Drugs act on central nervous system

Learning objectives: Learn about the drugs that act on central nervous system, their classification and mechanism of action

Sympathetic vs Parasympathetic nervous system  

Autonomic Nervous System (ANS)

• Controls involuntary body functions like heart rate, digestion, respiration, and gland activity.

• The Autonomic Nervous System (ANS) is divided into two main divisions that work in opposition to maintain body balance (homeostasis).:

1. Sympathetic nervous system (SNS) – “fight or flight”

2. Parasympathetic nervous system (PNS) – “rest and digest”

1. Sympathetic Nervous System (SNS)

• Function: Prepares the body for stressful or emergency situations.

• Origin: Thoracolumbar region of the spinal cord (T1–L2).

• Main neurotransmitters: Acetylcholine (preganglionic), Norepinephrine (postganglionic).

• Key effects:

• Increases heart rate and force of contraction

• Dilates bronchi to improve breathing (bronchodilation)

• Constricts blood vessels in the skin and gut

• Increase blood pressure

• Dilates pupils (mydriasis)

• Reduces gastrointestinal motility and secretions, thereby, digestion and intestinal activity

• Stimulates sweat glands

• Adrenal medulla releases adrenaline for rapid response

2. Parasympathetic Nervous System (PNS)

• Function: Conserves energy and promotes relaxation, digestion, and repair.

• Origin: Cranial nerves (III, VII, IX, X) and sacral spinal cord (S2–S4).

• Main neurotransmitter: Acetylcholine (both pre- and postganglionic).

• Key effects:

• Slows heart rate

• Constricts bronchi

• Stimulates digestion and intestinal activity

• Constricts pupils and focuses the lens for near vision

• Promotes urination

• Stimulates salivation

• SNS = fight or flight → prepares for action

• PNS = rest and digest → conserves energy and restores body function

Further reading

• Antibiotic Classes in 7 minutes

• A Brief Overview of Classes of Antibiotics

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