Special Senses

Question 1

What is the function of the eye?

Answer 1

Converts light into nervous impulses for processing in the brain. Responsible for vision.

Question 2

Describe the palpebrae?

Answer 2

Eyelids
Contain skeletal muscles
Outer surface is skin; inner surface is conjunctiva
Eyelids present on the free edge of the upper lid only
The angle that forms the junction between the two palpabra is the canthus

Question 3

What is the correct name and function of the third eyelid?

Answer 3

Nictitating membrane
Extra protection
Distributes even tear coat

Question 4

Where are the Meibomian glands found?

Answer 4

Small sebaceous glands situated beneath the conjunctiva of the eyelids

Question 5

What is the fornix?

Answer 5

The angle formed by the reflection of the conjunctiva

Question 6

Where is the lacrimal apparatus found?

Answer 6

Under the upper eyelids

Question 7

What is the function of the lacrimal apparatus?

Answer 7

Produce tears

Question 8

How do tears drain?

Answer 8

Drain via naso-lacrimal duct system. There are 2 small openings in the lids called the lacrimal punctata which lead to a pair of ducts called the lacrimal canniliculi, which join together to form the lacrimal duct which opens into the nasal cavity.

Question 9

What makes up the outer layer of the eye?

Answer 9

The sclera
- tough fibrous tissue which helps maintains eye shape
- appears white except over the aqueous humour (appears translucent) where its called the cornea
-provides a place for extra-ocular muscles to attach
(control movement of eye)
-the sclera and cornea meet at the limbus
-the cornea is an avascular membrane
-Helps focus the light

Question 10

What does the Middle layer (UVEA) of the eye consist of?

Answer 10

Choroid
Iris
Tapetum Lucidum
Ciliary Body

Question 11

Describe the structure of the choroid?

Answer 11

Has an area of light reflecting cells

Question 12

Describe the structure of the iris

Answer 12

Has central hole - pupil
Very vascular
- contraction and relaxation of smooth muscle of iris, alters size of pupil - controls the amount of light entering the eye/reaching the retina.

Question 13

Describe the Tapetum lucidum

Answer 13

lies amongst the innermost layer of the retina
Has an area of light reflecting cells, which reflects light back onto the retina - improving night vision.
Function is to optimise low levels of light

Question 14

Describe the ciliary body

Answer 14

Smooth muscle fibres
Control the thickness and shape of lens
Control how the eye focuses:
- distance - lens narrows
- close - lens fattens and rounds
It projects towards the centre of the eye and creates a point of attachment for the lens

Question 15

What attaches to the ciliary body?

Answer 15

The suspensory ligament

Question 16

What makes up the inner layer of the eye?

Answer 16

The retina - converts light to nervous impulses which then travel to optic disc where the optic nerve carries the info to the brain

Question 17

What makes us the retina?

Answer 17

2 layers of Photoreceptors

Question 18

Name and describe the photoreceptors

Answer 18

Rods

• sensitive to low light, not colour
• provide white and black and night vision
• located at periphery of retina

Cones

• sensitive to bright light
• provide colour vision
• located centrally

Question 19

Describe the make up of photoreceptors in dogs and cats

Answer 19

95% Rods and 5% Cones

Question 20

Name the 3 media found inside the eye

From front to back

Answer 20

Aqueous humour
Lens
Vitreous humour

Question 21

Describe the aqueous humour

Answer 21

Watery fluid circulates the anterior chamber
Provides nutrients to the lens
Produced by continuous cells of the ciliary body

Question 22

What is glaucoma?

Answer 22

When the aqueous humour isn’t reabsorbed properly, the fluid volume increases and increases the intraocular pressure and the eye will appear larger

Question 23

What is the vitreous humour

Answer 23

Semi-fluid transparent gel which separates the posterior aspect of the lens from the retina
Maintains the globe shape

Question 24

Describe the structure and function of the lens?

Answer 24

Solid, biconvex transparent structure situated behind the iris.
It is attached to the ciliary body by the suspensory ligament.
Made of elastic tissue
Responsible for more exact focusing of light onto the retina.

Question 25

What is opacity and how does it change with age?

Answer 25

Non-Transparency (cloudiness) | Lens becomes more transparent as animal gets older

Question 26

What is a cataract?

Answer 26

An abnormal opacity that will affect vision

Question 27

Describe the two reflexes of the eye used in practise

Answer 27

1. The Menace Reflex - Object waved in front of an animals face will cause the animal to blink 2. The pupillary reflex - Bright light shone into eye will cause the pupil to constrict (under ANS control)

Question 28

Describe how vision works?

Answer 28

1. Light enters the eye through the cornea where is starts to become focussed 2. The light then passes through the pupil 3. The iris controls the size of the pupil and therefore regulates the amount of light entering the eye 4. Light the passes through the lens where it focusses more finely 5. The light then hits the photoreceptors in the retina where it produces an upside down image 6. Any light that has missed the photoreceptors is reflected back onto the retina by the tapetum lucidum 7. The image is received via the optic nerve and interpreted in the cerebral hemisphere

Question 29

Describe the make up and functions of the external ear

Answer 29

Pinna of ear - external ear flap - composed of a layer of skin and a layer of cartilage with blood vessels in between - directs sound waves into ear canal External Auditory Meatus - opening leading to the auditory canal - contains ceruminous glands which produce ear wax

Question 30

Name the boundaries between the: External and Middle Ear Middle and Inner Ear

Answer 30

Tympanic membrane | Oval Window

Question 31

Describe the make up and functions of the middle ear

Answer 31

Auditory Ossicles: Malleus, Incus, Stapes Transmits vibrations from tympanic membrane to oval window Eustachian tube leaves middle ear and runs to pharynx - plays a role in equalising pressure on each side of the tympanic membrane

Question 32

What is the correct name for a middle ear infection and how could infection access this area?

Answer 32

Otitis media | Via pharynx and eustachian tube or via external ear

Question 33

Where is the inner ear located?

Answer 33

Deep within the temporal bone

Question 34

What process occurs in the cochlea?

Answer 34

Vibrations are converted to nerve impulses Contains the Organ of Hearing (corti) contains sensory hairs bathed in endolymph which react to different frequencies. Send impulses via cranial nerve 8 whose fibres start here

Question 35

Apart from the cochlea, what other structures are found in the inner ear?

Answer 35

Utricle, Saccule and Semi-circular canals

Question 36

What is the function of the saccule and utricle

Answer 36

``` Movement of calcium particles stimulates the hairs to pass info to cranial nerve 8. This info is processed by the brain to recognise the position of the head. Contain Maculae (receptors) that detect the position of the head relative to gravity ```

Question 37

What is the structure and function of the semi-circular canals?

Answer 37

At the base of each canal is an ampulla which has a group of sensory hair cells. When the head moves, the endolymph flows past the hairs in the ampulla pulling them. These sensory cells then send messages to the auditory nerve which regulates head position.

Question 38

Why are the semi-circular canals arranged in 3 planes?

Answer 38

To recognise all directions of head movement

Question 39

Where are taste buds found close to?

Answer 39

Papillae of tongue MM & soft palate Pharynx Epiglottis

Question 40

What nerves are involved in taste?

Answer 40

Facial (7), Glossopharyngeal (9) and Vagus (10)

Question 41

Where are the sensory nerve endings for smell found?

Answer 41

The ethmoturbinate bones at back of nasal cavity

Question 42

Where is the olfactory nerve located?

Answer 42

Runs from nose, passes through the mesethmoid bone into the Olfactory Bulb of the brain