Descending/Motor Pathways and Tracts

Descending/Motor Pathways and Tracts:
Located in anterior gray columns of spinal cord. Delivers efferent impulses from brain to spinal cord. Motor pathways involve two neurons  upper and lower motor neurons

1) Direct/Pyramidal
lateral corticospinal
transmits/carries motor impulses from motor area of cerebrum to spinal cord motor neurons  activate skeletal muscles on opposite side of body
form a pyramid shaped ridge on the anterior surface of the medulla oblongata (pyramidal tracts)
passes through the internal capsule, brainstem and crosses over to opposite side of body at junction between the brainstem and spinal cord
voluntary motor tract – rapid and skilled movements (especially distal ends of limbs)
anterior/ventral corticospinal
function is same as lateral corticospinal tract

2) Indirect/extrapyramidal
• tectospinal
• transmits motor impulses from midbrain, crosses to contralateral side of midbrain
• in lower medulla, branches into lateral and medial tectospinal tracts
• arises in area where visual and sensory inputs are processed
• connects the tectum of the midbrain with the spinal cord
• involved in reflex movements of the head
• co-ordination of head and eyes toward visual targets
• vestibulospinal
• transmits motor impulses that maintain muscle tone and activate ipsilateral limb and trunk extensors  help maintain balance
• connects the vestibular nuclei of the brainstem with the spinal cord
• facilitate activity of extensor muscles and inhibits activity of flexor muscles
• rubrospinal
• transmits motor impulses for muscle tone of distal limb muscles on opposite side of body
• connects the red nucleus of the midbrain and the spinal cord
• axons cross on mesencephalon and descend in dorsolateral aspect of spinal cord
• facilitates activity of flexor muscle and inhibits activity of extensor muscles
• reticulospinal
• transmits impulses for muscle tone and many visceral motor functions
• connects the reticular formation of the brainstem with the spinal cord
• inhibits or facilitates voluntary movement

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