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Nervous > Introduction to the nervous system > Flashcards

Introduction to the nervous system Flashcards

1
Q

What are the layers of the eye?

A
  • The fibrous layer (outside) composed of:
    - The sclera
    - The cornea
  • The vascular layer
    - The iris
    - The ciliary body
    - The choroid
  • The sensory coat
    - The retina
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2
Q

Explain the Fibrous layer of the eye

A
  • Muscle attach to the fibrous layer
    • It is made of collagen which is tidily arranged so that it is transparent.
    • This layers doesn’t have any blood vessels in it as they could burst and impede seeing
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3
Q

Explain the vascular layer of the eye

A
  • The Iris: controls the diameter of the pupil and controls the amount of light rays let into the eye
    • The ciliary body: suspends the lens and produces aqueous humor
    • The choroid: supplies blood to the outer layers of the retina
    • The vascular layer is incomplete as it doesn’t cover the pupil
    • This layer has a lot of blood vessels
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4
Q

Explain the sensory coat of the eye

A
  • This is the part with rods and cones

- It is where the image forms

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5
Q

What is the structure and function of the eyelids?

A

• The eyelids protect they eye and are composed of several layers:
- Skin (thin hair and sebaceous glands)
○ Eyelashes with sebaceous glands
- Mucous membrane (conjunctiva)
- Subcutaneous tissue
- 2 layers of muscle: laviatorpalpatorsuperiorus (LPS) and the orbicularis oculi
- Hard palate (tarsal plate): maintains shape

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6
Q

What is the structure and function of the conjunctiva?

A
  • Fornix: angle

- Does not continue over cornea

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7
Q

What is the structure and function of the Lacrimal apparatus?

A
  • Supratemporal part of eye
    • Produces fluid to keep the eye moist
    • Drains into the lacrimal sac when blinking
    • It is then carried through the nasolacrimal duct
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8
Q

Describe the development of the eye

A

• The eye is an extension of the brain and so is developed from the neurotube
• The specific part of the neurotube it develops from is the diencephalic vesical of the neurotube
- First they grow outwards latterly
- Then there is a lens placode (embryological thickening)
- There is then an invagination of the lens placode
- This forms the optic cup which is 2 layered
- The choroid fissure forms, it will eventually close up

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9
Q

Describe the chambers of the eye

A

• Posterior chamber: Chamber behind lens
• Anterior chamber: chamber in front of lens
- Posterior segment: posterior part of the anterior chamber (behind the iris)
- Anterior segment: anterior part of the anterior chamber (in front of iris)
• The anterior chamber contains the aqueous humor
• The posterior chamber contains the vitreous humor

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10
Q

Explain the functions of the aqueous and vitreous humor

A
  • The aqueous humour is a watery substance secreted by the ciliary body and helps maintain the pressure of the eyeball (intraocular pressure) at ~21mmHg by being constantly produced, circulated and absorbed
    • The Vitreous humor is a gel that pushes the retina back as well as cushions it
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11
Q

Describe the bony orbit

A
  • Frontal bone
    • Sphenoid bone (greater and lesser wing)
    • Zygomatic bone
    • Maxillary bone
    • Palatine bone (a tiny bit)
    • Lacrimal bone
    • Ethmoid bone
    • Optic foramen
    • Supraorbital fissure
    • Inferior orbital fissure
    • Inferior orbital groove
      • The nasal and superior walls of the orbit are particularly week
      • There is a large amount of fat behind the eyeball that cushions the eye
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12
Q

What are the intrinsic muscles of the eye?

A
  • Constrictor pupilae (parasympathetic) (in the iris)
    • Dilator pupilae (sympathetic) (in the iris)
    • Ciliaris muscle (in the ciliary body) (CN III, parasympathetic)
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13
Q

What are the extrinsic muscles of the eye?

A
  • Medial rectus (MR)
    • Lateral rectus (LR)
    • Superior rectus (SR)
    • Inferior rectus (IR)
    • Superior oblique (SO)
    • Inferior oblique (IO)
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14
Q

What are the nerves of the eye?

A

• SO 4, LR 6 and everything else by 3

- CN IV: Trochlea nerve
- CN VI: abducent nerve
- CN III: Oculomotor
- CN II: Optic nerve
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15
Q

Describe the histological features of the cornea

A
  • Non-keratinised stratified squamous epithelium
    • Bowman’s membrane
    • Stroma (regularly arranged collagen, no blood vessels)
    • Descemet’s layer
    • single layered endothelium
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16
Q

What are the layers of the tear film?

A
  • Mucinous layer overlying the corneal epithelium
    • Aqueous layer lies over the mucinous layer
    • Oily layer is the most superficial
17
Q

What are the functions of the tear film?

A
  • Keeps cornea moist, prevents dying
    • Washes away foreign bodies
    • Has antibodies and lysosomes to kill microbes
      • Smooths out surface of cornea providing a smooth surface for refraction
18
Q

What are the dynamic of the tear film?

A
  • During a blink, the sharp lower boarder of the upper eyelid distributes the tear film evenly
    • When the eyelids are open the aqueous component of tears begin to evaporate, the oily layer comes close to the mucin layer
    • When these 2 layers touch, the tear film breaks up and stimulates further blinking
19
Q

Explain the maintenance of corneal transparency

A
  • Histologically: the regular arrangement of the collagen fibres
    • No blood vessels
    • The endothelium cell layer has a pump that actively keeps the aqueous humor out as it is constantly trying to get into the stoma which would disrupt the regular arrangement of the collagen fibres
20
Q

Explain lens transparency with a note on aging

A
  • Avascularity keeps the lens transparent

* The avasuclarity is one of the factors that predisposes it to becoming opaque later in life (cataracts)

21
Q

Explain the blood aqueous barrier of the eye

A
  • Selectively permeable
    • Formed by the nonpigmented layer of the epithelium of the ciliary body and the endothelium of the blood vessels of the iris
22
Q

Explain the blood retinal barrier of the eye

A
  • The physiological barrier that regulates ion, protein and water flux into and out of the retina
    • The inner BRB is formed by tight junctions between the retinal capillary endothelial cells
    • The outer BRB is formed by tight junctions between the rental pigment endothelial cells

Nervous (21 decks)

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