Principles of Sensory Systems (finished)

Question 1

Transduction

Answer 1

conversion of stimulus energy to electrical potentials; physiological process that is common to all sensory systems

Multi-step process (italicized steps are optional)
Stimulus→ accessory structures→ receptor (conformational change in transducer protein)→ 2nd messenger systems→ ion channel activation/inactivation (conductance change)→ receptor potential→ neurotransmitter release→ action potential in primary afferent

Question 2

Transmission

Answer 2

impulses from one neuron to the next (a general sensory pathway vs. complex processing)

Question 3

general sensory pathway

Answer 3

receptors -> primary afferents -> brainstem or spinal cord nuclei -> thalamus -> primary sensory cortex

Question 4

Complex Processing

Answer 4

• CNS processing of sensory information occurs on many levels—and in both ascending and descending directions (basically, anytime you introduce a synapse, you create the potential for a signal to be modified)
• Connections can be either excitatory or inhibitory in nature
• Four types of complex processing

Question 5

Four types of complex processing

Answer 5

o Series processing: refers to information that is passed in an ascending manner, from one neuron to the next within a specific pathway→ fundamental component of the labeled line theory of sensory coding

• Divergence: sensory information that is expanded from the primary sensory pathway into multiple, parallel processing routes

o Convergence: sensory information that is converged both within a pathway and across modalities

o Descending input: descending control of all aspects of sensory processing. These control systems include:

— Centrifugal connections (i.e. those that provide feedback control within a sensory system such as modulation of outer hair cell function by efferent cells of the auditory brainstem)
— Non-sensory inputs such as those that allow for selective attention (i.e. pain)

Question 6

o Series processing

Answer 6

refers to information that is passed in an ascending manner, from one neuron to the next within a specific pathway→ fundamental component of the labeled line theory of sensory coding

Question 7

Divergence

Answer 7

sensory information that is expanded from the primary sensory pathway into multiple, parallel processing routes

Question 8

o Convergence:

Answer 8

sensory information that is converged both within a pathway and across modalities

Question 9

o Descending input

Answer 9

descending control of all aspects of sensory processing. These control systems include:

— Centrifugal connections (i.e. those that provide feedback control within a sensory system such as modulation of outer hair cell function by efferent cells of the auditory brainstem)
— Non-sensory inputs such as those that allow for selective attention (i.e. pain)

Question 10

Perception

Answer 10

a conscious process where CNS continues to filter sensory information and switches priority (e.g. paying attention). Perception is a conscious process (includes tran.smission) while sensation is unconscious processing

Question 11

Sensory unit

Answer 11

a primary afferent and the receptors that define its receptive field

Question 12

Receptor field

Answer 12

the spatial region where application of a stimulus causes a sensory neuron to respond
• Receptive fields can overlap
• Definition applies to higher order neurons, as well as to receptors and primary afferents
o Size/shape/properties vary among individual cells, especially as you go between cells in a pathway (i.e. the receptive fields of 2nd order neurons will be significantly different from the receptors

Question 13

Core principles underlying :specificity

Answer 13

3. Respond to one form of energy more than any other

4. Respond to only a narrow range of stimulus energy

Question 14

Threshold

Answer 14

minimum intensity of a stimulus that is required to produce a response from a sensory system
• Can be defined in terms of
o Receptor threshold
o Action potential threshold
o Perception threshold
• The adequate stimulus will produce the response with the lowest threshold

Question 15

Saturation

Answer 15

the maximum intensity of a stimulus that produces a response from a sensory system

Question 16

Dynamic range

Answer 16

the range of intensities that will produce a response from a receptor or a sensory system (i.e. the difference between threshold and saturation)
• Even within a modality, individual receptors will have different thresholds and dynamic ranges
• As a result, the sensory system as a whole will have a wider dynamic range than an individual receptor

Question 17

Describe the components of stimulus coding.

Answer 17

• What: stimulus modality
• How (big): stimulus intensity
• When: stimulus duration
• Where: stimulus location

Question 18

Contrast the principles of frequency vs. population coding of stimulus intensity

Answer 18

Frequency Coding
• Increasing the firing rate of individual primary afferent fibers by increasing the size of the receptor potential
• The most common way to do this is by increasing the size of the receptive field stimulated

Population Coding
• Increasing the number of primary afferent fibres responding→ called recruitment
• Recruited fibres will not respond equally
- because of frequency coding, the primary afferent whose receptive field is in the centre of the point of stimulation (i.e. the green fibre) will respond with the largest number of action potentials
- this concept is critical with respect to understanding lateral inhibition

Question 19

describe the differences between phasic and tonic receptors

Answer 19

• If the change in receptor potential occurs slowly, the response is called tonic (the olfactory system exhibits tonic adaptation)
• If it occurs rapidly, it is called phasic (the auditory system exhibits phase adaptation)

Question 20

Lateral inhibition

Answer 20

a CNS process whereby application of a stimulus to the center of the receptive field excites a neuron, but a stimulus applied near the edge inhibits it.
To understand the lateral inhibition process, start with intensity coding: (e.g. frequency and population coding)