Dorsal Column System + anterior lateral system Flashcards
in what area of the spinal cord does Fine touch, vibration and conscious proprioceptive
information ascend?
dorsal (posterior) columns
Fasciculus gracilis
sacral and coccygeal layer
lumbar and thoracic levels below T6
Fasciculus cuneatus
thoracic levels above T6
low cervical levels
upper cervical levels
How does sensory info ascend?
The first synapse:
In the dorsal column nuclei
Axons from second order
neurons then cross the
midline in the internal
arcuate and ascend in the
medial lemniscus
The second synapse:
In the VPL of the thalamus
Axons from third order
neurons then ascend to the
primary cerebral cortex
are these fibers organized?
yes, a map of the body is maintained throughout the pathway
remodel experiment
spinocerebellar
Crude (non-discriminative) touch. Poorly localize sensation.
Temperature
Pain
are part of which pathway?
anterior lateral system (ALS)
Somatic Sensory Pathway overview
Anterolateral system controls what?
temp, pain, itch, tickle. Associated w/ emotion, drives behavior. interoception (sense of physiological condition of body). homeostatic afferent pathway
sensor neurons in ALS
Sensory neurons in ALS system have free
nerve endings and small diameter axons (slowly
conducting)
Pain – nociception
Two major classes of nociceptive neurons:
* Aδ-nociceptors signal sharp pain (FIRST PAIN)
* polymodal C-nociceptors are slower and signal
burning pain (SECOND PAIN)
1st order neuron in ALS
Axons enter the spinal
column and can ascend or
descend one or two spinal
segments in Lissauer’s tract
before synapsing on second-
order neurons in the dorsal
horn.
First order neurons synapse in dorsal horn of the
spinal cord - ipsilateral
First synapse in
superficial layer
of the spinal
dorsal horn
2nd order neurons in ALS
decussate in the anterior white
commissure and ascend in the anterolateral system (also
called the spinothalamic tract)
Axons from 2nd
order neurons
ascend through
the spinal cord in
the ALS
Axons from 2nd
order neurons
ascend through
the brainstem in
the ALS
ALS vs DCML entry to SC
The ALS also projects to
regions in the brainstem
* Other thalamic nuclei
* anterior cingulate cortex
(emotional/motivational response
to pain)
* Insular cortex (pain intensity and
perception)
Pathway important for arousal,
emotional/motivational component
of pain
* Can drive autonomic responses
homeostatic regions:
Noradrenergic cell groups (A1-A2;
A5-A7)
* PB = Parabrachial nucleus
* PAG = periaqueductal gray
To what two areas in the thalamus does the ALS project
VM = ventral medial
nucleus
* MD = medial dorsal
nucleus
What 2 cortical areas do the thalamic connections from ALS project to, and what is their function?
Feeling:intensity and perception
VM -> Insular cortex
* High-resolution, modality-
specific sensory representation
of the physiological condition
of the body in interoceptive
cortex (insula)
* Corollary projection to area 3a
in the sensorimotor cortex.
Emotion/Motivation:
MD -> Anterior cingulate cortex
Integrates lamina I input with
brainstem homeostatic activity
(from PB and PAG) and produces
behavioral drive in limbic motor
cortex (anterior cingulate).
Descending modulation of pain
Many brainstem areas that receive
nociceptive inputs can modulate
transmission of nociceptive information
at spinal levels
is somatotopy also found in ALS pathway?
yes, but much less precise than DC
ALS pathway overview
Trigeminal pathway
1st order neuron:
cell body in trigeminal ganglion
First order sensory neurons
synapse in the ipsilateral
principal (or chief) trigeminal
nucleus
Second order neurons cross
(except for input from oral
cavity) and project to the
contralateral VPM of the
thalamus
Third order
neurons
project to the
primary
somatosensory
cortex
Third order
neurons
project to
insular cortex,
anterior
cingulate
cortex and
sensory cortex
also mediates pain/temp
main divisions of trigeminal nerve
Mesencephalic
trigeminal nucleus
(proprioception for
muscles of mastication) (midbrain)
Chief (or principal)
trigeminal nucleus
(fine touch, vibration etc) (pons)
Spinal trigeminal
nucleus
(pain, temperature,
crude touch) (medulla)
anatomy of primary sensory neuron
