pathway

[path´wa] a course usually followed. In neurology, the nerve structures through which a sensory impression is conducted to the cerebral cortex (afferent pathway), or through which an impulse passes from the brain to the skeletal musculature (efferent pathway). Also used alone to indicate a sequence of reactions that convert one biological material to another (metabolic pathway).accessory pathway (accessory conduction pathway) extra muscle tissue between the atrium and ventricle that bypasses all or part of the normal system" >conduction system. When the ventricles are activated prematurely via this pathway, initial forces are slow, producing the delta wave of wolff-parkinson-white syndrome, and preexcitation is said to exist; the delta wave causes the PR interval to shorten and the QRS interval to broaden.alternative complement pathway see complement.amphibolic pathway a group of metabolic reactions with a dual function, providing small metabolites for further catabolism to end products or for use as precursors in synthetic, anabolic reactions. The cycle" >tricarboxylic acid cycle is an example. See also anabolism and catabolism.biosynthetic pathway the sequence of enzymatic steps in the synthesis of a specific end-product in a living organism.classical complement pathway see complement.coagulation p's see common p. of coagulation, extrinsic p. of coagulation, and intrinsic p. of coagulation.common pathway of coagulation the steps in the mechanism of coagulation (see clotting) from the activation of factor x through the conversion of fibrinogen to fibrin. See also pathway of coagulation" >intrinsic pathway of coagulation and pathway of coagulation" >extrinsic pathway of coagulation.concealed accessory pathway an pathway" >accessory pathway that has only retrograde conduction; thus its PR and QRS complexes are normal on the electrocardiogram, but there is a tendency to develop premature tachycardia" >supraventricular tachycardia. If fibrillation" >atrial fibrillation develops, conduction will proceed across the atrioventricular node.Embden-Meyerhof pathway the series of enzymatic reactions in the anaerobic conversion of glucose to lactic acid, resulting in energy in the form of adenosine triphosphate (ATP).extrinsic pathway of coagulation the mechanism that produces fibrin following tissue injury, beginning with formation of an activated complex between factor" >tissue factor and factor vii and leading to activation of factor x, which induces the reactions of the pathway of coagulation" >common pathway of coagulation. See also pathway of coagulation" >intrinsic pathway of coagulation.final common pathway 1. the motor neurons by which nerve impulses from many central sources pass to a muscle or gland in the periphery.2. any mechanism by which several independent effects exert a common influence.intrinsic pathway of coagulation a sequence of reactions leading to fibrin formation, beginning with the contact activation of factor xii. This is followed by the sequential activation of factors xi and ix, which results in the activation of factor x. Activated factor X (factor Xa) initiates the pathway of coagulation" >common pathway of coagulation. See also pathway of coagulation" >extrinsic pathway of coagulation.pentose phosphate pathway a pathway of hexose oxidation in which glucose-6-phosphate undergoes two successive oxidations by NADP, the final forming a pentose phosphate.

path·way

(path'wā), 1. A collection of axons establishing a conduction route for nerve impulses from one group of nerve cells to another group or to an effector organ composed of muscle or gland cells. 2. Any sequence of chemical reactions leading from one compound to another; if taking place in living tissue, usually referred to as a biochemical pathway.

pathway

(păth′wā′, päth′-)n. Physiology a. A course usually followed by a body part or process.b. A chain of nerve fibers along which impulses normally travel.c. A sequence of enzymatic or other reactions by which one biological material is converted to another.

pathway

The route by which a process occurs.

pathway

The route by which a thing occurs. See Critical pathway, Fifth pathway.

path·way

(path'wā) 1. A collection of axons establishing a conduction route for nerve impulses from one group of nerve cells to another group or to an effector organ composed of muscle or gland cells. 2. Any sequence of chemical reactions leading from one compound to another; if taking place in living tissue, usually referred to as a biochemical pathway.

pathway

any defined route followed by a series of reactions leading to a specific product, e.g. a biochemical pathway.

pathway

1. A collection of nerve fibres (axons) along which nervous impulses travel. 2. A path or a route.
geniculocalcarine pathway See optic radiations.
geniculostriate pathway 1. See optic radiations. 2. Some authors consider this term to be a synonym of visual pathway.
magnocellular pathway See system, magnocellular visual.
motor pathway Pathway from the cortex to the muscles that control the movements of the eyes enabling them to act as a unit.
parvocellular pathway See parvocellular visual system.
retinotectal pathway 1. The nervous pathway connecting the retina to the pretectal region (anterior to the superior colliculi) and from there to the Edinger-Westphal nucleus. It is involved in the pupillary light reflexes. 2. The nervous pathway between the retina and the superior colliculus. It is involved in the involuntary blink reflex to a dazzling light and in the eye movements occurring in response to the sudden appearance of a novel or a threatening stimulus. See blind sight; pupillary fibres; pupil light reflex; pretectum.
uveoscleral pathway An unconventional route through which the aqueous humour drains out of the eye. The aqueous passes from the anterior chamber across the iris root through small spaces between the ciliary muscle fibres into the supraciliary space and suprachoroid space. The fluid is believed to escape the eye via veins in the ciliary muscle and anterior choroid. The amount of aqueous outflow through this route amounts to between 10% and 15%, the rest flows out through the conventional pathway via the trabecular meshwork and into Schlemm's canal. Prostaglandin drugs reduce the intraocular pressure by increasing the outflow through the uveoscleral pathway. This pathway is occasionally made use of in cyclodialysis.
visual pathway Neural path starting in the photoreceptors of the retina and travelling through the following structures: the optic nerve, the optic chiasma, the optic tract, the lateral geniculate bodies, the optic radiations and the visual cortex where the pathway ends. The fibres of the optic nerve of one eye meet with the fibres from the other eye at the optic chiasma, where approximately half of them (the nasal half of the retina) cross over to the other side. Thus, there is semidecussation in the visual pathway (Fig. P3). See visual area; decussation; cortical magnification; retinotopic map.

" >

Fig. P3 Visual pathway and nerve fibres distribution (X, fixation point; F, fovea)

Table P2 Clinical manifestations of lesions in the visual pathway
site of lesion	clinical manifestations
macula	central scotoma
papillomacular bundle	central or centrocaecal scotoma
other part of the retina	scotoma on the opposite side of the central fixation point
complete section of one optic nerve	total blindness of that eye
	absence of direct light reflex
	presence of consensual light reflex
	other eye: normal pupil reaction, direct but not consensual
pituitary enlargement pressing on inferior part of chiasma	bitemporal hemianopia or bitemporal superior quadrantanopia
aneurysm pressing on lateral part of the chiasma	binasal hemianopia
sagittal section in the middle of the chiasma	bitemporal hemianopia normal pupil reflexes if light falls on temporal retina
optic tract	contralateral incongruous homonymous hemianopia
	Wernicke's pupillary reflex
lateral geniculate body	contralateral incongruous homonymous hemianopia
	normal pupil reflexes
anterior optic radiations on one side	contralateral incongruous homonymous hemianopia
	often sparing of the macula
	normal pupil reflexes
visual cortex on one side	contralateral congruous homonymous
	hemianopia
	often sparing of the macula
	normal pupil reflexes

path·way

(path'wā) 1. Collection of axons establishing conduction route for nerve impulses from one group of nerve cells to another or to an effector organ composed of muscle or gland cells. 2. Any sequence of chemical reactions leading from one compound to another.

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PATHWAY

pathway

Synonyms for pathway

noun a bundle of myelinated nerve fibers following a path through the brain

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noun a trodden path

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