Section 36.1 Summary – pages

Section 36.1 Summary – pages 943 - 950
Neurons: Basic Units of the Nervous System Neurons conduct impulses throughout the nervous system. Dendrite Myelin sheath Axon Nucleus Axon endings Cell body Section 36.1 Summary – pages

Neurons: Basic Units of the Nervous System A neuron is a long cell that consists of three regions: a cell body, dendrites, and an axon. Dendrite Myelin sheath Axon Nucleus Axon endings Cell body Section 36.1 Summary – pages

Neurons: Basic Units of the Nervous System Dendrites are branchlike extensions of the neuron that receive impulses and carry them toward the cell body. Dendrite Myelin sheath Axon Axon endings Cell body Nucleus Section 36.1 Summary – pages

Neurons: Basic Units of the Nervous System Dendrite The axon is an extension of the neuron that carries impulses away from the cell body and toward other neurons, muscles, or glands. Myelin sheath Axon Axon endings Cell body Nucleus Section 36.1 Summary – pages

Neurons: Basic Units of the Nervous System Neurons fall into three categories: sensory neurons, motor neurons, and interneurons. Sensory neurons carry impulses from the body to the spinal cord and brain. Section 36.1 Summary – pages

Neurons: Basic Units of the Nervous System Interneurons are found within the brain and spinal cord. Sensory neuron Interneuron Spinal cord Motor neuron Receptor in skin Direction of impulse Muscle contracts Section 36.1 Summary – pages

Neurons: Basic Units of the Nervous System Motor neurons carry the response impulses away from the brain and spinal cord to a muscle or gland. Sensory neuron Interneuron Spinal cord Motor neuron Receptor in skin Direction of impulse Muscle contracts Section 36.1 Summary – pages

Relaying an impulse The nervous system sorts and interprets incoming information before directing a response. Section 36.1 Summary – pages

A neuron at rest Plasma membrane Outside cell Open ion channel Gated Na+ channel Open ion channel Gated Na+ channel Na+/K+ pump Section 36.1 Summary – pages

Motor Neuron NA K Pump Click image to view movie. Section 36.1 Summary – pages

A neuron at rest Under these conditions, which exist when the cell is at rest, the plasma membrane is said to be polarized. A polarized membrane has the potential to transmit an impulse. Section 36.1 Summary – pages

How an impulse is transmitted When a stimulus excites a neuron, gated sodium channels in the membrane open up and sodium ions rush into the cell. As the positive sodium ions build up inside the membrane, the inside of the cell becomes more positively charged than the outside. This change in charge, called depolarization, moves like a wave down the length of the axon. Section 36.1 Summary – pages

How an impulse is transmitted + + + — — K+ Gated K+ channel Outside cell Na+ Na+ Gated Na+ channel Inside cell + + — — — Na+ Section 36.1 Summary – pages

How an impulse is transmitted + + + + — — K+ K+ Gated K+ channel Gated K+ channel Impulse Gated Na+ channel Gated Na+ channel Na+ Na+/K+ pump — — + + — — Na+ Section 36.1 Summary – pages

How an impulse is transmitted + + + + + + Gated K+ channel 3Na+ Impulse Na+/K+ pump Gated Na+ channel — — — — — — Section 36.1 Summary – pages

How an impulse is transmitted Click image to view movie. Section 36.1 Summary – pages

White matter and gray matter Most axons are surrounded by a white covering of cells called the myelin sheath. Myelin sheath Section 36.1 Summary – pages

White matter and gray matter The myelin sheath insulates the axon, hindering the movement of ions across its plasma membrane. The ions move quickly down the axon until they reach a gap in the sheath. Section 36.1 Summary – pages

White matter and gray matter Here, the ions pass through the plasma membrane of the nerve cell and depolarization occurs. As a result, the impulse jumps from gap to gap, greatly increasing the speed at which it travels. Section 36.1 Summary – pages

White matter and gray matter The myelin sheath gives axons a white appearance. In the brain and spinal cord, masses of myelinated axons make up what is called “white matter.” The absence of myelin in masses of neurons accounts for the grayish color of “gray matter” in the brain. Section 36.1 Summary – pages

Connections between neurons Dendrite Axon Impulse Synapse Impulse Dendrite Axon Section 36.1 Summary – pages

Connections between neurons Vesicle fuses with membrane (exocytosis) Vesicle with neurotransmitters inside Dendrite Axon Axon Impulse Calcium channel Neurotrans-mitters released into synapse Synapse Synaptic space Neurotransmitter diffuses across synapse and binds with receptor on dendrite Impulse Dendrite Dendrite Axon Section 36.1 Summary – pages

The Central Nervous System Cerebrum Spinal cord Skull Vertebra Medulla oblongata Cerebellum Section 36.1 Summary – pages

Two systems work together Another division of your nervous system, called the peripheral nervous system, is made up of all the nerves that carry messages to and from the central nervous system. Section 36.1 Summary – pages

Two systems work together Brain Together, the central nervous system (CNS) and the peripheral nervous system (PNS) respond to stimuli from the external environment. Spinal cord Section 36.1 Summary – pages

Anatomy of the brain Cerebrum Motor area Sensory area Speech area Language area Vision area Taste area General interpretation area Intellect, learning, and personality Balance area Hearing area Brain stem Cerebellum Section 36.1 Summary – pages

Anatomy of the brain The brain stem is made up of the medulla oblongata, the pons, and the midbrain. Midbrain Cerebellum Pons Medulla oblongata Section 36.1 Summary – pages

Anatomy of the brain The medulla oblongata is the part of the brain that controls involuntary activities such as breathing and heart rate. Midbrain Cerebellum Pons Medulla oblongata Section 36.1 Summary – pages

Anatomy of the brain The pons and midbrain act as pathways connecting various parts of the brain with each other. Midbrain Cerebellum Pons Medulla oblongata Section 36.1 Summary – pages

The Peripheral Nervous System The peripheral nervous system can be separated into two divisions—the somatic nervous system and the autonomic nervous system. Section 36.1 Summary – pages

The somatic nervous system Brain (CNS) Spinal cord (CNS) The somatic nervous system is made up of 12 pairs of cranial nerves from the brain, pairs of spinal nerves from the spinal cord, and all of their branches. Spinal nerves (PNS) Section 36.1 Summary – pages

The somatic nervous system Brain (CNS) Spinal cord (CNS) The nerves of the somatic system relay information mainly between your skin, the CNS, and skeletal muscles. Spinal nerves (PNS) Section 36.1 Summary – pages

The somatic nervous system Brain (CNS) Spinal cord (CNS) This pathway is voluntary, meaning that you can decide whether or not to move body parts under the control of this system. Spinal nerves (PNS) Section 36.1 Summary – pages

Sensory neuron Reflexes in the somatic system Direction of impulse Motor neuron Flexor muscle contracts and withdraws part being stimulated Pain receptors in skin Section 36.1 Summary – pages

The autonomic nervous system The autonomic nervous system carries impulses from the CNS to internal organs. These impulses produce responses that are involuntary, or not under conscious control. Section 36.1 Summary – pages

The autonomic nervous system There are two divisions of the autonomic nervous system—the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system controls many internal functions during times of stress. Section 36.1 Summary – pages

The autonomic nervous system The sympathetic nervous system causes the release of hormones, such as epinephrine and norepinephrine, that results in the fight-or-flight response. A fight-or-flight response can occur when you see a rattlesnake. Section 36.1 Summary – pages

The autonomic nervous system The parasympathetic nervous system on the other hand, controls many of the body’s internal functions when it is at rest. Both the sympathetic and parasympathetic systems send signals to the same internal organs. Section 36.1 Summary – pages

Nervous System The autonomic nervous system Central Nervous System (CNS) Peripheral Nervous System (PNS) Somatic Nervous System (voluntary) Relays information to and from skin and skeletal muscles. Autonomic Nervous System (involuntary) Relays information to internal organs. Sympathetic Nervous System Controls organs in times of stress. Parasympathetic Nervous System Controls organs when body is at rest Section 36.1 Summary – pages

Sensing Chemicals Olfactory nerve Olfactory bulb Olfactory nerve receptors Taste bud Sensory neuron Smell Molecules Taste Molecules Section 36.2 Summary – pages

Sensing Chemicals Tastes that you experience can be divided into four basic categories: sour, salty, bitter, and sweet. As seen with the sequence of electrochemical changes a neuron undergoes as it is depolarized, each of the different tastes produces a similar change in the cells of taste buds. Section 36.2 Summary – pages

Sensing Chemicals As these cells are depolarized, signals from your taste buds are sent to the cerebrum. There, the signal is interpreted and you notice a particular taste. Section 36.2 Summary – pages

Sensing Light Iris Sclera Lens Choroid Light Retina Pupil Cornea Optic nerve Section 36.2 Summary – pages

Sensing Light The retina contains two types of light receptor cells—rods and cones. Rods are receptor cells adapted for vision in dim light. They help you detect shape and movement. Section 36.2 Summary – pages

Sensing Light Cones are receptor cells adapted for sharp vision in bright light. They also help you detect color. At the back of the eye, retinal tissue comes together to form the optic nerve, which leads to the brain, where images are interpreted. Section 36.2 Summary – pages

The Eye Rod and cone cells Visual field Visual cortex in cerebrum Optic nerve Lens Top view of brain Retina Depth perception Brain image projections Section 36.2 Summary – pages

Eye Structure and Function Click image to view movie. Section 36.2 Summary – pages

Sensing Mechanical Stimulation Hearing and touch, depend on receptors that respond to mechanical stimulation. Section 36.2 Summary – pages

Your sense of hearing Malleus Incus Stapes Semicircular canals Auditory nerve Ear canal Oval window Cochlea Eardrum Outer ear Middle ear Inner ear Section 36.2 Summary – pages

Ear Structure and Function Click image to view movie. Section 36.2 Summary – pages

Your sense of balance The inner ear converts information about the position of your head into nerve impulses which travel to your brain, informing it about your body’s equilibrium. Section 36.2 Summary – pages

Your sense of balance Semicircular canals Body upright Head upright Gel-like fluid Gel-like fluid Hair cells Hair cells Crista ampullaris Maculae Body rotating Head tilted Fluid Fluid Section 36.2 Summary – pages

Your sense of touch Free nerve ending Heat Hair Shaft Light Touch Opening of sweat gland Heavy pressure Cold Section 36.2 Summary – pages

Drugs Act on the Body A drug is a chemical that affects the body’s functions. Most drugs interact with receptor sites on cells. Section 36.3 Summary – pages

Drugs Act on the Body Increased synthesis Axon Increased release Decreased enzymatic breakdown Synaptic space Dendrite Section 36.3 Summary – pages

Medicinal Uses of Drugs A medicine is a drug that, when taken into the body, helps prevent, cure, or relieve a medical problem. Section 36.3 Summary – pages

Relieving pain Medicines that relieve pain manipulate either the receptors that initiate the impulses or the central nervous system that receives them. Section 36.3 Summary – pages

Relieving pain Pain relievers that do not cause a loss of consciousness are called analgesics. Some analgesics, like aspirin, work by inhibiting receptors at the site of pain from producing nerve impulses. Section 36.3 Summary – pages

Relieving pain Analgesics that work on the central nervous system are called narcotics. Many narcotics are made from the opium poppy flower. Section 36.3 Summary – pages

Relieving pain Opiates, as they are called, can be useful in controlled medical therapy because these drugs are able to relieve severe pain from illness or injury. Section 36.3 Summary – pages

Treating circulatory problems Many drugs have been developed to treat heart and circulatory problems such as high blood pressure. These medicines are called cardiovascular drugs. Section 36.3 Summary – pages

Treating circulatory problems In addition to treating high blood pressure, cardiovascular drugs may be used to normalize an irregular heartbeat, increase the heart’s pumping capacity, or enlarge small blood vessels. Section 36.3 Summary – pages

Treating nervous disorders Drugs that increase the activity of the central and sympathetic nervous systems are called stimulants. Amphetamines (am FE tuh meenz) are synthetic stimulants that increase the output of CNS neurotransmitters. Because they increase wakefulness and alertness, amphetamines are sometimes used to treat patients with sleep disorders. Section 36.3 Summary – pages

Treating nervous disorders Drugs that lower, or depress, the activity of the nervous system are called depressants, or sedatives. The primary medicinal uses of depressants are to encourage calmness and produce sleep. Section 36.3 Summary – pages

The Misuse and Abuse of Drugs Drug misuse occurs when a medicine is taken for an unintended use. Giving your prescription medicine to someone else, not following the prescribed dosage by taking too much or too little, and mixing medicines, are all instances of drug misuse. Section 36.3 Summary – pages

The Misuse and Abuse of Drugs Drug abuse is the inappropriate self-administration of a drug for non medical purposes. Drug abuse may involve use of an illegal drug, such as cocaine; use of an illegally obtained medicine, such as someone else’s prescribed drugs; or excessive use of a legal drug, such as alcohol or nicotine. Section 36.3 Summary – pages

Addiction to drugs When a person believes he or she needs a drug in order to feel good or function normally, that person is psychologically dependent on the drug. When a person’s body develops a chemical need for the drug in order to function normally, the person is physiologically dependent. Psychological and physiological dependence are both forms of addiction. Section 36.3 Summary – pages

Tolerance and withdrawal Tolerance occurs when a person needs larger or more frequent doses of a drug to achieve the same effect. The dosage increases are necessary because the body becomes less responsive to the drug. Withdrawal occurs when the person stops taking the drug and actually becomes ill. Section 36.3 Summary – pages

Classes of Commonly Abused Drugs Each class of drug produces its own special effect on the body, and its own particular symptoms of withdrawal. Section 36.3 Summary – pages

Table Commonly Abused Drugs Category • Substance Commercial or Street Name Potential Health Hazard Cannabinoid • Marijuana • Grass, joints, pot, reefer, weed Respiratory problems, impaired learning Stimulants • Cocaine • Blow, coke, crack, rock Increased heart rate and blood pressure, irregular heart beat, heart failure, and weight loss • Methylphenidate • Ritalin, Skippy, vitamin R • Nicotine • Chew, cigarettes, cigars • Methamphetamine • Ice, speed, glass • MDMA • Ecstasy, Eve Depressants • Benzodiazepines • Librium, Valium, Xanax, downers, sleeping pills Respiratory depression and arrest, lowered blood pressure, poor concentration • Barbiturates • Barbs, red birds, yellows Hallucinogens Chronic mental disorders, nausea, flashbacks • LSD • Cubes, microdot Opioids • H, junk, skag, smack Respiratory depression and arrest, collapsed veins • Heroin Other • Inhalants • Paint thinners, gasoline, butane, nitrates, laughing gas Headache, nausea, vomiting, unconsciousness, sudden death • Anabolic steroids • Juice Liver and kidney cancer, acne, high blood pressure • Ketamine • Special K, vitamin K Respiratory depression and arrest, nausea, vomiting Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Cocaine stimulates the CNS by working on the part of the inner brain that governs emotions and basic drives, such as hunger and thirst. Cocaine artificially increases levels of neurotransmitters in the brain. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine As a result, false messages are sent to reward centers indicating that a basic drive has been satisfied. The user quickly feels a euphoric high called a rush. This sense of intense pleasure and satisfaction cannot be maintained, however, and soon the effects of the drug change. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Physical hyperactivity follows. Often, anxiety and depression set in. Cocaine also disrupts the body’s circulatory system by interfering with the sympathetic nervous system. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Although initially causing a slowing of the heart rate, it soon produces a great increase in heart rate and a narrowing of blood vessels, known as vasoconstriction. The result is high blood pressure. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Other adverse side effects of amphetamine abuse include irregular heartbeat, chest pain, paranoia, hallucinations, and convulsions. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Caffeine—a substance found in coffee, some carbonated soft drinks, cocoa, and tea—is a CNS stimulant. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Caffeine also causes an increase in heart rate and urine production, which can lead to dehydration. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Nicotine, a substance found in tobacco, is also a stimulant. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine By increasing the release of the hormone epinephrine, nicotine increases heart rate, blood pressure, breathing rate, and stomach acid secretion. Section 36.3 Summary – pages

Stimulants: Cocaine, amphetamines, caffeine, and nicotine Although nicotine is the addictive substance in tobacco, there are many other harmful chemicals found in tobacco products. Smoking cigarettes leads to an increased risk of lung cancer and cardiovascular disease. Section 36.3 Summary – pages

Depressants: Alcohol and barbiturates One of the most widely abused drugs in the world today is alcohol. This depressant is distributed throughout a person’s body via the bloodstream. Section 36.3 Summary – pages

Depressants: Alcohol and barbiturates Alcohol also appears to block the movement of sodium and calcium ions across the cell membrane, a process that is important in the transmission of impulses and the release of neurotransmitters. Section 36.3 Summary – pages

Depressants: Alcohol and barbiturates Addiction to alcohol—alcoholism—can cause the destruction of nerve cells and brain damage. Cirrhosis, a hardening of the tissues of the liver, is a common affliction of alcoholics. Section 36.3 Summary – pages

Depressants: Alcohol and barbiturates Barbiturates (bar BIH chuh ruts) are sedatives and anti-anxiety drugs. When barbiturates are used in excess, the user’s respiratory and circulatory systems become depressed. Chronic use results in addiction. Section 36.3 Summary – pages

Narcotics: Opiates Most narcotics are opiates. They act directly on the brain. The most abused narcotic in the United States is heroin. It depresses the CNS, slows breathing, and lowers heart rate. Tolerance develops quickly, and withdrawal from heroin is painful. Section 36.3 Summary – pages

Hallucinogens: Natural and synthetic Hallucinogens stimulate the CNS—altering moods, thoughts, and sensory perceptions. Some hallucinogens are found in nature. Section 36.3 Summary – pages

Hallucinogens: Natural and synthetic The user sees, hears, feels, tastes, or smells things that are not actually there. This disorientation can impair the user’s judgment and place him or her in a potentially dangerous situation. Section 36.3 Summary – pages

Hallucinogens: Natural and synthetic Hallucinogens also increase heart rate, blood pressure, respiratory rate, and body temperature, and sometimes cause sweating, salivation, nausea, and vomiting. After large enough doses, convulsions of the body may even occur. Section 36.3 Summary – pages

Hallucinogens: Natural and synthetic LSD—or acid—is a synthetic drug. The mechanism by which LSD produces hallucinations is still debated, but it may involve the blocking of a CNS neurotransmitter. Section 36.3 Summary – pages

Anabolic steroids Anabolic steroids are synthetic drugs that are similar to the hormone testosterone. Section 36.3 Summary – pages

Anabolic steroids Anabolic steroids stimulate muscles to increase in size. Physicians use anabolic steroids in the treatment of hormone imbalances or diseases that result in a loss of muscle mass. Abuse of anabolic steroids is associated with infertility in men, high cholesterol, and extreme mood swings. Section 36.3 Summary – pages

Breaking the Habit Once a person has become addicted to a drug, breaking the habit can be very difficult. Besides the desire to break the addiction, studies have shown that people usually need both medical and psychological therapy—such as counseling—to be successful in their treatment. Section 36.3 Summary – pages

Nicotine replacement therapy Nicotine replacement therapy is one example of a relatively successful drug treatment approach. Section 36.3 Summary – pages

Nicotine replacement therapy To ease the intensity of the withdrawal symptoms, patients wear adhesive patches that slowly release small amounts of nicotine into their bloodstream. Alternatively, pieces of nicotine-containing gum are chewed periodically to temporarily relieve cravings. Section 36.3 Summary – pages

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