University:
Western Sydney University
Course:
MEDI 2003 | Clinical Sciences 2
Academic year:

2024
Views:

197

Pages:

2
Author:

Mariam A.

Types of sensory fibres Structures Function     Slowly-adapting SAI – Merkel’s disc receptor. SAII – Rufini endings. SAI – skin compressions. SAII – skin stretch. Fast-adapting FAI – Meisner’s corpuscle. FAII = Pacinian corpuscle. HFA – hair follicle receptor. Inform the dynamic components of a stimulus (how fast, etc.). Slowly-adapting fibres. o Merkel’s disc (epidermal) have small receptive fields that are sensitive to focal compression. They are for spatial acuity, 2 point discrimination and pattern recognition. o Ruffini endings (deep) have a large receptive field and are sensitive to stretch. They are responsible for kinaesthetic sensibility. Sense of force relies on the individual fibres and population of active fibres. o Compressions are graded as a function of stimulus intensity (e.g. the more push, the more response), forming a rate code. o With increasing intensity of stimulus, more fibres are recruited to help in localisation, creating the population response. Morphology of tactile receptors differs between hairy and glabrous skin. o Glabrous skin contains many Meisner’s corpuscles in the epidermal/superficial location, with density increasing distally. They also have Pacinian corpuscles in their dermal/deep location, which are responsible to remote stimuli. o Hairy skin contains hair follicle afferent receptors which are functionally equivalent to Meisner’s corpuscles. The Pacinian corpuscles are even deeper, being adjacent to bone. Fast-adapting fibres. o Responsible for velocity sensitivity, pattern recognition and texture recognition. o Meisner’s corpuscle is more responsive to low frequency stimuli (~5 – 100Hz). o Pacinian corpuscle is responsive to high frequency stimuli (~50 – 500Hz). o Both detect an increase in intensity and result in increasing discharge rate and number of fibres activated. o Discharge pattern matches periodicity of stimulus. o This patterning of impulse activity underpins our capacity to detect changes in vibration frequency/surface texture.  Texture recognition can be explored by using finger scans for any irregularities. o The relative motion of the fingertip and surface sets up a vibratory disturbance in the fingertip. o This vibratory stimulus can be mimicked/reproduced by applying vibration to the skin surface. o Sinusoidal vibration can be defined by duration, amplitude and frequency. o These parameters can be used to assess the sensitivity of different fibre classes to tactile stimuli.