1d and e. Sensory Encoding and Signal Processing

Question 1

Direct Sensory Transduction

- 2 Examples

Answer 1

• Cutaneous mechanoreceptor

- Hair cells in the inner ear

Question 2

Indirect Sensory Transduction

- 2 Examples

Answer 2

• Chemoreceptors in taste and smell

- Photoreceptors

Question 3

Long Receptors

- 3 Examples

Answer 3

• Cutaneous receptors
• Cranial sensory neurones
• Olfactory sensory neurones

Question 4

Short Receptors

- 3 Examples

Answer 4

• Taste receptors (can fire action potentials in extreme circumstances)
• Hair cells in the inner ear
• Photoreceptors in the retina

Question 5

A Current

Answer 5

Inward K+ current that inactivates with progressive depolarisation

Functions to spread out action potentials, allowing graded changes in action potential firing to occur, which is required for accurate signal transduction

Question 6

Bursting Behaviour

- Pattern

Answer 6

Steady stimulus triggers bursts of action potentials that subside then burst again

Occurs at relatively hyper-polarised resting potentials

Question 7

Bursting Behaviour

- Channels

Answer 7

T Ca2+ channel-

• Opens on slight depolarisation
• Inactivates with time

HCN channel

• Opens upon hyperpolarisation
• Inactivated by depolarisation

Question 8

Bursting Behaviour

- Mechanism

Answer 8

1. Hyperpolarised resting potential activates HCN channels which trigger cation influx and depolarisation
2. Depolarisation activates T Ca2+ channels which further the depolarisation
3. Burst of action potentials
4. Depolarisation inactives HCN channels and T Ca2+ channels inactivate with time
   - Cell returns to resting potential

Question 9

Bursting Behaviour

- Olfactory Receptor Mechanism

Answer 9

Oscillating current on prolonged stimulation to generate bursts of action potentials and avoidinng complete spike inactivation

Arises from coupled oscillations of Ca2+ and cAMP

Question 10

Tonic Firing

- Pattern

Answer 10

Steady stimulus triggers constant action potential firing rate.

Occurs at relatively depolarised resting potentials

Question 11

Tonic Firing

- Example

Answer 11

Some cortical pyramidal cells

Question 12

Pattern Switching

- 2 Examples

Answer 12

Cortical pyramidal cells

• Spike frequency accommodation
• Bursting behaviour

Thalamic relay neurones

• Tonic firing
• Bursting behaviour

Question 13

Spike Frequency Adaptation

- Pattern

Answer 13

Strong stimulus initiates high spike frequency which slows despite the stimulus intensity remaining high

Question 14

Spike Frequency Adaptation

- Mechanism

Answer 14

Ca2+ activated K+ channels

1. Voltage gated Ca2+ channels open during action potential firing, increasing Ca2+ influx
2. Activates Ca2+ activated K+ channels to allow K+ efflux to hyper-polarise the cell

This slows action potential frequency.

Question 15

Response Summation

Answer 15

• Non overlapping subliminal fringes = simple summation (linear)
• Overlapping subliminal fringe = supra-linear response summation
• Overlapping centres = sub-linear response summation