Meninges & Ventricles

• •Living brain is soft and mushy, despite the network of cytoskeletal proteins contained in neurons and glial cells.
• •Without support of some kind, the central nervous system (CNS) would be unable to maintain its shape, particularly as we walk and run around and occasionally bump our heads.
• •The brain and spinal cord are protected from outside forces by their encasement in the skull and vertebral column, respectively.

  •In addition, the CNS is suspended within a series of three membranous coverings, the meninges (from the Greek word meninx, meaning “membrane”), which stabilize the shape and position of the CNS in two different ways during head and body movements. First, the brain is mechanically suspended within the meninges, which in turn are anchored to the skull, so the brain is constrained to move with the head.
• Meninges

  Three layers of membranes, collectively serving to safeguard the central nervous system, provide support to blood vessels, and encase a cavity filled with cerebrospinal fluid (CSF).

  
• Meninges

  •These layers, arranged from outermost to innermost, are known as the

  •dura mater,

  •arachnoid mater,

  •and pia mater.

  
• Meninges structures

  A) superior sagittal sinus

  B) arachnoid granulation

  C) dura mater

  D) periosteal layer

  E) meningeal layer

  F) arachnoid mater

  G) subarachnoid space

  H) pia mater

  
• Dura Mater (Latin. “hard mother”)tough fibrous connective tissue arranged in two layers – periosteal(connected with the skull) and meningeal layer(connected with the Arachnoid mater). Meningeal layer of the dura mater of the brain in continuous with that of the spinal cord. 

  
• The meningeal dura mater has 3 major reflections

  •Falx cerebri - vertical reflection between the two cerebral hemispheres. Separating the two cerebral hemispheres

  •Tentorium cerebelli - a horizontal reflection between the posterior occipital parts of the cerebral hemisphere and the cerebellum. So it technically separates the cerebrum from the cerebellum posteriorly.

  •Falx cerebelli - a vertical reflection, which incompletely separates the two cerebellar hemispheres at the inferior surface.

  
• •Falx cerebri - vertical reflection between the two cerebral hemispheres. Separating the two cerebral hemispheres
• •Tentorium cerebelli - a horizontal reflection between the posterior occipital parts of the cerebral hemisphere and the cerebellum. So it technically separates the cerebrum from the cerebellum posteriorly.
• •Falx cerebelli - a vertical reflection, which incompletely separates the two cerebellar hemispheres at the inferior surface.
• Pia Mater

  thin translucent membrane that is closely adherent to the surface of the brain .

  
• •The arachnoid mater and the pia mater are collectively referred to a the pia-arachnoid membrane because of their close structural and functional relationships.
• Spaces between the meningeal layers and bony skull

  Epidural space – between the dura mater and the bony skull

  Subdural space – between the dura mater and the arachnoid mater

  Subarachnoid space – between the arachnoid and the pia mater. Contains cerebrospinal fluid and cerebral blood vessels

  Each of these spaces contains some important blood vessels that can give rise to haemorrhage.

  
• Trauma to the skull with Rupture of the middle meningeal artery , for instance, leads to epidural haemorrhage or the accumulation of arterial blood in the epidural space. Epidural haemorrhage is handled as an acute life-threatening emergency, calling for surgical intervention to evacuate the accumulated arterial blood in the epidural space and control the bleeding. If not, the person is going to have an increased intracranial pressure which can lead to brain death
• trauma to the skull may rupture the bridging veins, leading to subdural haemorrhage or the accumulation of blood in the subdural space. This condition also calls for surgical interventions to evacuate the accumulated venous blood and control the bleeding.
• subarachnoid haemorrhage or the accumulation of blood in the subarachnoid space. This condition may result from trauma to the head, congenital abnormalities in vessel structures such as aneurysms or high blood pressure.
• The subarachnoid space underlying the superior sagittal sinus contains arachnoid granulations and cytoplasm cerebral spinal fluid absorption, into the superior sagittal sinus.
• Cerebral Dural Venous Sinuses

  •endothelial-lined venous channels, devoid of valves, located between the periosteal and meningeal layers of dura mater.

  •Dural venous sinuses serve as low pressure channels for venous blood flow back to the systemic circulation.

  
• Cerebral Dural Venous Sinuses

  •Obstruction of one or more of these sinuses it connects trauma infection or hypercoagulable states results in major neurologic signs including stroke, increased intracranial pressure, loss of consciousness, and intracranial bleed.

  
• superior sagittal sinus and the inferior sagittal sinus, which are sinuses that lie in the superior and inferior margins of the false cerebri, caudally, the inferior sagittal sinus is joined by a vein known as the vein of Galen, to form this straight sinus, this straight sinus and the superior sagittal sinus all come to a point known as the confluence of sinuses. the two transverse sinuses arise from the confluence of sinuses and pass, laterally and forward into a groove in the occipital bone at the occipital petrosal junction

  
• •the two transverse sinus are curved downwards and backwards to form the sigmoid sinuses.  these sigmoid sinuses drain into the internal jugular veins.

  
• •from the  confluence of sinuses there is also the occipital sinus that runs on the occipital bone, and it's connects the confluence of sinuses to the marginal sinus at the foramen of magnum.

  
• •We also have the superior petrosal sinus and the inferior petrosal sinus which is named in relation to the petrosal part of the temporal bone. They lie in the dura, at the anterior border of the tentorium cerebelli

  
• •The cavernous sinus lies on each side of the sphenoid sinus in the Sella turcica and the pituitary gland

  
• Cerebral Dural Venous Sinuses

  A) superior sagittal sinus

  B) inferior sagittal sinus

  C) vein of Galen

  D) confluence of sinuses

  E) transverse sinuses

  F) sigmoid sinuses

  G) internal jugular vein

  H) occipital sinus

  I) marginal sinus

  J) superior petrosal sinus

  K) inferior petrosal sinus

  L) cavernous sinus

  M) sphenoid sinus

  N) straight sinus

  
• MeningitisInflammation of the meninges from infection with viruses, bacteria, fungi and protozoa.

  •Usually due to an infection of the cerebrospinal fluid in the subarachnoid space.

  
• •Meninges Inflammation Causes:

  •Viruses (e.g., lymphocytic choriomeningitis)

  •Bacteria (meningococcus, pneumococcus, haemophilus influenza, tuberculosis)

  •Fungi (cryptococcus)

  •Protozoa (toxoplasma)
• •Symptoms of Meninges Inflammation:

  •Headache

  •Photophobia

  •Vomiting

  •Fever

  •Neck stiffness upon attempting head movement
• •Types of Meningitis:

  •Viral Meningitis:

  •Generally mild and self-limiting.

  •Bacterial or Fungal Meningitis:

  •Leads to damage to cranial nerves and the brain.

  •Without treatment, progresses to raised intracranial pressure.

  •May result in brain displacement and, ultimately, death if left untreated.
• •The buoyant effect of the CSF environment greatly decreases the tendency of various forces (e.g. gravity to distort the brain. Thus, a brain that weighs 1500g in air effectively weighs less than 50 g in its normal CSF environment, where it is easily able to maintain its shape.

  •In contrast, an isolated fresh brain, unsupported by its usual surroundings, becomes seriously distorted and may even tear under the influence of gravity.
• The brain contains 4 ventricles

  A ventricle is an internal cavity of the brain, within the brain, which is filled with CSF

  
• •In each cerebral hemisphere, there is a relatively large lateral ventricle.

  •These paired ventricles connect with the third ventricle in the diencephalon through structures known as the interventricular foramina (of Monro).

  •The third ventricle, in turn, is linked to the fourth ventricle in the pons and medulla by the narrow cerebral aqueduct (of Sylvius) located in the midbrain.

  The fourth ventricle extends downward as the central canal into the caudal medulla and spinal cord. However, this canal is typically not open along much of its length.

  
• •In each cerebral hemisphere, there is a relatively large lateral ventricle.
• These paired ventricles connect with the third ventricle in the diencephalon through structures known as the interventricular foramina (of Monro).
• •The third ventricle, in turn, is linked to the fourth ventricle in the pons and medulla by the narrow cerebral aqueduct (of Sylvius) located in the midbrain.
• •The fourth ventricle extends downward as the central canal into the caudal medulla and spinal cord. However, this canal is typically not open along much of its length.
• •Lateral ventricle = telencephalon

  •3rd ventricle = diencephalon

  •4th ventricle = rhombencephalon

  •cerebral aqueduct (of Sylvius) = mesencephalon
• brains ventricles

  A) lateral ventricle

  B) lateral ventricle

  C) 3rd ventricle

  D) cerebral aqueduct (of Sylvius)

  E) 4th ventricle

  F) central canal

  G) interventricular foramina (of Monro).

  H) 3rd ventricle

  I) cerebral aqueduct (of Sylvius)

  J) 4th ventricle

  
• Lateral ventricles

  Two curved shaped cavities located in the cerebrum. They are separated by the septum pellucidum and do not communicate directly