How Nerves Work 3

Question 1

When is an action potential sent?

Answer 1

When the resting membrane potential of -70mV depolarises to threshold at around -55mV

Question 2

What causes the depolarisation of the resting membrane potential?

Answer 2

External stimuli acting on specific sets of ion channels to create graded potential where the size of potential is related to the size of the stimulus

Question 3

What is a synapse?

Answer 3

A junction/gap between 2 neurones where the action potential releases transmitter molecules that activate receptor on the second cell which open ion channels creating another graded potential

Question 4

What happens at an NMJ?

Answer 4

Motor neurone depolarises the muscle to threshold by evoking a graded potential known as the endplate potential

Question 5

What are examples of graded potential?

Answer 5

• Generator potentials at sensory receptors
• Postsynaptic potentials at synapses
• Endplate potentials at NMJ (skeletal muscle)
• Pacemaker potential in pace maker tissues

Question 6

What are properties of graded potentials?

Answer 6

• Electrotonic potentials
• Decremental potentials
• Non-propagated potentials
• Local potentials

Question 7

Why are graded potentials decremental and non-propagated?

Answer 7

As you further away from the site of stimulus, more current leaks out along the membrane and as a result the membrane potential gets smaller and smaller

Question 8

Where can graded potential signal stimulus intensity?

Answer 8

In their amplitude

Question 9

What is meant by graded potentials being graded?

Answer 9

A stronger stimulus would open more channels, creating a bigger current flow and therefore a bigger potential

Question 10

Why can graded potentials be depolarising or hyperpolarising?

Answer 10

• Firing an AP depends on reaching a firing threshold.

- Graded potentials can therefore excite or inhibit a cell

Question 11

What do EPSPs or IPSPs depends on?

Answer 11

Which ion channels are open

Question 12

Opening which ion channels would cause hyperpolarisation?

Answer 12

Potassium and chlorine

Question 13

What would opening potassium and chlorine channels do?

Answer 13

• Causes hyperpolarisation
• Takes them away from threshold
• IPSP

Question 14

What would opening Na and Cl channels do?

Answer 14

• Causes depolarisation
• Takes then towards threshold
• EPSP

Question 15

What are ligand-gated ion channels?

Answer 15

Postsynaptic potentials are produced by a neurotransmitter opening or closing ion channels

Question 16

What are voltage-gated ion channels?

Answer 16

Action potentials are produced by depolarisation of the membrane potential opening ion channels

Question 17

Why are graded potentials important in synaptic integration?

Answer 17

Graded potentials can summate

Question 18

What is temporal summation?

Answer 18

One stimulus that is stimulated again quickly and the second EPSP adds on.

Question 19

What is spatial summation?

Answer 19

When 2 separate stimuli add together

Question 20

What is integration

Answer 20

Looking at all of the inputs and deciding whether or not to send one of those long distance signals (AP)

Question 21

What is synaptic integration?

Answer 21

The process of summing all those inputs in space and time to determine whether or not the initial segment reaches threshold

Question 22

What do IPSPs tend to do?

Answer 22

Stop the cell reaching threshold