Somatic Sensory System Flashcards
somatic sesnory system =
representation of body in the brain
2 major inputs
mechanical stimuli
painful stimuli and tempertautre
input and interpretation enables us to…..
identify shape and texture
monitor internal and external forces acting on body
detect potentially harful circumstances
sensory receptors
golgi tendon organ
muscle spindles
sensory receptors
meissner (tactile) corpuscles
location - dermal papillae of skin, eyes, palms etc
modality - light, touch, texture (movement e.g friction)
sensitive to 30-50Hz
rapidly adapting
sensory receptors
pacinian (lamellated) corpuscles
location - dermis, joint capsules, viscera
modality - deep pressure, stretch, tickle, vibration
sensitive to 250 - 350 Hz
rapidly adapting
encapsulated nerve endings
meissener
pacinian
Ruffini
sensory receptors
ruffini corpuscles
location - dermis, subcutaneous tissue, joint capsules
modality - heavy touch, pressure, skin stretch
slowly adapting
sensory receptors
merkel (tactile) discs
location - superficial skin - epidermis
modality - light touch, texture, edges, shapes
slowly adapting
sensory receptors
free nerve endings
location - widespread in epithelia and connective tissues
modality - pain, heat, cold
unencapsulated nerve endings
merkel
free nerve endings
sensory receptors
hair follices
location - widespread in eptihelia
modality - varied according to type
both rapid and slow adapting
cellular vs molecular receptors
molecular = molecule on surface to detect other molecules cellular = group of cells organised to form receptor - detect pain, temp etc
sensory receptors = not always neurons
in above examples, cells are doing the sensing = they are the sensory neurons themselves
but, photoreceptors, auditory and vestibular hair cells are specialist cell types that synapse with sensory afferent to relay to CNS
classes of mechanoreceptor response
phasic
tonic
phasic response
rapidly adapting
give info about changes in the stimulus e.g. pacinian corpuscles
tonic
slow adapting
continue to respond as long as stimulus is present - gives info about presence of stimulus e.g. ruffini corpuscles
primary afferent sub types
according to conduction velocity which broadly reflects diameter (faster = larger diameter)
axons coming from skin
labelled with letters
A = fastest/largest
can be further broken down by greek letters, alpha = fastest
axons coming from muscles
Roman numerals
I = largest/fastest
Ia = faster than Ib
organisation of sensory info
in layers in spinal cord dorsal horn
cell bodies of different classes of sensory neurons are grouped in DRG and their projections organised to different layers of dorsal horn
somatosensory projections
2 routes to brain
medial lemniscal tract
spinothalamic tract
medial lemniscal tract
cary mechanoreceptive and proprioceptive signals to thalamus
spinothalamic tract
carries pain and temperature signals to thalamus