What is the tractus spinocerebellaris?
The spinocerebellar tract is the cerebellar lateral cord, which guides proprioceptive information from the spinal cord (medulla spinalis) to the cerebellum (cerebellum). If one translates the Latin term Tractus spinocerebellaris, the course can be partially derived. The term Tractus refers to a Gewebzug or a fiber group under -spino the spinal cord and cerebellaris refers to the cerebellum.
The spinocerebellar tract is subdivided into the anterior spinocerebellar tract (ventral nerve cord) and into the posterior spinocerebellar tract (dorsal nerve cord). The dorsally extending nerve cord probably has the fastest transmission of stimuli at 120 m / s in the central nervous system. The rapid transmission of stimuli has the advantage that movements in the subconscious can be carried out quickly in dangerous situations. This can be, for example, the pulling away of the hand from a hot stove or general escape from dangerous situations.
These neural pathways are mainly responsible for the transmission of subconscious sensitivity from the spinal cord to the cerebellum and thus trigger unconscious and routine movement sequences. They form an important function for sensitive motor skills and can be vital in various situations.
Anatomy & Construction
The spinocerebellar tract is subdivided into the lateral cerebellar tracts of the spinocerebellar tract anterior and the posterior spinocerebellar tract. These jointly conduct proprioceptive afferents from the medulla spinalis (spinal cord) to the anterior lobe of the spinocerebellum (anterior lobe of the cerebellum). Proprioceptive afferents refer to the inflow of depth sensibility information.
The origin of the nerve tracts is the spinal cord. The fiber tracts of the anterior tractus spinocerebellaris anterior receive their input from the spinal nerve at segment height in the posterior horn. Here they cross to the contralateral side and back. The result of the crossing is that the cerebellum receives only impulses from one side (Ipsilateral) of the spinal cord. The fibers of the posterior spinocerebellar tract receive their input from spinal nerves at segmental height in the thoracic nucleus posterior and do not intersect in the spinal cord.
In its course, the first nerve cell (neuron) of both fiber strands lies in the dorsal root ganglion. The spinal ganglion is an accumulation of nerve cell bodies found at the posterior nerve root of a spinal nerve. In a ganglion cell group located in the gray matter (dorsal nucleus) of the spinal cord, the fiber strands of the posterior spinocerebellar tract are switched to the lamina (nerve cell plates) V and VI to the second neuron (nerve cell). The interconnection of the tractus spinocerebellaris anterior takes place in the lamina V-VII.
The fiber tracts end in the cerebellum. The dorsally extending nerve pathway enters the cerebellum through the lower cerebellar peduncle (inferior cerebellar peduncle) and the ventral nerve pathway through the upper cerebellar peduncle (superior cerebellar peduncle). Both fiber tracts end in the anterior lobe and the intermediate longitudinal zone. Both parts belong to the cerebellum and give off collaterals to the nucleus emboliformis and nucleus globosus.
Function & Tasks
The spinocerebellar tract has the function of guiding the subconscious deep-sensitive stimuli in the form of information from the medulla spinalis to the cerebellum. The guided information basically includes the sensitive control and coordination of fine motor skills from the periphery.
The fiber strands differ not only by the interconnection on the neurons, but also in their main functions. The anterior spinocerebellar tract mainly conducts the stimuli from the periphery to the cerebellum. But feedback pulses of the descending pyramidal tracts are also supplied to the cerebellum in order to inform this about a currently initiated motor sequence of movements.
The posterior spinocerebellar tract conducts proprioceptive afferents unconsciously on the cerebellum. The main feature here is the state of tension of the muscle spindles and the individual joint positions with their tendons and joint capsules. The impulses from the deeper layers of the body thus pass through the spinocerebellar pathways to the organ of equilibrium. But also information of the proprioceptive perception of the skin receptors are directed via the dorsal nerve cord to the cerebellum.
The cerebellum is thus informed about all proprioceptive afferents and can influence the muscle tone in connection with the respective joint position via the polysynaptic effernzences.
If there is a dysfunction of the spinocerebellar tract due to a disease or a massive trauma, functions of unconscious depth-sensitivity are always disturbed. This can, for example, result in asynergia. Asynergia is a disorder of the coordination of muscle groups.
The temporal coordination of the muscle groups for an arbitrary sequence of movements is particularly affected here. In addition, movement disorders can occur in the form of a dysmetry. This leads to a hypermetry or a hypometry. The execution and sequence of movements can not be targeted and performed. Another consequence may be the so-called dys-diadochokinese. The coordination of movement is disturbed, that is, no movement sequences can be carried out consecutively.
Other complaints may include gait ataxia (general gait insecurity), falling inclination, intensity tremor (trembling of the limbs), phonation disorder and other speech disorders. In principle, disturbances of the spinocerebellar tract always lead to failures in the motor system. The main feature lies in all movements that occur in the periphery through muscle activity and joint movements. The activation of the necessary structures can not be adequately implemented. This results in uncertainty, instability or excessive movements.