Detection and central processing of touch Flashcards
What is the dorsal column-medial lemniscus pathway
The major afferent pathway for fine discriminatory touch, pressure, vibration and conscious proprioception
What properties of objects are coded for by sense of touch
Spatial dimensions, surface compliance (hard/soft), surface texture, motion- all combine for object recognition
What are different types of mechanical stimulation
Vibration, pressure, stroking or prodding
What is the proportions of different mechnoreceptors in the hand
40% Meissener’s, 25 % Merkel’s, 20% Ruffini’s, 1-15% Pacinian
Benefits of multiple touch receptors
Different receptive field sizes, can be specialised for dynamic and static sensitivity, broader range of intensities, parallel processing
What are the consequences of large receptive fields
Allow detection of changes over a wider area, leads to less precise perception
What are the consequences of small receptive fields
Allow detection over a small area, but with precise perception
What technique can be used to record sensory fields
Microneurography- single sensory axon recordings in the hand allow mapping of single receptive fields
How does the distribution of receptor types differ across the hand
eg high conc of Merkel’s and Meissner’s in fingertips allows fine discrimination
Why does 2 point discrimination ability differ across the body
Acuity of touch sensatino varies across the body as receptor field size changes- smaller fields allow greater acuity as points don’t fall in the same receptive field
Why does the spatial acuity of skin ni the fingertip deteriorate noticably with age
May be due to a decrease in the density and distribution of Meissner’s corpuscles and Merkel’s disks in the skin
What types of mechanoreceptors are specialised for dynamic or static sensitivity
Motion sensors that rapidly adapt to stimuli, pressure sensors that slowly adapt to stimuli
What is the benefit of lots of differenr mechanoreceptors with different sensory thresholds
extends the range of intensities encoded
What is the benefit of parallel processing from different mechanoreceptors
Parallel processing of different information from receptors allows brain to process many features at once, speeding up identification
Which mechanoreceptors are slowly adapting
Merkel’s disks and Ruffini’s endings
What does the firing rate in slowly adapting receptors reflect
The absolute level of indentation- intensity of stimulus is encoded in AP firing rate
AP firing rate can also reflect the size/shape of the indenting object
What mechanoreceptors are rapidly adapting
Meissner’s corpuscle and Pacianian corpuscle
What does the firing rate reflect in rapidly adapting receptors
Speed of indentation- stops firing APs when stimulus is constant, can encode responses to new changes in sensory input
Provides a temporal pattern
What qualities of the object can be knwon by combining responses of rapidly and slowly adapting receptors
Dynamic and static qualities about a stimulus
Where are Merkel’s disks located in the skin
Epidermis, aligned with the papillae that lie beneath the dermal ridges
Where are Merkel’s disks found in the body
Very dense in fingertips, lips and external genitalia
What sensation does stimulating Merkel’s disks give rise to
Light pressure
What are Merkel’s disks suited for
Extremely sensitive with very small receptive fields
Useful for fine touch and small object discrimination features eg static shapes/edges/rough textures
What are the adaptive properties of Merkel’s disks
Static, slowly adapting pressure detector (frequency range 0.3-3Hz, created by rubbing your features over an object)