Lecture 03 Tactile and Proprioceptive Pathways Flashcards
What is active touch?
2pt tactile discrimination; sterognosis(awareness of shape, size and texture); proprioception, vibratory sensations and weight perception
Conveyed via posterior column/medial lemniscal system
What does the Ventral spinothalamic pathway convey?
light (passive) touch, crude tactile sensations and pressure
Describe the primary neurons and their axons in the crude tactile pathway
Course through medial division of dorsal root
Enter posterior funiculus of spinal cord
Bifurcate and ascend 6-10 cord segments or descend
Terminate on 2dary neurons in ipsilateral nucleus proprius and intermediate gray
What do the collaterals of the primary axons in the crude tactile pathway often participate in?
intersegmental spinal reflexes
What are the receptors for the crude tactile pathway?
free nerve endings
peritrichial nerve endings
and merkel’s tactile disks
Where are the secondary neurons in the crude tactile pathway?
in nucleus proprius
Where do the secondary axons in the crude tactile pathway course?
cross in the anterior white commissure
decusate
and ascend to form ventral spinothalamic tract (VSTT)
What forms the spinal lemniscus?
In the medulla the VSTT joins with the LSTT and the spinotectal fibers to form the spinal lemniscus
Where does the spinal lemniscus terminate?
on tertiary neurons in the VPL (ventral posterior lateral) nucleus of the dorsal thalamus
Where do tertiary axons from the VPL nucleus project to?
through the posterior limb of the internal capsule and corona radiata to the primary somesthetic cortex
Whaat does unilateral lesions of the VSTT result in?
may be difficult to lose crude touch sensations, bc fibers ascend in both the posterior and anterolateral funiculi
Separation of info provides the system w a degree of bilaterality
Deficits may be masked if posterior column/medial lemniscal system is intact
What does unilateral lesion of the spinal lemniscus result in?
contralateral hemianalgesia and thermal hemianesthesia
Loss of passive touch may be masked by intact posterior column/medial lemniscal system
The sensory neurons from the upper extremity will form and ascend in what part of the spinal cord?
Fasiculus cuneatus
Sensory information from the lower extremity will form and ascend in what part of the spinal cord?
fasiculus gracilis
In the medulla, the primary axons in fasiculus cuneatus and fasiculus gracilis will terminate in what?
the corresponding nucleus gracilis and nucleus cuneatus
some of the collaterals from the fasciculi gracilis and cuneatus are part of what reflex?
the myotatic reflex circuit when the fibers synapse directly upon alpha motor neurons
What does the fasiculus gracilis convey?
proprioception, 2-pt tactile discrimination and vibratory sensation from the lowerr extremities and the body
(below T6)
What does the fasiculus cuneatus convey?
Proprioception, 2-pt tactile discrimination and vibratory sensations from the upper extremities and body (down to T7)
What do the secondary axons from the nucleus gracilis and cuneatus become ?
in the medulla they decussate as internal arcuate fibers and form the contralateral medial lemniscus
What does the dorsal spinocerebellar tract convey?
precise coordination, postural adjustments and precise movements of individual mm of the lower limbs and body
What does the ventral spinocerebellar tract convey?
gross postural adjustments and overall proprioception of the lower limb
What does the cuneocerebellar tract convey?
direct arcuate fibers convey fine coordination, postural adjustments and precise movements of individual mm of the upper limbs and body
What does the rostral spinocerebellar tract convey?
gross postural and limb proprioception from the upper limbs
What are the neurological tests for tactile and proprioceptive pathways?
testing positions sense: bend finger
Testing vibratory sense: activated tuning fork on joint
Testing stereognosis and 2 pt: distinguish two blunt tips of paper clip as being separate on hand
What results from complete unilateral lesions of the posterior columns?
ipsilateral loss of proprioception, 2-pt tactile discrimination and vibratory sensations below the level of the lesion
What does a lesion of the fasiculus gracilis result in?
ipsilateral loss of proprioception, 2 pt tactile discrimination and vibratory sensations from the lower half of the body
What do lesions of the fasiculus cuneatus result in?
ipsilateral loss of proprioception, 2 pt tactile discrimination and vibratory sensations from upper half of the body s
What does unilateral lesions of the medial lemniscus result in?
loss of proprioception and 2 pt tactile discrimination and vibratory sensations on the opposite side of the body and limbs
What is tabes dorsalis?
meningovascular inflammation of the blood vessels as they pierce through the pia at the junction of the dorsal rootlets and the posterior columns
What are most frequently affected by tabes dorsalis?
lumbosacral nn and spinal cord segments
When does tabes dorsalis occur?
during the tertiary (late) stage of syphilis and results in bilateral ischemic necrosis of the posterior columns
What does tabes dorsalis result in?
bilateral ischemic necrosis of the posterior columns and the dorsal roots at this lvl
What are the signs of tabes dorsalis?
pts complaint: lightning pains or rheumatic pains from the lower limbs for the last several years
atonic bladder and painless retention of urine
Locomotor ataxia: slapping feet
Positive romberg test
Argyll-Roberston pupils
Swollen distorted joints
What is locomotor ataxia?
broad-based gait with slapping feet bc of loss of proprioception information from lower extremities, both for reflexes and ascending conscious and unconscious pathways, causes this gait
Vibratory sensations: pt stops feet to obtain tactile cues
What is the Romberg test?
standing with feet together and arms extended in front. Pt will fall when eyes are closed: suggestive of posterior columns and/or cerebellum issues
What is passive touch?
sensory modalities such as roughness, texture, form and localization
conveyed via ventral spinothalamic pathway
Crude tactile
