Physiology Flashcards
what is CSF
clear, colourless liquid that supplies water, amino acids and ions while removing metabolites
three major functions of CSF
- mechanical protection= shock absorbing
- Homeostatic= pH of CSF affects pulmonary ventilation and cerebral blood flow. Hormone transport.
- circulation
how is clinical analysis of CSF obtained?
lumbar puncture
define the choroid plexus
network of capillaries in the walls of ventricles that produces CSF
what does the secretion of CSF by the choroid plexus depend on?
active transport of Na+ across the cells into CSF as the electrical gradient pulls along Cl- and both ions drag water by osmosis
is the concentration of K+, glucose and protein lower in CSF than blood?
yes
is the concentration of Na+ and Cl- higher in CSF than the blood?
yes
structure of the BBB
- consists of capillary endothelium, basal membrane and perivascular astrocytes
- tight junctions prevent paracellular movement of molecules
what parts of the brain lack the BBB?
circumventricular organs
pineal gland
tumour pathologies of the ventricles, choroid plexus and CSF
colloid cyst
ependymomas
choroid plexus tumours
examples of ventricular haemorrhage
- epidural haematoma
- subdural haematoma
- subarachnoid haemorrhage
describe an epidural haematoma
arterial bleed between skull and dura
describe a subdural haematoma
venous bleed between dura and arachnoid
describe hydrocephalus
accumulation of CSF in the ventricle system or around the brain
subsequent enlargement of one or more ventricles and increase in CSF pressure
what causes hydrocephalus
obstruction
overproduction
symptoms of idiopathic intracranial hypertension/pseudotumour cerebri
headache visual disturbance (fields > blindness, due to papilloedema)
what ion does aqueous humour contain?
bicarbonate HCO3-
what is the role of bicarbonate HCO3- in the aqueous humour?
it buffers H+ produced by the cornea and lens in anaerobic glycolysis
what are the two layers that cover the ciliary body and posterior surface of the iris
pigmented retinal layer (RPE)
non-pigmented epithelial layer (NPE)
how are HCO3- and H+ produced?
hydration of CO2 catalysed by carbonic anhydrase
where are HCO3- and H+ transported?
across the basolateral membranes of the pigmented epithelial cells into interstitial fluid in exchange for Cl- and Na+
how do Cl- and Na+ reach the aqueous humour?
they diffuse through gap junctions between PE and NPE and are transported into the aqueous humour via Na+/K+/Cl- co-transporter
what is the net movement of Cl- and Na+ to the aqueous humour accompanied by?
water moving through ciliary epithelial aquaporins and paracellular pathway
define glaucoma
raised intra-ocular pressure due to imbalance in secretion and removal of aqueous humour
management of glaucoma
CA inhibitors reduce production of aqueous humour e.g. dorzolamide and acetazolamide
side effects of acetazolamide
acidosis in kidneys
retinal structure
epithelial layer contains pigment
first neural layer is photoreceptors which release glutamate which attaches to bipolar cells which release neurotransmitters to ganglion cells
lateral connections- horizontal cells and amacrine cells
what is the photoreceptors resting membrane potential?
more positive -20mV than other neurones
what happens to the photoreceptors resting membrane potential with light exposure?
hyperpolarises
describe the dark currant
the positive resting membrane potential is due to a cGMP-gated Na+ channel being open in the dark causing a constant release of glutamate
what happens to the cGMP-gated Na+ channel when exposed to light
it closes
Na+/K+ in the dark
pump is equally permeable to both ions
Vm is therefore between ENa and EK
Na+/K+ in response to light
PNa is reduced (outer segments close), therefore Vm becomes closer to ion potential of K+ (-90mV)
what is the visual pigment in rods called?
rhodopsin= retinal (vitamin A) and opsin (GPCR)
describe how hyperpolarisation happens?
all-trans-retinal activates transducing (GPCR) activates PDE which hydrolyses cGMP closing Na+ channels
what is high visual acuity facilitated by?
photoreceptor spacing
what lighting do rods see best in?
dim light
how are rods distributed on the retina?
all across the retina with large spaces (low density= high convergence)
what lighting do cones see best in?
daylight
where are cones distributed on the retina?
concentrated at the fovea
three types of cone cells
- short-wave cones= blue
- medium-wave cones= green
- long-wave cones= red
properties of rod cells
achromatic peripheral retina high convergence high light sensitivity low visual acuity
properties of cones
chromatic central retina (fovea) low convergence low light sensitivity high visual acuity
visual fields on the retina
- each eye sees monocular visual field +/- 45 degrees
- they overlap to create a binocular visual field +/- 45 degrees
- retina is divided in half relative to the fovea into nasal and temporal hemiretina
- nasal cross at the optic chiasm, temporal do not
what do people with congenital cataracts struggle with?
perceiving shape and form as they cannot be removed until 10-20 years
define amblyopia (cortical blindness)
variety of visual disorders where there is no problem with the eye but one eye has better vision than the other
causes of amblyopia
strabismus (wandering eye) if not corrected in infancy
management of strabismus in childhood
cover good eye for some hours each day so weak eye still grows connections until it can be surgically corrected
define Hebb’s postulate
cells that fire together wire together (if not working, invades space)
