Flashcards in Physiology Deck (108):
What is the main constituent of CSF?
How should CSF normally appear?
Clear and colourless
Where is CSF produced?
Secretory epithelium of the choroid plexus
What rate is CSF produced at?
0.4ml/min x tissue weight in grams (500-600ml/day)
What CNS volume does CSF make up?
How many times is CSF replaced in the CNS a day?
Where does CSF circulate?
What does CSF supply to tissues?
What does CSF remove from tissues?
How does CSF provide mechanical protection?
(Brain 'floats' in cranial cavity)
How does CSF act in homeostasis?
pH of CSF affects:
- Pulmonary ventilation (if pH NIPPV)
- Cerebral blood flow
When CSF is collected (via lumbar puncture) what can it be used to diagnose?
Pathologies of the:
- Spinal cord
How much protein is usually present in normal CSF?
Is there a lot of very little Ig in CSF?
How many cells are present in CSF?
What happens is CSF accumulates?
In terms of CNS development, what is present at 3 weeks gestation?
What does the neural canal give rise to?
Spinal cord's central canal
Where does the choroid plexus develop from?
Cells in the walls of the ventricles
Describe the pathological process of hydrocephalus
1. CSF flow obstruction
2. Ventricular enlargement upstream
3. Bones of skull move apart
4. Significant head enlargement
How is hydrocephalus treated?
What forms the choroid fissure?
Developing arteries invaginating the roof of the ventricle
How is the choroid plexus formed?
Involuted ependymal cells and vessels enlagre into villi
Where are the choroid plexuses found?
In the lateral, 3rd and 4th ventricles
At what point in gestation does CSF begin to circulate through the ventricles?
End of the 1st trimester
What are the main ions involved in CSF production?
How does CSF secretion occur?
1. Active Na+ transport
2. Electrical gradient pulls Cl-
3. Water pulled by osmosis
What molecules and ions are in lower concentrations in CSF than in the blood?
Protein (substantially lower in CSF)
What ions are in higher concentrations in CSF than in the blood?
Is CSF production dependent on arterial BP?
What connects the lateral ventricles to the 3rd ventricle?
Intraventricular Foraminae (of Monroe)
What connects the 3rd ventricle to the 4th?
Cerebral Aqueduct (of Sylvius)
What is the median aperture that connects the 4th ventricle to the subarachnoid space?
Foramen of Magendie
What are the lateral apertures that connect the 4th ventricle to the subarachnoid space?
Foraminae of Luschka
How does CSF return to the circulation?
Arachnoid granulations into the superior sagital sinuses
What does the blood-brain barrier (BBB) do?
Restricts blood supply to most of the brain
What is tighter, the BBB or blood-CSF barrier?
How does brain ISF drain into the CSF?
Via perivascular spaces
What cells make up the BBB?
Endothelial cells in brain capillaries
What do the brain capillaries consist of?
What protects the brain from common bacterial infections and toxins?
Tight junctions between the cells of the BBB:
- Prevent paracellular movement
What parts of the brain don't have a BBB?
Roof of 3rd and 4th ventricles
Pineal glands and capillaries -> Melatonin
Roof of diencephalon
What is the main obstacle for drug delivery to the CNS?
Where does a colloid cysts often form?
What tumours arise from the ependymal cells lining the ventricles?
What is the other name for IIH?
Which of the following is not a visual symptoms of papilloedema:
- Enlarged blind spot
- Visual obscurities
- Loss of vision
- Blurring of vision
What does the aqueous humour provide to eye structures?
What ion does aqueous humour contain and what does it do?
- Buffers H+ produced by anaerobic glycolysis
-> Produced in cornea and lens
What antioxidant is present in the aqueous humour?
Where is aqueous humour produced and at what rate?
Epithelial layer of the ciliary body:
Where does aqueous humour first drain into? What is the volume of this space and how frequently is it replaced?
- Replaced in ~30 minutes
After the posterior chamber, where does aqueous humour drain to? What is the volume of this space and how often is it replaced?
- Replaced every 2 hours
How is aqueous humour drained from the eye? Where is this situated?
Through a trabecular meshwork and the canal of Schlemm
Situated in angle between iris and cornea:
- Iridocorneal angle
Where does aqueous humour drain to?
Scleral venous sinus
A small amount of aqueous humour diffuses through the vitreous humour; where is this absorbed?
By the retinal pigment epithelium
What are the ciliary body and posterior surface of the iris covered by?
2 juxtaposed layers of epithelial cells:
- Forward continuation of retinal pigment epithelium
- Overlain by an inner non-pigmented epithelium (NPE)
Where are bicarbonate and H+ formed in the ciliary epithelium? What is the function of these ions?
In the pigment epithelium
They are transported into the stroma in exchange for CL- and Na+ respectively (NaCl now in PE)
How do Na+ and Cl- get from the PE to the NPE?
Diffusion through gap junctions
How are Na+ and Cl- transported out of the NPE and into the aqueous humour?
Via the Na+/K+/2Cl- co-transporter
How is K+ recycled by the NPE?
How else can Cl- leave the NPE?
Via chloride channels
What accompanies the Na+ and Cl- leaving the NPE? Via what channels?
- Ciliary epithelial cell water channels
- Aquaporins (AQP1 of NPE cells)
- Paracellular path down osmotic gradient
What creates the IOP?
Secretion and drainage balance of aqueous humour
What is the IOP?
~17mmHg > Atmospheric
How do dorzolamide and acetazolamide work in the treatment of glaucoma?
They are carbonic anhydrase inhibitors:
- Reduced aqueous production -> Reduced IOP
Why would dorzolamide eye drops be preferred over PO acetazolamide?
Acetazolamide also targets the kidneys leading to acidosis
When light hits the back of the eye, what is the pathway that APs take to get to CN II?
-> Bipolar cells
-> Ganglion cells
What do horizontal cells do?
Receive input from photoreceptors:
- Project it to
-> Other photreceptors
-> Bipolar cells
What do amacrine cells do?
Receive input from bipolar cells:
- Project it to
-> Ganglion cells
-> Other amacrine cells
-> Other bipolar cells
What are the four regions of a photoreceptor?
Inner segment (-> Cell bodies)
What is the Vm of vertebrate photoreceptors?
-20mV (note this is more positive than other neurons)
Upon light exposure, what happens to the Vm of photoreceptors?
What is the dark current? Explain how it works
In the dark:
- A cGMP-gated Na+ channel is open
- Pna and Pk are equal
What happens when light reaches the photoreceptors in terms of ion changes? Is this change diffuse or local?
Pna is reduced as cGMP-gated channels close:
- Pk > Pna
Vm gets closer to Ek -> Hyperpolarisation
This is a local change
What is Rhodopsin composed of?
Opsin + 11-cis-retinal
What is opsin?
A G-protein coupled receptor
What group of light-sensitive photoreceptors allows colour vision?
Where are the visual pigment molecules found?
Membrane folds -> Discs
What does light do to Rhodopsin?
Rhodopsin -> All-trans-retinal (+ opsin)
What activates transducin?
What happens when transducin is activated?
1. Reduced cGMP
2. Closure of cGMP-gated Na+ channels
3. Reduced Na+ entry
What enzyme results in the reduction in cGMP? How many cGMP molecules can one molecule of this enzyme downregulate?
1 Phosphodiesterase -> 1000 cGMP
How many molecules of transducin are activated by the breakdown of 1 Rhodopsin molecule?
What two ways can All-trans-retinal be metabolised?
By all-trans-retinol dehydrogenases:
- Forming All-trans-retinol (Vitamin A)
- Forming 11-cis-retinal (can reform Rhodopsin)
What is the largest determinant of visual acuity?
What is visual acuity?
Ability to distinguish between two nearby points
What photoreceptors allow us to see in dim light?
What photoreceptors allow us to see in bright light?
In what system (rods or cones) in there higher convergance and what does this result in?
- Increased sensitivity
- Reduced acuity
What is the spacing like between cone cells; large or small?
Small -> High density
What are the three types of cones?
Short wavelength (cyanolabe) -> Blue light
Medium wavelength (chlorolabe) -> Green light
Long wavelength (Erytholabe) -> Red light
What photoreceptors are chromatic and which are achromatic?
Chromatic -> Cones
Achromatic -> Rods
What is the monocular visual field?
What each individual eye sees
When the visual fields overlap, what is this referred to?
Bilateral visual field
Each retina is divided in half relative to what? What is it divided into?
- Nasal hemiretina
- Temporal hemiretina
Nerve fibres from what hemiretina cross over/dessucate; where does this happen? How much of these fibres cross?
Nasal half (60% of nasal hemiretina)
Cross at the optic chiasm
What are the four parts that the visual field is mapped?
Lateral geniculate nucleus
What part of the visual field is over-represented?
What layer of the primary visual cortex do eye specific inputs segregate?
At the primary visual area in each visual cortex, eye specific inputs remain largely segregated into what?
Ocular dominance columns:
- Each dominated by input from one eye
Which eye projects to the left visual cortex?
Which layers of the primary visual cortex receive inputs from both eyes?
All but layer 4
When are congenital cataracts typically removed?
Between the ages of 10-20 years
People with congenital cataracts have difficulty perceiving what?
What is ambylopia?
Cortical blindness in a fully health eye, but one has still has better vision
What is thought to be the main cause of ambylopia? How can we treat this cause?
- Cover good eye with a patch for a few hours/day