| polar presentation | The presentation of either pole of the foetal oval; may be either a cephalic or breech presentation, or a longitudinal lie. (05 Mar 2000) |
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| polar ring | A thickened, electron-dense ring at the anterior end of certain stages of the Apicomplexa; part of the apical complex characteristic of these sporozoans. (05 Mar 2000) |
| polar solvents | Solvent's that exhibit polar forces on solutes, due to high dipole moment, wide separation of charges, or tight association; e.g., water, alcohols, acids. (05 Mar 2000) |
| polar star | One of the figures forming the diaster. Synonym: polar star. (05 Mar 2000) |
| polar zone | The region in the vicinity of an electrode applied to the body. See: electrotonus. (05 Mar 2000) |
| electro-polar | <physics> Possessing electrical polarity; positively electrified at one end, or on one surface, and negatively at the other; said of a conductor. Source: Websters Dictionary (01 Mar 1998) |
| zinco-polar | <physics> Electrically polarized like the surface of the zinc presented to the acid in a battery, which has zincous affinity. Source: Websters Dictionary (01 Mar 1998) |
| law of polar excitation | A given segment of a nerve is irritated by the development of catelectrotonus and the disappearance of anelectrotonus, but the reverse does not hold; i.e., excitation occurs at the cathode when the circuit is closed and at the anode when it is opened. Synonym: Pfluger's law. (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) |