Ventricular System DLA

Question 1

What is the ventricular system?

Answer 1

• The early embryonic brain comprises three parts, the prosencephalon, mesencephalon and rhombencephalon.
• The prosencephalon splits into the telencephalon, related to the (left and right) lateral ventricles, and the diencephalon, which surrounds the third ventrice

Question 2

What is the ventricular component if the mesencephalon?

Answer 2

• The ventricular component of the mesencephalon is the cerebral aqueduct. The rhombencephalon splits into the metencephalon and myelencephalon, both of which relate to the fourth ventricle. The caudal myelencephalon and the myelon (spinal cord) contain the central canal.

Question 3

What does the ventricular system comprised?

Answer 3

The ventricular system of the brain comprises four interconnected ventricles. They are lined by ependyma and filled with CSF, which is secreted by the choroid plexus, for example

Question 4

How do left & right ventricles communicate?

Answer 4

• The left and right lateral ventricles communicate with the third ventricle via the interventricular foramina (of Monro). The third ventricle communicates with the fourth ventricle via the cerebral aqueduct. The fourth ventricle communicates directly with the central canal of the medulla (myelencephalon), which is continuous with the central canal of the spinal cord. The spinal central canal terminates as the tiny terminal ventricle, located in the conus medullares.

Question 5

Describe the anterior (frontal) horn of the lateral ventricles

Answer 5

• Each lateral ventricle has four distinct parts:
– Anterior (Frontal) Horn

• Located in the frontal lobe (anterior to the foramen of
Monro)
• Anterior wall and roof are formed by the corpus callosum
• Medial wall is called the septum pellucidum
• Floor and lateral wall are formed by the head of the caudate nucleu

Question 6

Describe the body (corpus) of the lateral ventricles

Answer 6

• Body (corpus)

– Located in the frontal and parietal lobes (posterior to the foramen of Monro)
– Extends posteriorly to the splenium of the corpus callosum
– Corpus callosum forms the roof
– Septum pellucidum forms the medial wall
– Important structures on the floor: fornix, choroid plexus, dorsal thalamus, stria terminalis, and inferior body of the caudate nucleus

Question 7

Describe the posterior (occipital) lateral ventricles

Answer 7

Posterior (Occipital) Horn

– Located in occipital lobe
– Joins with the body and temporal horn at the atrium
– Roof is formed by corpus callosum
– An eminence, tied to the calcarine fissure, is found on its medial wall
– Inferior (Temporal) Horn
– Located in temporal lobe
– Tail of the caudate nucleus forms the roof
– Floor is formed by the hippocampus
– Amygdala forms the anterior wall

Question 8

Where is the third ventricle?

Answer 8

• The third ventricle is a thin vertical cavity, occupying the midline between the diencephalic hemispheres.
• Roof is formed by choroid plexus and the body of the fornix.
• Lateral walls are formed by the thalami, hypothalami, and subthalami.
• Basal hypothalamic structures also form the floor.

• Lamina terminalis and anterior commissure form the
anterior wall.
• Epithalamusformstheposteriorwall.

Question 9

Describe the fourth ventricle

Answer 9

• The fourth ventricle is a rhomboid cavity (hence the term “rhombencephalon”) overlying the pons and rostral medulla.
• It is connected to the third ventricle by the mesencephalic cerebral aqueduct, which is frequently involved in obstructive hydrocephalus.
• The medullary vela and choroid plexus form the roof.

Question 10

What does the fourth ventricle communicate with?

Answer 10

• Lateral boundaries of the floor are the superior and inferior cerebellar peduncles.
• This ventricle communicates with the subarachnoid space via the two foramina of Luschka (lateral near the cerebellopontine angle) and the foramen of Magendie (at the caudal midline).

Question 11

What is the significance of the choroid plexus?

Answer 11

• Lateral boundaries of the floor are the superior and inferior cerebellar peduncles.
• This ventricle communicates with the subarachnoid space via the two foramina of Luschka (lateral near the cerebellopontine angle) and the foramen of Magendie (at the caudal midline).

Question 12

What is CSF?

Answer 12

• CSF is a clear, colorless, almost protein-free filtrate of blood that forms in the ventricles and circulates though the subarachnoid space.
• CSF serves to support and cushion the CNS against injury.
• It may serve nutritive functions and remove metabolic waste.
• Its normal pressure (intracranial pressure, ICP) is 65 - 200 mm H2O (5 – 15 mm Hg).

Question 13

What is CSF produced by?

Answer 13

• Produced by choroid plexus, ependyma, glia, pial and arachnoid vessels.
• It is constantly formed (approximately 600-700 ml/day).
• Ions are actively transported with passive movement of water.
– CSF is clear and low in glucose, protein, K+, Ca++ and cells relative to serum.
– CSF is high in Na+, Cl- , and Mg++ relative to serum.
• Note that normal ranges for Na+ in serum and sodium overlap extensively, but the upper end of the range is slightly higher for Na+ in CSF.
• The total volume in the ventricles and subarachnoid space is about 140 ml.

Question 14

What are the functions of CSF?

Answer 14

• Functions
– Buoyancy
– Shock absorption
– Chemical stability
– Reduction of ischemia

Question 15

Whaat are the contents of the CSF?

Answer 15

Produced by choroid plexus, ependyma, astrocytes, pial and arachnoid vessels
• Ions are actively transported with passive movement of water (~0.5 ml/min)
• CSF is clear and low in glucose, protein, K+, Ca++ and cells
– Na+, Cl- and Mg++ higher than in serum
• Normal ranges of Na+ in CSF and serum largely overlap

Question 16

Explain the circulation path of CSF

Answer 16

• The brain and spinal cord effectively float within a shock-absorbing cushion of CSF.

• CSF flows through the ventricular system:
– From the lateral ventricles into the third ventricle via the interventricular foramina (of Monro).
– From the third ventricle into the cerebral aqueduct.
– From the cerebral aqueduct into the fourth ventricle.
– Very small amounts of CSF trickle between the fourth ventricle and the central canal.

• CSF exits the fourth ventricle into the subarachnoid space via the foramina of Luschka (lateral) and Magendie (medial).
• Extraventricular CSF follows the subarachnoid space. It returns to the venous system through small membranous villi, the arachnoid granulations, located along the superior sagittal sinus.
• The arachnoid villi react to pressure gradients between the subarachnoid space and venous system to form one-way valves, ensuring the unidirectional movement of fluid into the venous syste

Question 17

What is the clinical impact of brain sinuses and veins?

Answer 17

The venous dural sinuses are epithelium-lined spaces or channels between the two layers of dura of the brain, and drainage of blood from the brain is chiefly into these sinuses.

The dural sinuses do not have valves and are usually triangular in shape.
• The sinuses receive blood from three major sources:
• The cerebral veins are the major source of blood drainage:
– The great anastomotic vein drains into the superior sagittal sinus.
– The small anastomotic vein drains into the transverse sinus.
– The short midline great cerebral vein (of Galen) forms at the junction of the two internal cerebral veins and drains into the straight sinus.

• The venous sinuses have little tendency to collapse as do most other veins because of the fibrous consistency of the dura mater

Question 18

Explain this case: Following partial recovery from an intracerebral hemorrhage, a 56-yr-old male complains of increasingly severe headaches. His spouse reports irritability and confusion. The patient is nauseated and vomit

Answer 18

– Hemorrhagic blood has burst into the lateral ventricle. The clotting blood has blocked the narrow passage between the lateral and the third ventricle (foramen of Monro). The clot prevents drainage of CSF from the lateral ventricle, which subsequently expands to compress adjacent structures and to increase intracranial pressure. The clinical condition is obstructive hydrocephalus.

Intracerebral hemorrhage with secondary obstructive hydrocephalus

Question 19

What are the main sources of hydrocephalus?

Answer 19

• Obstructive (non-communicating) – Pathogens and immune cells
– Congenital stenosis
– Tumors

• Communicating
– Normal pressure hydrocephalus
– Secondary to subarachnoid hemorrhage
– Hydrocephalus ex vacuo
• Expansion of ventricles owing to degeneration of surrounding tissue