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Opthalmology > Physiology > Flashcards

Physiology Flashcards

1
Q

what are the role of CSF

A

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

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2
Q

where is CSF made and what is its path

A

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

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3
Q

what makes CSF

A

secretory epithelium of the choroid plexus

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4
Q

how is CSF obtained for clinical analysis

A

lumbar punsture

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5
Q

what does normal CSF look like

A

clear and colourless

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6
Q

describe the embryological development of the brain

A

3 weeks neural canal - its cavity makes ventricles and central canal (spinal chord)
choroid plexus develops from cells in the wall of the ventricles

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7
Q

what usually causes hydrocephalus

A

obstruction of CSF flow causing enlargement of ventricular space upstream to the blockage

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8
Q

how is the choroid plexus formed

A

arteries invaginate the roof of the ventricle to form the choroid fissure
the involuted ependymal cells + vssels enlarge into villiand form the choroid plexus

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9
Q

where is the choroid plexus found in adults

A

3rd, 4th and lateral ventricles

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10
Q

what is a choroid plexus

A

networks of capillaries in walls of ventricles

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11
Q

what cells line the capillaries in the choroid plexus

A

ependymal cells - make CSF

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12
Q

how do ependymal cells make CSF

A

absorb plasma from circulation, modify it, secreted from apical membrane of cells

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13
Q

what does CSF secretion involve

A

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

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14
Q

what does secretion of CSF depend on

A

Na+ transport across the cells into the CSF- electrical gradient brings along Cl-
both ions drag water

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15
Q

how does CSF ions compare to blood

A

lower K+, glucose, protein

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16
Q

what is the ventricular system of the braim

A

set of four interconnected cavities (ventricles) in thebrain, where the cerebrospinal fluid (CSF) is produced

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17
Q

how are the ventricles connected

A

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

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18
Q

where is CSF formed

A

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)

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19
Q

how much CSF is produced and absorbed each day

A

500 ml

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20
Q

how does CSF return to the venous circulation

A

through arachnoid granulations into superior sagittal sinus

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21
Q

where is the blood brain barrier

A

endothelial cells in brain capillaries

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22
Q

what makes up the BBB

A

capillary endothelium, basal membrane, perivascular astrocytes

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23
Q

what parts of the brain dont have a blood brain barrier

A

circumventricular organs

the pineal gland

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24
Q

what tumours can you get in the ventricles or choroid

A

colloid cyst (intraventricular foramen)
ependtmomas (arise from ependymal cells)
choroid plexus tumours

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25
Q

what are the types of ventricular haemorrhage

A

Epidural hematoma, arterial bleed between skull and dura
Subdural hematoma, venous bleed between dura and arachnoid
Subarachnoid hemorrhage

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26
Q

what is hydrocephalus and what causes it

A

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

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27
Q

what is idiopathic intracranial hypertension/ pseudotumor cerebri

A

increased CSF pressure

head ache and visual disturbances due to papilloaedema

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28
Q

what is papilloedema

A

optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve

29
Q

what are the visual symptoms of papilloedema

A

enlarged blind spot, blurring of vision, visual obscurations and loss of vision

30
Q

what is aqueous humor

A

fluid that bathe the structures within the eye

31
Q

what are the roles of aqueous humor

A

provides oxygen, metabolites and bicarbonate (buffers the H+ produced in the cornea and lens)

32
Q

where is aqueous humor produced- what is its path

A

epithelial layer in ciliary body- into posterior chamber, then anterior chamber, then drains to the scleral venous sinus though the canal od schlemm

33
Q

where is the angle of schlemm

A

angle between the iris and cornea - iridocorneal epithelium

34
Q

describe the epithelium of the ciliary body and posterior surface or iris

A

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

35
Q

describe the ionic composition of aqueous humour and how it happens

A

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

36
Q

how can you control aqueous humour production

A

block it with carbonic anhydrase (enzyme that makes HCO3- and H+) inhibitors

37
Q

what causes glaucoma

A

raised intra ocular pressure caused by an imbalance in rates of secretion and removal of aqueous humour

38
Q

what is the treatment for glaucoma

A

Carbonic anhydrase inhibitors

Dorzolamide - is administered as eye drops- avoiding systemic side effects
Acetazolomide - oral administration-also targets kidney-acidosis.

39
Q

what is the pathway of signal transduction in the eye

A

photoreceptors, bipolar cells, ganglion cells, optic nerve

opposite to the path light takes

40
Q

what lateral connections affect signal processing in the eye

A

horizontal and amacrine cells (project info to photoreceptors)

41
Q

what are the main regions of a photorecptor

A

outer and inner segment, cell body, synaptic terminal

42
Q

what neurotransmitter is released from photoreceptors

A

glutamate

43
Q

describe phototransduction

A

photoreceptors have depolarised resting membrane potential

with light exposure less glutamate is released hyperpolarising the cell generating a graded potential

44
Q

why is photoreceptors resting membrane potential positive

A

because of ‘dark current’ still making potentials when no light

45
Q

influx of what ion causes dark current

A

Na

46
Q

more glutamate is released by photoreceptors in thr dark or light

A

dark

47
Q

why is tlight signal graded and local

A

to allow visual acuity

48
Q

what is rhodposin

A

visual pigment molecules (for rods) made from retinal + opsin that photoconverts molecules by activating transducin

49
Q

what does rhodposin convert with light

A

11-cis-Retinal to all-trans-Retinal (activated form)

50
Q

what does all trans retinal do

A

activates transducin which causes a molecular cascade GMP= closure of cGMP gated Na+ channel, this lowers Na entry= hyperpolarisation

51
Q

is the dark current channel open or closed in the dark

A

open in the dark (cGMP gated and lots of cGMP in dark)

52
Q

what is visual acuity

A

Ability to distinguish two nearby points. Determined largely by photoreceptor spacing and refractive power

53
Q

what do rods do

A

see in dim light

54
Q

what do cones do

A

see in normal daytime light

55
Q

is there more convergence in rods or cones

A

rod (more photoreceptors going to each ganglion meaning less acuity)

56
Q

what is the fovea

A

where con of cones is highest

57
Q

what allows colour vision

A

different opsins for discrete wavelengths of light

58
Q

where in retina are rods and cones

A

reds peripheral retinal

cones central retina

59
Q

what photoreceptors see colour

A

cones

60
Q

do rods or cones have high light sensitivity

A

rods have high sensitivity, cones low

61
Q

does our vision detect local differences in light intensity or the absolute amounts on light

A

local differences

62
Q

what are the monocular and binocular visual fields

A

monocular is area seen by only one eye +/- 45 degrees

binocular seen by both eyes +/- 45 degrees

63
Q

where in primary cisual cortec are specific eye inputs segregate

A

layer 4 - segregated by ocular dominance columns (each coloumn dominated by input from one eye)

outside this layer receive input from both eyes

64
Q

how does congenital cataracts presents

A

impaired vision from birth

65
Q

what is amblyopia/ cortical blindness

A

when one eye has better vision than the other but no problems with eye

66
Q

what can cause amblyopia

A

wandering eye (strabisumus)

67
Q

how do you treat wandering eye

A

surgically, covering good eye for a few hours until then

68
Q

why is binocular vision important

A

for development of both eyes

deprived eye will have less branches of LGN axons

Opthalmology (16 decks)

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