Brain Blood Supply

Question 1

2 main arteries that supply the brain

Answer 1

1. Internal Carotid Arteries
2. Vertebral Arteries

Question 2

What is the Circle of Willis

Answer 2

Circular arrangement of cerebral blood supply arteries.
1. Anterior Communicating Artery
2. Anterior Cerebral Arteries
3. Internal Carotid Arteries
4. Posterior Communicating Arteries
5. Posterior Cerebral Arteries

Question 3

Importance of Circle of Willis

Answer 3

The circular arrangement allows for more than one pathway for blood flow; avoid ischemia if one of the arteries becomes blocked or narrowed

Question 4

Why is the blood-brain barrier (BBB) so important?

Answer 4

In addition to CSF and meninges; it is another layer of protection, specifically from the soluble substances in the blood supply affecting the brain. It helps to prevent and reduce the risk of blood infection from the fluctuation of solutes in the extracellular (blood flow outside of brain) environment
The BBB does however let essential solutes for brain function pass through facilitated diffusion, and removes blood-borne waste metabolites from the brain into the bloodstream.

Question 5

Structure of the BBB

Answer 5

Astrocyte “Foot” –> Pericyte inside Basement Membrane –> Endothelial Cell (tight junction) –> Cell nucleus

Question 6

What can pass through BBB and what can’t?

Answer 6

lipid soluble molecules (O2,CO2, fat, fatty acids, Alcohol, Nutrients)

Question 7

What are circumventricular organs?

Answer 7

Areas of the brain that are not protected by the BBB, and are surrounded by the ventricular system; posterior pituitary gland (endocrine), pineal gland (endocrine), area postrema (vomiting response). These areas don’t have BBB because they need access to bloodstream for vital regulatory functions.

Question 8

Cerebrospinal Fluid (CSF) Functions?

Answer 8

Protection: cushion around brain for protection against injury
Transport: nutrient supply to bloodstream, brain, and waste removal
Support: reduce net weight of the brain (important for neuronal tissue protection)

Question 9

Choroid Plexus: definition and functions

Answer 9

Definition: Network of cells located within ventricular system that produce CSF
Functions:
- Produce CSF
- Filter waste, unnecessary neurotransmitters, and foreign waste out of the CSF

Question 10

CSF composition

Answer 10

lower concentrations of potassium and amino acids, and way lower protein compared to blood plasma

Question 11

CSF Circulation

Answer 11

Within the ventricular system of the brain (two lateral, third, fourth) –> the subarachnoid space –> arachnoid granulations (one-way valve) –> bloodstream

Question 12

What is hydrocephalus (“water on the brain”)?

Answer 12

Blockage of CSF preventing drainage; causes pressure to compress blood vessels and crush soft nerve tissue; damaging the brain.

-not in babies because their brain has not fused yet

Question 13

Meninges definition

Answer 13

protective membranous barrier of the brain

Question 14

Layers of Meninges

Answer 14

External membrane = Dura mater
Middle membrane = Arachnoid mater
Internal membrane = Pia mater

Question 15

What are the layers of the dura mater?

Answer 15

• periosteal mater for skull’s inner surface
• TRUE layer is meningeal layer which covers brain and entire CNS; spinal cord where it is known as dural/thecal sac

Question 16

Arachnoid mater characteristics

Answer 16

• elastic ands loose-fitting; doesn;t follow the bumpy surface of the brain

Question 17

What is the subdural space

Answer 17

Thin, fluid-filled cavity between the arachnoid mater and dura mater

Question 18

Pia mater characteristics

Answer 18

Attached firmly to brain by astrocytes and follows the bumps of the brained formed by the grooves unlike arachnoid mater. Most delicate of the three membranes

Question 19

Subarachnoid Space and Characteristics

Answer 19

Space between arachnoid mater and pia mater.
- Filled with CSF
- Wider than subdural space
- Largest blood vessels that supply the brain
- Spiderweb-like extensions that extend from the arachnoid mater to the pia mater; hold two layers together

Question 20

What is a stroke

Answer 20

Brain’s blood supply is interrupted/reduced; rapid degeneration of the brain occurs due to the sudden lack of oxygen and glucose; PERMANENT damage to brain

Question 21

What are the types of stroke

Answer 21

• Ischemic
• Hemorrhagic
• Transient ischemic attacks (TIA)

Question 22

Ischemic Stroke Characteristics (two types)

Answer 22

Blood supply restricted in some way
1. Thrombotic- blood clot in an artery that supplies the brain. Could also occur from buildup of fatty deposits and cholesterol
2. Embolic- When blood clot that formed in another area of the body travels to and gets stuck in brain artery.

Question 23

Hemorrhagic Stroke Characteristics (two types)

Answer 23

Blood entering brain tissue from ruptured vessel; damaging surrounding brain tissue, also damaged due to reduction in blood supply.

1. Subarachnoid- bleeding into the subarachnoid space
2. Intracerebral- bleeding occurs within the brain tissue

Question 24

Transient Ischemic Attack Characteristics

Answer 24

Blood supply to brain is only BRIEFLY interrupted
Symptoms:
- weakness in face, arm, or leg
- confusion
- dizziness
- visual difficulties