Sympathetic division
One of two divisions of the autonomic nervous system of vertebrates; generally increases
energy expenditure and prepares the body for action.
Sympatric speciation
A mode of speciation occurring as a result of a radical change in the genome that produces a
reproductively isolated subpopulation in the midst of its parent population.
Symplast
In plants, the continuum of cytoplasm connected by plasmodesmata between cells.
Synapomorphies
Shared derived characters; homologies that evolved in an ancestor common to all species
on one branch of a fork in a cladogram, but not common to species on the other branch.
Synapse
The locus where one neuron communicates with another neuron in a neural pathway; a
narrow gap between a synaptic terminal of an axon and a signal-receiving portion (dendrite
or cell body) of another neuron or effector cell. Neurotransmitter molecules released by
synaptic terminals diffuse across the synapse, relaying messages to the dendrite or effector.
Synapsis
The pairing of replicated homologous chromosomes during prophase I of meiosis.
Synaptic cleft
A narrow gap separating the synaptic knob of a transmitting neuron from a receiving
neutron to an effector.
Synaptic knob
The relay point at the tip of a transmitting neuron's axon, where signals are sent to another
neuron or to an effector.
Synaptic terminal
A bulb at the end of an axon in which neurotransmitter molecules are stored and released.
Syncarpous
Having or consisting of united carpels. Used of a pistil.
Syncytial
Multinucleate mass of cytoplasm resulting from the fusion of cells.
Syngamy
The process of cellular union during fertilization.
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