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Head and Neck Anatomy > Cerebral meninges and CSF > Flashcards

Cerebral meninges and CSF Flashcards

1
Q

What is the arachnoid mater?
Location?

A

delicate, impermeable and avascular membrane covering the brain
> lies between pia mater (internally) and dura mater (externally)
> separated from dura mater by subdural space (filled by a film or fluid)
> separated from pia mater by subarachnoid space (filled with CSF)
Note: the outer and inner surfaces are covered with flattened mesothelial cells

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2
Q

What are arachnoid granulations?

A

they are the sites of reabsorption of cerebrospinal fluid
> only arachnoid and the endothelium of the sinuses separate cerebrospinal fluid from venous blood
> Dural walls of the sinuses, particularly the superior sagittal sinus, possess small defects which allow the underlying arachnoid to billow through into the sinus

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3
Q

Describe the consequences of thrombosis in the sinuses?

A

If the sinuses become thrombosed, reabsorption will be prevented and the pressure of cerebrospinal fluid in the subarachnoid space will rise.

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4
Q

What are subarachnoid cisterns?

A

Widening of subarachnoid space created by separation of pia and arachnoid
- the subarachnoid space is wider than at other sites
> contain pools of CSF

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5
Q

Name the 2 groups of CSF cisterns?

A
  1. supra-tentorial cisterns
  2. infra-tentorial cisterns
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6
Q

Name anterior supratentorial cisterns?

A
  1. carotid
  2. chiasmatic
  3. lamina terminalis
  4. olfactory
  5. sylvian
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7
Q

Name lateral supratentorial cisterns?

A
  1. crural
  2. ambient
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8
Q

Name posterior supratentorial cisterns?

A
  1. quadrigeminal
  2. vellum interpostium
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9
Q

Name superior supratentorial cisterns?

A
  1. pericallosal
  2. hemispheric
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10
Q

Name anterior infraterntorial cisterns?

A
  1. Inter peduncular
  2. Pre-pontine
  3. Premedullary
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11
Q

Name lateral infratentorial cisterns?

A
  1. Ambient
  2. Superior CPA
  3. Inferior CPA
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12
Q

Name posterior infratentorial cisterns?

A
  1. Cisterna magna
  2. Superior cerebellar
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13
Q

Name superior infratentorial cisterns?

A
  1. Vermian
  2. Hemispheric
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14
Q

State the location and contents of the chiasmatic cistern?

A

location = above sella
contents = optic chiasm + pituitary infundibulum

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15
Q

What are the perimesencephalic cisterns?

A
  1. interpeduncular
  2. crural
  3. ambient
  4. quadrigeminal
    > surround the midbrain
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16
Q

State the location of the quadrigeminal cistern?

A

• Posterior to the quadrigeminal plate
• Inferior to the splenium of corpus callosum
• Superior to the cerebellum

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17
Q

State the contents of the quadrigeminal cistern?

A

• Vein of Galen.
• Precentral V
• P3 of PCA

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18
Q

State the location and contents of the interpeuncular cistern?

A

Location
• Between the cerebral peduncles.
Contents
• Basilar tip.
• SCA.
• PCA.
• Interpeduncular V.
• CN3

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19
Q

State the location and contents of the crural cisterns?

A

Location
Crus cerebri (cerebral peduncles) - medially
Uncus of temporal lobe - laterally
Contents
• P2 segment of PCA.
• Superior cerebellar artery.
* Anterior choroidal artery.
• Basal vein of Rosenthal.

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20
Q

State the location and contents of the pontine cistern?

A

Location
• Anterior to the pons.
Contents
• Basilar A.
• AICA.
• Ant. Pontomesencephalic V.
• CN5
• CN6

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21
Q

State the location and contents of the cisterna magna?

A

• Largest and lies behind the medulla and below the cerebellar hemispheres.
• Continuos with 4th ventricle through median aperture of Magendie.
• Its lateral part contains the vertebral artery and its posterior inferior cerebellar branch.

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22
Q

What is the pia mater and its functions?

A

> Highly vascular and functions to support the vessels that nourish the underlying cells of the brain and spinal cord
is specialised over the roofs of the ventricles, where it contributes to the formation of the choroid plexuses

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23
Q

What is a ventricle?

A

an internal cavity of the brain which is filled with CSF

24
Q

What is the ventricular system composed of?

A

2 lateral ventricles
2 midline ventricles (3rd and 4th ventricles)

25
Q

Describe the 2 lateral ventricles?

A

Two lateral ventricles occupy a considerable part of the cerebral hemispheres, located below the corpus callosum in each hemisphere.
> Each lateral ventricle is connected to the 3rd ventricle by a narrow oval opening called the interventricular foramen [of Monroe]

26
Q

Describe the third ventricle?

A

is a narrow slit like cavity
> Located in the diencephalon between the thalami
> From it the CSF passes through the narrow cerebral aqueduct [ of sylvius] in the mid brain to reach the 4th ventricle.

27
Q

Describe the fourth ventricle?

A

is located in the brain stem , within the pons , cerebellum and medulla oblongata

28
Q

Describe normal CSF and where its produced?

A

is clear, colourless, and odourless
> produced by the choroid plexus

29
Q

Describe the choroid plexus?

A

Special capillary networks in certain places in the ventricular walls
> Contains Ependymal cells

30
Q

Function of the ependymal cells of the choroid plexus?

A

Fluid from plasma passes through the ependymal cells
- Cells have ion pumps
- Modify CSF
- Regulate and maintain the blood-brain barrier

31
Q

How much CSF is produced daily?

A

About 500 - 800 ml of CSF are produced each day
> only 140 – 200 ml are present at any one time
Note: A person lying horizontally has a slow but continuous circulation of cerebrospinal fluid with a fluid pressure of about 10 mm Hg [ mercury]

32
Q

State the CSF turnover?

A

x3

33
Q

What is the blood : CSF barrier?

A

Is the specialised ependymal lining of the choroid plexuses

34
Q

Describe how the choroidal epithelium differs from the general ependymal epithelium in 3 ways?

A
  1. cilia are almost completely replaced by microvilli
  2. the cells are bound by tight junctions – the actual site of the barrier
  3. the epithelium contains numerous enzymes specifically involved in the transport of ions and metabolites
35
Q

Penetration of molecules from the blood into the brain is regulated by?

A
  1. Tight junctions between capillary cells
  2. Thick basal lamina (connective tissue layer)
  3. Astrocytes pressed against capillaries
36
Q

How is the blood brain barrier a selective membrane?

A
  1. Some substances, particularly if lipid-soluble, pass easily from blood to the brain (water, glucose, O2, CO2, alcohol, caffeine, nicotine, heroin, most anesthetics)
  2. Most charged ions do not pass easily
  3. Proteins and most antibiotics do not pass at all
37
Q

Which sites is the blood brain barrier permeability variable?

A
  1. Choroid plexus – CSF production
  2. Vomiting center in brain stem - monitors the blood for toxic molecules and poisons
  3. Hypothalamus
    > has no blood-brain barrier
    > monitors blood composition for water balance, temperature, pH, osmolarity and many other homeostatic metabolic functions
38
Q

What are the functions of the cerebrospinal fluid?

A
  1. CSF is a clear lymph like fluid that forms a protective cushion around and within the central nervous system , protecting it from mechanical injury .
  2. The fluid buoys the brain - It spreads the force of an impact over a larger area
  3. It also helps remove metabolic waste from nervous tissue
    [the CNS lacks lymphatic circulation] as the pia is somewhat permeable
  4. controls brain excitability by regulating the ionic composition
39
Q

Describe the circulation of CSF?

A

Once CSF is formed in choroid plexuses in the ventricles.
It circulates through the
1. ventricles
2. the spinal canal
3. sub arachnoid space before being re- absorbed in the dural venous system.
> It is reabsorbed through the walls of the arachnoid granulations .

40
Q

Describe the parts of the CSF circulation system?

A
  1. The internal portion of the system
    > consists of two lateral ventricles, the interventricular foramens, the third ventricle, the cerebral aqueduct, and the fourth ventricle.
  2. The external part
    > consists of the subarachnoid spaces and cisterns.
    - Communication between the internal and external portions occurs through the apertures of the fourth ventricle.
41
Q

Describe the internal circulatory system of CSF?

A
42
Q

Describe the external circulating system of CSF?

A

The CSF escapes the 4th ventricle to flow over the surface of the brain and spinal cord in the sub arachnoid space. Squirts through
the medial foramen of magendie,
and 2 lateral foramen of luschka

The 4th ventricle also communicates posteriorly with the central canal [ but flow within the central canal of the spinal cord is negligible]

43
Q

Give a summary of CSF flow?

A
44
Q

What is the site of absorption of CSF?

A

arachnoid villi that project into the dural venous sinuses especially the superior sagittal sinus
> arachnoid villi tend to be grouped together to form elevations known as arachnoid granulations

45
Q

What are arachnoid granlations?

A

The arachnoid granulations are pinhead pouches of arachnoid mater projecting through the dural wall of the major venous sinuses
– especially the superior sagittal sinus and the small venous lacunae that open into it
> CSF is transported across the arachnoid epithelium in giant vacuoles

46
Q

What is hydrocephalus?

A

Hydrocephaluscan be defined broadly as a disturbance of:
1. formation,
2. flow, or
3. absorption of cerebrospinal fluid (CSF) that leads to an increase in volume occupied by this fluid in the CNS
> The obstruction of the flow of CSF leads to a rise in fluid pressure causing swelling of the ventricles

47
Q

What are the causes of hydrocephalus?

A
  1. Congenital : ( Arnold-Chiari malformation).
  2. Acquired :
    > Stenosis of the cerebral aqueduct by tumor of pineal region.
    > Obstruction of the interventricular foramina secondary to tumors, hemorrhages or infections such as meningitis
48
Q

Describe the types of hydrocephalus?

A
  1. Non communicating hydrocephalus [ internal hydrocephalus] - blockage of CSF flow through the ventricles
  2. Communicating hydrocephalus [ external hydrocephalus]
    = failure to reabsorb CSF
49
Q

Compare hydrocephalus in adults and chilren?

A

In young children the skull expands,
In older the intracranial pressure rises and needs urgent management

50
Q

Describe non communicating hydrocephalus?

A

Due to blockage of CSF flow through the ventricles
Normally at the foramina or aqueduct between ventricles and/or basal cistern
Caused by any space occupying lesion such as a tumour or a cyst or stenosis of the aqueduct
The location of the blockage must be found and the blockage removed surgically or a shunt placed.

51
Q

Describe communicating hydrocephalus?

A

when the CSF becomes blocked after leaving the ventricles
Obstruction can occur in basal cisterns or subaracnoid space.
It is called “communicating” because CSF can still flow between the brain’s ventricles, but cannot be reabsorbed in the arachnoid villi
May result from intracranial haemorrhage or meningitis [ acute pyogenic or chronic]
Often the cause is not known

52
Q

How do you treat hydrocephalus?

A

Decompression of the dilated ventricles
> achieved by inserting a shunt connecting the ventricles to the jugular vein or the abdominal peritoneum.

53
Q

Describe the optic nerve sheath?

A

The optic nerve has complete meningeal investment
Dura fuses with scleral shell of eye

The subarachnoid space is a tubular dead end

The central vessels of the retina pierce the meninges to enter the eye

54
Q

What is a papilloedema?

A

Any sustained elevation of intracranial pressure is transmitted to the subarachnoid sleeve surrounding the nerve and thus compresses the central vein of the retina
Causing swelling of the retinal tributaries of the vein and swelling of the optic nerve head or papilla where the optic nerve begins = papilloedema

55
Q

Describe the spinal dural sac?

A

Head and Neck Anatomy (37 decks)

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