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8 Cards in this Set

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Describe and trace the formation, circulation and absorption of cerebrospinal fluid?
CSF is secreted by cells lining the walls of the ventricles and by the choroid plexus, a multitufted vascular organ located in the lateral, third and fourth ventricles. It moves through the ventricles into the subarachnoid space, propelled by surges in blood volume and by the beating of cilia in the ventricles.
Briefly describe the ontogeny of the ventricular system?
A. Ventricles of brain and central canal originate from the primitive neural tube of the embryo.
1. The neuraxis bends during development leaving various bulges and stenoses in the neural tube producing reservoirs and passageways for the CSF; if a passageway becomes blocked at a narrow point such as at the Cerebral Aqueduct, pathology develops.
2. Choroid Plexus arises from mesodermal cells growing down into neural fold and joining ependymal cells from the inner layer of the neural tube
B. C-shape of lateral ventricles and other brain structures, e.g., caudate nucleus, hippocampus results from early growth of the lateral cerebral hemispheres in a rostro-caudal direction.
Explain how CSF differs from blood, from brain ISF?
A. Filtrate of Choroid Plexus - 90-150 ml total; formed .35ml/min; (500ml/day); Na+ is actively transported across the choroid epithelium.
1. Blood and CSF are in osmotic equilibrium
2. Active epithelial secretion of ions into CSF since digitalis glycosides inhibit the transport process
3. Sympathetic stimulation reduces CSF production

B. Differences in chemical distribution
1. Elevated Mg++ and Cl-
2. Lower K+, HCO3, Ca++, glucose
3. Very little protein - accounts for clarity of fluid
-albumin level of CSF is 0.5% of blood
4. Lumbar CSF is somewhat closer to blood in composition suggesting extra-choroid secretory elements
Explain the relationships between increased intracranial pressure and CSF flow?
The Monroe-Kellie doctrine states that an increase in the volume of any one of the compartments of the calvarium must be accompanied by a decrease in another compartment or intra-cranial pressure will rise.
1. Normal changes in brain blood volume are accompanied by surges in CSF movement from the VENTRICALS TO SUBARACHNOID SPACE.

Increased intracranial pressure is usually accompanied by papilloedema, a swelling and elevation of the optic disk with blurring of the disk margin and by increased CSF pressure in the lumbar cistern.
Explain the causes of hydrocephalus and brain edema?
B. Brain edema (increased brain volume) and hydrocephalus (increased ventricular volume) may result from defects in CSF production, movement or removal, e.g., papillomas are tumors of choroid plexus which secrete excess CSF
1. Communicating hydrocephalus is due to impaired excretion of CSF through the subarachnoid villi.
2. Noncommunicating hydrocephalus results from stenosis of the cerebral aqueduct of Sylvius or blockage of the foramina of Luschka or the foramen of Magendie
3. Vasogenic edema results from an increase in brain capillary endothelial cell permeability causing an increase in extracellular fluid volume
4. Cytotoxic edema is increased intracellular volume due to failure of mechanisms removing Na+ from cells, e.g., inactivation of Na+ pump by hypoxia
Describe the clinically useful information available from analysis of the CSF?
Because the CSF is a metabolic mirror of the brain, it is sometimes useful in diagnosis of neurological disease.

C. Normally CSF contains very few blood cells, so more than 5 cells per cubic mm suggests the presence of disease in the brain or meninges.
D. The protein content of the CSF is normally low and analysis by electrophoresis of the immunoglobulin fraction may help in diagnosis of certain diseases.
1. Oligoclonal bands of Ig G and multiple sclerosis
2. Myelin basic protein (MBP) and demyelinating disease; MBP is limited to the CNS; injection of MBP produces experimental allergic encephalomyelitis
Explain the circumstances under which the composition of CSF approaches that of blood plasma?
The blood-brain barrier (BBB) controls what enters the CSF and what enters the extracellular fluid of the brain.

D. The capillary endothelial cells act as metabolic regulators of what enters and exits the CNS.
E. The BBB may be disturbed in various disease states.
1. Tumors in the brain frequently have faulty BBB,s and this property may be helpful in localizing the tumor.
2. Some brain diseases, such as meningitis alter the BBB such that substances normally excluded may be used therapeutically, e.g., penicillin.
F. Brief periods of hyperosmolarity can "unzip" the tight junctions of the BBB and may be used to advantage in treating some brain infections.
Describe how intracranial pressure is measured?
CSF pressure can be measured by lumbar puncture using a manometer and can be considered a guide to the pressure in the brain, however lumbar puncture when intracranial pressure is high may result in herniation of the cerebellum through the foramen magnum. (Normal 50-200 mm H20)