Tractus Spinocerebellaris: Structure, Function & Diseases

The tractus spinocerebellaris is afferent nerve fiber tracts that supply information to the cerebellum from the spinal cord. This influx of information includes motor and coordinative stimulation of muscles, as well as positions of joints. This occurs through the subconscious deep sensory system, allowing for the unconscious direction and control of muscle activity and joint positions.

What is the tractus spinocerebellaris?

The tractus spinocerebellaris is the name given to the cerebellar lateral tracts that carry proprioceptive information from the spinal cord (medulla spinalis) to the cerebellum (cerebellum). Translating the Latin term tractus spinocerebellaris, the course can be partially deduced. The term tractus refers to a tissue tract or group of fibers, -spino refers to the spinal cord, and -cerebellaris refers to the cerebellum. The tractus spinocerebellaris is divided into the tractus spinocerebellaris anterior (ventrally running nerve cord) and the tractus spinocerebellaris posterior (dorsally running nerve cord). The dorsally running nerve cord is thought to have the fastest stimulus conduction at 120m/s in the central nervous system. The fast transmission of stimuli has the advantage that movements in the subconscious can be executed quickly in dangerous situations. This can be, for example, pulling the hand away from a hot stove top or general escape from dangerous situations. These nerve pathways are mainly responsible for the transmission of subconscious deep sensitivity from the spinal cord to the cerebellum, thus triggering unconscious and routine sequences of movements. They form an important function for sensitive motor function and can become vital in various situations.

Anatomy and structure

The spinocerebellar tract is divided into the cerebellar lateral tracts, tractus spinocerebellaris anterior and tractus spinocerebellaris posterior. These together conduct proprioceptive afferents from the medulla spinalis (spinal cord) to the lobus anterior of the spinocerebellum (anterior lobe of the cerebellum). Proprioceptive afferents are the influx of deep sensory information. The origin of the nerve tracts is the spinal cord. The fiber tracts of the ventrally running tractus spinocerebellaris anterior receive their input from the spinal nerve at segmental level in the posterior horn. Here they cross to the contralateral side and back. The crossing results in the cerebellum receiving impulses from only one side (ipsilateral) of the spinal cord. The fibers of the tractus spinocerebellaris posterior receive their input from spinal nerves at segmental level in the nucleus thoracicus posterior and do not cross in the spinal cord. In their course, the first nerve cell (neuron) of both fiber strands is located in the spinal ganglion. The spinal ganglion is a collection of nerve cell bodies found at the posterior nerve root of a spinal nerve. In a ganglion cell group located in the gray matter (nucleus dorsalis) of the spinal cord, the fiber strands of the tractus spinocerebellaris are switched posteriorly on the lamina (nerve cell plates) V and VI to the second neuron (nerve cell). The wiring of the tractus spinocerebellaris anterior occurs in the lamina V-VII. The fiber tracts terminate in the cerebellum. The dorsally running nerve tract enters the cerebellum through the inferior cerebellar peduncle (pedunculus cerebellaris inferior) and the ventrally running nerve tract enters the cerebellum through the superior cerebellar peduncle (pedunculus cerebellaris superior). Both fiber tracts terminate in the lobus anterior and the intermediate longitudinal zone. Both portions belong to the cerebellum and give off collaterals to the nucleus emboliformis and nucleus globosus.

Function and Tasks

The function of the tractus spinocerebellaris is to conduct the subconscious depth-sensitive stimuli in the form of information from the medulla spinalis to the cerebellum. The guided information principally involves the sensitive control and tuning of fine motor activity from the periphery. The fiber strands differ not only in their wiring to the neurons, but also in their main functions. The tractus spinocerebellaris anterior mainly conducts stimuli from the periphery to the cerebellum. However, feedback impulses from the descending pyramidal tracts are also thus fed to the cerebellum to inform it of a currently initiated motor movement sequence. The posterior spinocerebellar tract transmits proprioceptive afferents in unconscious form to 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 body layers thus reach the organ of balance via the spinocerebellar pathways. But also information of the proprioceptive perception of the skin receptors is conducted to the cerebellum via the dorsal nerve cord. The cerebellum is thus informed of all proprioceptive afferents and can influence muscle tone in relation to the particular joint position via the polysynpathetic efferents.

Diseases

If a functional disturbance of the tractus spinocerebellaris occurs due to a disease or a massive trauma, functions of the unconscious deep sensibility are always disturbed. This can result, for example, in an asynergy. Asynergy is a disturbance in the coordination of muscle groups. The temporal coordination of muscle groups for an arbitrary sequence of movements is particularly affected here. In addition, movement disorders can occur in the form of dysmetria. In this case, hypermetry or hypometry occurs. The execution and sequence of movements cannot be controlled and performed in a target-oriented manner. Another consequence can be the so-called dys-diadochokinesia. The coordination of movements is disturbed, i.e., no sequences of movements can be performed consecutively. Other complaints may include gait ataxia (general gait unsteadiness), tendency to fall, intensity tremor (trembling of the limbs), phonation disorder and other speech disorders. Basically, in a disorder of the tractus spinocerebellaris, there are always deficits in the area of motor function. The main characteristic is in all movement processes that take place in the periphery through muscle activity and joint movements. The control of the necessary structures cannot be adequately implemented. This results in insecurity, instability or overshooting movement sequences.