| Fischer projection formula | <biochemistry> Of sugars, representations, by projection, of cyclic sugars, or derivatives thereof, in which the carbon chain is depicted vertically. The lowest-numbered asymmetric carbon atom (C-1 in aldoses; C-2 in 2-ketoses, e.g., fructose) is drawn at the top, and the rest of the carbon atoms of the chain are drawn in sequence below the top carbon atom. For each carbon atom, depicted in projection as lying in the plane of the paper, the carbon-to-carbon bond(s), which actually point away from the viewer, are drawn as vertical lines. The left-hand and right-hand bonds of each carbon atom, which actually point toward the viewer, are, in projection, depicted as horizontal lines. The conventions for the Fischer formulas of cyclic sugars are as follows: 1) if the highest-numbered asymmetric carbon atom has its OH (or its replacement) lying to the right, as is the 2-OH of d-glyceraldehyde, the sugar has the d configuration; if the OH is to the left, the sugar has the l configuration. 2) On the anomeric carbon atom (C-1 in the aldoses; C-2 in the 2-ketoses), an OH or substituted OH that lies to the right, with the OH of the highest-numbered asymmetric carbon atom also to the right is defined to be a; if it is to the left, with the OH of the highest-numbered carbon atom still to the right, it is b; the reverse applies if the latter OH is to the left. 3) The orientation of a terminal CH2OH group in the aldoses carries no configurational significance, as it contains no asymmetric carbon atom. (05 Mar 2000) |
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| lateral projection | Radiographic projection with the X-ray beam in a coronal plane. (05 Mar 2000) |
| frog-leg lateral projection | A lateral projection of the femoral neck made with the thigh maximally abducted. (05 Mar 2000) |
| accelerator fibres | Postganglionic sympathetic nerve fibre's originating in the superior, middle, and inferior cervical ganglia of the sympathetic trunk, conveying nervous impulses to the heart that increase the rapidity and force of the cardiac pulsations. Synonym: augmentor fibres. (05 Mar 2000) |
| adrenergic fibres | Nerve fibres liberating catecholamines at a synapse after an impulse. (12 Dec 1998) |
| afferent fibres | Those that convey impulses to a ganglion or to a nerve centre in the brain or spinal cord. (05 Mar 2000) |
| A fibres | Myelinated nerve fibre's in somatic nerves, measuring 1 to 22 um in diameter, conducting nerve impulses at a rate of 6 to 120 m/sec. (05 Mar 2000) |
| alpha fibres | Large somatic motor or proprioceptive nerve fibre's conducting impulses at rates near 100 m/sec. (05 Mar 2000) |
| anastomosing fibres | Anastomotic fibres, individual fibre's passing from one nerve trunk or muscle bundle to another. (05 Mar 2000) |
| arcuate fibres | Nervous or tendinous fibre's passing in the form of an arch from one part to another. See: arcuate fibres of cerebrum, external arcuate fibres, internal arcuate fibres. (05 Mar 2000) |
| arcuate fibres of cerebrum | Short association fibres that connect adjacent gyri in the cerebral cortex. Synonym: fibrae arcuatae cerebri. (05 Mar 2000) |
| association fibres | Nerve fibre's interconnecting subdivisions of the cerebral cortex of the same hemisphere or different segments of the spinal cord on the same side. Synonym: endogenous fibres, intrinsic fibres. (05 Mar 2000) |
| astral fibres | Fibre's (fibrils) radiating from the centrosphere toward the periphery of the cell as seen with a light microscope; revealed as microtubules under the electron microscope. Compare: kinetochore fibres, polar fibres. (05 Mar 2000) |
| augmentor fibres | Postganglionic sympathetic nerve fibre's originating in the superior, middle, and inferior cervical ganglia of the sympathetic trunk, conveying nervous impulses to the heart that increase the rapidity and force of the cardiac pulsations. Synonym: augmentor fibres. (05 Mar 2000) |
| autonomic fibres, postganglionic | Nerve fibres which project from cell bodies of autonomic ganglia to synapses on target organs. (12 Dec 1998) |