The Human Eye

What are the three overlapping functions performed by the nervous system?

Sensory Input

Integration

Motor output

What does sensory input involve?

Light-detecting cells i.e. rods and cones of the retina in the eyes

What is Sensory Input?

Conduction of signals from sensory receptors to integration centre

Sensory Input is the conduction of signals from … to integration centre

sensory receptors

Sensory Input is the conduction of signals from sensory receptors to …

integration centre

What is Integration?

Process by which the information from the environmental stimulation of the sensory receptors is interpreted

What is information interpreted during integration then associated with?

With appropriate responses of the body

Where is integration carried out and what is it carried out by?

In the central nervous system (CNS) by the brain and spinal cord [in vertebrates]

What is Motor Output?

Conduction of signals from the Integration Centre, the CNS to the effectors, muscles or gland cells which actually carry out the body's response to stimulus

What is the integration centre in motor output?

CNS

What is the effector in motor output?

muscle cells or gland cells

From receptor to effector, how is information transmitted from one neurone to another?

a combination of electrical signals (nerve impulse) and chemicals (neurotransmitters)

What does the Peripheral Nervous System (PNS) do?

Communicate motor and sensory signals between the central nervous system and the rest of the body

Each eyeball lies in a socket in the skull called the …

orbit

The eyeball is attached to the eye socket by?

Six rectus muscles

What do the six rectus muscles do?

Enable the eyeball to rotate slightly within the socket

1

iris

2

upper eyelid

3

tear gland

4

sclerotic coat/sclera covered by conjunctiva

5

eye lashes

6

pupil

7

lower eyelid

8

remains of third eyelid (nicitating membrane)

9

tear sac empties into nasal cavity

10

tear ducts

1

choroid

2

vitreous humour

3

retina

4

fovea

5

optic nerve

6

blind spot

7

conjunctiva

8

suspensory ligament

9

lens

10

iris

11

aqueous humour

12

pupil

13

cornea

14

eyelash

15

ciliary body

16

eyelid

17

sclera

What type of membrane is the conjunctiva?

Thin transparent membrane

Mucous membrane

What is the conjunctiva continuous with?

skin of eyelids

What does the conjunctiva protect and from what?

protects cornea at front of eyeball against friction

What does the conjunctiva cover?

Covers sclera (white of eye) in front

Which part of the eye is a mucous membrane that secretes mucus and keeps the eyeball moist?

conjunctiva

What part of the eye forms a small bulge in front of the eye?

cornea

What is the cornea?

anterior end of sclera

Where does most refraction of light occur?

cornea

The cornea is the … portion of the sclera, allowing light to pass through it to reach the retina

transparent

The cornea is the transparent portion of the sclera, allowing light to pass through it to reach the …

retina

Where does the cornea refract light into?

pupil

What make up the wall of the eye?

Sclera

Choroid

Retina

What is the sclera?

Tough white outer layer of eyeball

What does the sclera do?

Protects eyeball against mechanical injury

What does the choroid contain?

blood vessels that supply the retina with oxygen and nutrients

Which part of the eye contains blood vessels that supply the retina with oxygen and nutrients?

choroid

What colour is the choroid?

Pigmented black

Why is the choroid pigmented black?

prevent internal reflection of light

What is the retina?

innermost layer of the eyeball that contains photoreceptors (rods and cones)

Which part of the eye contains photoreceptors?

retina

What do photoreceptors do?

detect stimuli

What are cones concerned with?

color vision in bright light

What are rods concerned with?

vision in dim light

What does the optic nerve do?

transmits nerve impulses (information) from photoreceptors to the brain

The iris is part of the …

choroid

The iris is the anterior end of the …

choroid

Which two parts of the eye are part of the wall of the eye and which part?

cornea = anterior end of sclera

iris = anterior end of choroid

What is the function of the iris?

controls the size of the pupil → controls amount of light entering eye

Which part of the eye controls the pupil size/how much light enters the eye?

Iris

What does the iris contain to control the size of the pupil?

two involuntary muscles: circular and radial muscles

Circular and radial muscles are an … action

involuntary

What do the circular and radial muscles control?

Size of pupil

What does the iris contain?

Pigment that gives the eye its colour

What is the pupil?

Hole in the centre of the iris that allows light to enter the eye

What is the function of the pupil?

Allow light to enter the eye

What is the function of the lens?

Focuses light rays onto retina by changing shape

Why are the lens elastic?

change thickness and shape to refract light onto retina

What type of structure do the lens have?

Transparent, biconvex, elastic

What is the function of the suspensory ligaments?

holds lens in position by attaching lens to ciliary body

How do the suspensory ligaments hold the lens in position?

By attaching lens to ciliary body

What does the ciliary body contain?

Muscles which control the curvature of the lens

What is the function of the ciliary body?

Control lens curvature and supports lens

What is the function of the vitreous humour?

supports lens

refracts light rays and keeps eyeball firm

The vitreous humour helps refract light onto the …

retina

What type of substance is the vitreous humour?

transparent, jelly-like

What type of substance is the aqueous humour?

transparent and watery fluid

What is the function of the aqueous humour?

refracts light and keeps eyeball firm

maintains shape of the anterior chamber of eyeball

Which part of the eye maintains shape of the anterior chamber of eyeball?

aqueous humour

Which parts of the eye are capable of refracting light?

cornea (into pupil)

lens (onto retina)

vitreous humour (onto retina)

Which part of the eye is used for protection?

conjunctiva (cornea at front against friction)

sclera (outer layer against mechanical injury)

vitreous humour (keeps eyeball firm)

aqueous humour (keeps eyeball firm)

What is the conjunctiva lubricated by?

Tears secreted by the lachrymal or tear gland

Where are the lachrymal or tear gland located?

outer corner of the upper eyelid

Where do tears flow out from?

Between eyelids and exposed part of the eyeball

Approximately how many rod cells and cone cells does the retina contain?

about 125 million rod cells and 6 million cone cells

How many types of photoreceptors (light-sensitive cells) are there?

Two types: rods and cones

What are rods and cones named after?

Their shapes

What is the fovea also known as?

yellow spot