CH 7: Proprioception, Touch & Tactile Discrimination Flashcards
tactile sensations are complex because they involve both ___ and ___?
tactile stimuli can also be ____ or ____?
a blending of light cutaneous contact (touch)
variable degrees of pressure depending on the intensity of the stimuli
can also be static or dynamic
tactile sensations are complex because they involve both ___ and ___?
tactile stimuli can also be ____ or ____?
a blending of light cutaneous contact (touch)
variable degrees of pressure depending on the intensity of the stimuli
can also be static or dynamic
tactile sensation is divided into ___ and ____?
light touch
tactile discrimination
light touch involves?
detection of contact with the skin
tactile discrimination involves?
perception of the size and shape of objects
tickling and itching sensations are related to ___?
related to pain and not to tactile sense
what are Von Frey hairs?
fine hairs of graduated stiffness used to apply stimuli at calibrated intensities to the skin
what are 4 methods used to test tactile discrimination?
1- stereognosis
2-two point discrimination
3- complex tactile discrimination
4- flutter-vibration
what is stereognosis?
eyes closed
identify common small objects placed in one hand
what is two point discrimination?
determine whether one touch stimulus or two simultaneous stimuli have been applied to the skin
what is complex tactile discrimination?
ask subject to identify numbers or letters written on the surface of the skin with a blunt object
what is flutter-vibration?
an important component of tactile sensation
flutter- is a feeling of repetitive movement
vibration– is a more diffuse and penetrating feeling of “humming” when the base of a vibrating fork contacts a bony prominence of the body
proprioceptive sensation includes both:
static limb position
kinesthesia- the sense of movement
what are the 2 different sets of sensory pathways in the SC that provide essential information to the brain about muscle action, joint position and the objects with which a person is in contact?
1: Pathways that project to the cerebellum
2: Pathways that project to the cerebral cortex
** both use mechanoreceptors
what 3 pathways project to the cerebral cortex by way of the thalamus?
- spinal lemniscus
- spinothalamic tract
- lateral cervical system
information carried by these pathways is perceived consciously
what 3 pathways project to the cerebral cortex by way of the thalamus?
- spinal lemniscus
- spinothalamic tract
- lateral cervical system
information carried by these pathways is perceived consciously
tactile sensation is divided into ___ and ____?
light touch
tactile discrimination
light touch involves?
detection of contact with the skin
tactile discrimination involves?
perception of the size and shape of objects
tickling and itching sensations are related to ___?
related to pain and not to tactile sense
what are Von Frey hairs?
fine hairs of graduated stiffness used to apply stimuli at calibrated intensities to the skin
what are 4 methods used to test tactile discrimination?
1- stereognosis
2-two point discrimination
3- complex tactile discrimination
4- flutter-vibration
mechanoreceptors are mostly innervated by:
large diameter myelinated fibers, with the exception of free nerve endings
the cell bodies of these peripheral nerve fibers are in the dorsal root ganglia and their central processes enter the medial side of the dorsal root zone
what is two point discrimination?
determine whether one touch stimulus or two simultaneous stimuli have been applied to the skin
what is complex tactile discrimination?
ask subject to identify numbers or letters written on the surface of the skin with a blunt object
what is flutter-vibration?
an important component of tactile sensation
flutter- is a feeling of repetitive movement
vibration– is a more diffuse and penetrating feeling of “humming” when the base of a vibrating fork contacts a bony prominence of the body
proprioceptive sensation includes both:
static limb position
kinesthesia- the sense of movement
what is the Ventral spinocerebellar tract?
the most peripheral tract in the ventral margin of the lateral funiculus
crosses (contralateral)
L1-S5 and ascends throughout the SC
terminates in the cerebellum (unconscious coordination of motor movements
Function: Ib, FRA from WRF
unconscious proprioception
what 4 pathways project to the cerebellum?
- dorsal spinocerebellar
- ventral spinocerebellar
- cuneocerebellar
- rostral spinocerebellar tract
uses the information for the coordination of movement but not for conscious perception
what 3 pathways project to the cerebral cortex by way of the thalamus?
- spinal lemniscus
- spinothalamic tract
- lateral cervical system
information carried by these pathways is perceived consciously
mechanoreceptors in the muscles, joints and skin mediate the various separate and integrated sensations of ____, ___ and _____
proprioception
touch
tactile discrimination
what is the dorsal spinocerebellar tract?
located just posterior to the ventral spinocerebellar tract in the lateral funiculus
origin- Laminae 7
T1-L2/3 and ascends throughout the SC
uncrossed (ipsilateral)
terminates at the cerebellum
function: Ia, Ib and II unconscious proprioception
muscle spindle afferents chiefly provide information about __?
static limb position
joint receptor afferents and receptors in the skin, muscles and joints provides information about ____?
kinesthetic sensation (joint movement)
what are pacinian corpuscles?
found in the skin and CT surrounding bones and joints
detect vibration
what are Meissner’s corpuscles?
mediates superficial phasic touch sensation
free nerve endings detect ..?
the movement of hairs in hair follicles- conveys a sense of touch
mechnoreceptors are mostly innervated by:
large diameter myelinated fibers, with the exception of free nerve endings
the cell bodies of these peripheral nerve fibers are in the dorsal root ganglia and their central processes enter the medial side of the dorsal root zone
after entering the SC, afferent fibers from mechanoreceptors distribute to what 3 different sites?
1- interneurons and motoneurons in the ventral horn of the SC
2- neurons in the dorsal and intermediate gray areas of the SC that are the origin of the ascending pathways
3- neurons of the dorsal column nuclei in the medulla
what is the rostral spinocerebellar tract?
the UE equivalent of the ventral spinocerebellar tract
originates: in the cervical enlargement (C4-8) from cells of the intermediate zone (laminae 7) of the SC gray area.
axons of these cels project to the cerebellum and terminate with fibers of the ventral spinocerebellar tract
function: Ib, FRA from WRF, unconscious proprioception, movement and posture
mediates info chiefly from GTOs and from pressure and pain receptors
GTO afferents (Aalpha Ib fibers) synapse on:
interneurons that inhibit motoneurons innervating the muscle in which the tendon organ is located. they also make excitatory polysynaptic connections with motoneurons of antagonist muscles
what are the 2 pathways that carry proprioceptive and other somatosensory stimuli from the lower limbs to the cerebellum?
ventral and dorsal spinocerebellar tracts
(some proprioceptive fiber collaterals, especially from GTOs, as well as fibers conveying other sensory modalities such as pressure and pain, synapse with neurons in the intermediate gray area and the base of the posterior horn of the SC)
what is the Ventral spinocerebellar tract?
the most peripheral tract in the ventral margin of the lateral funiculus
the nucleus dorsalis, or Clarke’s nucleus, is located at ?
the base of the posterior horn in spinal segments T1-L2
the cerebellar tracts are also concerned with.. ?
processes that govern standing and walking
axons of the neurons in the nucleus dorsalis ascend rostrally on the …?
ipsilateral side in the dorsal spinocerebellar tract
what is the dorsal spinocerebellar tract?
located just posterior to the ventral spinocerebellar tract in the lateral funiculus
origin- Laminae 7
T1-L2/3 and ascends throughout the SC
uncrossed (ipsilateral)
terminates at the cerebellum
function: Ia, Ib and II unconscious proprioception
proprioceptive afferents from dorsal roots T1-L2 synapse in the nucleus dorsal is at the level where they enter the SC. Corresponding afferents from dorsal roots L3-S5 ascend in the ______?
facsciculas gracilis of the dorsal funiculus until they can reach and synapse with the nucleus dorsalis at L2
the dorsal spinocerebellar tract, as a fascicle of fibers on the surface of the lateral funiculus begins at?
L2 segment of the SC
what are the 2 pathways that carry proprioception and other somatosensory information to the upper limbs?
1- cuneocerebellar tract
2-rostral spinocerebellar tract
afferent fibers from C2-T5 travel up the dorsal funiculus in the _____ to synapse on neurons in the ______?
fasciculus cuneatus
to synapse on neurons in the accessory (or lateral) cuneate nucleus (ACN) in the lower medulla
what is the ACN?
accessory cuneate nucleus
in the lower medulla
the upper-extremity counterpart of the nucleus dorsalis and gives rise to the ipsilateral cuneocerebellar tract
what does the cuneocerebellar tract mediate?
information chiefly from muscle spindles, cutaneous touch receptors and joint receptors
what is the cuneocerebellar tract?
originates from the ACN in the lower medulla
uncrossed/ ipsilateral
terminates at the cerebellum
function: Ia, Ib, II unconscious proprioception
what is the rostral spinocerebellar tract?
the UE equivalent of the ventral spinocerebellar tract
originates: in the cervical enlargement (C4-8) from cells of the intermediate zone (laminae 7) of the SC gray area.
axons of these cels project to the cerebellum and terminate with fibers of the ventral spinocerebellar tract
function: Ib, FRA from WRF, unconscious proprioception, movement and posture
mediates info chiefly from GTOs and from pressure and pain receptors
the ascending fibers of the dorsal spinocerebellar, cuneocerebellar, and rostral spinocerebellar pathways enter the cerebellum through the ___?
inferior cerebellar peduncle
ascending fibers of the ventral spinocerebellar tract continue through the ___?
pons and ascend into the cerebellum through the superior cerebellar peduncle
all 4 of the cerebellar tracts terminate primarily in the __?
midline (vermis and intermediate zone) portions of the cerebellum ipsilateral to the cells of origin of the tracts
the cerebellar tracts project especially heavily to the ___?
anterior lobe but also to the caudal part of the posterior lobe
the cerebellar tracts are also concerned with.. ?
processes that govern standing and walking
what are the 3 pathways to the cerebral cortex?
1- spinal lemniscal system
2- spinothalamic tract
3-lateral cervical system (spinocervicothalamic pathway)
what does the spinal lemniscal system to?
carries proprioceptive information from the receptors for position sense, kinesthesia and tactile discrimination to the cerebral cortex
what does the spinothalamic tract do?
from the anterolateral system
subserves light touch sensation and pain and temperature
what does the lateral cervical system do?
spinocervicothalamic pathway
mediates tactile, vibratory and proprioceptive sensation
afferent fibers from ___, _____ and ____ provide inputs to the spinal lemniscal system?
these inputs contribute to ___?
muscle spindles
GTOs
mechanoreceptors in joints and skin
contribute to conscious position and movement sense
other fibers in this system convey information about touch, pressure, and flutter-vibration
other fibers of the spinal lemniscal system that are responsible for information about touch, pressure and flutter vibration are…?
dorsal root afferents that ascend in the posterior funiculi without synapsing in the SC and end in relay nuclei in the lower part of the medulla
other fibers in this system are axons of dorsal horn cells that receive synapses from mechanoreceptor afferents
the posterior funiculus consists of two large bundles of fibers called ____ ?
fasciculi
what forms the fasciculus gracilis?
fibers from the leg ascend adjacent to the dorsal median septum and form the fasculus gracilis
what forms the fasciculus cuneatus?
fibers from the arm ascend lateral to the leg fibers and constitute the fasciculus cuneatus
the fibers in the posterior funiculus maintain a ____ organization?
somatotopic (body map)
fibers from the foot enter the spinal lemniscal system in the lower segments of the SC, followed in ascending order by thosefrom the leg, thigh, trunk, hand, arm, and neck
the fasciculus gracilis and the fasciculus cuneatus ascend to the ______, where they end in the ____ and _______
ascend to the lower medulla
end in the nucleus gracilis and nucleus cuneatus respectively
clinicians refer to the FG and FC tracts as the ___ and the nuclei as the _____?
dorsal column pathways
dorsal column nuclei
the dorsolateral pathway consists of :
the spinal lemniscal system
additional fibers of the spinal lemniscal system that travel within the dorsal part of the lateral funiculus and accompany the lateral cervical system
“dorsolateral pathway” = the entire lemniscal pathway in the SC
the cells of the dorsal column nuclei give rise to the ____ which promptly cross to the opposite side of the medulla in the ______?
they then ascend as the _______ to the thalamus and terminate in the _______?
internal arcuate fibers
decussation of the medial lemniscus
medial lemniscus
terminate in the ventral posterolateral nucleus (VPL)
the internal arcuate fibers of the spinal lemniscal system maintain a somatotopic organization in both the ____ and _____
medial lemniscus
VPL
in the medulla, medial lemniscus fibers from the nucleus gracilis convey information from the ___and lie ___?
in the pons and midbrain, these gracile fibers lie ____
leg
lie ventral to fibers from the nucleus cuneatus in the medulla
lie lateral to cuneate fibers in the pons and midbrain
the band of cerebral cortex in the postcentral gyrus of the parietal lobe that receives thalamocortical fibers from the VPL is the ___?
primary somatosensory cortex (where topographic representation of the body areas is imilar to that of the motor strip that lies parallel to it on the opposite side of the central sulcus)
the primary somatosensory area includes Brodmann’s areas __?
3, 1, and 2
the spinal lemniscal system mediates the senses of __, ____, ___, and ____
sense of limb position and movement (including the sense of steady joint angles)
sense of motion produced by active muscular contraction (kinesthesis) or passive movement
sense of tension exerted by contracting muscles
sense of effort
the conscious recognition of body and limb posture requires __?
cortical participation
in addition, the lemniscal pathway provides information about ___, ___, and ______ of neural activity evoked by mechanical stimulation of skin, particularly moving stimuli on the skin
thus this pathway to the cerebral cortex is necessary for ___?
place
intensity
temporal and spatial patterns
discriminative tactile sensation
also important in recognition of flutter-vibration
almost all neurons of the lateral cervical system respond to light mechanical stimulation of the skin on the ____
ipsilateral side of the body
*a few are activated by noxious stimuli
peripheral nerve fibers entering the lateral cervical system enter by:
making synaptic connections in the dorsal horn (primarily in lamina IV) throughout the length of the SC
heavily myelinated axons from the second order neurons arise in this lamina and ascend ipsilaterally in the most dorsal corner of the lateral funiculus to terminate in the lateral cervical nucleus (located just lateral to the dorsal horn of the first 3 cervical segments)
projections from the lateral cervical nucleus cross the spinal cord in the ventral white commissure to joint the __
contralateral medial lemniscus and proceed with it to terminate in the thalamus.
projects from the thalamus reacch the somatic sensory areas of the cerebral cortex
the fibers of the entire lateral cervical system conduct ..?
very rapidly
in the various relay nuclei of the pathways mediating tactile discrimination, each neuron receives synaptic input from many afferent fibers, and each afferent fiber ends on many relay cells. Thus, the relay cells receive sensory information that undergoes both ____ and ____
convergence and divergence
in addition, afferent fibers reaching relay nuclei activate not only relay cells but also excitatory and inhibitory interneurons.
Consequently, the sensory pathways both transmit information and modulate and transform the information as it moves along to higher levels of the NS
in the somatic sensory system, synaptic inhibition occurs:
not in the peripheral receptor but in the first synaptic site in the dorsal horn or dorsal column nuclei and in subsequent synaptic sites along the pathway
what are the 2 types of inhibitory processes?
1- local feedback inhibition
2-distal feedback inhibition
local feedback inhibition involves:
“lateral inhibition”
involves the inhibition of dorsal horn and dorsal column relay cells that surround the relay cells activated by incoming sensory volleys
this inhibition is mediated by collaterals of the activated cells synapsing on inhibitory interneurons in the relay nucleus
limits the extent of excitation among adjacent neurons and thereby functionally decreases the divergence of excitation and sharpens the localization of signals
distal feedback inhibition consists of:
“presynaptic inhibition”
the inhibition of presynaptic activity in the terminals of dorsal root ganglion cells in dorsal horn and dorsal column nuclei.
this inhibition comes from the axons of neurons in the motor and somatosensory areas of the cerebral cortex and in the brain stem
allows higher levels of the NS to regulate the information that moves upward
the receptive field of each neuron is:
the area on the body surface that, when stimulated, either excites or inhibits that neuron
neurons in each of the nuclei along the lemniscal pathway, including the dorsal column nuclei, the VPL and the somatosensory area of the cerebral cortex, have specific receptive fields
the size of the receptive fields of individual neurons varies considerably
the tips of the fingers, the lips and the tongue are the regions of the body that are most sensitive to touch bc they contain the highest density of sensory nerve endings per unit area. this increased density of afferent fibers serving a given region transmits information to larger numbers of relay cells with smaller receptive fields than the parts of the system serving less sensitive areas of the body (arm, back). the more sensitive regions therefore also have the larges areas of representation in the postcentral gyrus
what is inhibitory surround?
stimulation of skin within the receptive field of a neuron usually excites the neuron, and stimulation of skin surrounding the excitatory area usually inhibits the neuron
the result of this arrangement is max firing of a neuron in response to a stimulus limited to the area of its receptive field. if the stimulus impinges equally on the receptive field and the inhibitory surround, the neuron will show little or no response
what type of skin sensibility is the least likely to be impaired by SC lesions?
simple touch
thus, a lesion of the dorsal columns usually abolishes ipsilateral tactile discrimination of the direction of movement of a cutaneous stimulus, but recognition of light touch decreases only slightly or not at all bc the spinothalamic tract also transmits light touch sense.
conversely, after transection of the spinothalamic tract, pain perception is lost on the opposite side of the body, but light otuch generally persists bc the dorsolateral pathways can also mediate this function
complete loss of proprioceptive sensation from a spinal lesion requires :
bilateral interruption of the dorsolateral pathway (both dorsal columns and the lateral cervical system in the dorsal part of the lateral columns)
lesions in this location cause deficits in position sense, vibration sense, and tactile discrimination
the symptoms occur prominently on the same side of the body after unilateral injury of a dorsolateral pathway
lesions of the lemniscal pathway leaved preserved the :
sensation of pain, temperature and simple touch
interruption of the dorsal columns without injury to the lateral columns results in:
loss of tactile discrimination of the direction of a moving stimulus on the skin, but appreciation of touch and joint position sense remains intact
clinical signs of injury to the lemniscal (dorsolateral) pathways include:
these are frequently tested in neurologic examination
1- inability to recognize limb position 2- astereognosis-(keys) 3-loss of 2 point discrimination 4-loss of vibratory sense 5- + Romberg sign (pts with dorsolateral pathway lesions may be able to maintain balance with eyes opened but lose balance with eyes closed)
