JSS3 Basic Science Lesson Note on Sense Organ

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TOPIC: SENSE ORGAN

We respond to changes or stimuli in our environment through the sense organs. Sense organs are parts of our body which include the eye, ear, nose, tongue and skin. These are organs that link us with our environment.

The eye

The amount of light entering the eye (right) is controlled by the pupil, which dilates and contracts accordingly. The cornea and lens, whose shape is adjusted by the ciliary body, focus the light on the retina, where receptors convert it into nerve signals that pass to the brain. A mesh of blood vessels, the choroid, supplies the retina with oxygen and sugar. Lacrimal glands (left) secrete tears that wash foreign bodies out of the eye and keep the cornea from drying out. Blinking compresses and releases the lacrimal sac, creating a suction that pulls excess moisture from the eye’s surface.

The eye enables us to see things around us such as size, colour etc. the structure of the eye consists of iris, pupil, cornea, aqueous humour, ciliary muscle, sclera, lens, retina, vitreous humour, suspensory ligament, blind spot and optic nerve. We have two eyes which function by binocular vision. We see objects when light rays enter the eye and form an image at the back of the retina. From the retina the message is passed through the optic nerve to the brain that tells us what we see. Some eye defects are glaucoma, short sightedness(myopia), long sightedness(hypermetropia) etc.

The ear

Structure of the Ear

The human ear consists of three sections: the outer ear, the middle ear, and the inner ear. The outer ear includes the auricle (pinna), the visible part of the ear that is attached to the side of the head, and the waxy, dirt-trapping auditory canal. The tympanic membrane (eardrum) separates the external ear from the middle ear, an air-filled cavity. Bridging this cavity are three small bones—the malleus (hammer), the incus (anvil), and the stapes (stirrup). The cochlea and semicircular canals make up the inner ear.

The ear helps us to hear sound and also to maintain balance. The ear has three major parts namely, outer ear, (pinna), middle ear and inner ear. Other parts of the ear include eternal auditory meatus and ear drum. We hear sound when sound enters the outer ear as vibrations in the air which pass through the ear canal and beat against the ear drum. The ear drum vibrates passing the vibration to the ear bones in the middle ear. Which sends the vibration to the cochlea fluid, which transfers it to the brain through the auditory nerve and the brain gives the interpretation of the type of sound.

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