Article 13. 1 Drug effects on the nervous system

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Identify the choice that best completes the statement or answers the question.

Article 13.1 Drug effects on the nervous system

The business of the nervous system is to transmit information from one cell to another. Although this happens in different locations and with different neurotransmitters, the basic process is common to all cell-to-cell transmission. First, neurotransmitter molecules must be synthesized. Then, they must be packaged in synaptic vesicles. At the appropriate time, they must exit the cell by exocytosis, cross the synaptic cleft and bind and activate receptors on the post-synaptic neuron. The neurotransmitter molecules must then be either degraded or taken back into the presynaptic neuron, a process known as reuptake. Psychoactive drugs exert their effects by interfering with one or more of these steps.

Some of these drugs, known as stimulants, increase synaptic activity. Amphetamines, for example, increase the release from presynaptic cells of the group of neurotransmitters known as catecholamines. These include epinephrine, norepinephrine, and dopamine.

Caffeine is a competitive inhibitor of the neuromodulator adenosine, whose function is to inhibit the release of excitatory catecholamine transmitters. Nicotine activates certain acetylcholine receptors at neuromuscular junctions and in the central nervous system. Cocaine blocks the reuptake of catecholamines from synapses. The hallucinogens LSD and psilocybin are agonists of the serotonin recetros meaning that they mimic the effects of serotonin.

The so-called depressants decrease activity in the nervous system. Alcohol, for example, increases the number of GABA receptors on post-synaptic membranes. Because GABA is an inhibitory neurotransmitter, more GABA receptors allow more GABA molecules to affect post-synaptic neurons, decreasing their rate of firing. Opioids, including heroin and morphine, resemble endogenous molecules called endorphins that are involved in the control of pain.

In certain cases, two drugs interact so that one intensifies or negates the effect of the other. Alcohol and barbiturates are both depressant drugs. Taken together, they have a synergistic effect. Doses of these two drugs that would be tolerated if taken separately become lethal if taken together.

Source Citation: Rotundo, Lissa. "Drug effects on the nervous system." World of Anatomy and Physiology. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. Detroit: Gale, 2002. Science Resource Center. Thomson Gale. 25 February 2007

____ 1. Use Article 13.1 to answer the following.

Nicotine, a compound found in cigarette smoke, acts as a stimulant by


increasing the synthesis of neurotransmitters.


prevents the breakdown of neurotransmitters after synaptic discharge.


activates acetylcholine receptors on the pre-synaptic neuron.


activates acetylcholine receptors on the post-synaptic neuron.

____ 2. Use Article 13.1 to answer the following.

A drug that increases the amount of epinephrine and norepinephrine is


an amphetamine.







Article 13.2 Nervous system overview

The nervous system is responsible for short-term immediate control of the human body and for communication between various body systems. Although the endocrine system achieves long-term communication and control via chemical (hormonal) mechanisms, the nervous system relies on a faster method of alternating chemical and electrical transmission of signals, and commands through a network of specialized neural cells (neurons). In addition to neurons, there are a number of cell types that play a supportive role in the nervous system. Principal among these neuron-supporting cells are Schwann cells associated with an insulating myelin sheath that wraps around specific types of neural fibers or tracts.

Neurons contain key common components. At one end, the dendrite end, specialized cell processes and molecular receptor sites bind neurotransmitters released by other neurons and sensory organs across a gap known as the neural synapse. At the dendrite, the nerve impulse within a particular neuron is generated by a series of chemical and electrical events associated with the binding of specific neurotransmitters. The nerve impulse then travels down the neuron cell body, the axon, via an electrical action potential that results from rapid ion movements across the neuron's outer cell membrane. Ultimately, the action potential reaches the presynaptic terminus region where the electrical action potential causes the release of cell specific neurotransmitters that diffuse across the synapse (the gap between neurons) to start the impulse generation and conduction sequence in the next neuron in the neural pathway. The major chemical neurotransmitters include acetylcholine, norepinephrine, dopamine, and serotonin.

Neural transmission and the diffusion of neurotransmitters across the synapse do not always produce a subsequent action potential without the combined input of other neurons in a process termed summation. Depending on the specific neurotransmitters, receptor binding can produce either excitation or inhibition of action potential production. Subject to a refractory period during which a neuron returns to its normal state following the production of an earlier action potential, once the a neuron reaches a properly timed threshold stimulus, it will produce an action potential. The production of action potentials is an "all or none" process and once produced, the axon potential (nerve impulse) sweeps down the axon.

The nervous system is organized along morphological (structural) and functional lines. Structurally, the nervous system can be dived into the central nervous system (CNS) that includes the brain and spinal cord, and the peripheral nervous system (PNS) that contains all other nerves (e.g., sensory and motor neurons), ganglia, and associated cells.

Functionally, the nervous system can be divided into the somatic or voluntary nervous system (VNS) that coordinates voluntary muscles and reflexes, and the autonomic nervous system (ANS) associated with the regulation of viscera, smooth muscle, and cardiac muscle. The autonomic nervous system is further subdivided into sympathetic and parasympathetic systems.

The sympathetic nervous system (SNS), when related to the classic "fight or flight" response, heightens activity in bodily organs or systems and the metabolic rate. In contrast, the parasympathetic nervous system (PNS) lowers response and decreases the metabolic rate. The sympathetic and parasympathetic systems work in opposition to control bodily systems.

The brain is divided into various areas or lobes. The large left and right anterior lobes represent the convoluted (wrinkled) cerebral cortex or cerebrum. Posterior lobes represent the cerebellum. At the top of the spinal cord lies the pons and medulla. The cerebellum, pons, and medulla together are referred to as the hindbrain and are associated with many basic process involved in body maintenance, metabolism (e.g. breathing and heart rate) and homeostasis. In general, the forebrain (the cerebrum and some related areas) is the area responsible for higher intellectual functions involved in sensory interpretations, memory, language, and learning. The midbrain tract act as switching systems that direct, coordinate, and integrate impulses among various regions of the brain.

Nerves usually contain neuron cell bodies that lie in tracts or fibers. Unmyelinated axons form gray matter. When Schwann cells wrap around the axon they create a myelin sheath around neurons (in the peripheral nervous system) that in tracts or fibers are termed white matter. Because the myelin sheath disrupts the normal transmission of the electrical action potential down the neuron, a specialized form of conduction of the nerve impulse or action potential occurs between spaces in the myelin sheath termed the nodes of Ranvier. Accordingly, diseases that disrupt or destroy the myelin sheath (demyelinating diseases) can impair or destroy normal nerve function.

Schwann cells are only one form of neuroglia or glial cells that are required to support normal neural function. Other glial cells include astrocytes, microglia, ependymal cells, oligodendrocytes, and satellite cells. Astrocytes are necessary for the proper vascularization of nerve cells and for the transport of nutrients and the removal of cellular waste products across the blood brain barrier. Microglia cells engage in phagcytosis and are capable of helping defend neural cells from attacks by a range of pathogenic agents. Ependymal cells line brain and spinal ventricles (fluid filled cavities in the brain and spine) and produce and maintain cerebrospinal fluid. Oligodendrocytes are responsible for the production of the myelin sheath in the CNS. Satellite cells protect neurons in ganglia.

Source Citation: Lerner, K. Lee. "Nervous system overview." World of Anatomy and Physiology. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. Detroit: Gale, 2002. Science Resource Center. Thomson Gale. 25 February 2007

____ 3. Use Article 13.2 to answer the following.

The path taken by an electrical impulse in a neuron is


presynaptic terminus, dendrite, cell body, axon


dendrite, cell body, axon, presynaptic terminus


dendrite, cell body, axon, postsynaptic terminus


presynaptic terminus, dendrite, cell body, axon, postsynaptic receptors

____ 4. Use Article 13.2 to answer the following.

How does the body defend itself against disease-causing organisms?


Astrocytes remove waste products that could enhance the growth of pathogens.


Cerebrospinal fluid flushes pathogens out of the system.


Microglia cells attack and destroy pathogens using phagocytosis.


Schwann cells wrap around the axon, isolating it.

____ 5. Use Article 13.2 to answer the following.

The region of the brain that is thinking of answers to this question is the









Article 14.1 Sense Organs: Balance and Orientation

Embedded in the temporal bone inside the inner ear lays the vestibular system, which contains fluid-filled sacs and cavities that monitor the position and movement of the head and transmit that information to the brain. This system contains three semicircular canals, each oriented at right angles to the other two. The canals are connected to a saclike utricle, below which lies the sacule, another hollow structure.

The utricle and sacule contain receptors consisting of groups of hair-like cells, cilia, that are embedded in a gelatinous material. The gelatinous material contains many small particles of calcium carbonate called otoliths. These increase the sensitivity of the cilia. At the base of each receptor is a nerve fiber. The nerve fibers collectively carry information to the brain via cranial nerve VIII, the auditory vestibular nerve. The receptors of the saccule and utricle respond to static positions of the head. In other words, they tell the brain which way is up.

The semicircular canals also contain gelatin-embedded receptors bearing cilia. These cilia detect changes in the rate of rotation or angular movements of the head. When the head moves, the fluid in the semicircular canals presses against the hair cells, causing them to bend. Bending of the cilia triggers action potentials in the nerve fibers connected to the receptors. More rotation causes more bending, causing more action potentials. The specific direction of head movement stimulates different receptors in the canals in each of the three planes. A three-dimensional message about direction of head movement is therefore compiled and sent to the brain along the eighth cranial nerve.

Low frequency movements that a person can't control often lead to motion sickness. Most often, a person may experience motion sickness as a passenger, but not as the driver. Motion sickness is probably the result of the brain's receiving contradictory information from the eyes and the vestibular system. The eyes, fixed on the interior of the vehicle, report "no motion" to the brain, while the stimulation of the hair cells reports "motion." Destruction of the semicircular canals by antibiotics or other drugs eliminates motion sickness.

Some of the neurons of the auditory vestibular nerves synapse in the vestibular nuclei of the lower brain stem. From here, neurons synapse on the motor neurons that control the muscles that move the eyes and on nuclei in the thalamus, cerebral cortex, and other locations. Some of the neurons, however, carry information from the inner ear directly to the cerebellum, a structure that coordinates motor control. The cerebellum uses information about the position and movement of the head to regulate to regulate output from the motor cortex, helping to maintain balance.

Source Citation: Rotundo, Lissa. "Sense organs: Balance and Orientation." World of Anatomy and Physiology. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. Detroit: Gale, 2002. Science Resource Center. Thomson Gale. 25 February 2007

____ 6. Use Article 14.1 to answer the following question.

What is monitored by the fluid-filled structures of the inner ear?


position of the head


amplitude of sound waves


movement of the head


both a and c

____ 7. Use Article 14.1 to answer the following question.

What bends the cilia of the receptor cells when you tilt your head to one side?


fluid movement


gelatin movement


otolith movement


nerve fibres at the base of the receptor

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