Receptors

Receptors are part of the co-ordination systemthat detect the changes of the environment bymeans of stimuli. Two types ...• Interoceptors – receptors detecting internal stimuli, such as hunger, thirst, pain, need to urinate, and blood pressure changes, etc.• Exteroceptors – receptors detecting external stimuli, such as light, sound, movement (balance), temperature, pressure, pain, etc.

Sense organs – What to learn:

• Label diagrams of human eye and ear• List functions of parts of eye and ear• Using diagrams describe in writing formation

of an image, accommodation, binocular vision, pupillary mechanism, balance and hearing

• Long and short sightedness, astigmatism, cataracts

Internal structure of the eye

ciliary body retina choroid

yellow spot

blind spot

sclera

vitreous humour

lens

suspensory ligament

iris

aqueous humour

pupil

optic nerve

conjunctiva

Function(s) of parts of the eyeSclera: • maintains the shape of the eyeball and • is the point where the eye muscles attachCornea• front part of the sclera which is transparent to allow light to pass into the eye• light refraction occurs hereChoroid• middle layer contains many blood vessels and brings O2 & nutrients to the cells of the retina

Function(s) of parts of the eye (cont.)

Conjunctiva • Thin membrane covers the front of the eye has

sensory nerve endings that detect the presence of foreign objects (protect eye)

Suspensory ligaments• Holds the lens in placeLens• responsible for the refraction of light to create

a sharp focussed image

Function(s) of parts of the eye (cont.)

Retina• light-sensitive membrane lines the inside of the eye ball and is made up of photoreceptorsPhotoreceptors (photo=light+receptors convert stimulus into nerve impulse). Two types.. Rods• active in dim light, allow us to see black & whiteCones • active in bright light, allow us to see colour

Function(s) of parts of the eye (cont.)

Yellow spot (fovea)• small area on retina which contains only cones• the area of sharp visionBlind spot• area where the neurons from the photo- receptors leave the eye ball via the optical nerve• There are no cones or rods in this area• Blood vessels also leaves and enter the eye ball at the blind spot

AccommodationAccommodation is the adjustment of the shapeof the lens to see objects clearly whether they are far away or close by.

Near vision

Far vision

Use the two diagrams to memorise the summary of these two processes on the next slide

Summary of eye accommodation

Distant vision(objects further than 6 m)

Near vision(objects closer than 6 m)

Ciliary muscles relax Ciliary muscles contractSuspensory ligaments tighten (become taut)

Suspensory ligaments slacken

Tension on lens increases Tension on lens decreasesLens is less convex (flatter) Lens becomes more convex

(more rounded)Light rays are refracted (bend) less

Light rays are refracted (bend) more

Light rays are focused onto the retina

Light rays are focused onto the retina

Pupillary mechanismPupillary mechanism is the contraction of thepupil in response to light entering the eye.

Bright light

Dim light

Summary of pupillary mechanismBright light Dim light

Radial muscles of the iris relax

Radial muscles of the iris contracts

Circular muscles of the iris contracts

Circular muscles of the iris relax

Pupils constricts (gets smaller)

Pupils widens (gets bigger)

Less light enters the eye More light enters the eye

Structure of the human ear

The human ear consists of the following three parts

Labelled diagram of the ear

Summary of the hearing process