Descending tracts

Descending tracts

Motor neuron- lower motor neuronThese are situated in the anterior gray column of SC and send axons to innervate skeletal muscles through the anterior roots of the spinal nervesDescending tractsDescend in white matter from different supraspinal nerve centers which are segregated into nerve bundles called DESCENDING TRACTSUpper motor neuronsThese supraspinal neurons & their tracts are sometimes referred to as the upper motor neurons

They provide numerous separate pathways that can influence motor activityNames of descending tractsCorticospinal tracts (lateral and anterior)Reticulospinal tractsTectospinal tractsRubrospinal tractsVestibulospinal tractsOlivospinal tractsDescending autonomic fibers

FUNCTIONS OF THE DESCENDING TRACTSCorticospinal tractsVoluntary, discreet, skilled movements especially those of the distal parts of the limbsReticulospinal tractsMay facilitate or inhibit the activity of the alpha and gamma motor neurons in the anterior gray columnsTectospinal tractsIs concerned with reflex postural movements in response to visual stimuliRubrospinal tractsFacilitates the activity of flexor musclesInhibits the reflexes of extensor musclesVestibulospinal tractFacilitates the activity of extensor musclesInhibits the activity of flexor musclesConcerned with postural activity associated with balanceOlivospinal tractMay play a role in muscular activityFunction is doubtful Descending autonomic fibersConcerned with the control of visceral activity

Order neurons1st order neuron- cell body in cerebral cortex

2nd order neuron- from 1st order, axon descends to synapse on 2nd order neuron situated in the anterior gray column of SC

3rd order neuron- from 2nd order, axon is short and synapse with the 3rd order neuron to innervate the skeletal muscles through the anterior root & spinal nerves

TRACTLOCATION OF UMNDESTINATION(termination)SITE OF DECUSSATION(cross over)CORTICOSPINAL PATHWAYSLateral Primary motor cortex(cerebral hemisphere)LMN of ant gray hornof SCPyramids of medulla oblongataAnteriorLevel of LMNMEDIAL PATHWAYSVestibulospinal Vestibular nucleiUncrossed Tectospinal Midbrain LMN of ant gray hornsof SC (cervical spine)BrainstemReticulospinal Reticular formation(network of nuclei in brainstem)LMN of ant gray horns of SCUncrossed LATERAL PATHWAYRubrospinal Red nuclei (midbrain)LMN of ant gray hornsof SCBrainstem