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Opthalmology > physiology > Flashcards

physiology Flashcards

1
Q

where is the cerebrospinal fluid produced?

A

ependymal cells of the choroid plexus

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2
Q

where does the CSF fluid circulate?

A

it is formed in the ventricles of the brain and then circulates in the subarachnoid space then absorbed into venous circulation.

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3
Q

What are the main functions of cerebrospinal fluid?

A
  1. Mechanical: shock absorbing medium that protects brain tissue. Brain “floats” inside the cranial cavity
  2. Homeostatic: pH of CSF affects pulmonary ventilation and cerebral blood flow. Transport hormones
  3. Circulation: medium for minor exchange of nutrients and waste products between blood and brain tissue
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4
Q

How is CSF obtained for diagnosis ?

A

Lumbar puncture

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5
Q

what does normal CSF look like?

A

clear and colourless fluid

contains small amount of protein ( 15-45 mg/dl)

Contains small amount of immunoglobulins

contains small amount of cells (1-5 cells/ml)

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6
Q

Discuss the embryonic development of the brain and ventricular system.

A

at 3 weeks the developing nervous system consists of a tube - neural canal

Its cavity gives rise to the adult brain’s ventricles and the spinal cord’s central canal

the choroid plexus develops from cells in the walls of the ventricles

These choroidal cells are specialised secreting cells that produce CSF

developing arteries invaginate the roof of the ventricle form the choroid fissure

The involuted ependymal cells along with the vessels enlarge into villi and form the choroid plexus, responsible for CSF production

choroid plexus in the adult brain is found in the 3rd, 4th and lateral ventricles

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7
Q

what are the main ions required for CSF production

A

Na+ - absorbed into cell and then into apical surface

CL- - absorbed into cell and then into apical surface

HCO3- - diffused into blood ( basal lateral)

this also allows water to enter ependymal cells

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8
Q

what co transporter is found in the apical surface of the ependymal cells which is key in the formation of CSF?

A

Na-K-Cl cotransporter (NKCC)

allows all three to leave cell into CSF

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9
Q

the production of CSF is a an active secretory process true or false?

A

true

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10
Q

Compare the contents of CSF to Plasma.

A

In comparison to plasma, CSF has:

Lower k+

Lower glucose

Lower protein

Higher Na+

Higher CL-

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11
Q

what is the role of the intraventricular foramina (of Monroe)

A

connects lateral ventricles to third ventricle

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12
Q

What is the role of the cerebral Aqueduct?

A

connects third ventricles to fourth

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13
Q

What is the role of the Foramen of magendie?

A

Median aperture - connects fourth ventricle to subarachnoid space

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14
Q

what is the role of the Foramen of Luschka?

A

Lateral apertures - connects fourth ventricle to subarachnoid space

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15
Q

How does the CSF flow from the lateral ventricles to the third ventricle?

ii. what occurs at the third ventricle?

A

Via the interventricular foramina

ii. more CSF is added by choroid plexus in the roof of third ventricle

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16
Q

which ventricles create CSF first?

A

lateral ventricles

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17
Q

How does the CSF flow from the third ventricles to the fourth ventricles?

ii. what occurs at the fourth ventricle?

A

via the cerebral aqueduct

ii. more CSF is added by the choroid plexus in the fourth ventricle

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18
Q

what occurs during CSF circulation once it enters the subarachnoid space?

A

Enters subarachnoid space via:

one median apertures

paired lateral apertures

it then exchanges with the venous blood via the the arachnoid villi (granulations) of the dural venous sinuses (superior sagittal sinus)

it then enters the circulatory system

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19
Q

what makes up the final portion of CSF?

ii. how does it reach the CSF fluid?

A

brain interstitial fluid

ii. Via the perivascular spaces

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20
Q

What does the blood brain barrier consist of?

A

capillary endothelium

its basal membrane

perivascular astrocytes

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21
Q

what is the role of the BBB?

A

protects the brain from infections and toxins

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22
Q

Which parts of the brain do not have the BBB?

A

circumventricular organs - points of communication between the blood, the brain parenchyma, and the CSF

pineal gland

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23
Q

what problems can arise from the brain having a BBB?

A

prevents drug delivery to CNS

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24
Q

what is papilloedema?

A

optic disc swelling due to increased intracranial pressure transmitted to the subarachnoid space surrounding the optic nerve which has an enlarged amount of CSF due to inadequate draining

The CSF in the subarachnoid space will push on the eye creating a bulging optic disc

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25
Q

What is the aqueous Humor?

A

a specialised fluid that bathes the structures within the eye.

it provides oxygen and metabolites and contains bicarbonates (HCO3)

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

contains ascorbate which is a powerful antioxidant

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26
Q

Where is Aqueous humor produced?

A

epithelial layer of the ciliary body

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27
Q

Describe the drainage of the aqueous humor.

A
  1. It is produced in the cililary body
  2. Drains into the posterior chamber of the eye
  3. Then flows into the anterior chamber
  4. then drains to the scleral venous sinus through a trabecular meshwork and the canal of schlemm
  5. Small amount diffuses through the vitreous being absorbed across the retinal pigment epithelium
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28
Q

where is the canal of schlemm found?

A

Angle between the iris and cornea iridocorneal angle

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29
Q

what are the two epithelial layers which cover the cililary body and posterior surface of the iris?

A
  1. Pigment epithelium of the retina (PE)

2. Inner nonpigmented epithelial layer (NPE)

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30
Q

How does the ionic composition of aqueous humor occur?

A
  1. HCO3- and H+ is formed in the pitherlial cells from hydration of CO2 via carbonic anhydrase
  2. These ions travel to the basolateral membranes of the PE cells into the interstitial fluid in exchange for Cl- and Na+
  3. CL- and Na+ ions which enter the PE cells diffuse through the gap junctions between the PE and NPE cells
  4. These ions are then transported out of the NPE cells into the aqueous humor via the Na+/K+/2cl- co transporter
  5. K+ ions leaving the cells on either side are recycled by the Na+/K+ pumps and some CL- leave the cells on both sides too

water:

Net movement of Cl- and Na+ through the cells from interstitial fluid to aqueous humor is accompanied by water moving through the ciliary epithelial water channels (aquaporins - AQP1 of the NPE cells) and through paracellular pathway via osmosis

31
Q

Compare the contents the contents of Aqueous humor to Plasma.

A

In comparison to plasma, Aqueous humor has:

More Na+

More Cl-

More Ascorbate

Less HCO3-

Less Glucose

32
Q

when would you use Carbonic anhydrase inhibitors to reduce production of aqueous humor?

A

To reduce ocular pressure in glaucoma

33
Q

give examples of carbonic anhydrase inhibitors

A

Dorzolamide

Acetazolomide

34
Q

what 4 actions need to occur for us to see an object?

A
  1. Pattern of the object must fall on the vision receptors ( rods and cones in the retina)
  2. The amount of light entering the eye must be regulated (too much light will “bleach out” the signals)
  3. The energy from the waves of photons must transduced into electrical signals
  4. Brain must receive and interpret the signals
35
Q

what splits the retina into the nasal and temporal hemitretinas?

A

Fovea

36
Q

What does the monocular visual field refer to?

A

what each eye sees of the visual space ( its own part)

37
Q

What does the binocular visual field refer to?

A

When both eyes have their visual fields to overlap extensively

38
Q

which parts of the eyes view the left visual field?

A

Left nasal hemiretina

Right temporal hemiretina

39
Q

Which parts of the eyes view the right visual field?

A

Right nasal hemiretina

Left temporal hemiretina

40
Q

what occurs at the optic chiasm?

A

Nerve fibres from the nasal half of each retina cross over

this forms two separate optic tracts allowing them to reach separate visual cortex

41
Q

which cortex does the right optic tract go to?

A

Left visual cortex

42
Q

which cortex does the left optic tract go to?

A

right visual cortex

43
Q

which neurons in the retina will perceive upper portions of the visual field?

ii. which cortex will perceive upper portions of the visual field?

A

Lower neurons

ii. Lower visual cortex

44
Q

which neurons in the retina will perceive lower portions of the visual field?

ii. which cortex will perceive lower portions of the visual field?

A

Upper neurons

ii. Upper visual cortex

45
Q

which layer of the primary visual cortex receive the light signals from one eye only?

A

layer 4c - contains ocular dominance column so input is dominated by one eye

e.g. Left layer 4c receive input from right eye signals only

46
Q

How many layers are there in the visual cortex?

ii. what happens to light signals in the other layers of the cortex?

A

6

ii. they receive input from both eyes

47
Q

what is Amblyopia/ cortical blindness?

A

term refers to a variety of visual disorders where one eye has better vision than the other

even though the optics and retina of both eyes are fine

48
Q

what influences the arborization of axons in the LGN?

A

Visual activity

lack of visual activity leads to less branching

49
Q

Correlated activity between presynaptic and postsynaptic cells strengthens synaptic connections between them.

true or false?

A

true

50
Q

what happens if there is no competition between the axons from the right eye and left eye and is dominated by one of them?

A

One eye takes more neural space in layer 4c

this leads to the other eye axons’ branches to regress
and leads to permanent visual loss

51
Q

what is the role of the photoreceptors in the retina?

A

Carries out Transduction - conversion of electromagnetic radiation neural signals

52
Q

Describe the direct pathway for signal transmission of the eye.

A
  1. Photoreceptor
  2. Bipolar cells
  3. Ganglion cells
53
Q

Compare the direct vertical pathway for signal transmission of the eye to the direction of the light.

A

Both move in opposite directions:

Photoreceptor is the most posterior aspect of the eye

light travels first through ganglion cells then bipolar cells to reach the photoreceptor

it is the opposite once light has been converted into electricity

54
Q

what is the role of horizontal cells?

A

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

55
Q

what is the role of amacrine cells?

A

Receive input from bipolar cells and project to ganglion cells, bipolar cells and other amacrine cells

56
Q

what are the four main regions of the photoreceptors?

A

Outer segment

inner segment

cell body

synaptic terminal

57
Q

what are the two main types of photoreceptors?

A

Rods

Cones

58
Q

what is the resting potential of the photoreceptors of the neurons?

A

-20mv

59
Q

what effect does light exposure have on the photorecptors?

A

causes hyperpolarisation - cyclic GMP Gated Na+ channel in the photoreceptor closes in the light

Change in Na+ with light is the signal that enable s the brain to perceive objects

60
Q

what is the dark current?

A

During the dark it Refers to balance between

Permeability of Na+ and K+ in the photoreceptors

influx of Na+ = efflux of K+

Membrane potential is between equilibrium potentials of Na+ and K+

61
Q

what happens to the Modulation of the dark current when the photoreceptor detects light?

A

Permeability of Na+ decreases

therefore K+ leaves via Na+/K+ pump

it becomes hyperpolarised

62
Q

what is the name of visual pigment molecules in the rods?

A

Rhodospin

they are found in the disks in the outer segment

63
Q

what effect does light have on rhodospin?

A

converts it to all-trans-retinal

64
Q

what are the effects of all-trans-retinal on phototransduction?

A
  1. Activates transducin (G protein)
  2. Transducin activates cGMP phosphodiesterase (PDE)
  3. PDE hydrolyses cGMP reducing its concentration
  4. This leads to closure of Na+ channels
  5. Hyperpolarisation of Photorecptors
65
Q

More glutamate is released in the by hyperpolarised photoreceptors true or false?

A

false - they release less

66
Q

When is glutamate released by photoreceptors?

A

in the dark

67
Q

what is visual acuity?

ii. what determines it?

A

ability to distinguish between two nearby points

determined by photoreceptor spacing and refractive power

68
Q

when are rod photoreceptors used?

A

in dim light

69
Q

when are cone photoreceptors used?

A

normal daylight

70
Q

compare the convergence levels of rods and cones?

A

there is high convergence in rods

Low convergence in cones

71
Q

what does more convergence in rod system mean?

A

there is increased sensitivity to light

there is decreased acuity to light

72
Q

how can we see different colours?

A

Different opsins are used for different wavelengths

73
Q

what are the 4 types of photoreceptors in the retina?

A

A. Cones:

  1. Short-wavelength
  2. Medium wavelength
  3. Long wavelength

B. Rods

Opthalmology (3 decks)

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