DCML and ALS sensory pathways Flashcards
what general sensations does the anterior lateral system (ALS) do?
- crude (non discriminative) touch. cannot localize sensation
- temperature
- pain
what general sensations does the Dorsal column-Medial lemnisucs (DCML) do?
proprioception
vibration
Fine (discriminative) touch. Can localize sensation
T/F Receptor distribution is NOT uniform over the body surface; receptor density varies, as does receptive field size.
true, this results in distorted cortical maps representing different parts of the body
what is the primary sensory neuron type in the DCML pathway?
pseudo-unipolar neuron with a central and peripheral branch, with it’s cell body in the dorsal root ganglion
what are the skin mechanoreceptors that detect mechanical inputs?
fine touch, vibration, pressure, motion
DCML pathway
what do free nerve detect?
pain, temperature, itch
ALS pathway
what do proprioceptors detect?
muscle stretch, tension, and joint position
the speed of conduction depends upon axon diameter and degree of myelination, what are the two types of neurons in the DCML pathway?
Alpha(group I): largest diameter, fastest, proprioceptors in muscles
Beta(Group II): second largest diameter and speed, mechanoreceptors of skin
what is the receptive field?
the area detected by a single receptor neuron
what is a dermatome?
an area of skin that is mainly supplied by a single spinal nerve
where do mechanical and proprioceptive information go once the information is in the spinal cord?
dorsal (or posterior) columns
no synapse yet and still ipsilateral
what are the two tracts within the dorsal column and what part of the body do they contain?
- gracile tract (more medial tract): 1st order sensory neurons of the lower half of the body below thoracic level 6
- cuneate tract (more lateral): 1st order sensory neurons of the upper half of the body above thoracic level 6
where is the first synapse in the in the dorsal column nuclei?
caudal medulla
**still ipsilateral
after the synapse in the caudal medulla what happens?
the second order neurons then cross the midline (decussate) in the internal arcuate and ascend in the medial lemniscus.
where is the medial lemniscus?
just behind the pyramid of the medulla and medial to the inferior olive
is the information in the medial lemniscus ipsilateral or contralateral?
contralateral
where is the medial lemniscus in the pons?
just posterior to the pontocerebellar fibers and bobs big belly. its more in the middle part of the pons and is horizontal (medial lateral orientation)
in the inferior portion of the midbrain where is the the medial lemnisucs?
just behind the substantia nigra
in the rostral midbrain where is the medial lemniscus located?
just lateral to the red nucleus
is somatotopy maintained throughout the pathway?
- yes, it starts aligned ventral and dorsally with the arms(upper body) is dorsal and the legs are ventral.
- as it moves up the brainstem the medial lemniscus rotates laterally until in the midbrain the legs are more dorsal and the arms and ventral
where is the second synapse in the DCML pathway?
in the VPL of the thalamus
**this is contralateral to the original sensory input.
where do axons from the thalamus (3rd order neurons) ascend to?
to post central gyrus of the cortex traveling in the internal capsule
what does VPL mean?
ventral posteriolateral
how is the primary somatosensory cortex organized?
somatotopicly
can the cortical sensory map change?
yes, it is plastic.
if you lose a finger the region of the brain the neighboring finger can move into the now dead area
what types of general sensation is associated with the ALS or spinothalamic system?
crude touch (non discriminative) touch
temperature
pain
why is the anterolateral system related to feelings from our body?
associated with emotion, drives behavioral motivation, hunger, thirst, visceral sensations, TEMPERATURE, PAIN, ITCH, tickle
although the ALS has pseudo-unipolar neurons with a central and peripheral branch, which is different about the peripheral end?
it is a free nerve ending
what are the two neuron types of the ALS system?
delta (group III): 3rd smallest diameter and speed. Pain, temperature
C (group IV): smallest diameter and speed. Temperature pain and itch. not myelinated
which cell type is responsible for the first pain ada sharp pain?
delta nociceptors
which cell type is responsible for the second pain aka burning slower longer lasting pain?
polymodal C-nocicpetors
where does the ALS pathway decussate?
in the spinal cord via anterior white commissure to the ALS white matter(spinothalamic tract)
where do the first order neurons synapse in the ALS pathway?
dorsal horn of the spinal cord
ipsilateral
what is the tract of lissauer?
some of the 1st order neurons of the ALS pathway will not synapse at the level they enter the spinal cord, but will travel up to another level and synapse there.
where do second order neurons decussate?
in the anterior white commissure and ascend in the anteriolater system (ventral white commissure).
at the spinal cord (cervical level) are the ALS and DCML pathways ipsilateral or contralateral?
ALS is contralateral
DCML is ipsilateral
where is the anteriolateral (ventral white commissure) located?
just lateral the the ventral horn
is there somatotopy in the ALS system?
yes
where is the anteriolateral (ventral white commissure)?
just dorsal to the interior olive on the most lateral portion
what is unique about the medulla?
both the ALS and DCML pathways have decussated
in the pons what it the relationship in location of the ALS to the DCML
the anterolateral system is just dorsal and lateral to the medial lemniscus which is dorsal the the pontocerebellar tracts
in the midbrain where is the ALS in relation to the DCML?
dorsal to the most lateral edge of the medial lemniscus
where does the second order neuron synapse?
in the VPL (same as the DCML)
the third order neuron in the thalamus then follows a similar path the to post central gyrus via the internal capsule. T/F
true
does the ALS pathway follow somatotopic organization in the somatosensory cortex?
yes
