Neurovascular coupling and blood brain barrier Flashcards
What can brain scans reveal?
How brain function changes in response to a task, challenge or disease
What does fMRI stand for?
Functional Magnetic Resonance Imaging
What does fMRI detect?
Does not measure brain activity directly
This imaging detects signals associated with changes in cerebral blood flow
What does fMRI rely on?
The coupling between neuronal activation and cerebral blood flow
How does fMRI indirectly measure neural activity?
When neural activity in a region increases, blood flow to that region also increases
How active is the brain?
Most metabolically active of all organs in the body
How much does the brain weigh?
Roughly 2% of total body weight
How much cardiac output does the brain receive?
15%
How much body energy does the brain consume at rest?
20%
What does the brain not have?
Glycogen stores
What does the brain require because of the lack of glycogen stores?
Constant supply of glucose and O2 for ATP metabolism
Why does the brain use so much energy?
Communication of neurons requires a lot of energy
What is the main site of energy consumption?
Synapses
What is energy in the synapses for?
Energy is used to reverse the movement of ions at synapses during neuronal communication
What do synapses rely heavily on?
Local ATP synthesis
What is within each synapse which suggests the synapse needs a lot of energy?
Mitochondria
What is the ATP used to do in the synapse?
Resetting the synapse to its normal state
What is required to maintain synaptic activity?
Constant supply of glucose and oxygen
How are glucose and oxygen delivered to the brain?
Via its blood supply in cerebral circulation
What are the 2 sources the brain receive its blood supply from?
Arising from the dorsal aorta
o Common carotid→ internal carotid arteries
o Subclavian artery→ vertebral arteries
What do the right and left vertebral arteries join to form?
Single basilar artery
What does the basilar artery and two internal carotid arteries form?
Circle of Willis
Where is the Circle of Willis located?
Base of brain
What part is the Circle of Willis?
Arterial ring formed from basilar artery and internal carotid arteries
What does the Circle of Willis give rise to?
The major cerebral arteries
Where do pairs of left and right cerebral arteries arise from?
Circle of Willis
What do pairs of left and right cerebral arteries supply?
All parts of the brain
What happens if one of the main carotid or vertebral arteries are blocked?
The cerebral arteries can receive through blood through Circle of Willis
What is each cerebral hemisphere supplied by?
Three major arteries
What are the three major arteries that supply each cerebral hemisphere?
Anterior Cerebral Artery
Left Middle Cerebral artery
Posterior cerebral artery
Where does stroke usually form?
In the middle cerebral artery
What are symptoms of stroke related to?
Affected area
Where do cerebral arteries branch?
Over the brain structures
Arteries on brain surface–> Penetrating arterioles –> capillary bed
What do cerebral arteries give rise to?
Penetrating arterioles then capillaries
How vascularised is brain tissue?
Highly vascularised
What does functional activation by sensory stimulation lead to?
Regional increase in the glucose metabolism in corresponding cerebral structures
What is the relationship between glucose use in a brain region to the blood flow in that region?
Proportional
What is neurovascular coupling?
Changes in neural activity cause changes in local blood flow
What happens with neuronal activation
Neurotransmitter release
Increase ATP consumption
Increase O2 and glucose consumption
What happens with neurotrasmitter release and increase in O2 and glucose consumption?
Vasoactive chemical agents cause vasodilation
Increased cerebral blood flow
What is neurovascular coupling the basis for?
BOLD signal detected by fMRI
What does fMRI measure?
Scanner measures function-related changes in blood flow
What does fMRI indirectly measure?
Neuronal activity
What cells are responsible for dilation and constriction of arterioles?
Vascular smooth muscle
What are responsible for dilation and constriction of capillaries?
Pericytes
What does the blood brain barrier (BBB) restrict?
Movement of substances into and out of the brain
What does the term BBB refer to?
A complex of cells that separate the brain parenchyma from the luminal contents of the cerebral vasculature
What are the functions of the BBB?
Protects the brain from “foreign substances” in the blood that may injure the brain
Protects the brain from hormones and neurotransmitters released in the rest of the body
Maintains a constant environment for the brain to enable normal neuronal function
What lines the lumen of cerebral vessels?
Endothelial cells
what do cerebral endothelial cells have?
Tight junctions
What do tight junctions in endothelial cells restrict?
Free passage of substances from the blood to the brain
How does glucose enter the brain?
Transport carriers for glucose facilitate its entry into the brain
How does O2 enter the brain?
Diffuses freely from blood to brain
What is the first pathway across the blood-brain barrier?
Transcellular lipophillic pathway
Lipid-soluble agents
What is the second way across the blood brain barrier?
Transport proteins
Glucose, amino acids, nucleosides
What is the third way across the blood brain barrier?
Receptor mediated endocytosis
Insulin and transferrin
What is the last way across the blood brain barrier?
Absorptive endocytosis
Albumin, other plasma proteins
Do all areas if the brain have a BBB?
No
Where is there no BBB?
Structures in the midline of the ventricular system collectively referred to as circumventricular organs (CVOs)
What are some examples of CVOs?
Pituitary gland Median eminence Area postrema Preoptic recess Paraphysis Pineal gland Endothelium choroid plexus
