Spinomesencephalic pathway

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Spinomesencephalic pathway - Wikipedia

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Spinomesencephalic pathway
Diagram showing a few of the connections of afferent (sensory) fibers of the posterior root with the efferent fibers from the ventral column and with the various long ascending fasciculi. (Spinotectal fasciculus labeled at bottom right.)
Diagram of the principal fasciculi of the spinal cord. (Spinotectal fasciculus labeled at bottom left.)
Anatomical terminology [edit on Wikidata]

The spinomesencephalic pathway, spinomesencephalic tract or spino-quadrigeminal system of Mott, includes a number of ascending tracts in the spinal cord, including the spinotectal tract.^[1]^[2]^[3] The spinomesencephalic tract is one of the ascending tracts in the anterolateral system of the spinal cord that projects to various parts of the midbrain.^[1] It is involved in the processing of pain and visceral sensations.^[4]

In the ALS

The anterolateral system (ALS) is a bundle of afferent somatosensory fibers from different ascending tracts in the spinal cord. These fibers include those of the spinomesencephalic tract, spinothalamic tract, and spinoreticular tract amongst others.^[5] Spinomesencephalic fibres project to the periaqueductal gray, and to the tectum. Other fibers project to and terminate in the parabrachial nucleus, the pretectum, and the nucleus of Darkschewitsch.^[1] The fibers that project to the tectum are known as the spinotectal fibers.^[5] The spinotectal tract fibers project to the superior colliculus. Where they synapse onto cells of the deeper superior colliculus they are activated by noxious stimuli.^[1]

Anatomy

The spinomesencephalic tract consists mostly of myelinated fibers. The neurons are either low-threshold of a wide dynamic range, or high threshold,^[1] with many of the cells being nociceptive.^[1]

Origin

Cells of the spinomesencephalic tract arise mostly in Rexed lamina I, and to a lesser extent in Rexed laminae IV and VI-VIII) of the spinal cord. They are mostly concentrated in lamina V.^[1] The tract is in the same region as the spinothalamic tract.^[1]

Course

Most of the spinomesencephalic fibers decussate to ascend contralaterally, but there is a noted group of uncrossed fibers in the upper cervical levels.^[1]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Standring, Susan (2016). Gray's anatomy: the anatomical basis of clinical practice . Digital version (41st. ed.). Philadelphia, Pa.: Elsevier. p. 433. ISBN 9780702052309.
^ Patestas, Maria A.; Gartner, Leslie P. (2016). A Textbook of Neuroanatomy (2nd ed.). Hoboken, New Jersey: Wiley-Blackwell. pp. 112, 203–204, 224–225. ISBN 978-1-118-67746-9.
^ Gray, Henry (1918). Gray's Anatomy (20th ed.). p. 762.
^ Kiernan, John A.; Rajakumar, Nagalingam (2013). Barr's The Human Nervous System: An Anatomical Viewpoint (10th ed.). Philadelphia: Wolters Kluwer Lippincott Williams & Wilkins. p. 74. ISBN 978-1-4511-7327-7.
^ ^a ^b Haines, Duane (2018). Fundamental neuroscience for basic and clinical applications (Fifth ed.). Philadelphia, PA: Elsevier. p. 259. ISBN 9780323396325.

Spinal cord

General features

Grey columns

Posterior grey column	Marginal nucleus Substantia gelatinosa of Rolando Nucleus proprius Rexed lamina V Rexed lamina VI
Lateral grey column	Intermediolateral nucleus Posterior thoracic nucleus
Anterior grey column	Interneuron Alpha motor neuron Onuf's nucleus Gamma motor neuron
Other	Rexed laminae Central gelatinous substance Gray commissure

White matter

Sensory

Posterior	Posterior column-medial lemniscus pathway Gracile Cuneate
Lateral	Spinocerebellar dorsal ventral Spinothalamic lateral anterior Posterolateral Spinotectal
Anterior	Spinoreticular tract Spino-olivary tract

Motor

Lateral	Corticospinal Lateral Extrapyramidal Rubrospinal Raphespinal Reticulospinal Hypothalamospinal
Anterior	Corticospinal Anterior Extrapyramidal Vestibulospinal Reticulospinal Tectospinal Raphespinal Olivospinal

Both

Anterior white commissure

External features

Ventral
- Anterior median fissure
- Anterolateral sulcus
Dorsal
- Posterior median sulcus
- Posterolateral sulcus

Anatomy of the midbrain

Tectum
(Dorsal)

Corpora quadrigemina

Grey matter

Pretectal area

White matter

Sensory / ascending	Spinotectal tract Central tegmental tract
Motor / descending	Tectospinal tract

CSF

Cerebral aqueduct

Peduncle
(Ventral)

Tegmentum

White matter

Sensory / ascending	Lemnisci Medial Lateral Ascending MLF Vestibulo-oculomotor fibers Spinothalamic tract Ventral trigeminal tract Dentatothalamic tract
Motor / descending	Rubrospinal tract Rubro-olivary tract Descending MLF

Grey matter

cranial nuclei	GSA Mesencephalic GSE Oculomotor nucleus Trochlear nucleus GVE Edinger–Westphal nucleus
Ventral tegmental area	Rostromedial tegmental nucleus
Periaqueductal gray Red nucleus Rostral interstitial nucleus of medial longitudinal fasciculus Parabrachial area Interpeduncular nucleus
Midbrain reticular formation	Dorsal tegmental nucleus Raphe nuclei dorsal Reticulotegmental nucleus

Base

White / Cerebral crus	Pyramidal tracts Corticospinal tract Corticobulbar tract Corticopontine tract Frontopontine fibers Temporopontine fibers
Grey / Substantia nigra	Pars compacta Pars reticulata
Surface	Superior cerebellar peduncle Decussation Interpeduncular fossa

Brain and spinal cord: neural tracts and fasciculi

Sensory

DCML

1°:	Pacinian corpuscle/Meissner's corpuscle → Posterior column (Gracile fasciculus/Cuneate fasciculus) → Gracile nucleus/Cuneate nucleus
2°:	→ sensory decussation/arcuate fibers (Posterior external arcuate fibers, Internal arcuate fibers) → Medial lemniscus/Trigeminal lemniscus → Thalamus (VPL, VPM)
3°:	→ Posterior limb of internal capsule → Postcentral gyrus

Anterolateral/
pain

Fast/lateral	1° (Free nerve ending → A delta fiber) → 2° (Anterior white commissure → Lateral and Anterior Spinothalamic tract → Spinal lemniscus → VPL of Thalamus) → 3° (Postcentral gyrus) → 4° (Posterior parietal cortex) 2° (Spinomesencephalic tract → Superior colliculus of Midbrain tectum)
Slow/medial	1° (Group C nerve fiber → Spinoreticular tract → Reticular formation) → 2° (MD of Thalamus) → 3° (Cingulate cortex)

Motor

Pyramidal

flexion: Primary motor cortex → Posterior limb of internal capsule → Decussation of pyramids → Corticospinal tract (Lateral, Anterior) → Neuromuscular junction

Extrapyramidal

flexion:	Primary motor cortex → Genu of internal capsule → Corticobulbar tract → Facial motor nucleus → Facial muscles
flexion:	Red nucleus → Rubrospinal tract
extension:	Vestibulocerebellum → Vestibular nuclei → Vestibulospinal tract
extension:	Vestibulocerebellum → Reticular formation → Reticulospinal tract
Midbrain tectum → Tectospinal tract → muscles of neck

Basal ganglia

direct:	1° (Motor cortex → Striatum) → 2° (GPi) → 3° (Lenticular fasciculus/Ansa lenticularis → Thalamic fasciculus → VL of Thalamus) → 4° (Thalamocortical radiations → Supplementary motor area) → 5° (Motor cortex)
indirect:	1° (Motor cortex → Striatum) → 2° (GPe) → 3° (Subthalamic fasciculus → Subthalamic nucleus) → 4° (Subthalamic fasciculus → GPi) → 5° (Lenticular fasciculus/Ansa lenticularis → Thalamic fasciculus → VL of Thalamus) → 6° (Thalamocortical radiations → Supplementary motor area) → 7° (Motor cortex)
nigrostriatal pathway:	Pars compacta → Striatum

Cerebellar

Afferent

Vestibular nuclei → Vestibulocerebellar tract → ICP → Cerebellum → Granule cell

Pontine nuclei → Pontocerebellar fibers → MCP → Deep cerebellar nuclei → Granule cell

Inferior olivary nucleus → Olivocerebellar tract → ICP → Hemisphere → Purkinje cell → Deep cerebellar nuclei

Efferent

Dentate nucleus in Lateral hemisphere/pontocerebellum → SCP → Dentatothalamic tract → Thalamus (VL) → Motor cortex

Interposed nucleus in Intermediate hemisphere/spinocerebellum → SCP → Reticular formation, or → Cerebellothalamic tract → Red nucleus → Thalamus (VL) → Motor cortex

Fastigial nucleus in Flocculonodular lobe/vestibulocerebellum → Vestibulocerebellar tract → Vestibular nuclei

Bidirectional:
Spinocerebellar

Unconscious proprioception	lower limb → 1° (muscle spindles → DRG) → 2° (Posterior thoracic nucleus → Dorsal/posterior spinocerebellar tract → ICP → Cerebellar vermis) upper limb → 1° (muscle spindles → DRG) → 2° (Accessory cuneate nucleus → Cuneocerebellar tract → ICP → Anterior lobe of cerebellum)
Reflex arc	lower limb → 1° (Golgi tendon organ) → 2° (Ventral/anterior spinocerebellar tract→ SCP → Cerebellar vermis) upper limb → 1° (Golgi tendon organ) → 2° (Rostral spinocerebellar tract → ICP → Cerebellum)

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In the ALS

Anatomy

Origin

Course

See also

References