Physiology

Question 1

What is the membrane potential?

Answer 1

Voltage difference across the membrane
- lipid bilayer acts as insulator separating 2 conducting solutions (cytoplasm and extracellular fluid)
Current flows when channels are open
Flow of anions/cations will change membrane potential

Voltage collects AT the membrane

Vm - Vin = Vout
usually equals about -65

Question 2

what is the membrane potential of glial cells and what are they controlled by?

Answer 2

Dictate by Potassium (only permeable to K+)
Concentration inside 400 mM
outside 20mM

Chemical/concentration gradient rests around -75mV (equilibrium potential where k going out = k being pulled in by negativity)

Question 3

What is the Nernst Equation?

Answer 3

Used to determine equilibrium potential of an ion

Ex= RT/zF ln (xo)/(xi)

Ex= 58mv/1*log(xo/xi)

Question 4

why does the ln change to log??

Answer 4

ask jason!

Question 5

what is the equilibrium potential for na+?

Answer 5

55mv (50mM inside cell, 440mM outside)

Question 6

what prevents the contiual entry/exit of K+ eliminating concentration gradients?

Answer 6

Sodium Potassium Pump!
-pumping 2 K out
- pumping 3 Na In
Keeps resting membrane potential in tact

Question 7

what is the equilibrium potential for Cl?

Answer 7

-70, 560mM outside cell, 52mM inside the cell

Question 8

what is the goldman equation used for?

Answer 8

nernst for all the ions which factors in permeabilities

Vm=RT/F*ln(pKo/pK + pNao/pNai + pClo/pCli)

this gives the -65mV for resting potential

Question 9

what are relative permeabilities at rest for main 3 ions?

Answer 9

Pk=1
pNa= 0.04
pCl=0.45

Question 10

What are voltage gated channels?

Answer 10

Help regenerate and mediate signalling
Example: sodium voltage gated channels
i. channel at rest
ii. channels open due to depolarization and na rushes through
iii. channels inactivate: stops further flow of ions through ball and chain mechanism

Question 11

what are the relative permeabilities for the 3 ions when the na channels have opened?

Answer 11

Pk=1 (unchanged)
Pna=20
pcl= 0.45 (unchanged)

Question 12

Support the argument “different neurons have different firing patterns because they have different ion channels”

Answer 12

• there are some that fire in bursts, oscillations/rhythms etc

Question 13

What are some methods for recording action potentials and related activity?

Answer 13

Intracellular electrophysiology
Extracellular electrophysiology (putting it outside/nearby to detect local change)
EEG: clusters of action potentials
Calcium Imaging: fills with fluorescent die only when it binds calcium (which increases during an action potential), recorded as an increase in brightness
fMRI (functional imaging): measures bloodflow in the brain, which increases during activity because they need more nutrients etc. Not super specific, an indirect measure of neuronal activity

Question 14

How long is the delay from a presynaptic action potential to the excitatory postsynaptic potential?

Answer 14

1ms

Question 15

How does Calcium relate to the action potential?

Answer 15

Calcium floats outside the cell, so when channels open, calcium rushes into the cell, there are sensors that detect the Ca and cause vesicles to fuse with cell membrane
Postsynaptic receptors bind and become permeable to sodium (EPSP)

Question 16

Why is mitochondria needed in the cell? Why are so many vesicles needed in the NMJ?

Answer 16

for energy!

to enable it to be repeatedly active

Question 17

How do we visualize vesicles during synaptic transmission?

Answer 17

Freeze tissues at specific times

Question 18

How do we know that each receptor ion channel passes a unitary amount of current?

Answer 18

Poke an electrode into a membrane (individual channel- but realistically 3 channels) OR stick it really close then SUCK on the end of the glass to ‘stick’ to the membrane
If you put a bunch of NT in this pipette, you can measure currents as the NT binds the receptor (dont on NMJ)

this shows a specific amount of NT cmoing out. EPSP depends on how many channels are opening.
Each receptor channel is equivalnet,, just the number of them is what matters for summation

increases stepwise function in order of added channels

Question 19

How do ion channels close?

Answer 19

slowly and irregularly.
You get a decay current and then they come back to zero
Some bind for a long time and others bind quickly

Question 20

Support the statement “NT is released in unitary vesicles which are additive”

Answer 20

Experiments show that if you stimulate axons a tiny amount (depolarize), you can release about 1-4 vesicles, and determine how much stimulation is needed to cause an EPSP

• this can be variable depending on background activity
• needs to be depolarized 15mV ish

Question 21

What is Glutamate?

Answer 21

Primary Excitatory NT in the brain!
- Binds to the AMPA receptor (ionotropic)
which physically deforms and allows ions to pass through (cations only- but not selective about which)

Question 22

What is the AMPA receptor?

Answer 22

glutamate receptor (ionotropic) 
which physically deforms and allows ions to pass through (cations only- but not selective about which)
allow NA to enter and K to exit

reversal potential for ampar is 0mV because na and k act at the same time

Question 23

what is the difference between reversal potential and equilibrium potential?

Answer 23

reversal is the same as equilibrium EXCEPT that the two ions are always passing and never reach a true equilibirum (like in the AMPA receptor), will always sway to one side or the other.
You will ALWAYS be brought back/trying to reach zero

Question 24

what causes post synaptic hyper-polarization?

what are some examples of this? what is the effect?

Answer 24

Ionotropic inhibitory NT receptors
- GABA, which activates Cl- receptor channels (GABA a receptors)
[when channels open, chloride rushes into the cell]

Equilibrium potential of Gabaa is -70mV, which doesn’t seem like much, but when paired with an EPSP, this IPSP can prevent reaching threshold! it changes the rate of firing of neurons

SMALL IPSPs can have big effects! only have to depolarize a little bit!
-must act at a very specific window in time in order to silence EPSP

Question 25

How is information encoded in the stretch reflex circuit? What are the two types of info when converting sensory stimulation into APs?

Answer 25

A stimulus sensitive to stretch is applied, which causes depolarization at the trigger zone, just like an EPSP but no synapse or NT, just morphological change!

1) Strength/magnitude of stim is an increase in spike rate
2) Duration of stimulus is long period of AP firing

As you change amplitude/duration, you get more activity in the neuron and more NT released at the end

Question 26

what are receptor potentials vs. synaptic potentials?

Answer 26

receptor potentials happen when sending sensory signals from muscle spindles to sensory neurons
synaptic potentials happen between neurons

Question 27

how are synaptic potentials summed?

Answer 27

Temporal and spatial summation.
Input in dendrites and integration region in the cell body

If another EPSP can happen in the same window as the 1st, before it reaches baseline again, it will push the initial EPSP over the threshold and generate an AP

Question 28

How are Excitatory and Inhibitoy synapses placed on a cell? Are there other types of synapses mentioned?

Answer 28

Typically inhibitory ones are placed on the cell body or on shaft synapse (axosomatic/axodendritic), and exitatory ones are placed at the end of the dendrites (spines). This allows inhibitory synapses to intercept EPSPs before they reach the soma and generate an action potential

others that modify NT release are placed on axoaxonic synapses
-regulate presynaptic events at the terminal

Question 29

What is feedforward and feedback inhibition?

Answer 29

Feed Forward: regulates/selects which neurons will fire by activating forward flow to direct the cell to turn off. Direct, a bit faster. Selects which neurons will have activity

Feed Back: constrains activity at physiological levels, allows firing in to some extent, but then that firing ends up activating an inhibitory cell that inhibits ITSELF - keeps things in a range of activity. Can shut off its own circuit and nearby ones from the same circuitry

Question 30

What is an example of Feed Forward and Feed Back Inhibition?

Answer 30

The reflex circuit!
You want to activate the extensor muscles and inhibit flexor muscles by preventing activity there.

Feedforward: Afferent neurons send signals towards the muscles, and the same circuit that promotes extensor activity, inhibits flexor activity DIRECTLY

In another part of the same circuit, feedback inhibition is working on the extensors when its time for them to turn off, it’s own action inhibits itself by activating an inhibitory neuron in its own circuit

Question 31

what is convergence and divergence?

Answer 31

convergence: input from presynaptic neurons required to activate the single postsynaptic neuron-common in motor neurons
- neuron will only fire if there is enough activity, won’t cause a behavior if it isn’t sure there is enough stimuli
- allows integration of information

divergence: exemplified in sensory systems (one AP stretches out and activates many neurons)
- allows info to be processed in many different pathways for different purposes