Physiology Flashcards
What produces CSF?
secretory epithelium of the choroid plexus
What is CSF?
a clear, colourless liquid mostly composed of water, few proteins, immunoglobins and cells
Where does CSF travel generally?
formed in the ventricles and then circulates in the subarachnoid space then absorbed into venous circulation
What is the purpose of CSF?
mechanical protection
homeostatic function
circulation
What is the mechanical protection of CSF?
shock-absorbs that protects brain tissue- brain floats in cranial cavity
Whst is the homeostatic functions of CSF?
pH of CSF affects pulmonary ventialtion and cerebral blood flow, transports hormones
How does the developing nervous system initially appear?
a tube- neural canal
What does the cavity of the neural canal give rise to?
ventricles and spinal cords central canal
What does the choroid plexus develop from?
cells in the walls of the ventricles ( developing arteries invaginate the roof of ventricles, te involuted ependymal cells with vessels enlarge into villi to form the plexus
How is CSF formed?
transport of sodium; chloride and bicarbonate from blood across epithelium- polarised distribution of specific ion transporters allow transport
What ion is mainly responsible for CSF production? How?
sodium is actively tranported across cells, this electrical grad. pulls chloride and they both drag along water by osmosis
Why is CSF production not dependent on arterial BP?
it is an active secretory process
What constitutes the ventricular system?
lateral ventricle; third ventricle and fourth ventricle–all continuous
What connects the lateral ventricles to the third ventricle?
intraventricular foramina of Monroe
What connects the thrid ventricle to the fourth ventricle?
cerebral aqueduct of Sylvius
What connects the fourth ventricle to the subarachnoid space?
median and lateral apertures
Describe CSF circulation in the ventricles
CSF formed in each lateral ventricle- flows to third ventricle through the interventricular foramina, more CSF is added by third, flows into fourth through cerebral aqueduct of midbrain, more added in fourth
How does CSF travel from the fourth ventricle?
enters subarachnoid space through the median aperture and 2 lateral apertures and then it circulates in the central canal of spinal cord
What makes up the final portion of CSF?
brain interstital fluid which drains into the CSF through perivascular spaces
Where is the subarachnoid space?
between pia and dura mater
How does CSF return to venous blood?
through arachnoid granulations into the superior sagital sinus
What is the site of the blood brain barrier?
endothelial cells in brain capillaries- its basal membrane and perivascular astrocytes
What precents paracellular movement of molecules at the BBB?
tight junctions between endothelial cells
What is papilloedema?
optic disc swelling due to increased ICP transmitted to the subarachnoid space surroundin the optic nerve
What is aqueous humour?
a specialized fluid that bathes the structures within the eye
Why does the aqueous humour contain bicarbonate?
buffers the H+ produced in the cornea and lens by anaerobic glycolysis
Where is aqueous humor produced?
by epithelial layer of ciliary body (PE)
What is the pathway for aqueous humour?
drains into the posterior chamber and then into the anterior chamber
Where does aqueous humour drain?
into the scleral venous sinus through a trabecular meshwork and the canal of Schlemm
Where are the trabecular meshwork and canal of Schlemm located?
limbus
What are the 2 layers of cells found covering the ciliary body and posterior surface of the iris?
a continuation of the pigment epithelium of the retina and overlain by a nonpigemented epithelial layer
what enzyme conerts CO2 and water into bicarbonate?
carbonic anhydrase
How is bicardbonate transferred acorss the basolateral membrane?
in exchange for chloride and sodium
How are chlorine and sodium transferred in aqueous humour?
by the sodium, potassiu mand 2 chloride cotransporter
How is potassium recycled into the cell?
sodium/potassium pump
How does water enter into the aqueous humour?
aquaporins and paracellular- down the osmotic gradient
What is the pathway of signal transmission in the retina?
photoreceptors to bipolar cells to ganglion cells
How does light affect the photoreceptors?
amounth of light affects hyperpolarisation/depolaristion of the photoreceptors
What are hte lateral connections in the signal transmission in the retina?
horizontal cells and amacrine cells
What are the 4 main regions of the photoreceptor?
outer segment; inner segment (cell body in this) and synpatic terminal
What is the resting membrane potenetial of photoreceptors?
depolarised (more positive)
What happens on light exposure to the photoreceptors?
hyperpolarises
What causes the positive membrane potential?
dark current
What creates the dark current?
a cGMP-gated sodium channel that is open in the dark and closes in the light
Where are the cGMP gated sodium channels located?
the outer segment
What does the photoreceptor release at the synapse?
glutamate
When is glutamate release increased?
when the photoreceptor is hyperpolarised
What is rhodopsin made from?
retinal and opsin
How does light convert rhodopsin?
changes cis-retinal to trans retinal
What type of photoreceptor is rhodopsin found in?
rods
How does tran-retinal phototransduce?
activates transudcin and a moelcular cascade decreasing cGMP which closes cGMP gated sodium channels
What is visual acuity determined by?
photoreceptor spacing and refractive power
What is the significance of high convergence in rods?
increases sensitivity but reduces acuity
What gives a high sensitivty in rods to light?
masive amplication in the molecular cascades by trans-retinal
What are the 3 types of cone?
short wave; middle wave and long wave
What is convergence?
number of photoreceptors to a ganglion
How are shades of colour created?
light of a wavelength activates mulitple different cones (small, middle and long) and how much each opsin is activated gives a shade
What does crossing over of fibres at the chiasm do?
allows right and left visual fields to reach separately the left and right hemispheres respectively- corrects the inversion at the lens( nasal cross over- they were looking at the right side, haven’t “switched” yet, temporals visual field is the other side)
What is the visual pathway?
retina; lateral genicular nucleus; superior colliculu and cortex
What happens at the primary visual cortex?
the eyes information are separated into ocular dominance columns (each colum is dominated by input from one fo the 2 eyes)
When does the information from the eyes mix in the cortex?
outside of layer 4
What happens if both eyes aren’t active from birth?
those neurons never recover and will never take infor from bad eye as lack of activity leads to less branchingin the visual cortex for that eye
