gap junction

junction

 [jungk´shun]

a place of meeting or coming together. adj., adj junc´tional.

atrioventricular junction in the conduction system of the heart, the junction between the atrioventricular node and the nonbranching portion of the bundle of His.

cementoenamel junction the line at which the cementum covering the root of a tooth meets the enamel covering the crown.

gap junction a narrowed portion of the intercellular space, containing channels linking adjacent cells and through which can pass ions, most sugars, amino acids, nucleotides, vitamins, hormones, and cyclic AMP. In electrically excitable tissues the gap junctions serve to transmit electrical impulses via ionic currents and are known as electrotonic synapses; they are present in such tissues as myocardial tissue.

myoneural junction (neuromuscular junction) the site of junction of a motor nerve fiber and a skeletal muscle fiber that it innervates. The discoid expansion of the terminal branch of the axon forms the motor end plate, the neurotransmitter that diffuses across the synapse is acetylcholine.

sclerocorneal junction limbus (def. 2).

ureteropelvic junction the area where the renal pelvis meets the ureter.

Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

gap junc·tion

1. an intercellular junction formerly considered to be a tight, membrane-to-membrane junction (macula occludens) but now shown to have a 2-nm gap between apposed cell membranes; the gap is not void but contains subunits in the form of polygonal lattices, which are the intercellular aspects of the two connexons that fit together, forming a channel between the cytoplasms of the two cells; it occurs in epithelia, between certain nerve cells, and in smooth and cardiac muscle; it is believed to mediate electrotonic coupling, which allows ionic currents to pass from one cell to another.
See also: synapse.
See also: connexons.

2. areas of increased electrochemical communication between myometrial cells that aid in the propagation of the contractions of labor.
See also: connexons.

Synonym(s): communicating junction, electrotonic junction, electrotonic synapse, macula communicans, nexus

Farlex Partner Medical Dictionary © Farlex 2012

gap junction

n.

An intercellular network of protein channels that facilitates the cell-to-cell passage of ions, hormones, and neurotransmitters.

The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

gap junc·tion

(gap jŭngk'shŭn)

1. An intercellular junction having a 2-nm gap between apposed cell membranes; the gap contains subunits in the form of polygonal lattices; it occurs in epithelia, between certain nerve cells, and in smooth and cardiac muscle.
See also: synapse

2. Areas of increased electrochemical communication between myometrial cells that aid in the propagation of the contractions of labor.
Synonym(s): nexus.

Medical Dictionary for the Health Professions and Nursing © Farlex 2012

gap junction

a junction between animal cells which allows passage of material from one to the other.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

synapse 

The place where a nerve impulse is transmitted from one neuron to another. This transmission is usually mediated by neurotransmitters (e.g. acetylcholine, noradrenaline (norepinephrine), glutamate, etc.) that are released by the presynaptic neuron, then diffuse across the synaptic cleft (about 20-50 nm wide) to bind to receptor sites on the postsynaptic membrane and generate an electrical change in the postsynaptic neuron, which results in either depolarization (excitation) or hyperpolarization (inhibition). This is often referred to as a chemical synapse. There is another type of synapse called an electrotonic synapse (electrical synapse) in which electrical impulses are transmitted via ionic currents from one neuron to another by direct propagation across a gap junction (2-3nm wide). Electrotonic synapses are rare in vertebrates and have been found at only a few central nervous sites. It is estimated that a cortical neuron, for example, makes some 5000-10 000 synapses with surrounding neurons. See neuron; neurotransmitter; receptor potential.

Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann