5. Posterior Column Pathways
Post-cranial body (below the head and posterior portion of the head):
• mechanical stimuli: dorsal-column medial lemniscal system
Face (and anterior surface of the head):
• mechanical stimuli: pathway through the principal (chief) sensory
nucleus of the trigeminal complex
1
6. Posterior column pathways:
mechanosensation/
discriminative touch,
vibratory sense
Cerebrum
Midbrain
Mid-pons
Rostral
medulla
Caudal
medulla
Cervical
spinal cord
Lumbar
spinal cord
Internal arcuate fibers
Medial
lemniscus
Medial
lemniscus
Mechanosensory
receptors from
lower body
Mechanosensory
receptors from
upper body
Gracile tract
Cuneate tract
Gracile nucleus
(pathway from lower body)
Cuneate nucleus
(pathway from upper body)
Ventral posterior
lateral nucleus of
thalamus
Primary somatic
sensory cortex
Ventral posterior
medial nucleus of
thalamus
Trigeminal lemniscus
Medial
lemniscus
Trigeminal
ganglion
Principal
nucleus of
trigeminal
complex
Mechno-
sensory
receptors
from face
3 neurons from Skin – to - Cortex
1st: DRG
2nd: DCN
Gracile n. – lower body
Cuneate n. – upper body
3rd: VPL (thalamus)
DCMLS V-lemniscus
1st: G of V CN
2nd: in the pons
Principle nucleus of
trigeminal complex
3rd: VPM (thalamus)
Dorsal Column Medial Lemniscus System Trigeminal Lemniscus
1
11. Somatic Sensory Components of Thalamus
Axons from Gracile n.
Axons from
Cuneate n.
Axons from
Gracile n.
Axons from
Cuneate n.
Axons from
V CN principle n.
Ventral posterior lateral n.
Ventral posterior medial n.
Midbrain
14. Spinocerebellar pathways
I. Unconscious tracts (to the cerebellum)
II. Conscious tracts (to the cortex)
1. From the lower body (via the Clark’s nucleus)
2. From the upper body (via the external Cuneate nucleus)
3. From the face (via the spinal nucleus of V-CN)
2
15. Proprioceptors of the Musculoskeletal System
Muscle
spindles
Specialized muscle fibers
Golgi tendon
organ
Sensitive to
muscle force
Sensitive
to stretch
16. Posterior Spinocerebellar Tract
- muscle joint sense pathway to the cerebellum -
Thoracic spinal cord
Conveying of the proprioceptive information
from lower body
17. Conveying of the proprioceptive
information from the upper body
Medulla
19. Spinothalamic pathways
Post-cranial body (below the head and posterior portion of the head):
• pain and temperature: antero-lateral system
Face (and anterior surface of the head):
• pain and temperature: pathway through the spinal nucleus of the
trigeminal complex
3
20. Pain
Conductive capacity of
the A𝛿 fibers is much
higher than the C fibers.
C-fibers are polymodale:
they respond to mechanical,
chemical and temperature
stimuli.
DCMLS – dorsal column medial lemniscus system
DRG – dorsal root ganglion (axons ascend up forming gracile and cuneate tracts in the posterior column of the spinal cord).
DCN – dorsal column nucleus (the level of decussation – axons form the medial lemniscus, which runs across the tegmentum of caudal medulla)
VPL – ventral posterior lateral nucleus of the thalamus (axons ascend to the postcentral gurus)
3a – projection of proprioreceptors
3b – cutaneous receptors
1 – respond to activation of multiple skin areas
2 – shapes of objects
The route that conveys proprioceptive information for the lower part of the body to the dorsal column nuclei:
Lower body:
First-order proprioceptive afferents that enter the spinal cord between the mid-lumbar and thoracic levels (L2-T1) synapse on neurons in Clarke's nucleus, located in the medial aspect of the dorsal horn.
Second-order neurons in Clarke's nucleus send their axons into the ipsilateral posterior lateral column of the spinal cord, where they travel up to the level of the medulla in the dorsal spinocerebellar tract. These axons continue into the cerebellum, but in their course, give off collaterals that synapse with neurons lying just outside the nucleus gracilus (for the present purpose, "proprioceptive neurons" of the dorsal column nuclei).
Axons of these third-order neurons decussate and join the medial lemniscus, accompanying the fibers from cutaneous mechanoreceptors in their course to the VPL of the thalamus.
Upper body:
First-order proprioceptive afferents from the upper limbs have a course that is similar to that of cutaneous mechanoreceptors (blue arrow). They enter the spinal cord and travel via the dorsal column (fasciculus cuneatus) up to the level of the medulla, where they synapse on proprioceptive neurons in the dorsal column nuclei.
Second-order neurons send their axons across the midline, where they join the medial lemniscus and ascend to the VPL of the thalamus.
Parallel processing:
A fibers – precise localization of damage;
C fibers – motivate the response to that injury.
Raphe nuclei are located in the midline, along the rostrocaudal extension of the brainstem in humans. They include the raphe obscurus and raphe magnus nuclei, median and paramedian raphe nuclei, raphe pontis nucleus, and dorsal raphe nucleus, and consist mostly of serotonergic neurons. Studies in experimental animals have shown that raphe nuclei in the isthmus and rostral hindbrain mainly project to the neocortex, striatum, amygdala, hypothalamus, cerebellum, and other brainstem nuclei such as LC. The raphe nuclei in the caudal hindbrain are related to pain control. Those in the caudal hindbrain mainly project to the spinal cord.
The locus coeruleus is a nucleus in the pons involved with physiological responses to stress and panic.
The locus coeruleus is the principal site for brain synthesis of norepinephrine (noradrenaline). The locus coeruleus and the areas of the body affected by the norepinephrine it produces are described collectively as the locus coeruleus-noradrenergic system or LC-NA system.
Spinal trigeminal nucleus is an extension of the dorsal horn of the spinal cord. It has the same structure as the substancia gelatinosa.
Recently found: additional pathway for visceral sensation – through the dorsal column.
How it was discovered: the incurable visceral cancer patients who underwent the dorsal medial fasciculotomy were relived of pain.
Represent the integration of the visceral and somatic sensory system. Parallel input.
The dorsal horn was considered as a point of integration before the discovery of the proper visceral pathway.
Now – it is a question. Where exactly the integration of impulses from the viscera and soma happens? Thalamus? Cortex? Dorsal nuclei?
