Week 1 Lecture 5

Question 1

What is receptor potential?

Answer 1

Change in membrane potential as a result of the receipt of signal from exterior sensory cue

Question 2

Which sensory receptors do not depolarize?

Answer 2

Photoreceptors (hyperpolarize)

Question 3

Where are receptor proteins located and what happen when they receive signals?

Answer 3

In the sensory cell membrane and they change shape when specific energy is received

Question 4

What are the two results of receptor protein changing shape?

Answer 4

• Directly open ion channels
• Activation of enzymes that produce 2nd messengers that amplify the signal

Question 5

What are the two stages of amplification?

Answer 5

• G-coupled protein can activate a number of different enzymes molecules
• Each of these enzymes will produce a lot of secondary messengers

Question 6

How do odorants interact with olfactory receptors?

Answer 6

Specific odorants interact with specific olfactory receptors

Question 7

What is the signalling cascade associated with odorant binding to olfactory receptor? (5)

Answer 7

• activation of G-protein
• activation of adenyl cyclase
• production of cAMP
• cAMP binding directly to cation channels (Na+ and Ca++) and opening them
• the depolarization of the membrane

Question 8

What happens to the depolarizing current that resulted from olfactory receptor cascade?

Answer 8

The depolarizing current travels down the membrane via passive conduction to the trigger zone of the axon

Question 9

What are the two categories of sensory cell transmission? (2)

Answer 9

• Sensory cell generates action potential at spike generating zone e.g. mechanoreceptors
• Sensory cell releases vesicles by impulses generated by post-synaptic neuron when depolarized e.g. taste receptors

Question 10

How are signals transmitted via vesicles? (5)

Answer 10

• Binding of taste molecule to taste receptor produces depolarizing current
• Depolarizing current moves passively to the other end of the cell
• At the other end of the cell, depolarizing current activates voltage-gated calcium channels
• Voltage-gated Ca++ channels open resulting in influx of Ca++
• Ca++ promote exocytosis and the release of vesicles

Question 11

What is adaption?

Answer 11

The decay in membrane potential over time in which the original voltage is not sustained despite the stimulus being constant

Question 12

What are the two types of adaption?

Answer 12

Slow adapting and rapidly adapting

Question 13

What is slow adaption?

Answer 13

Receptor potential is sustained fro duration of stimulus

Question 14

What is rapid adaptation?

Answer 14

Receptor potential is a result of the change in stimulus energy, decay occurs when stimulus is constant

Question 15

What is of interest in slow and rapid adaptation?

Answer 15

In slow adaptation, the magnitude of the stimulus is of interest while with rapid adaptation the delivery and velocity of the stimulus is of interest

Question 16

What is habituation?

Answer 16

The response to successive stimuli becomes progressively weaker over time

Question 17

Do all cells show habituation response?

Answer 17

Habituation response depends on the cell the cell, some show large degree of habituation some don’t

Question 18

What is the receptor potential directly proportional to?

Answer 18

The intensity of the stimulus, the greater the intensity of the stimulus, the greater the depolarization

Question 19

What happens as stimulus intensity increases?

Answer 19

Higher threshold sensory neurons are recruited because refractory period limits impulse frequency

Question 20

What are strategies used to code for the strength of stimulus? (2)

Answer 20

• Increase frequency of AP at excitable membrane
• Recruiting addition receptors with higher threshold

Question 21

What strategy is used to distinguish differences in the modality of stimulus?

Answer 21

The ‘labeled line’ strategy

Question 22

What is the labeled line strategy?

Answer 22

The activity in one pathway is indicative of a particular stimulus quality and nothing else

Question 23

What is population coding?

Answer 23

Using the ratio of activity from a restricted number of receptor types to code information e.g. how colours are processed

Question 24

Why is population coding significant?

Answer 24

It is more efficient to use ratio of a restricted amount of receptor proteins for all qualities than a receptor for each quality.