Neurons

Question 1

What is Hyperpolarisation

Answer 1

Where the inside of the neuron becomes more negative

Question 2

Define Depolarisation

Answer 2

Where the inside of the neuron becomes more positive

Question 3

What types of cells are excitable and what does it mean

Answer 3

Neurons and muscle cells are excitable, this means they can respond with a transient change in membrane potential

Question 4

What influences membrane potential

Answer 4

1-The amount of ion channels present in the membrane influences the permeability of the P.M to the ions
2-The concentration gradients of these ions between the inside and outside of the excitable cell
3-Electrogenic action of Na-K pump (small contributor)

Question 5

How is the resting membrane potential changed

Answer 5

Change the concentration of ions inside and outside these excitable cells. Change in the number of ion channels in the membrane
Changes to the electrogenic action of the Na-K pump

Question 6

What is the typical resting membrane potential

Answer 6

-50 to -70 mv

Question 7

What is a neuron

Answer 7

A principle building block and the instument of communication within the brain

Question 8

What is the diameter of the soma and typical length of a dendrite projection

Answer 8

soma- 20um and dendrite- 1mm

Question 9

Where are synaptic potentials formed

Answer 9

They form from the dendritic region and travel towards the cell body

Question 10

What is the function of the soma

Answer 10

Acts as a computing region, that determines whether a response is carried out to the stimuli

Question 11

Where are action potentials transmitted

Answer 11

across the axon

Question 12

Nervous communication is made of what two components

Answer 12

Electrical signals (dendrites, cell body and axon) and chemical signals (synapse)

Question 13

Why is the membrane potential negative?

Answer 13

The difference in the concentrations of ions between the inside and the outside of the neurone, resulting in more negative charges inside the cell compared to outside

Question 14

How can you measure RMP

Answer 14

Place one electrode into the intracellular spaces and a reference electrode to extracellular space.

Question 15

How does the resting membrane potential of glial cells compare to a typical neuron

Answer 15

glial cells have a more negative resting membrane potential (-90mv) compared to a neuron (-60-70mv)

Question 16

How can you measure the RMP or intracellular potential

Answer 16

Using the patch clamp technique or microelectrode recording technique

Question 17

Describe the Microelectrode recording technique

Answer 17

A Glass capillary with a thin tip less than 1 micron wide is open and filled with an electrolyte solution. This solution is used to conduct a current and will be connected to an amplifier in order to measure the p.d between the inside and outside of the cell.
The capillary penetrates the cell and a reference or 2nd pole is in the extra cellular space

Question 18

Describe the patch clamp technique

Answer 18

A series of patch pipettes are used inorder to create a seal between the two ends of the lipid bilayer ( imagine it acting as a bridge which conducts ) l—-l

Question 19

What is the adv of patch clamp technique

Answer 19

Can measure the pd and current flows for a particular channel you want to look at

Question 20

Disadv of patch clamp technique

Answer 20

Need to fill the patch pipette with a electrolyte to allow for current to flow, however this has the consequence of causing the dialysis of the cell- a change in the composition of inside hence making an artificial situatuion

Question 21

What is the respective concentrations of Na+ inside and outside the neuron

Answer 21

150mM outside

15mM inside

Question 22

What is the concentration of K+ outside the neuron

Answer 22

outside 5mM

Inside 100mM

Question 23

How are conc gradients for K+ and Na+ maintained?

Answer 23

The action of the Na+ K+ pump. It is also reliant on the fact the membrane is not fully permeable to these ions otherwise the conc gradient would dissapear due to diffusion. NOTE the membrane is partially permeable to Na+ such that Na+ will gradually enter into the cell causing dissapation of the gradient. 3 Na+ out and 2K+ in, using energy from hydrolysis of ATP

Question 24

Explain the difference in permeability to different ions (Na+ and k+)

Answer 24

There are leaks channels (non gated) and Gated channels ( voltage, ligand, mechanically). Differences in the number of these channels in the membrane will affect the permeability . Note that there are many K+ leak channels and few Na+ leak channels resulting in a greater permeability to K+. K+ diffueses out as the conc inside the cell is much greater than outside the cell. Ratio of perm is 40:1 (K+ to Na+)

Question 25

What type of channel determines the rmp

Answer 25

leak channels

Question 26

What can act on the gated channels causing them to open

Answer 26

Mechanical, electrical and chemical can interact with these gated channels causing them to open

Question 27

Describe equilibrium potential

Answer 27

This is the intracellular potential at which there is no net flow of ions , despite the presence of a conc gradient. Two forces act on the cell at a time 1- Diffusion
2- Electrostatic forces .
E.g- conc gradients drive the movement of k+ ions out of the cell via passive diffusion, this leaves a negative charge into the cell as this occurs and this attracts the ions back into the cell at a point the force due to conc grad and electrical force balance hence no net flow.

Question 28

What is the E(Na+) and E(K+)

Answer 28

E(Na+)= +60mv E(K+)= -80mv

Question 29

How can you inteprate the Equil potent for na and k

Answer 29

If the permeability of the cell to K+ was greater than the permeability to na+ then the potential of membrane shifts closer to k+

Question 30

Nernst equation is used for what and state rmp for glial cells

Answer 30

calculating the ep of ions

glial cells have rmp of -80mv as they only havee leak channels for k+

Question 31

WHy is the RMP not exactly the ep for the ions in neurons

Answer 31

this is because both k+ and na+ leak channels affect rmp. Higher permeability to a particular ion means better ability of ion to shift rmp to eq value.

Question 32

Why do Neurons have lower RMP than glial cells

Answer 32

small number of leak Na+ channels that shift the rmp to wards the Ena+ slightly hence rmp is -65mv approx.

Question 33

Goldman equatin is for what

Answer 33

allows calc of rmp while taking into account the relative permeability to ions and conc