Ch15 Detecting the environment Flashcards
Irritability
Irritability is the ability of detecting stimuli and giving responses in organism. It is important for survival.
What does the receptor consist of?
Sensory cells which are concentrated to form part of a sense organ. 
Sense organ, type of receptor and stimulus detect
The Eye, photoreceptor, detect light
Ear , mechanoreceptor, detect sound
Nose, chemoreceptor, detect chemicals in the air
Tongue , chemoreceptor, detect chemicals in the food
Skin , mechanoreceptor, detect pressure
Thermoreceptor, detect temperature change
Structures around the eyes
The eyebrow prevents sweat from running into the eyes
The eyelash dust and prevents it from entering the eye
The eyelid can be closed to protect the eye from dirt and strong light And spread tears over the eye surface when we blink
The tear gland produces tears, which contains sodium, chloride and lysosome that can kill bacteria, and keep the eye, moist and clean
Tear duct drains tears into the nasal cavity
The eyeball
The eyeball is located in a socket in the skull called the orbit. It is attached by three pairs of eye muscles. These muscles enable the eyeball to rotate in different direction. Front surface of the eyeball and the inner surface of the eyelids are covered by a transparent membrane called conjunctiva. Help keeps front part of the eye, moist and lubricated.
Sclera
-maintains the shape of the eyeball and protect the inner structure
-provides a surface for the attachment of eye muscles
Cornea
-transparent, allows light to enter the eyes
-helps refract and focus light onto the retina
-no capillaries
Choroid
-middle layer of eyeball
-contains black pigment which absorbs light to reduce the reflection of light to help form sharp image
-rich in capillaries, supply oxygen and nutrients to the retina and sclera and remove waste from them
Iris
-muscle
-control the size of the pupil, to regulate the amount of light entering the eyes
-continuous with choroid
Pupil
-allow light to enter the eyes
-size controlled by iris
Retina
-contains many photoreceptors and nerve fibres
-innermost layer of the eyeball
Optic nerve
-nerve fibre are grouped together to form the optic nerve
-optic nerve transmits nerve impulses
Yellow spot
Central region of the retina is the yellow spot. High density of cone cells. No rod cells
Blind spot
Region where the optic nerve leaves the eyeball is called blind spot. No photoreceptors.
Lens
-transparent, elastic and biconvex in shape
-refract and focus light
-no capillaries
-made up of living cell. No nuclei
Suspensory ligament
-holds the lens
-held by ciliary body/circular ciliary muscle
Circular ciliary muscle
-controls the tension of the suspensory ligaments, changing the thickness of the lens
Aqueous humour and vitreous humour
Both maintains the shape of the eyeball and refract and focus light onto the retina
A: supplies oxygen and nutrients to the cornea and lens
Why is no blood capillaries in the lens important for the formation of clear image?
To let light pass through without obstruction to the retina.
Two changes in the lens at old age, that may result in poor vision
Lens become cloudy (cataract)
The lens become less elastic (long sight)
Why is the pupil always black?
All the light entering the eye is absorbed by the retina and choroid. No light can reflect out from the eyes.
Rod cells
Sensitive to dim light
Responsible for black-and-white vision
Located throughout the retina, none at yellow spot and blindspot
Cone cells
Sensitive to bright light
Responsible for colour vision
Concentrated at yellow spot, but none at blind spot
In bright light
The circular muscle of iris contract,
The radial muscle of iris relax,
The pupil constrict .
