Nervous System 2 - Membrane Potentials

Question 1

What is resting membrane potential?

Answer 1

The voltage (charge) difference across a cell membrane at rest

Question 2

What is variation of resting membrane potentials?

Answer 2

Resting membrane potential varies: -70mV - +5mV

Question 3

What is the resting membrane potential of a neuronal membrane?

Answer 3

Neuronal membrane - Polarised with respect to charge
Extracellular fluid - Positive at rest
Intracellular fluid - Negative at rest

Question 4

Size of resting membrane potential governed by 3 factors. What are they?

Answer 4

Unequal distribution of ions in intracellular & extracellular fluid
Inability of molecules to leave the cell
Relative permeability of neuronal membrane to different ions

Question 5

In resting membrane potentials, what is the concentration in extracellular fluid?

Answer 5

High concentration of sodium & chloride ions

Question 6

In resting membrane potentials, what is the concentration in intracellular fluid?

Answer 6

High concentration of potassium, phosphates & protein

Question 7

Negatively charged proteins are too big to leave the cell. True or False?

Answer 7

True

Question 8

What does the sodium potassium pump do?

Answer 8

Pumps more positive ions out of the cell membrane than it pumps in (Electrogenic)

Question 9

Most ion channels are gated. What does that mean?

Answer 9

They are either open or closed

Question 10

What factors control the gates ion channels?

Answer 10

Membrane potential (voltage)
Neurotransmitters (chemical)

Question 11

What are the 4 types of channel?

Answer 11

Leakage channel
Ligand-gated channel
Mechanically gated channel
Voltage-gated channel

Question 12

What are leakage channels?

Answer 12

Alternate between open & closed positions (randomly)
Found in all cells
Higher number of potassium leakage channels than sodium leakage channels in membrane

Question 13

What are ligand-gates channels?

Answer 13

Open & close in response to chemical stimuli
Found on dendrites & motor neurons
Opened via various chemical stimuli – Neurotransmitters | Hormones | Ions
E.g. Acetylcholine permits inward flux of sodium & calcium which is paired with outward flux of potassium

Question 14

What are mechanically gated channels?

Answer 14

Open & close in response to vibration (sound), pressure or stretching
Found on sensory neurons e.g. Touch receptors | Pressure receptors

Question 15

What are voltage gated channels?

Answer 15

Open in response to a change in membrane potential (voltage)
Enabler of action potentials
Found on all neurons e.g. Potassium gated channel

Question 16

Membrane is more permeable to Potassium. True or False?

Answer 16

True

Question 17

Membrane relatively impermeable to Sodium. True or False?

Answer 17

True

Question 18

K+ ions (i.e. positive charge) diffuses out of
neuron until K+ equilibrium potential is reached. True or false?

Answer 18

True

Question 19

Changes in membrane potential occur due to the movement of ions across the membrane. True or False

Answer 19

True

Question 20

What are the 4 terms used to describe the state of a membrane?

Answer 20

Local potential - Small changes in membrane
potential in response to stimulus

Action potential - Large & rapid depolarisation to nerve cells
causing the cell membrane potential to reverse

Inhibitory - Hyperpolarisation

Excitatory - Depolarisation

Question 21

Do local potentials travel short or long distances?

Answer 21

Short

Question 22

Can local action potentials add together?

Answer 22

Yes

Question 23

What are Inhibitory local potentials?

Answer 23

Opening of small number of K
+ or Cl- channels in membrane

Question 24

What are Excitatory local potentials?

Answer 24

Opening of small number of Na+ channels in membrane

Question 25

What are the 3 main phases of an action potential?

Answer 25

Phase 1 - Depolarisation Phase 2 - Repolarisation Phase 3 - Hyperpolarisation

Question 26

Nerve impulse travels the length of axon towards terminals. True or False?

Answer 26

True

Question 27

Resting membrane potential - Inside of neuron is negative & outside is positive. True or false

Answer 27

True

Question 28

Threshold potential (-55mV) – Action potential takes place due to a transient reversal in membrane polarity. True or False?

Answer 28

True

Question 29

Peak of action potential (+30mV) - Inside of neuron is positive, outside negative. True or false?

Answer 29

True

Question 30

What are Hyperpolarisation?

Answer 30

Overshoot in membrane potential that makes the membrane more polar

Question 31

An action potential can be generated from what?

Answer 31

Electrical stimulation of neuron Sensory receptors receiving stimulus from other neurons

Question 32

The action potential threshold can also be called the All or Nothing Law. True or false?

Answer 32

True

Question 33

For action potentials to be generated, neuronal membrane must depolarise to threshold potential (-55mV) True or false?

Answer 33

True

Question 34

What is subthreshold?

Answer 34

No action potential produced (local potential will be produced)

Question 35

What is threshold?

Answer 35

Action potential produced

Question 36

What is supra-threshold?

Answer 36

Action potential produced (same size as threshold)

Question 37

What is the refractory period?

Answer 37

Neuron is less excitable during & immediately after generation of an action potential than it is at rest

Question 38

What are the 2 phases the refractory period occurs in?

Answer 38

Absolute and Relative

Question 39

What is absolute refractory period?

Answer 39

Occurs from start of depolarisation to end of repolarisation A second action potential cannot be generated during absolute refractory periods During depolarisation – All Na+ channels open During initial repolarisation - Na+ gates are inactivated (closed) and cannot be opened by another stimulus

Question 40

What is relative refractory period?

Answer 40

Occurs immediately after absolute refractory period Possible to generate a 2nd action potential - Only in response to a stronger stimulus Some K+ channels remain open beyond repolarisation phase (temporary hyperpolarisation) It is ‘harder’ to depolarise the neuron but a stronger stimulus is required

Question 41

What are the 2 types of axons?

Answer 41

Unmyelinated and Myelinated

Question 42

What is Continuous propagation?

Answer 42

Conduction in unmyelinated axons

Question 43

What is Conduction in unmyelinated axons called?

Answer 43

Resting state

Question 44

What are myelinated neurons covered by?

Answer 44

Myelin Sheath

Question 45

Local potentials travel short distances & can be excitatory or inhibitory. True or false?

Answer 45

True

Question 46

Action potentials travel long distances & are only generated following threshold potential. True or false?

Answer 46

True

Question 47

True or false? Local & action potentials are underpinned by the movement of Na+ & K+ across the membrane?

Answer 47

True

Question 48

Action potentials propagate more quickly along myelinated axons. True or false?

Answer 48

True