| neuron | An excitable cell specialised for the transmission of electrical signals over long distances. Neurons receive input from sensory cells or other neurons and send output to muscles or other neurons. Neurons with sensory input are called sensory neurons, neurons with muscle outputs are called motoneurons, neurons that connect only with other neurons are called interneurons. Neurons connect with each other via synapses. Neurons can be the longest cells known, a single axon can be several metres in length. Although signals are usually sent via action potentials, some neurons are nonspiking. (18 Nov 1997) |
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| nonadrenergic, noncholinergic neuron | Autonomic efferent neuron whose transmission is not blocked by blocking adrenergic and cholinergic transmission. Nitric oxide may be the transmitter in some cases. (05 Mar 2000) |
| nonspiking neuron | <physiology> A neuron that can convey information without generating action potentials. As passive electrical potentials are attenuated over distances greater than the space constant for a neuron (typically 1mm), this implies that most nonspiking neurons are involved in signalling over relatively short distances. Typical examples are invertebrate stretch receptors and interneurons in the central nervous system. (12 Mar 1998) |
| intercalary neuron | A neuron interposed between and connecting two other neuron's. Synonym: intercalary neuron. (05 Mar 2000) |
| internuncial neuron | A neuron interposed between and connecting two other neuron's. Synonym: intercalary neuron. (05 Mar 2000) |
| facilitator neuron | <physiology> A neuron whose firing enhances the effect of a second neuron on a third. This allows the effects of neuronal activity to be modulated. (18 Nov 1997) |
| unipolar neuron | A neuron whose cell body emits a single axonal process resulting from the fusion of two polar processes during development; at a variable distance from the cell body, the process divides into a peripheral axon branch extending outward as a peripheral afferent (sensory) nerve fibre, and a central axon branch that enters into synaptic contact with neuron's in the spinal cord or brainstem. With the single known exception of the neuron's composing the mesencephalic nucleus of the trigeminus, unipolar neuron's are the exclusive neural elements of the sensory ganglia. The lack of dendritic processes of these primary sensory neuron's is only apparent: the dendritic pole of the unipolar neuron is represented by the unmyelinated terminal ramifications of the peripheral axon branch. Synonym: pseudounipolar cell, pseudounipolar neuron, unipolar cell. (05 Mar 2000) |
| 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) |
| 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) |
| lower motor neuron | Clinical term used to indicate the final motor neuron's that innervate the skeletal muscles; distinguished from upper motor neuron's of the motor cortex that contribute to the pyramidal or corticospinal tract. See: motor neuron. (05 Mar 2000) |
| lower motor neuron dysarthria | Dysarthria caused by dysfunction of the motor nuclei and the lower pons or medulla, or other neural connections, central and peripheral to the muscles of articulation. (05 Mar 2000) |
| lower motor neuron lesion | Injury to motor cells in the brainstem or spinal cord, or of the axons derived from them. (05 Mar 2000) |
| antidepressive agents, second-generation | A structurally and mechanistically diverse group of drugs that are not tricyclics or monoamine oxidase inhibitors. The most clinically important appear to act selectively on serotonergic systems, especially by inhibiting serotonin reuptake. (12 Dec 1998) |
| burns, second degree | Second degree burns look similar to the first degree burns in that it is red and sensation is intact; however, the damage is severe enough to cause blistering of the skin and the pain is usually somewhat more intense. (12 Dec 1998) |
| centimeter-gram-second system | The scientific system of expressing the fundamental physical units of length, mass, and time, and those units derived from them, in centimeters, grams, and seconds; currently being replaced by the International System of Units based on the meter, kilogram, and second. (05 Mar 2000) |