The Nervous System:


Invitation to Psychology, Carole Wade, Carol Tavris, Third Edition, page114
Invitation to Psychology, Carole Wade, Carol Tavris, Third Edition, page114
Invitation to Psychology, Carole Wade, Carol Tavris, Third Edition, page114

The nervous system consists of the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Within these systems are neurons and supporting cells. There are billions of neurons producing electrochemical impulses along with the supporting cells. As their name states, the supporting cells are helping the neurons and performing other specialized functions. These supporting cells are five times more abundant than neurons. Neurons have a basic structure of a cell body, dendrites and an axon.
Electrical activity in axons includes how the Na+ and K+ ions are able to get through the membrane, known as an action potential. The synapse is a connection between neurons and another cell. In the central nervous system the connection will be made with another neuron. In the peripheral nervous system the connection could be a neuron or an effector cell which could be within a muscle or gland.
Neurotransmitters have different chemicals contained in synaptic vesicles in nerve endings that are released into the synaptic cleft. The chemicals could be Acetylcholine, Dopamine, Norepinephrine, or Serotonin.




When we break down a neuron we have the cell body which is the larger portion of the neuron. It contains the nucleus and is considered the nutritional center of the neu
From Invitaion to Psychology, Third Edition, Carole Wade, Carol Tavris, Page115
From Invitaion to Psychology, Third Edition, Carole Wade, Carol Tavris, Page115

From Invitaion to Psychology, Third Edition, Carole Wade, Carol Tavris, Page115
ron because the macromolecules are produced here. In the CNS the cell bodies cluster together and are called nuclei. In the PNS the cell bodies cluster together and are called ganglia.
Dendrites, Greek meaning “tree branch”, are processes that extend from the cytoplasm of the cell body. They are a receptor that will transmit electrochemical impulses to the cell body.
The axon is a longer process which conducts the impulses—this is called action potential—away from the cell body. There is an area near the cell body called the axon hillock, this is where the action potential originates.



Classification of neurons can be either by the number of extensions that are coming from the cell body or by their function. To classify the neuron by function you look at which direction they conduct impulses. Examples: sensory neurons conduct impulses from its receptors into the CNS. Motor neurons conduct impulses out of the CNS to effector organs. When looking at the extensions coming from the neuron’s cell body, a neuron might have two processes call a bipolar neuron. Examples: retinal cells, olfactory epithelium cells. The cell body could have two axons rather than an axon and a dendrite. The one axon will extend centrally toward the spinal cord while the other axon extends toward the skin or muscle. This is called a pseudounipolar cell. Example: dorsal root ganglion cells. There is also a multipolar neuron with many processes that extend from the cell body. Each neuron will have only one axon. Examples: spinal motor neurons, pyramidal neurons, purkinje cells.
bipolar neuron
bipolar neuron

bipolar neuron

external image multipo.gif
external image multipo.gif


Pictures from Neuroscience for kids-cells of the nervous system, faculty.washington.edu



I found this video on the Schwann Cell, it also talks about the Myelin Sheath and its formation, describes the Action Potential, Nodes of Ranvier and compares the Myelinated sheath with the Nonmyelinated sheath. I thought it was very helpful. It is 5 minutes long but worth taking a look at. The Schwann Cell and Action Potential


Supporting Cells of the Nervous Systems:
Peripheral Nervous System:
  • Schwann Cells: cells that form the myelin sheaths around the myelinated axons of the PNS. They surround
all the axons both myelinated and nonmyelinated to form the sheath of Schwann.
  • Satellite Cells: also known as ganglionic gliocytes which support neuron cell bodies in the ganglia.
Central Nervous System:
  • Oligodendrocytes: form myelin sheaths around the central axons, producing white matter.
  • Microglia: perform phagocytosis and degenerate foreign material throughout the CNS.
  • Astrocytes: cover capillaries and induce the blood-brain barrier; interact and
modify exracellular environment of neurons.
  • Ependymal Cells: line the ventricles of the brain and central canal of the spinal cord. They also cover tufts
of capillaries to form choroid plexuses which are the structures that from cerebrospinal fluid.

Regeneration of a Cut Axon
When an axon is cut in a peripheral nerve, the distal portion of the axon will degenerate and phagocytosis is accomplished by Schwann Cells. A regeneration tube is formed by the Schwann cells and basement membrane by the axon that is connected to the cell body. As this grows it will exhibit amoeboid movement. It is believed that the Schwann cells of the regeneration tube secrete chemicals which attract the growing axon tip. This regeneration tube helps guide the regeneration axon to its proper destination. Central axons have a much more limited ability to regenerate than peripheral axons. There are inhibitory proteins within the membranes of the myelin sheaths in the CNS. There is also a glial scar that forms from astrocytes which prohibits regeneration of the axons in the CNS.

Here is a video on "What is Multiple Sclerosis". I though it would be a good idea to include this under regeneration. MS is a neurological disease that is more common in women between the ages of 20 and 40 years. It has a wider variety of symptoms than any other neurological disease, including: sensory impairments, motor dysfunction, bladder and intestinal problems, fatigue. The cause of MS is not understood but believed to involve a number of genes that affect a person's susceptibility to viruses which may trigger an immune attack on self-antigens therefore destroying the myelin sheaths.
<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/qgySDmRRzxY" frameborder="0" allowfullscreen></iframe>

Functions of Astrocytes:
Neuron: Astrocyte

Astrocyte - Astrocytes can be visualized in culture because they express glial fibrillary acidic protein.
Astrocyte - Astrocytes can be visualized in culture because they express glial fibrillary acidic protein.

Astrocyte - Astrocytes can be visualized in culture because they express glial fibrillary acidic protein.

Astrocytes can be visualized in culture because they express glial fibrillary acidic protein.
||
NeuroLex ID
sao1394521419
Dorlands/Elsevier
12165688
Picture from Wikipedia.com

Astrocytes are star-shaped glial cells in the central nervous system. They are also the most abundant glial cells in the CNS. Their ends are called end-feet which are used to surround capillaries. With the other extensions they have they are able to hold onto an axon terminal of one neuron and the dendrite of another neuron. With the ability to do this they become situated to influence the interactions between neurons and the blood.
They have several functions: they take up K+ from the extracellular fluid, take up some neurotransmitters released from the axon terminals of neurons, glucose is taken up from the end-feet which surround the blood capillaries, they are needed for the formation of synapses in the CNS, regulate neurogenesis n the adult brain, release transmitter chemicals that can stimulate or inhibit neurons.
Astrocytes also play a role in Blood-Brain Barrier. As defined in our text book: blood-brain barriers are structures and cells that selectively prevent particular molecules in the plasma from entering the central nervous system. It is believed that the Astrocytes can induce many of the characteristics including the tight junctions between endothelial cells, the production of carrier proteins and ion channels, and the enzymes that destroy potentially toxic molecules. They also influence the capillary endothelial cells by secreting neurotrophins. Then the endothelial cells secrete regulators that promote the growth and differentiation of astrocytes. The blood brain barrier is a dynamic structure. It also makes it harder to use chemotherapy on the brain because not all drugs can cross the brain barrier. With treatment of Parkinson’s Levodopa is given along with Dopamine because the Levodopa can penetrate the brain.



SYNAPSE:
According to our book, synapse is the junction across which a nerve impulse is transmitted from an axon terminal to a neuron, a muscle cell, or a gland cell either directly or indirectly (via the release of chemical neurotransmitters).

Types of Synapses:
Electrical—gap junctions:
Cells need to be equal in size and be joined by areas of contact with low electrical resistance to be electrically coupled. When the cells are electrically coupled they are joined together by a gap junction. These junctions are present in cardiac muscle allowing the muscle to stimulate and contract together, producing a strong contraction. Gap junctions are also found between the neurons of the brain this is where they synchronize firing of groups of neurons. They are also found between neuroglial cells, where they are believed to allow the passage of Ca2+, other ions and molecules between the connected cells. The function of the gap junctions is far more complex than scientists once thought.
Chemical:
Synapsis of the nervous system happens on a one-way pathway and occurs through the release of chemical neurotransmitters which start from presynaptic axon endings. These endings are called terminal boutons. There is a synaptic cleft that separates the terminal boutons and postsynaptic cell. To join the pre and post-synaptic membranes a cell adhesion molecule is present, this is a protein which projects from the membranes into the synaptic cleft. They then bond to each other. This is needed to keep the rapid chemical transmission going.
synapse.gif scienceblogs.compurpedantry/2007/03/neuron
synapse.gif scienceblogs.compurpedantry/2007/03/neuron
synapse.gif scienceblogs.compurpedantry/2007/03/neuron
Events in Excitatory Synaptic TransmissionPresynaptic neuron: Axon terminals: action potentials conducted by axon, opens voltage-gated Ca2+ channels, release of excitatory neurotransmitter. Postsynaptic Neuron: Dendrites and cell bodies: opens chemically (ligand) gated channels, inward diffusion of Na+ causes depolarization (EPSP), localized, decremental conduction of EPSP; Axon Hillock: opens voltage-gated Na+ and then K+ channels; Axon: conduction of action potential. Chart from our book, Human Physiology, Sturart Ira Fox, 12th Edition, page 182.


Neurotransmitters: Are chemicals which are contained in synaptic vesicles in nerve endings. These chemicals are released into the synaptic cleft, where they can cause the production of either an excitatory or an inhibitory postsynaptic potential. In the central nervous system there are a variety of chemicals in that function as neurotransmitters. Among these are Dopamine, Norepinephrine, and Serotonin. These molecules may have similar mechanisms of action but are used by different neurons in different functions.

Serotonin: is a monoamine neurotransmitter. It is derived from an amino acid, tryptophan. Serotonin is found in the gi tract, platelets and the central nervous system. It is used as a neurotransmitter by neurons with cell bodies located along the midline of the brain stem. It functions as a regulator of mood, appetite, sleep and muscle contractions. It also helps with memory and learning.

Dopamine: as a neurotransmitter plays a critical role in the control of movement. It stimulates the heart, circulation and the rate of metabolism. It is derived from a nonessential amino acid, tyrosine. Neurons that use dopamine as a neurotransmitter are called dopaminergic neurons. These are concentrated in the midbrain. If these dopaminergic neurons are destroyed Parkinson’s disease will develop.

Norepinephrine: is used as a neurotransmitter in the PNS and CNS. Neurons of the PNS use Norepinephrine to synapse with smooth muscles, cardiac muscle and glands. It can directly increase the heart rate, triggering glucose to be release from energy stores and increase the blood flow to the skeletal muscles. Neurons of the CNS seem to be involved with general behavioral arousal.

Nuerotransmitters.jpg schoolworkhelper.net
Nuerotransmitters.jpg schoolworkhelper.net
Nuerotransmitters.jpg schoolworkhelper.net


Application:
Experts say that Guillain-Barre syndrome is a relatively rare disease which affects the peripheral nervous system. The body’s own immune system attacks the nerves. The first symptoms are weakness and numbness in the extremities. The sensations can quickly spread through the whole body paralyzing the patient.
With working in the clinic and with Dr. Dan, we have had patients who have had symptoms of weakness, tingling in their fingers, toes and up into their legs. Usually the symptoms appear bilateraly not just on one side or the other. We had a patient that came in complaining of tingling in his fingers and toes. Dr. Dan had his suspisions but waited and had the patient return the next day. He was worse, his gate had changed with weakness moving up into his legs and hips. Needless to say Dr. Dan was on the phone right away with the neurologist in Sioux Falls and the patient was sent there to be hospitalized. He did not have to go by ambulance but he did need to have more testing done and started on some medication. I do not remember for sure what labs Dr. Dan did but I’m sure he would have started with a CBC to see what his white counts were. I do not know what all was done in Sioux Falls with this patient but he did have this disease. This is the second patient I can remember since I have been working with Dr. Dan, the last 5 years that was diagnosed with Guillain-Barre syndrome. We have had others with the same type symptoms but they did not have Guillain-Barre. One of the questions we ask when we are about to give a flu shot is if the patient has a history of having Guillain-Barre. Could the flu shot be increasing the number of cases we are seeing of this disease? This might give people another reason to stop and think about getting a flu shot each year.




Case Study on the Nervous System: The Soccer Mom:http://sciencecases.lib.buffalo.edu/cs/results.asp?search=soccer+mom

Part I---At the Soccer Game:
1) What problems does Phyllis seem to be experiencing?
Answer: Phyllis seems to be having problems with lack of concentration, irritability, forgetting things, like picking up her children from school, fainting spells, being unfocused and disoriented.
2) Which of these problems could be caused by dehydration?
Answer: Dehydration could be the cause of Phyllis’ irritability and confusion.
3) Which of these problems might make you consider that there's something more going on? Why?
Answer: What would make me think that there is more going on is the fact that she is having trouble with her memory and being more confused. Her husband isn’t the only one to notice changes in her and things have happened more than once.
4) Suppose Phyllis does have a more serious problem. Can you think of any neurological problems that could be the cuase of these symptoms?
Answer: The one problem that comes to mind is that she may have a brain tumor and it is pressing on areas that control her memory. With her symptoms and how they come and go would also make me think of MS.

Part II---The Doctor Visit:
1) What new signs or symptoms have been revealed?
Answer: Phyllis admits that she has also been having trouble with her coordination, having numbness in her fingers and feeling more fatigued.
2) Could any of Phyllis's symptoms be attributed to depression? If so, which?
Answer: People who have depression also may have symptoms of being irritable, have trouble concentrating and feel more fatigued.
3) What neurotransmitters are thought to be involved in depression?
Answer: Depression, anxiety and other mood disorders are thought to be directly related to imbalances with neurotransmitters. Hormones, brain chemicals and neurotransmitters have a major influence on our health. They help to regulate emotional processes such as mental performances, emotional states and pain responses. The four main neurotransmitters are: Serotonin--which is inhibitory, the most common and is the key to our feelings of happiness. Dopamine--is motivation, interest drive, if not enough we will have poor concentration and no energy. GABA, Gamma Amino Butyric Acid, is inhibitory, helps neurons recover after transmission, reduces anxiety and stress. Norepinephrine--is excitatory, with increased levels a person will be more anxious and stressed. With lower levels a person will have less energy and find it harder to focus and be motivated.
4) What neurological disorders could have put her grandfather in a wheelchair?
Answer: MS, Transverse Myelitis, ALS--Amyotrophic Lateral Sclerosis
5) Could any of these neurological disorders explain one or more of Phyllis' symptoms?
Answer: Yes, with her symptoms of fatigue, coordination being off, disoriented, numbness in fingers, lack of concentration and the fact that these symptoms come and go could be signs of MS.
6) Could Phyllis have inherited any of these disorders?
Answer: With MS it could have some genetic possibilities along with a virus, and environmental factors.
7) If you were in Dr. Warner's position, what tests might you suggest to confirm (or not) this diagnosis?
Answer: She should have an eye exam done to check for any changes in visual field. Spinal tap to test the cerebrospinal fluid and an MRI of her brain and spine to look for any abnormalities.


Part III---Diagnostic Tests:
1) Test your knowledge of the function of chemical synapses by filling in the flow diagram. See below
2) What type of cell is myelin?
Answer: outgrowth of glial cells.
3) What is the function of myelin in nerve cells?
Answer: It helps to increase the speed at which the impulses are traveling.
4) In myelinated axons, where are action potentials generated:
Answer: they are generated at the axon hillock.
5) Where, then, are voltage gated sodium channels concentrated in myelinated axons?
Answer: they are along the Nodes of Ranvier.
6) What happens to myelin in people who suffer from multiple sclerosis?
Answer: The myelin is being destroyed by the person’s own body, leukocytes are starting the inflammation process in the white matter, and plaque is beginning to build up on the axons.
7) Why is there an elevated level of myelin basic protein in the cerebrospinal fluid?
Answer: There is myelin in the spinal fluid because of it being broken down in the central nervous system.
8) What would be the effect on action potential conduction at a region of axon where the disease had its effect?
Answer: With the myelin sheath being gone, current from the initial action potential will not be able to spread far enough to affect the region of the axon where the gated channels are found.
9) What effect would this have on the coordination of movements if this took place in areas involved in control of finger movements?
Answer: The arms, hands, fingers will have stiffness, muscle weakness, tremors, loss of coordination. It will become very hard to pick anything up.

Part IV---The Diagnosis
1) During remission, axons affected by the disorder regain their function. If voltage-gated sodium channels are concentrated in certain regions of the myelinated axon prior to the disease, what do you think happens to these sodium channels after multiple sclerosis has had its effect?
Answer: Sodium channels are needed in greater numbers after there has been damage done to the myelinated sheath and axons. The sodium channels help to restore the action potential conduction, which contributes to remission in a patient with MS.
2) How would these three treatments (physical therapy, weekly injections of interferon beta, and corticosteroids) help to control Phyllis’s symptoms?
Answer: Physical therapy is needed to keep bones and muscles strong, helps to keep flexibility of the muscles also. The injection of Interferon Beta helps to slow the progression of physical disability. Has been noted to help with decreasing the frequency of clinical exacerbation. Corticosteroids are used to reduce inflammation of the brain and spinal cord during sudden attacks.



An action potential in an excitatory presynaptic nerve.
An axodendritic synapse in the dendrites of the postsynaptic nerve.
This spreads passively to the postsynaptic neuron.
Depolarization of this region opens voltage-gated Na+ channels.
Sufficient membrane depolarization to K+ channels open enough of these channels to produce an action potential.
Non-myelinated axon:
The currents associated with the action potential spread to the adjacent region of the axon
Myelinated axon:
The currents associated with the action potential spread to the next axon.
The action potential travels down the axon to the axon terminals.



The information for this section came from our book Human Physiology, 12th edition, Stuart Ira Fox, Anatomy & Physiology for Dummies, Donna Rae Siegfried, Wiley Publishing, Inc. WEBMD.com, integrativepsychiatry.net, PubMed Health.com, righthealth.com, Mayoclinic.com, internal.psychology.illinois.edu/~etaylor4/ne, Saunders Nursing Drug Handbbook 2009 and other sites that are noted by the pictures and video clips.

FYI: I had a very hard time with this page because of editing issues. No not sure how this page is going to look once I save it for the last time. Glad it is done! Susan