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Chapter 5
The Pharmacology and Physiology of
Drug Use
Drug Actions
Drugs affect various organs within the
body including the nervous system
The basic unit of the nervous system is
the neuron
The Neuron
A neuron contains two types of nerve
fibers: dendrites and axons
-Dendrites allow nerve impulses to be
transmitted to the nerve’s cell body
-Axons send away impulses from the
cell body
Electrical impulses originate in the
dendrite and pass through the cell
body via the action – this process is
called action potential
For an electrical message to be sent
from the axon of one neuron to the
dendrite of another neuron it must
transverse a space called a synapse.
At the end of the axons are saclike
structures called vesicles
Inside the vesicles are chemicals called
neurotransmitters
The neuron releases the
neurotransmitter into the synapse
and the chemical will then influence
the next neuron
1.Dendrite
2. Cell body
3. Axon
4. Vesicles
5. Neurotransmitter
6. Synapse
Neurotransmitters
Most drugs affect brain activity by
increasing or decreasing the activity
of various neurotransmitters.
Neurotransmitters enable the brain to
receive, process, and respond to
information by carrying impulses from
one neuron to the next
Selected Neurotransmitters
Acetylcholine
Serotonin
Gamma-aminobutyric Acid (GABA)
Catecholamines
Peptides
Acetylcholine
Acetylcholine acts as an excitatory
neurotransmitter in the skeletal
muscles but functions as an inhibitory
neurotransmitter in heart muscle.
Serotonin
Serotonin is an inhibitory
neurotransmitter and plays an
important role in regulating pain,
sensory perception, eating, sleep, and
body temperature
Gamma-aminobutyric Acid (GABA)
GABA is a neurotransmitter that inhibits
nerve impulses from being sent from
one neuron to another
Catecholamines
Catecholamines are a group of
neurotransmitters that impact
emotional issues. Examples are
dopamine and epinephrine
Dopamine plays a significant role in
emotional, mental, and motor
functions
Epinephrine (or adrenaline) speeds up
coronary blood flow and heart rate
and is a key neurotransmitter in the
fight-flight-fight syndrome
Peptides
Peptides are substances in which
sequences of amino acids are linked.
Whether peptides are truly
neurotransmitters is questionable
because they modulate the activity of
neurotransmitters
Central Nervous System
The Central Nervous System (CNS)
consists of the brain and spinal cord.
The key structures and areas of the CNS
include the reticular activating system
(RAS), hypothalmus, cerebral cortex,
limbic system, medial forebrain
bundle, basal ganglia, and the brain
stem.
Reticular Activating System (RAS): Plays
a role in sleep, attention and arousal.
Hypothalamus: Comparable to a
biological central computer from
which many smaller computers
receive their directions
Cerebral Cortex: Higher brain center
needed for processing and
understanding information
Limbic System: Consists of many
diverse structures which serves as
the emotional center of the brain
Medial Forebrain Bundle: Serves as a
communication route between the
limbic system and the brain stem
Basal Ganglia: Maintains involuntary
motor control
Periventricular System: Implicated in
punishment or avoidance behavior
Brain Stem: Responsible for vital
functions (heartbeat and breathing)
Peripheral Nervous System
Peripheral Nervous System
encompasses the somatic nervous
system and the autonomic nervous
system.
Somatic Nervous System: Control
skeletal muscles and relay sensory
information to the CNS
Autonomic Nervous System: Regulates
blood pressure, gastrointestinal and
urinary functioning, body
temperature, sweating, and other
involuntary bodily functions.
Two Branches: Sympathetic and
Parasympathetic (work in
opposition to each other)
Drugs and Major Body Systems
Drugs not only impact the nervous
system but all body systems
especially the endocrine system,
cardiovascular system, respiratory
system, and gastrointestinal system.
Factors Influencing the Effects of
Drugs
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Age
Gender
Dosage
Purity and Potency
Drug Interactions
Tolerance
Set and Setting
Age: Infants and the elderly are more
sensitive to the effects of drugs than
people between these two life stages.
Drug actions are prolonged in infants
and the elderly because they are less
able to metabolize and excrete drugs
Gender: Females and males respond to
drugs differently because of
difference in fat and water content.
When controlling for weight, women
have a higher percentage of body fat
and lower percentage of water
making them more susceptible to the
actions of drugs
Dosage: The higher the amount of the
drug consumer the greater the effect.
Effective dose: the amount needed
to achieve a specific response
Lethal dose: the amount of a drug
that could cause death
Purity and Potency: The purer the drug
the more intense the effect. Potency
refers to a drug’s ability to produce
an effect relative to other drugs.
Drug Interactions: Combination of drugs
can result in a drugs negating the
effect of one another (antagonism) or
exaggerating the effect (synergistic)
Tolerance: State of progressively
decreasing responsiveness to a drug
Pharmacological Tolerance: Body
adjusts to the drug
Behavioral Tolerance: Individual
learns to adjust to the drug
Cross-tolerance: Developing a
tolerance to one drug results
in tolerance to a similar drug
Reverse Tolerance: User feels the
desired effects with lesser
amounts of the drug
Set and Setting: Set refers to the user’s
psychological makeup, personality,
mood, and expectation when using
drugs. Setting refers the
environment in which drugs are
taken.
Methods of Administration
Oral: Consumed as pills, liquids, tablets,
or capsules
Injection (parenteral): Injecting drugs
into the vein (intravenous), muscle
(intramuscular) or under the skin
(subcutaneous)
Topical Application: Applied to skin and
absorbed
Inhalation: Administered into the lungs
through inhalation
Summary
 The Central Nervous System,
primarily the brain is the focal point
for drug activity
 The neuron is the basic unit of the
nervous system
 Neurons secrete neurotransmitters
which are responsible for many drug
actions
 Drugs affect all body systems
 Factors influencing the effects of
drugs include age, gender, dosage,
purity and potency
 Tolerance is the progressively
decreasing responsiveness to a drug
 Set and setting are two variables
influencing the drug experience
 Methods of administration include
oral, injection, topical and inhalation