Spinal cord, CSF & Blood Brain Barrier

Spinal cord

• Long narrow cylindrical structure located in the vertebral canal.
• Begins from the base of the skull at formane magnum and terminate at the lower border of first lumbar vertebra
• Below the first lumbar vertebra it continues as cauda equina (Horse tail)

Cross section

• Anterior median fissure
• Posterior median fissure
• Central canal

H shaped grey matter with anterior horn containing motor neurons and posterior horn containing sensory neurons

Surrounding the grey matter is white matter consisting of ascending and descending tracts. 

*Grey matter consists of cell bodies and white matter consists of axons.

The arrangement of grey and white matter in brain and spinal cord is different. In the brainstem and spinal cord white matter surrounds the grey matter while in cerebrum and cerebellum, it is the grey matter which surrounds the white matter. The fatty myelin on the myelinated nerve gives its white appearance and the cell bodies have grey appearance.

Cross section of Spinal cord

There are 31 pairs of spinal nerves

• 8 pairs of cervical nerves
• 12 pairs of thorasic nerves
• 5 pairs of lumbar nerves
• 5 pairs of sacral nerves
• 1 pair of coccygeal nerve

Cerebrospinal Fluid (CSF)

Brain and spinal cord is covered by 3 meninges: dura, arachnoid and pia matter. 

The space between the arachnoid and pia matter contains a fluid known as Cerebrospinal Fluid.

The CSF is also present in the chambers of the brain called ventricles namely lateral, third and fourth ventricle.

Composition of Cerebrospinal Fluid

• Clear colourless 
• Alkaline (pH>7)
• Specific gravity: 1.005-1.008
• Protein and cell free
• Volume: 130-150 ml
• Daily secretion: 500 to 550 ml
• Pressure: 130 mm of water

Formation of Cerebrospinal Fluid

• 50% by choroid plexuses
• 40% by blood vessels of th emeningeal and ependymal lining of ventricles
• 10% by blood vessels of brain and spinal cord.

Flow of Cerebrospinal Fluid

Functions of Cerebrospinal Fluid

• It serves as a fluid buffer providing an optimum environment to the neurons.
• Protective function: It supports the brain by cushioning. The brain actually floats in CSF.
• It keeps the total volume of cranial content constant.
• It helps in transfer of waste products of brain into the blood.
• It serves as a medium for nutrient exchanges in the nervous system.

Blood Brain Barrier

It is the barrier between the blood and the brain tissue.

It is present in two places with in the brain

1. One is located at the interface of Choroid plexus and CSF, called Blood CSF barrier.
2. Second one is located between Brain capillaries and CSF, called true Blood Brain Barrier.

These barriers are:

• Highly permeable to water, oxygen, carbondioxide and sulpha drugs.
• Slightly permeable to electrolytes and glucose.
• Impermeable to metal, urea, protein and bile salts.

Functions of Blood Brain Barrier

• They help in maintanace of constancy in the CNS environment.
• They protect the brain from endogenous and exogenous toxins in the blood.
• They prevent escape of neurotransmitters into the circulation.