| upper motor neuron | Clinical term indicating those neuron's of the motor cortex that contribute to the formation of the pyramidal or corticospinal and corticobulbar tracts, as distinguished from the lower motor neuron's innervating the skeletal muscles. Although not motor neuron's in the strict sense, these cortical neuron's became colloquially classified as motor neuron's because their stimulation produces movement and their destruction causes severe disorders of movement. See: motor neuron, motor cortex. (05 Mar 2000) |
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| upper motor neuron lesion | Injury to cerebral descending (corticonuclear) fibres above the brainstem or spinal motor nerve nucleus. Synonym: upper motor neuron lesion. (05 Mar 2000) |
| upper nodal extrasystole | An obsolete term for a nodal extrasystole supposed to arise from the upper part of the A-V node; recognised in the electrocardiogram by a retrograde P wave preceding the QRS complex by an abnormally short P-R interval. (05 Mar 2000) |
| upper respiratory infection | Any number of viral or bacterial infections that includes infections of the throat, nasopharynx, sinuses, larynx, trachea or bronchi. (27 Sep 1997) |
| upper respiratory tract | The nasopharynx, oral cavity, and throat. (09 Oct 1997) |
| upper subscapular nerve | Two branches of the posterior cord of the brachial plexus, an upper and lower, supplying the subscapularis muscle; the lower subscapular nerve also supplies the teres major muscle. Synonym: nervi subscapulares. (05 Mar 2000) |
| upper thoracic splanchnic nerves | Part of the cardiopulmonary splanchnic nerves from the second to fifth segments of the thoracic sympathetic trunk that pass medially and anteriorly to enter the cardiac plexus; they convey postsynaptic sympathetic fibres to, and visceral afferent (pain) fibres from, the heart. Synonym: nervi cardiaci thoracici, upper thoracic splanchnic nerves. (05 Mar 2000) |
| upper uterine segment | The main portion of the body of the gravid uterus, the contraction of which furnishes the chief force of expulsion in labour. (05 Mar 2000) |