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Class notes PHAR 100 (PHAR100)
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Comprehensive notes for Phar 100
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Drugs of AbusePhysiological and pharmacological aspects of the central nervous
system:
Many drugs affect the nervous system. In general, the nervous system is specialized to recognize,
process, integrate, and react to stimuli in the environment.
- Recognize – identify changes in the internal or external environment
- Process & Integrate – Perceive the changes in the environment
- React – Produce a response or an action to the changes in the environment.
Divisions of the nervous system:
The nervous system controls all bodily functions. It consists of two divisions: the central and peripheral
nervous systems.
- Central nervous system (CNS): Composed of brain and spinal cord
- Peripheral Nervous system (PNS): All other nervous tissue
The Central Nervous System:
It is composed of two major parts:
The Brain
- Receives and processes information
- Initiates a response
- Stores memory
- Generates thoughts and emotion
The brain is made up of several parts:
The Forebrain:
This part of the brain is made up of:
- Cerebral Cortex: The largest part of the brain. Functions are sensory and motor coordination,
mental processes, intelligence, memory, vision, judgement, thought, speech, emotions, and
consciousness. The cerebral cortex can be stimulated or depressed by drugs.
- Thalamus: The relay centre where impulses are transmitted to the cerebral cortex. The thalamus
coordinates and filters incoming signals.
- Limbic System: Closely associated with the hypothalamus, the limbic system integrates memory,
emotion, and reward. Together with the hypothalamus, it regulates emotion and behavior. It
also contains the dopaminergic reward centers which are the targets of drugs for abuse.
- Hypothalamus: Consists of various specialized regions near the base of the skull. One function is
to control involuntary functions. It also controls feeding, drinking, sexual, and emotional
responses. The hypothalamus produces substances called releasing factors which modify
hormone release from the pituitary glad. Many drugs can affect the hypothalamus.
, - Pituitary: A small gland located at the base of the brain that secretes hormones. These
hormones act on peripheral issues, and control growth, behavior, and metabolism.
The Midbrain:
The midbrain is the area that links the forebrain with the hindbrain. It is a relay centre for visual and
auditory stimuli.
The Hindbrain:
The hindbrain has many components. Only three are mentioned here:
- Pons: Connects the midbrain to the medulla and cerebellum. As such, the pons is involved in
conducting signals from the cerebral cortex down to the medulla and cerebellum
- Medulla: The medulla is the site of origin of many cranial nerves. It is also where regulation of
respiration, heart rate, blood pressure and some involuntary activity occurs. Several drugs which
depress respiration and blood pressure will do so by depressing the medulla
- Cerebellum: Responsible for coordination and posture. The cerebellum does not initiate
movement, but is an organizer of voluntary activity initiated elsewhere. Drugs that affect the
cerebellum (Alcohol) will cause ataxia (loss of coordination).
Neurons:
These are the main cell in the nervous system. They are composed of three main parts:
1. Dendrites – Short, highly complex branching arms that function to receive incoming information.
Upon receipt of this information from another cell, electric current is generated and directed
down the neuron.
2. Cell body (Soma) – The largest part of the neuron. Contains a nucleus and cytoplasm. Contains
vesicles which can be secreted.
3. Axon – A single fibre that extends from the soma and ends at a synapse. The axon continues to
carry the incoming information away from the dendrites and cell body by way of electrical
pulses. This information is then passed on to subsequent neurons. Some neurons are activated
by others, and some can activate themselves spontaneously.
Drugs and synaptic transmission:
The synapse can be a target site for many drugs, with some drugs interrupting synaptic transmission,
while other enhance or facilitate it, thereby modifying the activity of the brain.
Neurotransmitters and Receptors:
In the human brain, hundreds of different types of receptors exist for a large number of
neurotransmitters.
, - Glutamate: The primary excitatory neurotransmitter in the CNS and is found in almost all
neurons. Glutamate acts on a family of receptors called the glutamatergic receptors.
Glutamatergic neurons are responsible for learning.
- Gamma-amino butyric acid (GABA): The primary inhibitory neurotransmitter in the CNS.
GABAgeric neurons and receptors are found in high concentrations in the cerebral cortex,
hippocampus, and cerebellum. A number of CNS depressants enhance GABA receptor function.
- Acetylcholine: Produces an excitatory response in the CNS. Receptors that bind acetylcholine
are termed cholinergic receptors. There are two types of these:
1. Nicotinic receptors – Found in certain regions of the brain. These can be stimulated by
acetylcholine or nicotine
2. Muscarinic receptors – Found in many regions of the brain and are involved in learning,
memory, and cognitive function. These receptors can be stimulated by acetylcholine or
muscarine. Drugs that block the action of acetylcholine at these receptors produce amnesia.
Loss of these cholinergic neurons is thought to be associated with Alzheimer’s
- Catecholamines: There are two major catecholamines:
1. Dopamine – Dopaminergic pathways are involved in control of some hormonal systems,
motor coordination, and motivation and reward. Disturbances in these pathways are
associated with Parkinson’s and schizophrenia, depending on the location
2. Norepinephrine – Can bind to a large number of receptor types, the two main classes are
alpha and beta. Activation of these receptors usually leads to the excitation of a cell. This
pathway is targeted by some CNS stimulants.
- Serotonin: In the CNS, hyperactivity of the serotonergic system is involved in anxiety, and
hypoactivity has been implicated in depression. Some classes of CNS stimulants act by increasing
serotonin at the synapse.
- Opioid peptides: There are three main types of opioid: enkephalins, endorphins, and
dynorphins. They have varying degrees of selectivity for three receptors: mu, delta, and kappa.
All opioids interact with all receptors.
-
Substance abuse and dependence
Why do people abuse drugs?
They gain something from their use. The gain may be an altered feeling, benefits from social interaction,
or the thrill of experiencing something new and risky. The greater the “good feeling” obtained from a
drug, the more likely the use of the drug will be repeated. This is known as reinforcement.
Factors that influence substance use disorder (SUD):
- Genetic factors: these can predispose someone to SUD. Sons of alcoholic parents are more likely
to become alcoholics themselves
- Coexisting disorders: Issues like depression and schizophrenia can affect if someone develops
SUD
- Environmental Factors: Family, social circles, and culture can all have an effect of substance use
- Developmental factors: Adolescence and early adulthood are when most SUD’s develop.
, The dopamine hypothesis:
This hypothesis suggests that drugs of abuse increase dopamine in the reward systems of the brain. (the
limbic system). Other systems are involved as well, but dopamine seems to be the most important.
Dopaminergic systems are also responsible for natural rewards as well as stimulus-based rewards. Drugs
of abuse can cause exaggerated increases in dopamine.
Features of addictive drugs:
Addictive drugs can be classified into three categories:
1. Increase dopamine
- Cocaine
- Nicotine
- Caffeine
- Morphine
- Alcohol
- Cannabis
2. Produce novelty:
- LSD
- Ecstasy
3. Reduce Anxiety:
- Benzodiazepines
- Barbiturates
The use of addictive drugs can lead to substance abuse and then dependence.
Medical Perspective: Substance abuse is a pattern of use that has adverse consequences. These include
hazardous use, failure to fulfill obligations, legal problems and social/personal problems.
Social Perspective: By this definition, substance abuse refers to the use of any drug in a manner that
deviates from the approved medical or social patterns within a given culture. Conveys social disapproval
and not necessarily adverse effects.
Criteria for substance abuse:
Based on the above perspectives, the following criteria for substance abuse were created:
- The use of prohibited drugs
- The use of any therapeutic drug for other than it’s purpose
- Intentional intake of therapeutic drug in higher doses or ways other than medically prescribed
- Combining drugs to achieve greater effect
- Excessive use of legal social drugs
- The use of non-therapeutic substances of abuse
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