1: Intro to Sensory Systems Flashcards
Explain the general organization and function of a sensory system.
Basic organization:
- Sensory receptor in the periphery
- Chain of neurons that transmit the information
- Final target in the CNS
Function: provide information to an organism, allowing it to respond appropriately to the environment
List the five types of stimuli and the receptor types/modalities that are associated with them.
Five types of stimuli:
- Photons
- Detected by photoreceptors
- Modality: vision - Specific molecules
- Detected by chemoreceptors
- Modalities: taste, smell - Mechanical force
- Detected by mechanoreceptors
- Modalities: touch, hearing, proprioception - Temperature
- Detected by thermoreceptors
- Modality: temperature - Chemicals released by tissue damage
- Detected by nociceptors
- Modality: pain
Define the concept of adequate stimulus.
The form of energy a receptor is particularly sensitive to
Describe the process of sensory transduction.
Receptors convert the energy of a stimulus into an AP that can travel through the NS
- Receptor deformed by stimulus energy
- Membrane permeability altered
- Receptor potential generated
- Action potential generated (if stimulus is strong enough)
Discuss the properties of the stimulus that are conveyed during sensory transduction and what conveys each. (4)
- Modality: conveyed by labeled line
- NS interprets any activity along labeled line as specific to the modality of the pathway (pressure on eye -> light) - Intensity: conveyed by frequency of AP generation
- Faster frequency = stronger intensity - Duration: conveyed by differing rates of adaptation
- Faster adaptation = shorter duration - Location: conveyed by receptive field
- Smaller receptive field = more precise location
Describe the concept of adaptation. Why would you want fast adaptation? Slow adaptation?
The response of a receptor to a constantly applied stimulus diminishes with time
Rapidly adapting receptors tell you onset and offset (change, good for vibration)
Slowly adapting receptors maintain firing as long as the stimulus is applied (like a painful pinprick)
What are the two classification schemes for axon size and speed?
Aalpha, Abeta, Agamma, Adelta, B, C group (Erlanger and Gasser)
- Axons classified by CONDUCTION VELOCITY
- Aalpha fastest, C slowest
Ia, Ib, II, III, IV group (Lloyd)
- Axons classified by DIAMETER
- Ia largest, IV smallest
- Solely for sensory fibers
What is conveyed by C fibers/group IV afferent fibers? How fast are they?
Convey dull pain, temperature, itch Very slow (<1m/s)
What is conveyed by Abeta fibers/group II afferent fibers? How fast are they?
Convey touch and pressure sensation and joint position
Very fast, ~33-75m/s
Explain how diameter and myelination relate to conduction velocity. What is the range of axonal conduction in humans?
Larger diameter = faster fiber
More myelin = faster fiber
Range: 100m/s
Functional types of fibers have specific diameters and speeds. Which functions do the largest fibers conduct? The smallest?
Largest fibers: proprioception, skeletal muscle function
Smallest fibers: pain, temperature, itch, some visceral sensations
Define exteroception.
Perception of stimuli originating outside of the body
-Receptors found at or near body surface
Define interoception.
Perception of stimuli originating inside the body
- Receptors found within the body
- Includes things like pH, BP, osmolarity, distention of GI tract and bladder, ischemia
Define proprioception.
Perception of body position and movement
-Receptors found within muscles, tendons, and joints
What is teloception?
When stimuli act at a distance from the individual (as in hearing and vision)
True or false: More neural tissue is devoted to sensory systems than motor systems.
True
How is membrane permeability altered by a stimulated photoreceptor?
Absorption of photons by rods and cones in retina
How is membrane permeability altered by a stimulated chemoreceptor?
Ion channels open when specific molecules bind to them
-Could also activate coupled G-protein
How is membrane permeability altered by a stimulated mechanoreceptor?
Ion channels linked to cytoskeleton -> open when mechanical force is applied
How is membrane permeability altered by a stimulated thermoreceptor?
Unclear, probably involves channels in the TRP family
How is membrane permeability altered by a stimulated nociceptor?
Unclear, can respond to noxious temperatures, mechanical stress, and noxious chemicals
-Many receptors in TRP family
What is a graded potential?
A depolarization that is larger in amplitude with a stronger stimulus, but not an “all or none” even like an AP
If large enough (enough ion channels opened), can produce an AP
What is the two-point discrimination test?
A test to determine the smallest distance required to perceive two stimuli as distinct
-Almost 5cm on calf, versus <5mm on fingertips
