Principles of Sensory Systems (finished) Flashcards
Transduction
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
Transmission
impulses from one neuron to the next (a general sensory pathway vs. complex processing)
general sensory pathway
receptors -> primary afferents -> brainstem or spinal cord nuclei -> thalamus -> primary sensory cortex
Complex Processing
- 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
Four types of complex processing
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)
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)
Perception
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
Sensory unit
a primary afferent and the receptors that define its receptive field
Receptor field
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
Core principles underlying :specificity
- Respond to one form of energy more than any other
4. Respond to only a narrow range of stimulus energy
Threshold
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
Saturation
the maximum intensity of a stimulus that produces a response from a sensory system
Dynamic range
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
Describe the components of stimulus coding.
- What: stimulus modality
- How (big): stimulus intensity
- When: stimulus duration
- Where: stimulus location
Contrast the principles of frequency vs. population coding of stimulus intensity
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
describe the differences between phasic and tonic receptors
- 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)
Lateral inhibition
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)
