The central nervous system (CNS) consists of two parts:

  • Brain:
    • Within the cranium
    • Developed from the three primary vesicles of the neural tube: prosencephalon, mesencephalon and rhombencephalon
    • Consists of the forebrain, cerebellum and brainstem
  • Spinal cord: in the vertebral canal

Both are surrounded by membranes: the meninges

The structure of the nervous central system consists of

Grey substance

  • Consists mainly of nerve cell bodies and branching neurites
  • Central in the brainstem and the spinal cord
  • Peripheral (cortex) and central (nuclei) in the forebrain and cerebellum

White substance

  • Contains only axonal fibre tracts
  • Rich in myelin
  • Peripheral in the brainstem and spinal cord
  • Subcortical in the forebrain and cerebellum

Reticular formation: poorly delimitated mixture of fibres and neurones

Orientation and anatomical terminology

Because of the angle between the brain and spinal cord, some words may designate different orientations for

  • The brain
  • The spinal cord

In order to avoid any misunderstanding, we shall use the following terms:

  • Superior
  • Inferior
  • Anterior
  • Posterior

Section planes used

  • Axial sections
    • Or horizontal sections
    • In magnetic resonance imaging, the axial plane is defined by a line passing through the anterior commissure and the posterior commissure (ACPC line)
    • Usually displayed as superior view
  • Coronal sections
    • Or frontal sections
    • In magnetic resonance imaging, the coronal plane is considered as being parallel to the floor of the fourth ventricle (dorsal part of the pons and medulla oblongata
    • Usually displayed as anterior view
  • Sagittal sections