What is the definition of the nervous system?

Definition of the Nervous System

The nervous system is a complex network of specialized cells and tissues that coordinates and regulates body functions through the detection of sensory stimuli, integration of information, and generation of responses via electrical and chemical signals. 1

Major Components of the Nervous System

The nervous system is divided into two primary components:

1. Central Nervous System (CNS):

   • Comprises the brain and spinal cord
   • Functions as the command center for processing information
   • Contains nuclei that give rise to cranial nerves 1

2. Peripheral Nervous System (PNS):

   • Consists of nerves and ganglia outside the CNS
   • Serves as the important bridge for transmission of neural signals
   • Connects the CNS to different parts of the body 1, 2

Autonomic Nervous System

The autonomic nervous system, a specialized component of the nervous system, has three main divisions:

• Sympathetic Division: Often called the "fight or flight" system

  • Originates from the reticular formation in the brainstem
  • Projects to postganglionic neurons that control various organs 1

• Parasympathetic Division: Known as the "rest and digest" system

  • Originates from the nucleus ambiguus and dorsal motor nucleus
  • Works with postganglionic neurons in ganglionated plexi 1

• Enteric Division: Controls digestive processes 1

The autonomic nervous system maintains homeostasis in the organism and performs adaptation responses to changes in the external and internal environment 3.

Cellular Components

The nervous system contains millions of:

• Neurons: The primary functional units for signal transmission
• Glial cells: Supporting cells including:
  • Astrocytes
  • Oligodendrocytes
  • Microglia 4

Glial cells play crucial roles in:

• Creating the blood-brain barrier
• Protecting and nourishing neuronal cells
• Providing antioxidant activity
• Maintaining immunological control 4

Key Functions of the Nervous System

The nervous system performs several critical functions:

• Signal Detection: Afferent neurons relay information about mechanical, chemical, and thermal changes to higher order structures
• Information Processing: Local circuit neurons integrate signals from afferent and efferent neurons
• Response Generation: Efferent neurons provide control over muscles, glands, and organs
• Information Coding: Neural signals encode information through amplitude, power, coherency, and phase relationships 1

Central-Peripheral Interactions

The nervous system facilitates important two-way interactions between the brain and peripheral organs:

• The brain regulates peripheral metabolic systems through the autonomic nervous system and neuroendocrine system
• Peripheral signals (like GI hormones, insulin, and leptin) are transported to the brain where they regulate behaviors and cognitive functions
• The brain can recognize peripheral inflammatory cytokines and induce appropriate responses 5

These interactions are essential for maintaining vital bodily functions, resulting in homeostasis—the natural balance in the body's systems 5.

Clinical Significance

Understanding the nervous system's structure and function is essential for:

• Proper clinical localization of potential lesions
• Appropriate application of imaging protocols for neurological disorders
• Recognition that damage to one area may affect multiple functions due to the interconnected nature of neural pathways 1

Unbalanced activation of components within the nervous system (such as glial cells) may lead to neurodegeneration and various pathological conditions 4.