Introduction to Pharmacology of CNS

CNS consists of two main organs;

• Brain
• Spinal Cord
• This is the information superhighway of the body. It carries information up to the brain and instructions back down.

Brain

It consists of following parts;

Cerebellum

• Mostly deals with movement. It regulates and coordinates movement, posture and balance. Also involved in learning movement

Cerebrum

• The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action.

Midbrain

• Midbrain/ Mesencephalon- the rostral part of the brain stem, which includes the tectum and tegmentum
• It is involved in functions such as vision, hearing, eyemovement, and body movement.

Types of Drugs in CNS

• In CNS, synapses are the main junctions at the neuronal terminals.
• Drugs are based on the type of neurotransmitters which are of 2 types;
• Excitatory
• Inhibitory

Stimulants

• Drugs stimulating the excitatory neurotransmitters are called stimulants. E.g. Ach, Dopamine, epinephrine and nor-epinephrine.

Depressants

• Drugs stimulating inhibitory neurotransmitters are called depressants. E.g. GABA (gamma amino butyric acid)(Brain), Glycine (spinal cord).
• Depressants are mainly used in human practice.

Stages of Stimulation

Stages of Depression

Terminology

Sedation

There is slight depression but animal is awake.

Hypnosis

Animal is greatly depressed and seems to be asleep but can be awakened.

Tranquilizers

Slight Depression but animal behaves abnormally to external stimuli.

Narcosis

There is greater depression and animal is asleep and can be awakened but will again sleep. There is good analgesia.

Anesthesia

Animal is under greater depression and asleep but cannot be awakened. There is hyporeflexia.

Dissociative Anesthetics

Animal is superficially anesthetized and there is myotonia (movement in muscles).

There is analgesia but reflexes are present.

Basal Anesthetics

This anesthesia is maintained by other agents.