Lecture 6.1: Special Senses – The Eye and the Ear Flashcards
How many fibres does the Optic nerve have?
> 1million
How many fibres does the Auditory nerve have?
30,000
What percentage of blindness is preventable?
50%
Name 4 preventable causes of blindness (4)
- ARMD
- Glaucoma
- Cataracts
- Diabetic Retinopathy
What is Phototransduction?
Process by which light energy is translated into electrical
energy
What are the 2 Photoreceptors found in the Eye?
Rods and Cones
What are Rods sensitive to? Where are they found?
- Sensitive to low level light – night vision
- All areas of retina except fovea
What are Cones sensitive to? Where are they found?
- 3 different photopigments – red, green and blue
- Daytime vision
- Highest density at fovea
What is Myopia?
- 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
What is Hypermetropia?
- 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
What is Visual Acuity?
- How well we can resolve fine detail
- Snellen chart
What is the Ishihara Test?
- Test of colour vision
What do you check when assessing vision? (8)
- Visual acuity
- Ishihara test
- Pupillary reflexes
- Blind spot
- Ophthalmoscopy (retina, optic nerve)
- Visual fields
- Eye movements
- Ocular alignment
Why is an Ophthalmoscopy done?
- Visualisation of the vitreous and retina
- Can use pupillary dilatation
What does Black blobs in the Vitreous mean?
Vitreous haemorrhage
What is found in the Fovea?
Region of highest density of photoreceptors in retina
What is Presbyopia?
- 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
Who uses a convex lens?
People with farsightedness
Who uses a concave lens?
People with shortsightedness
Corneal Reflex
- 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
Pupillary Reflex
An autonomic reflex that constricts the pupil in response to light, thereby adjusting the amount of light that reaches the retina
Optic Pathway (7)
- Eye
- Optic Nerve
- Optic chiasm
- Optic tract
- Lateral geniculate nucleus
- Optic radiation
- Visual cortex
Conditions that affect the Eye: Front
- Cataract
- Glaucoma
- Vitreous Humour (flashes and floaters)
Conditions that affect the Eye: Retinal Diseases (5)
- Retinitis Pigmentosa
- Retinal Detachment
- Red/Green Colour Blindness
- Diabetic Retinopathy
- ARMD (age related macular degeneration)
Conditions that affect the Eye: Optic Nerve (2)
- Multiple Sclerosis
- Raised ICP (Intracranial Pressure)
Conditions that affect the Eye: Nervous (4)
- Visual Field Defects
- CVA (cerebrovascular accident)
- Pituitary Tumour
- RAPD (relative afferent pupillary defect)
Conductive Hearing Loss
When sounds are unable to pass from your outer ear to your inner ear
Sensorineural Hearing Loss
Occurs if the sensitive hair cells inside the cochlea are damaged, or as a result of damage to the auditory nerve
What happens in the Cochlea?
- 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
How does Auditory Transduction work?
- 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)
Auditory Pathway: Primary (Lemniscal) Pathway
Main pathway through which auditory information reaches the primary auditory cortex
Auditory Pathway: Non-Lemniscal Pathway
Mediating unconscious perception eg. attention, emotional response, and auditory reflexes