Blood Brain barrier and CSF Flashcards
what are the 3 cerebral meninges
- Dura
- Arachnoid
- Pia
where is the subarachnoid space and what cells does it consist of
Subarachnoid space is underneath the arachnoid, constsist of trabecular cells
describe the dura
- Dura is adjacent to skull and attached to skull in places.
- It has two layers= Periosteal and meningeal,
- Contains collagen, thick and strong.
describe the arachnoid
- presses against inner surface of dura
- Supports meshwork of blood vessels
- Has outer compact layer of ‘barrier’ cells and inner ‘trabecular’ meshwork
describe the Pia
Pia is thin membrane tightly attached to basement lamina of brain
where are arteries in the brain found
- There are veins within the inner layers of the dura that cross between the dura and arachnoid
- Many more blood vessels are found in the subarachnoid space which is filled with CSF
what are the 3 types of cerebral haemorrhage
epidural haemorrhage
subdural haemorrhage
subarachnoid haemorrhage
describe an epidural haemorrhage
- outside the dura
- there are arteries that are in the bone such as the middle meningeal artery, there is a bleed as the artery is to the bone therefore it cannot contract therefore if it bleeds inwards it creates arterial pressure forming between the dura and bone
- This tears the dura away from the bone and the blood and arterial pressure push on the dura and compress the brain
describe a subdural haemorrhage
- formed one elderly people where the brain shrinks
- the brain slides as there is a sheer force between the brain
- There is a slow leak of blood that pushes the arachnoid away from the dura
- Spreads widely over the brain
- the venous blood is from bridging veins
describe a subarachnoid haemorrhage
- Bleeding into arachnoid space (between pia and arachnoid).
- Subarachnoid haemorrhage usually arterial
- similar cause and symptoms to an intracranial haemorrhage
what are the symptoms of an epidural haemorrhage
- There may be no symptoms at first then severe headache as haematoma compresses the brain
- If you do nothing it can be fatal
what are the symptoms of a subdural haemorrhage
Venous bleed thus slower: signs and symptoms (confusion, headache, vomiting etc) may show up in minutes, but can be delayed as much as 2 weeks.
what is more serious a subdural haemorrhage or an epidural haemorrhage
- epidural haemorrhage as a subdural haemorrhage is only venous pressure
what can be a cause of subarachnoid haemorrhage
often from ruptured arterial aneurysm; a form of stroke
what are the symptoms of a subarachnoid haemorrhage
sudden severe headache ‘thunderclap headache’
what divides the two hemispheres
The dura extends down between the hemispheres to form a sheet called the falx. It runs antero-posteriorly, dividing the two hemispheres
what happens to the Falx at the occipital lobe
- At the occipital pole the falx makes a ‘t-junction’ with a second sheet of dura that lies between the cerebrum and cerebellum, and forms the the tentorium cerebelli.
what does the tentiorium cerebelli do
- it separates the cerebrum from the occipital part of the brain and the rest of the brain n
what is the gap in the tentiorium and what does it allow to happen
There is a gap between the middle of the tentorium for the brainstem to go form, this is called the tentorium inscia
what are the tentoria
- The tentoria are a pair of approximately transverse sheets of dura that extend laterally below the base of the occipital cerebrum
- They divide the cerebrum above from the cerebellum below
what do the ventricles contain
- These are spaces within the brain that contain CSF
what are the ventricles in the Brain
- There are two lateral ventricles, a third and fourth ventricle
How do the ventricles all link to each other
- Lateral ventricle penetrates into the frontal lobe with the anterior horn, then it goes all the way back into the posterior horn then it comes forwards and forms the inferior horn of the lateral ventricle
- The lateral ventricle communicates diagonally with the third ventricle throught he interventricular foramina
- The cerebral aqueduct stems from the third ventricle and passes through the midbrain and then connects to the 4th ventricle
what makes up the lateral wall of the lateral ventricle
basal ganglia
what makes up the lateral wall of the third ventricle
thalamus
describe the structure of the lateral ventricle
- has an anterior horn
- has an posterior horn
- has an inferior horn
what is the 4th ventricle between
brainstem and cerebellum
what is the CSF formed by
- Formed by the choroid plexus
what is the choroid plexus
- It is a meshwork of capillaries that are covered by ependymal cells that protrude into the ventricles of the brain
where is the choroid plexus
- There is choroid plexus in all the ventricles, but the majority is in the lateral ventricles
what Iines the ventricles
- Lining the ventricle there is ependymal cells
where is the most of the cerebrospinal fluid produced
most of the cerebrospinal fluid is produced in the lateral ventricle
how does the choroid plexus filter and make CSF
- It is an ultrafiltrate of plasma and should have little protein in it therefore so you don’t have a large amount of protein in the CSF
- blood passes through fenestrations into the subependymal layer
- gaps between ependymal cells regulate flow to approximately 500ml/day
describe a characteristic of the CSF
- it is pulsatile in phase with the heart rate
how many plasma proteins does the CSF have in It
Healthy CSF contains approximately 0.3-1.0 % plasma proteins about 1/100 of the concentration in plasma.
describe the buffering changes in CSF
Without proteins it is not pH buffered in the same way as blood: this is why small changes in paCO2 in blood cause appreciable changes in csf pH
how much CSF in the Brian
- The brain holds from 135-150 ml csf at any one time
- it drains into veins primarily arachnoid granulations in the superior sagittal sinus
how much glucose is in the CSF
CSF contains about 60% of the glucose concentration of plasma
what is the pressure of the CSF
- CSF pressure ranges from 4.4 - 7.3 mmHg (0.6-0.9 kPa) - most variations due to coughing or internal compression of jugular veins in the neck.
how is the CSF immune system controlled
CSF normally contains no blood cells (in particular no T or B lymphocytes). Its immune system is different to that of the body, controlled by microglia.
describe CSF flow int he ventricles and into the subarachnoid space
- CSF flows from the lateral ventricle to third ventricle to fourth ventricle to where it flows out of the median aperture into the subarachnoid space.
- From here it flows upward over the surface of the brain to the superior sagittal sinus.
- Here it is absorbed in the arachnoid granulations and joins the venous blood .
what are cisterns of CSF
- this is when at certain points the brain is convoluted and there are cisterns of CSF where the arachnoid is at some distance from the Pia
what are examples of cisterns in the CSF
- cisterna magna
- the superior (cerebellar) cistern
- the interpeduncular cisterns,
what do arachnoid granulation do
- Arachnoid granulations penetrate the dura at the top of the brain and enable cerebrospinal fluid to drain into the superior sagittal sinus
- this then drains into the Confluence of sinuses at the rear of the skull.
- There is a low pressure here
What is hydrocephalus
Is accumulation of cerebrospinal fluid (CSF) in the ventricular system
what causes hydrocephalus
- the aquaduct is blocked
- there is a problem with drainage throught he cisterna magna
- these both mean there is an obstruction of normal CSF circulation
describe hydrocephalus
- Therefore in the fetal brain the pressure builds up as the CSF is continousally being produced and is not being drained away
- Therefore the fetal brain can get squahed and as the ventricles enalgre you have no cortex and large ventricles
how do you treat hydrocephalus
Repaired by shunt (tube inserted in third ventricle leading to subarachnoid space) Prognosis good if done early.
how do you detect hydrocephalus
- Can detect it as light will pass through
what are most brain tumours
- Gliomas
why are most brain tumours Gliomas
- This is because neurons cannot divide (undergo mitosis).
- . Most brain tumours are astrocytomas -undergo mitosis
what is epilepsy caused by
often caused by a malfunction of the glial cells in a region where an infract or other neuronal ‘insult’ (contusion, impact, infection) has occured
normal working of nerve cells requires….
glial cells
myelination of neurones requires…
glial cells
what are the two main types of glial cells
astrocytes and oligodendrocytes
what is MS caused by
autoimmune attack on the olgiodendrocytes
describe what oligodendoryctes do
- Oligodendrocytes produce myelin for intracerebral axons.
- Unlike Schwann cells in the peripheral nerves, one oligodendrocyte may provide the myelin for several adjacent axons.
- Surface antigens on oligodendrocytes are different to those on Schwann cells.
what do ependymal cells do
- Ependymal cells line the walls of the ventricles
- are involved in transport of materials in and out of the CSF
what to microglia cells do
Microglia cells act like macrophages; they phagocytose and remove cellular debris and have a role in immune function in the brain
what do astrocytes do
- They maintain local pH and glucose in the correct range, and remove excess neurotransmitters, metabolites etc. Astrocytes vary in form between grey matter (protoplasmic astrocytes) and white matter (fibrous astrocytes).
- Astrocytes secrete growth factors vital to the support of some neurons. In disease processes, astrocytes may secrete cytokines, which regulate the function of immune cells invading CNS tissue.
- If injury to the CNS results in cell loss, the space created by the breakdown of debris is filled by proliferation and/or hypertrophy of astrocytes, resulting in the formation of an astrocytic scar.
- they can release vitamin C and therefore act as antioxidant
- in particular they can suck up glutmate to make sure that the synaptic transmission is not adversely affected
what do astrocytes do
- They maintain local pH and glucose in the correct range, and remove excess neurotransmitters, metabolites etc. Astrocytes vary in form between grey matter (protoplasmic astrocytes) and white matter (fibrous astrocytes).
- Astrocytes secrete growth factors vital to the support of some neurons. In disease processes, astrocytes may secrete cytokines, which regulate the function of immune cells invading CNS tissue.
- If injury to the CNS results in cell loss, the space created by the breakdown of debris is filled by proliferation and/or hypertrophy of astrocytes, resulting in the formation of an astrocytic scar.
- help form the blood brain barrier
- they can release vitamin C and therefore act as antioxidant
- in particular they can suck up glutmate to make sure that the synaptic transmission is not adversely affected
what do astrocytes end in
Many of the processes of astrocytes end in expansions called end feet
what is covered by astrocyte end feet
Most of the free surface of neuronal dendrites and cell bodies, as well as some axonal surfaces
what is the glia limitans
- The outer surface of the brain, where it meets the inner surface of the pia is covered with a coating of joined end feet called the glia limitans
- Similarly, every blood vessel in the CNS is jacketed by a layer of astrocyte end feet that separate it from the neural tissue
what do astrocyte end feet do
- they separate every blood vessel from neural tissue
- They may secrete material onto the endothelial cells.
- overal function is unclear
what does the pericyte do
– contains actin and myosin – acts as a contractile cell and allows the cerebeal capailary to be contracted
what makes up the blood brain barrier
- tight junctions
- astrocyte end feet
describe the tight junctions in the blood brain barrier
Between the endothelial cells lining cerebral capillaries there are tight junctions that prevent proteins leaving the blood
what do tight junctions prevent from entering the blood brain barrier
The tight junctions between endothelium almost completely prevent macromolecules (eg proteins) from entering or leaving the CNS.
how can molecules enter the brain through the blood brain barrier
- Some molecules do pass from the blood into the brain extracellular space- these molecules have a special transport mechanism.
- For example, amino acids have three specific transport systems designed for acidic, neutral, and basic amino acid and D-Glucose also has a specific transporter.
- However, many lipid-soluble molecules can cross the blood-brain barrier unaided
what drugs can quickly cross the blood brain barrier
- Opiates such as diacetylmorpine (heroin) are lipid soluble and so can cross the bbb rapidly after I.v. injection. This increases their effect on the brain.
- The same goes for ‘crack’ cocaine
when does the blood brain barrier break down
- the blood-brain barrier breaks down due to inflammation in certain pathological conditions.
- This can be useful. For example, in meningitis the meningeal inflammation breaks down the bbb and this enables penicillin to penetrate the brain tissue
what is the problem with the blood brain barrier
most antibiotics are polar molecules soluble in water, it normally prevents them from reaching the brain
- therefore treating CNS infection is hard
