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1、No. 28 1. Motor Pathwaysno28no28辽宁医学院辽宁医学院. The Motor (descending) PathwaysnThe motor pathways are concerned with motor function, and composed of upper motor neurons and lower motor neurons. The upper motor neurons are the efferent neurons from the cerebral cortex to the motor nuclei of cranial nerv
2、es and anterior horns of spinal cord. The lower motor neurons are the nerves in the motor nuclei of cranial nerves and the anterior horns of spinal cord. The cell bodies and axons of lower motor neurons serve as the final common pathway connecting motor impulses.nThe motor pathways include pyramidal
3、 and extrapyramidal systems.no28no28辽宁医学院辽宁医学院) The Pyramidal SystemnIt is concerned with the voluntary movement of the skeletal muscles and is composed of two orders of neurons, i.e. the upper and lower motor neurons.nThe upper motor neurons are composed of the giant pyramidal cells (Betz cells) an
4、d other pyramidal cells of various sized which are located in the precentral gyrus and the anterior part of paracentral lobule and the pyramidal cells in the some areas of frontal, parietal lobes. no28no28辽宁医学院辽宁医学院nTheir axons form the descending pyramidal tract, among which, the fibers ending in t
5、he cranial motor nuclei are designated as the corticonuclear tract and those terminating in the anterior horn of the spinal cord as corticospinal tract.nThe lower motor neurons include the cranial motor cells of the brain stem and spinal motor cells of the spinal cord.no28no28辽宁医学院辽宁医学院1. The cortic
6、ospinal tractnThe upper motor neurons are the pyramidal pyramidal cells in the superior and middle parts of the precentral gyrus and the anterior part of paracentral lobule.nThe axons arising from these upper motor neurons form the corticospinal tract.no28no28辽宁医学院辽宁医学院no28no28辽宁医学院辽宁医学院nIt traverse
7、s the posterior limb of internal capsule, the intermediate 3/5 of the crus cerebri, the basilar part of the pons, and the ventral part of the medulla oblongata. In the caudal part of the medulla oblongata the greater part (75-90%) of the tract crosses to the opposite side to form the pyramidal decus
8、sation and continues as the lateral corticospinal tract in the lateral funiculus of the spinal cord. The fibers of the lateral corticospinal tract terminate in the anterior gray horns of all the spinal segments controlling the movements of muscles of the limbs.no28no28辽宁医学院辽宁医学院no28no28辽宁医学院辽宁医学院no2
9、8no28辽宁医学院辽宁医学院nThe non-crossed fibers continue as the anterior corticospinal tract directly into the anterior funiculus of the same side and cross the median plane in the anterior white commissure and synapse, as do those of the lateral tract, directly or indirectly with the motor neurons of the an
10、terior gray horn. The anterior corticospinal tract is generally believed to exist above the level of the mid-thoracic segments, controlling the muscles of trunk and limbs. A small part in the anterior corticospinal tract do not crosses to the opposite side, terminating in the ipilateral anterior hor
11、ns of the spinal cord. These uncrossed fibers innervate the trunk muscles by way of the motor cells of the anterior gray horn. So that the trunk muscles are controlled by bilateral motor cortex of the hemisphere.no28no28辽宁医学院辽宁医学院nThe lower motor neurons are the large multipolar cells of the anterio
12、r gray horn.nThey give rise to the motor fibers that leave the spinal cord through the anterior roots to be distributed by way of the spinal nerves to the skeletal muscles.nBecause of the inhibitory functions of the upper motor neurons to the lower ones, there are different clinical signs in the cas
13、es of damage to the upper or lower motor neuronsno28no28辽宁医学院辽宁医学院2. The corticonuclear tractnThe upper motor neurons are the giant pyramidal and certain other smaller pyramidal neurons in the inferior part of the precentral gyrus.nThe axons arising from these upper motor neurons form the corticonuc
14、lear tract.no28no28辽宁医学院辽宁医学院no28no28辽宁医学院辽宁医学院nIn the course of descending through the genu of internal capsule and the brain stem, it give rise to the collaterals of the bilateral oculomotor, trochlear, trigeminal motor, ambiguous, accessory nuclei and superior part of the facial nucleus, and to t
15、he contralateral hypoglossal nucleus and the inferior part of the facial nucleus. So, the hypoglossal nucleus and inferior part of the facial nucleus receive the fibers only from the contralateral corticonuclear tract.no28no28辽宁医学院辽宁医学院nThe lower neurons are the cells in the above cranial motor nucl
16、ei.nThe lower neurons give rise to axons joining the corresponding cranial nerves that control the movements of the innervated skeletal muscles.nBecause the inferior part of the facial nucleus and hypoglossal nucleus receive fibers just from the contralateral corticonuclear tract, the injury of the unilateral corticonuclear tract can usually cause paralysis of the contralateral glossal muscles and facial muscles below the palpebral fissure. This is designated as supranuclear paralysis.no28no28辽宁
