Neuronal Communication

Question 1

Give two reasons why a refractory period should follow an action potential?

Answer 1

• Ensures action potentials are unidirectional
• Ensures action potentials occur as discrete impulses

Question 2

List three factors that affect the rate of conduction of an action potential:

Answer 2

• Myelination
• Temperature
• Axon diameter

Question 3

Name two types of synapses:

Answer 3

• Excitatory synapse
• Inhibitory synapse

Question 4

What effect do inhibitory synapses have on the post-synaptic membrane?

Answer 4

Hyperpolarisation

Question 5

What term describes the process in which more than one impulse is needed to generate an action potential at a synapse?

Answer 5

Summation

Question 6

Name the process by which an action potential is generated from a single presynaptic neurone releasing neurotransmitters a number of times.

Answer 6

Temporal summation

Question 7

Name the process by which an action potential is generated from multiple presynaptic neurones releasing neurotransmitters.

Answer 7

Spatial summation

Question 8

What is a response?

Answer 8

An action carried out by an effector

Question 9

What is a stimulus?

Answer 9

A change in the external/ internal environment of an organism

Question 10

What are the two main features of sensory receptors?

Answer 10

• Contain specialised cells
• Act as transducers

Question 11

What do olfactory receptors detect?

Answer 11

Volatile chemicals

Question 12

What do gustatory cells detect?

Answer 12

Soluble chemicals

Question 13

Explain how changes in the pressure in the skin leads to the generation of an impulse in the sensory neuron.

Answer 13

When the Pacinian Corpuscle is deformed by the pressure, stretch mediated Na ion channels open in the sensory neurone. Na ions enter the sensory neurone by diffusion across the electrochemical gradient, depolarising the membrane and generating an action potential

Question 14

What are the Nodes of Ranvier?

Answer 14

Gaps in the myelin sheath which expose the axon of the neurone to the extracellular fluid

Question 15

Explain how an action potential is generated:

Answer 15

At resting potential, the inside of the cell is more negative (-70mV) than the outside of the cell due to the action of the Na/K pump. 3 Na out and 2 K in via active transport from the tissue fluid outside of the axon. All voltage gated channels are closed at this point. All Na are closed with a few K open causing some K ions to diffuse.

When pressure is applied to the Pacinian corpuscle, it is deformed and stretch mediated Na ion channels are opened, causing the diffusion of Na across the electrochemical gradient into the sensory neurone, depolarising the neurone and generating an action potential. The potential difference increases to -55mV which induces a positive feedback reaction, some Na voltage gated ion channels open causing Na to diffuse across the electrochemical gradient into the axon from the extracellular tissue. +40mV is reached (peak action potential), once depolarisation has reached the threshold potential, it generates an impulse.

Question 16

Explain repolarisation and hyperpolarisation: