The ventricular system

Question 1

Development of ventricles

Answer 1

Neuroectoderm froms neural tube

Lumen of neural tube becomes ventricles and central canal

Ependymal layer lines ventricles and central canal

Lumen expands at cranial end to form ventricles

There is a ventricle associated with each part of the brain

Question 2

Lateral ventricles

Answer 2

Two ventricles- very large

One for each cerebral hemisphere

Body, anterior, posterior and inferior horn corresponding to lobes of the hemisphere

Surrounded by telencephalon

Question 3

Lateral ventricle borders

Answer 3

Septum pellucidum separates lateral ventricles

Corpus callosum sits in roof

Caudate nucleus sits in lateral wall

Hippocampus sits in floor of inferior horn

Question 4

Interventricular foramen

Answer 4

Lateral ventrciles communicate with the thrd ventricle through the interventricular foramen

Also called foramen of monro

Question 5

Third ventricle

Answer 5

Slit like cleft between thalami

Fornix forms roof

Question 6

Cerebral aqueduct

Answer 6

Third ventricle communicates with fourth ventricle through cerebral aqueduct

Also called aqueduct of sylvius

Surrounded by midbrain

Question 7

Fourth ventricle

Answer 7

Surrounded by hind brain

• cerebellum posterior
• pons and medulla anterior
• cerebellar peduncles lateral

Characteristic rhomboid shape

Continuous with the central canal of the spinal cord and subarachnoid space

Question 8

Fourth ventricle communication

Answer 8

Three foramen exit into subarachnoid space:

• two foramen of luschka
• one foramen of magendie

Question 9

Choroid plexus

Answer 9

CSF produced by choroid plexus

Filters blood from branches of internal carotid and basilar arteries

Choroid plexus present throughout ventricles

Question 10

Structure of the choroid plexus

Answer 10

Very simple

Capillary network surrounded by cuboidal epithelium

During CSF production:

1. Blood filtered through fenestrated capillaries
2. Components transported through cuboidal epithelium into ventricles

Tight junctions between epithelial cells

Question 11

Tight junctions between epithelial cells in choroid plexus

Answer 11

Prevent macromolecules from entering CSF

Permeable to water and CO2

Question 12

Cuboidal epithelium

Answer 12

Specialised ependyma

Villi present to increase surface area

Active transport of CSF components

Bidirectional

Question 13

CSF composition

Answer 13

Differs in ionic composition compared to plasma

Differences due to regulation by active transport

Very few cells

Ideal for physiological functioning of neurones

Question 14

CSF circulation

Answer 14

Lateral ventricles -> . (interventricular foramen)

Third ventricles -> (cerebral aqueduct)

Fourth ventricle -> (luschka and magendie foramina)

Cisterna magna (subarachnoid space)

Question 15

Subarachnoid space

Answer 15

Lies between pia and arachnoid

Subarachnoid space follows contours of brain

Functionally important: CSF in contact with brain parenchyma

• transfer of micronutrients into brain
• removal of metabolites

Question 16

Arachnoid granulations

Answer 16

Herniations of arachnoid membrane through dura mater into venous sinuses

Mainly within the superior sagittal and transverse sinuses

Question 17

Absorption of CSF

Answer 17

CSF pressure must exceed that in venous sinuses

• 150mm water in subarachnoid space
• 80mm water in venous sinuses

If venous pressure exceeds CSF pressure
- tips of villi close off

Question 18

CSF volume

Answer 18

500ml CSF produced per day

Total volume in system = 90-140ml

Continuously moving

Excess absorbed by arachnoid granulations

Question 19

Main functions of CSF

Answer 19

Hydraulic buffer to cushion brain against trauma

Vehicle for removal of metabolites from CNS

Stable ionic environment for neuronal funciton

Transport of neurotransmitters and chemicals

Question 20

Colour of CSF in disease

Answer 20

CSF normally clear sterile fluid

Discoloured in some pathological states

• yellow (xanthocromia): e.g. subarachnoid haemorrhage
• cloudy: e.g. multiple sclerosis, bacterial meningitis

Question 21

CSF sampling

Answer 21

Taken by lumbar puncture

At lumbar cistern
- no spinal cord

Question 22

Hydrocephalus

Answer 22

Dilation of brain ventricules

Due to blocked CSF circulation, impaired absorption or over secretion

Increased intracranial pressure

Pressure on surrounding tissues affect neurological function

Can be congenital or acquired

Question 23

Non- communicating hydrocephalus

Answer 23

Blockage within the ventricular system
- due to cyst, tumour, stenosis

CSF does not circular over surface of brain

Insert shunt to reduct intracranial pressure

Question 24

Dandy- Walker syndrome

Answer 24

Congenital malformation of the cerebellum

Obstruction within foramina of fourth ventricle

In infancy, child’s head may become enlarged

Question 25

Communicating hydrocephalus

Answer 25

Obstruction in the arachnoid villi

Movement of CSF into venous sinuses is impeded

E.g. impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis