Nervous System – Structure and Functions
Introduction
The nervous system is one of the most vital systems of the human body. It controls and coordinates all body functions, both voluntary (like walking) and involuntary (like heartbeat and digestion).
It allows the body to respond quickly to changes in the internal and external environment through electrical signals called nerve impulses.
Definition
The nervous system is a complex network of nerves and specialized cells called neurons that transmit signals between different parts of the body to maintain coordination and control.
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Divisions of the Nervous System
The human nervous system is divided into two main parts:
- Central Nervous System (CNS)
- Consists of the brain and spinal cord.
- It is the control center of the body, responsible for processing information and giving instructions.
- Peripheral Nervous System (PNS)
- Consists of cranial nerves (arising from the brain) and spinal nerves (arising from the spinal cord).
- It connects the CNS to the rest of the body.
- Divided into:
- Somatic Nervous System: Controls voluntary actions (e.g., movement of skeletal muscles).
- Autonomic Nervous System (ANS): Controls involuntary actions (e.g., heartbeat, digestion).
- Sympathetic Division: Prepares the body for “fight or flight.”
- Parasympathetic Division: Maintains “rest and digest” activities.
Structure of Neuron
The neuron is the structural and functional unit of the nervous system. It is specialized for transmitting electrical impulses.
Parts of a Neuron:
- Cell Body (Soma): Contains the nucleus and cytoplasm.
- Dendrites: Branch-like extensions that receive impulses from other neurons and carry them toward the cell body.
- Axon: A single long fiber that carries impulses away from the cell body to other neurons or effectors (muscles or glands).
- Myelin Sheath: A fatty layer covering the axon that insulates and speeds up nerve impulse transmission.
- Axon Terminals: Endings of axon that release neurotransmitters to transmit impulses to the next neuron.
Types of Neurons:
- Sensory Neurons: Carry impulses from sense organs to the CNS.
- Motor Neurons: Carry impulses from CNS to muscles or glands.
- Interneurons: Connect sensory and motor neurons within the CNS.
Brain – Structure and Functions
The brain is the control center of the body. It is protected by the skull and covered by three membranes called meninges (dura mater, arachnoid mater, and pia mater).
Main Parts of the Brain:
- Cerebrum
- Largest part of the brain.
- Divided into right and left hemispheres.
- Responsible for intelligence, memory, reasoning, emotions, and voluntary movements.
- Cerebellum
- Located below the cerebrum at the back of the brain.
- Controls balance, posture, and coordination of voluntary movements.
- Brainstem
- Connects the brain with the spinal cord.
- Consists of the midbrain, pons, and medulla oblongata.
- Controls involuntary functions like breathing, heartbeat, and blood pressure.
Spinal Cord – Structure and Functions
The spinal cord is a cylindrical structure extending from the brainstem down through the vertebral column.
It is protected by the vertebrae and meninges and surrounded by cerebrospinal fluid (CSF).
Functions:
- Acts as a pathway for transmitting impulses between the brain and body.
- Controls reflex actions through reflex arcs, which are automatic and quick responses to stimuli (e.g., withdrawing hand from a hot surface).
Physiology of Nerve Impulse Transmission
- Resting State: The neuron membrane is polarized, meaning there is a difference in charge inside and outside the neuron.
- Depolarization: When stimulated, sodium ions enter the neuron, changing the electrical charge.
- Impulse Conduction: The change in charge travels along the axon as an action potential.
- Repolarization: The neuron restores its resting potential by pumping out sodium ions.
- Synaptic Transmission: At the axon terminal, neurotransmitters are released into the synapse to carry the impulse to the next neuron or effector cell.
Functions of the Nervous System
- Control and Coordination: Regulates all body functions.
- Sensory Input: Receives information from the environment via sense organs.
- Integration: Processes and interprets sensory information.
- Motor Output: Sends instructions to muscles or glands to act.
- Maintains Homeostasis: Keeps body functions in balance.
- Higher Mental Functions: Enables thinking, learning, and memory.
Disorders of the Nervous System
- Epilepsy: Sudden bursts of abnormal electrical activity in the brain causing seizures.
- Meningitis: Inflammation of meninges due to infection.
- Stroke: Interruption of blood supply to the brain causing cell death.
- Paralysis: Loss of muscle control due to nerve injury.
- Parkinson’s Disease: Degeneration of brain cells causing tremors and slow movements.
- Alzheimer’s Disease: Progressive brain disorder affecting memory and behavior.
