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
Damage of Anterolateral pathway causes loss of what?
- Pain and temperature
- Itch and tickle sensations
- Bowel & bladder pressure, sexual sensation ascend bilaterally so injury does not leave a deficit.
Function of Posterior spinocerebellar tract (PSCT)…
- Conveys proprioceptive info
- Ipsilateral leg proprioception
Clarke’s nucleus and PSCT does not exist _____ to about ______.
Caudal to about L2.
What is the function of the Anterior spinocerebellar tract?
- conveys more complex info to the cerebellum.
- primarily concerned with leg but differs from PSCT..
*Note crosses midline twice so ultimately fibers end ipsilateral to their source.
Where is the origin of the Anterior spinocerebellar tract?
- lateral surface of anterior horn at lumbar levels.
where is the origin of Cuneocerebellar tract?
Lateral cuneate nucleus in medulla.
Where is origin of PSCT?
Clarkes Nucleus (T1-L2/3)
PSCT uses what peduncle to enter cerebellum?
Inferior
ASCT uses what peduncle to enter the cerebellum?
Superior
CCT uses what peduncle to enter the cerebellum?
Inferior
What are Somatosensory receptors, and what do they do?
- Detect mechanical, chemical or thermal changes.
- All are pseudo unipolar neurons with:
- cell body in DRG or cranial nerve ganglion
- A central CNS process (Spinal Cord or Brainstem)
- Peripheral process with an ending in skin, muscle or a joint.
Skin is richly innervated with cutaneous receptors which are divided into 2 types…what are they?
Encapsulated and Non-encapsulated receptors
Pacinian corpuscles (Encapusulated? Adaptation? Modality?)
- Encapsulated
- rapid adaptation
- Modality = vibration
Meissner corupuscles (Encapsulated? Adaptation? Modality?)
- Encapsulated
- Rapid adaptation
- Modality = Touch
Ruffini ending receptors (Encapsulated? Adaptation? Modality?)
- Encapsulated
- slow adaptation
- Modality = pressure
Receptor Endings around hairs (Encapsulated? Adaptation? Modality?)
- Non-encapsulated
- Rapid adapting
- modality = touch
Merkel endings (Encapsulated? Adaptation? Modality?)
- Non-encapsulated
- slow adaptation
- modality = touch
Free nerve endings (Encapsulated? Adaptation? Modality?)
- Non-encapsualted
- Adaptation varies
- Modality = pain, touch, temperature, itch
In the Medial lemniscus system spinal afferents have their cell bodies in ________ DRG’s.
Ipsilateral
In the Medial lemniscus system DRG rootlets enter cord fibers and divide into what two divisions?
- Medial = heavily myelinated, large diameter fibers; enter posterior column and ascend to brainstem.
- Lateral = finely myelinated and unmyelinated small diameter fibers.
What would happen if the Posterior column-Medial lemniscus system were injured?
- Injury leads to impaired proprioception and discriminative tactile functions, especially complex tactile discrimination.
- If posterior columns are injured, large deficit at first but some recovery is possible.
The Anterolateral pathway follows _______ organization.
Somatotopic orgainzation = caudal body parts in posterolateral portion & rostral parts in anteromedial portion.
