Many psychoactive substances are used or abused for their mood and perception altering effects, including those with accepted uses in medicine and psychiatry. Classes of drugs that are frequently abused include some of the drugs listed in Table below. Drugs that are deemed by to have no medical uses and a high potential for abuse are usually illegal.
Not all drugs are physically addictive, but any activity that stimulates the brain reward system can lead to psychological addiction. Drugs that are most likely to cause addiction are drugs that directly stimulate the dopaminergic system, like cocaine, nicotine, and amphetamines. Drugs that only indirectly stimulate the dopaminergic system, such as psychedelics, are not as likely to be addictive.
Some Common Drugs of Abuse Psychoactive Drugs Effects Examples Some Common Forms or Names
Stimulants Elevate the central nervous system and raise level of alertness and wakefulness Caffeine, cocaine, amphetamine, methamphetamine Coffee, coke, meth, ecstasy (X)
Hallucinogens Induce perceptual and cognitive distortions LSD, psilocybin, mescaline, PCP Acid, magic mushrooms, peyote, angel dust
Hypnotics Depress the CNS, and induce sleep Barbiturates, opioids (e.g. codeine, morphine, oxycodone), benzodiazepines, ethanol Diazapam, alcohol
Analgesics Induce euphoria, reduce sensation of pain Codeine, morphine, ketamine, heroin, phencyclidine (PCP), tetrahydrocannabinol (THC) Horse, angel dust, cannabis, marijuana
Lesson Summary
Neurons are typically made up of a cell body, dendrites, and an axon. The cell body contains the nucleus and other organelles similar to other body cells. The dendrites extend from the cell body and receive a nerve impulse from another cell. The cell body collects information from the dendrites and passes it along to the axon. The axon is a long, membrane-bound extension of the cell body that passes the nerve impulse onto the next cell.
Voltage is electrical potential energy that is caused by a separation of opposite charges across the membrane. The voltage across a membrane is called membrane potential. Membrane potential is the basis for the conduction of nerve impulses along the cell membrane. In an action potential, the cell membrane potential changes quickly from negative to positive as sodium ions flow into and potassium ions flow out of the cell through ion channels.
A neurotransmitter is a chemical message that is used to relay electrical signals between a neuron and another cell. Neurotransmitter molecules are made inside the presynaptic neuron and stored in vesicles at the axon terminal.
The central nervous system represents the largest part of the nervous system, and includes the brain and the spinal cord. The brain is the central control of the nervous system, and the spinal cord carries nerve impulses between the brain and the body, and from the body to the brain.
The sense organs include the eyes, ears, nose, mouth, and skin. They all have sensory receptors that are specific for certain stimuli. The eyes have photoreceptors for sight. The ears have mechanoreceptors that interpret stimuli as sound and also endolymph that aids in body balance. The nose has chemoreceptors for odors. The mouth has chemoreceptors for taste. The skin has a variety of mechanoreceptors and baroreceptors for touch.
Psychoactive drugs affect how neurons in the CNS communicate with each other. In this way a psychoactive drug changes how we feel, think, and interact with the world. Medicinal uses of psychoactive drugs include their use as anesthetics, painkillers, and antidepressants.
For an animation of the neuromuscular junction see http://www.youtube.com/watch?v=ZscXOvDgCmQ.
Review Questions
How does the body transmit electrical signals?
Describe the structure of a neuron.
Distinguish between a neuron and a glial cell.
Use this image of an action potential to answer the following questions.
Figure 20.35
What is the membrane potential at the peak (after 2 milliseconds)? Is it positive or negative?
What happens to the membrane potential after 5 ms?
At the peak point when the membrane potential is 40mV, does the cell have an overall negative charge or positive charge?
Hyperpolarization, which means the cell becomes more negatively charged than it is at resting potential (more negative than -70 mV),can happen as a result of the binding of an inhibitory neurotransmitter to its receptor. Propose what happens to sodium and potassium ions during hyperpolarization.
How does voltage relate to the membrane potential?
What would happen to a cell if its sodium and potassium pumps failed to work at the end of an action potential?
The backflow of a nerve impulse is prevented by the fact that at a chemical synapse, the axon terminal does not have neurotransmitter receptors and dendrites cannot secrete neurotransmitter chemicals. What does this statement tell you about the direction of nerve impulses in neurons?
Identify two types of synapses in the nervous system.
What is the purpose of the digestive enzymes found in the synaptic cleft?
Distinguish a neurotransmitter from a hormone.
What is the major function of the central nervous system?
Outline the major functions of the cerebral cortex.
Use this image of the lobes of the brain to answer the following questions.
Figure 20.36
What is the name of the blue structure?
Identify a sense that is interpreted in the yellow-colored lobe (center left), and name that lobe.
Identify the two main divisions of the peripheral nervous system, and describe their roles in the body.
What are the two divisions of the autonomic nervous system?
Distinguish between the sympathetic and parasympathetic nervous systems.
What type of sensory receptors are found in the eyes?
Distinguish between rods and cones.
Why are taste and smell called the “two chemical senses”?
Outline how the ear is important to the sense of body balance.
What role does skin have in detecting external stimuli?
What kind of effects should a drug have for it to be called psychoactive?
Identify the main effect of psychoactive drugs on the CNS.
How do the effects of a stimulant differ from the effects of a depressant?
What is the brain reward system and how is it affected by an addictive drug?
How does cocaine affect the brain reward system?
Use this graph that shows the differences in blood concentration of nicotine over time to answer the following questions.
Figure 20.37
Review the graph that illustrates the increases in blood-nicotine concentrations from four different forms of tobacco; Cigarettes, oral snuff, chewing tobacco, and nicotine gum. Which of the four forms of nicotine increases blood-nicotine concentration the fastest?
Which of the four forms of nicotine increases blood-nicotine concentration the least?
Can you tell from this graph whether one form of tobacco is safer than another?
Further Reading / Supplemental Links
http://training.seer.cancer.gov/module_anatomy/unit5_2_nerve_tissue.html
http://brainmaps.org/
http://teens.drugabuse.gov/index.asp
http://www.nida.nih.gov/scienceofaddiction
Vocabulary
action potential
An electrical charge that travels along the membrane of a neuron.
agonists
Drugs that increase activity in particular neurotransmitter systems; act by increasing the synthesis of one or more neurotransmitters or reducing its reuptake from the synapses.
antagonists
Drugs that reduce neurotransmitter activity; work by interfering with synthesis or blocking postsynaptic receptors so that neurotransmitters cannot bind to them.
astrocytes
A type of glial cell in the brain; important for the maturation of neurons and may be involved in repairing damaged nervous tissue.
autono
mic nervous system (ANS)
The part of the peripheral nervous system that maintains homeostasis in the body; controls such actions as heart rate, digestion, respiration rate, salivation, and perspiration; also called the involuntary nervous system.
axon
A long, membrane-bound extension of the cell body that passes the nerve impulse onto the next cell.
axon terminal
The end of the axon; the point at which the neuron communicates with the next cell.
brain stem
Part of the brain involved with unconscious (autonomic) functions such as breathing, heartbeat, and temperature regulation; contains the midbrain, the pons, and the medulla oblongata.
cerebellum
The part of the brain that is involved in coordination and control of body movement.
cerebral cortex
The highly-folded outer layer of the cerebrum; controls higher functions, such as consciousness, reasoning, emotions, and language; also controls sensory functions such as touch, taste, smell, and responses to external stimuli.
cerebrum
The part of the brain that generally controls conscious functions such as problem-solving and speech.
central nervous system (CNS)
Made up of the brain and spinal cord; the brain is the central control of the CNS; the spinal cord carries nerve impulses from the brain to the body and from the body to the brain.
chemical synapse
A synapse that uses chemical signaling molecules as messengers.
cochlea
A coiled tube within the ear; filled with a watery liquid which moves in response to the vibrations coming from the middle ear through the oval window; as the fluid moves, thousands of mechanoreceptors called hair cells bend, releasing a neurotransmitter.
cone cells
Photosensitive cells important to vision; located in the retina; respond to different wavelengths of bright light to initiate a nerve impulse; also responsible for the sharpness of images.
dendrites
Extend from the cell body and receive a nerve impulse from another cell.
diencephalons
The region of the brain that includes structures such as the thalamus, the hypothalamus, and a portion of the pituitary gland.
dorsal root
The “nerve highway;” carries sensory information from sensory receptors in the body to the CNS.
drug
Any chemical or biological substance that affects the body’s structure or functions.
drug abuse
The repeated use of a drug without advice or guidance of a medical professional, and use for reasons other than for what the drug was originally intended.
electrical synapse
Synapse that uses ions as messengers.
endocrine system
A system of glands around the body that release chemical signal molecules into the bloodstream.
glial cell
Cell that provides a support system for the neurons; also involved in synapse formation.
hallucinogens
Psychedelic drugs, such as lysergic acid diethylamide (LSD), phencyclidine (PCP), and ketamine; psychoactive drugs that do not increase or decrease a certain feeling or emotion, but rather they induce experiences, such as sensory distortions and “out-of-body experiences,” that are very different from those of ordinary consciousness.
hearing
The sense of sound perception that results from the movement of tiny hair fibers in the inner ear.
hypnotics (depressants)
Drug that decreases the activity of the central nervous system; slows down brain function and give a drowsy or calm feeling; includes alcohol, codeine, barbiturates, and benzodiazepines.
interneurons
Neurons that connect sensory and motor neurons in neural pathways that go through the CNS; also called association or relay neurons.
medicine (or medication)
A drug that is taken to cure or reduce the symptoms of an illness.
membrane potential
The voltage across a membrane; the basis for the conduction of nerve impulses along the cell membrane of neurons.
midbrain
Part of the brain involved with unconscious (autonomic) functions such as breathing, heartbeat, and temperature regulation.
motor division
Subdivision of the PNS; carries nerve impulses from the CNS to the muscles, glands and organs of the body; also called the efferent division.
motor neurons
Neurons that carry signals from the central nervous system to muscles and glands; sometimes called efferent neurons.
myelin sheath
An electrically insulating phospholipid layer; covers the axon; speeds up the transmission of a nerve impulse along the axon.
nerve
An enclosed, cable-like bundle of axons.
nervous system
A complex network of nervous tissue that sends electrical and chemical signals; includes the central nervous system (CNS) and the peripheral nervous system (PNS) together.
neuromuscular junction
A synapse between a neuron and a muscle cell.
neuron
The "conducting" cell that transmits electrical signals; the structural unit of the nervous system.
neurotransmitter
Chemical messages which are released at the synapse and pass the “message” onto the next neuron or other type of cell.
nociceptor
A type of pain receptor which responds to potentially damaging stimuli.
Nodes of Ranvier
Regularly spaced gaps between the myelin; the only points at which ions can move across the axon membrane, through ion channels.
olfactory receptors
The chemoreceptors of smell.
oligodendrocytes
Glial cells that supply myelin to neurons of the brain and spinal cord.
parasympathetic division
Subdivision of the ANS; controls non-emergency functions such as digestion.
peripheral nervous system (PNS)
Made up of the nervous tissue that lies outside the CNS, such as the nerves in the legs, arms, hands, feet and organs of the body.
pinna
The folds of cartilage surrounding the outer ear canal; gathers sound waves which are channeled down the auditory canal, a tube-shaped opening of the ear which ends at the tympanic membrane, or eardrum.
psychoactive drug
A substance that affects the central nervous system by altering cognitive function.
reflex
An automatic (involuntary) action caused by a defined stimulus and carried out through a reflex arc.
resting potential
The resting state of the neuron, during which the neuron has an overall negative charge.
reuptake
The removal of a neurotransmitter from the synapse by the pre-synaptic neuron; a way of controlling the effect the neurotransmitter has on the post-synaptic cell.
rod cells
Photosensitive cells important to vision; located in the retina; highly sensitive to light which allows them to respond in dim light and dark conditions, but, they cannot detect color.
Schwann cells
Cells that supply the myelin for neurons that are not part of the brain or spinal cord.
sensory division
Subdivision of the PNS; carries sensory information from sensory receptors in the body to the CNS; also known as the afferent division.
sensory neurons
Neurons that carry signals from tissues and organs to the central nervous system; sometimes called afferent neurons.
sight (vision)
Describes the ability of the brain and eye to detect certain wavelengths of electromagnetic radiation (light), and interpret the image.
sodium-potassium pump
Transport protein that removes Na+ ions from the cell by active transport; also brings K+ ions into the cell.
somatic nervous system
The part of the PNS that is associated with the conscious (voluntary) control of the body through the movement of skeletal muscles and the perception of external stimuli through senses such as touch, hearing, and sight.
spinal cord
A thin, tubular bundle of nervous tissue that extends from the medulla oblongata and continues to the lower back; functions as an information superhighway that links the sensory messages from the body to the brain.
stimulant
Psychoactive drug, such as cocaine, nicotine, and amphetamine, that increases the activity of the sympathetic nervous system, the central nervous system, or both; generally increase heart rate, blood pressure, and increase the sense of alertness.
sympathetic division
Subdivision of the ANS; generally stimulates body systems during emergency situations.
synapse
A specialized junction at which neurons communicate with each other.
synaptic cleft
Gap between the axon terminal of the presynaptic neuron and the receiving cell.
CK-12 Biology I - Honors Page 96