SA (sinoatrial) node
The pacemaker of the heart, located in the wall of the right atrium. At the base of the wall
separating the two atria is another patch of nodal tissue called the atrioventricular node
(AV).
Sacral
Of, near, or relating to the sacrum.
Saltatory conduction
Rapid transmission of a nerve impulse along an axon resulting from the action potential
jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of
membrane.
Saprobe
An organism that acts as a decomposer by absorbing nutrients from dead organic matter.
Sarcolemma
The specialized plasma membrane surrounding a muscle cell (muscle fiber); capable of
propagating action potentials.
Sarcomere
The fundamental, repeating unit of striated muscle, delimited by the Z lines.
Sarcoplasmic reticulum
A modified form of endoplasmic reticulum in striated muscle cells that stores calcium used
to trigger contraction during stimulation.
Satellites
In genetics, a knob of chromatin connected by a stalk to the short arm of certain
chromosomes.
Saturated fatty acid
A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus
maximizing the number of hydrogen atoms that can attach to the carbon skeleton.
Savanna
A tropical grassland biome with scattered individual trees, large herbivores, and three
distinct seasons based primarily on rainfall, maintained by occasional fires and drought.
Schizocoelus
The type of development found in protosomes. Initially solid masses of mesoderm split to
form coelomic cavities.
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