The Nervous System

Cells of the Nervous System


THERE IS NOTHING LIKE THE BRAIN






Cells of the Nervous System

Parts of the Brain

The Nervous System

Here is a diagram of the way the nervous system can be broken down;
           The nervous system is made up the central nervous system and the peripheral nervous system.  The CNS consists of the brain and the spinal cord. The PNSconsists of all the nerves outside of the brain and the spinal cord.  Specifically, it consists of the autonomic nervous system and the somatic nervous system.

The Autonomic Nervous System

          


First, the
autonomic nervous system regulates the internal environment in an individual and controls functions that can be inhibited to provide or conserve energy appropriate to the environmental needs of the person.  This system is involuntary.  It is important to note that control of the body’s internal environment is not an all-or-none affair. In order to maintain the balance we have two divisions of the autonomic nervous system; the sympathetic division, and the parasympathetic division.
The sympathetic nervous system kicks into gear when energy expenditure is necessary (ex: during times of stress or excitement).  Because of this, it has earned the nickname the “fight or flight response”.  This system can do things such as increase heart rate and blood pressure, stimulate secretion of adrenaline, and increase blood flow to skeletal muscles.
The parasympathetic nervous system returns our body back to homeostasis. It kicks in when energy reserves can be conserved and saved for later use.  This system is capable of increasing salivation, digestion, and storage of glucose and it can slow down heart rate as well as decrease respiration.

The Somatic Nervous System

Second, the somatic nervous system consists of motor nerves and sensory nerves.  Motor nerves send movement signals to the body to create motor movements.  Sensory nerves receive information from the body (senses) to send to the brain. Basically, they convert the physical stimuli around us into electrical signals and transmit that information to our brain.

The Neuron


"Neuron" is just another way of saying “nerve cell.”  The important parts and occurences of the neuron are the nucleus, cell body, dendrite, axon, myelin sheath, terminal button, and the synapse. The nucleus is located in the cell body. It contains genetic material and is responsible for the functioning part of the rest of the nerve cell. The cell body (sometimes referred to as the soma) is the part of the neuron that encompasses and maintains the nucleus and other organelles. The dendrites are the many short extensions on the cell body.  They have sensory receptor sites that receive signals from other neurons. The axon is the long skinny portion of the neuron that conducts its electrical impulses.  From here they go to the terminal buttons and then into the synapse. The myelin sheath is the protective encasement around the axon of the neuron. It insulates the axon and facilitates the regeneration of its fibers. (This functions like the coating on the outside of an electrical wire. It allows the signal to travel through the neuron faster, and it stops any other signals traveling through nearby neurons from interfering.) The terminal buttons (sometimes referred to as the axon terminal) are the tips of the branch like endings of the axons.  The electrical signal is released from here. The synapse is the space between the sending neuron (presynaptic cell) and the receiving neuron (postsynaptic cell).  This is where neurotransmitters hang out until they are sucked up by receptors on the postsynaptic cell.

Neurotransmitters


Serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter in the brain that has an enormous influence over many brain functions. It is synthesized, from the amino acid L-tryptophan, in brain neurons and stored in vesicles. Serotonin is found in three main areas of the body: the intestinal wall; large constricted blood vessels; and the central nervous system. The most widely studied effects have been those on the central nervous system. The functions of serotonin are numerous and appear to involve control of appetite, sleep, memory and learning, temperature regulation, mood, behavior (including sexual and hallucinogenic behavior), cardiovascular function, muscle contraction, endocrine regulation, and depression.

Communication of information between neurons is accomplished by movement of chemicals across a small gap called the synapse. Chemicals, called neurotransmitters, are released from one neuron at the presynaptic nerve terminal. Neurotransmitters then cross the synapse where they may be accepted by the next neuron at a specialized site called a receptor. The action that follows activation of a receptor site may be either depolarization (an excitatory postsynaptic potential) or hyperpolarization (an inhibitory postsynaptic potential). A depolarization makes it more likely that an action potential will fire; a hyperpolarization makes it less likely that an action potential will fire.

There are many types of chemicals that act as neurotransmitter substances. Below is a list of some of them.

Small Molecule Neurotransmitter Substances
Acetylcholine (ACh) Dopamine (DA) Norepinephrine (NE)
Serotonin (5-HT) Histamine Epinephrine

Amino Acids
Gamma-aminobutyric acid (GABA) Glycine Glutamate
Aspartate

Transport and Release of Neurotransmitters
Neurotransmitters are made in the cell body of the neuron and then transported down the axon to the axon terminal. Molecules of neurotransmitters are stored in small "packages" called vesicles. Neurotransmitters are released from the axon terminal when their vesicles "fuse" with the membrane of the axon terminal, spilling the neurotransmitter into the synaptic cleft. Neurotransmitters will bind only to specific receptors on the postsynaptic membrane that recognize them.
The action of neurotransmitters can be stopped by four different mechanisms:
1. Diffusion: the neurotransmitter drifts away, out of the synaptic cleft where it can no longer act on a receptor.
2. Enzymatic degradation (deactivation): a specific enzyme changes the structure of the neurotransmitter so it is not recognized by the receptor. For example, acetylcholinesterase is the enzyme that breaks acetylcholine into choline and acetate.
3. Glial cells: astrocytes remove neurotransmitters from the synaptic cleft.
4. Reuptake: the whole neurotransmitter molecule is taken back into the axon terminal that released it. This is a common way the action of norepinephrine, dopamine and serotonin is stopped...these neurotransmitters are removed from the synaptic cleft so they cannot bind to receptors.

Study Tools

Nervous System PowerPoint
Answer key for the labeling worksheet
Short answer/matching answer key

Want to know more?

Nervous system disorders
Diagnostic tests for nervous system disorders

Fun Links

plushie neuron
serotonin necklace
BBC's neuron game

Works Cited

BBC, (2008). Nervous System - Nerve Cells and Nerves. Retrieved May 4, 2009, from Science & Nature: Human Body & Mind Web site:http://www.bbc.co.uk/science/humanbody/body/factfiles/nervecellsandnerves/nerve_cells_and_nerves.shtml
Chudler, Eric H. (2008). Neurotransmitters and Neuroactive peptides. Retrieved May 4, 2009, from Neuroscience For Kids Web site:http://faculty.washington.edu/chudler/chnt1.html
Draper, M. (2008). UT/College/School/BIO365R/Documents/About/Additional Science Notes Message posted tohttp://www.utexas.edu/courses/bio365r/documents/about/about.php
Mader. S. S. (Ed.). (2008). Human Biology. (10th ed). New York: McGraw-Hill.
Merriam-Webster. (2008). Central Nervous System. Retrieved May 2, 2009, from Merriam-Webster Visual Dictionary Online Web site:http://visual.merriam-webster.com/human-being/anatomy/nervous-system/central-nervous-system_1.php
Meyer. J. S & Quenzer. L. F. (2005). Psychopharmacology: Drugs, the Brain, and Behavior. Sunderland, MA: Sinauer Associates, Inc.
Nevid. J. S, Rathus. S. A, & Greene. B.. (Ed.). (2006). Abnormal Psychology in a Changing World. (Vol. 6th Ed). Upper Saddle River, NJ: Prentice Hall.
Pedersen, D. D. (2008). Psych Notes: Clinical Pocket Guide. (2nd Ed,). Philidelphia: F. A. Davis Company.
Rush University Medical Center. (2008). Overview of Nervous System Disorders. Retrieved May 4, 2009, from Rush University Medical Center Web site: http://www.rush.edu/rumc/page-1098987329209.html
Wade. C. & Tavris. C. (Ed.). (2003). Psychology. (7th ed). Upper Saddle River, NJ: Prentice Hall.

Axonal Signaling.
In order for a neuron to "fire" it must go from -65mV to -50mV.
If -50mV is reached, the cell well send an action potential from the cell body to the axon terminal.  

Once the action potential reaches the axon terminal, a neurotransmitter is released.

Each neuron is specialized for 1 type of neurotransmitter.
Neurotransmitters may be excitatory and cause the next cell to be positive, or inhibitory and cause the next cell to be negative.  

If negative, the next cell is less likely to fire because it is further away from the -50mV threshold.
If positive, then the next cell is more likely to send an action potential.

Input is determined by number of signals and how close they are to the cell body (soma).



Subpages (1): Sensation and Perception
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