The nervous system and sensory organs
The nervous system and sensory organs help the body receive stimuli form from the
environment and react to it.
There are 5 sensory organs:
® Sight
® Hearing
® Taste
® Touch
® Smell
Eye (sight)
The eyes are held in place in the eye socket by six different muscles. The eyelids and
eyelashes prevent foreign objects; dust and small insects from entering the eye. Regular
blinking provides fluid to the eye and prevent from drying out.
Sclera- Is the white part of the eye.
Cornea- Is a transparent layer that bends incoming light and helps the eye to focus.
Aqueous Humour - It’s the fluid in the space just behind the cornea
Iris- Is the colour of the eye. Small muscles contract and relax to make the pupil smaller
and bigger.
Pupil- It’s the black part centre of the eye which is actually a hole. Light enters the eye
through the pupil.
Lens- It focuses light to the retina which is at the back of the eye.
Retina
Retina -Contains millions of photoreceptors. Photoreceptors; are sensors that convert
light into electrical impulse which is then sent to the brain through the nerve.
There are 2 types of photoreceptors
® Rods: allow us to see in dim light
® Cones: Allows us to see colour
, Optic nerve -It sends signals to the brain which are perceived as colour, light and
darkness. The brain interprets the signals and forms the image that is seen
The lens reflects the light which changes the direction of objects. The image that falls on
the retina is upside down and the brain then flips the image the right way around.
How do we see?
1.Items reflect light. Light enters the eye through the cornea and the pupil.
2.Lens bends the light and focuses on the retina.
3.Photoreceptors convert the image to electrical. Impulse and this is sent to the brain
4.The brain interprets impulses as an image.
Ear (hearing)
The ear is divided into 3 parts:
® Outer ear; which contains pinna (ear lobe)
® Middle ear; which contains eardrum, 3 ossicles (hammer, anvil, stirrup)
® Inner ear; which contains semi-circular canals, cochlea, auditory nerve
1.Outer ear
Pinna: (ear lobe)
Funnels sound waves and reflects them into the external auditory canal. The auditory
canal is where sound waves move through it to the eardrum.
2.Middle Ear
Eardrum/ tympanic membrane:
It’s a thin membrane that vibrates due to sound waves.
Ossicles:
They are 3 tiny bones:
1.Hammer
2.Anvil
3.Stirrup
The vibrating of the eardrum makes the hammer move which knocks the anvil and the
anvil pushes against the stirrup which moves and sends sound waves to the cochlea.
The stirrup is the smallest bone in the human body
The nervous system and sensory organs help the body receive stimuli form from the
environment and react to it.
There are 5 sensory organs:
® Sight
® Hearing
® Taste
® Touch
® Smell
Eye (sight)
The eyes are held in place in the eye socket by six different muscles. The eyelids and
eyelashes prevent foreign objects; dust and small insects from entering the eye. Regular
blinking provides fluid to the eye and prevent from drying out.
Sclera- Is the white part of the eye.
Cornea- Is a transparent layer that bends incoming light and helps the eye to focus.
Aqueous Humour - It’s the fluid in the space just behind the cornea
Iris- Is the colour of the eye. Small muscles contract and relax to make the pupil smaller
and bigger.
Pupil- It’s the black part centre of the eye which is actually a hole. Light enters the eye
through the pupil.
Lens- It focuses light to the retina which is at the back of the eye.
Retina
Retina -Contains millions of photoreceptors. Photoreceptors; are sensors that convert
light into electrical impulse which is then sent to the brain through the nerve.
There are 2 types of photoreceptors
® Rods: allow us to see in dim light
® Cones: Allows us to see colour
, Optic nerve -It sends signals to the brain which are perceived as colour, light and
darkness. The brain interprets the signals and forms the image that is seen
The lens reflects the light which changes the direction of objects. The image that falls on
the retina is upside down and the brain then flips the image the right way around.
How do we see?
1.Items reflect light. Light enters the eye through the cornea and the pupil.
2.Lens bends the light and focuses on the retina.
3.Photoreceptors convert the image to electrical. Impulse and this is sent to the brain
4.The brain interprets impulses as an image.
Ear (hearing)
The ear is divided into 3 parts:
® Outer ear; which contains pinna (ear lobe)
® Middle ear; which contains eardrum, 3 ossicles (hammer, anvil, stirrup)
® Inner ear; which contains semi-circular canals, cochlea, auditory nerve
1.Outer ear
Pinna: (ear lobe)
Funnels sound waves and reflects them into the external auditory canal. The auditory
canal is where sound waves move through it to the eardrum.
2.Middle Ear
Eardrum/ tympanic membrane:
It’s a thin membrane that vibrates due to sound waves.
Ossicles:
They are 3 tiny bones:
1.Hammer
2.Anvil
3.Stirrup
The vibrating of the eardrum makes the hammer move which knocks the anvil and the
anvil pushes against the stirrup which moves and sends sound waves to the cochlea.
The stirrup is the smallest bone in the human body
