The nervous system is the body’s master communication and control network. It coordinates every thought, emotion, and action—whether it’s as simple as blinking or as complex as solving a math problem. This system allows humans to sense their environment, process information, and respond quickly through a network of specialized cells called neurons.
The two main parts of the nervous system are:
1. Central Nervous System (CNS) – includes the brain and spinal cord.Structure of the Nervous System
1. Central Nervous System (CNS)
The CNS acts as the control center. It processes information and sends out commands.
Brain: The brain is the seat of consciousness, intelligence, memory, and emotions. It controls voluntary actions like walking and speech, and involuntary actions like heart rate and breathing.2. Peripheral Nervous System (PNS)
The PNS connects the CNS to limbs and organs. It is divided into:
Somatic Nervous System: Controls voluntary movements (e.g., moving your hand).The ANS itself is divided into:
Sympathetic Nervous System: Prepares the body for “fight or flight.”
Functions of the Nervous System
The nervous system works through electrical impulses and chemical signals to transmit messages between different body parts.
Major functions include:
- Sensory Input: Gathering information from sensory organs.
- Integration: Processing and interpreting sensory information.
- Motor Output: Sending instructions to muscles or glands for response.
This rapid communication ensures that the body reacts instantly to external and internal changes.
Key Terms and Medical Concepts Related to the Nervous System
Let’s break down some important terms commonly used in pharmacology and neurology to describe drugs or conditions that affect the nervous system.
| Term | Meaning / Function | Example / Description |
|---|---|---|
| Amnesia | Loss of memory | May occur after trauma or anesthesia |
| Analgesic | Loss of pain | Painkillers like morphine or paracetamol |
| Anesthetic | Loss of sensation | Used during surgery to block pain |
| Anticholinergic | Opposes acetylcholine effects | Used to relax muscles or reduce secretions |
| Antiepileptic | Prevents seizures | Used to treat epilepsy |
| Antipsychotic | Treats psychotic disorders | Used in schizophrenia and bipolar disorder |
| Antipyretic | Reduces fever | Commonly used drugs include ibuprofen |
| Anxiolytic | Reduces anxiety | Drugs like diazepam (Valium) |
| Dopaminergic | Increases dopamine levels | Used in Parkinson’s disease treatment |
| Hypnosis | Induces deep sleep or sedation | Extreme relaxation or unconsciousness |
| Narcotics | Derived from opium; relieve pain | Examples include codeine and morphine |
| Neuroleptic | Drugs that may cause neurological side effects | Often seen with certain antipsychotics |
| Sedation | Reduces awareness and reaction to surroundings | Used before surgery or in anxiety management |
Autonomic Nervous System in Detail
The autonomic nervous system (ANS) controls all automatic, involuntary body functions—heartbeat, digestion, breathing, and glandular secretions.
Sympathetic Nervous System — “Fight or Flight”
This system activates during stress or emergencies.
- Increases heart rate (HR), blood pressure (BP), and respiration rate (RR)
- Dilates pupils
- Slows digestion
Purpose: Prepares the body for quick response or danger.
Parasympathetic Nervous System — “Rest and Digest”
This system helps the body relax and conserve energy.
- Decreases HR/BP/RR
- Increases gastrointestinal (GI) motility for digestion
- Promotes relaxation and recovery
Purpose: Maintains balance and restores calm after stress.
How Nerves Communicate: The Role of Neurotransmitters
Communication between neurons occurs through neurotransmitters, chemical messengers that transmit signals across synapses.
Key Neurotransmitters:
- Acetylcholine (ACh): Involved in muscle activation and memory.
- Dopamine: Controls motivation, pleasure, and motor control.
- Serotonin: Regulates mood, sleep, and appetite.
- Norepinephrine: Controls alertness and arousal.
- GABA (Gamma-Aminobutyric Acid): Main inhibitory neurotransmitter; reduces anxiety.
Anticholinergic drugs, as shown in the image, block acetylcholine and can cause effects like dry mouth, blurred vision, or memory issues.
Clinical Disorders Associated with the Nervous System
1. Epilepsy: Caused by abnormal electrical activity in the brain. Treated using antiepileptic drugs.Sedation, Hypnosis, and Anesthesia
Sedation and hypnosis are controlled states used medically:
- Sedation: A mild loss of awareness, often used for anxiety or before procedures.
- Hypnosis: A deeper level of sedation leading to sleep or reduced consciousness.
- Anesthesia: Complete loss of sensation or consciousness during surgical procedures.
Different drugs are used based on the depth of control required—from mild relaxation to complete unconsciousness.
Drug Classes and Their Role in the Nervous System
| Drug Class | Mechanism / Function | Clinical Use |
|---|---|---|
| Analgesics | Block pain signals in the brain | Pain relief |
| Antiepileptics | Stabilize neural membranes | Epilepsy, seizures |
| Antipsychotics | Modify dopamine and serotonin activity | Schizophrenia, bipolar disorder |
| Anxiolytics | Enhance GABA neurotransmission | Anxiety, panic disorders |
| Narcotics | Act on opioid receptors | Severe pain control |
| Antipyretics | Act on hypothalamic centers | Fever reduction |
| Anticholinergics | Block parasympathetic activity | Asthma, motion sickness, GI disorders |
Understanding these helps in interpreting drug actions and predicting side effects.
Importance of Homeostasis and Neural Balance
The nervous system’s goal is homeostasis—maintaining a stable internal environment despite external changes. Both the sympathetic and parasympathetic systems work like a seesaw, balancing body energy and relaxation.
For example:
- During stress, the sympathetic system raises HR and BP.
- After the stress passes, the parasympathetic system restores calm.
This balance ensures proper digestion, circulation, and organ health.
Study Tip for Students
Remember this phrase to recall the autonomic system functions:
- “Fight or Flight” → Sympathetic Nervous System
- “Rest and Digest” → Parasympathetic Nervous System
And for neurotransmitters:
- Dopamine = Drive, Delight, Decision
- Serotonin = Satisfaction and Sleep
- Acetylcholine = Attention and Activation
Mnemonics make learning nervous system pharmacology easier to recall during exams.
| Division | Main Components | Function |
|---|---|---|
| CNS | Brain and Spinal Cord | Controls and processes information |
| PNS | Cranial and Spinal Nerves | Connects CNS to the body |
| Somatic System | Voluntary muscles | Controls body movements |
| Autonomic System | Internal organs | Regulates involuntary functions |
| Sympathetic | Nerves from spinal cord | Prepares for action |
| Parasympathetic | Cranial/sacral nerves | Calms and restores energy |
FAQ
Q1. What are the main parts of the nervous system?
The nervous system consists of the brain, spinal cord, and peripheral nerves that connect the body to the central nervous system.
Q2. What is the difference between the sympathetic and parasympathetic systems?
The sympathetic system prepares the body for emergencies (“fight or flight”), while the parasympathetic system conserves energy and promotes relaxation (“rest and digest”).
Q3. What is a neurotransmitter?
A neurotransmitter is a chemical that transmits messages between neurons. Examples include dopamine, serotonin, and acetylcholine.
Q4. How do anesthetics and analgesics differ?
Analgesics relieve pain without affecting consciousness, while anesthetics block sensation or induce unconsciousness.
Q5. What causes amnesia?
Amnesia can result from brain injury, stroke, psychological trauma, or drug effects (especially anesthesia).
Q6. Why are antiepileptic drugs important?
They control abnormal electrical activity in the brain and prevent seizures, improving patient safety and quality of life.
Q7. How does dopamine affect behavior?
Dopamine regulates pleasure, motivation, and motor functions. Too little can cause Parkinsonism, while too much is linked to psychosis.
