Sensory coding Flashcards
Sensory cells (2)
specialized cells that change their properties in response to stimuli
convey info to the CNS regarding sensation/stimulus
sensory transduction
transformation of physical energy into electrical and/or chemical energy - establishes common language throughout CNS
How are biological sensory receptors classified? 1-3
based on the origin of the stimulation to which they primarily respond
- exteroceptors: stimuli in external environemnt
- interoceptors: stimuli within the body
- proprioceptors: mechanical stimuli associated with configuration and movement of body and body segments
photoreceptors
light
mechanoreceptors
mechanical energy - vestribular and touch receptors
chemoreceptors
chemical substances (taste and smell receptors)
thermorceptors
thermal energy
noci(o)receptors
intense energy of uniform or combined states
5 modalities of receptors?
vision hearing touch taste smell
submodalities of vision - 2
colour/movement
submodalities of hearing - 2
high/low frequency
submodalities of touch
-
submodalities of pain -2
dull ache/stabbing pain
submodalities of temp -2
hot/cold
proprioception vs kinesthesia
static position vs dynamic movement - awareness of the position and movement of segments of our body in space and in relation to one another
four pieces of info conveyed with a sensation
modality
intensity
duration
location
Definition of sensory modality
Type of information (vision/hearing etc)
Sensory modality is coded in what two ways?
Receptor sensitivity: receptors sensitive to specific energy forms - sometimes stimulus can stimulate one or more receptors to work simultaneously.
Labelled lines: axons of receptors function as modality specific lines of communication between periphery and CNS
Stimulus intensity
The amount of stimulus
What’s stimulus intensity coded by?
AP discharge frequency
Stimulus intensity clinical application
- threshold for stimulation
- sensory threshold
Lowest stimulation intensity at which receptor “fires”
Lowest detectable stimulus intensity
- influenced by practice, fatigue, aging, injury
I.e. pain threshold in competitive state vs non-competitive state, and post injury (protective and sensitive)
Stimulus duration?
What’s it coded by?
Length of time for stimulus application
Coded by duriation of AP firing
Perceived vs sustained duration
Perceived duration of application (and intensity) may vary, sustained duration means intensity of perveived stimulus diminishes over time
Why does sustained duration happen?
Adaptation - intensity of perceived stimulus diminishes over time coded by firing frequency and duration
Receptor adaptation
Mechanoreceptors show diff firing patterns to code duration
Cutaneous and subcutaneous mechanoreceptors - low threshold/high sensitivity
Rapidly vs slowly adapting receptors
Slowly - contribute to fire as long as stimulus is maintained - changing shapes
Rapidly - falls silent even when stimulus is maintained - movement and stimulus
Stimulus location
Site of stimulation - where applied
Why are we able to localize where stimulus occurs
Body mapped on sensory cortex(post central gurus) - sensory map/homunculus - somatotropin Oder in the human primary somatic sensory cortex -lips, hands, fingers, genitalia (cortical tissue)
Species specific - for racoons its paws
Variation in sensitivity of tactile discrimination is a function of
location of body surface
Variation in tactile discrimination due to 2
Varying receptor density throughout body - more receptors=more sensitivity - finger vs back because finger needs a to manipulate
Regional diff in “receptive field” - input area for the receptor - arm larger, finger small
Receptive fields (of a somatosensory afferent fibre)
The total area of the skin surface within which suitable stimulation will evoke a response (change in firing state) in the afferent fibre
All somatic sensory info conveyed by
Overlaps of receptor fields and receptor types
Where does the sensory information go?
Inputs from afferent neurons are transmitted to the brain to provide sensory awareness - all somatic sensory info conveyed by pseudounipolar neurons in the dorsal root ganglia
How many groups of somatosensory tracts? What are they?
6 - peripheral and central axons Dorsal column medial lemniscus pathway Spinothalamic tracts Spinocerebellar tracts Spino-Olivary tracts Spinotectal tracts - textile Spinoreticular tracts - reticular
Somatosensory info is transmitted from thalamus to what three regions of in parietal lobe?
Primary somatosensory area (SI) - post central gyrus
Secondary somatosensory area (SII) - by lateral sulcus
Posterior parietal area
3 steps of sensory neuron input
Sensory receptors reside at the terminal of peripheral branch
Central branch leads to spinal cord
Cell body located in ganglion external to spinal cord
How is the somatosensory system organized? 3
Typographically
Areas of body where skin is densely populated by mechanoreceptors have large cortical representation
Size of receptive fields of afferent fibres INNERVATION gets the mechanoreceptors is an important determinant of tactile sensitivity
What does aging do to the number of receptors?
Decreases
Clinical application of perceiving stimulus location
Two point discrimination - minimal inter-stimulus distance required to perceive simultaneously applied stimuli as distinct
6th sense:
Sensory awareness: Kinaesthesia/ proprioception - awareness of the position and movement of segments of our body in space and in relation o one another - we dont notice it until it has been affected or we have to use it to compensate for something
- static position sense - proprioception
- dynamic position sense - kinaesthesia
Proprioceptors
Special receptors that media kinesthesia/ proprioception
Three sources of sensory fdbk contribute to kinesthetic sense
Articulate receptors: mechanoreceptors in joint capsule
Muscle mechanoreceptors: muslce spindle and GTO - length.tension
Cutaneous mechanoreceptors: macro discs
Iwasa - proprioceptive improvement in knees with ACL surgery - 3
Assessed by joint angle reproduction
Significant diff from pre-operative state and 9 months
Continued improvement up to 8 months
Min of 18 months after ACL reconstracution may be needed for complete restoration of the proprioceptive function in knees
What does full kinesthetic sensitivity depend on?
Combined actions of mechanoreceptors in muscles, joints and skin
Sensory coding modalities
Type of information (vision, hearing) coded in 2 ways
What are receptors sensitive to?
Different energy forms
Labelled lines
Axons of receptors function as modality specific lines of communication between periphery and CNS
2 point discrimination in
Regional difference
Ventral and dorsal roots vs afferent and efferent
Ventral efferent dorsal afferent
Dorsal root ganglia
Cell bodies of afferent neurons made of pseudounipolar neurons
Ventral corticospinal tract supply
Neck and upper limbs
