physiology Flashcards
what is cerebrospinal fluid produced by
the secretory epithelium of the choroid plexus of each lateral ventricle
where does CSF circulate
in the subarachnoid space
where is CSF absorbed
into venous circulation
3 functions of CSF
- mechanical protection - shock absorbing medium that protects brain tissue
- homeostatic function - pH affects pulmonary ventilation and cerebral blood flow, transports hormones
- circulation - medium for minor exchange of nutrients and wast products between blood and brain tissue
what is normal CSF like
contains little protein and little immunoglobulins
-clear and colourless
what is the choroid plexus
networks of capillaries in walls of ventricles
what ions does CSF secretion involve the transport of from basolateral to apical
Na+
Cl-
HCO3-
what are the ventricles of the brain
a communicating network of cavities filled with cerebrospinal fluid (CSF) and located within the brain parenchyma
what are the four ventricles connected by
CSF circulation
- formed in lateral ventricles
- flows to third ventricle through interventricular foramina
- more CSF added by choroid plexus in roof of third ventricle
- flows through aqueduct of midbrain
- into fourth ventricle
- another choroid plexus in fourth adds more CSF
- then enters subarachnoid space
- then circulates in central canal of spinal cord
how does CSF return to venous blood
through arachnoid granulations into superior sagittal sinus
what is blood supply ot the brain restricted by
the blood-brain barrier
what is hydrocephalus
accumulation of CSF in the ventricular system of around the brain
what is papilloedema
optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve
visual symptoms of papilloedema
- enlarged blind spot
- blurring of vision
- visual obscurations
- loss of vision
what is the aqueous humour
a specialized fluid that bathes the structures within the eye
-provides oxygen and metabolites and contains bicarbonate
what does bicarbonate do
buffers the H+ produced in the cornea and lens by anaerobic glycolysis
where is aqueous humour produced
epithelial layer of ciliary body
what are the two layers of ciliary epithelium
pigmented and non-pigmented
what is the net movement of Cl- and Na+ through cells from interstitial fluid to aqueous humour accompanied by
water moving through ciliary epithelial cells water channels, aquaporins and through paracellular pathway down the osmotic gradient created by solute movement
which enzyme is responsible for the production of these ions
carbonic anhydrase
what must happen to see an object
- the pattern of the object must fall on the vision receptors (accommodation)
- the amount of light entering the eye must be regulated
- the energy from the waves of photons must be transduced into electrical signals
- the brain must receive and interpret the signals
where is superior visual field seen
lower cortex
where is right visual field seen
lower cortex
what is involved in the visual field
- retina
- LGN
- superior colliculus
- cortex
cells outside which layer of the cortex receive input from both eyes
4C
2,3,5,6
what is amblyopia
aka coritcal blindness
term that refers to a variety of visual disorders when there is no problem with the eye but one eye has better vision that the other
what does lack of activity cause in the LGN axons
less branching
what is Hebb’s postulate
when an axon of cell A is near enough to excite a cell B and repeatedly or persistently takes part in firing it
what does correlated activity between presynaptic and postsynaptic cells do
strengthens synaptic connections between them
cells that fire together, wire together
direction of signal transmission in the retina
photoreceptors > bipolar cells > ganglion cells
what do horizontal cells do
receive input from photoreceptors and project to other photoreceptors and bipolar cells
what do amacrine cells do
receive input from bipolar cells and project to ganglion cells, bipolar cells and other amacrine cells
what do photoreceptors do
convert electromagnetic radiation to neural signals (trasnduction)
name types of photoreceptors
rods and cones
what causes closure of cGMP-gated Na+ channel
all-trans-retinal activates transducin > molecular cascade > decreases cGMP
what does lowered Na entry result in
hyperpolarization
what is the molecular mechanism of phototransduction
- light stimulation of rhodopsin leads to activation of a G-protein, transducin
- activated G-protein activates cGMP phosphodiesterase (PDE)
- PDE hydrolyses cGMP reducing its concentration
- this leads to closure of Na+ channels
features of the Dark-current channel
- open in dark
- closes in light
- opened by cGMP
- permeable to Na+
- keeps photoreceptor Vm more positive than most neurons
- steady release of neurotransmitter
is there more or less glutamate in the dark
more
what is visual acuity
ability to distinguish two nearby poitns
what is visual acuity determined by
photoreceptor spacing and refractive power
what are rods used for seeing in
dim light
what are cones used for seeing in
normal daylight
the rod system has a high convergence, what does this mean?
increases sensitivity which decreasing acuity
do cones have low or high convergence
low
differences between rods and cones
