Lecture 6.1: Special Senses – The Eye and the Ear

Question 1

How many fibres does the Optic nerve have?

Answer 1

> 1million

Question 2

How many fibres does the Auditory nerve have?

Answer 2

30,000

Question 3

What percentage of blindness is preventable?

Answer 3

50%

Question 4

Name 4 preventable causes of blindness (4)

Answer 4

• ARMD
• Glaucoma
• Cataracts
• Diabetic Retinopathy

Question 5

What is Phototransduction?

Answer 5

Process by which light energy is translated into electrical
energy

Question 6

What are the 2 Photoreceptors found in the Eye?

Answer 6

Rods and Cones

Question 7

What are Rods sensitive to? Where are they found?

Answer 7

• Sensitive to low level light – night vision
• All areas of retina except fovea

Question 8

What are Cones sensitive to? Where are they found?

Answer 8

• 3 different photopigments – red, green and blue
• Daytime vision
• Highest density at fovea

Question 9

What is Myopia?

Answer 9

• Short-sightedness is a very common eye condition
  where you cannot see objects far away clearly
• Eyeball too long or lens too curved
• Image formed in front of the retina

Question 10

What is Hypermetropia?

Answer 10

• Long-sightedness is where you find it hard to see
  things nearby, but you can see things far away clearly
• Eyeball too short or lens too flat
• Image formed behind the retina

Question 11

What is Visual Acuity?

Answer 11

• How well we can resolve fine detail
• Snellen chart

Question 12

What is the Ishihara Test?

Answer 12

• Test of colour vision

Question 13

What do you check when assessing vision? (8)

Answer 13

• Visual acuity
• Ishihara test
• Pupillary reflexes
• Blind spot
• Ophthalmoscopy (retina, optic nerve)
• Visual fields
• Eye movements
• Ocular alignment

Question 14

Why is an Ophthalmoscopy done?

Answer 14

• Visualisation of the vitreous and retina
• Can use pupillary dilatation

Question 15

What does Black blobs in the Vitreous mean?

Answer 15

Vitreous haemorrhage

Question 16

What is found in the Fovea?

Answer 16

Region of highest density of photoreceptors in retina

Question 17

What is Presbyopia?

Answer 17

• Lens becomes stiffer with age resulting in a decrease
  in accommodation/focusing
• Close objects no longer focused onto the retina
• Corrected with convex lens’ of increasing strength

Question 18

Who uses a convex lens?

Answer 18

People with farsightedness

Question 19

Who uses a concave lens?

Answer 19

People with shortsightedness

Question 20

Corneal Reflex

Answer 20

• Also known as the blink reflex or eyelid reflex
• It is an involuntary blinking of the eyelids elicited by
  stimulation of the cornea
• Caused by a loop between the trigeminal sensory
  nerves and the facial motor (VII) nerve innervation of
  the orbicularis oculi muscles

Question 21

Pupillary Reflex

Answer 21

An autonomic reflex that constricts the pupil in response to light, thereby adjusting the amount of light that reaches the retina

Question 22

Optic Pathway (7)

Answer 22

• Eye
• Optic Nerve
• Optic chiasm
• Optic tract
• Lateral geniculate nucleus
• Optic radiation
• Visual cortex

Question 23

Conditions that affect the Eye: Front

Answer 23

• Cataract
• Glaucoma
• Vitreous Humour (flashes and floaters)

Question 24

Conditions that affect the Eye: Retinal Diseases (5)

Answer 24

• Retinitis Pigmentosa
• Retinal Detachment
• Red/Green Colour Blindness
• Diabetic Retinopathy
• ARMD (age related macular degeneration)

Question 25

Conditions that affect the Eye: Optic Nerve (2)

Answer 25

* Multiple Sclerosis * Raised ICP (Intracranial Pressure)

Question 26

Conditions that affect the Eye: Nervous (4)

Answer 26

* Visual Field Defects * CVA (cerebrovascular accident) * Pituitary Tumour * RAPD (relative afferent pupillary defect)

Question 27

Conductive Hearing Loss

Answer 27

When sounds are unable to pass from your outer ear to your inner ear

Question 28

Sensorineural Hearing Loss

Answer 28

Occurs if the sensitive hair cells inside the cochlea are damaged, or as a result of damage to the auditory nerve

Question 29

What happens in the Cochlea?

Answer 29

* Vibration of stapes at oval window→ vibrations of perilymph in scala vestibuli * Transmitted to endolymph in cochlear duct and spiral organ of Corti on basilar membrane * Hair cells stimulated→impulses travel along CNVIII to brain

Question 30

How does Auditory Transduction work?

Answer 30

* 4 rows of hair cells * 1 inner hair cells row (provide most of the signal to CN VIII) * 3 outer hair cell rows (role in modulating the response of the inner hair cells)

Question 31

Auditory Pathway: Primary (Lemniscal) Pathway

Answer 31

Main pathway through which auditory information reaches the primary auditory cortex

Question 32

Auditory Pathway: Non-Lemniscal Pathway

Answer 32

Mediating unconscious perception eg. attention, emotional response, and auditory reflexes