L23 Somatosensory system Flashcards
what 5 different modalities are seen in the somatosensory system
touch
vibration
proprioception
pain
temperature
*most of the somatic sensory modalities refer to sensations of the skin, proprioception refers to sensory receptors originating int he skeleto-musclar system
all of the receptors in the somatosensory system are what type (morphology) of neurons?
pseudo-unipolar neurons
where are the somatosensory system receptor endings found?
skin or in (or close to) muscle
where do the fibers of somatosensory system receptor run?
in peripheral nerve
where are the somatosensory system receptor cell bodies found?
ganglia (DRG)
what transduces touch?
Merkel’s disks - discriminative touch
Ruffini’s endings - skin stretch
what transduces vibration
Meissner’s corpuscles - high sensitivity, low threshold for freq of 50 Hz
Pacinian corpuscles - high sensitivity, low threshold for freq of 300 Hz
how is pain transduced?
rapidly adapting mechno-sensitive or thermo-sensitive receptors - pricking pain
slowly adapting polymodal receptors - burning pain
how is temperature transduced?
free nerve endings (cold receptors and warm receptors)
how is proprioception transduced?
prorioceptors - muscle spindles, golgi tendon organs
what is the primary receptor of a muscle spindle
rapidly adapting receptor with a 1a afferent fiber (info on muscle stretch) = forms afferent limb of myotactic reflex
what is the secondary receptor of a muscle spindle
slowly adapting receptor carrying info about muscle length = uses class 2 afferent fiber
where are golgi tendon organs located? what fibers do they have
close to the border of muscle and tendon
IIb afferent fibers = form afferent limb of reverse myotactic reflex
what are the 4 types of fiber types used by the somatosensory system?
- large myelinated
- medium myelinated
- small myelinated
- small UNmyelinated
what are characteristics of large and medium myelinated fibers (diameter, conduction velocity, used by, info carried)
diameter - 20 micrometers
conduction velocity = 120 m/s
used by - cut. mechanoreceptors and proprioceptors
info - carry sensory info of touch, vibration and proprioception
what are characteristics of small myelinated fibers (diameter, conduction velocity, used by, info carried)
diameter - 1 micrometer
conduction velocity - 5 m/s
info - pain and temp
what are characteristics of small UNmyelinated fibers (diameter, conduction velocity, used by, info carried)
diameter - 0.2-1.5 micrometer
conduction velocity - 0.5-2 m/s
info - pain and temperature
how do you calculate conduction velocity?
diameter (micrometers) x 6
Where is dermatome C2?
back of the head
Where is dermatome C6
thumb
Where is dermatome C7
middle finger
Where is dermatome C8
pinky!
Where is dermatome T4
nipple
Where is dermatome T10
umbilicus
Where is dermatome L1
groin
Where is dermatome L5
big toe
Where is dermatome S1
little pinky toe
what pathway within the somatosensory system is touch, vibration and proprioception carried?
dorsal column/medial lemniscus system
DCML
what pathway within the somatosensory system is pain and temperature carried?
anterolateral system ALS
