J Neurol Neurosurg Psychiatry 69:262, 2000.
Thach WT Jr, Montgomery EB Jr: Motor system. In: Pearlman AL, Collins RC (eds): Neurobiology of Disease. New York, Oxford University Press, 1990, pp 168–196.
Tower SS: Pyramidal lesion in the monkey. Brain 63:36, 1940.
Van Gijn J: The Babinski Sign. A Centenarary. Universitiet Utrecht. Utrecht, 1996.
Vulliemoz S, Raineteau O, Jabaudon D. Reaching beyond the midline: Why are human brains cross wired? Lancet Neurol 4:87, 2005.
Figure 3-1. A. Patellar tendon reflex. Sensory fibers of the femoral nerve (spinal segments L2 and L3) mediate this myotatic reflex. The principal receptors are the muscle spindles, which respond to brisk stretching of the muscle affected by tapping the patellar tendon. Afferent fibers from muscle spindles are shown entering only the L3 spinal segment, while afferent fibers from the Golgi tendon organ are shown entering only the L2 spinal segment. In this monosynaptic reflex, afferent fibers entering spinal segments L2 and L3 and efferent fibers issuing from the anterior horn cells of these and lower levels complete the reflex arc. Motor fibers show leaving the S2 spinal segment and passing to the hamstring muscles demonstrate the disynaptic pathway by which inhibitory influences are exerted upon an antagonistic muscle group during the reflex. B. The gamma loop is illustrated. Gamma efferent fibers (γ) pass to the polar portions of the muscle spindle. Contractions of the intrafusal fibers in the polar parts of the spindle stretch the nuclear bag region and thus cause an afferent impulse to be conducted centrally. The afferent fibers from the spindle synapse with many alpha motor neurons. Because the alpha motor neurons innervate extrafusal muscle fibers, excitation of the alpha motor neurons by spindle afferents causes a cocontraction of the muscle. In this way, both gamma and alpha fibers can simultaneously activate muscle contraction. Both alpha and gamma motor neurons are influenced by descending fiber systems from supraspinal levels. (Adapted by permission from Carpenter MB, Sutin J: Human Neuroanatomy, 8th ed. Baltimore, Williams & Wilkins, 1983.)
Posterior limb of internal capsuleUpper limbEye fieldFaceMOTORCORTEXLower limbGenu of internal capsuleV N. motor nucleusVII N. nucleusXII N. nucleusVI N. nucleusCerebral peduncleMIDBRAINPONSMEDULLAMotor decussationMotor neurons for upper limbCrossed lateralcorticospinal tractPyramidUncrossed lateral corticospinal fibersVentral corticospinal tractMotor neurons for lower limbCERVICAL ENLARGEMENTLUMBOSACRAL ENLARGEMENT
Figure 3-2. Corticospinal and corticobulbar tracts. The various lines indicate the trajectories of these pathways, from their origin in particular parts of the cerebral cortex to their nuclei of termination.
1Numbered areas in this and subsequent chapters refer to Brodmann areas of the cerebral cortex that are discussed in Chap. 22. “Layers” refer to the six neuronal layers of the cerebral cortex, also shown in detail in Chap. 22, on Cerebral Localization.