(3) Excitability (and channelopathies)

Question 1

part of the membrane that acts as a capacitor

Answer 1

lipid bilayer (stores charge)

Question 2

part of the membrane that acts as resistors or capacitors

Answer 2

ion channels

Question 3

At rest the membrane is mostly permialble to what ion? what is the resting potential?

Answer 3

K+; -70 mV

Question 4

maintains resting potential/ion conc

Answer 4

Na/K ATPase

Question 5

time constant is (longer or shorter) for larger diameter cable/ Why?

Answer 5

longer bc there is less leakage of charge

Question 6

the direction of a response reflects _____ of the stimulus. the amplitude of the response reflects the ____ of the stimulus

Answer 6

polarity (hyper or depolarizing)

size

Question 7

Under what conditions would you expect the membrane potential to be 0mV

Answer 7

complete loss of membrane selectivity for ions (i.e. it will all equilibrate)

Question 8

Describe the ionic basis and movement for an action potential

Answer 8

once threshold is reached, the Na channels open and Na flows in = depolarization. Then Na close and K open = repolarization. there is an afterhyperpolarization bc the K+ channels remain open for a little while after repolarization

Question 9

relative refractory period vs absolute refractory period

Answer 9

relative = during afterhyperpolarization a larger stimulus would be needed to generate another AP

absolute = too many of the Na channels are inactivated to generate another AP

Question 10

What are the 2 ways to increase conduction velocity?

Answer 10

increase diameter and myelinate the axons

Question 11

Why is AP propagation unidirectional

Answer 11

Na channel inactivation/refractory period

Question 12

Why does myelination increase conductane velocity

Answer 12

the membrane is not able to hold as much charge (dec capacitance) therefore more charge is available to travel down the axon (in the axoplasm) to the next node of ranvier

myelin also prevents charge from leaking out (inc resistance)

Question 13

describe the structure of the voltage gated Na channel

Answer 13

alpha subunit with 4 domains (each w/ 6 TM regions) that form a pore. there is also an auxillary subunit

Question 14

cause of generalized epilepsy with febrile seizures

Answer 14

pt mutation that causes slowed inactivation of Na channels → hyper excitability

Question 15

cause of periodic paralysis

Answer 15

gain of function mutation in Na channel in skeletal muscle and T tubules that leads to hyperexcitability/repetitive activation

**overactive Na channels = not enough resting ones to be available for AP transmission

Question 16

Cause of myotonia

Answer 16

mutation in Na channel

Question 17

cause of familial hemiplegic migrane

Answer 17

mutation in P/Q type Ca channel (found in cerebellum) → dec NT released

Question 18

cause of episodic ataxia type 2

Answer 18

truncated CaV2.2 Ca channels (found in CNS and PNS) → dec NT released

Question 19

cause of lambert-eaton syndroms

Answer 19

Abs to voltage gated Ca channels

**assc with small cell carcinomas

Question 20

cause of CSNB

Answer 20

truncated L-type Ca channels in the retina

Question 21

cause of benign familial neonatal seizures

Answer 21

mutation in Cl- channel of muscle cells such that the resting potental becomes depolarized/closer to threshold → hyperexcitability

Question 22

mutation in K+ channels in purkingie cells leads to

Answer 22

episodic ataxia type 1