Nervous System – Structure, Function, and Physiology Anatomy & Physiology – NHPC Exam Guide (For PCL General Medicine )

 Introduction to the Nervous System

The nervous system is the master controlling and communicating system of the human body. It coordinates all body functions, both voluntary and involuntary, and allows the body to respond to internal and external stimuli. It works closely with the endocrine system to maintain homeostasis.

For NHPC and PCL General Medicine students, understanding the nervous system is essential for clinical diagnosis and patient care.

Structure of the Nervous System

The nervous system is divided into two main parts:

1. Central Nervous System (CNS): Consists of the brain and spinal cord. It integrates information and makes decisions.

2. Peripheral Nervous System (PNS): Includes cranial and spinal nerves that connect the CNS to the rest of the body.

Cells of the Nervous System

The basic structural and functional unit of the nervous system is the neuron. Neurons are specialized cells designed for transmitting electrical impulses. Supporting cells, called neuroglia or glial cells, provide nourishment, protection, and structural support to neurons.

Structure of a Neuron

A neuron has three main parts:1. Cell Body (Soma): Contains the nucleus and organelles for metabolic activity.2. Dendrites: Receive impulses from other neurons.3. Axon: Transmits impulses away from the cell body toward other neurons or effectors.[Diagram Placeholder: Structure of a Neuron]

Physiology of the Nervous System

The function of the nervous system is based on the transmission of electrical impulses known as action potentials. These impulses travel along neurons and across synapses to communicate information rapidly and precisely.

Action Potential

An action potential is a brief change in the electrical charge of a neuron’s membrane. It involves depolarization (influx of sodium ions) followed by repolarization (efflux of potassium ions). The sodium-potassium pump restores the resting membrane potential.

Synapse and Neurotransmitters

A synapse is the junction between two neurons or a neuron and a muscle. Neurotransmitters such as acetylcholine, dopamine, and serotonin are chemical messengers that transmit impulses across the synaptic cleft. [Diagram Placeholder: Synapse Mechanism]

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord. It is protected by meninges, cerebrospinal fluid (CSF), and the skull. The brain is the control center of all voluntary and involuntary activities.

Brain – Structure and Function

The brain has several parts with distinct functions:1. Cerebrum – Controls voluntary actions, thought, memory, and sensation. It has two hemispheres and four lobes:   • Frontal Lobe – Movement, speech, personality   • Parietal Lobe – Sensation and spatial orientation   • Temporal Lobe – Hearing, memory, emotion   • Occipital Lobe – Vision2. Cerebellum – Coordinates movement and balance.3. Brainstem – Includes midbrain, pons, and medulla oblongata; controls vital functions such as heartbeat and respiration.4. Diencephalon – Includes thalamus and hypothalamus, which regulate emotions, temperature, and endocrine activity.[Diagram Placeholder: Brain Anatomy with Labeled Lobes]

Cerebrospinal Fluid (CSF) and Ventricular System

CSF is a clear fluid that circulates through the ventricles of the brain and spinal cord. It cushions the CNS, maintains pressure, and removes metabolic waste. It is produced by the choroid plexus and flows through the lateral, third, and fourth ventricles before being absorbed into the venous system.[Diagram Placeholder: CSF Circulation Pathway]

Spinal Cord – Structure and Reflexes

The spinal cord extends from the medulla oblongata to the lumbar region. It serves as a communication link between the brain and body. It has gray matter (inner butterfly shape) and white matter (outer area containing tracts). Reflex arcs are the functional units of the spinal cord allowing quick, involuntary responses.[Diagram Placeholder: Reflex Arc]

Autonomic Nervous System (ANS)

The ANS regulates involuntary body functions such as heartbeat, digestion, and glandular secretion. It has two divisions:1. Sympathetic System – Prepares the body for “fight or flight” response (increases heart rate, dilates pupils).2. Parasympathetic System – Promotes “rest and digest” functions (slows heart rate, stimulates digestion).[Diagram Placeholder: Sympathetic vs Parasympathetic Comparison]

Clinical Insights

• Stroke (Cerebrovascular Accident): Interruption of blood supply to the brain causing paralysis or speech loss.• Meningitis: Inflammation of meninges due to infection.• Epilepsy: Recurrent seizures due to abnormal brain activity.• Parkinson’s Disease: Degeneration of basal ganglia leading to tremors and rigidity.• Multiple Sclerosis: Demyelination of neurons causing weakness and vision loss.

NHPC Exam Focus Points

• Understand structure and function of neurons.• Know the difference between CNS, PNS, and ANS.• Learn functions of brain lobes and spinal cord tracts.• Study neurotransmitters and their clinical roles.• Be familiar with common neurological disorders.

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