somatosensory part 2 Flashcards
what is glabrous skin
palms of hands, lips and soles of feet
what types of cutaneous receptors are on glabrous skin
Merkel cells (ABeta SAI-LTMR)
Ruffini ending (ABera SAII-LTMR)
Meissner corpuscle (ABeta RAI-LTMR)
Pacinians corpuscle (ABeta RAII-LTMR)
what types of cutaneous receptors are on hair skin
Abeta RA-LTMR
Adelta-LTMR
C-LTMR
circumferential lanceolate endings
free nerve endings (HTMR)
SA and RA =
slowly adapting and rapidly adapting
LTMR and HTMR =
low and high threshold mechanoreceptor
Abeta, Adelta and C refer to
classes of nerve fibres
high threshold means…
it required a strong stimulus compared to low threshold
how does the sensory receptors and spinal cord connect
nerve travels from the skin along the limb and reaches the spinal cord through the dorsal root
they enter the spinal cord at the dorsal horn of the grey matter
what is the dorsal root ganglion
a swelling when the cell bodies of these nerve fibres are found
Abeta nerve fibres
myelinated
larges diameter
fastest conduction velocity
Adelta nerve fibres
myelinated
C fibres
unmyelinated
smallest diameter
slowest conduction velocity
RA fibres
the nerve fibre fires when the stimulus is applied and when it is removed, theres no response during the maintained phase of the stimulus
SA fibres
higher rate of firing near the beginning of the stimulus bit the firing is maintained throughout the time the stimulus is being maintained
RA only respond during the onset and offset of a stimulus
SA fire throughout the duration
so RA highlight…
what is changing
which of the glabrous receptors are deep in the dermis
Ruffini ending and pacinians corpuscle
which of the glabrous receptors are between the dermis and the epidermis
merkel cells and meissner corpuscle
free nerve endings are not specialised, they are HTMR and they are nociceptor fibres that respond to…
pain (something sharp for example)
hairy skin:
longest hairs =
guard
smallest hairs =
zigzag
middle length
auchene
what receptor is present at the top of the guard hair follicle
merkel cells
longitudinal receptor types are LTMR.
how are they arrange
around the hair so which ever direction the hair is bent it will push against some parts of these receptors are trigger action potentials in these nerve fibres
Merkel receptor (SA1)
the nerve fibres branch at their terminals and associate with merkel cells which embed into the lower layer of the epidermis
Ruffini corpuscle (SA2)
consists of a collagen capsule with an axon that enters the capsule
the best stimulus for these is being stretched along this axis
meissner corpuscle RA1
collagen fibres that spiral around to form the corpuscle and the axon also coils around the layers of collagen
anchored into the base of the epidermis so as the epidermis moves it tugs on the meissner corpuscle
pacinian corpuscle (RA2)
found deep in the dermis
axon through the core and then around it
thermoreceptors
free nerve endings
warm and cold spots
max sensitivity: cold 25-30, warm 40-43
cold receptors are highly sensitive to temperature changes
what type of receptors are cold thermoreceptors
small myelinated ADeltas fibres
what type of receptors are warm thermoreceptors
unmyelinated C fibres
nociceptors
fibres terminate as free nerve endings
mechanoreceptors (responds to a prick, squeeze etc)
Adelta fibres - first pain
mechano - thermal: sensitive to painfully hot or cold temperatures
C fibres - second pain (throbbing pain after injury)
defining cutaneous receptive fields using micro-neurography
electrode pushed in through the skin to reach a nerve
can record individual AP from a single nerve fibre and therefore from THE single receptor
then you use a probe to map out on the surface of the hand the area of skin which activates that particular nerve fibre
that region of the skin is known as the receptive field of that fibre and that receptor
SA1 (merkel) and RA1 (meissner) receptive fields
the receptive fields are quite small and increase in density at the finger tops
SA2 (ruffini) and RA2 (pacinian) receptive fields
have larger receptive fields
what is spatial resolution
ability to recognise two points of stimuli (two point discrimination)
at the finger tips there is higher spatial resolution which correlates with an increase in density of…
RA1 and SA1 receptors
which receptor type shows the highest spatial resolution
SA1 (merkel)
its responsible for detecting fine details of texture etc
RA nerve fibres
respond best to a stimulus that is changing as they respond to onset and offset of stimulus
RA2 (pacinian) has a low threshold (low pressure will cause a response) and is most sensitive at 300Hz
