Lecture 17: Principles of Sensory Processing & Somatosensation Flashcards
What are the different features of sensory stimuli? (4)
MODALITY, SPATIAL INFORMATION, INTENSITY, QUALITY
- Modality (the type of information encoded)
E.g. light, sound, pain, heat, cold, smell, taste - Spatial information (the location of the sensory information)
- Can be: body location (e.g. pain, touch) or location in external space (e.g. light, sound) - Intensity (how strong is that stimulus)
- Perceived strength of stimuli
- Does it reach the threshold? - Quality (unique to individual senses)
- E.g. colour, sharpness of pain, pitch of sound
What forms of stimulus energy can we detect?
- Modalities of stimulus energy: (4)
- Mechanical:
– Sense of touch, limb position, hearing, balance - Chemical:
– Taste, smell - Photic:
– vision - Thermal:
– hot and cold
How do we detect and respond to sensory stimuli? (2)
1 * Each sensory system will selectively transduce a sensory stimulus into an electrical signal (i.e. an action potential)
2 * Made possible through the presence of specialised ion channels present in the membranes of sensory neurons
How do we detect and respond to sensory stimuli?
EXAMPLE STRETCH
An example:
- mechanosensitive neurons have stretch-activated ion channels to detect a stretch
Cellular basis for transduction of a sensory stimuli (nerve ending)
**Can occur directly through a nerve ending:
- Stimulus sensitive nonspecific cation channel
- Sensory receptor (modified ending of afferent neuron)
- Voltage-gated Na+ channel
- Action potential
—-Graded receptor potential in nerve ending
THRESHOLD
Action potential initiation
—> Propagated action potentials
Cellular basis for transduction of a sensory stimuli (receptor cell)
**Can occur via a specialised receptor cell:
- Graded receptor potential in receptor cell
- Graded generator potential in nerve ending
- Action potential initiation
- propagated action potentials
Sensory neurons are specialised for different modalities
- taste
- smell
- somatosensory
- muscle
- hearing
- vision
Cellular basis for transduction of a sensory stimuli
- Can occur directly through a NERVE ENDING
- Can occur via a SPECIALISED RECEPTOR CELL
How do we encode the intensity of a sensory stimuli? (4)
A. RECEPTOR POTENTIAL: graded in amplitude and duration, proportional to the stimulus
B. INTEGRATIVE ACTION: transforms a receptor potential to an AP if the threshold is reached. Increase in stimulus intensity is coded into the frequency of AP firing
C. ACTION POTENTIAL
D. OUTPUT SIGNAL: transmitter release
from synaptic terminal. Amount of transmitter released is determined by the total number of APs per unit time
Accessory structures - WHAT ARE THEY?
Accessory structures play an important ROLE in determining HOW THE STIMULUS ENERGY GETS TO THE TRANSDUCING CELLS
Features of Accessory Structures: (3)
1 * Accessory structures DO NOT TRANSDUCE STIMULUS ENERGY
2 * Are NOT NEURONS OR RECEPTOR CELLS
3 * Can be CELLULAR OR NON-CELLULAR
The labelled line concept: Key principle?
EACHSENSORY RECEPTOR HAS ITS OWN UNIQUE PATHWAY from the RECEPTOR ITSELF TO SOMATOSENSORY CORTEX
Examples of The labelled line concept:
Examples:
1 * E.g Trauma to the optic nerve generates a visual percept
2 * E.g. electrical stimulation of the auditory nerve generates a sound percept (tinnitus)
3 * We can exploit the labelled line concept for medical advances
* E.g. bionic ear or bionic eye
The labelled line concept application: bionic eye (5)
- CAMERA:
captures image and transmits data to an external, body worn processing unit. - DATA PROCESSED: and sent to implanted system via external wire.
- IMPLANTED RECEIVER: passes signals onto retinal implant.
- IMPLANTED ELECTRODE ARRAY: stimulates retina
- ELECTRICAL SIGNALS SENT FROM RETINA: via visual pathway to vision processing centres in the brain.
What is Somatosensation?
The process that CONVEYS INFORMATION regarding theBODY SURFACE and its INTERACTION WITH THE ENVIRONMENT
Four modalities of somatosensation?
TOUCH, NOCIOCEPTION, PROPRIOCEPTION, TEMPERATURE
1. Touch
2.Nociception
(perception of pain)
- Temperature
- Proprioception (gives information about where different body parts are located)
* Predominately from the muscles and joints
Proprioceptive receptors: MUSCLE SPINDLE: 3
1 * Mechanosensitive nerve fibres wrap around the central part of the muscle spindle
2 * When stretched mechanosensitive ion channels are activated
3 * Respond to changes in LENGTH
Proprioceptive receptors: GOLGI TENDON ORGAN (3)
1 * Nerve endings are interwoven between collagen fibres
2 * Muscle contracts→collagen fibres pulled→nerve endings compressed → activates mechanosensitive ion channels
3 * Respond to MUSCLE TENSION (FORCE)
Proprioceptive receptors: JOINT RECEPTORS (3)
FREE NERVE ENDING IN JOINTS, CHANGES AP FIRING RATE THROUGH PARTICULAR RANGE OF MOTION = RESPOND TO JOINT POSITION AND ANGLE
1 * Free nerve endings innervate different regions around the joint
2 * Each nerve ending changes its firing rate as the joint passes through a particular range of motion
3 * Respond to JOINT POSITION/ANGLE
What are thermoreceptors?
1 * Separate ‘cold’ and ‘hot’ receptors
2 * Thermosensitive nociceptors ACTIVATE ATTEMPERATURES which could ELICIT TISSUE damage (protective effect)
Discovery of receptors involved in temperature and touch: 2021 Nobel prize
Temperature sensation by TRPV1 channels
Pressure sensation mediated by Piezo channels
Thermoreceptors will adapt rapidly to changes in temperature EXPLAIN (3)
1 * GREATEST STIMULUS comes from the INITIAL TEMPERATURE
2 * A LARGER CHNAGE in temperature will CAUSE A GREATER CHNAGE IN FIRING RATE
3 * FIRING RATE RATE ADAPTS TO THE NEW TEMPERATURE
Nociceptors - WHAT IS IT?
Nociceptors respond SELECTIVELY to NOXIOUS STIMULI that can DAMAGE TISSUE
Some specifics of Nociceptors (2)
1 * Often have very high (or low) thresholds or very precise ones
2 * Can be thermal, chemical or mechanical
