The Sense Organs

The Sense Organs What you will learn in this section The main senses Definitons of receptor, stimulus and accommodation. Draw and name the parts of the eye. Explain the function of each part of the eye. Explain how vision works. Know the main eye defects and how they are corrected. Be able to label diagram of the ear and state the function of each part. Explain how hearing takes place. Understand the need for ear protection and some causes of deafness. Understand the role of the ear in balance.

The Sense Organs Animals have specialised senses to provide them with information about their environment. The five senses are sight, hearing, touch, taste and smell. A receptor is a cell that can detect a stimulus A stimulus is any change in your environment, e.g. light, sound. Show video clip on eye

The Sense Organs Answer the following questions on the video clip. Which sense organ gives us the most information? Why do we rely on sight? What conversion takes place for brains to interpret light? How is the amount of light controlled coming into the eye? Whats the pupil in low and bright light? What is the viteous humour? Where does the light focus? What part is sensitive to dim light, coloured light? How does light information get to the brain?

The Sense Organs Sense Organ Stimulus detected Sense Organ Sense Smell Taste Touch Hearing Sight Sense Nose Tongue Skin Ear Eye Organ chemicals [receptors in the nasal cavity detect vapours] chemicals [taste buds detect sweet, sour, salt and bitter]. touch, pressure, temperature and pain [receptors spread throughout body] sound [receptors in cochlea] light [by rods and cones in the retina] Stimulus detected Smell Taste Touch Hearing Sight Sense Nose Tongue Skin Ear Eye Organ Smell Taste Touch Hearing Sight Sense

The Sense Organs

The Sense Organs The EYE Eyelids can cover and protect the eyes. Conjunctiva Eyelids can cover and protect the eyes. Cornea Conjunctiva — thin transparent lining protecting the cornea. Cornea—front transparent part of the sclera. It focuses light rays on the retina.

The Sense Organs Retina Sclera Sclera—tough fibrous outer layer – the ‘white’ of the eye; it maintains the shape of the eyeball. Choroid Retina Choroid—contains blood vessels supplying food and oxygen to the cells of the eye. Retina—the innermost layer that contains the receptor cells [rods and cones].

The Sense Organs The fovea is where our best vision is [mainly cones] Fovea The front region of the choroid is specialised into the iris Iris Iris—contains blood vessels and melanin [giving us our eye colour], and controls the amount of light entering the eye [through the pupil].

The Sense Organs Pupil In bright light, pupil constricts. In dim light, the pupil dilates.

The Sense Organs Ciliary muscle Suspensory ligaments Lens Ciliary body [muscle] — thickened edge of the choroid that controls the shape of the lens Ciliary muscle Suspensory ligaments Lens Suspensory ligaments —hold the lens in place. Lens—like a magnifying glass, it focuses the light rays on the retina.

The Sense Organs Lens—focuses the light rays on the retina. Accommodation is the ability of the lens to change its shape (focal length) to form a clear image.

LEARNING CHECK Name the 5 senses and the organs involved. Name the 3 main layers of the eye and the function of each. What is the function of the [a] iris, [b] lens, [c] cornea, [d] fovea What is accommodation?

The Sense Organs Close Vision For close vision, the ciliary muscle contracts, the suspensory ligaments relax, the lens becomes thicker.

Distant Vision When the eye is at rest, the lens is thin, has a long focal length and is adapted for seeing distant objects.

Accommodation is the ability of the lens to change its shape (focal length) to form a clear image.

Seeing things at different distances For distant objects, the ciliary muscle relaxes and so the suspensory ligaments pull tight, pulling the lens thinner – the light doesn’t bend as much. For close objects the ciliary muscle contracts, allowing the lens to go fat, thus bending the light more.

The Sense Organs Aqueous humour Vitreous humour Aqueous humour— watery liquid that supplies the lens and cornea with nutrients and helps keep the shape of the cornea and lens. Aqueous humour Vitreous humour Vitreous humour—gel that helps maintain the shape of the eye.

The Sense Organs Optic nerve Blind Spot When light rays focus on the retina, receptor cells are stimulated and impulses are carried along the optic nerve to the brain. Optic nerve Blind Spot Blind spot—where the optic nerve fibres pass through the retina and there is no room for receptors.

The Sense Organs Eye Defects Long-sighted : You are long-sighted if you can clearly see objects a long way off, but you cannot see things close by. Reading glasses [convex lenses] can correct the problem.

The Sense Organs Eye Defects Short-sighted You are short-sighted if you can clearly see objects close to you, but you cannot see things in the distance. Glasses with concave lenses can correct the problem.

LEARNING CHECK Explain how the ciliary body and suspensory ligaments alter the lens. What is the function of the [a] humours, [b] optic nerve? If you are longsighted, what does it mean? What could be a possible cause? What type of lens can rectify it?

The Sense Organs Look at the video clip on the ear and answer the following questions. What are the three parts to the ear? What part of our ear catches the sound? What does ear wax do for us? What is the eardrum and how does it work? What are the ossicles and what do they do? What does the cochlea do? How is the sound sent to the brain?

The Sense Organs

The Sense Organs The EAR Eardrum Pinn a Ear Cana l Pinna—outer visible ear, funnels sound into the ear canal. Ear canal —tube leading to the ear drum. It has hairs and wax glands to trap dirt and germs. Eardrum Pinn a Ear Cana l Eardrum—membrane of skin that vibrates when sound waves hit it.

The Sense Organs Middle Ear Ossicles Middle ear—air-filled cavity containing three small bones [ossicles] and the Eustachian tube Ossicles— 3 small bones [hammer, anvil and stirrup], that amplify the sound. Eustachian tube—keeps air pressure equal on each side of the eardrum. It opens when we swallow, cough, etc. Eustachian tube

The Sense Organs Inner Ear Semi-circular canals Cochlea Inner ear—contains a coiled, fluid-filled tube called the cochlea and the semi-circular canals. Cochlea—contains nerves that convert sound vibrations into electrical impulses. Semi-circular canals—help us keep our balance and posture. Cochlea

The Sense Organs The pinna (ear lobe) channels the sound (vibrations in the air) towards the eardrum, which then vibrates. In turn, this vibrates the hammer, anvil and stirrup bones, which amplify the sound.

The Sense Organs The stirrup pushes on the oval window of the cochlea, moving the liquid inside. Special hairs on 30,000 receptor cells detect the movement and send signals to the brain along the auditory nerve. The brain interprets these as sounds, and we ‘hear’.

The Sense Organs Semi-circular canals— help us keep our balance and posture. The three semicircular canals are curved tubes, each about 15mm long and filled with fluid. Show video clip on balance

The Sense Organs Head movements are detected by nerves inside the canals. The brain responds by sending messages through the cerebellum, which trigger reflex actions in our muscles. This helps us keep our whole body balanced as we move.

The Sense Organs Deafness Ear Defects Deafness can be caused by long exposure to a high level of noise, drugs, or ear infections. Damage to the eardrum, ossicles [bones], and cochlea, which can be caused by loud sounds, produces incurable deafness. Ear Defects Workers exposed to prolonged sounds of over 90 decibels [dB] are obliged by law to wear ear protection. Any exposure to 140 dB causes immediate damage to hearing.

The Sense Organs The SKIN as a Sense Organ

LEARNING CHECK What is the function of the [a] pinna, [b] 3 ossicles, [c] cochlea, [d] semi- circular canals, [e] eustachian tube? Outline how vibrations in the air are eventually “heard” by our brain. Name a common ear defect. Give some possible causes & treatments. How might you reduce your risks of this defect? Show video clip covering human responses – endocrine, nerve and sense organs.