Ascending sensory system Flashcards
Receptor types in hairy skin (2 Types)
- Nerve ending (NT)
- Merkel Cell (M) in the basal layer
*Receptor endings wrap around hair.
Receptor types in glabrous (Hairless) skin (4 types)
- Meissner corpuscles (M)
- Merkel cell (Me)
- Pacinian corpuscle (PC)
- Ruffini ending (R)
Describe location and function of Meissner corpuscles…
- Discriminative touch (two pt discrimination)
- concentrated in finger tips
- A-beta fiber (fast conducting)
Describe location and function of Merkel Nerve Endings…
- Discriminative touch (two pt discrimination)
- Fine touch detail (texture, edges)
- A-beta fiber (fasting conducting)
Describe location and function of Pacinian Corpuscles…
- Detection of vibration
- Concentrated in fingers and in palm.
- A-beta fiber (fast acting)
Describe function of Free nerve endings…
- sensation of pain, crude touch and temperature.
* Can be myelinated or unmyelinated.
Describe two phases of pain….
- sharp prick (aka fast pain or delta pain) short duration and carried out by myelinated fibers.
- slow pain, poorly localized, aching pain, (carried out by unmyelinated fibers)
Three types of fibers in the ascending and descending pathways….
- Long, ascending fibers going to thalamus, cerebellum or various brainstem nuclei.
- Long descending fibers going from cerebral cortex or various brainstem nuclei to spinal gray matter.
- Short, propriospinal fibers interconnecting different spinal cord levels. (help coordinate flexer reflexes)
Ascending tracts are found in __ _____ _______.
All three funiculi (AF, LF & PF)
Descending tracts primarily located in ______ & ______ _______.
Anterior & Lateral funiculi
_________ fibers surround the spinal cord gray matter.
Propriospinal fibers
Functions of the Posterior Column/Medial leminiscus system are…
- Conveys touch and limb position.
- Posterior columns = mostly ascending large myelinated primary afferent from various mechanoreceptors.
- Main way info from cutaneous, joint and muscle receptors reaches cortex.
As DRG rootlets enter cord fibers divide into two divisions….
- Medial – heavily myelinated, large diameter fibers; enter posterior column and ascend to brainstem
- Lateral – finely myelinated and unmyelinated, small diameter fibers
Functions of the spinothalmic tract/Anterolateral pathway is…
- One of multiple pathways that convey pain and temperature info
- Involved in awareness and localization of painful stimuli
- Ultimately ends in VPL of thalamus and some nearby thalamic nuclei
- Other pain pathways end in reticular formation or limbic system to mediate other pain responses, these tracts and the spinothalamic tract together are known as the anterolateral pathway (in anterior half of lateral funiculus.
What is Cordotomy?
- Destroy spinothalamic tract to produce contralateral analgesia in patients with intractable pain
- Cut lateral funiculus from dentate ligament to ventral root rostral to highest dermatomal pain level
- Analgesia lasts several months