Description
In this collection, we will go over The Nervous System talking about the General functions of the CNS, Generation and propagation of an action potential, The Peripheral Nervous System, The Sympathetic and Parasympathetic Systems, Nervous Tissue, The Limbic System and Higher Mental Functions.
This collection is important to all medical students
Study Set Content:
Human Physiology/The Nervous System
21
Because different nerves are affected at different times, MS symptoms often worsen (exacerbate), improve, and
develop in different areas of the body. Early symptoms of the disorder may include vision changes (blurred vision,
blind spots) and muscle weakness. MS can progress steadily or cause acute attacks (exacerbations) followed by
partial or complete reduction in symptoms (remission). Most patients with the disease have a normal lifespan.
There are different types of MS
Multiple sclerosis is classified according to frequency and severity of neurological symptoms, the ability of the
CNS to recover, and the accumulation of damage.
Treating Depression
Every now and then we all feel a little blue, these feelings can be caused by losing a loved one. Clinical depression
goes much further than just feeling down. Depression has many symptoms, including lack of energy, abnormal
eating habits (either too much or too little) and sleeping problems (also too much or too little). Often a person can
feel worthless and have thoughts of committing suicide. The cause of depression and its symptoms are a mystery but
we do understand that it is an illness associated with biochemical changes in the brain. A lot of research goes on to
explain that it is associated with a lack of amines serotonin and norephinephrine. Therefore pharmacological
treatment strategies often try to increase amine concentrations in the brain.
One class of antidepressants is monoamine oxidase inhibitors. Mono amine oxidase is a enzyme that breaks down
your amines like norephinephrine and serotonin. Because the antidepressants inhibit their degradation they will
remain in the synaptic cleft for a longer period of time making the effect just as if you had increased theses types of
neurotransmitters.
A newer class of antidepressants is selective serotonin reuptake inhibitors (SSRI's). With SSRI's decreasing the
uptake of serotonin back into the cell that will increase the amount of serotonin present in the synaptic cleft. SSRI's
are more specific than the monoamine oxidase inhibitors because they only affect serotonergic synapses. You might
recognize these SSRI's by name as Prozac and Paxil.
Human Physiology/The Nervous System
22
Drugs
A drug is, generally speaking, any substance that changes the way your body works. Some drugs have a medicinal
effect, and some are used recreationally. They have diverse effects, depending on the drug. Drugs can do anything
from diminish pain, to preventing blood clots, to helping a depressed person.
Different drugs work in different ways, called the mechanism of action, the drugs covered here will all act on the
nervous system via receptors on different neurons. There are also drugs that change how enzymes work, but that's
not part of the nervous system (at least directly) and will not be discussed here.
You've probably heard the terms stimulant (excitatory) and depressant (inhibitory). This is a broad way of classifying
drugs that work on the CNS. Depressants slow down neural function, and stimulants speed it up.
Most of the common depressants (including alcohol, benzodiazepines, barbiturates and GHB) work on GABA
receptors, although there are others. Opiates, for example, work on mu opioid receptors and also produce inhibitory
effects, and some antipsychotics block serotonin. See the alcohol section below to see one way this can work.
Stimulants work mostly with epinephrine, dopamine or serotonin (or a combination of them). Many of them either
mimic one, or stop them from leaving the synapse, causing more action potentials to be fired. Methamphetamine,
discussed below, is a fairly typical stimulant drug.
Drug Abuse
Scientists have long accepted that there is a biological basis for drug addiction, though the exact
mechanisms responsible are only now being identified. It is believed that addictive substances
create dependence in the user by changing the brain's reward functions, located in the mesolimbic
dopamine system
—
the part of the brain that reinforces certain behaviors such as eating, sexual
intercourse, exercise, and social interaction. Addictive substances, through various means and to
different degrees, cause the synapses of this system to flood with excessive amounts of dopamine,
creating a brief rush of euphoria more commonly called a "high
”
. Some say that abuse begins when the user begins
shirking responsibility in order to afford drugs or to have enough time to use them. Some say it begins when a person
uses "excessive" amounts, while others draw the line at the point of legality, and others believe it amounts to chronic
use despite degenerating mental and physical health in the user. Some think that any intoxicant consumption is an
inappropriate activity. Here are some drugs that are abused frequently: Acid/LSD, Alcohol, various tryptamines and
phenethylamines, Cocaine, Ecstasy/MDMA, Heroin, Inhalants, Marijuana, Methamphetamine, PCP/Phencyclidine,
Prescription Medications, Smoking/Nicotine and Steroids.
Alcohol
Alcohol is, and has been for thousands of years, one of the most commonly used drugs in the world. It is legal, with
some restrictions and exceptions, nearly everywhere. It is a common misconception that somehow alcohol is 'better'
or 'safer' than other recreational drugs. This is simply NOT the case. Alcohol is a depressant, and as such it has the
potential to cause coma, respiratory depression/arrest and possibly death. Compared with some other (illegal in most
places) drugs of recreational value (such as marijuana, serotonin based hallucinogens like LSD or psilocybin)
alcohol is far more toxic and has more risk of overdose. That doesn't mean that moderate drinking will probably hurt
you, though, either.
Short term effects from drinking (listed roughly as they appear, and as dosage goes up) are: decreased inhibitions and
thusly judgment, flushing of the face, drowsiness, memory problems begin, severe motor impairment, blurry vision,
dizziness, confusion, nausea, possible unconsciousness, coma, death (due to respiratory arrest or possibly aspiration
on vomit).
Alcohol produces these effects mainly via the GABA receptors in the brain. When GABA (or in this case alcohol)
binds to it's receptor, it lets either Cl- ions in, or K+ out. This is called hyperpolarization, or an inhibitory
Human Physiology/The Nervous System
23
postsynaptic potential (IPSP). It makes it harder for the neuron to depolarize and hence harder for it to fire an action
potential, slowing neural function. At higher doses alcohol will start to block NMDA. NMDA is involved in memory
(see the long-term potentiation section) so this is thought to account for memory blackouts.
Methamphetamine
In the US, medically prescribed
methamphetamine
is distributed in tablet form under the brand name Desoxyn®,
generally for Attention Deficit Hyperactivity Disorder (ADHD) but also for narcolepsy or obesity.
Illicit methamphetamine comes in a variety of forms. Most commonly it is found as a colorless crystalline solid, sold
on the street under a variety of names, such as: crystal meth or crystal. Methamphetamine may also be referred to as
shards, rock, pony, crissie, crystal, glass, ice, Jib, critter, Tina, tweak or crank. Dope may refer to methamphetamine
or other drugs, especially heroin or marijuana. The term "speed" can denote any stimulant including other
amphetamines (e.g. adderall), cocaine and methylphenidate (Ritalin).
Methamphetamine can be injected (either subcutaneous, intramuscular or intravenous), smoked, snorted, swallowed,
or used rectally or sublingually. The latter two being fairly uncommon. After administration, methamphetamine
takes from a few seconds (smoked or injected IV) to around 30 minutes (oral) for effects to arise, lasting around
eight hours depending on the route of administration. Effects/side effects include euphoria, anorexia, increased
energy, clenching of the jaw/grinding of teeth (bruxism), weight loss, insomnia, tooth decay and psychosis among
others.
Methamphetamine is neurotoxic to at least some areas of the brain, and owes most of it's effects to the
neurotransmitters dopamine, norepinephrine and serotonin it releases. It also blocks the reuptake of those
neurotransmitters, causing them to stay in the synaptic cleft longer than normal.
Human Physiology/The Nervous System
24
Marijuana
Cannabis sativa.
Marijuana contains a myriad of chemicals, called
cannabinoids, that have psychoactive and medicinal
effects when consumed, the major one being
tetrahydrocannabinol (THC). THC serves to mimic the
endogenous neurotransmitter anandamide (also found in
chocolate) at the CB
1
receptors in the brain. Other
cannabinoids include Cannabidiol (CBD), cannabinol
(CBN) and tetrahydrocannabivarin (THCV). Although
THC is found in all parts of the plant, the flower of the
female plant has the highest concentration, commonly
around eight percent. The flowers can be used, or they
can be refined. Trichomes contain most of the THC on
the flowers and can be removed by a few different
methods. These removed trichomes are called kief. Kief
can, in turn, be pressed into hashish. By far the most
common way to consume any of these products is by
smoking, but it can be taken orally as well.
Cannabis has a very long, very good safety record.
Nobody on record has ever died because of marijuana,
directly at least. It is estimated that it would take 1-1.8
kilograms of average potency marijuana, taken orally, to
have a fifty percent chance of killing a 68kg human.
Despite this, the possession, use, or sale of psychoactive
cannabis products became illegal in many parts of the
world in the early 20th century. Since then, while some countries have intensified the enforcement of cannabis
prohibition, others have reduced the priority of enforcement to the point of de facto legality. Cannabis remains illegal
in the vast majority of the world's countries.
The nature and intensity of the immediate effects of cannabis consumption vary according to the dose, the species or
hybridization of the source plant, the method of consumption, the user's mental and physical characteristics (such as
possible tolerance), and the environment of consumption. This is sometimes referred to as set and setting. Smoking
the same cannabis either in a different frame of mind (set) or in a different location (setting) can alter the effects or
perception of the effects by the individual. Effects of cannabis consumption may be loosely classified as cognitive
and physical. Anecdotal evidence suggests that the Cannabis sativa species tends to produce more of the cognitive or
perceptual effects, while Cannabis indica tends to produce more of the physical effects.
Human Physiology/The Nervous System
25
Review Questions
Answers for these questions can be found here
1. The junction between one neuron and the next, or between a neuron and an effector is called:
A ) A synapse
B ) A dendrite
C ) A neuotransmitter
D ) A ventricle
E ) None of the above
2. A fast excitatory synapses follows this order:
A ) (1) neurotransmitter released (2) diffused across the synaptic cleft to a receptor protein (3) binding of the
transmitter opens pores in the ion channels and positive ions move in.
B ) (1) neurotransmitter released (2) diffused across the synaptic cleft to a receptor protein (3) binding of the
transmitter opens pores in the ion channels and negative ions move in.
C ) (1) neurotransmitter released (2) diffused across the synaptic cleft to a receptor amino acid (3) binding of
the transmitter opens pores in the ion channels and positive ions move in.
D ) (1) diffused across the synaptic cleft to a receptor protein (2) neurotransmitter released (3) binding of the
transmitter opens pores in the ion channels and positive ions move in.
E ) None of the above
3. Resting potential is
A ) excess positive ions accumulate inside the plasma membrane
B ) excess negative ions accumulate inside the plasma membrane
C ) excess positive ions accumulate outside the plasma membrane
D ) both b & c
E ) both a & c
4. Sensory neurons have:
A ) A short dendrite and a long axon
B ) A short dendrite and a short axon
C ) A long dendrite and a short axon
D ) A long dendrite and a long axon
E ) Their axons and dendrites may be either long or short
5. ________blocks Acetylcholine receptor sites causing muscle relaxation.
A ) Novocain
B ) curare
C ) Nicotine
D ) Nerve gases
6. Transmission across a synapse is dependent on the release of _______?
A ) neurotransmitters
B ) synaptic vesicle
C ) neurons
D ) receptor proteins
Human Physiology/The Nervous System
26
7. Motor neurons take messages
A ) from the muscle fiber to the central nervous system
B ) away from the central nervous system to the central nervous system
C ) that are classified
D ) away from the central nervous system to muscle fiber
8. The medulla oblongata helps to regulate which of the following:
A ) Breathing
B ) Heartbeat
C ) Sneezing
D ) Vomiting
E ) All of the above
9. The nervous systems main components are what?
A) The Synapses and Sprinal cord
B) The neurons and the synapses
C) The bain and the neurons
D)The brain and the spinal cord
10. Explain what LTP does to enhance communication between two neurons, on the postsynaptic end.
11. Explain what LTP does to enhance communication between two neurons, on the presynaptic end.
Glossary
Afferent Messages:
carry sensations such as heat, cold, or pain
Autonomic System:
deals with the visceral organs, like the heart, stomach, gland, and the intestines
Axon:
the part of the neuron that conducts nerve impulses
Cannabis:
a psychoactive drug produced from parts of the cannabis plant
Central Nervous System (CNS):
the system that includes the brain and the spinal cord
Cerebellum:
part of the brain that is located posterior to the medulla oblongata and pons, coordinates skeletal
muscles to produce smooth, graceful motions
Cerebrospinal Fluid (CSF):
acts a shock absorber for the central nervous system, protecting the brain and spinal
cord from injury; it also has a high glucose content which serves as a nutritional factor
Cerebrum
motor control, learning, speech, somatic sensory functions, vision,hearing and more.
Dendrites:
short pieces that come off of the cell body that receive the signals from sensory receptors and other
neurons
Episodic Memory:
represents our memory of events and experiences in a serial form
Excitatory Neurotransmitter:
a neurotransmitter that acts to elicit an action potential by opening chloride ion
channels
Longitudinal Sulcus:
separates the cerebrum in to the right and left hemispheres
Long Term Memory:
used for storage of information over a long time
Long-Term Potentiation (LTP)
long term communication enhancement between two neurons. Results in neural
pathways that store memoris.
Medulla
control center for respiratory, cardiovascular and digestive functions.
Human Physiology/The Nervous System
27
Myelin:
a fatty substance that surrounds and insulates the nerve fibers and facilitates the conduction of the nerve
impulse transmissions
Multiple Sclerosis (MS):
disease that affects the CNS by causing hardening and scaring of the myelin
Nodes of Ranvier:
unmyelinated gaps between sections of myelin
Peripheral Nervous System (PNS):
a way of communication from the central nervous system to the rest of the
body by nerve impulses that regulate the functions of the human body
Pons
control centers for respiration and inhibitory functions.
Postganglionic Cells:
have their cell bodies in the ganglia and send their axons to target organs or glands
Postsynaptic Cells
the cell on the receiving (second) end of the synapse.
Presynaptic Cell
The cell on the sending (first) end of the synapse.
Proprioception
the sense that indicates whether the body is moving with required effort, as well as where various
parts of the body are located in relation to each other.
Sensory Receptor:
structure that can find any kind of change in it's surroundings or environment
Somatic Nervous System (SNS):
the part of the peripheral nervous system associated with the voluntary control of
body movements through the action of skeletal muscles, and also reception of external stimuli
Synapses:
the gap between two neurons; new synapses lead to learning
References
Esther Wednesday, October 19, 2005
References
[1] http:/
Article Sources and Contributors
28
Article Sources and Contributors
Human Physiology/The Nervous System
Source
: http://en.wikibooks.org/w/index.php?oldid=1970244
Contributors
: AmWengert, Andybee, BrendaJohnson, Brentwaldrop, Brittine
Krmpotich, Carlosmoreno, Clareceglanville, CommonsDelinker, Danseyffert, Darklama, Derbeth, DorothyD, Fishpi, Gopherusagassizii, Hagindaz, Herbythyme, Horn Eaas, Iamunknown,
JamBam, Jaredjohnson, Jennifer72, Jennifermorley, Jguk, Jomegat, Macsking, Mike.lifeguard, Msol, Nataliehaveron, Never2late, Nikkjeppson, Princess8107, Provophys, Pwoodson, Recent
Runes, RiRi82, SBJohnny, Shakah, Shaleneroberts, Shanowac, Shellybird2, Stephanie greenwood, Sterlingsilver, Sunlight2, Tannersf, Thatgadgetgirl, Thenub314, Whiteknight, Winn, 120
anonymous edits
Image Sources, Licenses and Contributors
Image:Nervous system diagram.png
Source
: http://en.wikibooks.org/w/index.php?title=File:Nervous_system_diagram.png
License
: Public Domain
Contributors
: ¤~Persian Poet Gal (talk)
Image:Central nervous system.svg
Source
: http://en.wikibooks.org/w/index.php?title=File:Central_nervous_system.svg
License
: Public Domain
Contributors
: Camilaastrid, Cohesion,
Ericalens, Grm wnr, Mani1, Meno25, Tryphon, Was a bee, Wouterhagens, Xxxx00, 36 anonymous edits
Image:Synapse_v_int.png
Source
: http://en.wikibooks.org/w/index.php?title=File:Synapse_v_int.png
License
: Public Domain
Contributors
: Osnimf, 2 anonymous edits
Image:Action_potential_vert.png
Source
: http://en.wikibooks.org/w/index.php?title=File:Action_potential_vert.png
License
: GNU Free Documentation License
Contributors
: Davepape,
DrKiernan, LeonardoG
Image:Brain-anatomy.jpg
Source
: http://en.wikibooks.org/w/index.php?title=File:Brain-anatomy.jpg
License
: unknown
Contributors
: User:Primalchaos
Image:Brain_limbicsystem.jpg
Source
: http://en.wikibooks.org/w/index.php?title=File:Brain_limbicsystem.jpg
License
: Public Domain
Contributors
: Deadstar, Joey-das-WBF, Nathanael
Bar-Aur L., Nevit, Phy1729
Image:Hypothalamus.jpg
Source
: http://en.wikibooks.org/w/index.php?title=File:Hypothalamus.jpg
License
: Public Domain
Contributors
: Denniss, Lipothymia, Methoxyroxy, Nevit,
OldakQuill, Thuresson, Was a bee
Image:Gray686.png
Source
: http://en.wikibooks.org/w/index.php?title=File:Gray686.png
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Contributors
: Arcadian, Lipothymia
Image:Dermatoms.svg
Source
: http://en.wikibooks.org/w/index.php?title=File:Dermatoms.svg
License
: Public Domain
Contributors
: Ralf Stephan (mailto:ralf@ark.in-berlin.de)
image:Gray838.png
Source
: http://en.wikibooks.org/w/index.php?title=File:Gray838.png
License
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Contributors
: Magnus Manske
Image:Neuron.svg
Source
: http://en.wikibooks.org/w/index.php?title=File:Neuron.svg
License
: Creative Commons Attribution-Sharealike 2.5
Contributors
: User:Dhp1080
Image:Types_of_MS.jpg
Source
: http://en.wikibooks.org/w/index.php?title=File:Types_of_MS.jpg
License
: Public Domain
Contributors
: InvictaHOG, Lipothymia, 1 anonymous edits
Image:PCP.jpg
Source
: http://en.wikibooks.org/w/index.php?title=File:PCP.jpg
License
: Public Domain
Contributors
: Original uploader was Kwertii at en.wikipedia
Image:Cannabis sativa.jpg
Source
: http://en.wikibooks.org/w/index.php?title=File:Cannabis_sativa.jpg
License
: GNU Free Documentation License
Contributors
: BLueFiSH.as, D-Kuru,
Greatpatton, Hiuppo, Timeshifter, WayneRay, 8 anonymous edits
License
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http:/
