M6 L1 : Nerve structure

Question 1

Describe the 3 main parts of a vertebrae neuron

Answer 1

Soma (cell body) and two processes: dendrites to the cell body and axon coming out of it.

Question 2

What are synaptic inputs vs action potentials and where are they received

Answer 2

Synaptic inputs are inputs from other neurons and are received on the dendritic tree and soma. Whereas Action potentials are conducted away from the soma to the tips of axons: synaptic boutons (axon terminals) communicate with other neurons

Question 3

What are the two ways by which neurons communicate and where on the neuron does it take place

Answer 3

Electrical signals (dendrite, axon, cell body) and Chemical signals (synapses)

Question 4

Is communication a chain of events that have conversion between electrical to chemical to electrical

Answer 4

yes

Question 5

RMP varies between cells but what is the general value and what

Answer 5

between -50 and -70. Usually -65mV

Question 6

2 ways RMP of neurons measured in real life

Answer 6

using intracellular glass microelectrodes filled with electrolytes placed in the soma, measuring electrical signal
Or with patch- clamp technique using larger tip glass pipettes to measure current in ion channels

Question 7

What is the problem with patch clamp technique

Answer 7

It dialyses the cell and changes the ionic/ chemical composition

Question 8

What is the difference of neurons and muscle fibres compared to all cells with respect to RMP

Answer 8

Almost all cells in the body have a negative resting membrane potential. Only neurons and muscle fibres can suddenly respond with a transient change of this potential( ie action potential) in response to stimulus = excitable

Question 9

What are the 3 causes of the RMP

Answer 9

1. The unequal concentrations of Na+ and K+ inside and outside the cell, resulting in electrochemical gradient.
2. The unequal permeability (P) of the cell membrane to these ions.
3. Electrogenic action o the Na/K pump ( only small)

Question 10

At rest, describe the separation of charges across the cell membrane and its effect

Answer 10

There are more negative charges inside the cell in comparison to the extracellular fluid. Therefore there is an electrical potential difference.

Question 11

What is the potential outside the cell referred to

Answer 11

0

Question 12

What is the contribution of the Na+/K pump to the RMP

Answer 12

It maintains the conc gradient for these ions. It pushes out 3 Na+ but only drags in 2 K+ so a net charge of -1 is built inside the cell.

Question 13

What are the approximate concentrations of K+ and Na+ ions inside and outside neurons.

Answer 13

K+ is 5mM outside and 100mM inside

Na+ is 150 mM outside and 15 mM inside

Question 14

What affects the permeability of the cell membrane to Na+ and K+

Answer 14

Selectively permeable: Non-gated ion channels (leak) that are open at rest and Gated ion channels (voltage or ligand) that are usually closed at rest.

Question 15

What is the ratio of K+ leak channels (K+ permeability) (PK) to Na+ leak channels (Na+ permeability) (PNa) at rest

Answer 15

PK:PNa = 40:1. Therefore there is more passive (positive charges leaving (K+)) than (positive charges entering (Na))

Question 16

How does the unequal concentration AND unequal cell membrane permeability to Na+ and K+ result in a negative RMP

Answer 16

It sets up an equilibrium potential for each ion which balances out to get a negative RMP

Question 17

What is the equilibrium potential and why does it happen

Answer 17

The intracellular potential at which the net flow of ions is zero inspite of conc gradient and permeability. This is because ions moving through passive diffusion are actually moving against their electrochemical gradient. When these are balanced, the same amount of ions leaving for diffusion are coming back for electrostatic force.

Question 18

What does the Nernst equation calculate and what is the equation

Answer 18

equilibrium potential for each ion that contributes to RMP.

Eion= 61.5mV * log [ion]outside / [ion] inside

Question 19

What is equilibrium potential for an ion proportional to and inversely proportional to

Answer 19

Eion is proportional to Temperature and inversely proportional to charge of ion.

Question 20

What are the limitations of the Nernst equation

Answer 20

applies only to a situation where a cell membrane is permeable only to one ion

Question 21

What is the RMP of glia cells

Answer 21

-80mV because they only have leak channels for K+

Question 22

What does the Goldman equation calculate

Answer 22

Calculating the RMP accounting for both K+ and Na+ equilibrium potentials

Question 23

If the cell has a higher permeability to one ion how does this affect the RMP of neurons

Answer 23

This ion will have a greater ability to shift the RMP towards its equilibrium. at rest, there is higher permeability to K+ than Na+ so RMP is closer to equilibrium potential for K+. The contribution of Na+ leak channels makes it slightly more positive than -80mV though

Question 24

What is the ENa and EK+

Answer 24

ENa = +60 mV

EK=-80 mV

Question 25

What is the goldman equation

Answer 25

Vm= Pk[K+]outside + Pk[Na+]outside divided by

/ Pk[K+]inside + Pk[Na+] inside