Special Senses

Question 1

What is the structure and function of the eyelids?

Answer 1

Continuation of the skin
Blinking keeps surface of eye lubricated
Remove dust/debris
Can shut completely for protection
Connect at medial and lateral canthus
Eyelashes prevent foreign matter reaching the surface of the eye
Lacrimal caruncle – small, triangular pink structure at the medial angle of the eye
Conjunctiva - the mucous membrane that covers the front of the eye and lines the inside of the eyelids

Question 2

What is the structure and function of the lacrimal apparatus? (vision)

Answer 2

Produces, distributes and removes tears
Keep surface moist, reduce friction, prevent infection, remove debris
Lacrimal gland
Lacrimal canaliculi
Lacrimal sac
Nasolacrimal duct

Question 3

What is the retina?

Answer 3

Innermost layer of the eye
Photoreceptors
Rods
Highly sensitive to light
Cannot discriminate colours
Cones
Colour vision
Not evenly distributed across retina

Question 4

What is the lens?

Answer 4

Focuses the visual image on the photoreceptors
Refracts light to focus image on retina
Changes shape by contraction and relaxation of the ciliary muscle
Muscle contract, ciliary body moves towards lens, reduces tension in lens, lens rounds
Muscles relax, ciliary body moves away from lens, increases tension in lens, lens flattens

Question 5

What is the structure of the ear?

Answer 5

Internal ear responsible for hearing and equilibrium
External ear (pinna) directs sound waves down the ear canal towards the inner ear
Ear canal ends at the eardrum – tympanon
Middle ear – air-filled chamber

Question 6

How do we hear?

Answer 6

Vibration of eardrum by sound waves converted into mechanical movements of auditory ossicles

Cochlea (in the inner ear) converts mechanical movements of the middle ear into electrochemical impulses which are passed on to the brain via the auditory nerve

Question 7

What is the function of the semicircular canals?

Answer 7

Each canal is filled with fluid and contains hair cells which act as motion sensors
Otoliths (composed of calcium carbonate) are present in the fluid
Theinertiaof these small particles causes them to stimulate hair cells when the head moves
Hair cells send signals downsensory nerve fibres, which are interpreted by the brain as motion

The brain interprets the orientation of the head by comparing the input from both ears to the input from the eyes, allowing the brain to discriminate a tilted head from movement of the entire body

Question 8

What is gustation?

Answer 8

Taste sense

Question 9

What are the five primary taste sensation?

Answer 9

-Sweet
-Sour
-Salty
-Bitter
-Umami (savoury)

Question 10

How are salt and sour tastes detected?

Answer 10

Na ions or H ions diffuse through ion channels
Increase in intracellular cation conc.
Depolarisation of receptor cell
Release of neurotransmitter

Question 11

How are sweet, bitter and unami tastes detected?

Answer 11

Stimuli bind to receptors linked to GPCR
G protein is converted from inactive to active
Produces a second messenger which produces downstream effects

Question 12

What is olfaction?

Answer 12

smell

Question 13

How do we receive input to smell?

Answer 13

Receives input from receptors cells from olfactory epithelium
Exposed receptor cells have dendrites which extend into the nasal passage
Dendrites have large surface area to detect odourants

Question 14

how do we smell?

Answer 14

Odourant binds to a GPCR (G protein couple receptor) on plasma membrane of dendrite of receptor cells
Activates adenylyl cyclase, converts ATP to cAMP
Opens Na channels on membrane
Membrane depolarisation
10-20 million receptor cells in 5 cm2
Large surface area due to dendrites allows us to detect very small concentrations of odorants
Olfactory receptor cells undergo high turnover