Igneous Rocks of Dark Color Are Generally Rich in the Chemical

question 27

Essay

Igneous rocks of dark color are generally rich in the chemical elements ____________________ and ____________________,while those of light color are generally rich in ____________________ and ____________________.

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Definitions:

Node of Ranvier

Gaps in the myelin sheath of nerve fibers where the axonal membrane is exposed, facilitating rapid signal conduction along the neuron.

Axon

The long extension of the neuron that transmits nerve impulses away from the cell body. Compare with dendrite.

Dendrite

A branched extension of a neuron that receives stimuli and conducts impulses toward the cell body.

Myelin Sheath

The fatty layer that surrounds and insulates the axons of some neurons, which enables faster transmission of electrical impulses.