We can learn about the past by studying the present.
The Principle of Uniformitarianism states that current geological processes are the same processes that were at work in the past. This principle was proposed by Charles Lyell in the 1800's
Absolute Dating
Involves finding the absolute age (actual age) of a rock or fossil.
Elements that emit particles and energy are radioactive.
As radioactive elements emit particles and energy, they form new isotopes or elements.
Acetylcholine is a chemical that is found between the nerve synapses, or gaps, between nerve cells. When activated, it causes the contraction of skeletal muscles and activates glandular functions in the endocrine system. Think of acetylcholine as a mailperson; residents cannot receive their mail until he or she comes and delivers it to the mailbox. Like mailpersons who deliver the mail and move on to the next house, acetylcholine acts quickly and does not hang around. As a result, acetylcholine is rapidly broken down by another chemical substance called cholinesterase.
Acetylcholine was the first neurotransmitter scientists discovered, as well as the most abundant neurotransmitter in the body. A neurotransmitter is a chemical that is released by a neuron, or nerve cell, that sends a signal to another neuron across a synapse. The neurotransmitter binds to receptors to affect how the signal is received. The purpose of the neurotransmitter is to either amplify or inhibit the signals sent between the neurons.
Acetylcholine plays an important role in the signal of muscle movement, sensation of pain, learning and memory formation, the regulation of the endocrine system and rapid eye movement (REM) sleep cycles.
