Physiology Flashcards
What produces the cerebrospinal fluid?
secretory epithelium of the choroid plexus
What are the main functions of the cerebrospinal fluid?
- shock-absorbing to protect brain tissue
- pH of CSF affects pulmonary ventilation and cerebral blood flow
- exchange of nutrients and waste
How is cerebrospinal fluid obtained for analysis?
lumbar puncture
What is meant by the brain’s ventricles?
larger areas of the neural canal
How is the choroid plexus formed?
- Developing arteries invaginate the ventricle to form the choroid fissure
- These then enlarge into villi and form the choroid plexus
Plasma from the blood vessels in the choroid plexus contributes to the CSF. TRUE/FALSE?
TRUE
epithelial cells absorb plasma and modify it
then released from opposite
What constituents are found in higher concentrations in CSF than in plasma?
CO2
Cl
Na
What constituents are in higher concentrations in plasma than CSF?
Protein
Cholesterol
What connects the lateral ventricle to the third ventricle?
intraventricular foramina (of Monroe)
What connects the third and fourth ventricles?
Cerebral Aqueduct (of Sylvius)
What structures allow the CSF to exit the ventricles and enter the subarachnoid space?
Foramen of Magendie
Foramina of Luschka
What creates the blood brain barrier?
Tight junctions between brain endothelial cells prevent paracellular movement of molecules
What parts of the brain do NOT contain the blood brain barrier?
circumventricular organs or pineal gland
What tumours most commonly arise in the ventricles, choroid plexus and CSF?
- Colloid cyst (found at interventricular foramen)
- Ependymomas (from ependymal cells lining ventricles)
- Choroid plexus tumours
An arterial haemorrhage between the skull and dura matter is known as what?
Epidural hematoma
Subarachnoid hemorrhage
A subdural hematoma occurs between which layers?
venous bleed
between dura matter and arachnoid
what is hydrocephalus?
- accumulation of CSF in ventricular system (obstruction or overproduction)
- enlargement of one or more ventricles and increase in CSF pressure
How is papilloedema caused?
optic disc swelling due to increased intracranial pressure
transmitted to the subarachnoid space surrounding the optic nerve
How does the optic disc appear on the fundus exam if there is papilloedema?
optic disc bulges and appears blurred
Describe the course of the aqueous humour
ciliary body posterior chamber flows into the anterior chamber drains to the scleral venous sinus through trabecular meshwork and the canal of Schlemm
Describe the 2 layer structure of the ciliary epithelium
pigmented epithelium faces the blood
non-pigmented epithelium faces opposite direction
Briefly describe how Na and Cl make their way into the aqueous humour
Carbonic anhydrase catalyses a reaction to produce H+ and HCO3
H+ is exchanged for Na into the pigmented cell
HCO3 is exchanged for Cl into the pigmented cell
Na and CL then pass to non-pigmented cell via gap junctions
Na and Cl use the Na/K/CL co transporter to leave non-pigmented cell and enter aqueous humour
What drugs can be used to halt the production of aqueous humour?
Carbonic anhydrase inhibitors
Give examples of carbonic anhydrase inhibitors which can be used in glaucoma
Dorzolamide - eye drops (=> avoids systemic side effects )
Acetazolomide - oral (beware of kidney acidosis)
After light hits the photoreceptors, what cells does the signal pass to?
photoreceptor -> bipolar cell -> ganglion cell
Where are Action Potentials generated after light is sensed at the photoreceptors?
Only at ganglion cell
the rest only depolarise the membrane, but dont generate an AP
What are the two shapes of photoreceptors?
Rods
Cones
What effect does light have on the cell membrane potential?
hyperpolarizes
closes cGMP gated Na channel => less positive into cell
How do photosensitive rods hyperpolarize the membrane?
Cis-retinal + opsin = Trans-retinal
Trans-retinal activates transducin
Transducin activates cGMP phosphodiesterase (PDE)
PDE hydrolyses cGMP and prevents Na influx
=> HYPERPOLARISED
What characteristics of photoreceptors can increase visual acuity?
spacing of photoreceptors (closer increases acuity)
volume of photoreceptors
Rod photoreceptors are usually used for seeing in normal daylight. TRUE/FALSE?
FALSE
cone receptors are for seeing in daylights
rod receptors are for seeing in dim light
How do photoreceptors allow us to see different shades of the same colour?
mixture of long, middle and short wave cones can create different shades
What part of the retina contains cones rather than rods?
Fovea (centre of macula)
