1.12 Protection of the Brain: Meninges, Ventricles, CSF, Blood Brain Barrier

Question 1

What is the Dura mater?

Answer 1

The tough outermost membrane enveloping the brain and spinal cord.

Question 2

What is the Arachnoid mater?

Answer 2

-A fine, delicate membrane, the middle one of the three membranes or meninges that surround the brain and spinal cord, situated between the dura mater and the pia mater.

Question 3

What is the pia mater?

Answer 3

The delicate innermost membrane enveloping the brain and spinal cord.

Question 4

What is the Falx cerebri?

Answer 4

– Vertical sheet of dura between hemispheres.
- Named from its sickle-like form, is a strong, arched fold of dura mater that descends vertically in the longitudinal fissure between the cerebral hemispheres

Question 5

What is the Tentorium?

Answer 5

• Horizontal sheet of dura between cerebrum and cerebellum.

- A fold of the dura mater forming a partition between the cerebrum and cerebellum

Question 6

How much CSF is in an adult human?

Answer 6

140 mL (4 floz= 118 mL)

Question 7

Where is CSF secreted from?

Answer 7

• Secreted by choroid plexus (0.35 mL/min, 500 mL/day) in lateral, third and fourth ventricles.

Question 8

What cells present a barrier to the flow from the blood to the formation of CSF?

Answer 8

Epithelial cells of the choroid plexus

Question 9

Which ventricle is the largest?

Answer 9

Lateral ventricles are the largest and most important locations

Question 10

Where is CSF absorbed

Answer 10

• Absorption: Arachnoid Villi Superior Saggital Sinus

- Absorption occurs through arachnoid granulations that protrude into the sagittal venous sinus.

Question 11

What is the path of CSF?

Answer 11

1) Choroid Plexus
2) Lateral ventricles (one and two)
3) Foramina of Monro (interventricular foramina, bilateral)
4) Third ventricle
5) Aqueduct of Sylvius (cerebral aqueduct)
6) Fourth ventricle
7) Foramina of Magendie (median) and Luschka (lateral (bilateral)
8) Around spinal cord and cerebellum.
9) Slower movement, determined by shifts of vertebral column.
10) Flows from spinal cord, around cerebral cortex and then to superior sagittal sinus.

Question 12

What is the function of CSF?

Answer 12

• The brain weighs 1400-1500 g in air but effectively only 50 g when suspended in the CSF.
• Removal of brain metabolites from brain interstitial fluid to venous sinuses.
• Regulates brain tissue. CSF and the extracellular fluid in the brain are essentially the same. The pH of the CSF influences both pulmonary ventilation and cerebral blood flow for homeostasis.

Question 13

What is the Monro-Kellie doctrine?

Answer 13

An increase in volume of brain tissue, blood, CSF or other brain fluids will produce an increase in intracranial pressure because the bony calvarium fixes the total cranial volume.

Question 14

What are examples that can increase intracranial pressure?

Answer 14

• Mass lesions can increase intracranial pressure through their associated edema
• Acute changes in arterial or venous blood pressure can change intracranial pressure dramatically.
• Chronic changes in blood pressure can be compensated for by venous collateralization and increased absorption or decreased production of CSF.
  * Edema
  * Hydrocephalus

Question 15

How is Glucose transported through the BBB?

Answer 15

• Hexose transporter (glucose transporter isotype-1, Glut1)

- Concentration driven (from plasma into the brain)

Question 16

How are amino acids transported through the BBB?

Answer 16

Transported by the L system, A system and the ASC system.

Question 17

What does the ASC system transport?

Answer 17

Energy dependent and moves alanine, serine, and cysteine.

Question 18

What is Vasogenic edema?

Answer 18

• Most common
• Caused by increased permeability of brain capillary endothelial cells which leads to increased volume of extracellular fluid.
• More swelling occurs around white matter than gray matter because fluid tends to accumulate along fiber tracts which are hydrophobic.

Question 19

What is Cytotoxic edema?

Answer 19

• Is when injured neurons, glia, or endothelial cells swell.
• This occurs after hypoxia from asphyxia or global cerebral ischemia after cardiac arrest.
• Failure of the Na+/K+ ATP-dependent pump allows Na+ and thus H20 to accumulate within cells.
  • Water intoxication can do the same thing. Systemic hypo-osmolarity forces water into the cells.

Question 20

What are the three ways to produce hydrocephalus?

Answer 20

• Impaired absorption of CSF at
• Oversecretion of CSF
• Tumors of choroid plexus (papilomas

Question 21

What likely causes headaches?

Answer 21

• Headache is likely to be caused by activation of nociceptors from changes in the meninges and vascular changes

Question 22

How can Tumors affect CSF flow?

Answer 22

• Obstruction of CSF pathways

Question 23

What are methods that headaches can be triggered in the brain?

Answer 23

• Pain from a loss of CSF: nociceptors at the base of the skull, imbalance in CSF pressure
• Pain from inflammation of the meninges
• Pain from stretching of the dura (tumors, hydrocephalus)
• Pain from migraines: vasodilation and stretching of vessels are involved but not exclusively
• Pain from dental infection and sinusitis are referred to the face skin and forehead along the trigeminal nerve.
• Pain from reading: Tonic spasm of the ciliary muscle in the eye can cause orbital headaches.

Question 24

What is the blood supply to the dura matter?

Answer 24

•Internal carotid, maxillary, ascending pharyngeal, occipital, and vertebral arteries supply the dura mater.

Question 25

What artery is most often injured that is part of the blood supply to the brain?

Answer 25

•Middle meningeal artery is most often injured.

Question 26

What is the innervation of the dura mater?

Answer 26

• The dura above the tentorium is innvervated by the trigeminal nerve.
• The dura below the tentorium is innvervated by the first three cervical nerves and the vagus nerve.