Cranial Layers

Cranial bones interconnected by immovable fibrous joins

The Cranium is the outermost layer of the protective layers. Underneath the cranium is the Dura mater, Venoussinus, Subdural space, Arachnoid membrane, Pia mater and finally the Brain itself.

CNS neural cells are located not only in structures such as the Cerebral Hemispheres but also within the Spinal structures e.g. Cervical spinal nerves all the way down to the Coccygeal nerve

Spinal Layers

The Central Canal is surrounded by both Gray and White matter, from here, Spinal nerves branch outward. Next the Spinal cord is surrounded by the Meninges (composed of Pia mater, Arachnoid membrane and the Dura mater). Ganglionic cells and spinal nerves branch from these Meninges. Vertebrae surround and protect these areas.

Vertebrae (7 cervical, 12 thoracic, 5 lumbar, 5 fused sacral and 5 fused coccyx) are separated by intervertebral disks comprised of cartilaginous joints that allow limited amounts of movement

The cranium and vertebral column are the OUTERMOST layers of protection of the Brain and Spinal cord

Meninges are membranes and with CSF provide protection, located between the bone and nervous tissues:

Dura Mater (outer), Arachnoid membrane (subarachnoid space between arachnoid membrane and pia mater contains CSF) and Pia Mater (inner)

CSF also provides chemical protecton such as regulating ionic fluctuations 

Fluid compartments of CNS

1.4 litres = internal cranial volume (1 litre of cells and 0.4 of fluid)

CSF is located in Ventricles and Subarachnoid Space

Interstitial Fluid is located in Pia mater 

Ventricles are cavities filled with CSF, there are multiple:

First and second (Lateral) ventricles --> Third ventricle --> Fourth Ventricle --> Central canal of spinal cord


Cerebrospinal Fluid is produced in the Choroid Plexus. CSF is a filtrate of blood which contains no blood cells, little protein and different ionic composition. It is absorbed back into blood by villi located on the Arachnoid membrane

Choroid Plexus

An area of transporting epithelia and capillaries which lines the ventricles, it acts in filtering blood, removing cells, proteins and


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