Unit 7 - Sensory Modalities Flashcards
overview of modalities
mechanoreceptors
tactile info - skin and also visceral system
mostly associated with large diameter (Aβ) myelinated axons
Merkel Cell complexes
proportion of mechanoreceptors composed of Merkel cell complexes
25% of mechanoreceptors - particularly dense in fingertips
where can merkel cells be found
lie in primary epidermal ridges - fingerprints
channels associated with merkel cells
VG Ca2+ channels
resolution of merkel cell complexes
high spatial resolution - small receptive fields
high spatial resolution ⇒
small receptive fields
freq of stimulation merkel cells respond to
low freq stimulation - slight skin deformation
Merkel cells are sensitive to
rate of adaptation
sensitive to points, edges, curvatures - form and texture
slowly adapting
firing of merkel cells
As objects pass over your fingers they will cause deformations
Causing lamina surrounding nerve endings to change - open Ca2+ channels to depolarise neuron - reach threshold, travels towards Aβ fibre to CNS
meissner corpusles - proportion of mechanoreceptors
40% of mechanoreceptors
where are meissner corpusles found
tips of dermal papillae adjacent to primary ridges
describe structure of meissner corpusles
elongated receptors - lamelle of Schwann cells
what are meissner corpusles sensitive to
skin deformation
particularly low freq vibrations - objects moving over skin
objects slipping from hand - control of grip
receptive fields of meissner corpusles
rate of adaptation
small receptive fields
rapidly adapting
pacinian corpusles - proportion of mechanoreceptors
10-15% of mechanoreceptors
where are pacinian corpusles located
deep in dermis
freq of stimulation - pacinian corpusles
filters out low freq stimulation
responds to high freq (250-350 Hz)
receptive fields of pacinian corpusles
large receptive fields
type of stimulation associated with pacinian corpusles
pressure, vibration
important for skilled use of tools
rate of adaptation of pacinian corpusles
rapidly adapting and low response to threshold
highly sensitive
ruffini endings - proportion of mechanoreceptors
20% of mechanoreceptors
shape and location of ruffini endings
elongated, spindle shaped, capsular
orientated parallel to stretch line in skin
where are ruffini endings located
dermis, ligaments and tendons
what do ruffini endings respond to
stretch and movement
info on finger position and hand conformation
as they stretch, open ion channels, allow Ca2+ and Na+ into neuron, activating AP
rate of adaptation of ruffini endings
slowly adapting
mechanoreceptors overview
receptive field architecture
comparing merkel, meissner, pacinian and ruffini afferents
how do mechanoreceptors respond to braille
Merkle and Meissner recognise details of pattern
Pacinian and Ruffini track movement and position of fingers
what is proprioception
perception of joint position, joint movements, velocity of joint movements and unconscious sensations
mechanoreceptors involved in proprioception
low threshold mechanoreceptors
golgi tendon organ
muscle spindles
joint receptors
Not always conscious - constantly firing
joint receptors role
resemble mechanoreceptors
only minor role in proprioception
important for judging finger position - Work with ruffini endings in order to allow us to know position of fingers in relation to each other - stretch skin
protective role in signalling limits of joint range of motion
GTO and muscle spindle
rate of adaptation and fibre structure - thermoreceptors and nociceptors
free nerve ending associated with small diameter myelinated (Aδ) or unmyelinated (C) fibres
slowly adaptation - continuous firing
different ion channels - thermoreceptors and nociceptors
thermoreceptors
cold (Aδ - more numerous)
warm (c fibres) - unmyelinated
nociceptors
Aδ - fast, ouch
C - dull throbbing pain
