Two structures are important in the anatomy of the human spine cord: the medial lemniscus (or dorsolateral) and the dorsolateral (or dorsal) column. Both structures provide sensory input and somatotopic organization to nerves. Each person involved in the initiation and control of movement has their own name. In this article, we will discuss their roles. We will also learn about the medial lemniscus, and the dorsolateral faciculus.
The medial lemniscus and fasciculus graccilis are two of the five primary pathways in the spinal cord. The axons that travel from the upper limb travel up to the fasiculus Cuneatus and the synapses in nucleus gracilis. These pathways could be damaged and result in permanent loss or vibration.
In the medial lemniscus, the axons of the lower and upper body originate. The axons traveling up the lemniscus are ventral to the arm and lateral to the leg. Trigeminal nerve fibers travel up the lemniscus, coming in dorsally to the arm. The medial lemniscus rotates 90° at the pons, while secondary axons remain in the same spot.
The dorsal column contains neurons of second-order order. These neurons cross over the medulla, forming the medial lemniscus. They project to the primary somatosensory cortex. The medial lemniscus also contains sensory information. It also contains the receptors to heat and pain. Eventually, this would help us in our quest for a cure for Parkinson’s disease.
The dorsal column houses the cuneatus and gracilis, which are located in the upper limbs. These fasciculi receive information form the upper and lower extremities, arms, and send it to the brain. The axons of these neurons travel to the cuneus and gracilis nuclei of the hindbrain. These fibers eventually form the medial lemniscus.
The dorsal column-medial lemniscal pathway carries sensory information from various parts of the body to the cerebral cortex. These pathways are also known as somatosensory pathways. The dorsal column-medial lemniscal pathway (DMML) comprises the dorsal column and the anterolateral system. In addition, the dorsal column-medial lemniscal pathway (DCML) receives information from sensory receptors throughout the body. This pathway transmits vibrations and discriminative touch.
The dorsal column can be divided into two parts, the dorsolateral faciculus gracili or the fasciculus cuneatus. The axons for the legs are contained in the dorsolateral fasciculus, while the fasciculus cuneatus includes the axons for the arms and upper body. Both components are linked by nerve fibers. The descending fasciculus carries the sensory information associated to the DCML pathway.
The dorsal column is comprised of two large ascending tracts, the gracile fasciculus and the cuneate fasciculus. The gracile faciculus starts at the distal end the spinal cord. It is made up of fibers that transmit sensory information from the lower part of the body to the upper. The lateral fasciculus, on the other hand, starts at the mid-spinal level and lies medial to the fasciculus cuneatus at the upper level. The dorsal column is also home to the dorsal root ganglion, and sensory information travels from the trunk to the upper limb via this fiber.
The treatment of traumatic brain injury would be possible by the use of the fasciculus cuneatus and the dorsolateral faciculus gracilius. The latter is a neuroanatomical muscle that controls movement in the upper leg. Friedrich Goll (1829-1903), a neuroanatomist, first described the structure in 1884. Both have been identified as essential components of spinal cord function.
The dorsal column carries the axons of the upper and lower body, continuing to the medial lemniscus. The fibers in the upper bodies are connected by the neck and head axons. The correspondence between the two structures preserves the anatomical information, but it does not produce a miniature version of the human body. It actually exaggerates sensitive areas.
The two areas of the spinal cord that receive axons are the cuneate and gracile fasciculi. The cuneate fasciculus contains axons from lower spinal cord levels. They are located in the dorsal root and T6 of the coccygeal spine nerve. The gracile fasciculus receives axons from the dorsal column nuclei.
The dorsal root gland ganglia is responsible for the axisons of the cuneate fasciculi and gracile faciculi. The axons from the cuneate fasciculus end at the second-order neurons in the nucleus cuneatus. These fibers then travel up as the medial lemniscus fibers and the internal arcuate fibres.
The cuneate and gracile nuclei are the equivalent of the posterior spinocerebellar tract of the spinal cord. The cuneate nucleus contains first-order fibers that ascend through the fasciculus cuneatus and synapse in the lateral cuneate nucleus of the caudal medulla.
The gracile fasciculus has more cutaneous afferents that deep-proprioceptors. Deep-proprioceptors exit the dorsal column at the lower segments and synapse with neurons in the dorsal nucleus, also known as the nucleus of Clarke. The dorsal column pathway is highly somatotopic. The lateral segments are located posteriorly, and the rostral segments are lateral to them. The sacral segments and the cervical segments are responsible for the lateral fibers.
The fasciculus gracilis, fascineatus and fasciculus symphysis are both part of the dorsal columns system. The fasciculus is the central route for alpha-beta fibres. The lateral fibers transmit information from the lower thoracic segments of the thalamus to the somatosensory cortex and the thalamus.
The somatotopic arrangement of fasciculus gramilis and fasciculus cuneatus includes a single cluster that receives axons from different regions of the body. During the development of the visual system, axons from the lower body enter the posterior column below the level of T6 and continue their journey in the cuneate fasciculus, a section of the posterior column outside the gracile fasciculus. Glial cells are located on either side the posterior intermediate sulcus and divide both regions of the spinal column.
The somatotopic arrangement in fasciculus gracili is thought to lead to a higher pain tolerance than other sensory regions. However, there are a number of differences between the fasciculus gracilis and fasciculus cuneatus, and further research is needed to clarify their role in human pain and motor function.
The somatotopic arrangement of fasciculus gracile and fasciculus cuneatus refers to the connections between the two different sensory areas. The cuneate fasciculus connects the upper and lower limbs, while the gracile fasciculus provides sensation in the lower limb. Friedrich Goll (1829-1903) was the neuroanatomist who gave his name to the somatotopic fasciculus gracilis, and fasciculus cuneatus.
The spinal cord is where the sensory information from the lower extremities, trunk, neck, and fasciculus cuneatus is processed. The somatotopic arrangement between fasciculus cuneatus and fasciculus gracilis mediates conscious proprioception as well as kinesthesia.
The fasciculus gracilis and fascicle cuneatus are fiber tracts in the spinal cord that carry sensory information. The latter is responsible for proprioception and fine tactile discrimination. The two fiber tracts are part of the medial lemniscus system in the brain. They are located in the midbrain and the medulla, respectively.
The first one is responsible to transmit sensory information from the upper extremities. The second-order neurons travel ventromedially in an ascending tract and then cross the midline to form the medial lemniscus. The medial lemniscus receives axons from the fasciculus gracilis and fasciculus cuneatus. The medial lemniscus contains third-order neurons that travel to the lateral side of the sensory motor cortex. The fasciculus gracilis, fasciculus cuneatus, and fasciculus cuneatus play an important role in mediating conscious touch, kinesthesia, and conscious proprioception.
The large tracts of the posterior spinal cord that are called the cuneate or gracile fasciculi, are located in the cuneate and gracile. These nerve tracts carry sensory information from the upper and lower portions of the body. They are separated by the posterior intermediate sulcus and septum. They act as extensions of anterior cuneate faciculus. Further, both tracts carry information from the spinal cord.
The cuneate fasciculus and gracile fasciculus are first-order neurons found in the dorsal roots ganglia. The cuneate fasciculus axons exit the dorsal column at the lower segments and synapse on neurons in the dorsal nucleus, also known as the nucleus of Clarke. The pathway has a high level of somatotopic organization with successive rostral sections located laterally to the lower segments. The sacral and cervical segments are the source of the lateral fibers.