Introduction to Sensory Physiology and Perception

Question 1

Compare and contrast “all-in-one” receptors with receptors that are separate cells.

Answer 1

All-in-one:

• Receptors are also the primary afferents
• E.g. somatosensory system, olfactory system - nociceptive C and A delta fibres
• Resilient to injury

Separate cells:

• E.g. photoreceptors, auditory hair cells
• Delicate and irreplacable

Question 2

Define action potential threshold.

Answer 2

The membrane potential at which action potentials are triggered

Question 3

Define activation threshold

Answer 3

The minimum stimulus strength that will produce action potentials

Question 4

Define perceptual threshold.

Answer 4

The minimum stimulus strength that will generate enough action potentials to be detected

Question 5

What is a sensory neuron’s receptive field?

Answer 5

The particular region of sensory space in which a stimulus will modify the action potential firing of one sensory neuron - i.e. an area in which all the receptors transmit information to the CNS via a single sensory neuron.

Question 6

Describe the relationship between the receptive field size of a region and the cortical representation.

Answer 6

The smaller the receptive field size, the higher the density of innervation - thus, more cortex is needed to deal with the sensory input - i.e. the area is larger on the sensory homunculus.

Question 7

How is the temporal resolution of sensory information limited?

Answer 7

There is a maximum “firing rate” of action potentials that can encode a stimulus

Question 8

Explain what temporal adaptation is and why it is useful.

Answer 8

• Adaptation that damps down responses to homogeneous temporal information
• This highlights salient moments, where stimulus strength changes
• It allows receptors to encode changes in stimulus strength over a huge range without saturation

Question 9

Explain what lateral inhibition is and why it is useful.

Answer 9

• Receptive fields overlap, meaning a stimulus may activate multiple sensory neurons simultaneously
• Lateral inhibition damps down the response of adjacent sensory neurons, allowing enhanced spatial discrimination
• Homogeneous spatial stimuli are suppressed
• This highlights salient locations
• It allows receptors to encode stimulus contrast over a huge range without saturation

Question 10

In primary cortical areas, how are different sensory qualities represented?

Answer 10

• Different sensory qualities represented in “columns”
• Information from different receptors is widely distributed between different cortical areas

Question 11

Give 3 examples of brain dysfunction that lead to abnormalities in sensory perception.

Answer 11

• Epileptic activity
• Synaesthesia - e.g. “seeing” a sound
• Phantom limb pain