Ls 2 Lecture 12

Front 1

What are the three most important types of channels?

Back 1

voltage gated (channels are either open or closed)

ligand gated

second messenger gated channels (binding site is on the inside)

Front 2

Voltage Gating

Back 2

charged amino acids within the structure of the channel move in response to a change in voltage

-causes a change in the conformation that opens the gate of the channel

Front 3

inactivate

Back 3

opening of channel exposes site on cytoplasmic side of protein that acts as a binding site for the part of the channel itself, which bind to an blocks (inactivates) the channel

Front 4

How do we know how channels work?

Back 4

patch clamp recording

pipette is pushed up against cell and pressure is applied

glass fuses with membrane of cell, making possible the recording of the currents of single channels

Front 5

stochastic

Back 5

opening is stochastic: not every channel opens at exactly the same time, and once channel opens, it stays open for a random interval and then inactivates (closes)

Front 6

What is the most important thing that channels do?

Back 6

produce action potentials (spikes)

first one recorded by hodgkin and huxley from giant axon of squid

= 1 ms

Front 7

Action Potential

Back 7

resting potential = -60 mV

up to 50 mV = depolarizing

repolarization - below resting membrane potential

sudden, brief reversal of polarity of the membrane potential

membrane potential at any given time depends on how many and which channels are open

Front 8

What causes depolarization?

Back 8

glutamate binding to receptors

produced by synaptic input

next: Na+ enters the cell, depolarizes cell more, more Na+ channels open
-causes a rapid spike = depolarizatoin to +50 mV.


amount of Na in cell is actually very small, but enough charge has entered cell to create an action potential

Front 9

All or none action potentials

Back 9

depolarization opens Na channels, which lets in positive ions which depolarize the membrane and open more channels

-this is why AP's are always of the same amplitude

as soon as enough NA channels open, membrane is de-polarized enough to trigger response

Vm then depolarizes to Nernst potential for NA (+50mV)

Front 10

Refractory Period

Back 10

limits rate at which action potential can be produced

after inactivation gate closes during AP, remains closed for a few milliseconds even though the mem pot goes back to resting.

membrane is resistant to initiation of a further action potential

length of refractory period sets the max rate at which a neuron can fire repeating AP's

Front 11

Saltatory Conduction

Back 11

how an action potential propagates by jumping down axon from node of ranvier to node, because of myelinated schwann cells

the node is packed with voltage gated ion channels.

myelin = no ion channels

voltage spreads efficiently from node to node

myelinated action potentials can go up to 100 meters per second

Front 12

Ca 2+ is more concentrated inside or outside of the cell?

Back 12

outside

Ca ATPase pumps CA out of the cell

Front 13

What breaks down Ach after it is released from the presynaptic cell?

Back 13

achetylcholinesterase

Front 14

why is it that when Ach binds, the channel opens?

Back 14

thought to be because the amino acids twist around the channel pore, change conformation

kinks of amino acids are no longer orientated in a way that closes the channel, leaves space for things to pass through

Front 15

what is the most common neurotransmitter in the brain?

Back 15

glutamate

Front 16

Ach and Glutamate open channels that allow____

Back 16

cations like Na

this produces a depolarization

Front 17

Glycine and GABA activate receptors whose channels allow ______

Back 17

anions like Cl- (chlorIDE)

activation of these receptors produces a hyperpolarization
-action potential will never reach threshold

that is why these are INHIBITORS!

Front 18

Excitatory Ligand-Gated Channels

Back 18

permeable to cations (Na+ K+)

produce depolarizations (excitatory postsynaptic potentials or EPSP's)

ex. receptors for ach, glutamate, serotonin

Front 19

Inhibitory Ligand-Gated Channels

Back 19

permeable to anion (Cl- chlorIDE)

produce hyperpolarizations (inhibitory postsynaptic potentials of IPSP's)

ex. receptors for glycine, GABA

Front 20

summation and the generation of an action potential occurs where?

Back 20

at the axon hillock which is unmyelinated and has many voltage gated Na+ channels

Front 21

spatial summation

Back 21

adds up simultaneous influences of synapses at different sites on the postsynaptic cell

Front 22

temporal summation

Back 22

adds up postsynaptic potentials generated at the sam site in a rapid sequence