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Neurology > Intro to the nervous system > Flashcards

Intro to the nervous system Flashcards

1
Q

Which part of the neural tube do the eyes emerge from?

A

Optic vesicles grow laterally from the diencephalic part of the neural tube.

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2
Q

Describe the development of the eyes in the embryo.

A

1) Optic vesicles grow laterally until they reach the surface ectoderm
2) Cells of the surface ectoderm thicken to form the lens placode
3) Lens placode pushes inwards (invaginates) which causes the optic vesicle to form an optic cup (2 layered)
4) Optic vesicle loses its connection with the surface ectoderm

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3
Q

What is the choroid fissure?

A

The fissure in the inferior wall of the optic cup that supplies it with blood vessels as it is developing. This usually disappears before birth.

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4
Q

What happens if the choroid fissure persists?

A

A coloboma (hole) is formed: of the iris, retina or optic disc. This can cause variable degrees of vision problems depending on where it is.

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5
Q

Which structures are formed from the outer layer of the optic cup?

A

Outer layer of the optic cup (layer 10) forms the pigmented layer of the retina and iris.

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6
Q

Which structures are formed from the inner layers of the optic cup?

A

Inner layer (layers 1-9) grows much faster than the outer layers and forms: neural layer of the retina, ciliary body and inner layer of the iris.

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7
Q

If a patient presents with a sudden, painless loss of vision, what may be the cause?

A

Retinal detachment - when fluid gets in between the inner and outer layers of the retina. This can occur due to trauma if VH gets into this space.

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8
Q

What features of the orbit make it weak?

A

The inferior orbital fissure and the medial ethmoid bone.

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9
Q

What is an orbital blow out fracture?

A

When one of the walls of the orbit is fractured but the orbital rim remains intact. These often herniate into the maxillary sinus and cause tear-drop sign on CT (herniation of orbital fat).

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10
Q

What can cause hypertrophy of orbital fat?

A

Graves disease - hyperthyroidism. Causes a staring appearance.

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11
Q

What is the retina?

A

A light-sensitive sensory layer at the back of the eye that contains cells sensitive to light (rods and cones) - these trigger nerve impulses which pass via the optic nerve to the brain.

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12
Q

What are the components of the fibrous coat of the eye and what are their functions?

A

Sclera and cornea - fibrous layer so both contain collagen.

1) Sclera: opaque posterior 5-6th of the eyeball which gives attachment to the muscles moving the eyeball. Irregularly arranged collagen.
2) Cornea: anterior 1/6 which is transparent and allows light to enter the eyeball. Regularly arranged collagen.

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13
Q

Describe the histology of the cornea.

A

Epithelium: stratified squamous, non-keratinised.

Bowman’s membrane: basement membrane.

Stroma: regularly arranged collagen with no blood vessels - these may leak and cause opacity.

Descemets layer: 1 layer of simple squamous epithelium.

Endothelium: single layer.

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14
Q

How is transparency maintained in the cornea?

A

1) Regular arrangement of collagen
2) No blood vessels in the stroma
3) Endothelium has a pump that actively gets rid of VH

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15
Q

Name and inflammatory and non-inflammatory disorder of the cornea.

A

Disorders of the cornea often cause opacity.

Inflammatory: corneal ulcers.

Non-inflammatory: dystrophies.

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16
Q

What is a keratoplasty? What is the advantage of this type of transplant?

A

Corneal transplant - cornea has no blood vessels and so doesn’t need to match the patients HLA haplotype.

17
Q

What are the components of the vascular layer of the eye?

A

Choroid: suspends the lens and produces AH.

Iris: controls the diameter of the pupil and therefore controls the amount of light rays entering the eyeball.

Choroid: supplies blood to the outer layers of the retina.

18
Q

What is the component of the sensory layer of the eye?

A

Retina: has light sensitive rods and cones which enable us to see.

19
Q

How is the retina supplied with blood?

A

Outer layer by the choroid, which is made of fenestrated blood vessels.

Inner layers by branches of the central retinal artery.

20
Q

Describe the important layers of the retina.

A

Layer 1: closest to the outside - pigmented epithelial layer that absorbs light

Layer 2: layer of rods and cones where light gets transduced into AP’s.

Layer 9: nerve fibre layer where the cells are modified neurones.

21
Q

What is the optic disc?

A

The physiological blind spot - this is where the head of the optic nerve lies so there are no rods or cones here. On fundoscopy this is where all the vessels run towards.

22
Q

What is the fovea centralis?

A

The area of highest visual acuity as it is packed with cones. Surrounded by the macula.

23
Q

What is the lens?

A

Crystalline, biconvex structure which is suspended by the suspensory ligaments from the ciliary body - these allow it to change shape.

24
Q

What is a cataract?

A

Opacity of the lens.,

25
Q

Describe the segments of the eye.

A

Anterior segment is in front of the lens and it is filled with aqueous humour.

Posterior segment is behind the lens and it is filled with vitreous humour.

26
Q

What are the 2 chambers of the eye?

A

Anterior chamber is in front of the iris.

Posterior chamber is behind the iris.

27
Q

What are the functions of AH and VH?

A

AH: fluid that helps to maintain intraocular pressure.

VH: transparent gel that cushions the retina.

28
Q

Describe the circulation of AH.

A

AH is produced by the ciliary body in the posterior chamber. It flows out through the pupil to the anterior chamber. It then reaches the angle of the AC and gets filtered out via the trabecular meshwork.It then goes through Schlemm’s canal where it is taken to the normal venous network.

29
Q

What happens when the circulation pathway of AH is obstructed?

A

Glaucoma - raised IOP (intraocular pressure) putting pressure on the optic nerve.

30
Q

What is the conjunctive?

A

A thin vascular layer that convers the sclera and inner surface of the eyelids. Does not cover the cornea.

31
Q

Describe the lacrimal apparatus.

A

Lacrimal gland (lateral) produces tears and carries them to the conjunctival sac (medial) with parasympathetic innervation from CNVII. Tears drain into the medial lacrimal sac, nasolacrimal duct then into the inferior meatus of the nasal cavity.

32
Q

What are the functions of the tear film?

A
  • Keeps cornea moist
  • Washes away foreign bodies
  • Antibodies and lysozyme to kill microbes
  • Smoothes over surface of cornea providing a smooth surface for refraction
33
Q

What are the 3 layers of the tear film and what causes blinking?

A

1) Mucinous (30%) - innermost
2) Aqueous (69%) - aqueous
3) Oily (1%) - outermost

When eyelids are open and lears begin to evaporate, oily and mucinous layers become closer to each other. When they touch this stimulates blinking.

Neurology (23 decks)

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