ANAT 610 - Touch & Pain Pathways

touch

__ also includes pressure, vibration, kinesthesia, and proprioception.

2-point discrimination

___ measure of the resolution of touch pathway.

temperature

___ information travels in the same pathway as pain

nonconscious somatosensation

___ information is carried via the spinocerebellar tract

• DO NOT DECUSSATE aka info stays ipsilateral

ateral spinothalamic tract

conscious BODY pain and temperature information travels via the ___

dorsal column system

conscious BODY fine touch information travels through the ___

trigeminal system

conscious HEAD somatosensation information travels via the ___

modality

quality of stimulus, or type of sensation

proprioception

sense of static and dynamic position of limbs and body

kinesthesia

sense of limb and body movement

stereognosis

ability to recognize objects based on touch alone

receptive fields

location of stimulus is picked up based on the ____ size and overlap and samatotopic map

intensity

The __ of stimulus is picked up via the frequency of Ap firing in the first order axon

• higher firing frequency = higher ___ stimulus

rapidly adapting

some end organs are ___ meaning that they are good at detecting CHANGES in the stimulus

• aka you get used to the stimulus and can mentally ignore it

slowly adapting

some end organs are ___ meaning that they are good at detecting the DURATION of the stimulus

transduction

Main function of end organs is ___ aka conversion of mechanical energy into electrical energy in order to signal modality, location, intensity and time course

Meissner’s corpuscle

• RAPIDLY adapting

• small & superficial aka smaller receptive fields and thus higher resolution

• detects fluttering and stroking

Pacinian corpuscle

• RAPIDLY adapting

• large and deep aka bigger receptive fields and thus lower resolution

• detects vibrations

merkel’s disk

• SLOWLY adapting

• small & superficial aka smaller receptive fields and thus higher resolution

• detects pressure and texture

• used for fine discrimination touch especially in fingertips

Ruffini endings

• SLOWLY adapting

• large & deep aka larger receptive fields and thus lower resolution

• detects skin stretch

1st order axons types

• Alpha fibers

• Beta fibers

• Delta fibers

• C fibers

alpha fibers

• group I

• biggest diameter

• heaviest myelination

• fastest conduction speed

• conscious & nonconscious proprioception

beta fibers

• group II

• medium diameter

• heavy myelination

• fast conduction speed

• touch, pressure, vibration

delta fibers

• group III

• small diameter

• thin myelination

• low conduction speed

• fast pain, temperature, touch

C fibers

• NO myelination aka free nerve ending

• very small diameter, thinnest afferent fibers

• slowest conduction speed

• nociception-thermal information

dorsal column pathway

Pathway carrying BODY fine discrimination touch information

• 1st order cell body in DRG & connects end organs to the medulla via dorsal funiculus

• 2nd order called internal arcuate fibers as they decussate & medial lemniscus AFTER decussation. Synapse in VPL in thalamus.

• 3rd order connects VPL to primary sensory cortex in postcentral gyrus

gracile

The LOWER body fine discrimination touch information is represented MEDIALLY in the ___ funiculus and nucleus on the dorsal side of spinal cord.

cuneate

The UPPER body fine discrimination touch information is represented LATERALLY in the ___ funiculus and nucleus on the dorsal side of spinal cord

posterior intermediate sulcus

the cuneate and gracile funiculus are separated in the PSC by the ___

medial lemniscus

name of the fine discrimination tract AFTER decussation

contralateral, ipsilateral, bilateral

If a SOC lesion happens

• AFTER decussation it leaves ___ deficits

• BEFORE decussation it leaves ___ deficits

• On BOTH sides of the SPC, it leaves ___ deficits

tract

If the lesion happens not in a region but in a SPC ascending ___, then there is loss of the modality carried by that ___ at the level of the lesion AND BELOW

Pain and Temperature pathway

Pathway that is very primitive and carry essential BODY sensory info. Called lateral spinothalamic tract after decussation

• 1st order axon has the cell body in DRG and connects the end organ with the dorsal horn of SPC AFTER ASCENDING 2-3 levels

• 2nd order axon is called ventral white commissure of SPC when decussating, and lateral spinothalamic tract AFTER decussation. Synapses in VPL of thalamus

• 3rd order connects VPL to primary sensory cortex in postcentral gyrus areas 3,1,2

somatotopy

___ aka body map is maintained though ALL CNS levels

• axons coming in line up with the ones already there

• head somatosensory info is more medial compared to body somatosensory info through all levels of CNS for example.

anterior spinothalamic tract

tract carrying crude touch information, follows the same path as the one for body pain and temperature EXCEPT it travels in the anterior funiculus instead of the lateral one

• very LOW resolution hence crude

cell bodies/gray matter

Lesions of __/__ in SPC tracts results in very FOCAL deficits at the level of lesion and the ones near it (especially above it for pain and temperature)

bilateral

when the lesion is at the crossing point/decussation point, you get ___ deficits/loss of somatosensation

What to ask about lesions

• what somatosensation pathway is it on? = what sense you lose

• did it cross over? yes = contralateral, no = ipsilateral, at = bilateral

• where is the lesion? = where/how much of sense you lose

medulla

lesions at the ___ or higher results in COMPLETE LOSS of modality/whole body loss

DRG

lesions in __ causes ipsilateral loss of all somatosensation at a focal level

anterolateral

the pain and temperature pathway is also called ___ pathway

slower

The pain and touch pathway is primitive and protopathic aka ___

faster

the dorsal column system aka fine touch discrimination pathway is epicritic aka __

where they decussate

The main anatomical difference between the anterolateral and dorsal column pathways is ___

• the first is in the dorsal horn of SPC

• the second is in the medulla

hemi lesion

___ of SPC causes contralateral widespread loss of pain and touch & ipsilateral loss of fine touch & ipsilateral focal loss of pain and temperature

trigeminal nucleus

axons of trigeminal ganglion cells synapse in the ____

• exception is proprioception axons as their cell body is not in the trigeminal ganglion but in the actual ___

mesencephalic nucleus

Part of the trigeminal nucleus that relates to the proprioception neurons of the FACE

• contains their cell bodies

• located in the midbrain

main sensory nucleus

part of trigeminal nucleus linked to fine touch and pressure neurons of the FACE

• located in the pons

spinal trigeminal nucleus

part of trigeminal nucleus linked to pain and temperature neurons of the FACE

• located in the medulla and SPC

Regions of trigeminal nerves

• ophthalmic (top of face)

• maxillary (middle of face)

• mandibular (jaw/lower face)

EACH REGION of the face has projections to ALL 3 PARTS of trigeminal nucleus

ventral trigemino-thalamic tract

The facial touch and pain/temperature signal go from the end organs to the trigeminal nucleus, which then projects to the VPM via the ____ aka VTT, and the 4th order neurons connect the VPM to the cortex

VPM

region of thalamus where facial/head/neck sensory tracts synapse

• lesion there leads to CONTRALATERAL loss of all somatosensations in the FACE

trigeminal ganglion

ipsilateral loss of ALL somatosensations in the face when the lesion is at the ___ because the proprioception axons are cut as well as the cell bodies of touch and pain/temperature

spinocerebellar pathway

pathway for nonconscious somatosensations

• 1st order connects end organ to dorsal nucleus of Clarke in SPC with cell body in DRG

• 2nd order ascends to restiform body in inferior cerebellar peduncle aka in the cerebellum

• DO NOT DECUSSATE