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Chapter Two The Brain • • • • Made up of cells (neurons and glial cells) Weight = 3 pounds 2 hemispheres (right and left) The brain never sleeps Neuron • • • • 100 Billion cells No two cells are identical Few are produced after birth Grow with stimulation creating more synaptic connections • Support by glial cells which 10 time more abundant • Most reside in the brain but are found all over the body Glial Cell • Support cell to the neuron • Helps metabolism, respiration and efficiency of the neuron • In the peripheral nervous system glial cells are called Schwann cells • Often surround the neuron creating a myelin sheath that greatly improves the speed and efficiency of the neural impulse Types of Neurons • Sensory (or afferent) neurons: send information from sensory receptors (e.g., in skin, eyes, nose, tongue, ears) TOWARD the central nervous system. • Motor (or efferent) neurons: send information AWAY from the central nervous system to muscles or glands. • Interneurons (Associative): send information between sensory neurons and motor neurons. Most interneurons are located in the central nervous system. • Reflex Arc: Body to the spine back to the body before ever reaching the brain Receives stimulation from either sense receptors or other cells’ axons Neuron Structure The cell’s life support center Small gaps in the myelin sheath of nerve fibers Executor of the cell Forms junctions with other cells also called terminal knobs synaptic buttons Passes messages away from the cell body to other neurons, muscles, or glands Insulates the axon that speed neural impulse Difference between Axons and Dendrites • Axons • Take information away from the cell body • Generally only 1 axon per cell • More efficient if it has a myelin sheath • Branch further from the cell body • Dendrites • Bring information to the cell body • Usually many dendrites per cell • No myelin insulation • Branch near the cell body Neural Impulse within the Neuron • Electrical part of the electro-chemical impulse • All or None Action Potential- There is either enough stimulation or the neuron doesn’t fire • Action Potential- Enough stimulation received from another cell that causes the axon membrane to become permeable that opens gates that causes depolarization (cell becomes positively charged) to occur that allow positively charged particles (sodium ions) to enter the cell • Neurons can fire up to 270 miles per hour helped by the diameter of the axon and myelination. • The cell needs only to reach –60 millivolts to fire and allow more sodium to enter and cause the cell to reach +30 millivolts • Then a refractory period begins where the cell can not fire in which the cell repolarizes below –70 millivolts • Resting Potential- Period when the cell is at –70 millivolts • The cell can fire many times a second but it must rest between firings. • When the cell is polarized it has no sodium ions in it and a negative charge. Action Potential/ Depolarized Refractory Period Resting Potential/ Polarized Stimulus Threshold Neurotransmission • Electrical transmission causes synaptic vesicles to release neurotransmitters in the axon terminals • The neurotransmitters leave the terminal and cross the synaptic space to the near by dendrite receptor sites. • The neurotransmitter bind to the receptor sites and triggers that neuron to either fire or blocks it from firing What happens at the Synapse • Excitation neurotransmitter- Causes neurons to fire • Inhibitation- Causes neurons not to fire • Reuptake- Neurotransmitters that are not used are retaken by the terminal buttons to be used again • Enzyme Action- Breaks down neurotransmitters, that are not used, to be recycled for later use Neurotransmitters • Acetycholine-Essential for movement- usually activates movement and muscles (to contract), learning and memory • Found especially in the PNS along with Norepinephrine • Curare – blocks receptor site causing paralysis - lung contractions stop • Botulism – blocks muscle contractions – used in Botox injections for wrinkles • Rat studies show memory improvements with tissue transplants • Loss linked to Alzheimer’s • Dopamine- affects voluntary movement, attention, thought & memory – Too much leads Psychosis – schizophrenia – Too little leads to Parkinson’s • Epinephrine and Norepinephrine are neurohormones which means they can act like hormones are also referred to as adrenaline and noradrenaline in the old nomenclature • Norepinephrine- Emotional arousal, anxiety and fear – involved in the activation of the sympathetic nervous system • Seratonin- Sleep and emotional arousal; implicated in aggression – Too low leads to depression and too high masked aggression – High achievers or leaders tend to have higher levels of seratonin – Tryptophan produces seratonin Neurotransmitters • GABA- Inhibits brain excitability and anxiety • Endorphines – Pain relief and elevation of mood heroin and morphine act like endorphines Common Drugs and their Interactions • Depressants – Alcohol- stimulates release of dopamine and depresses RAS and possibly mimics GABA – Valium – causes the release of GABA which causes relaxation • Stimulants – Cocaine – blocks the reuptake of dopamine causing heightened elevation in mood – causes blood vessel constriction- used in eye surgeries – How drugs work – Caffeine – slows reabsorption of NT by blocking enzymes – Amphetamines- increases release of Dopamine and norepinephrine and blocks reabsorption – in the past used for weight loss – today used for narcolepsy and ADHD (Ritalin) • Overdoses can lead to psychotic episodes lasting up to six months Common Drugs and their Interactions • Narcotics (Opiates) – Heroin – stimulates the neuronal firing rate of dopamine • Binds to endorphin receptor sites • Tolerance occurs quickly • Hallucinogenics – Cannabis/Hash- May affect the release of a newly discovered neurotransmitter Anandamide which may reduce stress and pain – LSD- (Psychedelics) Act on seratonin receptors – Ecstasy- causes the release and blocks reuptake and depletes the amount of seratonin in the brain – PCP – stimulates both the sympathetic and peripheral nervous system Involuntary movement Body Voluntary Movement Recovery Action The Autonomic Nervous System Structure Sympathetic Stimulation Parasympathetic Stimulation Iris (eye muscle) Pupil dilation Pupil constriction Salivary Glands Saliva production reduced Saliva production increased Oral/Nasal Mucosa Mucus production reduced Mucus production increased Heart Heart rate and force increased Heart rate and force decreased Lung Bronchial muscle relaxed Bronchial muscle contracted Stomach Peristalsis reduced Gastric juice secreted; motility increased Small Intestine Motility reduced Digestion increased Large Intestine Motility reduced Secretions and motility increased Liver Increased conversion of glycogen to glucose Kidney Decreased urine secretion Adrenal medulla Norepinephrine and epinephrine secreted Bladder Wall relaxed Sphincter closed Increased urine secretion Wall contracted Sphincter relaxed The Brain • The brain has three regions we will discuss in detail – Cerebral Cortex – Subcortex – Limbic System • The Brain is often divided up into – Forebrain – Midbrain – Hindbrain • The brain has two unique qualities – Plasticity – the brain is malleable and changes function after injury – Corticalization- wrinkling of the brain which increases its size • Cerebral Cortex – Frontal Lobe –thinking, planning, voluntary movement and control of emotions and includes the motor cortex and the Broca’s region – Occipital Lobe – organizes our visual information – Parietal Lobe - Sensation reception includes the somatosensory cortex – Temporal Lobe – organizes our auditory information and includes the Wernicke’s region – Thalamus – relays information from the senses (except smell) to the appropriate lobe and regulates attention, motivation and emotion • Motor Cortex – handles voluntary movement Somatic Nervous System • Somatosensory Cortex – handles all of your sensations of touch from your body • Both systems partition off the cortex space based on the sensitivity and fine motor skills of each part of the body – A more sensitive part of the body has a large portion of the Somatosensory cortex Broca’s and Wernicke’s Regions Broca's Area • Broca’s Region – If damaged speech production is unattainable – Located in the frontal lobe Wernicke's Area • Wernicke’s Region – Jumbled speech and incoherent sentences if damaged – Located in the temporal lobe Two Hemispheres of the Cerebral Cortex Left Hemisphere • • • • Language Math Logic Analytic side • Spatial abilities • Face recognition • Visual imagery • Music • Creative side Split Brain Surgeries • Corpus Callosum – Connects the two hemisphere so they can directly communicate – Epilepsy causes violent, uncontrollable neural firings across the corpus callosum – The CC is cut in severe cases which led to split brain research and understanding of the roles of each hemisphere • Cerebellum Subcortex – Recorded movement and balance • Brain Stem – basic bodily function Brain Stem – Medulla – heart and respiration functions – Pons – Crossover point between other parts of the brain to the cerebellum – Reticular Formation (RAS) – regulates sleep and attention RAS Limbic System • Amygdala– regulates emotion esp. fear • Hippocampus– consolidates memory from shortterm to long-term • Hypothalamus– regulates the Autonomic Nervous System and the Endocrine system Hypothalamus – Homeostatic regulator including temperature, blood pressure, heartbeat, thirst, and hunger • Pituitary Gland often referred to as the master gland CT Scans • CT scans use a series of X-ray beams passed through the head. • The images are then developed on sensitive film. • This method creates crosssectional images of the brain • Shows the structure of the brain, but not its function. Computed Tomography Scan (CT Scan) Pet Scan Positron Emission Topography • A scanner detects radioactive material that is injected or inhaled to produce an image of the brain. • Commonly used radioactivelylabeled material includes oxygen, fluorine, carbon and sugar. • When this material gets into the bloodstream, it goes to areas of the brain that use it. • When the radioactive material breaks down, it gives off a neutron and a positron. MRI Scans • MRI uses the detection of radio frequency signals produced by displaced radio waves in a magnetic field. • It provides an anatomical view of the brain. Magnetic Resonance Imaging Endocrine System –Secretes Hormones • Pituitary– master gland, regulates growth and stimulates milk for nursing • Dwarfism and giantism • Pineal- (Melatonin) – Regulates sleep cycle • Thyroid- (Thyroxin) – Regulates metabolism rate • Hypo- underproduction-lethargic • Hyper- overproduction- hyperactive • Adrenal- (Adrenaline –Epinephrine) – Stimulates the body into action and responds to stress • Pancreas- (Insulin) – Regulates blood sugar and insulin levels and regulates hunger • Gonads- (Testosterone and Estrogen) – Ovaries- regulates female sexual behavior and female characteristics – Testes- regulates male sexual behavior and male characteristics Pineal Gland GHB and the Brain Although GHB can be made in the laboratory, it is also produced normally in the brain through the synthesis of a neurotransmitter called GABA. Some of the greatest concentrations of GHB are found in the substantia nigra, thalamus and hypothalamus. When GHB is ingested by a user, it affects several different neurotransmitter systems in the brain: •GHB can increase acetylcholine levels. •GHB can increase serotonin levels. •GHB can reduce dopamine activity, especially in the basal ganglia. This action is probably the result of the inhibition of the release of dopamine from synaptic terminals. Some studies show that GHB first inhibits the release of dopamine, then causes the release of dopamine. The effect on the dopamine system may depend on the dose of GHB. •GHB can activate GHB receptors and GABA receptors on neurons in the brain. GHB was first developed as a general anesthetic, but because it did not work very well to prevent pain, its use as an anesthetic declined. The observation that GHB may cause the release of growth hormone led some people, especially athletes and body-builders, to take it because they thought it would increase muscle development. At the time, GHB was available as a dietary supplement and as such was not regulated by the US Food and Drug Administration. In 1990, after numerous reports that GHB caused illness, the FDA began investigating the drug. It is now classified as an illegal substance. Research is being conducted to investigate the use of GHB in the treatment of the sleep disorder called narcolepsy. GHB has been grouped with other drugs in the "date-rape drug" category such as Rohypnol, because it can be slipped easily into a drink and given to an unsuspecting victim, who often does not remember being assaulted. GHB is especially dangerous when combined with alcohol. LSD was first synthesized from a fungus that grows on rye and other grains. In 1938, Albert Hofmann working in the Swiss pharmaceutical company called Sandoz, produced LSD for the first time. He was hoping that this new drug could be used to stimulate circulation and respiration. However, the tests he conducted were all failures and he forgot about LSD for 5 years. In 1943, Hofmann accidentally ingested (or somehow absorbed) a bit of LSD and experienced some of the psychedelic effects of this chemical: dizziness, visual distortions and restlessness. A few days later he prepared 0.25 mg of LSD in water and drank it. He again experienced the mood and thought altering effects of LSD. Effects of LSD on the Nervous System LSD is water soluble, odorless, colorless and tasteless - it is a very powerful drug - a dose as small as a single grain of salt (about 0.010 mg) can produce some effects. Psychedelic effects are produced at higher doses of about 0.050-0.100 mg. The effects of LSD depend on a user's mood and expectations of what the drug will do and last several hours. The behavioral effects that LSD can produce include: •Feelings of "strangeness" •Vivid colors •Hallucinations •Confusion, panic, psychosis, anxiety •Emotional reactions like fear, happiness or sadness •Distortion of the senses and of time and space •"Flashback" reactions - these are the effects of LSD that occur even after the user has not taken LSD for months or even years. •Increases in heart rate and blood pressure •Chills •Muscle weakness