Sensory Tracts Flashcards
(15 cards)
In the bodies ascending sensory system, there are usually 3 neruonal chains that complete it.
- Receptor (lots of overlap)
- Modality (lots of overlap)
- Location (1st, 2nd 3rd order neurons)
Describe where the neurons are located.
1st: dorsal root ganglion
2nd: in CNS and crosses midline
3rd: cell body in thalamus projecting to cortex
The somatosensory system is split in a conscious and unconscious system. The conscious system is comprised of touch, pressure, vibration, proprioception modalities within the dorsal column. (more discriminative system). Describe both in terms of their location.
CONSCIOUS
-spinothalamic (pain, temp, crude touch)
UNCONSCIOUS
-spinocerebellum (unconcious proprioception)
The dorsal column medial lemniscal system coneys information with a high degree of spatial and temporal resolution. How?
High density of receptors and small receptor fields.
There are 5 modalities in the dorsal column medial lemniscal system (DCMLS):
- tactile discrimination
- vibration
- deep touch (pressure)
- 2 point discrimination
- conscious proprioception (position sense)
What type of receptors allow this (4)?
- hair follicle receptors
- Pacinian corpuscles
- Meissner’s corpuscles
- GTO, joint receptors, muscle spindles
The DCMLS consists of a 3 neuronal chain. In the 1st order neuron in the peripheral process and the cell bodies are located in the dorsal root ganglion. What pathway does it take through the central process?
DRG > fasciculus cuneatus (no synapse in SC)
- fibers from lower trunk and LE ascend via fasciculus gracilis
- fibers from upper trunk and UE ascend via fasciculus cuneatus
In the 2nd order neuron (DCMLS), the cell body is located in the ___ (upper trunk and UE) and the ___ (lower trunk and LE). Where do they synapse and cross?
cuneatus, gracilis.
Synapse and cross in the caudal medulla; ascend in brainstem via medial lemniscus.
The 3rd order neuron (DCMLS) are destined for the somatosensory cortex in the postcentral gyrus area 3,1,2. Where do the cell bodies synapse?
The ventral posterior lateral (VPL) nucleus of the thalamus.
The DCMLS is the only one in the body that carries vibration and conscious proprioception. In that regard, what is (sensory) ataxia?
- The inability to recognize objects in hand or letters drawn down back.
- look at feet during gait
- feet wide apart, look drunk
Happens when there is damage to the posterior spinal arteries which damages dorsal columns.
In the spinothalamic system, pain, temperature and nondiscriminative touch are the modalities. What receptors (more simple) enable this?
- free nerve endings (pain)
- mechanoreceptors, thermoreceptors and chemoreceptors
- other receptor types conveying nociception
In the spinothalamic system, the cell bodies of the 1st order neuron are also in the DRG and is a peripheral process. Through what tract do they ascend the spinal cord?
Lissauer’s tract - 2 to 3 segments.
-useful in recruiting certain reflexes
The 2nd order neuron occurs when there is a crossover, using A delta fibers (where pain) to travel upwards through lamina ___ and ____, into the anterior grey matter. In the intermediate grey or dorsal horn, C fibers are used. What type of pain is this?
I and V.
Slow pain - what are you going to do about it.
The 3rd order neuron’s cell bodies are located in the VPL nucleus for fast pain and the intralaminar nucleous for slow pain. What is the destination of the spinothalamic track?
Cortex somatosensory cortex (postcentral gyrus, area 3,1,2).
Lesions to the spinothalamic tract cause contralateral losses of pain and temperature sensation (also itch and tickle carried on pain system). Does the same happen with a lesion of the cerebellum?
No, these are ipsilateral deficits. It doesn’t cross the spinal tract.
Thalamic pain syndrome is chronic pain caused by dysfunction of the thalamus. What causes it?
CVA affecting the posterior cerebral artery.
Unconscious proprioception in the cerebellum is moderated by GTOs, muscle spindles and joint mechanorecptors by 1st order neurons in the DRG and 2nd order neurons in the dorsal horn. What specific tracts does it take?
- Dorsal (Posterior) Spinocerebellar Tract
- Ventral (Anterior) Spinocerebellar Tract
- Cuneocerebellar Tract
