נוירואנטומיה - ב

The Medial Hemispheres Are Involved in Adjusting Limb Movements The major inputs to the medial hemispheres (paravermal cortex) are superimposed, somatotopically arranged projections from the motor cortex and spinal cord (see Fig. 20-16 ). The major output of this part of the cerebellum is via the interposed nucleus back to motor cortex (through VL/VA; see Fig. 20-22B ) and to the magnocellular red nucleus. Thus the medial hemispheres can influence spinal cord motor neurons through the corticospinal tract and also, to a minor extent, through the rubrospinal pathway. This led to the hypothesis that the intermediate zone of the cerebellum compares the commands emanating from motor cortex (it receives this information via pontine nuclei) with the actual position and velocity of the moving part (it receives this information via spinocerebellar and similar tracts) and then, by way of the interposed nucleus, issues correcting signals. This is consistent with the observation that most neurons of the interposed nucleus have firing rates related to voluntary movements, but unlike those of dentate neurons, their rates tend to change during rather than before movement ( Fig. 20-23 ). Note that here again, a given side of the cerebellum winds up affecting ipsilateral motor neurons (e.g., left side of cerebellum→right thalamus→right motor cortex→left side of spinal cord).

הפגיעה אנטריורית ביותר תרגום לפגיעה באיזור שמייצג את הרגליים וכתוצאה מכך ל ataxic gate - - קושי בשמירה על האיזון הבליכה, ולכן הליכה על בסיס רחב, Nystagmus - נין לראות את הריצוד של העיניים בקצה התנועה, כמו כן ריצוד בנסיון מיקוד אופייני לפגיעה צרברלית slurred speach - פגיעה בתזמון הדיבור

The thalamic reticular nucleus, unlike all other thalamic nuclei, has no projections to the cerebral cortex. Rather, the reticular nucleus is a sheet of neurons that receive inputs from the cortex and from thalamic projection neurons and send inhibitory (GABA) projections back to the thalamus ( Fig. 16-19 ). Inspection of Figures 16-7 to 16-13 reveals that axons traveling from thalamus to cortex or from cortex to thalamus must traverse the reticular nucleus. As they do so, these fibers give off collaterals to the reticular nucleus. For example, the portion of the reticular nucleus adjacent to VPL/VPM receives convergent inputs from somatosensory fibers on their way to the postcentral gyrus, and from regulatory fibers on their way from the postcentral gyrus to VPL/VPM. The output of each portion of the reticular nucleus goes to that thalamic nucleus from which it receives its input. This makes the reticular nucleus an important source of regulatory input to the thalamus.

שכבת הנוירונים שיוצרת את ה reticular nucleus נמצאת מעל הLamina ומפרידה בינה לקפסולה הפנימית