SENSE ORGANS

TONGUE, NOSE, SKIN SEPTEMBER 29, 2015

Our sense organs (nose, eyes, ears, tongue, and skin) take in information and send it to the brain for processing. Our senses collect information about our environment or may detect changes within the body.

SENSE ORGANS AND STIMULI

A stimulus must excite receptors in our sense organs. The receptors send nerve impulses along sensory nerves to the brain which tells you what the stimulus is. If a person loses one of their senses, the remaining senses of these persons become “heightened” in order to “compensate” for the sense that is lacking.

TONGUE Taste is detected by the 10,000 tiny, delicate taste buds in the mouth, located on different areas of the tongue which detect four basic tastes: sour, sweet, bitter and salt. Chemicals in the food we eat stimulate the taste buds and nerves in the tongue send messages to the brain which tells us what it is that is being tasted.

THE TONGUE

THE TONGUE

Peppery, hot, cold etcetera are sensations felt by the heat sensors in the tongue and the skin of the mouth.

TASTEBUD

NOSE Chemical molecules in the air are detected by nerves at the back of the throat called olfactory receptors. There are seven different olfactory receptors, and each one detects a particular odour. Impulses from the olfactory receptors are sent to the olfactory nerve which carries the inputs to the brain. The brain then interprets what the odor is.

THE NOSE

OCTOBER 1, 2015 INTEGRATED SCIENCE 11 DM SKIN AND EAR OCTOBER 1, 2015 INTEGRATED SCIENCE 11 DM

THE SKIN Recall the layers of the skin so far.

The body has about twenty different types of nerve endings that all send messages to your brain (e.g. heat, cold, pain, pressure or touch receptors).

Pain receptor Light touch receptor Temperature receptor Pressure receptor

Some areas of the body are very sensitive because they have more nerve endings (e.g hands, lips, face, neck, tongue, fingertips and feet). Your tongue is not as good at sensing hot or cold so its easy to burn it. The least sensitive part of your body is the middle of your back.

THE EAR The ear has two functions: For hearing For balance The three parts of the ear are: the outer ear the middle ear the inner ear

THE EAR Outer ear includes the pinna (made of cartilage and skin) and the auditory canal.

Middle ear contains the ear drum, ossicles (smallest bones in the body), and the oval/ round window. The middle ear is connected to the back of the throat by the Eustachian tube which helps to maintain pressure as we swallow.

THE OSSICLES (smallest bones in the body)

THE EAR The inner ear consists of the semi-circular canals, the cochlea, and the auditory nerves.

How We Hear Sound waves travel from air into the pinna where they create the following vibrations like a ripple effect in the ear: Auditory canal → ear drum → malleus (hammer)→ incus (anvil)→ stapes (stirrup) → oval window → fluid and sensitive cells in cochlea → auditory nerves → brain for interpretation.

Balance The semi-circular canals help with keeping balance. They are filled with fluid and are at right angles to each other. The semi-circular canals are sensitive to the movements of the head. When we move our head, the liquid moves. The brain interprets the movements of the liquid, then decides what function(s) is necessary to maintaining balance.

THE EYE AND SIGHT

The human eye is responsible for the sense of sight. The process of seeing requires the eyes to recognize external properties, such as color and movement, and then share the information with the brain.  

Important parts of the eye are: Eyelid: protects the eye Sclera: white part of the eye Iris coloured part of eye Cornea: transparent covering at front of eye Pupil: Hole in the iris Lens: helps to bend light rays Retina: Image forms here Optic nerve: Image sent to brain

RODS AND CONES The light sensitive cells of the retina are the rods and cones. The rods help us to see black and white and are useful in dim light). The cones help us to see colours.

The blind spot of the eye is an area of the retina that lacks rods and cones, so no image is formed at this region. The fovea (or yellow spot) is a part of the retina rich in cones, therefore, our best vision is there.

SEEING Images are formed on the eye when: Light enters the eye through the cornea. The rays are bent slightly. Light passes through the pupil and through the lens. The light rays are bent again as they pass through the lens. Light passes through the vitreous humor and strikes the retina. The image created by the lens is focused on the retina. Image is created when rod and cone cells are stimulated by the light rays. Impulse from the rods and cones stimulates the optic nerve, which carries the impulse from the retina to the brain. Impulse arrives at the vision center of the cerebrum.

IMAGE FORMED IN THE EYE

Note that the image formed on the retina is inverted (upside down), reversed (backwards) and smaller than the object. Therefore, a part of the brain interprets the image so that we see what the object really looked like.

FOCUSING ON OBJECTS In a normal eye we can see near and distant objects clearly. For this to happen, the shape of the lens must change. This is called accommodation.

When we look at near objects the lens must be short and fat. For this to happen, the suspensory ligament relaxes and the ciliary muscles contract.

When we look at a distant object, the lens must be long and thin. For this to happen, the suspensory ligament contracts and the ciliary muscles relax.

BRIGHT AND DIM LIGHT To protect out eyes, the pupils become smaller in bright light. In dim light, however, the pupil gets larger to let in enough light to see by.

SIGHT DEFECTS AND CURES

MYOPIA Also called nearsightedness or shortsightedness. The nearsighted eye is too long from front to back which causes the object to be focused in front of the retina instead of on it. Image is clear only when object is close to the eye. Corrective lenses (concave or diverging lens) spread out the light rays so that they fall further and reach the retina.

HYPERMETROPIA Also called farsightedness or longsightedness. The farsighted eye is too short from front to back which causes the image to be focused behind the retina, not on it. Image clear when object far away. Corrective lenses (convex or converging lens) bend the light rays so that they are focused directly on the retina.

ASTIGMATISM If the surface of the cornea is uneven and not smooth, it will bend light rays unevenly and the image formed on the retina will be blurred. Correct by wearing glasses or contacts with irregularly curved lenses.

CATARACT The lens becomes cloudy over time so light cannot pass through easily to the retina. Lens may be removed and may or may not be replaced.

GLAUCOMA Pressure in the eye. A blockage in the eye causes aqueous humour to build up and distort the image. Corrected by making a drainage canal.