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Year 2 - Ophthalmology (DP) > Physiology > Flashcards

Flashcards in Physiology Deck (108):
1

What is the main constituent of CSF?

Water

2

How should CSF normally appear?

Clear and colourless

3

Where is CSF produced?

Secretory epithelium of the choroid plexus

4

What rate is CSF produced at?

0.4ml/min x tissue weight in grams (500-600ml/day)

5

What CNS volume does CSF make up?

150ml

6

How many times is CSF replaced in the CNS a day?

3-4 times

7

Where does CSF circulate?

Subarachnoid space

8

What does CSF supply to tissues?

Water
Ions
Amino acids

9

What does CSF remove from tissues?

Metabolites

10

How does CSF provide mechanical protection?

Shock-absorption
(Brain 'floats' in cranial cavity)

11

How does CSF act in homeostasis?

pH of CSF affects:
- Pulmonary ventilation (if pH NIPPV)
- Cerebral blood flow
Transports hormones

12

When CSF is collected (via lumbar puncture) what can it be used to diagnose?

Pathologies of the:
- Brain
- Meninges
- Spinal cord

13

How much protein is usually present in normal CSF?

15-45mg/dL

14

Is there a lot of very little Ig in CSF?

Very little

15

How many cells are present in CSF?

1-5cells/ml

16

What happens is CSF accumulates?

Neurological defects

17

In terms of CNS development, what is present at 3 weeks gestation?

Neural canal

18

What does the neural canal give rise to?

Adult ventricles
Spinal cord's central canal

19

Where does the choroid plexus develop from?

Cells in the walls of the ventricles

20

Describe the pathological process of hydrocephalus

1. CSF flow obstruction
2. Ventricular enlargement upstream
3. Bones of skull move apart
4. Significant head enlargement

21

How is hydrocephalus treated?

Surgical shunting

22

What forms the choroid fissure?

Developing arteries invaginating the roof of the ventricle

23

How is the choroid plexus formed?

Involuted ependymal cells and vessels enlagre into villi

24

Where are the choroid plexuses found?

In the lateral, 3rd and 4th ventricles

25

At what point in gestation does CSF begin to circulate through the ventricles?

End of the 1st trimester

26

What are the main ions involved in CSF production?

Na+
Cl-
Bicarbonate

27

How does CSF secretion occur?

1. Active Na+ transport
2. Electrical gradient pulls Cl-
3. Water pulled by osmosis

28

What molecules and ions are in lower concentrations in CSF than in the blood?

K+
Glucose
Protein (substantially lower in CSF)

29

What ions are in higher concentrations in CSF than in the blood?

Na+
Cl-

30

Is CSF production dependent on arterial BP?

Not directly

31

What connects the lateral ventricles to the 3rd ventricle?

Intraventricular Foraminae (of Monroe)

32

What connects the 3rd ventricle to the 4th?

Cerebral Aqueduct (of Sylvius)

33

What is the median aperture that connects the 4th ventricle to the subarachnoid space?

Foramen of Magendie

34

What are the lateral apertures that connect the 4th ventricle to the subarachnoid space?

Foraminae of Luschka

35

How does CSF return to the circulation?

Arachnoid granulations into the superior sagital sinuses

36

What does the blood-brain barrier (BBB) do?

Restricts blood supply to most of the brain

37

What is tighter, the BBB or blood-CSF barrier?

BBB

38

How does brain ISF drain into the CSF?

Via perivascular spaces

39

What cells make up the BBB?

Endothelial cells in brain capillaries

40

What do the brain capillaries consist of?

Endothelium
Basal membrane
Perivascular astrocytes

41

What protects the brain from common bacterial infections and toxins?

Tight junctions between the cells of the BBB:
- Prevent paracellular movement

42

What parts of the brain don't have a BBB?

Circumventricular organs
Roof of 3rd and 4th ventricles
Pineal glands and capillaries -> Melatonin
Roof of diencephalon

43

What is the main obstacle for drug delivery to the CNS?

BBB

44

Where does a colloid cysts often form?

Interventricular foramen

45

What tumours arise from the ependymal cells lining the ventricles?

Ependyomas

46

What is the other name for IIH?

Pseudotumour cerebri

47

Which of the following is not a visual symptoms of papilloedema:
- Enlarged blind spot
- Flashes
- Visual obscurities
- Loss of vision
- Blurring of vision

Flashes

48

What does the aqueous humour provide to eye structures?

Oxygen
Metabolites

49

What ion does aqueous humour contain and what does it do?

Bicarbonate:
- Buffers H+ produced by anaerobic glycolysis
-> Produced in cornea and lens

50

What antioxidant is present in the aqueous humour?

Ascorbate

51

Where is aqueous humour produced and at what rate?

Epithelial layer of the ciliary body:
At 1-3ml/min

52

Where does aqueous humour first drain into? What is the volume of this space and how frequently is it replaced?

Posterior chamber:
- ~60ml
- Replaced in ~30 minutes

53

After the posterior chamber, where does aqueous humour drain to? What is the volume of this space and how often is it replaced?

Anterior chamber:
- ~250ml
- Replaced every 2 hours

54

How is aqueous humour drained from the eye? Where is this situated?

Through a trabecular meshwork and the canal of Schlemm
Situated in angle between iris and cornea:
- Iridocorneal angle

55

Where does aqueous humour drain to?

Scleral venous sinus

56

A small amount of aqueous humour diffuses through the vitreous humour; where is this absorbed?

By the retinal pigment epithelium

57

What are the ciliary body and posterior surface of the iris covered by?

2 juxtaposed layers of epithelial cells:
- Forward continuation of retinal pigment epithelium
- Overlain by an inner non-pigmented epithelium (NPE)

58

Where are bicarbonate and H+ formed in the ciliary epithelium? What is the function of these ions?

In the pigment epithelium
They are transported into the stroma in exchange for CL- and Na+ respectively (NaCl now in PE)

59

How do Na+ and Cl- get from the PE to the NPE?

Diffusion through gap junctions

60

How are Na+ and Cl- transported out of the NPE and into the aqueous humour?

Via the Na+/K+/2Cl- co-transporter

61

How is K+ recycled by the NPE?

Na+/K+ pump

62

How else can Cl- leave the NPE?

Via chloride channels

63

What accompanies the Na+ and Cl- leaving the NPE? Via what channels?

Water:
- Ciliary epithelial cell water channels
- Aquaporins (AQP1 of NPE cells)
- Paracellular path down osmotic gradient

64

What creates the IOP?

Secretion and drainage balance of aqueous humour

65

What is the IOP?

~17mmHg > Atmospheric

66

How do dorzolamide and acetazolamide work in the treatment of glaucoma?

They are carbonic anhydrase inhibitors:
- Reduced aqueous production -> Reduced IOP

67

Why would dorzolamide eye drops be preferred over PO acetazolamide?

Acetazolamide also targets the kidneys leading to acidosis

68

When light hits the back of the eye, what is the pathway that APs take to get to CN II?

Photoreceptors
-> Bipolar cells
-> Ganglion cells

69

What do horizontal cells do?

Receive input from photoreceptors:
- Project it to
-> Other photreceptors
-> Bipolar cells

70

What do amacrine cells do?

Receive input from bipolar cells:
- Project it to
-> Ganglion cells
-> Other amacrine cells
-> Other bipolar cells

71

What are the four regions of a photoreceptor?

Outer segment:
- Cone/Rod
Inner segment (-> Cell bodies)
Cell bodies
Synpatic terminal

72

What is the Vm of vertebrate photoreceptors?

-20mV (note this is more positive than other neurons)

73

Upon light exposure, what happens to the Vm of photoreceptors?

Hyperpolarises

74

What is the dark current? Explain how it works

In the dark:
- A cGMP-gated Na+ channel is open
- Pna and Pk are equal
- Ek

75

What happens when light reaches the photoreceptors in terms of ion changes? Is this change diffuse or local?

Pna is reduced as cGMP-gated channels close:
- Pk > Pna
Vm gets closer to Ek -> Hyperpolarisation
This is a local change

76

What is Rhodopsin composed of?

Opsin + 11-cis-retinal

77

What is opsin?

A G-protein coupled receptor

78

What group of light-sensitive photoreceptors allows colour vision?

Photopsins/Iodopsins

79

Where are the visual pigment molecules found?

Membrane folds -> Discs

80

What does light do to Rhodopsin?

Rhodopsin -> All-trans-retinal (+ opsin)

81

What activates transducin?

All-trans-retinal

82

What happens when transducin is activated?

1. Reduced cGMP
2. Closure of cGMP-gated Na+ channels
3. Reduced Na+ entry
4. Hyperpolarisation

83

What enzyme results in the reduction in cGMP? How many cGMP molecules can one molecule of this enzyme downregulate?

1 Phosphodiesterase -> 1000 cGMP

84

How many molecules of transducin are activated by the breakdown of 1 Rhodopsin molecule?

1000

85

What two ways can All-trans-retinal be metabolised?

By all-trans-retinol dehydrogenases:
- Forming All-trans-retinol (Vitamin A)
By isomerase:
- Forming 11-cis-retinal (can reform Rhodopsin)

86

What is the largest determinant of visual acuity?

Photoreceptor spacing

87

What is visual acuity?

Ability to distinguish between two nearby points

88

What photoreceptors allow us to see in dim light?

Rods

89

What photoreceptors allow us to see in bright light?

Cones

90

In what system (rods or cones) in there higher convergance and what does this result in?

Rod system:
- Increased sensitivity
- Reduced acuity

91

What is the spacing like between cone cells; large or small?

Small -> High density

92

What are the three types of cones?

Short wavelength (cyanolabe) -> Blue light
Medium wavelength (chlorolabe) -> Green light
Long wavelength (Erytholabe) -> Red light

93

What photoreceptors are chromatic and which are achromatic?

Chromatic -> Cones
Achromatic -> Rods

94

What is the monocular visual field?

What each individual eye sees

95

When the visual fields overlap, what is this referred to?

Bilateral visual field

96

Each retina is divided in half relative to what? What is it divided into?

Fovea:
- Nasal hemiretina
- Temporal hemiretina

97

Nerve fibres from what hemiretina cross over/dessucate; where does this happen? How much of these fibres cross?

Nasal half (60% of nasal hemiretina)
Cross at the optic chiasm

98

What are the four parts that the visual field is mapped?

Retina
Lateral geniculate nucleus
Superior colliculus
Cortex

99

What part of the visual field is over-represented?

Central

100

What layer of the primary visual cortex do eye specific inputs segregate?

Layer 4

101

At the primary visual area in each visual cortex, eye specific inputs remain largely segregated into what?

Ocular dominance columns:
- Each dominated by input from one eye

102

Which eye projects to the left visual cortex?

Both!

103

Which layers of the primary visual cortex receive inputs from both eyes?

All but layer 4

104

When are congenital cataracts typically removed?

Between the ages of 10-20 years

105

People with congenital cataracts have difficulty perceiving what?

Shape
Form

106

What is ambylopia?

Cortical blindness in a fully health eye, but one has still has better vision

107

What is thought to be the main cause of ambylopia? How can we treat this cause?

Infantile strabismus:
- Cover good eye with a patch for a few hours/day

108

What is Hebb's postulate and what can it explain?

1. When cell A's axon is close to cell B's it excites it
2. Continuous firing from cell B
3. Growth process in both cells
4. Increased efficiency in cell A
Can explain the loss of binocularity