📜Classification of the Nervous System: Complete Guide for GPAT & University Exams (2026)

📚 Table of Contents

1. Introduction to the Nervous System
2. Structural Classification (Anatomical)
3. Functional Classification (Physiological)
4. Autonomic Nervous System in Detail
5. Comparison Tables
6. Pharmacy Perspective: Drugs Acting on the Nervous System
7. GPAT & Exam Pearls
8. Quick Revision Box
9. Frequently Asked Exam Questions

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📜 Introduction to the Nervous System

The nervous system is the body's master control and communication system. It processes information from the environment and coordinates responses. For pharmacy students, understanding nervous system classification is crucial because most drugs act on specific parts of this system.

The nervous system can be classified in two main ways:

1. Structural (Anatomical) Classification – Based on location
2. Functional (Physiological) Classification – Based on function

Let's break down each classification step-by-step.

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🏗️ Structural Classification of the Nervous System

The structural classification divides the nervous system based on where the components are located in the body.

1. Central Nervous System (CNS)

The CNS is the control center of the body. It consists of:

• Brain – Located in the skull; processes information and controls most body functions
• Spinal Cord – Runs down the vertebral column; transmits signals between the brain and the rest of the body

Functions:

• Integration of sensory information
• Decision-making and processing
• Initiation of motor responses

Clinical Relevance: CNS drugs include antidepressants, antiepileptics, sedatives, and general anesthetics.

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2. Peripheral Nervous System (PNS)

The PNS consists of all nerves outside the CNS. It connects the CNS to limbs and organs.

Components:

• Cranial Nerves (12 pairs) – Arise from the brain
• Spinal Nerves (31 pairs) – Arise from the spinal cord

Functions:

• Carries sensory information to the CNS
• Carries motor commands from the CNS

Structural Classification of the Nervous System

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⚙️ Functional Classification of the Nervous System

The functional classification divides the nervous system based on what it does – how it controls body functions.

1. Somatic Nervous System (SNS)

The somatic nervous system controls voluntary movements and processes conscious sensory information.

Components:

• Sensory (Afferent) Division – Carries signals from sensory receptors to CNS
• Motor (Efferent) Division – Carries signals from CNS to skeletal muscles

Key Features:

• Controls skeletal muscles
• Under conscious control
• Single neuron pathway from CNS to muscle

Example: When you decide to pick up a pen, your somatic nervous system controls the muscle movements.

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2. Autonomic Nervous System (ANS)

The autonomic nervous system controls involuntary functions like heart rate, digestion, and breathing.

Key Features:

• Controls smooth muscle, cardiac muscle, and glands
• Works automatically (unconsciously)
• Two-neuron pathway: preganglionic and postganglionic neurons

The ANS is further divided into three subdivisions:

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A. Sympathetic Nervous System

Mnemonic: "Fight or Flight" "S for Stress, S for Sympathetic"

Origin: Thoracolumbar region (T1–L2 spinal segments)

Functions:

• Increases heart rate
• Dilates pupils
• Inhibits digestion
• Releases glucose from the liver
• Dilates bronchioles
• Prepares body for emergency

Neurotransmitters:

• Preganglionic: Acetylcholine (ACh)
• Postganglionic: Norepinephrine (NE) – except sweat glands (ACh)

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B. Parasympathetic Nervous System

Mnemonic: "Rest and Digest" "P for Peace, P for Parasympathetic"

Origin: Craniosacral region (Cranial nerves + S2–S4 spinal segments)

Functions:

• Decreases heart rate
• Constricts pupils
• Stimulates digestion
• Promotes salivation
• Constricts bronchioles
• Conserves energy

Neurotransmitters:

• Preganglionic: Acetylcholine (ACh)
• Postganglionic: Acetylcholine (ACh)

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C. Enteric Nervous System (ENS)

Often called the "Second Brain", the ENS controls the gastrointestinal system.

Location: Embedded in the walls of the digestive tract

Functions:

• Controls gut motility
• Regulates secretion of digestive enzymes
• Regulates blood flow in the gut

Key Point: The ENS can function independently of the CNS but is influenced by the sympathetic and parasympathetic systems.

Functional Classification – Autonomic Nervous System

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📊 Comparison Tables

Table 1: CNS vs PNS

Feature	Central Nervous System (CNS)	Peripheral Nervous System (PNS)
Location	Brain and spinal cord	Nerves outside CNS
Components	Brain, spinal cord	Cranial nerves, spinal nerves
Function	Processing and integration	Transmission of signals
Protection	Skull and vertebral column	No bony protection
Example Drugs	Antiepileptics, sedatives	Local anesthetics

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Table 2: Somatic vs Autonomic Nervous System

Feature	Somatic Nervous System	Autonomic Nervous System
Control	Voluntary	Involuntary
Effectors	Skeletal muscles	Smooth muscle, cardiac muscle, glands
Neuron Pathway	Single neuron	Two neurons (pre- and postganglionic)
Neurotransmitter	Acetylcholine	ACh and Norepinephrine
Example	Moving your hand	Heart beating

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Table 3: Sympathetic vs Parasympathetic

Feature	Sympathetic	Parasympathetic
Origin	Thoracolumbar (T1–L2)	Craniosacral (Cranial + S2–S4)
Function	Fight or Flight	Rest and Digest
Heart Rate	Increases	Decreases
Pupil Size	Dilates	Constricts
Digestion	Inhibits	Stimulates
Bronchioles	Dilates	Constricts
Postganglionic NT	Norepinephrine (mostly)	Acetylcholine
Ganglion Location	Close to spinal cord	Close to target organ

Sympathetic vs Parasympathetic Effects on Organs

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💊 Pharmacy Perspective: Drugs Acting on the Nervous System

Understanding nervous system classification is essential because drugs target specific divisions.

1. Drugs Acting on the Sympathetic Nervous System

A. Sympathomimetics (Adrenergic Agonists)

• Examples: Adrenaline, Noradrenaline, Salbutamol
• Mechanism: Mimic sympathetic activity by activating adrenergic receptors (α and β)
• Uses: Asthma (bronchodilation), cardiac arrest, hypotension

B. Sympatholytics (Adrenergic Antagonists)

• Examples: Propranolol (β-blocker), Prazosin (α-blocker)
• Mechanism: Block adrenergic receptors
• Uses: Hypertension, angina, arrhythmias

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2. Drugs Acting on the Parasympathetic Nervous System

A. Parasympathomimetics (Cholinergic Agonists)

• Examples: Pilocarpine, Bethanechol
• Mechanism: Mimic parasympathetic activity by activating cholinergic receptors
• Uses: Glaucoma, urinary retention

B. Parasympatholytics (Anticholinergics)

• Examples: Atropine, Scopolamine
• Mechanism: Block muscarinic receptors
• Uses: Bradycardia, motion sickness, pre-anesthetic medication

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3. CNS Drugs

• Sedatives/Hypnotics: Diazepam, Zolpidem
• Antiepileptics: Phenytoin, Carbamazepine
• Antidepressants: Fluoxetine, Amitriptyline
• Antipsychotics: Haloperidol, Risperidone

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Exam Pearl 💡

Why do anticholinergics cause dry mouth? Because they block muscarinic receptors in salivary glands, which are normally stimulated by the parasympathetic nervous system to produce saliva.

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📌 GPAT & Exam Pearls

✅ The sympathetic system originates from T1–L2 (Thoracolumbar)

✅ The parasympathetic system originates from cranial nerves and S2–S4 (Craniosacral)

✅ All preganglionic neurons release acetylcholine

✅ Sympathetic postganglionic neurons mostly release norepinephrine (except sweat glands)

✅ Parasympathetic postganglionic neurons release acetylcholine

✅ Atropine blocks muscarinic receptors → used in bradycardia

✅ Propranolol is a non-selective β-blocker → used in hypertension

✅ The enteric nervous system can function independently of the CNS

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⌛ Quick Revision Box

Division	Origin	Function	Key NT	Example Drug
Sympathetic	T1–L2	Fight or Flight	NE	Adrenaline
Parasympathetic	Craniosacral	Rest & Digest	ACh	Atropine (blocker)
Somatic	CNS	Voluntary movement	ACh	Tubocurarine (blocker)
Enteric	GI tract	Gut control	ACh, Serotonin	Ondansetron

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❓ Frequently Asked Exam Questions

Q1. What is the origin of the sympathetic nervous system? 

A: Thoracolumbar region (T1–L2 spinal segments)

Q2. Which neurotransmitter is released by parasympathetic postganglionic neurons? 

A: Acetylcholine (ACh)

Q3. Name one drug that blocks muscarinic receptors. 

A: Atropine

Q4. What is the main function of the somatic nervous system? 

A: Control of voluntary skeletal muscle movements

Q5. Which part of the nervous system is called the "second brain"? 

A: Enteric Nervous System (ENS)

Q6. What effect does the sympathetic system have on heart rate? 

A: Increases heart rate

Q7. Give an example of a β-blocker. 

A: Propranolol

Q8. What is the functional unit of the nervous system? 

A: Neuron

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Pro Tip for Exam Success: Create a mind map of the nervous system classification and stick it on your study wall. Visual learning helps retain complex classifications better than reading alone!

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Happy Learning! 🎓💊