The spinomesencephalic pathway, spinomesencephalic tract or spino-quadrigeminal system of Mott, includes a number of ascending tracts in the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

, including the spinotectal tract. The spinomesencephalic tract is one of the ascending tracts in the anterolateral system of the

that projects to various parts of the midbrain. It is involved in the processing of pain and visceral sensations.

In the ALS

The anterolateral system (ALS) is a bundle of afferent

somatosensory The somatosensory system, or somatic sensory system is a subset of the sensory nervous system. The main functions of the somatosensory system are the perception of external stimuli, the perception of internal stimuli, and the regulation of bod ...

fibers from different ascending tracts in the spinal cord. These fibers include those of the spinomesencephalic tract,

spinothalamic tract The spinothalamic tract is a nerve tract in the anterolateral system in the spinal cord. This tract is an ascending sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upwar ...

, and

spinoreticular tract The spinoreticular tract (also paleospinothalamic pathway, or indirect pathway of the anterolateral system) is a partially decussating (crossed-over) four-neuron sensory pathway of the central nervous system. The tract transmits slow nociceptive/ ...

amongst others. Spinomesencephalic fibres project to the

periaqueductal gray The periaqueductal gray (PAG), also known as the central gray, is a brain region that plays a critical role in autonomic function, motivated behavior and behavioural responses to threatening stimuli. PAG is also the primary control center for ...

, and to the

tectum The midbrain or mesencephalon is the uppermost portion of the brainstem connecting the diencephalon and cerebrum with the pons. It consists of the cerebral peduncles, tegmentum, and tectum. It is functionally associated with vision, hearing, mo ...

. Other fibers project to and terminate in the parabrachial nucleus, the

pretectum In neuroanatomy, the pretectal area, or pretectum, is a midbrain structure composed of seven nuclei and comprises part of the subcortical visual system. Through reciprocal bilateral projections from the retina, it is involved primarily in mediati ...

, and the nucleus of Darkschewitsch. The fibers that project to the tectum are known as the spinotectal fibers. The spinotectal tract fibers project to the

superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum or optic lobe. The adjective f ...

. Where they synapse onto cells of the deeper superior colliculus they are activated by noxious stimuli.

Anatomy

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

nociceptive In physiology, nociception , also nocioception; ) is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular ...

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. The tract is in the same region as the

Course

Most of the spinomesencephalic fibers

decussate Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named aft ...

to ascend contralaterally, but there is a noted group of uncrossed fibers in the upper cervical levels.

References

{{Authority control Central nervous system pathways Sensory systems

In the ALS

Anatomy

Origin

Course

See also

References