L12. Ventricular system (AD)

Question 1

give an overview of the ventricular system

Answer 1

• Series of CSF-filled interconnected spaces

- Continuous with the subarachnoid space and central canal

Question 2

how do the ventricles develop (embryonic stage )

Answer 2

• Neuroectoderm forms neural tube
• Lumen of neural tube becomes ventricles and central canal
• Ependymal layer lines ventricles and central canal

Question 3

describe the lateral ventricles

Answer 3

• Two ventricles – Very large

One for each cerebral hemisphere

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

Question 4

look at labelling for lateral ventricles in slide 6

Answer 4

how was it

Question 5

what are the borders of the lateral ventricles

Answer 5

• Septum pellucidum separates lateral ventricles
• Corpus callosum sits in roof
• Caudate nucleus sits in lateral wall
• Hippocampus sits in floor of inferior horn

slide 9

Question 6

describe the interventricular foramen

Answer 6

Lateral ventricles communicate with the third ventricle through the interventricular foramen

• Also called Foramen of Monro

Question 7

describe the third ventricle

Answer 7

• cleft between thalami

- fornix forms roof

Question 8

study slide 12

Answer 8

how was it

Question 9

describe the cerebral aqueduct

Answer 9

• Third ventricle communicates with fourth ventricle through the cerebral aqueduct
• Also called Aqueduct of Sylvius

– Surrounded by the midbrain

Question 10

describe the 4th ventricle

Answer 10

Surrounded by hindbrain:

• Cerebellum posterior
• Pons and medulla anterior
• Cerebellar peduncles lateral

Characteristic rhomboid shape (coronal view)

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

Question 11

describe 4th ventricle communication

Answer 11

Three foramen exit into subarachnoid space:

• Two Foramen of Luschka (lateral)
• One Foramen of Magendie (middle)
  - Into Cisterna Magna

Question 12

study slide 17

Answer 12

how was it

Question 13

describe the choroid plexus

Answer 13

CSF produced by choroid plexus

Filters blood from branches of internal carotid and basilar arteries

Choroid plexus present throughout ventricles:

Question 14

describe the structure of the choroid plexus

Answer 14

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

3) Tight junctions between epithelial cells
- Prevent macromolecules from entering CSF
- Permeable to water and CO2

4)- Forms blood-CSF barrier

Question 15

study slide 20

Answer 15

how was it

Question 16

describe the cuboidal epithelium

Answer 16

Specialized ependyma

Villi present to increase surface area

Active transport of CSF components

Bidirectional (uptake of metabolites into circulatory system)

Question 17

give the estimate % of CSF production in the head

Answer 17

60% CSF produced in ventricles

40% CSF from other sites within brain

Question 18

what is the CSF composition ideal for

Answer 18

physiological functioning of neurons

Question 19

what are the differences in protein composition between CSF and Plasma

Answer 19

CSF- 0.18g/l

Plasma- 75g/l

Differences due to regulation by active transport

Question 20

describe the route of CSF circulation

Answer 20

Lateral ventricles
(Interventricular foramen)

Third ventricle
(Cerebral aqueduct
)

Fourth ventricle
(Luschka and Magendie
foramina)

Cisterna magna
(subarachnoid space)

CSF passes out of ventricles into the subarachnoid space

then up spinal
subarachnoid space

Over cerebral hemispheres

(including arachnoid granulations & superior sagittal sinus)

then down dorsal spinal subarachnoid space

(central canal usually blocked in adults)

slides 23-24

Question 21

describe the subarachnoid space

Answer 21

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 22

describe the arachnoid granulations

Answer 22

Herniations of arachnoid membrane (villi) through dura mater into venous sinuses

Mainly within the superior sagittal and transverse sinuses

Question 23

describe the absorption of CSF

Answer 23

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
(Prevents reflux of blood into subarachnoid space)

		Arachnoid villi act as one-way valves

Question 24

describe CSF volume and its factors

Answer 24

500ml CSF produced per day (0.35ml/min)

Total volume in system = 90-140ml
- Normally quoted 140ml
30 ml ventricles
110ml subarachnoid space

Continuously moving

Excess absorbed by arachnoid granulations

Question 25

what is the main functions of CSF

Answer 25

Hydraulic buffer to cushion brain against trauma 2. Vehicle for removal of metabolites from CNS 3. Stable ionic environment for neuronal function (communicates with brain interstitial fluid via pia) 4. Transport of neurotransmitters and chemicals

Question 26

describe the different colours of CSF in disease

Answer 26

CSF normally clear sterile fluid Discoloured in some pathological states: Yellow (Xanthocromia) E.g. Subarachnoid haemorrhage - Lysis of red blood cells, haemoglobin release Cloudy E.g. Multiple sclerosis - Protein content (gamma globulin) increase E.g. Bacterial meningitis - Leukocytes are increased, indicative of infection

Question 27

how is CSF sampled

Answer 27

Taken by lumbar puncture At lumbar cistern - No spinal cord

Question 28

describe the condition hydrocephalus

Answer 28

Dilation of brain ventricles Due to blocked CSF circulation, impaired absorption, or over secretion Increased intracranial pressure Pressure on surrounding tissues affects neurological function Can be congenital or acquired

Question 29

what are the symptoms of hydrocephalus

Answer 29

-- Symptoms include: headaches, vomiting, visual disturbances, papilledema (swelling of optic disc), seizures, altered cognition, balance and coordination problems

Question 30

describe non-communicating hydrocephalus

Answer 30

Blockage within the ventricular system - Due to tumour, cyst, stenosis (e.g. narrowing of cerebral aqueduct) CSF does not circulate over surface of brain Surgery: Insert shunt to reduce intracranial pressure

Question 31

describe Dandy-walker syndrome

Answer 31

Congenital malformation of the cerebellum (1:30,000 births) Obstruction within foramina of fourth ventricle: -Symmetrical dilation of lateral, third and fourth ventricles In infancy, child’s head may become enlarged:

Question 32

describe communicating hydrocephalus

Answer 32

Obstruction in the arachnoid villi Movement of CSF into venous sinuses is impeded - E.g. Impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis