Central Nervous System Physiology Flashcards
What is the normal cerebrospinal fluid pressure?
When lying in a horizontal position, the normal cerebrospinal fluid pressure is about 130 mm of water or 10 mmHg.
What are some common causes of increased cerebrospinal fluid pressure?
A brain tumor can result in the decreased reabsorption of the CSF, which can result in an increased CSF pressure. Hemorrhage or infection are other potential causes as the appearance of red blood cells or white cells can obstruct the absorption channels in the arachnoid villi. Hydrocephalus is an inborn cause of increased CSF pressure.
Where in the brain are the choroid plexuses located? Which locations are associated with the greatest quantity of cerebrospinal fluid produced?
The choroid plexuses are located in the four ventricles. The ones located in the two lateral ventricles produce the greatest quantity of cerebrospinal fluid.
What is the rate of formation of cerebrospinal fluid?
About 500 mL of CSF is formed each day. This translates into about 21 mL/hour.
About how much cerebrospinal fluid is in the subarachnoid space at any given time?
about 125 mL
How does secretion of cerebrospinal fluid by the choroid plexus occur?
It is dependent upon the active transport of sodium through the epithelium of the choroid plexus. As the sodium is transported out, chloride is pulled outward as well because of its electrochemical attraction to sodium. The combination of sodium and chloride increases the osmotic pressure on the outside of the plexus which results in the osmosis of water through the plexus membrane. It is the fluid that forms the principal constituent of cerebrospinal fluid.
Where is the cerebrospinal fluid secreted and where is it absorbed?
Cerebrospinal fluid is secreted by the choroid plexus and absorbed by the arachnoid villi.
What is the brain’s preferred energy source?
The brain is able to metabolize some lactate as a source of energy although glucose is the preferred energy source.
How much glucose does the brain utilize each minute?
Brain glucose utilization is about 5 mg/100g/min. This is about 75 mg/min in the average adult.
About how long will the glycogen stored inside neurons last if it must be converted to glucose during a period of hypoglycemia?
The neurons only contain about a 2 minute supply of glycogen.
What percentage of cardiac output goes to the brain?
The brain only comprises about 2% of body mass but receives about 15% of the cardiac output.
What are the four arteries that supply blood to the brain?
The left and right carotid arteries and left and right vertebral arteries.
What is the most effective method for protecting the brain during ischemic episodes?
Profound hypothermia is the most effective method for protecting the brain during episodes of ischemia. It is often used for up to 60 minutes of total circulatory arrest for cardiopulmonary or neurosurgical procedures with little evidence of neurologic sequelae. Even mild hypothermia at 33- 35 degrees Celsius provides some protective benefits. Although propofol, thiopental, and isoflurane offer many protective advantages, no anesthetic has been shown to consistently provide these effects.
What is the normal cerebral blood flow?
The normal blood flow to the brain is about 50-65 milliliters per 100 grams of brain tissue per minute. This amounts to about 750-900 milliliters/minute in the average adult.
What is the normal cerebral metabolic rate (CMRO2) in adults?
The average CMRO2 in adults is 3-3.8 mL/100g/min or about 50 mL/min
