Protective Layers of the Brain & Spinal Cord

• Meninges


  the meninges = 3 connective tissue membranes that lie just external to the CNSthe meninges = 3 connective tissue membranes that lie just external to the CNS organs
• Function of the Meninges


  cover + protect the the CNS

  protect blood vessels + enclose venous sinuses

  contain cerebrospinal fluid

  form partitions in the skull
• The Three Layers of the Meninges


  dura mater

  arachnoid mater

  pia mater
• Layers of the Meninges - Dura Mater


  the leathery dura mater = strongest meninx (singular layer of the meninges)

  where it surrounds the brain, it is a 2-layered sheet of fibrous connective tissue

  = superficial periosteal layer + deeper meningeal layer
• Superficial Periosteal Layer of the Dura Mater


  the superficial periosteal layer attaches to the inner surface of the skull (periosteum)

  there is no dural periosteal layer surrounding the spinal cord
• Deeper Meningeal Layer of Dura Mater


  the deeper meningeal forms the true external covering of the brain + cont caudally in the vertebral canal as the spinal dura mater

  the brain's 2 dural layers r fused together, except i certain areas where they separate to enclose dural venous sinuses that collect venous blood from the brain + direct it into the internal jugular veins of the neck
• Structure of Dura Mater


  layers of dura mater

  
• Dural Septa


  in several places, the meningeal dura mater extends inward to form flat partitions that subdivide the cranial cavity

  these dural septa, which limit excessive movement of the brain w in the cranium:

  falx cerebri

  falx cerebelli

  tentorium cerebelli
• Arachnoid Mater


  middle meninx = arachnoid mater

  forms a loose brain covering, never dipping into the sulci at the cerebral surface

  it's separated from the dura mater by a narrow serous cavity = subdural space, which contains a film of fluid
• Arachnoid Mater - Subarachnoid Space


  between the arachnoid membrane = wide subarachnoid space

  spiderweb-like extensions span this space + secure the arachnoid mater to the undelying pia mater

  the subarachnoid space is filled w cerebrospinal fluid + also contains the largest blood vessels serving the brain

  cos the arachnoid mater is fine + elastic, these blood vessels r protected
• Arachnoid Mater - Arachnoid Granulations


  knob-like projections of the arachnoid mater = arachnoid granulations

  = protrude superiorly thru the dura mater + into the superior sagittal sinus

  these granulations absorb cerebrospinal fluid into the venous blood of the sinus
• Structure of Arachnoid Mater


  spider-like extensions that fills the subarachnoid space

  
• Pia Mater


  pia mater = composed of delicate connective tissue + contains many tiny blood vessels

  only meninx that clings tightly to the brain, following its every convolution

  small arteris entering the brain tissue carry ragged sheaths of pia mater inward w them for short distances
• Structure of Pia Mater


  covers the arteries that enter the brain tissue

  
• Cerebrospinal Fluid (CSF)


  CSF = found in + around the brain + spinal cord

  forms a liquid cushion that gives bouyancy to CNS strutures
• Functions of CSF - Providing Bouyancy & Protection


  by floating the jelly-like brain, the CSF effectively reduces brain weight by 97% + prevents the brain from crushing under its own weight

  also protects the brain + spinal cord from blows + other trauma
• Functions of the CSF - Nourishment of the Brain


  altho the brain has a rich blood supply, CSF helps nourish the brain

  it carries chem signals like hormones from one part of the brain to another
• Composition of CSF


  CSF = watery broth similar in composition to blood plama, from which it is formed

  however, it contains less protein that plasma + its ion conc r diff

  CSF contains more Na+, Cl-, H+ than does blood plasma

  less Ca2+, K+