posterior (dorsal) column-medial lemniscus pathway

Examples of posterior (dorsal) column-medial lemniscus pathway in the following topics:

• Proprioceptive Sensations

  • Conscious proprioception is communicated by the posterior (dorsal) column–medial lemniscus pathway to the cerebrum.
  • Unconscious proprioception is communicated primarily via the dorsal and ventral spinocerebellar tracts to the cerebellum.

• Functions of the Brain Stem

  • This includes the corticospinal tract (motor), the posterior column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception) and the spinothalamic tract (pain, temperature, itch, and crude touch).
  • The ascending pathways from the body to the brain are the sensory pathways, including the spinothalamic tract for pain and temperature sensation and the dorsal column, fasciculus gracilis, and cuneatus for touch, proprioception, and pressure sensation. 
  • The facial sensations have similar pathways and also travel in the spinothalamic tract and the medial lemniscus.

• Sensory and Motor Tracts

  • The spinothalamic tract is a sensory pathway originating in the spinal cord.
  • The pathway decussates at the level of the spinal cord.
  • Somatosensory organization is divided into the dorsal column–medial lemniscus tract (the touch/proprioception/vibration sensory pathway) and the anterolateral system, or ALS (the pain/temperature sensory pathway).
  • Both sensory pathways use three different neurons to get information from sensory receptors at the periphery to the cerebral cortex.
  • In both pathways, primary sensory neuron cell bodies are found in the dorsal root ganglia, and their central axons project into the spinal cord.

• Somatic Sensory Pathways

  • The somatosensory pathway is composed of three neurons located in the dorsal root ganglion, the spinal cord, and the thalamus.
  • In the case of touch and certain types of pain, the third neuron has its cell body in the ventral posterior nucleus of the thalamus and ends in the postcentral gyrus of the parietal lobe.
  • This is the target for neurons of the dorsal column–medial lemniscal pathway and the ventral spinothalamic pathway.
  • Other ascending pathways, particularly those involved with control of posture, are projected to the cerebellum, including the ventral and dorsal spinocerebellar tracts.
  • The formation of the spinal nerve from the dorsal and ventral roots.

• Overview of the Spinal Nerves

  • Outside the vertebral column, the nerve divides into branches.
  • The medial branches (ramus medialis) of the posterior branches of the upper six thoracic nerves run between the semispinalis dorsi and multifidus, which they supply.
  • This branch is called the medial cutaneous ramus.
  • The medial branches of the posterior divisions of the lumbar nerves run close to the articular processes of the vertebrae and end in the multifidus muscle.
  • These pathways have both afferent and efferent fibers.

• Vertebrate Axis Formation

  • However, animal bodies have lateral-medial (toward the side-toward the midline), dorsal-ventral (toward the back-toward the belly), and anterior-posterior (toward the front-toward the back) axes .
  • Many of these genes are involved in the Wnt signaling pathway.
  • Wnt signaling activity in anterior-posterior development can be seen in several organisms including mammals, fish, and frogs.
  • Wnt proteins guide the axons of the spinal cord in an anterior-posterior direction.
  • Animal bodies have three axes for symmetry: anterior/posterior (front/behind), dorsal/ventral (back/belly), and lateral/medial (side/middle).

• Parts of the Cerebellum

  • Based on surface appearance, three lobes can be distinguished in the cerebellum: the flocculonodular lobe, anterior lobe (above the primary fissure), and the posterior lobe (below the primary fissure).
  • Excluding the flocculonodular lobe, which has distinct connections and functions, the cerebellum can be parsed functionally into a medial sector called the spinocerebellum and a larger lateral sector called the cerebrocerebellum.
  • The medial zone of the anterior and posterior lobes constitutes the spinocerebellum, also known as the paleocerebellum.
  • It receives proprioception input from the dorsal columns of the spinal cord (including the spinocerebellar tract) and from the trigeminal nerve, as well as from visual and auditory systems.
  • It receives input exclusively from the cerebral cortex (especially the parietal lobe) via the pontine nuclei (forming corticopontocerebellar pathways), and sends output mainly to the ventrolateral thalamus (in turn connected to motor areas of the premotor cortex and primary motor area of the cerebral cortex) and to the red nucleus.

• Medulla Oblongata

  • A stroke can injure the pyramidal tract, medial lemniscus, and the hypoglossal nucleus.
  • This causes a syndrome called medial medullary syndrome, a type of alternating hemiplegia characterized by recurrent episodes of paralysis on one side of the body.
  • An open or superior part where the dorsal surface of the medulla is formed by the fourth ventricle.
  • The posterior part of the medulla between the posterior median and posterolateral sulci contains tracts that enter it from the posterior funiculus of the spinal cord.
  • These are the fasciculus gracilis, lying medially next to the midline, and the fasciculus cuneatus, lying laterally.

• Spinal Cord Grey Matter and Spinal Roots

  • The spinal cord is the main pathway for information connecting the brain and peripheral nervous system.
  • The length of the spinal cord is much shorter than the length of the bony spinal column.
  • The cord has grooves in the dorsal and ventral sides.
  • The posterior median sulcus is the groove in the dorsal side, and the anterior median fissure is the groove in the ventral side.
  • The dorsal root ganglia lie along the vertebral column by the spine.

• Organization of Motor Neuron Pathways

  • The motor pathway, also called the pyramidal tract or the corticospinal tract, serves as the motor pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive brainstem motor nuclei.
  • Cortical upper motor neurons originate from Brodmann areas 1, 2, 3, 4, and 6, then descend into the posterior limb of the internal capsule, through the crus cerebri, down through the pons, and to the medullary pyramids, where about 90% of the axons cross to the contralateral side at the decussation of the pyramids.
  • The lateral tract contains upper motor neuronal axons that synapse on the dorsal lateral lower motor neurons, which are involved in distal limb control.
  • These lower motor neurons, unlike those of the dorsal lateral, are located in the ventral horn throughout the spinal cord.
  • This diagram of spinal cord tracts shows the motor and efferent pathways in red and the sensory and afferent pathways in blue.