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.Dendrite2. Cell body

3. Axon4. Vesicles

5. Neurotransmitter6. 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

AcetylcholineSerotoninGamma-aminobutyric Acid (GABA)CatecholaminesPeptides

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

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 thedesired 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