The posterior thoracic nucleus, (Clarke's column, column of Clarke, dorsal nucleus, nucleus dorsalis of Clarke) is a group of
interneuron
Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, enab ...
s found in the medial part of
Rexed lamina VII, also known as the intermediate zone, of 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 ...
. It is located from the cervical segment C8 to lumbar segment L3 of the spinal cord and is an important structure for
proprioception
Proprioception ( ) is the sense of self-movement, force, and body position.
Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...
of the lower limb.
Anatomy
It occupies the medial part of the base of the
posterior grey column and appears on the transverse section as a well-defined oval area.
It begins caudally at the level of the second or third
lumbar nerve, and reaches its maximum size opposite the twelfth thoracic nerve. Above the level of the eight thoracic nerve its size diminishes, and the column ends opposite the last cervical or first thoracic nerve.
It is represented, however, in the other regions by scattered cells, which become aggregated to form a cervical nucleus opposite the third cervical nerve, and a sacral nucleus in the middle and lower part of the sacral region.
Nerve cells in the posterior thoracic nucleus are most abundant between the lower thoracic and upper lumbar segments. Cell bodies are of medium size and oval- or pyriform-shape. These cells characteristically present coarse Nissl granules and have characteristic eccentric nuclei.
Axonal projections from neurons in this nucleus give rise to the dorsal
spinocerebellar tract which ascends ipsilaterally through the spinal cord and ends as
mossy fibers in the ipsilateral cerebellar cortex after passing through the inferior cerebellar peduncle.
Axons originating from the posterior thoracic nucleus which ascend contralaterally through the
lateral funiculus
The most lateral of the bundles of the anterior nerve roots is generally taken as a dividing line that separates the anterolateral system into two parts. These are the anterior funiculus, between the anterior median fissure and the most lateral ...
of 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 ...
are named
ventral spinocerebellar tract which cross over again within the white matter of the cerebellum, to ultimately end on its ipsilateral side.
Function
The posterior thoracic nucleus is a major relay center for unconscious
proprioception
Proprioception ( ) is the sense of self-movement, force, and body position.
Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...
. Sensory information from
muscle spindles and
tendon organs is carried by axons of larger neurons in dorsal root ganglia, which synapse onto neurons in the spinal cord including the posterior thoracic nucleus. From here information continues rostrally until it reaches the
cerebellar cortex. This relay pathway is generally known as the
dorsal spinocerebellar tract.
Diseases
It has been observed that in
Friedreich's ataxia
Friedreich's ataxia (FRDA) is a rare, inherited, autosomal recessive neurodegenerative disorder that primarily affects the nervous system, causing progressive damage to the spinal cord, peripheral nerves, and cerebellum, leading to impaired ...
there is evident degeneration of the posterior thoracic nucleus as well as other proprioceptive spinal tracts. These patients might present with ataxia,
dysarthria
Dysarthria is a speech sound disorder resulting from neurological injury of the motor component of the motor–speech system and is characterized by poor articulation of phonemes. It is a condition in which problems effectively occur with the ...
, muscle weakness or paralysis and skeletal defects.
Eponym
Clarke's column is named for
Jacob Augustus Lockhart Clarke.
References
External links
* https://web.archive.org/web/20080331064830/http://isc.temple.edu/neuroanatomy/lab/atlas/L3/
* http://www.neuroanatomy.wisc.edu/sc97/text/p3/Pathway.htm
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Spinal cord