Lecture 5 actual lecture... Blood Supply to CNS; Artery & Veins Flashcards
Although the brain represents only 2% of the body weight, it receives _____
Although the brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization
There are _____ of blood circulating in the brain every minute
There are 740 milliliters of blood circulating in the brain every minute
ARTERIAL SUPPLY OF CNS
2 ARTERIES ARISE AT THE BASE OF THE NECK TRAVERSE THE NECK TO REACH THE BRAIN:
VERTEBRAL ARTERY
INTERNAL CAROTID ARTERY
*Remember, both are bilateral.
VERTEBRAL ARTERY
Enters skull through foramen magnum after coursing posteriorly over C1.
20% of blood flow to brain.
ARTERIAL SUPPLY TO:
MEDULLA
PONS
MIDBRAIN
CEREBELLUM
SUPPLIES ANTEROLATERAL MEDULLA, POSTERIOR CEREBELLUM, AND SPINAL CORD
INTERNAL CAROTID ARTERY
Ascends in lateral part of neck to reach base of skull.
Enters skull through carotid canal located just below cavity of middle ear.
Rostral to vertebral artery at the base of the skull.
DIRECT BRANCHES OF VERTEBRAL:
- Posterior Inferior Cerebellar (PICA)
- Posterior Spinal Artery. (USUALLY A BRANCH OF PICA)
- Anterior Spinal Artery. - RIGHT AND LEFT BRANCHES ANASTAMOSE TO FORM SINGLE VESSEL
ANASTOMOSIS
An anastomosis is a connection between two structures. It usually means a connection that is created between tubular structures, such as blood vessels.
An anastomosis (plural anastomoses, Greek for communicating opening) is the reconnection of two streams that previously branched out, such as blood vessels or leaf veins.
aneurysm
An aneurysm is a bulging in the wall of the aorta caused by a weakening of the wall.
Incidence Of Paraplegia Following Repair Of Aortic Aneurysms
The damaged section of the aorta must be surgically removed and replaced with a graft (synthetic tube) which is sewn into place.
To accomplish this, the vessel is clamped above and below the area to be replaced. The goal is to keep this time at less than 20–30 minutes.
Paraplegia from spinal cord ischemia occurs in 5–40% of patients undergoing surgical repair of thoracoabdominal aortic aneurysms (TAA). The injury results from inadequate perfusion to the anterior spinal artery while the blood supply from the descending thoracic aorta is occluded by the cross clamps.
The importance of these anastomotic connections is demonstrated by the relatively high incidence of paraplegia following a repair of an aortic aneurysm. An aneurysm is a bulging of the aorta caused by a weakening of the wall. It is correlated with high blood pressure and prolonged cigarette smoking.
To repair the aneurysm, the damaged section of the aorta is removed and replaced with a synthetic tube that is sewn into place. However, to accomplish this, the vessel must be clamped above and below the area to be replaced. The goal is to keep the time below 20-30 minutes.
Paraplegia (paralysis of the lower limbs) occurs in 5-40% of patients undergoing this surgical repair due to inadequate blood flow to the ventral portion of the spinal cord where motor neurons are located. The connection between the single anterior spinal artery and the radicular branches of the aorta are essential to maintain adequate perfusion of this area.
Paraplegia
a condition in which you are permanently unable to move or feel your legs and the lower half of your body because of injury or illness.
perfusion
In physiology, perfusion is the process of a body delivering blood to a capillary bed in its biological tissue.
BASILAR ARTERY
AT THE LEVEL OF THE ROSTRAL MEDULLA, THE R & L VERTEBRAL AA. ANASTAMOSE TO FORM A SINGLE BASILAR A; SUPPLIES THE PONS AND ROSTRAL CEREBELLUM.
- Anterior Inferior Cerebellar A. (AICA); just caudal to CN VI (ABDUCENS Nerve)
- Pontine Including: Paramedian, Short Circumferential, Long Circumferential
- Superior Cerebellar Artery just caudal to CN III (OCULOMOTOR Nerve)
VASCULAR SUPPLY TO CEREBELLUM
Superior Cerebellar Arteries
Anterior inferior Cerebellar Arteries
Posterior Inferior Cerebellar Artery
POSTERIOR CEREBRAL ARTERY
At pontomidbrain junction, basilar artery divides into R & L POSTERIOR CEREBRAL Artery which supplies midbrain, thalamus, ventral and medial surface of temporal and occipital lobes. Just rostral to CN III.
What you feel when you take your pulse under your jaw.
INTERNAL CAROTID ARTERY
INTERNAL CAROTID ARTERIAL SUPPLY TO:
FOREBRAIN
Supplies medial cortex including motor and sensory cortex, motor and sensory paralysis can occur if occluded.
CIRCLE OF WILLIS
Circle of vessels that loop around optic chiam and tracts, crosses cerebral peduncle and joins at pons-midbrain junction.
Anastamotic connection between vertebral/basilar arterial system and internal carotid arteries allowing for collateral circulation.
Cerebrovascular Disease
Cerebrovascular disease is the most common life threatening neurological event in the U.S.
3rd leading cause of death in the U.S.
Ischemic Stroke (most common)
Hemorrhagic Stroke (more likely to be fatal)
Brain cells begin to die within minutes of being deprived of oxygen.
Ischemic stroke treatment
Give clot busting drug (t-PA) within 3 – 4.5 hours.
Cerebral Arterial Dissection
An arterial dissection is a tear in the lining of an artery.
When such a tear occurs in the carotid or vertebral arteries, the major arteries to the brain, this is called a Cerebral Arterial Dissection.
The flow of blood in between the layers of the torn blood vessel may cause the artery to narrow and even close off entirely. This may affect the blood flow to certain areas of the brain that are supplied by the affected artery, resulting in stroke.
In some cases, the blood causes a bulge in the wall of the artery called a pseudoaneurysm.
Arterial dissection is a leading cause of stroke in young people.
Blood vessels contain multiple layers.
Normally, blood flows through the center of the vessel which is lined by an endothelium.
If there is a tear in the endothelium, blood can work its way behind this layer and it become trapped behind the endothelium. This can cause a narrowing of the blood vessel as it bulges into the lumen.
Likewise, the pressure may cause the vessel to balloon outward resulting in a pseudoaneurysm.
Neural Activity Regulates Blood Flow To The Brain
The rate of blood flow to specific regions of the brain may increase or decrease in a pattern correlated with neural activity.
The rate of blood flow to specific regions of the brain may increase or decrease in a pattern correlated with neural activity. These regional changes in blood flow can be measured using several different techniques.
One of these imaging techniques is positron emission tomography (PET) scanning. It measures glucose utilization and oxygen consumption depending on which isotope is used.
Another technique is the more recently developed functional magnetic resonance (fMRI). This technique measures oxygen differences. It is based on the principal that more active regions of the brain require more oxygen. Different types of sensory or cognitive inputs results in activation of distinct regions of the brain.
PET Scan
Measures glucose utilization and oxygen consumption
fMRI
Measures differences in oxygen in blood
