Topic 1 Flashcards
Neuron
electrically excitable cell that receives, processes, and transmits information through electrical and chemical signals
unipolar neuron
cell body with a nucleus and a projection (neurite) that is either an axon or a dendrite or both ⇒ has a specialized structure at the end
Pseudo bipolar (Pseudo unipolar) neuron
cell body that has an initial segment branching into 2 different directions
bipolar neuron
has a cell body with 2 very distinct processes that go in different directions
multipolar neuron
has the cell body with one end on of a specialized structure (dendrites) and then another longer process (axon)
Axosomatic
When it synapses on the soma ⇒ less likely to trigger an action potential
Axosomatic properties
inhibitory and strongly impacting (shunting) of post synaptic potential near the trigger zone
Axodendritic
presynaptic neurons synapse on the dendrites
Axodendritic properties
- excitatory with sub cellular targets
- shaft (between soma and dendrite projection tip)
spine (on the shaft of the dendrite and is a specialized projection)
Axo-axonic neurons
presynaptic cell synapses on the axon which has no impact of response from the cell body (excitatory/inhibitory)
Axo-axonic properties
modulatory and have no direct effect on the trigger zone (downstream)
- Controls the amount of NT released
- Presynaptic excitation or inhibition is not affected but can modulate the signal as it travels down the axon to make it stronger or weaker by opening or closing channels at the axon channel
projection neuron
dendrites and cell body in one region, axon projects to and synapses in another region
local interneuron
project in the same region instead of a different region ⇒ can be excitatory or inhibitory
efferent
exiting from ⇒ such as going from CNS to periphery
afferent
going to ⇒ such as periphery to CNS
T/F both projection neurons and interneurons can be excitatory and inhibitory
true
excitatory vs inhibitory
- Excitatory: will increase activity of a neuron on which it synapses
- Inhibitory: will reduce activity of a neuron on which it synapses
concentration gradient
the inside and outside of the neuron have different salt concentrations
electrical gradients (voltage)
salt ions have charge and can generate gradients
- Na+, K+, Ca2+, Cl-
transmembrane voltage
the recording electrode measures the difference in charge
- To generate voltage requires 2 chambers separated by an insulator (such as a membrane)
polarized
in most neurons, the inside is more negative than the outside
membrane potential
the charge inside vs outside (not outside vs inside)
- the membrane potential is not the action potential but instead is the steady state potential of the membrane when it isn’t receiving information
- the membrane acts as the insulator and barrier between the outside and inside of the cell to generate the potential difference
most neurons have a resting membrane potential of what?
-40 to -80 mV
how is membrane potential generated?
by the differential distribution of ions across the cell membrane
- The pumps are housekeeping proteins which make sure the appropriate concentration of ions are present inside and outside of the cell
is sodium high on the outside or inside of the resting neuron?
Sodium is high on the outside and low on the inside
is potassium high on the outside or inside of the resting neuron?
Potassium is high on the inside and low on the outside
is calcium high on the outside or inside of the resting neuron?
Calcium is higher outside the cell
is chloride high on the outside or inside of the resting neuron?
Chloride is higher outside of the cell
why is the neuron inside negative?
potassium has a high permeability at rest so it flows across the membrane more easily than the other ions
what are types of neuronal responses? (3)
- receptor potential
- synaptic potential
- action potential
receptor potential
for sensory neurons, when stimulated, membrane potential is stable the first 10 ms because it is resting potential
- When ion channels open the membrane potential becomes depolarized and less negative
- When the stimulus is removed it drops back down to resting membrane potential gradually
synaptic potential
reception from the postsynaptic cell receives a presynaptic axon that binds and activates channels on the post synaptic channel leading to transient synaptic potential ⇒ opens channels leading to a depolarization
- Can be recorded in the soma
action potential
travels along the axon and can be recorded in the soma or in the axon where a depolarization occurs and then a hyperpolarization occurs before returning to resting potential
- This is very short in duration
current
flow of ions and electrical charge ⇒ causes change in membrane potential (membrane voltage = Vm)
what does current depend on? (3)
- The concentration gradient of the ion
- The voltage across the membrane
- Whether or not the membrane is permeable
Voltage
difference in electrical potential between 2 points
what does voltage depend on? (2)
Must have 2 compartments - separated by a barrier ⇒ space filled with air, membrane, etc.
- Will have voltage only if there are charged molecules on at least 1 side of the barrier
what doesn’t voltage depend on?
Voltage does not require movement of ions ⇒ the barrier can be impermeable
Diffusion
molecules move along a gradient from high to low concentration
- Charged molecules move toward the opposite charge ⇒ such as negative moves to positive
Electrochemical gradient aka driving force (DF)
concentration/chemical gradient + electrical gradient/voltage (EG)
DF equation
DF = CG + EG
- CG is concentration gradient
- EG is electrical gradient (voltage)
EG
determined by the sum of all charges on each side of the barrier ⇒ group charge
- The direction an ion moves depends on its charge related to the EG
CG
can be determined for each ion based on relative concentrations
what is the equation for electrical current (I)?
- I = DF x G
- I = (CG + EG) x g
where g is conductance
conductance
how well an ion can pass through the barrier/membrane ⇒ permeability (resistance is opposite)
what happens when g is 0?
there can be no current even if there is DF
what happens when DF is 0?
the ion does not want to move so the current for the ion is zero even if there is conductance
equilibrium potential (Ex)
Membrane potential at which an ion stops moving or stops flowing across the membrane
- Ions only move if there is DF
when does DFx = 0?
If CG + EG is equal and opposite
- there will be no net movement of ions Ix, even if there is permeability gx
- Equilibrium potential for ion X (Ex) occurs at a voltage (Vm) at which CG and EG for the ion are equal and opposite (DFx = 0 and Ix = 0)
what does the magnitude of DFx depend on?
how far Ex is from Vm
- DFx = Vm - Ex
what is the current and electrochemical equilibrium equation?
- Ix = gx*(Vm-Ex)
- Ix = gx*DF
what does the Nernst equation calculate?
ion equilibrium potential Ex
- Ex = 58/z x log[X]o/[X]i
what does the Nernst equation predict?
how the equilibrium potential changes with ion concentration
what are the X and Y axis in the ion concentration 10 fold rule graph?
Y-axis is the membrane potential and X-axis calculates the log of the inside and outside concentrations
10 fold rule
at 19 degree C, every 10 fold change in ion gradient causes a change in Ex of 58/z
- this applies only to Ex (Nernst equation) it does not apply to Vm
inward current
if the gradient is set to -116 the net flux of K+ will be outside to inside
- Vm < Ex
outward current
if the gradient is set to 0 mV, then calcium flows from the inside to outside of the cell
- Vm > Ex
reversal potential
(the -58 mV) point where the direction of the flow of the potassium ion reverses either inside or outside
- Membrane potential and driving force established direction of flow
what does driving force do regarding Vm and Ex?
Driving force makes ions want to move until Vm = Ex
- if the membrane potential (Vm) is equal to the equilibrium potential of an ion (Ex) this means Vm = Ex and there will be no net current for the ion
T/F DF is linear?
true
- When DF = 0, the ion does not want to move so current is 0
T/F current is linear
False
- Current is not linear due to voltage dependent changes in conductance ⇒ channel opening/closing is affected by membrane potential
when Px = 0 [ion] what will happen?
The ion will have very little effect on membrane potential
