lecture 20

Question 1

2 characteristics of ion channels

Answer 1

1. ion selectivity
   - selectivity filter= narrowest part of the channel, only allows ions of appropriate size and charge to pass through
2. not continuously open

Question 2

do channels need to go through a conformational change with each ion that passes?

Answer 2

no!

Question 3

channels
-rate of transport?
-passive or active transport?

Answer 3

channels have a much faster rate of transport

channels only facilitate passive transport (not active!!)

Question 4

resting membrane potential=

Answer 4

the voltage difference across the plasma membrane when a cell is not stimulated

Question 5

[K+] is high in the cell and has the tendency to move out when ion channels (K+ leak channels)..

Answer 5

open

Question 6

K+ moves out until resting membrane potential is 0 because [K+] gradient is balanced by

Answer 6

voltage gradient

Question 7

Patch-Clamp Recording

Answer 7

-Allows the measurement of changes in electrical current in living cells
-Concentration of ions can be adjusted on both sides of the membrane
-You can set a constant membrane potential
-Activity of ion channels is “all or none”
-The proportion of time that a channel is open or closed will depend on cellular conditions

Question 8

Gated Ion channels

Answer 8

Voltage gated= probability of being open is controlled by membrane potential

Ligand gated= opening is controlled by binding of a ligand

Mechanically gated= opening is controlled by a mechanical force

Question 9

example of a mechanically gated ion channel

Answer 9

auditory hair cells
- Sound makes stereocilia to tilt which stretched a linking filament which causes ion channels to open
- Influx of positive ions stimulate the auditory nerve fibers and convey auditory signals to the brain

Question 10

when the membrane potential has changed enough…. the probability of finding a fully open channel

Answer 10

increases

Question 11

action potential

Answer 11

traveling wave of electrical excitation, carries messages to neurons

Question 12

Voltage-gated K+ channels

Answer 12

• Open in response to depolarization
• Delayed relative to the Na+ channels

Question 13

Propagation of action potential

Answer 13

When a patch of the plasma membrane becomes depolarized, the self-amplifying depolarization spreads out.
Only spreads in one direction due to the inactivation of phase of the Na+ channel that is not going to allow them to be excited again.

Question 14

Transmitter-gated ion channel

Answer 14

a subclass of ligand-gated ion channels that convert the chemical signal of a neurotransmitter back into an electrical signal

Question 15

a ligand-gated cation on a postsynaptic cell would be….

Answer 15

Excitatory
(Cations Na+ or Ca2+ flow into the cell causing depolarization of the membrane and propagation of action potential)

Question 16

Neurotransmitters can excite or inhibit

Answer 16

the post-synaptic cell (depending on the receptor).

Question 17

Common excitatory receptors for neurotransmitters are ligand-gated

Answer 17

cation channels

Question 18

Common inhibitory receptors for neurotransmitters are ligand-gated

Answer 18

Cl- channels

Question 19

Acetylcholine and glutamine are

Answer 19

excitatory neurotransmitters

Question 20

Y-aminobutyric acid (GABA) and glycine are

Answer 20

inhibitory neurotransmitters

Question 21

Cocaine

Answer 21

Dopamine is taken up by dopamine transporters to limit the duration and spread of the signal. Cocaine blocks the uptake and removal of dopamine from the synaptic cleft causes happy feeling.

• Cocaine is excitatory

Question 22

Synaptic plasticity

Answer 22

the ability of a synapse to adjust its strength depending on how heavily it has been used in the past