Somatosensory System Flashcards
organization ofareas within the CNS (SC and Brain)
somatotopic
Peripheral Sensory neurons have 2 axons:
________ axons conduct messages from receptor to cell body
________axons project from cell body into spinal cord or brainstem
distal
proximal
somatosensory peripheral neurons do what?
pain pressure temperature touch etc
main difference between motor and sensory neuron?
cell body
which axons transmit faster and why
larger diameter because they are myelinated so their resistance to current flow is less
types of axons
large (myelinated- fastest)
medium
small
unmyelinated (slowest)
which axon does proprioception of skeletal muscle
largest
axon: mechanoreceptors of skin
medium
axon: paint, temperature
small
axon: temperature, pain, itch
unmyelinated
Area of skin innervated by single afferent neuron
receptive field
which part on your body would have smaller and greater density receptive field
fingers
which part of your body would have larger and less dense receptive field
back
3 types of skin sensation
touch
pain
temperature
2 point discrimination tool: how does this work on your fingers and back?
on your fingers you can feel both pins but on your back you can only feel one
In general, the type of environmental energy that a specific receptor responds to is
unique and unimodal
classify receptors by (4)
structure
source
type
rate
Free and diffuse nerve endings
Encapsulated receptors
structure classification
Exteroreceptors– Interoreceptors
– Proprioceptors
classifying by source of stimulus
Slowly adapting
– Rapidly adapting
classifying somatic receptors by rate of adaption
Primary source of information to Spinal Cord
somatic receptors
somatic receptors determine what?
activity and output of the CNS
5 types of receptors
chemo photo thermo mechano noci
Smell, taste, pH, metabolites
chemoreceptors
visual receptors
photoreceptors
temperature (hot or cold)
thermoreceptors
Physical Deformation (Touch, Pressure, Stretch, or Vibration)
mechanoreceptors
Noxious – sensitive to stimuli that damage or threaten todamage tissues.
– Stimulation of these receptors leads to pain
nociceptors
2 superficial fine touch receptors
Meissner’s Corpuscles
Merkel’s Disks
light touch
vibration
Meissner’s corpuscle
pressure touch receptor structure
Merkel’s disks
hair follicle receptors
displacement of hair
2 subcutaneous fine touch receptors
pacinian corpuscles
ruffini endings
pacinian corpuscle does what>
touch and vibration
ruffini endings do what
stretch of skin
(crude localized touch/ pressure, tickle, and itch)
free nerve endings
Sensory organ in muscle
muscle spindle
muscle spindles transmit info regarding:
muscle length, tension, and load
Detect when there is a stretch on the muscleand initiate reflex to resist that stretch
muscle spindle
specialized fibers inside spindle
- nuclear bag and chain fibers
- stretching muscle stretches these fibers
intrafusal fibers
ordinary skeletal fibers outside the spindle
extrafusal fibers
primary endings of muscle spindle aka annulospiral endings do what?
FAST
respond to rate of muscle stretch and length change
secondary endings aka flower spray endings of a muscle spindle do what?
type II
medium-slower
responds to changes in length no matter rate of stretch
primary endings discharge
phasic and tonic
secondary endings discharge
tonic only
phasic is what?
reflex hammer- quick stretch and fade
tonic is what?
rate is proportional to stretch of spindle fibers
function of muscle spindle
passive stretch on extrafusal fiber causes intrafusal fiber to stretch
Structures that relay tension intendons
Sensitive to
golgi tendon organs
golgi tendon organs function to do what? 2 things
1] Control speed of contraction for coordinated, fine, precise movements
2] protect against muscle tears/pulls
activated to reduce effects of cramping
golgi tendon organs
Signal extreme of joint range
– Respond more to passive stretch than active
joint receptor
ruffini’s endings (II)
Respond to movement (not when joint position is constant)
joint receptor
paciniform corpuscle (II)
Similar to GTOs – signal tension
joint receptor
ligament receptors (Ib)
Stimulated by inflammation
joint receptor
free nerve endings (alphay and C)
how does conscious relay pathways to brain?
via projection neurons in white matter
myelinated pathways transmit info super fast
2 structures for conscious relay pathway
Dorsal Column/Medial Lemniscus
Anterolateral Tracts
dorsal column/medial lemniscus does what?
discriminative touch
conscious propriception
Localization of touch and being able to tell if touch is one point or two
discriminative touch
Awareness of movements and relative position of bodyparts
conscious proprioception
3 neurons for dorsal column pathway and where they synapse:
1st order: nucleus cuneatus/gracilis
2nd order: VPL nucleus
3rd order: somatosensory cortex
afferent=
efferent=
sensory neurons
motor neurons
Sensory stimulus (vibration, proprioception, fine touch) to sensory receptor (pacinian corpuscle - mechanoreceptors)
– Stimulus travels through dorsal root ganglion of spinal cord and
continues superiorly via the ipsilateral fasciculus cuneatus (upper
extremity) or fasciculus gracilis (lower extremity)
– Stimulus travels within same axon to medulla where it synapses at the Nucleus cuneatus or nucleus gracilis
1st order neuron
Post synapse the fibers decussate (cross) and travel contralaterallyvia the Medial Lemniscus through the pons, midbrain and synapseat the thalamus (VPL nucleus)
second order neuron
Fibers from the thalamus then travel to the appropriate location on the primary somatosensory cortex
third order neurons
which fasciculus is used for UE and LE?
fasciculus cuneatus= UE
fasciculus gracilis= LE
name the 3 anterolateral pathways
spinothalamic**
spinoreticular
spinomesencephalic
spinothalamic tract processes sensations of what?
pain
temperature
crude touch
what are the sensory receptors of the spinothalamic pathway?
free nerve endings
Enter spinal cord and synapse immediately in gray matter of spinal cord
first order neurons of spinothalamic
Cross spinal cord immediately via anterior commuisure
and ascend through spinothalamic tract until reahcing theVPL nucleus of the thalamus.
2nd order neurons of spinothalamic
Synapse with the primary somatosensory cortex in postcentral gyrus
3rd order neurons of spinothalamic
what is the gate control theory?
If mechanical afferents MORE active – closes
the gate to nociceptiveinput.
Inhibit nociceptive signals by stimulation of nonnociceptive receptors
counterirritant theory
counterirritant theory occurs in which horn?
dorsal horn
counterirritant theory: In theory branches from the mechanoreceptorpathway synapse with an interneuron that
activate to release ________
enkephalins
temperature sensation is Detected by _________ of _______ myelinated and unmyelinated neurons
free nerve endings
small
Enkephalins depress release of Substance P
which inhibits the transmission of nociceptivesignals
counterirritant theory
which fibers carry impulse for cooling?
A y fibers
which fibers carry info for heating?
C fibers
