Ventral Corticospinal Tract : these are corticospinal axons that do NOT decussate in the medulla. However, at each spinal cord level some of these axons decussate via the ventral white commissure. They then synapse with local circuit neurons or LMNs in the ventral gray horn of the spinal cord. Axons of these LMNs exit the cord in the ventral roots of spinal nerves to terminate at skeletal muscles that control movements of the trunk and the proximal parts of the limbs.
2. Corticobulbar Pathway
Conducts impulses for the control of skeletal muscles in the head.
Axons of UMNs from the cerebral cortex form this tract and descend through the internal capsule of the cerebrum and cerebral peduncle of the midbrain. Some axons of this tract decussate, while others do not. The axons terminate in the motor nuclei of nine pairs of cranial nerves in the brain stem: oculomotor III (eyes), trochlear IV (eyes), trigeminal V (mastication), abducens VI (eyes), facial VII (facial expression), glossopharyngeal IX (swallowing), vagus X (swallowing), accessory XI (swallowing, voice, cervical muscles) hypoglossal XII (lingual muscles). The LMNs of these cranial nerves convey impulses that control precise, voluntary movements of the eyes, tongue, and neck, plus chewing, facial expressions, and vocalization.
Indirect Motor Pathways Aka Extrapyramidal Pathways
Axons of UMNs give rise to indirect motor pathways and descend from various nuclei of the cerebrum & brain stem into five major tracts of the spinal cord and terminate on the local circuit neurons or LMNs. These tracts carry information regarding gross, synergic movements requiring large muscle groups. The tracts are: Rubrospinal (facilitates limb flexors), Tectospinal (regulate auditory & visual reflexes), Vestibulospinal (regulate extensor muscle tone to maintain balance & posture), Pontine Reticulospinal, (facilitate limb extensors) and Medullary Reticulospinal (inhibit limb extensors) .
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