Mod4-Obj7: Meninges, Cerebrospinal fluid and the blood brain barrier

Question 1

The brain is protected by

Answer 1

• The cranium
• Meninges
• Cerebrospinal fluid (CSF)
• The blood-brain barrier

Question 2

The meninges

Answer 2

Three connective tissue membranes that lie external to the central nervous system which:

1. ) Cover and protect the CNS
2. ) Protect blood vessels and enclose venous sinuses
3. ) Contain CSF
4. ) Form partitions in the skull

Question 3

The meninges: membranes (superficial to deep)

Answer 3

• Dura mater=Top layer
• Arachnoid mater=middle layer
• Pia mater=Inner most layer

Question 4

The meninges: The dura mater

Answer 4

Tough mother=strongest meninx

• Two layered sheet of fibrous connective tissue
• Dural periosteal (endosteal) layer: superficial, attached to the inner surface of the skull
• Dural meningeal layer: deep, covers the brain and spinal tissue
• Two layers are fused, except in certain areas where they form venous sinuses=collect and drain venous blood
• Dura mater folds form divisions within the cranium

Question 5

The meninges: The arachnoid mater

Answer 5

Spider mother-Middle meninx

• Separated from the dura mater by the subdural space which contains blood vessels (site of subdural haemorrhage)
• Loose covering with web-like extensions that extend to the subarachnoid space
• The subarachnoid space is filled with CSF and contain large blood vessels (subarachnoid haemorrhage)
• Arachnoid villi=projections of the meninx through the dura mater into the dural venous sinus=allows CSF to drain away

Question 6

The meninges: The pia mater

Answer 6

Gentle mother-Inner most layer

• Delicate connective tissue that clings tightly to the brain and closely follows its contours
• Contains mainly small blood vessels

Question 7

The meninges sequence

Answer 7

• Bone (skull or vertebral column)
• Epidural space (spinal cord only)
• Dura mater (3 components)
• Subdural space (serous fluid and blood vessels)
• Arachnoid mater
• Subarachnoid space (CSF & blood)
• Pia mater
• Nervous tissue

Question 8

Meningitis

Answer 8

Inflammation of the meninges

-Generally caused by a bacterial or viral infection (bacterial generally more serious)

Question 9

Typical route of infection-Meningitis

Answer 9

Microbes infect the nasal mucosal surface=blood=subarachnoid blood vessels=large-scale inflammation=cerebral oedema=increased ICP

Question 10

Symptoms of meningitis

Answer 10

Severe headache, neck stiffness, fever

Question 11

Diagnosis of meningitis

Answer 11

CSF sample examined for WBC and microbes

Question 12

Treatment of meningitis

Answer 12

Antibiotics, corticosteroids

Question 13

Cerebrospinal fluid

Answer 13

Clear fluid that circulates within and around the brain and spinal cord

• Capillary filtrate derived from plasma but has very little protein and limited ca2+ and K+ ions
• Total volume=150ml, replaced every 8 hours

Question 14

Functions of CSF

Answer 14

1. ) Buoyancy-reduces brain weight by 97% and thus prevents crushing of inferior brain tissues
2. ) Shock absorption (prevent physical trauma)
3. ) Helps nourish the brain and removes wastes

Question 15

CSF formation-ventricles

Answer 15

Site of CSF production

• 4 chambers within the brain
• Continuous with each other
• 4th connects to the subarachnoid space and central canal of the spinal cord

Question 16

CSF formation

Answer 16

CSF is produced by a choroid plexus (network of capillaries) found within each ventricle

• Capillaries are surrounded by ependymal cells, which control the composition of the capillary filtrate
• Ependymal cells bear cilia, which keeps the CSF in motion

Question 17

CSF

Answer 17

1. ) CSF is produced by the choroid plexus of each ventricle
2. ) CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord
3. ) CSF flows through the subarachnoid space
4. ) CSF is absorbed into the dural venous sinuses via the arachnoid villia

Question 18

CSF exit

Answer 18

The CSF flows from the subarachnoid space into dural venous sinuses (e.g. superior sagittal sinus) through arachnoid villi-and drains away

Question 19

Cerebrospinal fluid production and drainage

Answer 19

CSF is produced at a constant rate and must be drained at the same rate

Question 20

Obstruction in CSF

Answer 20

Leads to fluid accumulation 
-Increase ICP 
Condition=HYDROCEPHALUS 
symptoms include:
-Headache
-Irritability
-Nausea
-vomiting
-sleeplessness 
-coma 
May be caused by:
-Blockage to flow e.g.) tumor, haemorrhage 
-Inflammation e.g.) meningitis 
-Birth injury

Question 21

Hydrocephalus in young children

Answer 21

Enlargement of the head as cranial bones are not yet fused

-Minor symptoms, minimal long-term effects if treated properly

Question 22

Hydrocephalus in adults

Answer 22

Cranial bones are fused

• Increased ICP
• Impaired neuron function and damage
• Impaired blood flow=ischaemic damage, CVA
• Midline shift and herniation (coning)

Question 23

Treatment of hydrocephalus

Answer 23

Shunt fluid to other body cavities

Question 24

The blood brain barrier

Answer 24

A protective mechanism that helps provide a stable environment for the brain=controls ISF composition

Question 25

Formation of the blood brain barrier

Answer 25

Formed by astrocytes (glial cells) that encircle capillaries and stimulate the endothelial cells to form tight junctions=least permeable capillaries in the body

Question 26

The blood-brain barrier: Selective barrier-water soluble substance

Answer 26

Must pass through endothelial cells to enter the ISF - Nutrients (e.g. glucose, essential amino acids) and some electrolytes move into ISF by facilitated diffusion - Metabolic wastes, proteins, certain toxins and most drugs are denied entry - Non-essential amino acids and K+ ions are excluded and/or actively pumped out

Question 27

The blood-brain barrier: Selective barrier-Lipid soluble substance

Answer 27

Readily pass through endothelial cells and enter the ISF - O2, CO2, lipid hormones - Alcohol, nicotine anaesthetics

Question 28

The blood-brain barrier is incomplete in the adult in the:

Answer 28

- Vomiting centre of medulla oblongata - Hypothalamus - Monitors chemical composition of the blood e.g.) glucose levels=regulates appetite - Monitors blood temperature

Question 29

The blood-brain barrier is incomplete in the newborn brain:

Answer 29

Sever jaundice can interfere with normal neuronal development (kernicterus)

Question 30

Blood supply to the brain

Answer 30

Right and left internal carotid arteries and the right and left vertebral arteries take blood to the cerebrum

Question 31

Each internal carotid artery branched to form an:

Answer 31

``` -Anterior cerebral artery Supplies anterior/superior cerebrum -Middle cerebral artery Supplies lateral cerebrum -Posterior communicating artery ```

Question 32

The vertebral arteries...

Answer 32

Fuse to form the basilar artery which gives rise to the R. and L. posterior cerebral arteries=supplies posterior cerebrum

Question 33

The cerebral arterial circle (circle of Willis)

Answer 33

- Unites the anterior and posterior blood supplies - Equalises blood pressure - Provides alternate routes for blood to reach the cerebrum if a vessel is occluded (supplying the circle, within the circle) - Provides a constant blood supply to the cerebrum

Question 34

Venous drainage

Answer 34

Most venous blood and CSF drains from the brain into the dural venous sinuses - Dural venous sinuses converge at the back of the skull to form the sigmoid sinus - The sigmoid sinus gives rise to the internal jugular veins

Question 35

Meninges summary

Answer 35

Cover and protect the CNS - Dura mater-tough membrane, includes venous sinuses - Arachnoid mater-space includes blood vessels and CSF - Pia mater-covers neural tissue

Question 36

CSF summary

Answer 36

Buoyancy, shock absorption, nourishment -Produces by choroid plexus in ventricles, composition controlled by ependymal cells, circulates in subarachnoid space, exits via dural venous sinuses

Question 37

Blood brain barrier summary

Answer 37

Controls the composition of the ISF to maintain stable environment -Incomplete in the medulla and hypothalamus

Question 38

Blood supply summary

Answer 38

Internal carotid and vertebral arteries supply much of the brain via the - Cerebral arterial circle: blood reservoir that supplies the cerebrum, equalises pressure and compensates for blockages - Venous blood exits via the dural venous sinuses