Unit 9 Flashcards
How does the brain get oxygenated blood?
through the cardiovascular system
The brain
soft
1.4 kg
can’t even support it’s own weight
-> needs support
Where does the brain lie?
the floor of the cranial cavity
What are foramina, and which foramen does the medulla pass through?
holes in cranium allowing cranial nerves and blood vessels to enter cranium
foramen magnum
The meninges
dura mater
arachnoid
pia mater
Where is the subarachnoid space?
between arachnoid and pia mater
filled with CSF
What are the two large folds that extend down from the dura mater occupying major fissures?
falx cerebri -> great longitudinal fissure
tentorium cerebelli -> separates posterior part of cerebral hemispheres from cerebellum
Where does the soft and spongey arachnoid membrane get its appearance from?
arachnoid trabeculae
-> filaments of connective tissue
What is the pia mater attached to and what does it contain?
The surface of the brain and spinal cord, following every convolution
small surface blood vessels of brain and spinal cord
What can head trauma cause?
Can fracture or depress cranium
-> can tear meninges and brain
can also cause unconsciousness, concussions, psychological deficits and post- traumatic epilepsy
What can displacement of the brain due to trauma lead to?
Contusions (bruising)
tearing of white matter
intercerebral haematoma (bleeding)
What is an extradural/ epidural haematoma and how is it caused?
bleeding in extradural/ epidural space (between cranium and dura mater)
tearing of middle meningeal artery
What does an increase of blood flow into the brain due to epidural haematoma result in?
blood occupies more space and compresses brain
-> followed by coma several hours after initial trauma
What can you do against an extradural haematoma?
Neurosurgery to remove intracranial pressure
-> otherwise brain displacement and death
What are subdural haematoma?
bleeding in subdural (between arachnoid and dura mater) space
Which type of haematoma will lead to coma quicker?
epidural haematoma (hours) quicker than subdural haematoma (weeks-months)
Meningitis
inflammation of meningis
can be caused by viruses, bacteria, fungi and protozoa
sypmtoms: headache, vomiting, increased sensitivity to light, stiffness of neck
Which meningitis is potentially more dangerous and why?
Bacterial or fungal
-> can damage cranial nerves and brain
-> can lead to high intracranial pressure and death
What is cerebrospinal fluid and how does it aid the brain?
Shock-absorber against trauma
brain floats in it
-> decreases weight drastically
=> 1.4kg -> 80g
What produces CSF and when is it reproduced?
Choroid plexus of all four ventricles
-> produced continuously
-> half of CSF replaced every 3 hours
How can the continuous reproduction of CSF be dangerous?
When the old CSF can’t be reabsorbed
-> increases pressure
-> Reasons: e.g. Tumor, born with an abnormally small cerebral aqueduct
Obstructive hydrocephalus
pressure causing walls of ventricles to expand
if untreated
-> blood vessels occluded
-> permanent, maybe fatal brain damage
How can hydrocephalus be treated?
driling hole into cranium and inserting shunt tube in a ventricle
tube placed under skin and connected to pressure relief valve in abdomen
-> allows CSF to drain into abdomen if pressure becomes obsessive
The production of CSF
Produced by lateral ventricles
-> flows into third ventricle
-> more CSF produced
-> flows through cerebral aqueduct to fourth ventricle
-> more CSF produced
-> leaves through small opening into subarachnoid space
What reabsorbs CSF in the subarachnoid space?
arachnoid granulations (arachnoid villi)
What exactly do arachnoid villi do?
deposit CSF in venous sinuses
What are dural venous sinuses?
blood vessels within dura mater
-> drain contents into veins which take venous blood away from brain
Where do two importan sinuses lie?
superior sagittal sinus within fold of falx cerebri
sinus within tentorium cerebelli
Which three veins drain venous blood from the brain?
dural venous sinuses
deep veins
superficial veins
Deep veins
drain blood from internal structures of forebrain
superficial veins
within subarachnoid space
drain venous blood from surface of cerebral hemispheres
Where do deep and superficial veins drain into?
dural venous sinuses
How much blood flow from the heart does the brain approximately get, what happens if that blood flow gets interrupted and why does that effect occur?
~20%
brain can only store small amount of energy which it can’t extract without oxygen
- 1s disruption: most dissolved oxygen in cells used up
- 6s: unconsciousness
- few minutes: permanent damage
=> brain needs constant supply
What are the two main arteries delivering oxygenated blood to the brain?
internal cartoid artery
vertebral artery
What are the two main types of stroke/ cerebrovascular accidents?
haemorrhagic: caused by bleeding because of malformed or weakened blood vessel (e.g. through high blood pressure)
ischemic: caused by restricted blood flow due to blocked blood vessels
What causes blockages (ischemic stroke)?
trombus (blood clots)
embolus (material/ debris floating around vascular system)
What does restricted blood flow result in?
infarction
-> death of brain tissue
How was the blood-brain-barrier discovered?
by Ehrlich
blue dye injected into animals bloodstream
-> all tissues except CNS turned blue
blue dye injected into brain ventricles
-> only CNS turned blue
Capillaries
in the body: small gaps which allow most substances to pass through
in the brain: substances must be actively transported by transporter proteins
Why do we need a blood-brain-barrier?
neurones require delicate balance between substances within neurones and extracellular fluid
-> barrier assures that balance isn’t disrupted
Is the BBB equally strong in all areas?
weaker in area postrema (controls vomiting)
-> allows neurones to detect toxins
-> initiates vomiting
-> additional barrier around area postrema to prevent toxins from spreading
