L5 - Meninges

• Meninges are a connective tissue covering that covers the brain and is continuous with the spinal cord
• The meninges consists of 3 layers

  • dura mater
  • arachnoid mater
  • pia mater
• The dura mater is the outermost layer and consists of two layers the outer periosteal layer and the inner meningeal layer
• The meningeal layer of the dura mater is reflected in to make the dural folds
• The dura mater is separated from the arachnoid mater by the subdural space. This space only exists if it fills with blood
• The space between the bone and the dura mater is called the epidural space. It is a potential space that exists if this space fills with blood/fluid
• Label the parts of the dura mater

  A) dura mater

  B) epidural space

  C) periosteal layer

  D) meningeal layer

  E) dural fold

  F) subdural space

  
• The meningeal layer of the dura mater is continuous with the spinal cord and the periosteal layer wraps around and is continuous with the bone
• The arachnoid mater is the middle layer of the meninges and is a thin, transparent membrane that covers the brain but does not enter the sulci
• The arachnoid mater is separated from the pia mater by the subarachnoid space. This is a true space that contains cerebrospinal fluid, cerebral arteries and veins
• The arachnoid mater forms arachnoid granulations that are projections into the superior sagittal sinus. This is the mechanism that allows for drainage of the cerebrospinal fluid into the venous circulation
• The pia mater is the innermost layer of the meninges that is a thin, delicate membrane only one cell layer thick. This layer adheres to the brain and enters the sulci
• Label the parts of the arachnoid mater

  A) arachnoid mater

  B) subarachnoid space

  C) arachnoid granulation

  D) cerebral artery and vein

  
• The dura extends to second sacral vertebrae (S2). Below L2 level, dural sheath encloses descending lumbar and sacral spinal nerves and subarachnoid space containing cerebrospinal fluid (like a bag)
• Pia mater of the spinal cord forms tooth-like reflections that pass laterally between ventral and dorsal roots of spinal nerves. These are called denticulate ligaments. Their function is to attach to the dura, and stabilize the spinal cord from excessive movements. (anchor the spinal cord)

  
• The pia mater of the spinal cord continues below the end of the spinal cord as a ligament called filum terminale. The filum terminale is attached to the dura at its end at S2 level. Below S2, filum terminale continues as a reflection of the dura, and attached to the coccyx. Its function is to stabilize the spinal cord
• The lateral ventricles drain into the third ventricle by the interventricular foramen
• Cerebrospinal fluid leaves the ventricles by either the lateral apertures or the median aperture
• Cerebrospinal fluid is formed by the choroid plexus in the third and fourth ventricles
• The cerebrospinal fluid drains into the venous circulation at the superior sagittal sinus through arachnoid granulations
• The cerebrospinal fluid leaves the lateral or median apertures to either circulate the brain in the subarachnoid space or continue down into the spinal cord
• Label

  A) superior sagittal sinus

  B) choroid plexus

  C) interventricular foramen

  D) third ventricle

  E) arachnoid granulation

  F) subarachnoid space

  
• Obstruction to CSF flow in ventricles or decreased reabsorption of CSF at arachnoid granulations may result in increased volume of cerebrospinal fluid - this is called hydrocephalus
• The brain on the left is normal and the brain on the right has the condition known as hydrocephalus

  
• Meningitis is a condition where the meninges becomes inflamed and infected
• Physical tests to test for meningitis

  • kernig's sign - raising leg causes pain and discomfort
  • brudzinski's sign - involuntary lifting of legs when lifting patient's head
  • nuchal rigidity - inability to flex neck due to rigid muscles
  • lumbar puncture - take a sample of cerebrospinal fluid
• Dural reflections are formed by the internal meningeal layer of the dura mater. They physically support the brain and separate regions of the brain
• The cerebral falx is a dural fold that separates the right and left cerebral hemispheres. It attaches to the frontal crest, crista galli, internal occipital protuberance, and the midline of the calvaria
• The cerebellum tentorium is a dural fold that separates the cerebellum from the cerebrum. It is continuous with the cerebral falx. The tentorial notch anteriorly allows passage of brainstem
• Label the dural reflections

  A) cerebrum

  B) cerebellum

  C) cerebral falx

  D) cerebellar tentorium

  
• The sella diaphragm is a dural fold over the roof of the pituitary. It contains a small opening for the infundibulum. Lies on the sella turcica. of the sphenoid.
• The cerebellar falx is a dural fold that separates the left and right cerebellar hemispheres.
• Label dural folds

  A) sella diaphragm

  B) cerebellar falx

  
• Label

  A) superior sagittal sinus

  B) cerebral falx

  C) straight sinus

  D) transverse sinus

  E) cerebellar tentorium

  
• The venous sinuses of the brain are located between the periosteal and meningeal layer of the brain. Large veins from the brain will empty into sinuses which drain into the internal jugular vein
• Label the venous dural sinuses

  A) superior sagittal

  B) inferior sagittal

  C) straight

  D) confluence

  E) sigmoid

  F) cevernous

  G) internal jugular vein

  
• Arachnoid granulations empty into lateral venous lacunae that enter the superior sagittal sinus
• Label the venous dural sinuses

  A) cavernous

  B) inferior petrosal

  C) superior petrosal

  D) sigmoid

  E) transverse

  F) straight

  
• Veins in the head do not have valves
• The cavernous sinus has a lot of nerves running through it. Therefore tumors in this region could impact in many different ways. The nerves in this area are:

  • optic chasm (CN II)
  • oculomotor nerve (CN III)
  • trochlear nerve (CN IV)
  • abducent nerve (CN VI)
  • ophthalmic nerve (CN V1)
  • maxillary nerve (CN V2)