Download The Nervous System

Chapter 21
Brain Structure and Function
The Nervous System
The Nervous System
3 categories of neurons:
1. Sensory neurons
carry information to
the CNS
2. Motor neurons carry
information away from
CNS toward effector
tissue
3. Interneurons are
located between
sensory and motor
neurons
The Nervous System
• Sensory information
passed to and from the
brain travels along the
main nerve pathway –
the spinal cord
• The spine, made up of
vertebrae, protects the
spinal cord
• Spinal nerves branch
out between vertebrae
The Nervous System
•
•
•
•
•
The spinal cord also is a reflex
center
Reflexes – automatic
responses to stimuli
Reflex arc – prewired circuit of
neurons
– Sensory neuron receiving
stimulus
– Interneuron transmitting
information
– Motor neuron sending
message to muscle
Reflexes allow a person to react
quickly to dangerous stimuli
Withdrawal reflex – when
touching something hot
–
The pain stimulus travels from the spinal
cord to the brain and takes a little longer
than the reflex
–
You have removed your hand from the
heat before you feel the pain
21.2 The Brain
• The brain is where
decisions are
reached and bodily
activities are
directed and
coordinated
• The human brain is
roughly the size of a
small cantaloupe
The Brain
• There are about 100 to
200 billion neurons in
the brain
• There are also glial
cells
– About 10 times as
many as there are
neurons
• Glial cells do not carry
messages, but rather
support neurons by
– Supplying nutrients
– Helping to repair the
brain after injury
– Attacking invading
bacteria
There are 2 hemispheres, each
divided into 4 lobes
1.
2.
3.
4.
The temporal lobe
involved in auditory and
some visual information;
memory and emotion
Occipital lobe processes
visual information from
eyes…
Parietal lobe processes
information from touch;
self-awareness
Frontal lobe processes
involuntary muscle
movements; planning and
organizing future
expressive behavior
Cerebrum
• Cerebral cortex – wrinkled
outer surface
• If unfolded, a human
cerebral cortex would be
the size of a 16’ pizza
– Lots of surface area in a
small space
•
Fissure – deep groove
dividing the cerebrum and
cortex
– Divided into right and
left cerebral
hemispheres
•
Corpus callosum – bundle of
nerve fibers at base of fissure
– linking two hemispheres
Brain Stem
3 main parts of brain
stem:
1. Midbrain: light
and sound
sensitivity)
2. Pons: bridge for
messages
between brain
and spinal cord)
3. Medulla
oblongata:
continuation of
the spinal cord
• Functions of the brain are
divided between the right
and left hemispheres
– The left hemisphere
controls the right half of
the body
– The right hemisphere
controls the left half of
the body
• The left hemisphere
controls speech, reading
and ability to solve
mathematical problems
• The right hemisphere
controls spatial ability and
musical and artistic
creation
The Brain
Neuron Structure
• Neurons are highly
specialized cells that
usually don’t divide
• Damage to neurons
can’t be repaired by cell
division – many times
results in permanent
impairment
Neuron
Structure
• Many neurons have axons
covered in a protective layer
– myelin sheath – that
insulates to prevent
sideways transmission
– Increases speed of
transmission (100x)
– composed mainly of
lipids and is white like
animal fat
• Nervous tissue of myelinated
cells is called white matter
•
•
•
•
Action potential
transmits a signal along
the length of a neuron
– Brief reversal of the
electric charge of the
nerve cell membrane
This causes a wave of
electrical current to travel
down the length of the
neuron
A resting neuron has a
charge difference from
inside to outside
(polarized)
– Negative charge on
inside
Source of stored energy
in membrane, since it
separates the charges
that want to move toward
each other
Action Potential
•Potassium channels are ‘leaky’ and allow potassium to passively move to the outside
•The sodium-potassium pump in the neuron membrane moves sodium out and
potassium in
•Using ATP, the sodium-potassium pump moves 3 Na+ out for every 2 K+ in
•This restores the potassium levels in the cell
•The depolarization – loss of charge difference – moves in a wave down the cell
• Repolarization
– when
potassium ions
leave and
internal cell state
is more negative
than outside
Synaptic Transmission
• After traveling along
the axon, the signal
must be passed
along to the next
neuron
– Most neurons are
not physically
connected
• Synapse – the gap
between two neurons
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ansmission.htm
Synaptic Transmission
•
•
•
•
Synapse structure:
– presynaptic
– Space
– postsynaptic
Vesicles are in the
terminal boutons of the
presynaptic neuron 
neurotransmitters
When the impulse
reaches the terminal
bouton of a nerve cell,
the neurotransmitters are
released
The neurotransmitters
diffuse across the
synapse and bind to
receptors on the
postsynaptic cell
membrane
•
•
•
This binding stimulates the
postsynaptic cell to rapidly
uptake sodium
– Sodium gates open
and cell is depolarized
– Action potential is
generated
After the neurotransmitter
causes the response
– Removed from
synapse
– Enzymes break down
neurotransmitters
– Reuptake – some
neurotransmitters are
reabsorbed by the
presynaptic neuron
By enzymatically breaking
down and reuptake of
neurotransmitters, there is
no continuous stimulation
of the postsynaptic cell
Synaptic
Transmission
Neurotransmission, Alzheimer’s,
Depression, Parkinson’s, and ADD
• Depression is a
disease
– Feelings of
helplessness and
despair and thoughts
of suicide
• It may involve three
neurotransmitters
– Serotonin &
dopamine (inhibitory)
and norepinephrine
(excitatory)
Ritalin®
•
•
•
Ritalin is thought to increase
dopamine’s ability to stimulate
postsynaptic cells
– Block reuptake receptors in
presynaptic cells
– Dopamine in synapse
longer
Stimulants in high doses result
in
– Euphoric feeling
– More energy and endurance
– Sense of power
– Feeling of mental sharpness
After the stimulants wear off,
user feels
– Heightened fatigue
– Insomnia
– Poor concentration
– Irritability
– Tearfulness
– Depression
Opiates
• Morphine is readily extracted from
opium and is used to synthesize heroin.
• Addicts frequently dissolve heroin in water
by heating it in a spoon, and then inject in
the skin.
• Heroin produces a “high” that is
accompanied by drowsiness and a sense of
well-being that generally last for three to four
hours.
Opiates
• Codeine is also present in
opium, but it is usually
prepared synthetically from
morphine.
• OxyContin, with the active
ingredient oxycodone, is not
derived from opium or
morphine, but does have the
same physiological effects on
the body as do opium
narcotics.
– prescribed to patients for
treatment of chronic pain.
• Methadone is another
well-known opiate
– pharmacologically related
to heroin, appears to
eliminate the addict’s
desire for heroin while
producing minimal side
effects.
Hallucinogens
 Another class of drugs is
hallucinogens; marijuana is
the most well-known
member of this class.
 Hallucinogens cause
marked changes in normal
thought processes,
perceptions, and moods.
 Marijuana is the most
controversial drug in this
class because its long-term
effects on health are still
largely unknown.
Marijuana
•
Marijuana refers to a
preparation derived from the
plant Cannabis.
•
The chemical substance largely
responsible for the
hallucinogenic properties of
marijuana is known as
tetrahydrocannabinol, or THC.
– The THC content of Cannabis
varies in different parts of the
plant, generally decreasing in
the following sequence: resin,
flowers, leaves, with little THC
in the stem, roots or seeds.
– The THC-rich resin is known as
hashish.
•
Marijuana does not cause
physical dependency, but the
risk of harm is in heavy, longterm use.
Other Hallucinogens
 Other hallucinogens include
LSD, mescaline, PCP,
psilocybin, and MDMA
(Ecstasy).
 Phencyclidine is often mixed with
other drugs, such as LSD, or
amphetamine, and is sold as a
powder (“angel dust”), capsule,
or tablet.
 LSD is synthesized from
lysergic acid, and can cause
hallucinations that can last
for 12 hours.
 Oral intake of PCP first leads to
feelings of strength and
invulnerability, which may turn to
depression, tendencies toward
violence, and suicide.
 Phencyclidine, or PCP, is
often synthesized in
clandestine laboratories and
is often smoked, ingested,
sniffed.
Depressants
• Depressants are substances
used to depress the functions
of the central nervous system.
• Depressants calm irritability
and anxiety and may induce
sleep.
• These include alcohol (ethanol),
barbiturates, tranquilizers, and various
substances that can be sniffed, such
as airplane glue, model cement, or
aerosol gas propellants such as freon.
•
Sniffing has immediate effects such as
exhilaration, but impairs judgment and
may cause liver, heart, and brain damage,
or even death
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hways.htm
Stimulants
 The drug classification of
stimulants includes
amphetamines, sometimes
known as “uppers” or
“speed,” and cocaine, which
in its free-base form is
known as crack.
 Stimulants are substances
taken to increase alertness
or activity, followed by a
decrease in fatigue and a
loss of appetite.
• Amphetamine and
methamphetamine, often
injected intravenously,
cause an initial “rush,”
followed by an intense
feeling of pleasure.
• This is followed by a period
of exhaustion and a
prolonged period of
depression.
• Cocaine, extracted from the
leaves of Erythroxylin coca,
causes increased alertness
and vigor, accompanied by
the suppression of hunger,
fatigue, and boredom.
Stimulants
• Crack is cocaine
mixed with baking
soda and water, then
heated.
• Crack is often
smoked in glass
pipes, and like
cocaine stimulates
the brain’s pleasure
center.
Club Drugs
• The term club drugs
refers to synthetic drugs
that are used at
nightclubs, bars, and
raves (all-night dance
parties).
• Substances that are often
used as club drugs
include, but are not
limited to, MDMA
(Ecstasy), GHB (gamma
hydroxybutyrate),
Rohypnol (“Roofies”),
ketamine, and
methamphetamine.
• GHB and Rohypnol are
central nervous system
depressants that are
often connected with
drug-facilitated sexual
assault, rape, and
robbery.
• Methylenedioxymethamphet
amine, also known as
MDMA or Ecstasy, is a
synthetic mind-altering drug
that exhibits many
hallucinogenic and
amphetamine-like effects.
Club Drugs
 Ecstasy enhances selfawareness and
decreases inhibitions,
however, seizures,
muscle breakdown,
stroke, kidney failure,
and cardiovascular
system failure often
accompany chronic
abuse.
 Ketamine is primarily
used as a veterinary
animal anesthetic that in
humans causes
euphoria and
hallucinations.
 can also cause impaired
motor functions, high
blood pressure, amnesia,
and mild respiratory
depression.
Anabolic
Steroids
 Yet another category of drugs
is the anabolic steroids.
 These are synthetic
compounds that are
chemically related to the male
sex hormone testosterone.
 Anabolic steroids are often
abused by individuals who are
interested in accelerating
muscle growth.
 Side effects include
unpredictable effects on mood
and personality, depression,
diminished sex drive, halting
bone growth, and liver cancer.
Drug-Control Laws
 The U.S. federal law known as the Controlled
Substances Act will serve to illustrate a legal
drug-classification system created to prevent and
control drug abuse.
 This federal law establishes five schedules of
classification for controlled dangerous substances
on the basis of a drug’s
 potential for abuse
 potential for physical and psychological
dependence
 medical value
Schedules of Classification
 Schedule I drugs have a
high potential for abuse
and have no currently
accepted medical use
such as heroin, marijuana,
methaqualone, and LSD.
 Schedule II drugs have a
high potential for abuse
and have medical use
with severe restrictions
such as cocaine, PCP,
and most amphetamine
and barbiturate
prescriptions.
• Schedule III drugs have less
potential for abuse and a
currently accepted medical use
such as all barbiturate
prescriptions not covered
under Schedule II, such as
codeine and anabolic steroids.
• Schedule IV drugs have a low
potential for abuse and have a
current medical use such as
darvon, phenobarbital, and
some tranquilizers such as
diazepam (valium) and
chlordiazepoxide (librium).
• Schedule V drugs must show
low abuse potential and have
medical use such as opiate
drug mixtures that contain
nonnarcotic medicinal
ingredients.
Drug Identification
• The challenge or difficulty of forensic drug
identification comes in selecting analytical
procedures that will ensure a specific
identification of a drug.
• This plan, or scheme of analysis, is divided
into two phases.
– Screening test that is nonspecific and
preliminary in nature to reduce the
possibilities to a manageable number.
– Confirmation test that is a single test that
specifically identifies a substance.
Preliminary Analysis
• Faced with the prospect that the unknown
substance may be any one of a thousand or
more commonly encountered drugs, the analyst
must employ screening tests to reduce these
possibilities to a small and manageable
number.
• This objective is often accomplished by
subjecting the material to a series of color tests
that will produce characteristic colors for the
more commonly encountered illicit drugs.
Preliminary Analysis
• Microcrystalline tests can also be used to
identify specific drug substances by studying
the size and shape of crystals formed when
the drug is mixed with specific reagents.
Confirmational Determination
• Once this preliminary analysis is completed, a
confirmational determination is pursued.
• Forensic chemists will employ a specific test
to identify a drug substance to the exclusion
of all other known chemical substances.
• Typically infrared spectrophotometry or gas
chromatography-mass spectrometry is used
to specifically identify a drug substance.
Qualitative vs. Quantitative
• Another consideration in selecting an
analytical technique is the need for either a
qualitative or a quantitative determination.
• The former relates just to the identity of the
material, whereas the latter requires the
determination of the percent composition of
the components of a mixture.
Chromatography
• Chromatography is a means of separating
and tentatively identifying the components of
a mixture.
Chromatography
 The theory of chromatography is based on the
observation that chemical substances have a
tendency to partially escape into the surrounding
environment when dissolved in a liquid or when
absorbed on a solid surface.
 Those materials that have a preference for the
moving phase will slowly pull ahead and separate
from those substances that prefer to remain in the
stationary phase.
TLC
• TLC uses a solid stationary phase usually
coated onto a glass plate and a mobile liquid
phase to separate the components of the
mixture.
TLC
• The liquid will slowly rise up the plate by
capillary action causing the sample to
become distributed between the stationary
phase and the moving liquid phase.
• Because most compounds are colorless, the
materials must be visualized by placing the
plates under ultraviolet light or spraying the
plate with a chemical reagent.
• The distance a spot travels up a thin-layer
plate can be assigned a numerical value
known as the R value.
Gas Chromatography
• In GC, the moving phase is actually a gas
called the carrier gas, which flows through a
column.
Gas Chromatography
• The stationary phase is a thin film of liquid
contained within the column.
• After a mixture has traversed the length of the
column, it will emerge separated into its
components.
Gas Chromatography
• The written record of this separation is called
a chromatogram.
• The time required for a component to emerge
from a GC column is known as retention time.
Spectrohotometry
• Just as a substance can absorb visible light to
produce color, many of the invisible radiations
of the electromagnetic spectrum are likewise
absorbed.
• Spectrophotometry, an important analytical
tool, measures the quantity of radiation that a
particular material absorbs as a function of
wavelength and frequency.
• The quantity of light absorbed at any
frequency is directly proportional to the
concentration of the absorbing species. This
is known as Beer’s Law.
UVand IR Spectrophotometry
• Currently, most forensic laboratories use UV
and IR spectrophotometers to characterize
chemical compounds.
• The simplicity of the UV spectrum facilitates its
use as a tool for determining a material’s
probable identity, although it may not provide a
definitive result.
• The IR spectrum provides a far more complex
pattern.
UVand IR Spectrophotometry
• Different materials always have distinctively
different infrared spectra; each IR spectrum is
therefore equivalent to a “fingerprint” of that
substance.
The Spectrophotometer
• The spectrophotometer is the instrument
used to measure and record the absorption
spectrum of a chemical substance.
• The components of a spectrophotometer are:
– A radiation source
– A monochromator or frequency selector
– A sample holder
– A detector to convert electromagnetic
radiation into an electrical signal
– A recorder to produce a record of the
signal
• Absorption spectra can be done in the visible,
ultraviolet (UV) or infrared (IR) regions.
Mass Spectrometry
• In the mass spectrometer, a beam of highenergy electrons collide with a material,
producing positively charged ions.
Mass Spectrometry
• These positive ions almost instantaneously
decompose into numerous fragments, which
are separated according to their masses.
• The unique feature of mass spectrometry is
that under carefully controlled conditions, no
two substances produce the same
fragmentation pattern.
GC and Mass
• A direct connection between the GC column
and the mass spectrometer allows each
component to flow into the mass spectrometer
as it emerges from the GC.
GC and Mass
• The separation of a mixture’s components is
first accomplished by the GC.
• Then, fragmentation of each component by
high-energy electrons in the mass
spectrometer, will produce a distinct pattern,
somewhat like a “fingerprint”, of the
substance being examined.
GC and Mass
Collection and Preservation
• The field investigator has the responsibility of
ensuring that the evidence is properly
packaged and labeled for the laboratory.
• Generally common sense is the best guide,
keeping in mind that the package must prevent
the loss of the contents and/or crosscontamination.
Collection and Preservation
• Often the original container in which the drug
was seized will suffice.
• All packages must be marked with
information that is sufficient to ensure
identification by the officer in the future and
establish the chain of custody.