The ventricular system

Question 1

What are the four ventricles of the brain?

Answer 1

Paired lateral ventricles (in the cerebrum)

Third ventricle (within diencephalon)

Fourth ventricle (between pons and cerebellum)

Question 2

How do the lateral ventricles communicate with the third ventricle?

Answer 2

Through the interventricular foramina of Monro.

Question 2

What are the subdivisions of the lateral ventricles?

Answer 2

Anterior (frontal) horn

Body

Atrium (collateral trigone)

Inferior (temporal) horn

Posterior (occipital) horn

Question 3

Which part of the lateral ventricle contains the glomus?

Answer 3

The atrium (collateral trigone), which is a large tuft of choroid plexus.

Question 3

What structure connects the third and fourth ventricles?

Answer 3

The mesencephalic aqueduct (Aqueduct of Sylvius).

Question 4

What is the function of the choroid plexus?

Answer 4

To produce cerebrospinal fluid (CSF).

Question 5

Where is the choroid plexus located?

Answer 5

In the roofs of the third and fourth ventricles and the medial walls of the lateral ventricles.

Question 6

What are the openings through which CSF exits the fourth ventricle into the subarachnoid space?

Answer 6

Median aperture (foramen of Magendie)

Lateral apertures (foramina of Luschka)

Question 6

How is CSF absorbed back into the bloodstream?

Answer 6

Through arachnoid villi (or granulations) that project into venous sinuses, like the superior sagittal sinus.

Question 7

What is the role of CSF in the CNS?

Answer 7

Buoyancy: Reduces the brain’s apparent weight.

Protection: Acts as a liquid cushion.

Environmental stability: Transports nutrients and removes waste.

Question 8

What is hydrocephalus?

Answer 8

An abnormal increase in CSF volume within the skull, caused by overproduction, blockage of circulation, or diminished absorption of CSF.

Question 9

What is the purpose of a spinal tap (lumbar puncture)?

Answer 9

To withdraw CSF for examination.

To inject drugs (e.g., for anesthesia or infection treatment).

Question 10

Where does the spinal cord terminate in adults vs. infants?

Answer 10

Adults: Lower border of the first lumbar vertebra (L1).

Infants: May extend to the third lumbar vertebra (L3).

Question 11

What is the Queckenstedt sign used for?

Answer 11

To test for spinal cord blockage by observing changes in CSF pressure during jugular vein compression.

Question 12

Do ependymal cells secrete CSF?

Answer 12

No, they primarily line the ventricles and help circulate CSF. The choroid plexus is responsible for CSF production.

Question 13

Which ventricles contain choroid plexus, and which do not? (High-yield detail)

Answer 13

Contain choroid plexus: Lateral ventricles (body/atrium/inferior horn), 3rd ventricle, 4th ventricle.

No choroid plexus: Anterior/posterior horns of lateral ventricles, cerebral aqueduct.

Question 14

What structures form the roof and floor of the 4th ventricle? (Exam favorite)

Answer 14

Roof: Superior/inferior medullary velum (+ cerebellum).

Floor: Rhomboid fossa (pons/medulla).

Key detail: Foramina of Luschka (lateral) and Magendie (median) pierce the inferior velum.

Question 15

Which ventricle is surrounded by periaqueductal gray matter, and why is this clinically relevant?

Answer 15

Cerebral aqueduct (of Sylvius).

Relevance: Blockage → obstructive hydrocephalus; PAG modulates pain (target for analgesia).

Question 16

Trace the path of CSF from production to absorption. (Classic exam question)

Answer 16

Produced: Choroid plexus (lateral/3rd/4th ventricles).

Flow: Lateral → 3rd → aqueduct → 4th → subarachnoid space via Luschka/Magendie.

Absorbed: Arachnoid granulations → dural venous sinuses.

Question 17

What is the normal CSF volume and production rate? (Easy-to-miss number)

Answer 17

Total volume: ~150 mL.

Production rate: 20–25 mL/hr (0.5 mL/min).

Question 18

Why does CSF have higher Na⁺/Cl⁻ but lower K⁺/Ca²⁺ vs. plasma? (Physiology nugget)

Answer 18

Selective transport by choroid plexus epithelium (blood-CSF barrier).

Question 19

A patient presents with headache, papilledema, and dilated ventricles on imaging. What is the most likely cause if the cerebral aqueduct is narrowed?

Answer 19

Obstructive hydrocephalus (aqueductal stenosis → CSF backs up into 3rd/lateral ventricles).

Question 20

Why is a lumbar puncture performed below L2 in adults? (Must-know clinical anatomy)

Answer 20

To avoid puncturing the spinal cord (ends at L1/L2), targeting the lumbar cistern (subarachnoid space extends to S2).

Question 21

What does a positive Queckenstedt sign indicate?

Answer 21

Spinal CSF blockage (no rise in pressure with jugular compression).

Question 22

A patient with a 4th ventricle tumor develops hydrocephalus. Which foramina are likely obstructed?

Answer 22

Foramina of Luschka and Magendie → CSF can’t exit 4th ventricle.

Question 23

Which part of the lateral ventricle is most likely to calcify in adults, and why? (Radiology pearl)

Answer 23

Glomus (choroid plexus in the atrium) → calcifies with age → visible on CT.

Question 24

Why does the anterior horn of the lateral ventricle lack choroid plexus? (Embryology twist)

Answer 24

Choroid plexus grows from the tela choroidea in the medial wall/roof; anterior horn is too rostral.

Question 25

What is the obex, and why is it clinically relevant?

Answer 25

Definition: Inferior tip of the 4th ventricle floor (marks transition to central canal). Relevance: Landmark for surgeries/tumors (e.g., medulloblastoma)

Question 26

What structure forms the medial boundary of the anterior horn of the lateral ventricle?

Answer 26

Septum pellucidum (often damaged in TBI → "bat-wing" ventricles on imaging).

Question 27

A patient with raised ICP has visual deficits. Which subarachnoid space extension is compressed?

Answer 27

Optic nerve sheath (subarachnoid space around optic nerve → papilledema).