MR 3&4 The Resting Cell Membrane and electrical excitability

Question 1

What is a membrane potential?

Answer 1

The electrical potential difference (voltage) across the plasma membrane

Question 2

What is the Resting Membrane Potential expressed as?

Answer 2

Potential inside the cell relative to the extracellular solution

Question 3

What is the range of RMPs in nerve cells?

Answer 3

-50 to -75mV

Question 4

What is the RMP of smooth muscle cells?

Answer 4

-50mV

Question 5

What is the range of RMPs in cardiac and skeletal muscle?

Answer 5

-80 to -90mV

Question 6

What sets up RMP in cells?

Answer 6

open K+ channels

Question 7

What happens when chemical and electrical gradients are equal and opposite?

Answer 7

There is no net ion movement

Question 8

What is the equilibrium potential for an ion?

Answer 8

The membrane potential at which there is no net movement of the ion across the membrane (conc grad=elec grad)

Question 9

What is depolarisation and what channels may cause it?

Answer 9

Membrane potential decreases in size/ becomes more positive
may only be a few mV
Cell interior becomes less negative
e.g opening Na+ or Ca2+ channels

Question 10

What is hyperpolarisation and what channels may cause it?

Answer 10

Membrane potential increases in size/ becomes more negative
Potential falls below resiting
e.g opening Cl- or K+ channels

Question 11

What is fast synaptic transmission?

Answer 11

synaptic transmission where the receptor protein is also an ion channel. Binding of transmitter causes channel to open

Question 12

What is slow synaptic transmission?

Answer 12

Where receptor protein and ion channel are separate proteins linked by either G-proteins or intracellular messengers

Question 13

What occurs at excitatory synapses?

Answer 13

excitatory transmitters open ligand channels(Na+,Ca2+ or just general cations) causing membrane depolarisation
give an Excitatory Post-Synaptic Potential (EPSP)
longer time course than AP
graded with amount of transmitter

Question 14

Give 2 excitatory transmitters

Answer 14

Acetylcholine, glutamate

Question 15

What occurs at inhibitory synapses?

Answer 15

Inhibitory transmitters open ligand-gated(e.g K+, Cl-) channels, causing hyperpolarisation
give an Inhibitory Post-Synaptic Potential

Question 16

Give 2 inhibitory transmitters

Answer 16

Glycine, gamma-aminobutyric acid (GABA)

Question 17

What is the absolute refractory period? (ARP)

Answer 17

Peroid in which another action potential cannot be fired because nearly all Na+ channels are in the inactivated state

Question 18

What is the relative refractory period? (RRP)

Answer 18

Period in which it is difficult to initiate another action potential due to some Na+ channels still being inactive. Excitability returns to normal an number of inactivated channels decreases

Question 19

What is accommodation?

Answer 19

Where slow depolarisation means that no action potential is fired even after the threshold is passed because sodium channels are inactivated

Question 20

What is the basic structure of voltage gated Na channels?

Answer 20

Four repeats of 6 transmembrane domains, the 4th transmembrane domain being a voltage sensor.
1 alpa subunit

Question 21

What is the inactivation particle of a channel?

Answer 21

section of 3 amino acids which when any of them are changed make the channel inactive by blocking the pore

Question 22

What is the general structure of a voltage gated K+ channel?

Answer 22

4 alpha sub units, each having 6 transmembrane domains with the 4th being voltage sensitive

Question 23

How do local anaesthetics like procaine act?

Answer 23

Blocking Na+ channels

Question 24

What nerves does MS affect?

Answer 24

All CNS nerves

Question 25

What nerves does Devic’s disease affect?

Answer 25

Optic and spinal cord nerves only

Question 26

Name two myelin affecting diseases of the peripheral nervous system

Answer 26

Landry-Guillain-Barre syndrome

Charcot-Marie-Tooth disease

Question 27

What is capacitance?

Answer 27

ability to store charge

Question 28

How does channel density differ in myelinated and unmyelinated neurones?

Answer 28

Myelinated neurones have high Na+ channel density in the nodes of ranvier while the channels are evenly distributed in unmyelinated axons

Question 29

How does myelin ensure faster action potentials?

Answer 29

Acts as an insulator allowing local current circuits to remain above threshold and depolarise the next node

Question 30

Are myelinated axons always faster than unmyelinated axons?

Answer 30

No when the diameter is less than 1um unmyelinated neurones are faster

Question 31

What happens when myelin is damaged?

Answer 31

The length constant is shorter and dnensity of action current reduced due to resistive and capacitive shunting causing failure to reach threshold

Question 32

In what two ways can a G protein open an ion channel in slow synaptic transmission?

Answer 32

Directly interacting with the channel

Interacting with an enzyme starting a signalling cascade stimulating an intracellular messenger or protein kinase