General Organisation of the Nervous System

Original Editor - Pierre Beunardeau

Top Contributors - Pierre Beunardeau and Kim Jackson  

Introduction

The nervous system commands muscles, controls the functioning of all organs and provides information about the outside world through sensory information. It is the seat of the intellectual faculties. From an anatomical point of view, we distinguish: the central nervous system (CNS) and the peripheral nervous system (PNS). [1]

NS diagram
Source: Wikimedia Commons

Functions of the nervous system

The nervous system (along with the endocrine system) is the the body's regulatory and communication center.

The nervous system fulfilled three functions:

  • Sensitive function: sensory information.
  • Integration.
  • Effector function: motor / glandular response.

Anatomical division

Source: Pierre Beunardeau

Functional division[2]

  • Sensory-afferent : It receives nerve impulses from sensitive receptors and leads them to the CNS
  • Motor-efferent: sensory information : It drives CNS nerve impulses up to the effector organs :
    1. Somatic : responsible for reflex control and voluntary skeletal muscle.
    2. Autonomous : innervates involuntary effectors: lise muscle, heart and glands: sympathetic and parasympathetic.
Source: Wikimedia Commons

Cell types of SN:

1. Neurons[3]

Source: Wikimedia Commons

Role: Reception or production, conduction and transmission of messages in the form of an electrical signal.

Structure:

  • Cell body or soma
  • Extensions:
    1. Dendrites
    2. Axon

Grey matter

It contains cell bodies, dendrites and axons.

  • In the brain it is found in the most superficial regions.
  • In the spinal cord, in the anterior and posterior horns

White matter

It contains myelinated axons.

In the SNC:

  • Nuclei: region where bodies neurons come together
  • Tracts: package axons that have an origin anda common destination

In the SNC:

  • Ganglia: group of neuron cell bodies
  • Tracts: Axons that start from a same central origin and which lead throughout the body (cranial or spinal).


2. Glial cells or neuroglia[4]

Closely associated with neurons, more numerous but smaller in size. They are the support of neurons and have other important and unique functions (nutrition, immune ...)

The neuroglia comprises 6 cell types, depending on location, structure and function:

  • 4 types in the CNS
  • 2 types in the SNP
Source: Wikimedia Commons

Peripheral nervous system

Neurolemmocytes or Schwann cells

They are the producers of myelin (substance lipid that forms the myelin sheath + several concentric insulating layers that surround the large axons and facilitate nerve control).

Satellite glial cells

They form a capsule surrounding the cell body of neurons located in the lymph nodes. They provide a large number of support functions.

Central nervous system

Oligodendrocytes

They form the myelin sheaths (equivalent to Schwann cells)

Astrocytes

Very branched cells, their extensions adhere to neurons and cover the surrounding capillaries and are part of the blood-brain barrier.

Microglia

Protective role: specialized immune cells. They phagocytose microorganisms,damaged cells and debris from dead neurons.

Ependymocytes

Epithelial cells that line the cavities central CNS (ventricles with CSF).

They constitute a permeable barrier. It is a source of "stem cells" nerves that can differentiate into neurons or gliocytes.


References

  1. Oregon State University. Structure and Function of the Nervous System. Available from :https://open.oregonstate.education/aandp/chapter/12-1-structure-and-function-of-the-nervous-system/
  2. National Cancer Institute. Organization of the Nervous System. Available from:https://training.seer.cancer.gov/anatomy/nervous/organization/
  3. Dr Alan Woodruff. The University of Queensland. What is a Neuron ? Available from: https://qbi.uq.edu.au/brain/brain-anatomy/what-neuron
  4. NCBI. Neuroscience. 2nd Edition. Neuroglial Cells. Available from: https://www.ncbi.nlm.nih.gov/books/NBK10869/ (accessed 2001)