Week 1 Flashcards
What is cerebrospinal fluid
Clear colourless liquid composed mostly of water but also contains amino acids and ions
What produces CSF
Secretory epithelium of choroid plexus
How much CSF is produced per day
500-600ml
Where is the choroid plexus located
Ventricles in brain
Describe the flow of CSF
Formed in ventricles by epithelium of choroid plexus
Circulates around the subarachnoid space
Drain into venous system
The CSF circulate around different ventricles. Describe the flow.
- CSF produced by choroid plexus in each lateral ventricle
- Flows to third ventricle through inter ventricular foramina
- More CSF added by choroid plexus in roof of third ventricle
- CSF then flows through cerebral aqueduct to reach into the fourth ventricle
- Choroid plexus of fourth ventricle adds more CSF
How does CSF enter subarachnoid space
Through 3 openings in the roof of fourth ventricle
What are the 3 openings of fourth ventricle that allows CSF to pass into subarachnoid space
1 median aperture
2 lateral apertures
Function of CSF
- mechanical protection
- homeostatic funciton
- Medium for exchange of nutrients and waste between blood and brain
How does CSF produce mechanical protection
It is a shock absorbing medium
How does CSF produce homeostatic function
pH of CSF affects pulmonary ventilation and cerebral blood flow
Transports hormones
How is CSF secreted
Due to transport of movement of ions, drawing water in
What ventricles are there in the brain
Lateral ventricle
Third ventricle
Fourth ventricle
How are the ventricles connected
Foramen of Monroe
Cerebral aqueduct (aqueduct of sylvius)
Foramen of Magendie
Foramina of Luschka
If a drug wants to be used for the nervous system, what does it must be able to do
Cross the Blood brain barrier
Where is the blood brain barrier
Endothelial cells in brain capillaries are sites of BBB
Do all parts of brain have BBB
No
What is hydrocephalus
Accumulation of CSF in the ventricular system or around the brain causing enlargement of ventricles and increase in intracranial pressure
Increase in intracranial pressure can cause
Headache
Visual disturbances due to papilloedema
What is papilloedema
Swelling of optic disc due to increased intracranial pressure
How does the increase in intracranial pressure transmit to the optic disc
Increase in intracranial pressure transmits to subarachnoid space surrounding optic nerve
The space contains CSF as well
Symptoms of papilloedema
Enlarged blind spot
Blurring of vision
Visual obscurations
Loss of vision
What fluid is present in the circulatory system of the eye
Aqueous humour
What does the aqueous humour contain
Oxygen
Metabolites
Bicarbonate
What is the bicarbonate in aqueous humour used for
Buffer the H+ produced in the cornea and lens by anaerobic glycolysis
Where is aqueous humour produced
Epithelial layer of ciliary body
Describe the flow of aqueous humour from where it is produced
- Aqueous humour is produced by the ciliary body and secreted into posterior chamber
- It then flows into the anterior chamber
- Then drains into canal of Schlemm to drain into scleral venous sinus
Where is the canal of Schlemm
Iridocorneal angle (angle between the iris and cornea)
What causes glaucoma
Imbalance between the rates of secretion and removal of aqueous humour causing raised intra-ocular pressure
What type of drug is used in glaucoma
Carbonic anhydrase inhibitors
How do carbonic anhydrase inhibitors treat glaucoma
reduce production of aqueous humour to reduce intra-ocular pressure
Examples of carbonic anhydrase inhibitors
Dorzolamide
Acetazolomide
how is signal transmitted from the retina to the brain
Photoreceptors -> bipolar cells -> ganglion cells
What other cells are responsible for signal transmission from the retina to brain
Horizontal cells
Amacrine cells
What are horizontal cells
Lateral connection between synapse of photoreceptor cells and bipolar cells
Function of horizontal cells
They receive input from photoreceptors and project to other photoreceptors and bipolar cells
What are amacrine cells
Lateral connection between synapses of bipolar and ganglion cells
Function of amacrine cells
Receive input from bipolar cells and project it to other bipolar cells and ganglion cells
Types of photoreceptors
Rods
Cones
How do photoreceptors create a signal
Via phototransduction - conversion of light into electrical potential
How does phototransduction occur in photoreceptors
Light exposure causes membrane potential of photoreceptors to hyperpolarize
How does light exposure cause the hyperpolarisation of photoreceptor cells
Due to closing of cGMP-gated Na+ channel = dark current
The change in Na+ signals the brain to perceive objects in the visual field
What molecule is stimulated by light stimulation and triggers the subsequent dark current
Rhodopsin
Describe how the stimulation of rhodopsin leads to hyperpolarisation of the photoreceptors
- light stimulation of rhodopsin leads to activation of transducin
- transducin activates cGMP phosphodiesterase (PDE
- cGMP PDE hydrolyses cGMP
- Less cGMP = closure of cGPMP- gated Na+ channels
- less Na+ entry = hyperpolarization
What is visual acuity
Ability to distinguish 2 nearby points
Visual acuity is determined by
Photoreceptor spacing
Refractive power
Why can we only see blurry images in the dark
Due to low visual acuity caused by high convergence in rod system
Large spacing of rods
What allows colour vision
Different opsins in cone
Difference between rods and cones
Rods
- no colour
- at peripheral of retina
- high convergence
- low visual acuity
- high light sensitivity
Cones
- colour
- at central of retina
- low convergence
- high visual acuity
- low light sensitivity
Innate immunity of the eye
Blink reflex
Chemical properties in tear film
Immune cells in the eye
Layers of the tear film
Lipid layer
Aqueous layer
Mucin layer
How does blink reflex provide immune defence
Flushes the substance / pathogen away
Mucous layer is anti-adhesive
What are the chemicals in tears that protect against pathogens
Lysozymes
Secretory IgA
tear lipids (antibacterial effect)
Cytokines that recruit immune cells
Immune cells in the eye
Neutrophils
Macrophages
Conjunctival mast cells
What is the main antigen presenting cell at the eye surface
Langerhan cells
Where are langerhan cells mostly located at
Corneo-scleral limbus (junction between cornea and sclera)
Which part of cornea are langerhan cells present in
Peripheral cornea (but not a lot)
Langerhan cells are not found in
Central 1/3 of cornea
Why can other mucosal diseases affect the conjunctiva
Because it has mucosa associated lymphoid tissue - a network of lymphoid tissue covering different mucosal membranes
Which part of the eye is the only part with lymphatic drainage
Conjunctiva
Immune features of conjunctiva
Lymphatic drainage
MALT
Presence of APC, T cells, IgA secreting plasma cells
Presence of Macrophages, langerhan cells and mast cells
What circulate around the MALT frequently
Langerhan cells
Macrophages
Mast cells
Why is cornea and sclera down regulated immune environment
No lymphatics / lymphoid tissue
Relatively less APC
Langerhan cells only in peripheral cornea
What immune features does the lacrimal gland have
IgA secreting plasma cells
CD8+ T cells
What immune feature does the lacrimal drainage system have
MALT
Besides from cornea and sclera, which other part of the eye is also a down regulated immune environment
Retina
Choroid
Vitreous humour
What does immune privilege mean
Sites that are able to tolerate the introduction of antigens without causing an inflammatory cascade
Which parts of the eye are immune-privileged
Cornea
Anterior chamber
Lens
Vitreous cavity
Subretinal space (space between retinal epithelium and photoreceptors)
How does immune privilege occur
lack of lymphatic drainage / blood
Lack of APC
Immunosuppressive molecules
Blood tissue barrier
Anterior chamber immune deviation
Why is immune privilege beneficial
It protects these structures in the eye from ocular inflammation
Why do patients who receive corneal transplant require less immunosuppression compared to other organ transplants
Due to immune privilege of the cornea
How does lack of lymphatic drainage and blood allow immune privilege
Prevents APCs from coming in
Prevents antigenic information from coming in
What is an disadvantage of immune privilege of the eye
Because the immune system of the eye is separated from the systemic immune system, the eye has a higher chance of developing autoimmune reaction to an antigen that the systemic immune system has already tolerated (= the eye immune system does not know this antigen is not harmful because the systemic immune system cannot communicate with it)
What condition is an example of disadvantage of immune privilege of the eye
Sympathetic ophthalmia
What causes sympathetic ophthalmia
Autoimmune reaction to ocular antigens exposed after injury / surgery
