the potential that just balances the concentration gradient of and ion where ions aren’t leaving or entering the cell
equilibrium potential is controlled by the ____ but can be manipulated by changing the ____
concentration gradient, voltage
Nerst Equation for potassium
E(k) = 58log ([K]outside)/([K]inside)
what does the Nerst equation measure?
the equilibrium potential
potassium has a big impact on the ___ of the cell
equilibrium
Why do squids have a Squid Giant Axon
it requires a large action potential to create a large movement and therefore need a large axon
why is the squid giant axon easy to study
it is giant and visible to the naked eye
who studied the squid giant axon and won a nobel prize for their discovery?
Huxley and Hodgkin
at high concentrations, potassium influences the potential, but at low concentrations ___
it doesn’t, Sodium does
why does the Sodium-potassium pump contribute to the voltage of the cell?
because it pumps out 3 sodiums and pumps in 2 potassiums, therefore not balanced electrically. **it’s not pumping in as much as it’s pumping out
what can the voltage clamp do?
-can measure voltage and current
-command voltage by making up the difference in voltage needed for action potential
-can depolarize or hyperpolarize the cell and hold it there
-tells us magnitude and direction of current
how does the voltage clamp work in simple terms?
by clamping the membrane at a specific voltage and measuring the current
who used the voltage clamp?
Huxley and Hodgkin
what 3 currents did the voltage clamp exp. discover?
capacitative current
early current
late current
what happens during capacitative current?
ions rearrange quickly
what happens during the early current?
sodium rushes into the cell
what happens during the late current
potassium rushes out of the cell
late current - capacitative current = ?
early current
what ion channel does TTX (puffer fish toxin) block?
sodium ion channel
what ion channel does TEA toxin block?
potassium ion channel
what happens to the current of Na+ and K+ during hyperpolarization?
they don’t respond (inhibition)
what happens to the current of Na+ and K+ as depolarization increases?
the current increases allowing Na+ to flow into the cell and K+ to flow out of the cell (excitation)
What happens to Na+ and K+ current at some point of increase in depolarization?
Na+ current stops increasing, K+ continues to increase, then Na+ current decreases causing an opposite outward flow of Na+ while K+ continues to increase
What is happening when Na+ current stops increasing?
Na+ has reached equilibrium potential, causing the sodium channels to close and become inactive. Here Na+ cannot flow in or out of the cell
What is the voltage of Na+ equilibrium potential?
+52 mV
what does the flow of current depend on?
voltage, conductance, and the ion channels themselves
What does I=GV represent?
it represents the relationship between the current and its dependence on conductance and voltage
I= current (amps)
G= conductance (G=1/R )
(R= resistance)
V= voltage
describe the conductance of Na+ during the action potential
starts quickly and ends quickly
describe the conductance of K+ during the action potential
starts slowly and continuously increases
- almost starts as Na+ current ends
what is conductance?
the speed at which ions are flowing in or out of the cell
Describe the current of Na+ and K+ during action potential
Na+ increases, K+ decreases
what causes the capacitative current?
the gating current of the sodium-potassium channel
describe the model that explains how a voltage gate opens
gate is opened by attracting positive amino acids
-when current shifts, gate opens due to change in charged particle
Threshold
when sodium conductance overcomes potassium leak
refractory period
a period where the membrane can’t make new action potentials right away
absolute refractory
inactivation of sodium channels blocks future depolarization
relative refractory
large activation of K+ channels need larger Na+ activation to overcome
describe the ball-and-chain model of inactivation
this is how sodium channels are able to open quickly and close quickly. a particle from the gate plugs the entry
Why does current move differently through axons?
because axons are not spheres
how does current flow through the axon?
it diffuses along the cell membrane further away from the center of where the current started
why is the axon directional?
because of the refractory period
what influences the speed of the signal from the action potential in the axon?
the diameter of the axon itself and if it is myelinated (insulated)
describe the axon in terms of its parts
insulated myelin chunks and nodes of ranvier
What does this physiological feature of myelin and node of ranvier add to the axons?
allows propagation to jump from one node to another allowing for quicker and more efficient action potential at a higher frequency
what do gap junctions allow neurons to do?
allows for good synchronicity
what does the speed of the action potential in the dendrites rely on?
calcium potential, it has the ability to stimulate an action potential in the dendrites that will spread to another cell body
what was the voltage clamp experiment used to observe?
it was used to dissect the action potential
what ions are concentrated at nodes of ranvier?
Na+ ions
connexons
connects to cells together in the gap junction
passive transport
doesn’t require energy
active transport
requires energy, typically ATP
what are the two types of passive transports?
simple diffusion and facilitated diffusion
simple diffusion
net flow of matter from a region of high concentration to a region of low concentration
facilitated diffusion
like simple diffusion but occurs at a cell membrane and uses a transport molecule
ex: an ion channel
what are the two types of active transport?
primary active transport and secondary active transport
primary active transport
uses ATP to transport ions against their electrochemical gradients
secondary active transport
uses the potential energy of another ion’s gradient
what type of transport is the sodium-potassium pump?
primary active transport, it requires ATP
what happens when the snail neuron was injected with sodium? what about with lithium?
the cell become hyperpolarized, nothing happened without sodium
what does the snail experiment suggest?
that the sodium-potassium pump contributes to an action potential
the pump has a charge that reacts to Na+
what is the charge of the sodium-potassium pump?
1/3 amount of Na+ (related to the pump releasing 3Na+ and receiving 2K+)
Describe the model for ion translocation of the sodium-potassium pump
A) 3Na+ leave, 2K+ enter the cell
the gate is open facing inside of the cell. It is ATP bound and has an affinity for Na+
B) ATP loses a charge, loses ADP
C) Pump shifts and opens facing the outer cell
D) Na+ is kicked out into the outside of the cell concentration
and now the binding site has an affinity for K+
E) K+ binds to the site and loses a phosphate group
F) Gate shifts and opens inwardly again and ATP binds
A2) K+ is released inside the cell concentration and pump now has an affinity for Na+
what is a huge consumer of ATP?
sodium-potassium pump
Calcium ion transport want Calcium in or out of the cell?
out of the cell
what type of transport is calcium transport?
it can be either facilitated diffusion or secondary active transport, depending on the mode of transport
what type of transport is Chloride transport?
secondary active transport. It uses Na+ to co-transport Cl- into the cell and K+ to co-transport Cl- out of the cell
