Spread of the nerve impulse

Question 1

What are the 4 types of neuron

Answer 1

Unipolar, pseudo-unipolar, bipolar and multipolar

Question 2

Describe resistance in nerve conduction

Answer 2

• Large diameter, lower resistance so faster passive current flow
• But there is not enough space to continually increase the size of diameter to maintain speed of conductance over long distances

Question 3

What is a capacitor

Answer 3

2 conducting regions separated by an insulator

Question 4

Describe capacitance in nerve conduction

Answer 4

For current to pass along nerve, it must overcome the membrane capacitance eg. stored charge

Question 5

Describe the generation of an action potential

Answer 5

1. Incoming stimuli cause
   DEPOLARISATION of Vm (membrane potential)
2. If stimulus large enough to cross THRESHOLD, rapid depolarisation occurs by NaVs opening
3. NaV inactivate rapidly, voltage-gated K+
   channels open allowing K+to exit cell causing REPOLARISATION
4. Because voltage-gated K+channels are slow to close, K+ continues to leave cell down its electrochemical gradient causing a HYPERPOLARISATION
5. Voltage gated K+
   channels close and Vm resets due to action of Kleak and Na+/K+ ATPase pumps

Question 6

What is the absolute refractory period

Answer 6

The period when it is not possible to generate a second action potential immediately after the first due to inactivation of Nav

Question 7

What is the relative refractory period

Answer 7

The period when it is more difficult to elicit a second action potential due to inactivated channels returning to closed state taking time

Question 8

What are Nodes of Ranvier

Answer 8

Gaps between insulated sections where voltage gated Na+ channels are found

Question 9

What is saltatory conduction

Answer 9

When action potentials jump at high speed from one gap to the next