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Y2 Opthalmology > Physiology > Flashcards

Physiology Flashcards

1
Q

Where is CSF produced?

A

Secretory epithelium of the choroid plexus

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2
Q

What are the 3 major functions of CSF?

A
  1. Mechanical protection - shock absorption to protect brain tissue
  2. Homeostatic function - pH affects pulmonary ventilation and cerebral blood flow, hormone transport
  3. Circulation - medium for minor exchange of nutrients and waste products between blood and brain tissue
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3
Q

Where do the ventricles derive from embryologically?

A

Neural Canal

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4
Q

What is the choroid plexus?

A

Network of capillaries in the walls of ventricles.

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5
Q

Secretion of CSF from choroid plexus is dependent on what ion transport?

A

Na+ –> Cl- follow –> water follows by osmosis

CSF has higher Na+ and Cl- thn blood plasma, and has lower K+, glucose and protein

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6
Q

What lies between the lateral and third ventricles?

A

Intraventricular Foramen of Monroe

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7
Q

What is between the third and fourth ventricle?

A

Cerebral Aqueduct of Sylvius

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8
Q

What two structures are between the fourth ventricle and the subarachnoid space?

A

Foramina of Magendie (medial)

Foramina of Luschka (lateral)

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9
Q

Where does CSF join the venous blood circulation?

A

through arachnoid granulations into the superior sagittal sinus

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10
Q

What is the function of the BBB?

A

Protection of brain from bacterial infection and toxins, and prevent paracellular movement of molecules

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11
Q

What cells make up the BBB?

A

Basal endothelial cells and perivascular astrocytes in brain capillaries

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12
Q

What is the common site of colloid cysts?

A

Interventricular foramen

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13
Q

3 types of ventricular haemorrhage

A

Epidural (between skull + dura)
Subdural (dura + arachnoid)
Subarachnoid

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14
Q

What is hydrocephalus?

A

Accumulation of CSF in the ventricular system or around the brain due to obstruction or overproduction, causing ventricular enlargement and pressure

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15
Q

Symptoms of Idiopathic Intracranial HTN?

A

headache + visual disturbances (due to papilloedema)

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16
Q

What is the function of Aqueous Humor?

A

Provides oxygen and metabolites
Contains bicarbonate to buffer H+ produced in cornea and lens
Ascorbate = antioxidant

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17
Q

Where is aqueous humor produced?

A

epithelial layer of ciliary body, into the posterior chamber of the eye (energy dependent)

18
Q

Describe the drainage of aqueous humor

A

Posterior chamber
Anterior chamber
Scleral venous sinus through trabecular network and the canal of Schlemm

NB small amount through vitreous, absorbed across retinal pigment epithelium

19
Q

What enzyme is responsible for the hydration of CO2 into HCO3 and H+ in the epithelial cells?

A

Carbonic Anhydrase

20
Q

What ions are HCO3 and H+ exchanged for across the basolateral membrane in PE cells?

A

Cl- and Na+ (respectively)

21
Q

How is the ionic movement of Cl- and Na+ into PE cells opposed?

A

Via Na+K+2Cl- cotransporter at NPE cells (pumps into aqeuous humor)

22
Q

How does aqueous humor secretion relate to Glaucoma?

A

Raised IOP occurs due to imbalance in the rates of secretion and removal of aqueous humor

23
Q

What type of drugs can be used to help reduce IOP in Glaucoma?

A

Carbonic Anhydrase inhibitors e.g. Dorzolamide (eye drops) or Acetazolomide (oral - wary of systemic SEs e.g. acidosis)

24
Q

Describe the direct vertical pathway for signal transmission in the retina.

A

Photoreceptors
Bipolar Cells
Ganglion Cells

25
Q

Where do ganglion cells project to and via what nerve?

A

towards forebrain via CNII (optic)

26
Q

What are the lateral connections which influence signal processing in the retina?

A
  1. Horizontal cells (from photoreceptors to bipolar)

2. Amacrine cells (from bipolar to ganglion, bipolar and amacrine)

27
Q

What is the role of photoreceptors?

A

Conversion of electromagnetic radiation into neural signals

28
Q

What are the 4 components of photoreceptors?

A

Outer segment (variable membranous discs, contain photopigment)
Inner segment
Cell body
Synaptic terminal

29
Q

What are the two types of photoreceptors?

A

Rods - dim light

Cones - normal light

30
Q

What is the rough resting membrane potential of vertebrae photoreceptors?

A

-10mV

31
Q

Light exposure results in depolarisation or hyperpolarisation of vertebrae photoreceptors?

A

hyperpolarisation - opposite to others

32
Q

What is the ionic basis of hyperpolarisation of vertebrae photoreceptors?

A

Dark current - open cGMP-gated Na+ channels

Light exposure - closure

33
Q

What visual pigment molecule is present in rods, and where are they found?

A

Rhodopsin

Membrane folds

34
Q

What are the components of Rhodopsin?

A

Retinal (vitamin A derivative) and Opsin (GPCR)

35
Q

How does light exposure trigger hyperpolarisation in Rods?

A
  1. Light converts 11-cis-retinal to all-trans-retinal
  2. Activates transducin
  3. Decreases cGMP activity via molecular cascade
  4. Hyperpolarisation
36
Q

Define Visual Acuity

A

The ability to distinguish between two nearby points

37
Q

How is visual acuity determined?

A
  1. Photoreceptor spacing

2. Refractive power

38
Q

What are the three subtypes of cones?

A

S - short wavelength - blue
M - middle - green
L - long - red

39
Q

From which hemiretina do nerve fibres cross over at the optic chiasm?

A

Nasal

40
Q

Define Amblyopia.

A

Cortical blindness - one eye has better vision with no apparent problem with eye

41
Q

Common cause of Amblyopia

A

Strabismus if not corrected early enough

42
Q

What is Hebb’s Postulate?

A

Loss of binocularity occurs when axon A is near enough to excite axon B, causing strengthening of synaptic connections

“cells that fire together wire together”

Y2 Opthalmology (5 decks)

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