| Popis: |
The two types of motor neurons in the anterior horn of the spinal cord are alpha motor neurons, which innervate extrafusal muscle, and gamma motor neurons, which innervate intrafusal fibers in the muscle spindle. A third source of input to alpha motor neurons are reflex collaterals of primary afferent; these synapse on alpha and/or gamma motor neurons in the brainstem, their main processes ascending in somatosensory pathways. Neurons located in the reticular nuclei/formation, the vestibular nuclei, and the red nucleus are the main sources of brainstem input to spinal motor neurons. Reticulospinal tracts (medial and lateral) descend mainly ipsilaterally and terminate in spinal laminae VII and VIII to innervate, through interneurons to alpha motor cells, extensor musculature. Spinovestibular tracts (medial, bilateral, to cervical levels: lateral, ipsilateral, to multiple levels) arise from medial and inferior vestibular nuclei and from the lateral vestibular nucleus, and terminate mainly in spinal laminae VII and VIII, where they excite extensor limb musculature. Rubrospinal fibers arise in the red nucleus, cross in the ventral tegmental decussation, and enter the lateral funiculus of the spinal cord; rubrospinal fibers terminate in cervical levels and excite flexor motor neurons of the upper extremity. The red nucleus and reticular nuclei also receive input from the cerebral cortex, while the vestibular nuclei receive extensive input from the cerebellum. Damage above the tentorium may result in decorticate rigidity; if the lesion extends through the tentorial notch and into the red nucleus, the patient may present with decerebrate rigidity. |
