Ascending tract of Spinal cord
Dorsal spinocerebellar tract
Dorsal spinocerebellar tract Occupies a portion of the lateral funiculus between the lumbar vertebrae and medulla. This fiber tract originates from the ipsilateral dorsal nucleus and ends within the ipsilateral cerebellar cortex. The fibers terminate in two regions of the cerebellar cortex. Conduction velocity of these fibers range from 30 to 110 m /sec.
Dorsal spinocerebellar tract carries afferent impulses from muscle spindle through dorsal root ganglion of the spinal cord and project to cerebellar cortex.
Ventral spinocerebellar tract
Ventral spinocerebellar tract arises from the cells occupying the lateral part of nucleus proprius and nucleus intermedialis. This tract is not excited by afferents from the forelimbs
The axons are mostly contralateral. The tract reaches the cerebellum exclusively by brachium conjunctivum. Most terminate contralaterally which make them ipsilateral to their origin. Conduction velocity of these fibers range from 70 to 120 m /sec
Ventral spinocerebellar tract contains afferent fibers of both exteroceptive and proprioceptive systems (Golgi tendon mostly).
Rostral spinocerebellar tract
Forearm equivalent of Ventral spinocerebellar tract. Activated from ipsilateral forelimb nerves and uncrossed.
Rostral spinocerebellar tract reaches the cerebellum through the restiform body and the bracium conjunctivum. it is activated monosynaptically by Golgi tendon organ afferents and polysynaptically by flexor reflex afferents.
Spinocervical tract
Spinocervical tract arises from the nucleus intermedialis. it terminates in the lateral cervical nucleus from where it is relayed to the ventero – postero-lateral nucleus of the thalamus. this mostly involved with tactile afferents.
Spinothalamic tract
The lateral and ventral Spinothalamic tracts which are present in primates, are absent in domestic animals. Instead these exist as a single tract concerned with tactile , thermal and pain sensations.
The fibers project through the lateral lemniscus of the brain stem to the ventro – postero-lateral nucleus of the thalamus. The fibers also project through the reticular formation and central tegmental fasciculus to the intralaminar nuclei and the nucleus medialis dorsalis of the thalamus.
In primates, the fiber system is very important for the relay of pain sensations but in domestic animals transection of this tract does not affect pin perception because pain perception continues due to the diffuseness of the propriospinal fiber which crosses and re crosses.
Hence unilateral hemisection of the spinal cord in primate alleviates pain from contralateral lower extremity. This is not seen in domestic animals. Spinothalamic tracts arise from cells located in the dorsal horn in the region of the nucleus proprius of the spinal cord.
Spino olivary tract
Spino olivary tract arise from cells of the nucleus proprius of the spinal cord. It terminates in the caudal olivary complex of the medulla (medial and dorsal accessory olivary nuclei).
This forms another pathway to the cerebellum for exteroceptive and proprioceptive afferents. Action potentials reach the cerebellar cortex ipsilateral to their origin within the peripheral nerves. This tract is important in informing the cerebellum of the position of the limbs and the external environment.
Spino reticular tract
Spino reticular tract arise bilaterally from all levels of the spinal cord and terminate within many portions of the nuclei of the Brain stem reticular formation. These nuclei all receive afferents from the spinal cord.
Nucleus lateralis reticularis: Projects fibers ipsilateral to cerebellar cortex
Nucleus reticularis paramedianus: Projects fibers both ipsilateral and contralateral to cerebellar cortex. This forms another spino reticular cerebellar pathway
Roller nucleus and Nucleus intrafascicularis: Project fibers ipsilateral to cerebellar cortex and forms a third spino reticular cerebellar pathway
Nucleus reticularis tegmenti pontis: Forms a fourth spino reticular cerebellar pathway.
Functions of Spino reticular tract
- Important in many facets of normal activity.
- Carry sensory information from the skin and deep tissues and play an important role in the regulation of somatic and visceral motor activity.
- In maintenance of consciousness and perception .
- Accommodation of motor activities occur if this is transected bilaterally in domestic animals.
- Relay ascending activity to higher centers of the brain.
- Significant in pain perception.
- Modify respiration by terminating some of the fibers on nucleus of the pneumotaxic center.
- Control micturition.
- The tract terminates on neurons of the BSRF and serves as a feedback system for control of spinal cord activities.
Spino vestibular tract
Fibers ascend ipsilaterally in Spino vestibular tract. Serve as part of a feedback system for the control of activity within the lateral vestibular nucleus and modifies activities within the spinal cord. Plays an important role in regulating muscle tone.
Spino tectal tract
Spino tectal tract arise from cells located within the nuclei proprius and nuclei intermedialis of the gray matter. They decussate to the contralateral side and project to the cerebellum through rostral colliculi.
Functions of Spino tectal tract
- Convey tactile and thermal information and the sensation of pain.
- Also modifies activity within the descending tectospinal tract which is important in the control of motor activities of neck muscles.
- Also functions as a part of a multisynaptic pain pathway.
- Descending fiber tracts of the lateral and ventral funiculi.