Transcript How is the CNS protected from Injuries?

How is the CNS
protected from
Injuries?
1. The Meninges
O Composed of 3 Connective Tissue
Membranes
O 1. Dura Mater – “Tough Mother” outer layer
of protection that covers and protects the
brain
O A. Falix Cerbri- extension of the dura mater
that separates the two hemispheres of the
cerebrum
Meninges Continued
O B. Tenorium Cerebelli- extension of the dura
mater that separates the cerebrum from the
cerebellum
O C. Falx Cerebelli- separates the two
hemispheres of the cerebellum
Meninges Cont.
O 2. Arachnoid Mater- middle layer of the
meningies
O Threadlike layer that looks like spider webs
through the entire surface
O Creates an open space where CSF can
circulate
3. Pia Mater
O Innermost meningeal layer
O Clings to the surface of the brain and spinal
cord
O Arachnoid villi project up into the arachnoid
layer from here and re-absorb CSF to
maintain a steady pressure within the
meningeal space
CSF
O Water based cushioning fluid
O Formed by the choroid plexus of each lateral
ventricle (networks of capillaries within the
walls of the ventricles)
O Formed by blood plasma
Circulation of CSF
O Flows from choroid plexus to the third ventricle
O More CSF is added at the 3rd ventricle and it
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moves through the cerebral aqueduct through
the midbrain and onto the 4th ventricle
Choroid plexus here adds more CSF and it
enters the subarachnoid space
From here it circulates into the central canal of
the spinal cord, through the subarachnoid space
around the brain
Pressure is 150 mL per vol
Spinal tap is used to check it for infection
Blood-Brain Barrier
O Maintains a constant internal environment for the
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brain
Tight junctions seal together the endothelial cells of
the brain capillaries preventing free passage of
substances
Glucose passes via active transport
Creatinine, Urea, and ions cross slowly
Proteins and antibiotic drugs do not pass at all
This barrier is useless against fat-soluble substances
So, Oxygen, Carbon Dioxide, alcohol, and fat-soluble
drugs all pass freely