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
MEDULLA & SPINAL CORD
Vertebral a. and its branches including:
- Posterior inferior cerebellar artery.
- Posterior and anterior spinal aa.
MIDBRAIN
Basilar artery Via:
Posterior cerebral artery
CEREBELLUM
Vertebral a. Via:
- Posterior inferior cerebellar a.
- Anterior inferior cerebellar a.
Basilar a.: Via
Superior cerebellar a.
TELENCEPHALON (CEREBRAL CORTEX)
Middle cerebral a. (Lateral surface)
Anterior cerebral a. (Medial surface, except occipital and temporal lobe )
Posterior cerebral a. (Medial surface occipital and temporal lobe)
TELENCEPHALON (CEREBRAL CORTEX)
Middle cerebral a. (Lateral surface)
Anterior cerebral a. (Medial surface, except occipital and temporal lobe )
Posterior cerebral a. (Medial surface occipital and temporal lobe)
Dura – 2 layers
Periosteal layer – adheres to inner surface of skull. This layer ends at Foramen magnum; not present on
spinal cord
Inner layer Dural border cells – innermost layer loose arrangement provides a potential plane of separation between dura
and arachnoid. Location of subdural hematomas (bleeds).
Periosteal layer
layer of dura that adheres to inner surface of skull.
This layer ends at Foramen Magnum; it is not present on spinal cord.
Inner layer
Dural border cells – innermost layer.
Loose arrangement provides a potential plane of separation between dura and arachnoid.
Location of subdural hematomas (bleeds).
Arachnoid – 2 layers
Outer Layer = barrier cells
Inner Layer = trabeculae in subarachnoid space
Pia mater
Intimately applied to the surface of the brain and spinal cord, following all contours.
Surrounds blood vessels.
DURAL PROJECTIONS
FALX CEREBRI
FALX CEREBELLI
TENTORIUM CEREBELLI
FALX CEREBELLI
Small projection that separates 2 hemispheres of cerebellum
Superior edge fuses with tentorium cerebelli
FALX CEREBRI
Midline projection of dura that separates the 2 cerebral hemispheres.
Sickle shape, with a free lower edge.
Posterior, inferior edge forms a right angle with tentorium cerebelli
TENTORIUM =
TENT
TENTORIUM CEREBELLI
Tentorium cerebelli = tent that separates cerebellum from occipital lobe of cerebral cortex
Rostral edge of tentorium is the free forming “tentorial notch” through which the brainstem passes
Falx cerebri fuses at right angles with tentorium on midline superiorly
Falx cerebelli fuses at right angles with tentorium on midline inferiorly
DURAL SINUSES
Openings between periosteal and meningeal layers of dura and where 2 layers of dura meet.
Represent the major routes by which venous blood is drained from the brain.
Blood filled spaces are called Venous (or Dural) Sinuses
DURAL SINUSES
specifics
SUPERIOR SAGITTAL SINUS – Upper edge falx cerebri (where it attaches to skull)
INFERIOR SAGITTAL SINUS – Lower free edge falx cerebri
STRAIGHT SINUS – At point of fusion between falx cerebri and tentorium cerebelli
TRANSVERSE SINUS – In tentorium cerebelli where it is attached to skull
OCCIPITAL SINUS – Small channel in falx cerebelli along occipital bone
CONFLUENS OF SINUSES – Point where superior sagittal, occipital, and transverse sinuses converge
CAVERNOUS SINUS – Dural enlargement on either side of sella turcica
EPIDURAL HEMATOMAS
MIDDLE MENINGEAL ARTERY
SUBARACHNOID (SUBDURAL)
HEMATOMA
??
VENTRICLES
CHAMBERS IN THE BRAIN THAT PRODUCE AND/OR CONDUCT CSF
By the 3rd week of development, the CNS is a tube closed at both ends. The cavity of the tube becomes the ventricles in the adult.
LATERAL VENTRICLE
Largest ventricle.
Portions are present in all lobules of the cerebral cortex
CHOROID PLEXUS
SECRETES CSF
ARISES FROM TUFTS OF CELLS WITHIN THE WALLS OF THE VENTRICLES
SECRETION OF CSF IS ACTIVE PROCESS REQUIRING ENERGY
CSF
Entire volume of CSF is
turned over 3-4 times/day
Flows through the ventricular system and out into the subarachnoid space.
FLOW OF CSF
Ventricles are internal to the brain thus there must be some way CSF can reach outside of brain to flow in the subarachnoid space. Two openings in 4th ventricle:
FORAMEN OF LUSCHKA
FORAMEN OF MAGENDIE
CSF must be taken up by some mechanism and removed to avoid excess buildup. In areas of dural sinus, specialization of arachnoid:
ARACHNOID GRANULATIONS
ARACHNOID GRANULATIONS
Arachnoid granulation is an outgrowth of arachnoid into the superior sagittal sinus.
Allows CSF to enter venous system.
SHUNTS TO TREAT HYDROCEPHALUS
A ventriculoperitoneal (VP) shunt diverts excess CSF from the brain into the space in the abdomen that surrounds the digestive organs (peritoneal cavity).
A ventriculoatrial (VA) shunt diverts excess CSF from the brain into the right atrium of the heart.
THIRD VENTRICULOSTOMY
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