Excitable cell

Question 1

3 mains roles of neurons

Answer 1

Collect
Integrate
Output

Question 2

Role of the nervous system

Answer 2

System of communication that allows an organism to react rapidly and modifiably to changes in its environment

Question 3

What are the 2 mechanisms of the nervous system?

Answer 3

Electrical activity for rapid speed
Chemical messengers for flexibility

Question 4

What are 2 subsections of electrical signals?

Answer 4

Grading potential
Action potentials

Question 5

Define an action potential

Answer 5

A fixed size, all or nothing signal that propagates an axon

Question 6

Define a grading potential

Answer 6

A variable size, local signal which can pass both ways along neuronal membranes

Question 7

How are APs coded?

Answer 7

By frequency

Question 8

How are GPs coded?

Answer 8

By size

Question 9

When can neurons transmit action potentials?

Answer 9

When they reach a depolarisation threshold

Question 10

What causes neurons to have a resting potential?

Answer 10

Selectively permeable membrane
Unequal distribution of charged molecules/ions
Physical forces

Question 11

What happens to the membrane potential if the membrane becomes non-selective?

Answer 11

Membrane potential becomes 0

Question 12

What is the difference between a membrane channel and a membrane pump?

Answer 12

A channel confers selectivity
A pump assists unequal charge distribution

Question 13

What 2 forces control the flow of ions in an aqueous solution?

Answer 13

Diffusion
Electrical field

Question 14

Why does a membrane have to have a potential difference and channels?

Answer 14

Bilayers provide a barrier to ion movement
So, if no channel/potential difference, conductance is 0

Question 15

What is current flow dependent on?

Answer 15

Electrical potential (voltage)
Electrical conductance
Electrical resistance

Question 16

What would not occur without ion pumps?

Answer 16

Resting membrane potential

Question 17

In which direction does the Na+/K+ ATPase work?

Answer 17

Against the conc gradient
Internal sodium for extracellular potassium
(High Na+ outside membrane, high K+ inside membrane)

Question 18

Why is a low intracellular Ca+ important?

Answer 18

High Ca+ is toxic and can kill neurons
Ca is a signalling ion

Question 19

When does Equilibrium potential occur?

Answer 19

When electrostatic force exactly counteracts the diffusional force

Question 20

What determines the rate at which ions are driven across the membrane ?

Answer 20

Rate proportional to the diff between membrane and equilibrium potential

Question 21

What is the Nernst equation?

Answer 21

Eion = 2.303 x (RT/zF) x log (ion o/ion i)

R = gas constant
T = temperature in K
z = charge of ion
F = faraday constant
i = intracellular
o = extracellular

Question 22

Which ion is the neuronal membrane permeable to at rest?

Answer 22

K+

Question 23

What does increasing the extracellular K+ do to membrane potential?

Answer 23

The membrane potential will increase and the membrane will become depolarised

Question 24

What is the goldman equation used for?

Answer 24

To estimate the real Vm (membrane potential) when the membrane is permeable to other ions

Question 25

What is the goldman equation?

Answer 25

Vm = 61.54 mV x log Pk(K+)o + PNa(Na+)o / PK(K+)i + PNa(Na+)i

Question 26

How do ionic gradients influence membrane potentials?

Answer 26

They determine the membrane potential that would have to be achieved in a neurone if the membrane was selectively permeable to the ion

Question 27

What is ion movement rate proportional to ?

Answer 27

IDF proportional to Vm -Eion

Question 28

What are the 4 features of an action potential?

Answer 28

Rising phase Overshoot Falling phase Undershoot

Question 29

Describe the rising phase

Answer 29

Rapid depolarisation of the membrane

Question 30

Describe the overshoot

Answer 30

Membrane potential is above 0

Question 31

Describe the falling phase

Answer 31

Rapid repolarisation of the membrane (more -ve than the starting resting membrane potential)

Question 32

Describe the undershoot

Answer 32

After hyperpolarisation - gradual decline so the membrane potential comes back to resting level

Question 33

Does amplitude change if you change the holding membrane potential?

Answer 33

No it doesn't change

Question 34

When does a neurone depolarise?

Answer 34

When the permeability to Na is increased

Question 35

Describe the change in sodium channels with an action potential

Answer 35

At rest - most sodium channels ar closed Depolarisation - sodium channels open, selective permeability increases for sodium Repolarisation - sodium channels close, a decrease in membrane potential causes the channels to close again fully at rest

Question 36

What is the structure of the voltage-gated Na+ channels?

Answer 36

Several transmembrane domains, Domain 4 has lots of positively charged amino acids

Question 37

Describe the conformational change of a voltage-gated Na+ channel

Answer 37

Due to small ion movements Lipid part of the protein tries to move from one side of channel to the other Minimal opening of the pore allows selectivity

Question 38

How fast is Na+ channel inactivation?

Answer 38

1ms

Question 39

When does the relative refractory period occur?

Answer 39

Whilst voltage gated K channels remain open

Question 40

When does the undershoot ware off?

Answer 40

As voltage gated K+ channels close

Question 41

How does an action potential conduct down the axon?

Answer 41

Spread of charged particles (Na+)

Question 42

Why does an action potential only travel in one direction?

Answer 42

As the ap travels down the axon, Na channels behind the ap close, therefore Na+ cannot move retrospectively.

Question 43

What happens to membrane potential after ap?

Answer 43

The membrane potential rises due to depolarisation

Question 44

What factors affect conduction velocity?

Answer 44

Diameter Myelination Permeability of the membrane

Question 45

How does diameter affect conduction velocity?

Answer 45

Resistance to current flow increases as the cross sectional diameter decreases

Question 46

How does myelination affect convection velocity?

Answer 46

Prevents membrane from leaking Allows ap to 'jump' from node to node (saltatory conduction)

Question 47

Why may some small axons not be myelinated?

Answer 47

Myelination costs lots of energy Benefit of high membrane resistance is reduced by the high internal resistance

Question 48

Why does a myelin sheath not wrap the whole axon?

Answer 48

Space is needed for the voltage gated channels

Question 49

What is the difference between an axon and a dendrite?

Answer 49

Dendrites have voltage sensitive channels but rarely produce action potentials

Question 50

How do action potentials carry electrical signals?

Answer 50

In a non-decremental manner (amplitude remains the same)

Question 51

What is action potential frequency dependent on?

Answer 51

The size of the depolarising stimulus

Question 52

What is the absolute refractory period?

Answer 52

1 ms - the neuron is incapable of generating another ap

Question 53

What is the relative refractory period?

Answer 53

A few ms - you can fire another ap but a stronger stimulus is required due to threshold being raised

Question 54

What is stimulus intensity controlled by?

Answer 54

The action potential frequency in the nervous system

Question 55

What are the 2 types of graded potential?

Answer 55

Inhibitory (hyperpolarizing) Excitatory (depolarizing)

Question 56

What are graded potentials caused by?

Answer 56

Opening of neurotransmitter gated ion channels or Opening/closing of potassium channels

Question 57

What is an EPSP?

Answer 57

Excitatory post synaptic potential

Question 58

What is an IPSP?

Answer 58

Inhibitory post synaptic potential

Question 59

What is summation?

Answer 59

The act of integrating multiple neuronal inputs together to reach a threshold

Question 60

What is spatial summation?

Answer 60

When progressively larger numbers of primary afferent neurons are activated simultaneously

Question 61

What is shunting?

Answer 61

Making the membrane leaky to dissipate the shunting effect caused by the opening of non-selective cation channels in axon membrane

Question 62

How do ions travel through the membrane?

Answer 62

Through GAP junctions