Scenario 25 Flashcards
What is the incidence of stroke?
114/100,000 75% over 65
What is the mortality of stroke?
64,000 deaths per year 12% of deaths
What are the vascular risk factors for stroke?
High BP, Diabetes, Smoking, high cholesterol
What is left hemiplegia?
Arm in flexion, leg in extension
What should you do if suspected stroke?
CT to see if caused by a clot and can use thrombolytics in under 3 hours
How much of the cardiac output does the brain receive?
17%
What are the 2 main arterial routes to the brain?
ICA (carotid canal into middle cranial fossa adj to optic chasm) and Vertebral arteries (foramen transversaria entering via formamen magnum passing through cavernous sinus)
What does the ICA give rise to?
Anterior and middle cerebral arteries and opthalmic artery
What does the Anterior cerebral artery supply
Medial and superior aspects of the parietal and frontal lobes
What does occlusion of the ACA cause?
Paralysis and sensory defecits to contralateral leg and perineum, mental confusion and sometimes contralateral fact, tongue and upper limb due to IC
What does the MCA supply?
Lateral cerebral cortes, anterior temporal lobes and insular cortices
What does occlusion of MCA cause?
(most common) paralysis of contalateral face and arm and sensory loss, hemianopia of contralateral visual fields
Damage to dominant hemisphere results in aphasia (Broca/ Wernickes) and non-dominant results in contralateral neglect syndrome
Where does the posterior cerebral artery arise?
Intersection of post communicating and basilar
Where does the PCA supply?
Posterior aspect of the brain (occipital lobe) and part of temporal lobe
What does PCA occlusion cause?
Blindness in contralateral visual field, hippocampal memory may be affected but usually temp
What does the vertebrobasiliar system supply?
Brainstep, cerebellum and posterior aspect of cerebral hemispheres
What is the basilar artery formed from?
Union of the two vertebral arteries
What does the basilar artery give rise to?
Splits into posterior cerebral arteries before this giving rise to superior cerebellar arteries, before this several small pontine arteries and before this the anterior inferior cerebellar arteries
What do the vertebral arteries give rise to?
Posterior inferior cerebellar arteries, anterior and posterior spinal arteries
Where do the 2 systems anastamose?
Circle of Willis
What are the advantages of anastamoses?
Provide an alternative route if normal one is occluded
What are the disadvantages of anastamoses?
Can cause aneurysms which can leak or explode causing a sub arachnoid haemmorhage
What does occlusion of vertebral or basilar arteries lead to?
Cerebellar defects, instantly fatal due to coma and loss of resp control, cranial nerve defects, deafness, infarction of ventral pons leads to loss of all voluntary movements except eyes
What is the blood supply to the IC?
Small perforating arteries from circle of willis mostly supplied by ACA and MCA (LENTICULOSTRIATE)
What is the venous drainage of the brain?
Intracranial veins drain into dural venous sinuses then to internal jugular via jugular foramen in post cranial fossa
Where is the superior saggital venous sinus
Down midline
Where is falx cerebri?
Between superior and inferior saggital sinus
Where are left and right transverse sinus?
at the back of the head horizontally
Where is the sigmoid sinus and where does it exit skull?
At the sides of the head a continuation of transverse, exits through jugular foramen
Where does the middle meningeal artery enter the intracranial region?
Foramen spinosum
What does the middle meningeal artery supply?
The bones of the vault
What could a leak from the MMA cause?
Extradural haemmorhage- prolonged
What is a subdural haemmorhage?
Caused by leak of superior cerebral vein, low pressure slow accumulation (between dura and arachnoid) pushes on the brain
What is a sub-arach?
Between arachnoid and pia eg from ruptured aneurysm form curcle of willis very sudden and painful
Intracerebral haemmorhage
Within the brain tissue itself
What is the blood supply to the spinal cord?
Posterior and anterior spinal arteries from vertebras and radicular arteries from segmental spinal arteries
What does the brain consume at rest?
60% of glucose, 20% of oxygen (120g glucose a day)
How do NTs work?
AP arrives at the cell presynaptic cell depolarises and releases vesicles which diffuse across the synapse and cause Na to enter the next cell and K to be released, depolarising the postsynaptic cell.
How is NT removed?
Uptake into astrocytes- powered by ionic gradients (Na/K ATPase) and then glutamate is converted into glutamine (requires another ATP) and glutamine is exported and taken up pre-synaptically, converted back and packed into vesicles (another ATP)
Why does glutamate need to be removed?
Highly active at receptors, depolarises post-synaptic cells
What is neurovascular coupling?
Activity at the synapses leads to increased blood flow to deliver oxygen and glucose
How is glucose used for energy in the brain??
glucose transported from blood into glial cells where its converted into glucose-6-phosphate and then metabolised or stored as glycogen (very small store)
How is glucose metabolised in the presence of oxygen?
glucose gives 2 pyruvate, 2 ATP but uses 2 NAD and the pyruvate feeds into the next step, NAD regenerated elsewhere
How is glucose metabolised in the absence of oxygen?
Pyruvate is converted to lactate and NADH to NAD allowing glycolysis to continue using lactate
What happens in oxidative phosphorylation
In the mitochondrion pyruvate in the presence of oxygen gives CO2 and NADH which feeds into ox phos to give 34 ATP (overall 36ATP)
Without mitochondria how many ATP can be made?
2
What is the leptomeningeal collateral circulation made up of?
The A, M and P cerebral arteries
What happens if the MCA is occluded?
Blood flow initially drops but by 2 minutes the collateral circulation form the ACA takes oevr but cant reach the core of the MCA territory
What perfusion is below survival threshold (core)
What is the perfusion in the penumbra?