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Ophthalmology > Physiology > Flashcards

Physiology Flashcards

1
Q

What produces CSF?

A

secretory epithelium of the choroid plexus

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2
Q

What is CSF?

A

a clear, colourless liquid mostly composed of water, few proteins, immunoglobins and cells

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3
Q

Where does CSF travel generally?

A

formed in the ventricles and then circulates in the subarachnoid space then absorbed into venous circulation

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4
Q

What is the purpose of CSF?

A

mechanical protection
homeostatic function
circulation

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5
Q

What is the mechanical protection of CSF?

A

shock-absorbs that protects brain tissue- brain floats in cranial cavity

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6
Q

Whst is the homeostatic functions of CSF?

A

pH of CSF affects pulmonary ventialtion and cerebral blood flow, transports hormones

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7
Q

How does the developing nervous system initially appear?

A

a tube- neural canal

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8
Q

What does the cavity of the neural canal give rise to?

A

ventricles and spinal cords central canal

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9
Q

What does the choroid plexus develop from?

A

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

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10
Q

How is CSF formed?

A

transport of sodium; chloride and bicarbonate from blood across epithelium- polarised distribution of specific ion transporters allow transport

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11
Q

What ion is mainly responsible for CSF production? How?

A

sodium is actively tranported across cells, this electrical grad. pulls chloride and they both drag along water by osmosis

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12
Q

Why is CSF production not dependent on arterial BP?

A

it is an active secretory process

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13
Q

What constitutes the ventricular system?

A

lateral ventricle; third ventricle and fourth ventricle–all continuous

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14
Q

What connects the lateral ventricles to the third ventricle?

A

intraventricular foramina of Monroe

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15
Q

What connects the thrid ventricle to the fourth ventricle?

A

cerebral aqueduct of Sylvius

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16
Q

What connects the fourth ventricle to the subarachnoid space?

A

median and lateral apertures

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17
Q

Describe CSF circulation in the ventricles

A

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

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18
Q

How does CSF travel from the fourth ventricle?

A

enters subarachnoid space through the median aperture and 2 lateral apertures and then it circulates in the central canal of spinal cord

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19
Q

What makes up the final portion of CSF?

A

brain interstital fluid which drains into the CSF through perivascular spaces

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20
Q

Where is the subarachnoid space?

A

between pia and dura mater

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21
Q

How does CSF return to venous blood?

A

through arachnoid granulations into the superior sagital sinus

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22
Q

What is the site of the blood brain barrier?

A

endothelial cells in brain capillaries- its basal membrane and perivascular astrocytes

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23
Q

What precents paracellular movement of molecules at the BBB?

A

tight junctions between endothelial cells

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24
Q

What is papilloedema?

A

optic disc swelling due to increased ICP transmitted to the subarachnoid space surroundin the optic nerve

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25
Q

What is aqueous humour?

A

a specialized fluid that bathes the structures within the eye

26
Q

Why does the aqueous humour contain bicarbonate?

A

buffers the H+ produced in the cornea and lens by anaerobic glycolysis

27
Q

Where is aqueous humor produced?

A

by epithelial layer of ciliary body (PE)

28
Q

What is the pathway for aqueous humour?

A

drains into the posterior chamber and then into the anterior chamber

29
Q

Where does aqueous humour drain?

A

into the scleral venous sinus through a trabecular meshwork and the canal of Schlemm

30
Q

Where are the trabecular meshwork and canal of Schlemm located?

A

limbus

31
Q

What are the 2 layers of cells found covering the ciliary body and posterior surface of the iris?

A

a continuation of the pigment epithelium of the retina and overlain by a nonpigemented epithelial layer

32
Q

what enzyme conerts CO2 and water into bicarbonate?

A

carbonic anhydrase

33
Q

How is bicardbonate transferred acorss the basolateral membrane?

A

in exchange for chloride and sodium

34
Q

How are chlorine and sodium transferred in aqueous humour?

A

by the sodium, potassiu mand 2 chloride cotransporter

35
Q

How is potassium recycled into the cell?

A

sodium/potassium pump

36
Q

How does water enter into the aqueous humour?

A

aquaporins and paracellular- down the osmotic gradient

37
Q

What is the pathway of signal transmission in the retina?

A

photoreceptors to bipolar cells to ganglion cells

38
Q

How does light affect the photoreceptors?

A

amounth of light affects hyperpolarisation/depolaristion of the photoreceptors

39
Q

What are hte lateral connections in the signal transmission in the retina?

A

horizontal cells and amacrine cells

40
Q

What are the 4 main regions of the photoreceptor?

A

outer segment; inner segment (cell body in this) and synpatic terminal

41
Q

What is the resting membrane potenetial of photoreceptors?

A

depolarised (more positive)

42
Q

What happens on light exposure to the photoreceptors?

A

hyperpolarises

43
Q

What causes the positive membrane potential?

A

dark current

44
Q

What creates the dark current?

A

a cGMP-gated sodium channel that is open in the dark and closes in the light

45
Q

Where are the cGMP gated sodium channels located?

A

the outer segment

46
Q

What does the photoreceptor release at the synapse?

A

glutamate

47
Q

When is glutamate release increased?

A

when the photoreceptor is hyperpolarised

48
Q

What is rhodopsin made from?

A

retinal and opsin

49
Q

How does light convert rhodopsin?

A

changes cis-retinal to trans retinal

50
Q

What type of photoreceptor is rhodopsin found in?

A

rods

51
Q

How does tran-retinal phototransduce?

A

activates transudcin and a moelcular cascade decreasing cGMP which closes cGMP gated sodium channels

52
Q

What is visual acuity determined by?

A

photoreceptor spacing and refractive power

53
Q

What is the significance of high convergence in rods?

A

increases sensitivity but reduces acuity

54
Q

What gives a high sensitivty in rods to light?

A

masive amplication in the molecular cascades by trans-retinal

55
Q

What are the 3 types of cone?

A

short wave; middle wave and long wave

56
Q

What is convergence?

A

number of photoreceptors to a ganglion

57
Q

How are shades of colour created?

A

light of a wavelength activates mulitple different cones (small, middle and long) and how much each opsin is activated gives a shade

58
Q

What does crossing over of fibres at the chiasm do?

A

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)

59
Q

What is the visual pathway?

A

retina; lateral genicular nucleus; superior colliculu and cortex

60
Q

What happens at the primary visual cortex?

A

the eyes information are separated into ocular dominance columns (each colum is dominated by input from one fo the 2 eyes)

61
Q

When does the information from the eyes mix in the cortex?

A

outside of layer 4

62
Q

What happens if both eyes aren’t active from birth?

A

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

Ophthalmology (10 decks)

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