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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 http://science.education.nih.gov/supplemen ts/nih2/Addiction/activities/lesson2_neurotr 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 http://science.education.nih.gov/supplem ents/nih2/Addiction/activities/lesson3_pat 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.