Sinoatrial (SA) Node: A region of modified muscle cells in the right atrium that sends timed impulses to the hearts other muscle cells, causing them to contract; the hearts pacemaker.

 

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Sinoatrial (SA) Node: A region of modified muscle cells in the right atrium that sends timed impulses to the hearts other muscle cells, causing them to contract; the hearts pacemaker.

Nodes: The two points in a planet's orbit which intercept the Earth's path around the sun (otherwise known as the ecliptic).

Node Of Ranvier: A gap between two of the Schwann cells that make up an axons myelin sheath; serves as a point for generating a nerve impulse.

Node Factor (F): A factor depending upon the longitude of the Moon's node which, when applied to the mean coefficient of a tidal constituent, will adapt the same to a particular year for which predictions ar . . . View Full Definition

Palinode: An ode or song that retracts what the poet wrote in a previous poem: a recantation.

Reishi Mushroom (Ganoderma sinensis): An immunostimulant

Simian Immunodeficiency Virus (SIV): A virus that is found, in numerous strains, in primates.

Severe Combined Immunodeficiency (SCID): A genetic disorder in which affiicted individuals have no functional immune system and are prone to infections. Both the cell-mediated immune response and the antibody-mediated response are absent.

Node Cycle: Period of approximately 18.61 Julian years required for the regression of the Moon's nodes to complete a circuit of 360° of longitude. It is accompanied by a corresponding cycle of changing . . . View Full Definition

Planetary Node: The point at which a planet's path intersects the ecliptic; declination, 0°. The term is usually reserved for nodes other than the Moon's Nodes.