BIOMED 1 Flashcards
What 2 things does blood carry to the brain?
Oxygen
Glucose
What is oxygen in the brain crucial for?
Celllar respiration in neurons (mainly aerobic in mitochondria)
What is low oxygen in tissues called?
Hypoxia
What is complete loss of oxygen in tissues called?
Anoxia
What happens if the brain is deprived of oxygen?
ATP depletion in cells
-> loss of function (eg: ATPase pump)
How long does it take for irreversible brain damage to occur in hypoxia vs anoxia?
Hypoxia= 4-6min
Anoxia= 2-3min
What is glucose in the brain crucial for?
Making ATP
but… brain can use other substances (eg: ketones, a breakdown product of fat) in ST
What are the arteries supplying the brain with blood?
Cerebral arteries
In relation to SLT, what happens if blood supply to the brain is disrupted?
Can starve important areas of blood…
- Broca’s area
- Wernicke’s area
- motor/sensory regions (articulation/oral motor control)
What are the 5 main upper body arteries?
What are the 4 main blood vessels to head and neck?
Common carotid arteries
- external carotid arteries
- internal carotid arteries
Vertebral arteries
Where do the common carotid arteries branch into external/internal carotid arteries?
Carotid bifurfaction
What do the external carotid arteries do?
Several branches deliver oxygenated blood to external tissues of the head
What do the internal carotid arteries do?
Delivers oxygenated blood to anterior brain
In the brain, what do the internal carotid arteries branch into?
The cerebral arteries
- Middle cerebral arteries (MCA), biggest
- Anterior cerebral arteries (ACA), smaller
What do the middle cerebral arteries do?
Provide blood mainly to lateral regions of brain
Which specific areas of the brain do the middle cerebral arteries bring blood to?
Most of motor and somatosensory cortex (not lower limbs, as at top of homunculus)
Auditory cortex
Broca + Wernicke’s areas
What do the anterior cerebral arteries do?
Provide blood mainly to medial regions of brain
Which specific areas of the brain do the anterior cerebral arteries bring blood to?
1cm strip of most medial regions at edge of each hemisphere (frontal + parietal lobes’ medial surface)
What do the vertebral arteries do?
Deliver oxygenated blood to posterior brain + cerebellum + brainstem
Where do the vertebral arteries pass through to form?
Foramen magnum (either side of medulla)
Merges to form basilar artery (vertebral-basilar arterial system)
Then divides to form L/R posterior cerebral arteries
Which specific areas of the brain do the vertebral arteries bring blood to?
Entire occipital lobe (incl. visual cortex)
Inferior + medial surfaces of temporal lobe
What are the 2 communicating arteries?
Posterior communicating artery
Anterior communicating artery
What does the posterior communicating artery connect?
Connects posterior cerebral artery (PCA) with main internal carotid as it enters the brain
note: red arrow
What does the anterior communicating artery connect?
Connects the 2 anterior cerebral arteries (ACA)
note: blue arrow
What is the Circle of Willis?
The communicating arteries connect blood flow between anterior blood supply and posterior blood supply
What are 2 disadvantages of the Circle of Willis?
May not be able to provide enough blood to
compensate for large artery blockage eg: basilar artery, carotid artery (communicating
arteries are very narrow)
May be incomplete in 50-90% of people
What are the perforating arteries?
Small arteries that branch off cerebral arteries
Supplies deep tissues: thalamus, internal capsule, basal ganglia
What is a problem with the perforating arteries?
Narrow- prone to cerebrovascular accident (CVA), can become blocked/damage, can cause stroke
Is the brain in direct contact with the skull bones (cranium)?
No- is covered by 3 layers of membrane: meninges
What do the meninges do?
Cover and protect the brain + spinal cord
What are the 3 main layers of the meninges?
Dura mater (orange)
Arachnoid mater (white)
Pia mater (red)
Describe the dura mater
Very thick, fibrous, protective layer lining the cranial bones
2 layers closely adherent to each other
Why does the dura mater have 2 layers?
To tightly wrap around brain so no gaps for it to move around
What is the space directly beneath the arachnoid mater called?
Subarachnoid space
CSF circulates between the arachnoid mater and pia mater in this space
What are the fibrous structures that attach the arachnoid mater to the pia mater?
Mainly strong, flexible collagen fibres
Describe the pia mater
Thin layer in close contact with brain
Connective tissue, tough, but thin
Closely follows contours of most sulci and gyri
Vascularised- blood vessels branch and go deep into brain tissue to supply brain with blood
On which layer of the meninges do the cerebral arteries start?
Starts by running on top of pia mater in subarachnoid space
What are 2 functions of the dural folds?
Provides space for drainage of venous blood (venous sinuses)
Creates folds that separate and encase regions of the brain
What are the names of the 2 main dural folds that separate and encase brain regions?
Falx cerebri
Tentorium cerebelli
What does the falx cerebri do (dural fold)?
Vertical
Between the cerebral hemispheres
Stabilises brain during sudden movement L/R
What does the tentorium cerebelli do?
Horizontal
Forms roof over cerebellum, separating it from occipital + temporal lobes
Stabilises brain when head moved forward/backward
Where does the cerebrospinal fluid (CSF) move?
Continually moves around the brain + spinal cord
What are the 4 functions of the cerebrospinal fluid (CSF)?
Cushions brain + spinal cord (shock absorber)
Gives buoyancy to brain (lowers force brain exerts on tissue during mechanical injury)
Nutrient exchange + removal of waste products from the brain
Contains dissolved CO2- high CO2 detected by medulla (will increase ventilation rate to clear CO2)
Where is CSF made?
Ventricles of the brain (spaces/chambers) by tissue called choroid plexus, by ependymal cells in CNS
How many ventricles are there in the brain?
4
Right + left lateral ventricles
Third ventricle
Fourth central
What is the volume of CSF humans have?
120-150ml
How fast is CSF produced and replaced?
Produced slowly
Replaced approx 6 times/day
What does the blood-brain barrier do?
Very tightly regulates molecule transport in/out of CNS
Prevents blood cells + plasma components + pathogens from entering brain
How are capillaries in the blood-brain barrier specially adapted?
Tight junctions prevent water-soluble agents from crossing into cerebral tissues
- small molecules (eg: glucose, amino acids, ions) cross with special transporter protein
Surrounded by astrocytes as partly effective barrier (second line of defence, alongside tunica intima with endothelial cells)
Which drugs can pass through the blood brain barrier, and which can’t?
Lipophilic drugs can dissolve through phospholipid bilayer of endothelial cells and into brain
Water soluble drugs can’t pass into brain as no receptor transport proteins
