Physiology Flashcards
What are the features of CSF?
- clear, colourless and mostly water
- made by the secretory epithelium of the choroid plexus
- formed in the ventricles, circulates in the subarachnoid space and then into the venous circulation
- supplies water, amino acids and ions
- removes metabolites
What are the main functions of the CSF?
- Mechanical protection: absorbs shock
- Homeostatic function: pH affects pulmonary ventilation and cerebral blood flow
- Circulation: exchange of nutrients and waste
What secretes CSF?
the choroid cells which are in many choroid plexuses (the Blood-CSF-Barrier or BCSFB is used)
What is involved in the secretion of CSF?
transport of ions across the epithelium from blood to CSF
What is the difference in components of CSF compared to blood plasma?
- lower K, glucose and much lower protein than blood plasma
- higher Na and Cl
What is hydrocephalus?
accumulation of CSF fluid causing enlargement of one or more ventricles and an increase in CSF pressure
What are the features of papilloedema?
- excessive CSF production
- optic disc swelling
- enlarged blind spot, blurring of vision, visual obscurations and loss of vision
- flow of CSF pushes on the eye at the back/the optic nerve
- this can be seen with an ophthalmoscope
What is involves in aqueous humour production?
- contains bicarbonate to buffer H+ produced in anaerobic glycolysis
- ciliary body produces aqueous humour, it flows into anterior chamber, then drains into scleral venous sinus
What is the pathway for things being seen?
- pattern of the object must fall on the vision receptors
- accommodation
- correct amount of light needs to enter the eye
- energy from the waves of photons must be transduced into electrical signals
- brain must receive and interpret the signals
What is the order of cells to go through for light?
ganglion cells –> bipolar cells –> photoreceptors
the direction of the signal is opposite
What do photoreceptor cells do?
convert electromagnetic radiation to neural signals by transduction
What is happening in the neurones when there is no light?
- neurone is depolarised
- cGMP-gated Na+ channel is open
- permeability to Na+ and K+ is equal
What happens in the neurones when light hits them?
- it becomes hyperpolarised
- permeability to K+ is increased
What is the pigment in rod cells?
rhodopsin
What happens when rhodopsin is stimulated by light?
- activation of G protein called transducin
- activated cGMP phosphodiesterase so cGMP –> GMP
- Na+ channels are closed
What is visual acuity?
the ability to distinguish two nearby points
this is determined by photoreceptor spacing
What light levels are rods and cones used in?
rods= dim light cones= normal light
Where are the rods and cones situated?
- cones at fovea
- rods more general
- more rods overall than cones
What is the sensitivity of rods?
- high because there are many rods to one ganglion
- ganglion is triggered even in low light
- low acuity therefore
How are different colours seen?
each cone has a different wave that it sees and so a different colour
How is a wandering eye in a child treated?
covering one of the child’s eyes to stop it developing to amblyopia/lay eye which is cortical blindness
What are the main adaptions of the innate immune system for the eye?
- Blink reflex
- Physical and chemical properties of eye surface
- Limit exposure/size
What are the features of the blink reflex?
- tears flush when blinking to remove pathogens
- anti-adhesive layer doesn’t allow pathogens to stick to the eye
What are the features of the chemical properties of the eye surface?
- tears have many elements that are antimicrobial, antiadhesive etc
- immune cells include neutrophils, macrophages and mast cells
