Lecture 4: The Blood brain barrier and CSF

Question 1

Which arteries supply the lobes of the brain?

Answer 1

Frontal Lobe:
- Lateral Orbitofrontal artery
- Ascending frontal artery
- precentral artery
- central artery

Parietal Lobe
- anterior parietal artery
- posterior parietal artery
- angular artery

Temporal Lobe
- Anterior temporal artery
- middle temporal artery
- posterior temporal artery

Question 2

What percentage of the cardiac output goes to the brain?

Answer 2

15%

Question 3

Arterial supply from the heart to the brain

Answer 3

1. Internal carotid artery (telencephalon and diencephalon)
2. Vertebral Arteries (brain stem, cerebellum, spinal cord, occipital lobe, temporal lobe) fuse to form basilar artery

Internal carotid artery and vertebral arteries (basilar) connect via the circle of Willis

Question 4

Describe the BBB

Answer 4

Endothelial cells

Restrict entry of gases and non-lipophilic molecules (which don’t have a transport system in)

Consists of tight junctions in the endothelium, a basement membrane, and Astrocytes

Role in protection
- protection from chemical fluctuations
- minimises possibility of harmful substances reaching the CNS
- stops peripheral hormones which could act as NT from entering the brain

Question 5

Transport across the BBB

Answer 5

Diffusion
- small molecules, gases, lipophilic substances

Special Transport proteins
- GLUT1

Transcytosis
- movement across the Barrier within a vesicle

Question 6

What are the differences between the BBB and the blood-CSF barrier?

Answer 6

The tight junctions in the BCSF barrier are in the choroid cells, whereas in the BBB they’re in the endothelium

There are choroid cells in the BCSF barrier instead of Astrocytes like in the BBB

The BCSF has fenestrations (pores) in the endothelium which allow for molecules to pass through, unlike the BBB which is lines with gap junctions

Question 7

Describe the venous drainage of the brain

Answer 7

The superior Sagittal sinus and straight sinus meet at the confluence of the sinuses —> transverse sinus —> sigmoid sinus —> internal jugular vein

Question 8

Describe CSF

Answer 8

Produced in the Choroid plexus (via selective diffusion from blood) in lateral and 4th ventricle

Clear, colourless body fluid found in the CNS

Total volume is 140-270ml

Produced at a rate of 0.2 - 0.7 mL/day

Lateral ventricle —> interventricular foramens —> 3rd ventricle —> cerebral aqueduct —> 4th ventricle (lateral aperatures and medial foramen) —> subarachnoid space —> over brain and SC

Pumped by flexion and extension of the occipital bone and sacrum

Reabsorption occurs in the subdural cavity, where the blood leaves the brain

Functions
- cushion
- nutrient/messenger/waste transport
- communication with interstitial fluid
- brain buoyancy

Pathology
- increased intracranial pressure via obstruction, oversecretions, impaired venous absorption

Whilst fairly similar in composition to plasma, CSF has notably more PCO2, and less glucose

Reabsorption at arachnoid villi into the venous sinuses in the dura mater, possible via transpinocytosis via vacuoles

Question 9

Describe some forms of hydrocephalus

Answer 9

1. Meningitis
   - acute meningeal inflammation
2. Spina bifida
   - displaced cerebellum disrupts CSF flow —> raised intracranial pressure
3. Encephalitis
   - brain tissue infection
4. 4th ventricle or cerebral aqueduct occlusion

Question 10

Describe the meninges

Answer 10

3 protective layers which cover the CNS

1. Dura Mater (lines the skull, forms Dural sinuses)

Dural sinus

2. Arachnoid (middle layer, bridges sulci, forms arachnoid villi into dural sinuses)

Subarachnoid space (contains CSF)

3. Pia Mater (innermost, soft, follows exact sulci and giri pattern of the brain)