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Ophthalmology > Physiology > Flashcards

Physiology Flashcards

1
Q

Describe the appearance of CSF

A

Clear, colourless mostly composed of water

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2
Q

Where is CSF produced?

A

Secretory epithelium of the choroid plexus in the ventricles

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3
Q

What is the volume of CSF circulating in the CNS at any one time?

A

150ml

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4
Q

State three major function of CSF

A
  • Mechanical protection (shock absorber of which the brain sits in)
  • Homeostatic function (pH and transport of hormones)
  • Circulation (exchange of nutrients/waste)
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5
Q

How obtained for analysis?

A

Lumbar puncture

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6
Q

How does the choroid fissure develop?

A

Arteries invaginate the roof of the ventricle to form the choroid tissue, this causes the ependymal cells and vessels to enlarge to villi and form the plexus

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7
Q

What causes hydrocephalus?

A

CSF outflow obstruction which can cause enlargement of the ventricular space

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8
Q

How are the ependymal cells held together?

A

Tight junctions

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9
Q

What ions are involved in the production of CSF from blood?

A

Na+
Cl-
HCO3-

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10
Q

How does fluid move across the membrane?

A

Active sodium transport, electrical gradient pull chloride and water moves by osmosis

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11
Q

How is CSF different to blood?

A

Lower potassium, glucose and protein

Higher sodium and chlorine

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12
Q

Is the production of CSF active or passive?

A

Active process does not depend on arterial BP

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13
Q

How many ventricles are there?

A

Two lateral, a third and a fourth

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14
Q

State the connections between the ventricles

A

Foramen of monroe - laterals to third
Aqueduct of sylvius - third to fourth
Foramen of magendie and foramen of luschka - fourth ventricle to subarachnoid space

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15
Q

Where does the CSF go from the subarachnoid space?

A

Drains into the arachnoid villi of dural venous sinuses

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16
Q

What does the blood brain barrier consist of?

A

Capillary endothelium, its basal membrane and perivascular astrocytes

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17
Q

In the BBB what type of junction are between the endothelial cells?

A

Tight junctions - prevent paracellular movement

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18
Q

Do all areas of the brain have a BBB?

A

No - circumventricular organs and the pineal gland do not

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19
Q

Name three types of tumour related to CSF

A
  • colloid cyst (often in interventricular foramen)
  • ependymonas
  • choroid plexus tumour
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20
Q

What can ventricular haemorrhage result in?

A
  • epidural haematoma
  • subdural haematoma
  • subarachnoid haematoma
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21
Q

What are the symptoms of idiopathic intracranial hypertension?

A

Headache and visual disturbance

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22
Q

What is papilloedema?

A

Optic disc swelling due to increased intracranial pressure as a result of excess CSF

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23
Q

What are the symptoms of papilloedema?

A

Enlarged blind spot, blurring of vision and visual obscurations

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24
Q

What is the serious complication of papilloedema?

A

Compression of optic nerve which can lead to loss of vision

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25
Q

Describe aqueous humour

A

Fluid that provides oxygen, metabolites and bicarbonate to the structures within the eye

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26
Q

What is the purpose of bicarbonate in aqueous humour?

A

Buffers hydrogen ions produced in the cornea and lens by anaerobic glycolysis

27
Q

Describe the pathway of aqueous humour

A
  1. produced in ciliary body
  2. posterior chamber
  3. anterior chamber
  4. canal of schlem (iridocorneal angle)
  5. scleral venous sinus
28
Q

Name the two types of epithelial cells in the ciliary body

A

pigmented and non-pigmented

29
Q

What ion exchanges occur in the PE?

A

Bicarbonate and hydrogen ions are transported in exchange for Cl- and Na+

30
Q

Where do the bicarbonate and hydrogen ions that go into the PE come from?

A

Hydration of carbon dioxide catalysed by carbonic anhydrase

31
Q

What happens to the sodium and chloride ions?

A

Diffuse through the gap between PE and NPE cells and are transported by the Na+/K+/2Cl- co-transporter

32
Q

What other transporters are also involved in the NPE?

A

Sodium potassium pump and chloride channels

33
Q

Overall what ions move into the aqueous posterior chamber?

A

Sodium, chloride and water (due to osmosis)

34
Q

What drug can be used in glaucoma and why?

A

Carbonic anhydrase inhibitors - decrease aqueous and reduce ocular pressure

35
Q

Describe the retina structure

A

Photoreceptors
Bipolar cells
Ganglion cells

36
Q

What is the purpose of horizontal cells?

A

Receive input from photoreceptors and project to other photoreceptors and bipolar cells

37
Q

What is the purpose of amacrine cells?

A

Respond to glutamate produced by bipolar cells by projecting signals to ganglion cells, other bipolar cells and amacrine cells

38
Q

Name two types of photoreceptors

A

Rods

Cones

39
Q

Describe rods

A

Sensitive to light found on the periphery of the eye and responsible for night vision

40
Q

Describe cones

A

Responsible for colour vision, found in the fovea. Three types - short, middle and long

41
Q

Describe phototransduction in rods

A
  1. Light hits the photoreceptor
  2. Retinal and rhodopsin change shape
  3. Transducin alpha unit breaks away and binds to PDE thus activating it
  4. cGMP is converted to GMP
  5. cGMP no longer keeps the sodium channels open, they shut and hyper-polarisation occurs
42
Q

What happens when hyper polarisation occurs?

A

Bipolar cells transmit the signal to ganglion cells and ultimately the brain

43
Q

Define visual acuity

A

Ability to distinguish two nearby points determined by photoreceptor spacing and refractive power

44
Q

Describe the visual acuity of rods

A

Large spacing between rods, high convergence as many rods contribute to one large ganglion but decreased acuity

45
Q

Describe the visual acuity of cones

A

High density in fovea, low convergence lots of small ganglion cells

46
Q

After cataract surgery what do people who have had congenital cataracts often struggle with?

A

Perceiving shape and form

47
Q

What is amblyopia?

A

No pathology but one eye is better than the other

48
Q

What can cause amblyopia if not corrected early?

A

Strabismus

49
Q

How is amblyopia treated?

A

Eye patch over good eye to help brain process signals from bad eye but ultimately surgery

50
Q

What conditions can increase intracranial pressure?

A
  • tumours
  • head injury
  • hydrocephalus
  • meningitis
  • stroke
51
Q

What is the Monro Kellie Hypothesis?

A

Intracranial volume is constant and the cranial cavity is inelastic so there is no room for expansion

52
Q

What are the ocular symptoms for increased intracranial pressure?

A 
Blurred vision 
Double vision 
Loss of vision 
Papilloedema 
Pupillary changes
53
Q

What is special with the optic nerve?

A

They are tracts of the CNS covered by meninges

54
Q

What happens to the optic nerve when ICP increases?

A

It gets compressed as well as the central artery and vein which leads to a bulging/swollen optic disc

55
Q

What is a swollen optic disc known as?

A

papilloedema

56
Q

If compression of the oculomotor nerve occurs what happens?

A

Only the superior oblique and lateral rectus still have innervation so the pupil will be turned down and out

57
Q

How will oculomotor nerve compression present?

A

Dilated pupil, ptosis, down and out look

58
Q

How can the oculomotor nerve be stretched or compressed?

A

The brain can herniate through folds created by the dura mater and if the medial temporal lobe herniates through the tectorial notch the oculomotor nerve can be affected

59
Q

Why is the trochlear nerve susceptible to damage?

A

It has a long intracranial course

60
Q

What is the effect of compression of the trochlear nerve?

A

Paralysis of the superior oblique which means the inferior oblique is unopposed

61
Q

How will trochlear nerve compression present?

A

Eye cannot move inferomedially - diplopia when looking down

62
Q

What will stretching of the abducent nerve cause?

A

Paralysis of the lateral rectus muscle

63
Q

How will stretching of the abducens present?

A

Medial deviation of the eye

Ophthalmology (12 decks)

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