MODULE 4- Touch + Proprioception Flashcards
how are mechanical forces on the skin conveys to the CNS
via an array of somatosensory affect neurons
what is reflected by the wide variety of mechanical forces that can impinge on the skin
the comparably diverse array of mechanoreceptors embedded in the skin
2 types of skin
-glabrous
-hairy
**glabrous skin
-found on the soles of heads, feet, lips
-capable of highly discriminative touch
**hairy skin
-covers 90% of the body
-capable of both discriminative + non-discriminative touch
somatosensory afferent neurons (2)
-mechanoreceptors
-dorsal root ganglion
**mechanoreceptors
-detect innocuous (harmless) mechanical stimuli impinging on the skin
-transduce mechanical forces into neural signals
-serve as the path by which signals reach the CNS
**dorsal root ganglion
pseudo-unipolar neurons soma with a bifurcating axon with one branch from the PNS + the other to the CNS
trigeminal ganglia/nerve
sensory receptors for the face
**dermatome
the territory innervated by each spinal nerve
-aka each fiber of the cell is from a single dorsal root ganglion
do dermatological maps vary?
yes, they vary among individuals
how do dermatomes maintain sensation
they overlap significantly for touch, pressure, + vibration so that injury to one set of dorsal root doesn’t result in a complete loss of sensation
what are the sensations where dermatomes do not overlap
pain + temperature
how do somatosensory afferent neurons vary
vary widely in
-size
-conduction
-velocity
-types of stimuli to which they respond
-response properties
which afferent sensory neurons have the smallest diameter + slowest velocity
pain + temperature
which afferent sensory neurons have medium diameter + medium velocity
cutaneous mechanoreceptors
which afferent sensory neurons have the largest diameter + fastest velocity
muscle spindles
where else are muscle spindles used
balance
**receptive fields
the area of the skin surface that results in the firing of APs when touched/activated
**how is size of receptive field determined
by the amount of branching of the afferent axons
**what test determines size of receptive field
2-point discrimination test
**2-point discrimination test
-uses calipers to measure
-distinguishing closer together is harder than far apart
**somatic acuity
how sensitive each region is
-region-specific
-some body parts are more sensitive than others
why are some body parts more sensitive than others
due to overlapping receptive fields in the former
more sensitive body parts
-fingertips
-lips
less sensitive body parts
-thigh
-back
**slowly adapting afferents
fire continuously for as long as the stimulus is occurring
what information do slowly adapting afferents provide
information about the size + shape of the stimulus
-ex: carrying a heavy object
**rapidly adapting afferents
fire when the stimulus starts + sometimes when the stimulus stops
what information do rapidly adapting afferents provide
information about the movement of a stimulus
-ex: the feel of clothing on your body
what do slowly adapting afferents look like on graph
spaced out
what do rapidly adapting afferents look like on graph
small rapid blips
what do specialized cells types in the skin do
transduce unique aspects of touch information
**4 classes of mechanosensory end organs
-merkel cells
-meissner’s
-pacinian
-ruffini corpuscles
**free nerve endings
afferent nerve fibers lacking specialized receptor cells
-aka there are none of the mechanosensory end organs listed above in free nerve endings
what are free nerve endings important for
pain detection
layers of skin (superficial to deep)
-epidermis
-dermis
-subcutaneous layer
what are found in the epidermis (3)
-free nerve endings
-meissner corpuscle
-markel cell-neurite complex
what is found in the dermis (1)
ruffini corpuscle
what is found in the subcutaneous layer (1)
pacinian corpuscle
**merkel cells
-highest spatial acuity
-smallest receptive field
-slowly adapting
-detect points, edges, curves (i.e., shape + textures)
**meissner’s
-high density close to skin surface
-rapidly adapting on-off responses
-larger receptive field than merkel cell
-respond to low-frequency vibrations
-detect motion, like the slippage of an object
**pacinian
-located deep in dermis
-rapidly adaptive
-low response threshold
-have large receptive fields because they’re so sensitive
-detect vibration
**ruffini
-least understood
-maybe slowly adapting
-respond to skin stretch
-located deep in the skin
-helps provide information about finger position
sensory transudction from the skin involves what
converting mechanical forces into electrical signals
sensory transduction
converting the energy of a stimulus into an electrical signal
**receptor potential
depolarizing current resulting from a stimulus opening an ion channel in afferent nerve endings
**what channels do merkel cells have
piezo2 ion channels
**piezo2 ion channels
open as a result of mechanical stimuli
proprioception involves sensing forces in what 3 things
-muscles
-joints
-connective tissue
mechanoreceptors for proprioception (2)
-muscle spindles
-golgi tendon organs (GTOs)
**proprioception
involves information about position of the limbs + body
**muscle spindles
consist of 4-8 INTRAFUSAL MUSCLE FIBERS surrounded by a capsule of connective tissue
**what changes do muscle spindles detect
changes in muscle length
-muscle stretch
**how do muscle spindles convey information to CNS
sends information via group 1a + 2 afferents
how does density of muscle spindles vary
by muscles
**where are golgi tendon organs (GTOs) found
in tendons
**what changes do GTOs detect
changes in muscle tension
**how do GTOs convey information to CNS
sends information via group 1b afferents
**joint receptors
mechanoreceptors embedded in joints
-3 types
-signal positions near joint ROM limits
what conveys different aspects of somatosensory information to the brain
a variety of neural pathways
which pathways convey tactile information (sense of touch)
spinal cord pathways
-dorsal columns
**gracile nucleus + tract is medial/lateral
medial
**gracile nucleus + tract conveys what information
information about lower body (lower limbs)
**cuneate nucleus + tract is medial/lateral
lateral
**cuneate nucleus + tract conveys what information
information about upper body (neck, trunk, upper limbs)
main ascending touch pathway (lower extremity)
(ipsilateral until crossover)
lower extremity ->
dorsal root ganglion (DRG) ->
gracile nucleus ->
CROSSOVER ->
ventral posterior lateral nucleus (VPL) ->
S1
main ascending touch pathway (upper extremity)
(ipsilateral until crossover)
upper extremity ->
dorsal root ganglion (DRG) ->
cuneate nucleus ->
CROSSOVER ->
ventral posterior lateral nucleus (VPL) ->
S1
how does upper extremity differ from lower extremity main ascending touch pathway
-upper is the same process but more laterally (lower more medial)
-upper will synapse with cuneate nucleus of brainstem
main ascending touch pathway (face)
(ipsilateral until crossover)
face ->
trigeminal nucleus ->
principal nucleus ->
CROSSOVER ->
ventral posterior lateral nucleus (VPL) ->
S1
**trigeminal nerve (V)
tactile information from the head + face
what nerve provides somatosensation of the face
trigeminal nerve (V)
trigeminal nerve enters brainstem + sends information to ____
trigeminal brainstem complex
**principle nucleus
site where most afferents carrying information from cutaneous LTMRs terminate
central pathways conveying proprioceptive information (2)
-lower body
-upper body
**lower body central pathway to convey proprioceptive information
proprioceptive afferents ascend via clarke’s nucleus ->
dorsal spinocerebellar tract ->
ipsilateral cerebellum
**upper body central pathway to convey proprioceptive information
proprioceptive afferents ascend via dorsal column nuclei (external cuneate nucleus) ->
ipsilateral cerebellum
thalamic neurons (2)
-VPM
-VPL
**VPM
transmits somatosensory information carried by the trigeminal system from the face
**VPL
transmits somatosensory information by the rest of the body
**how is the primary somatosensory cortex mapped
somatotopically
-homunculus reveals that the sensitivity of a body part is proportional to the AMOUNT of somatosensory cortex receiving input from that body part
-for both sensation + motor control
how is homonculus scaled
size represents how mcuh area is dedicated to each region
primary somatosensory cortex
-S1 neurons respond to a variety of tactile features, such as texture, orientation, velocity, direction, speed
-must know where a limb is in space + that type of sensory information to be able to move it
how do corticocortical connections process somatosensory information
establish a functional hierarchy for processing of somatosensory information
what pathways are beyond S1 (primary somatosensory cortex)
-corticocortical pathway
-descending pathway
what does S1 do in parietal areas
projects to parietal areas where information derived from proprioceptive afferents signaling the current state of muscle contraction gains access to circuits that initiate voluntary movements
what are corticocortical + descending pathways critical for
integration of sensory + motor information
there are more ascending/descending projections
far more descending
-we have no idea why
central representations of the body are ____ + ____
-plastic
-modified by experience
plasiticity
our brain is adaptable + can change based on experiences
plasticity in the adult cerebral cortex
somatosensory cortex representations of each body part changes in response to experiences of the person
example of plasticity in the adult cerebral cortex
the amount of cortex represented by the 3rd finger will be invaded by adjacent cortical areas, such as that innervated by the 2nd + 4th fingers, if the 3rd is lost (amputated)
-monkey example
___ leads to greater cortical reprsentation of that body part
increased used of a body part (ex: finger,hand, etc)
