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BMA1901-Module 4 > Mod4-Obj7: Meninges, Cerebrospinal fluid and the blood brain barrier > Flashcards

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

1
Q

The brain is protected by

A
  • The cranium
  • Meninges
  • Cerebrospinal fluid (CSF)
  • The blood-brain barrier
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2
Q

The meninges

A

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
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3
Q

The meninges: membranes (superficial to deep)

A
  • Dura mater=Top layer
  • Arachnoid mater=middle layer
  • Pia mater=Inner most layer
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4
Q

The meninges: The dura mater

A

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
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5
Q

The meninges: The arachnoid mater

A

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
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6
Q

The meninges: The pia mater

A

Gentle mother-Inner most layer

  • Delicate connective tissue that clings tightly to the brain and closely follows its contours
  • Contains mainly small blood vessels
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7
Q

The meninges sequence

A
  • 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
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8
Q

Meningitis

A

Inflammation of the meninges

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

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9
Q

Typical route of infection-Meningitis

A

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

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10
Q

Symptoms of meningitis

A

Severe headache, neck stiffness, fever

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11
Q

Diagnosis of meningitis

A

CSF sample examined for WBC and microbes

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12
Q

Treatment of meningitis

A

Antibiotics, corticosteroids

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13
Q

Cerebrospinal fluid

A

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
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14
Q

Functions of CSF

A
  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
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15
Q

CSF formation-ventricles

A

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
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16
Q

CSF formation

A

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
17
Q

CSF

A
  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
18
Q

CSF exit

A

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

19
Q

Cerebrospinal fluid production and drainage

A

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

20
Q

Obstruction in CSF

A 
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
21
Q

Hydrocephalus in young children

A

Enlargement of the head as cranial bones are not yet fused

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

22
Q

Hydrocephalus in adults

A

Cranial bones are fused

  • Increased ICP
  • Impaired neuron function and damage
  • Impaired blood flow=ischaemic damage, CVA
  • Midline shift and herniation (coning)
23
Q

Treatment of hydrocephalus

A

Shunt fluid to other body cavities

24
Q

The blood brain barrier

A

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

25
Q

Formation of the blood brain barrier

A

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

26
Q

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

A

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
27
Q

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

A

Readily pass through endothelial cells and enter the ISF

  • O2, CO2, lipid hormones
  • Alcohol, nicotine anaesthetics
28
Q

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

A
  • Vomiting centre of medulla oblongata
  • Hypothalamus
  • Monitors chemical composition of the blood e.g.) glucose levels=regulates appetite
  • Monitors blood temperature
29
Q

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

A

Sever jaundice can interfere with normal neuronal development (kernicterus)

30
Q

Blood supply to the brain

A

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

31
Q

Each internal carotid artery branched to form an:

A 
-Anterior cerebral artery
Supplies anterior/superior cerebrum 
-Middle cerebral artery 
Supplies lateral cerebrum
-Posterior communicating artery
32
Q

The vertebral arteries…

A

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

33
Q

The cerebral arterial circle (circle of Willis)

A
  • 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
34
Q

Venous drainage

A

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
35
Q

Meninges summary

A

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
36
Q

CSF summary

A

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

37
Q

Blood brain barrier summary

A

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

38
Q

Blood supply summary

A

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

BMA1901-Module 4 (7 decks)

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