Lecture 4 - the excitable cell

Question 1

What does the nervous system do?

Answer 1

• system of communication that allows an organism to react rapidly & modifiable to changes in its environment

Question 2

What must neurones do?

Answer 2

• collect
• integrate
• output

information

Question 3

Describe how sensory information is processed

Answer 3

sensory nerves detect information - travels to spinal cord - some send to brain - then sent to the motor neurones

Question 4

How are does information need to travel to the spinal cord and back?

Answer 4

2m

Question 5

How does the nervous system allow fast transmission?

Answer 5

• electrical activity provides a rapid, reliable (& flexible) mRNAs for neurons to receive, integrate & transmit signals
• chemical messengers (& receptors) between & within cells provide much more flexibility e.g. for inhibition

Question 6

What is the speed of the nervous system?

Answer 6

• speed is approximately 45-50 meters per second

Question 7

How can electrical properties of neurons and electrical signals be divided?

Answer 7

• action potentials
• graded potentials

Question 8

Describe the properties of an action potential

Answer 8

• fixed size
• all or nothing signals - that travel along (propagate) the axon

Question 9

Describe the properties of an graded potential

Answer 9

• variable size
• local signals not propagated over long distances

Question 10

Describe the direction that action potentials travel

Answer 10

can pass either way along an axon, but tend to go one way (with important exceptions)

Question 11

Describe the direction that graded potentials travel

Answer 11

can pass both ways along the neuronal membrane

Question 12

How are action potentials coded?

Answer 12

coded by FREQUENCY as they are of a unit size

Question 13

How are graded potentials coded?

Answer 13

by size & vary according to the strength of the stimulus

Question 14

What is an absolute requirement for a functioning nervous system?

Answer 14

a negative membrane potential

Question 15

Why do neurons have a negative resting potential?

Answer 15

inevitable consequence of:
- selectively permeable membrane
- unequal distribution of charged molecules/ions
- physical forces

Question 16

Where does the selective permeability of the membrane come from?

Answer 16

• the membrane contains proteins within the membrane - the proteins are ion channels
• the pores in the membrane that allow only some of the ions to travel through

(channels confer selectivity)
(pumps assist unequal charge distribution)

Question 17

Do channels carry out active or passive transport?

Answer 17

passive transport

Question 18

Do pumps carry out active or passive transport?

Answer 18

active transport

Question 19

What does the neuronal membrane separate?

Answer 19

electrically charged ions

Question 20

How can ions cross the membrane?

Answer 20

only by way of protein channels and pumps, which can be highly selective for specific ions

Question 21

What does movement of any ion through its channel depend on?

Answer 21

the concentration gradient and the difference in electrical potential across the membrane

Question 22

What sets up the ionic concentration gradients found in neurons?

Answer 22

Ion pumps:
- Na+/K+ ATPase
- Ca2+ pumps (not just in the plasma membrane)

Question 23

What would occur without ion pumps?

Answer 23

the resting membrane potential wouldn’t exist and the brain wouldn’t function - but the effect of pump inhibitors take some time to work

Question 24

How do ionic gradients influence membrane potential?

Answer 24

by determining Equilibrium Potentials Eions

Question 25

What is Eion?

Answer 25

the membrane potential that would be achieved in a neuron, if the membrane were selectively permeable to that ion

Question 26

What is the equilibrium?

Answer 26

electrostatic forces = diffusional forces (Vm = Ek)

Question 27

At rest, what is the neuronal membrane very permeable to?

Answer 27

K+ (it is slightly permeable others)

Question 28

At rest, the real membrane potential is close to what?

Answer 28

Diffusional forces (Ek)

Question 29

What effect does increasing extracellular K+ have on membrane potential?

Answer 29

depolarise

Question 30

Describe the properties of potassium channels

Answer 30

• 4 subunits
• only allows molecules of a certain size & charges

Question 31

What equation is needed to calculate the real Vm for K+?

Answer 31

Goldman Equation