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What are the origins of the left and right common carotids?
Left side is the aortic arch, right side is the brachiocephalic artery.
Once the internal carotid passes through the neck, what happens?
It heads into the cavernous sinus and splits off to become the opthalmic artery, coursing along the optic nerve, through the orbit, and supplying the retina with blood.
What happens to the internal carotid after the opthalmic artery branching?
It traverses superiorly and splits off into two other branches: posterior communicating artery and anterior choroidal artery.
What does the posterior communicating artery do?
It usually connects the internal carotid to the posterior cerebral artery.
Where else can the anterior choroidal artery branch off from?
The middle cerebral artery.
What is the last substantial bifurcation of the internal carotid, after the ophthalmic artery and the posterior communicating artery?
The anterior cerebral artery and the middle cerebral artery.
How much blood flows through carotid arteries per minute?
How much blood flows through the vertebral-basilar system per minute?
General description of what is supplied by the internal carotid and its branches.
anterior 2/3 of the cerebral hemisphere including its deep white matter and the basal ganglia.
Part of brain supplied by vertebral-basilar arteries.
posterior and medial regions of the hemispheres not supplied by internal carotid, most of the diencephalon, the brainstem, cerebellum, and cervical spinal cord.
Connecting carotid and vertebral-basilar circulations:
circle of Willis. However, these connections usually cannot carry enough blood flow to maintain adequate cerebral circulation if either a carotid or a vertebral arterery is suddenly blocked. This is because in most cases the connecting vessels have small diameters, and pressure differences between the two circulations are usually too small to drive much blood flow through them.
Most frequent sites for atheromatous plaques to form in carotid system.
internal carotid artery at its origin from the common carotid, int he stem of the MCA or its bifurcation into superior and inferior divisions, and in the ACA as it curves backwards over the corpus callosum.
Lenticulostriate vessels are end arteries so have very little collateral blood supply. They are small arteries are very susceptible to hypertension. Lenticulostriate vessels can rupture or get blocked.
Consequences of a hemorrhage in lenticulostriate vessels.
hemorrhage may remain localized to the putamen (and caudate), may involve neighboring structures like the internal capsule and other more distant white matter of the hemisphere, or may even rupture into the ventricular system
Occlusion of one of the penetrating arteries going to the brain's deep regions: putamen-37%, thalamus -14% and caudate -10%.
MCA, once in the Sylvian fissure:
the MCA stem divides into two or, in a small number of cases, three main cortical branches that supply almost the entire lateral surface of the brain as well as the insula.
Key functional areas supplied by superior branches of MCA:
Primary motor cortex for face and arm, and axons originating in the leg as well as face and arm areas that are headed for the internal capsule as part of the corticobulbar or corticospinal tracts. Broca's area and other related gray and white matter important for language expression--in the language-dominant (usually left) hemisphere. Frontal eye fields (important for 'looking at' eye movements to the opposite side). Primary somatosensory cortex for face and arm. Parts of lateral frontal and parietal lobes important for 3-D visuospatial perceptions of one's own body and of the outside world, and for ability to interpret and express emotions--in the nondominant (usually right) hemisphere
Key functional areas supplied by inferior branches of MCA:
Wernicke's and other related areas important for language comprehension in the language-dominant (usually left) hemisphere. Parts of the posterior parietal lobe important for 3-D visuospatial perceptions of one's own body and of the outside world, and for the ability to interpret emotions--in the nondominant (usually right) hemisphere. Optic radiations, particularly fibers that represent information from the contralateral superior quadrants and loop forward into the temporal lobe (they are located anterior and lateral to the temporal horn of the lateral ventricle) as they travel from the lateral geniculate body to the striate cortex, located in the occipital lobe.
Reasons why emboli are less likely to block the vertebral-basilar system:
Takes off from the subclavian at a sharp angle. Has a much smaller diameter than the subclavian. Handles 20% of total cerebral blood flow.
What supplies the upper cervical cord?
A single vessel that is a fusion of posterior spinal arteries and two anterior spinal arteries. There is a lot of variability in this and arterial supplies to the thoracic and abdominal aortas.
What supplies the brainstem and the cerebellum?
vertebral and basilar arteries. There is a lot of variability in size and position of arteries to occlusions result in variable clinical syndromes.
What is the distribution patter of brainstem arteries?
- Medial parts of the brainstem as far dorsal as the ventricle are supplied by long, slender penetrating branches called the paramedian branches. Dorsolateral parts of the brainstem are supplied by direct circumferential branches of the vertebral or basilar arteries, or by branches of one of the major 'cerebellar' vessels as they curve around the brainstem on their way to the part of the cerebellum they supply.
- What regions are at high risk due to hypertension?
- Paramedian vessels branching off the vertebral-basilar arteries, particularly in the pons. Large pontine hemorrhages classically involve the corticospinal tracts and reticular formation bilaterally. Pontine lacunar infarcts may also damage the corticospinal tracts. Also the lenticulostriate branches of the MCA stem, branching off at right angles and having much smaller diameter than the MCA. Occlusion of these vessels leads to stereotyped stroke syndromes.
- What three arteries together form the basilar artery?
- two vertebral arteries and a midline anterior spinal artery.
What are the three major vessels that supply the cerebellum?
Posterior inferior, anterior inferior, and superior vessels.
What happens if there is a hypertensive hemorrhage of the cereballar vessels?
Bleeding near the dentate nucleus can produce deficits related to the cerebellum such as postural instability or limb ataxia. It may also affect brainstem function by compression or by rupture into the fourth ventricle.
What functional areas are supplied by the vertebral-basilar branches?
Rostral midbrain, mid-pons, caudal pons, rostral medulla.
Name the medial structures of the rostral midbrain.
Pyramidal tracts (PT) in cerebral peduncle, Superior cerebellar peduncle (SCP), Oculomotor nucleus/ 3rd nerve, Medial longitudinal fasciculus (MLF), Reticular formation (RF)
Name the medial and dorsolateral structures of the mid-pons.
- medial: Medial longitudinal fasciculus (MLF), Reticular formation (RF), Pyramidal tracts (PT); dorsolateral: Middle cerebellar peduncle (MCP), Trigeminal sensory and motor nuclei/5th nerve
- Name the medial structures of the caudal pons.
- Abducens nerve/ 6th nerve, Motor fibers of 7th nerve, PPRF-lateral gaze center, Pyramidal tracts (PT)
Name the dorsolateral structures of the caudal pons.
Facial motor nucleus/7th nerve, Middle cerebellar peduncle (MCP), Descending tract/nucleus of 5th nerve, Spinothalamic tract(ST) , Vestibular (VN) and Cochlear nuclei/8th nerve.
Name the medial structures of the rostral medulla.
Hypoglossal nucleus/12th nerve, Pyramidal tracts, Medial lemniscus
Name the dorsolateral structures of the rostral medulla
Nucleus ambiguus, Exiting 9th and 10th nerves, Descending tract/ nucleus of 5th nerve, Spinothalamic tract(ST) , Vestibular nuclei (VN), Inferior cerebellar peduncle (ICP)
Describe coursing of PCA.
passes around the cerebral peduncles, series of branches to the midbrain; bunch of long, slender arteries that supply hypothalamus and thalamus.
What are the most likely places for hypertensive intracerebral hemorrhage?
Basal ganglia and internal capsule, then the thalamus, leading to lacunar infarcts.
What do cortical branches of PCA supply?
The cortical branches of PCA supply the posterior medial parietal lobe and the splenium of the corpus callosum, inferior and medial part of the temporal lobe including the hippocampal formation, and the medial and inferior surfaces of the occipital lobe.
Penetrating branches of PCA participated in supplying the following key functional areas:
Diencephalon including thalamus, subthalamic nucleus, and hypothalamus. Midbrain including cerebral peduncle, third nerve and nucleus, red nucleus, and its connections, superior cerebellar peduncle, reticular formation.
Cortical branches of PCA participate in supplying the following key functional areas:
Posterior branches to the parietal and occipital lobe: Optic radiations and striate cortex (the primary visual cortex may be entirely supplied by PCA, or the tip of the occipital lobe where the fovea is mapped may be located in the border zone shared by PCA and MCA); Splenium of the corpus callosum (these crossing fibers participate in the transfer of visual information to the language-dominant hemisphere). Anterior branches to the medial temporal lobe: Hippocampal formation and the posterior fornix (these structures are critical for laying down new declarative memories.
What is auto regulation?
It is the means by which cerebral blood flow remains constant. Blood vessels contract and dilate in order to maintain the same flow. As pressure fluctuates up and down, the vessels respond to keep flow the same. Increases in CO2 leads to vessel dilation and increase in flow.
What is anastomosis?
Reconnection of two streams that previously branched out.
What are MCA-fed regions that do not have anastomoses?
Lenticulostriate branches that supply the basal ganglia and internal capsule, penetrating branches from vessels on the brain surface that supply deep white matter.
Common and important anastomoses occurring between:
External carotid and internal carotid via branches of the ophthalamic artery. The major intracranial vessels via the circle of Willis (for example one carotid might supply parts of the contralateral hemisphere by connections through the anterior cerebral and anterior communicating vessels). Muscular branches of cervical arteries and the extracranial vertebral or external carotid arteries. Small cortical branches of ACA, MCA, and PCA, or branches of the major cerebellar arteries
Describe the general coursing of the main cerebral arteries in the brain.
The MCA, ACA, and PCA reaching the cortex, then traverse perpendicular as long arteries and arterioles passing through gray matter to white matter at a depth of 3-4 cm. The various networks usually do not interconnect
How effective are anastomoses to take up flow from a blocked artery?
Not very. They may be able to supply the border zone and reduce the size of an infarction but if the systemic blood pressure is impacted too greatly, the border zones are more likely to experience damage because of how far away they are from most other vasculature.
ACA-MCA border zone may include these key functional areas:
- Hip, shoulder or less usually arm region of primary motor or somatosensory cortex;
- Areas related to language production - in the dominant hemisphere. Frontal eye fields. Frontal lobe motor planning area.
ACA/MCA-PCA border zone may include these key functional areas:
Visual radiations; Foveal region of the striate cortex in some people (in others it may be in PCA territory); Inferior temporal lobe cortex important for visual recognition; regions related to language comprehension, word finding, and possibly reading - in the dominant hemisphere; Regions of parietal lobe important for visuospatial perceptions - in the non dominant hemisphere.
Why are cerebral veins minimally discussed with respect to stroke?
There are a lot of anastomoses; a blockage reduces arterial flow that in turn produces arterial ischemia and infarction.
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