Form 2 Chapter 1.1

7/29/2019 Form 2 Chapter 1.1

1/8

Form 2 ScienceChapter 1: The World Through Our Senses

1

Sensory Organs, Stimuli and Senses

Response to stimuli

Sense Sensory Organ Stimuli Detected

Touch Touch, pressure, pain, heat, cold

Taste Taste (chemicals in food)

Smell Smell (Chemicals in air)

Sight Light

Hearing Sound

Sense of Touch - Skin

Pressure receptor Pain receptor Cold receptor

Touch receptor Heat receptor Sweat glands

(f)

7/29/2019 Form 2 Chapter 1.1

2/8


2

Receptor Function

Sensitive to touch. Many are found in hairless areas such as lips

and fingertips.

Sensitive to pain. They lie in the epidermis, close to the surface

to detect the slightest pain.

Sensitive to heat.

Sensitive to cold. Together with heat receptors, they enable us

to know how hot or cold an object is.

Sensitive to heavy pressure. Found deep within the skin

especially at the soles of the feet. Together with the touch

receptors, they enable us to identify the texture and weight of an

object.

Sensitivity of the

skin depends on:

The larger the concentration of

receptors, the more sensitive the skin isThe thicker the epidermis, the

deeper the receptors lie in the skin,

thus the less sensitive the skin is

Parts of body which is more sensitive Parts of body which is less sensitive

Elbows Back of body Lips Knees Fingertips

7/29/2019 Form 2 Chapter 1.1

3/8


3

Sense of Touch - Nose

Smell Receptor Nasal cavity Brain

Adaptation of the nose to detect smell

The smell receptors are

always covered with

mucus.Smells must dissolve in the

mucus before they can be

detected.

Smell receptors are located at

the roof of the nasal cavity.

This position allows thereceptors to have the maximum

exposure to the air current.

Sense of Touch - Tongue

How tastes are detected:

As we chew the food, chemicals in the food

dissolve in the saliva.

The dissolved chemicals stimulate the taste

receptors in the taste buds to produce

nerve impulses that are sent along nerves

to the brain.

The brain interprets the impulses andidentifies the taste of the food.

7/29/2019 Form 2 Chapter 1.1

4/8


4

Sense of Touch - Ear

Part Structure Function

Outerear

Pinna Shaped like a funnel.

Made of cartilage and

skin.

Ear /

auditory

canal

A 2.5cm long, narrow

tube lined with hair

Middleear

Eardrum A thin, stretched

membrane at the end ofthe ear canal.

Ossicles 3 small bones that

connect the eardrum

and oval window.

Oval

window

A thin, small membrane

at the end of the

ossicles.

Eustachiantube

A narrow tube thatconnects the middle ear

to the back of the throat.

Innerear

Cochlea A coiled tube filled with

fluid and lined with hair-

like sensory throat.

Auditory

nerve

Nerve fibres that

connect the ear to the

brain.

Semi-

circular

canals

3 semi-circular tubes

situated at right angles

to each other. Contain

fluid and sensory cells.

7/29/2019 Form 2 Chapter 1.1

5/8


5

Mechanism of hearing:

Sound reaches the ear Sounds is heard

7/29/2019 Form 2 Chapter 1.1

6/8


6

Sense of Touch - Eyes

7/29/2019 Form 2 Chapter 1.1

7/8


7

Parts Structure Function

Sclera White, tough outer layer.

Fibrous and opaque.

Choroid Black, middle layer. Rich with

blood vessels.

Retina Innermost layer.

Contains photoreceptors known

as cones and rods.

Cornea Curved transparent layer of the

sclera in front of the eye.

Conjunctiva Thin transparent layer in front of

the cornea.

Iris Coloured front part of the eye

that is continuous with the

choroid.

Consist of muscles.

Pupil The hole in the centre of the

iris.

Lens Transparent, biconvex andelastic disc.

Ciliary body Muscles attached to the lens.

Suspensory

ligaments

Strong fibres that connects the

lens to the ciliary body.

Aqueous Humour Watery, transparent liquid

between the cornea and lens.

Vitreous humour Thick, transparent jelly-like

substance inside the eyeball

Yellow spot (fovea) The most sensitive spot on the

retina.

Located directly opposite the

pupil.

Blind spot The spot where the optic nerveleaves the eye.

Has no photoreceptor at all.

Optic nerve Consists of nerves that connect

the retina to the brain.

7/29/2019 Form 2 Chapter 1.1

8/8


8

Mechanism of sight:

Light rays from object Object is seen

Documents

Form 2 Chapter 1.1