Download ANPS 019 Beneyto-Santonja 11-26

ANPS 019 Beneyto-Santonja 11/26/12
Blood Supply & CSF
Two sets of arteries supply the brain
 2 Internal Carotid Arteries
o 1 for the left hemisphere & 1 for the right hemisphere
 2 Vertebral arteries join to form 1 basilar artery
 Jugular vein returns blood to heart
 Arteries  take oxygenated, high nutrient blood away from the heart
 Veins  return low oxygen, low nutrient blood to the heart
Anterior Circulation  From Internal Carotid Artery
Posterior Circulation  From Vertebral- Basilar Arteries
Branches off the vertebral and basilar arteries supply the brainstem, cerebellum and spinal cord.
Three main arteries supply the Cerebrum and Diencephalon
 Anterior Cerebral Artery  Trunk & Lower Extremity
 Middle Cerebral Artery (largest vascular territory)  upper extremity & face, speech,
auditory
 Posterior Cerebral Artery  occipital lobe (vision), inferior temporal lobe (face
recognition)
Circle of Willis
 Connects the anterior & posterior circulation allows collateral flow between the 2
hemispheres
 The only problem is the territory of the Middle Cerebral Artery doesn’t have collateral
flow!
How do you know if someone’s having a stroke?  Think F.A.S.T.
 Check their FACE  Has their mouth drooped?
 Can they lift both ARMS?
 Is their SPEECH slurred? Do they understand you?
 TIME is critical. If you see any of these signs, call 911 immediately.
Types of Stroke  insufficient blood supply to the brain
 Thrombotic “clot”
 Hemorrhagic “bleeding in the brain”
Aneurysms
 Microaneurysms
o Develop in small arteries
o Due to hypertension
o Most common cause of hemorrhage
o Common cause of vascular dementia
 Berry
o Congenital, not related of hypertension
o Rupture is the most common cause of subarachnoid hemorrhage
o 90% are found in the circle of Willis
Subarachnoid Hemorrhage
 Sudden excruciating headache: “The worst headache I’ve ever had in my life”
 Most often caused by aneurysm rupture in Circle of Willis vessels
 Lumbar puncture has bloody appearance
Ventricles and Cerebrospinal Fluid
 Ventricles – spaces inside brain filled with cerebrospinal fluid (CSF)
 CSF – delivers nutrients to and removes waste from the brain
 The Brain floats in Cerebrospinal Fluid (CSF)
Cranial Meninges
 Meninges have 3 Layers:
o Dura mater= outermost, toughest, provides physical support to brain/vessels
o Arachnoid mater= middle, blood vessels in CSF-filled subarachnoid space
o Pia Mater= innermost, single cell layer against brain
Dural Septa divide up the brain, help support the weight of the cerebrum
 Falx cerebri
o Separates the 2 cerebral hemispheres
o Protects brain from lateral movements
 Tentorium cerebellum
o Separate cerebellum and cerebrum
o Protects brain from up/down movement
How is blood turned into CSF?
 CSF is a clear, ultra low protein filtrate from plasma
 Contains both nutrients and waste (brain lacks a lymphatic system)
 Endothelial cells lining blood vessels in the brain are held together by special proteins
that prevent only certain substances from entering
 Ion and glucose levels tightly regulated  brain not subject to variations seen in blood
CSF is produced within ventricles by tissue called choroid plexus
 Choroid plexus:
o Secrete CSF
o Remove Waste
o Adjust CSF composition
 Totally Volume in ventricles & subarachnoid space = 150 ml
 500 ml/day made; therefore turns over about 3x/day
 Blood-Brain Barrier & Choroid plexus Barrier only allows certain substances to enter the
brain
Circumventricular Organs
 Lack a blood-brain barrier
 Informs the brain about blood composition
CSF Circulation
1. Produced in ventricles by choroid plexus
2. Passes through ventricles:
a. Lateral Ventricles
b. Third Ventricle
c. Cerebral Aqueduct
d. Fourth Ventricle
e. Cisterna Magna – enlarged CSF space at base of brain
3. Leaves ventricles to subarachnoid space surrounding brain and spinal cord
4. Returns to venous system at arachnoid granulations that drain CSF into dural sinuses,
primarily superior sagittal sinus.
Dural Sinus  venous-filled cavities that CSF drains into
Subdural Hematoma
 Tearing of the veins entering dural sinuses
 Commonly seen in elderly after a fall
 Shaken Baby Syndrome
Bacterial Meningitis
 Headache, fever, & stiff neck
 Common in communal living situations (dorms) in fall term
 Bacteria block CSF reabsorption
 CSF continues to be made
 Considerable increased intracranial pressure
Hydrocephalus  “water on the brain”
 More severe in adults because skull solid
Herniation due to increased intracranial pressure
Spinal Cord Meninges
 Epidural space between dura and bone – fat cushion, vessels
 Site of anesthesia administration
Spinal Tap (lumbar puncture)
 Used to obtain CSF samples for analysis
 Needle is inserted between L4 & L5 vertebrae
 No spinal cord at this level, only roots