Neuroscience Basics: The Neuron
What is a Neuron?
Neurons are a special type of cell which make up vast networks of the nervous system. The brain contains roughly 100 billion neurons that are continually communicating with each other while forming complex circuits across one's life. Unlike blood cells or tissue cells, neurons are asymmetrical in structure with far reaching processes. In the image above, you might notice that it resembles a tree with extending branches. It uses these branches to reach out and "talk" to other nerve cells using electrochemical signaling. The more activity that occurs between them, the stronger their bonds become allowing us to think, feel, move and sense the world around us.
Morphology of Nerve Cells
Structure & Function
- Soma (Cell Body) - The spherical aspect of the neuron containing the nucleus and other organelles. The nucleus contains DNA and is responsible for manufacturing proteins that make up neurotransmitters and hormones.
- Dendrite - Branches connected to the soma that receive information from other neurons. They operate as the neurons "antennae" and are covered in numerous synapses.
- Synapse - Junctions that bridge the gap between other neurons. There are two types of synapses, electric and chemical. Electric synapses transmit electrical impulses whereas chemical synapses communicate signals using neurotransmitters. Synapses serve a purpose in modulating, inhibiting or exciting signal transfer between axon terminals and dendrites.
- Axon - The main conducting portion of the neuron that can communicate signals between the brain and across large spans of the body.
- Myelin Sheath - Outer portion of the axon branch composed of Schwann Cells. This layer covers the fibers outside the brain and spinal cord. It provides insulation and improves conduction of electrical impulses. (quicker firing).
- Axon Terminal - A small point in which impulses and neurotransmitters are released from the axon to the dendritic branches of neighboring nerve cells.
Definitions & Common Neurotransmitters
As mentioned earlier, neurotransmitters do different things. To clarify, let's define some of the terminology.
Excitatory - Increases the probability of an action potential (signal firing)
Inhibitory - Decreases the probability of an action potential.
Modulatory - Regulation of electric or chemical release between neurons. Can be both excitatory and inhibitory depending on the surrounding influences.
*Keep in mind that inhibitory signals can also serve an excitatory function by stalling specific neurotransmitters that are inhibitory by nature. The same is true for excitatory signaling for neurotransmitters that are inhibitory.
- Acetylcholine (Excitatory) - Stimulates muscle movement, learning and memory. Plays a large role in involuntary reflexes such as digestion.
- Gamma aminobutyric acid/GABA (Inhibitory) - Reduces the cadence in which action potentials are fired therefore dampening the effects of anxiety and stress.
- Dopamine - (Exitatory) - Provides reward and positive affects (emotions). Part of the seeking/expectancy mechanisms in the brain that propel us forward in search of novel experiences or sustenance. Dopamine is produced in large quantities after using stimulants such as cocaine, nicotine, caffeine and amphetamines.
- Serotonin (Modulatory) - Stabilizes mood by counter-balancing excess or deficient affective neurochemicals . Regulates appetite, sleep, and pain. Deficiency of serotonin is also associated with immune dysfunction.
- Norepinephrine (Excitatory) - Commonly known as a stress hormone. Increases heart rate, blood pressure and the release of glucose (sugar) from energy stores. Diverts blood flow from digestion to muscle tissues.
- Glutamate (Excitatory) - The most common excitatory neurotransmitter. Found in nearly 50% of all brain cells. Strongly increases stimulation of action potentials. In large quantities, glutamate can actually be toxic to neurons.
Sensory Neurons - Move signals from the outer portion of the body to the central nervous system (brain/spinal cord)
Interneurons - Links various neurons together between the brain and spinal cord.
Motor Neurons - Move signals from the CNS back to the outer portions of the body. i.e. skin, muscles, glands.
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PubMed (2017) Neurons & Neurotransmitters. U.S. National Library of Medicine. Retrieved from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMHT0024269/
© 2017 Jessie Watson