Physiology Flashcards
what are the role of CSF
medium for exhange of nutrients (amino acids, ions and water) and waste products/ metabolites between blood and brain tissue
pH of CSF affects pulmonary ventilation and cerebral blood flow
transports hormones
shock absorping medium, suspends the brain inside the cranial cavity
where is CSF made and what is its path
produced by secretory epithelium of the choroid plexus in the ventricles
flows into third ventricle through two narrow openings (interventricular foramina)
floes through cerebral aqueduct in the midbrain
circulates in the subarachnoid space (gets into it via apetures in the roof of the fourth ventricle)
circulates in the central canal of spinal chord
absorped into the venous circulation
what makes CSF
secretory epithelium of the choroid plexus
how is CSF obtained for clinical analysis
lumbar punsture
what does normal CSF look like
clear and colourless
describe the embryological development of the brain
3 weeks neural canal - its cavity makes ventricles and central canal (spinal chord)
choroid plexus develops from cells in the wall of the ventricles
what usually causes hydrocephalus
obstruction of CSF flow causing enlargement of ventricular space upstream to the blockage
how is the choroid plexus formed
arteries invaginate the roof of the ventricle to form the choroid fissure
the involuted ependymal cells + vssels enlarge into villiand form the choroid plexus
where is the choroid plexus found in adults
3rd, 4th and lateral ventricles
what is a choroid plexus
networks of capillaries in walls of ventricles
what cells line the capillaries in the choroid plexus
ependymal cells - make CSF
how do ependymal cells make CSF
absorb plasma from circulation, modify it, secreted from apical membrane of cells
what does CSF secretion involve
transport of ions Na+, CL- and HCO3- across the epithelium from blood to CSF
(HCO3- out, Na and Cl in)
water secretion along with these ions
what does secretion of CSF depend on
Na+ transport across the cells into the CSF- electrical gradient brings along Cl-
both ions drag water
how does CSF ions compare to blood
lower K+, glucose, protein
what is the ventricular system of the braim
set of four interconnected cavities (ventricles) in thebrain, where the cerebrospinal fluid (CSF) is produced
how are the ventricles connected
Intraventricular Foramina (of Monroe): Lateral Ventricles to Third Ventricle
Cerebral Aqueduct (of Sylvius): Third Ventricle to Fourth
Foramen of Magendie: Median aperture – Fourth ventricle to subarachnoid space
Foramina of Luschka: Lateral apertures – Fourth ventricle to subarachnoid space
where is CSF formed
in choroid plexus of each lateral ventricle
some made in subarachnoid membrane and cicumventricular organs structures in the brain that are characterized by their extensive vasculature and lack of a normal blood brain barrier)
how much CSF is produced and absorbed each day
500 ml
how does CSF return to the venous circulation
through arachnoid granulations into superior sagittal sinus
where is the blood brain barrier
endothelial cells in brain capillaries
what makes up the BBB
capillary endothelium, basal membrane, perivascular astrocytes
what parts of the brain dont have a blood brain barrier
circumventricular organs
the pineal gland
what tumours can you get in the ventricles or choroid
colloid cyst (intraventricular foramen)
ependtmomas (arise from ependymal cells)
choroid plexus tumours
what are the types of ventricular haemorrhage
Epidural hematoma, arterial bleed between skull and dura
Subdural hematoma, venous bleed between dura and arachnoid
Subarachnoid hemorrhage
what is hydrocephalus and what causes it
accumulation of CSF in the ventricular system/ around brain
subsequent enlargement of one or more ventricles and increase in CSF pressure
too much generation of CSF or obstruction
what is idiopathic intracranial hypertension/ pseudotumor cerebri
increased CSF pressure
head ache and visual disturbances due to papilloaedema
what is papilloedema
optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve
what are the visual symptoms of papilloedema
enlarged blind spot, blurring of vision, visual obscurations and loss of vision
what is aqueous humor
fluid that bathe the structures within the eye
what are the roles of aqueous humor
provides oxygen, metabolites and bicarbonate (buffers the H+ produced in the cornea and lens)
where is aqueous humor produced- what is its path
epithelial layer in ciliary body- into posterior chamber, then anterior chamber, then drains to the scleral venous sinus though the canal od schlemm
where is the angle of schlemm
angle between the iris and cornea - iridocorneal epithelium
describe the epithelium of the ciliary body and posterior surface or iris
covered by two layers
one a continuation of pigment epithelium of the retina (PE)
this is covered by an inner non pigmented epithelial layer (NPE)
pigment cells under non pigment
describe the ionic composition of aqueous humour and how it happens
HCO3- and H+ go across basolateral membranes of pigmented epithelium into interstitial fluid
in exchange Cl- and Na+ go in via gap junctions out of non pigemented epithelium into aqueous humour (Na+/K+/2Cl- transporter)
water goes with ions via aquaporins
how can you control aqueous humour production
block it with carbonic anhydrase (enzyme that makes HCO3- and H+) inhibitors
what causes glaucoma
raised intra ocular pressure caused by an imbalance in rates of secretion and removal of aqueous humour
what is the treatment for glaucoma
Carbonic anhydrase inhibitors
Dorzolamide - is administered as eye drops- avoiding systemic side effects
Acetazolomide - oral administration-also targets kidney-acidosis.
what is the pathway of signal transduction in the eye
photoreceptors, bipolar cells, ganglion cells, optic nerve
opposite to the path light takes
what lateral connections affect signal processing in the eye
horizontal and amacrine cells (project info to photoreceptors)
what are the main regions of a photorecptor
outer and inner segment, cell body, synaptic terminal
what neurotransmitter is released from photoreceptors
glutamate
describe phototransduction
photoreceptors have depolarised resting membrane potential
with light exposure less glutamate is released hyperpolarising the cell generating a graded potential
why is photoreceptors resting membrane potential positive
because of ‘dark current’ still making potentials when no light
influx of what ion causes dark current
Na
more glutamate is released by photoreceptors in thr dark or light
dark
why is tlight signal graded and local
to allow visual acuity
what is rhodposin
visual pigment molecules (for rods) made from retinal + opsin that photoconverts molecules by activating transducin
what does rhodposin convert with light
11-cis-Retinal to all-trans-Retinal (activated form)
what does all trans retinal do
activates transducin which causes a molecular cascade GMP= closure of cGMP gated Na+ channel, this lowers Na entry= hyperpolarisation
is the dark current channel open or closed in the dark
open in the dark (cGMP gated and lots of cGMP in dark)
what is visual acuity
Ability to distinguish two nearby points. Determined largely by photoreceptor spacing and refractive power
what do rods do
see in dim light
what do cones do
see in normal daytime light
is there more convergence in rods or cones
rod (more photoreceptors going to each ganglion meaning less acuity)
what is the fovea
where con of cones is highest
what allows colour vision
different opsins for discrete wavelengths of light
where in retina are rods and cones
reds peripheral retinal
cones central retina
what photoreceptors see colour
cones
do rods or cones have high light sensitivity
rods have high sensitivity, cones low
does our vision detect local differences in light intensity or the absolute amounts on light
local differences
what are the monocular and binocular visual fields
monocular is area seen by only one eye +/- 45 degrees
binocular seen by both eyes +/- 45 degrees
where in primary cisual cortec are specific eye inputs segregate
layer 4 - segregated by ocular dominance columns (each coloumn dominated by input from one eye)
outside this layer receive input from both eyes
how does congenital cataracts presents
impaired vision from birth
what is amblyopia/ cortical blindness
when one eye has better vision than the other but no problems with eye
what can cause amblyopia
wandering eye (strabisumus)
how do you treat wandering eye
surgically, covering good eye for a few hours until then
why is binocular vision important
for development of both eyes
deprived eye will have less branches of LGN axons
