Neurophysiology: Neural Signals and Transmission

Question 1

Is the electrical potential negative or positive in cells?

Answer 1

Negative

Question 2

What is the resting membrane potential?

Answer 2

Within excitable cells there is the capacity to change and become more and less negative

Question 3

What is concentration gradient?

Answer 3

Difference in concentration of a dissolved substance in a solution between a region of high density and one of lower density

Question 4

What is the resting membrane potential in most neurones?

Answer 4

-70mV

Question 5

What generates an electrical current?

Answer 5

The difference in the electric potential

Question 6

What happens when the neurone is inhibited?

Answer 6

Hyperpolarisation, the inside of the membrane is more negative than typically

Question 7

What is depolarisation?

Answer 7

When the neurone is stimulated and moves closer towards 0

Question 8

What are the phases during action potential?

Answer 8

Resting potential, rising phase, overshoot (depolarisation), the falling phase, the undershoot (hyperpolarisation), repolarisation

Question 9

What is passive diffusion

Answer 9

Movement of particles in a fluid from regions of high conc to low until equilibrium is reached

Question 10

What happens when the molecules are evenly distributed across a fluid?

Answer 10

No net diffusion

Question 11

What causes the resting membrane potential?

Answer 11

The movement of potassium ions out of the cell

Question 12

What is the reversal potential?

Answer 12

The point at which direction the net current flow reverses which is the same as the membrane potential

Question 13

What is the driving force

Answer 13

The rate of net current flow for a particular ion being proportional to the difference between the membrane potential and the equilibrium potential

Question 14

What is the graded potential?

Answer 14

The local depolarisation of the cell membrane in response to a stimulus

Question 15

What causes the action potential?

Answer 15

The movement of sodium ions into the cell

Question 16

What creates an electrostatic gradient?

Answer 16

Charged particles that generate electrostatic forced due to oppositely charged ions being attracted to each other

Question 17

What is the ratio of the sodium gradient?

Answer 17

10:1, sodium is higher outside the cell

Question 18

What is the ratio of the potassium gradient?

Answer 18

40:1, potassium is higher inside the cell

Question 19

What does the sodium-potassium pump do?

Answer 19

Maintains the sodium and potassium gradients of the cell, 3 NA out of the cell and 2 K into the cell

Question 20

How much energy does the sodium potassium pump consume?

Answer 20

A single ATP molecule

Question 21

What ion is the neuronal membrane mainly permeable to?

Answer 21

Potassium

Question 22

What occurs when the potassium diffuses out of the cell?

Answer 22

The inside of the cell builds up a slight excess of negative charge

Question 23

What occurs at equilibrium in the resting membrane potential?

Answer 23

No net flow of potassium

Question 24

What will occur if sodium enters the cell?

Answer 24

The inside of the membrane will build up a slight excess of positive charge

Question 25

What is the action potential dependent on?

Answer 25

Voltage-gated ion channels

Question 26

What are the two gated channels?

Answer 26

Ligand-gated and voltage-gated ion

Question 27

What is a ligand-gated channel

Answer 27

A channel that opens in the presence of a signalling molecule that acts as a binding site on the extracellular area of the channel

Question 28

What is a voltage gated ion channel?

Answer 28

Channels that open and close in response to changes in the membrane potential

Question 29

What is the structure of the voltage gated ion channel?

Answer 29

Integal membrane proteins, pore loops for a selective filter and a charged domain as a voltage sensor

Question 30

What is the structure of the VG sodium channel?

Answer 30

Single large protein with 4 repeating motifs

Question 31

What is the structure of the VG potassium channel?

Answer 31

4 subunits and a characteristic motif

Question 32

What happens to VG ion channels at rest compared to depolarisation?

Answer 32

Rest= closed. Depolarisation= open

Question 33

Why do the VG ion channels ion in depolarisation?

Answer 33

Due to the voltage sensors (S4)

Question 34

What happens to the voltage gated sodium and potassium channels in depolarisation?

Answer 34

NA= open very quickly K= open after a delay of 1 millisecond

Question 35

How is an action potential triggered?

Answer 35

By the neuronal cell body being depolarised by 15mV to reach the threshold value of -55mV

Question 36

What occurs at the threshold depolarisation?

Answer 36

A positive feedback loop so NA+ flows into the neuron so more VG NA channels open so NA+ can enter the cell

Question 37

When will the action potential be propagated?

Answer 37

During depolarisation to the threshold, in a series of action potentials

Question 38

What does the inactivation gate on the VG NA channels do?

Answer 38

Closes at the peak of action potential and will not re-open until repolarisation

Question 39

What is the refractory period?

Answer 39

When an action potential cannot be triggered until the sodium channel inactivation gate has reopened during repolarisation

Question 40

What is an electrotonic wave?

Answer 40

When the action potential is triggered in a certain part of the axon so a localised current of sodium is generated

Question 41

How does the electrotonic wave spread?

Answer 41

Along the axon in both directions and then decays when the positive charge goes across the neuronal membrane

Question 42

What occurs to the electrotonic wave in an unmyelinated axon?

Answer 42

Action potentials are close together as the electrotonic wave reaches a short diatance to trigger the next action potential

Question 43

How does bigger axon diameters effect nerve impulses?

Answer 43

Speed them up as there is less electrical resistance to the current flow so the electrotonic wave moves further as action potentials are not close together

Question 44

What does myelin sheath do?

Answer 44

Insulates axons and prevents current leakage

Question 45

What is myelin sheath made of?

Answer 45

300 layers of lipid rich cell membrane

Question 46

What are nodes of Ranvier?

Answer 46

Gaps between myelinated segments on an axon