Senses

THE SENSES

Hilgard morgan and Sartain explain that there are more than eight senses that we use to explore and learn about the world.Each of these senses has a specific sense organ within which are receptor cells or receiving mechanisms that are sensitive to certain stimuli in the environment.

The Eye Is the organ of vision, is sometimes compared to a camera lens because it works roughly the same way as the latter which focuses images of objects at various distances o the film as it moves toward or away from the place of the film.
The lens of the eye focuses light images on a sensitive surface.This surface in the eye is the retina,which is composed of rods and cones.

Rods which are cylindrical and number about 100 million,do not distinguish colors but are more sensitive to light than are the cones.
Cones which are conical in shape and more than six million in number,allow us to see the different wave lengths of light as different hues or colors.

Hilgard presents the process of seeing,light enters the eye through the cornea,a tough transparent membrane.The amount of light entering the eye is regulated by the diameter of the pupil,a small hole in front of the eye formed by the iris.The iris consists of a ring of muscles that can contract or expand,thereby controlling pupil size.

The Ear Is the sense organ of hearing which is sensitive to sound waves,the mechanical vibrations in the air.
There are three parts of the ear:The outer ear,Midle ear and the inner ear.The two main sensations in hearing are those of pitch and loudness.Sounds pounds on the eardrum which moves the three bones of the middle ear.the last of the three bones,the stirrup,vibrates the surface of the inner ear,which transmits the mechanical force of the fluid inside.
The outer ear consists of pinna,the protruding part of the ear which catches sound waves.these sound waves pass through the tubular auditory canal that leading to the eardrum.
The inner side of the eardrum is the cavity housing the bony transmitter of the middle ear the hammer the anvil and the stirrup.

The hammer is attached firmly to the eardrum and the stirrup to another membrane,the oval window.
The oval window conducts the sound waves to the cochlea,the auditory portion of the inner ear.
Because the oval window is much smaller than the eardrum,small movements at the eardrum are condensed into a magnified pressure at the ear window,which sets into motion the fluid inside the cochlea.

The Tongue Is the sense of taste or gustatory sense is excited by substances in solution in the mouth.The taste receptors are found in the taste buds,on the edges and toward the back of the tongue,the sense organ for taste.At the bottom of these taste buds are the taste cells which are sensitive to the taste stimuli.These taste cells are connected to nerve cells,so that when they are stimulated,a nerve impulse is sent on the brain.There are four different qualities of taste:salty,sweet,sour,bitter
Each of the approximatey 10,000 taste buds in the human adult tongue has 15 to 20 taste cells arranged in budlike form on its tip.

This taste cells continuously reproduce themselves every seven days.it is believed that as we got older,the number of our taste buds decreases.
Hence,older people are less sensitive to taste than do children.

Taste in everyday usage refers to more sensations than just those of taste.

The Nose The stimuli for the sense of smel or olfactory sense are gases that enter the nose.As we inhale, air stimulates the receptors in the olfactory epithelium,which is located in the upper reaches of the nose.if the air contains an odorous gas,certain reactions occur in the cells of the epithelium,causing nerve impulses to go to the brain.Only few molecules of gas need to enter the nose to be smelled.

Both taste and smell are often classed as the chemical senses since ther are stimulated by chemical substances.As has been pointed out, in taste the chemicals are in watery solutions bathing the tongue and surfaces of the mouth.In smell,they are gases that can be absorbed by the receptor cells of the nose.
Hilgard says that the insects and some higher animals secrete chemicals known as pheromones that float through the air to attract members of the species.These chemicals serve a communicative function.

The skin There are four skin or cutaneous senses:pressure,pain,warmth,and cold.The sense organs for the cutaneous senses are very small free nerve endings in the skin.When they are stimulated,nerve impulses are tripped off and they travel to the spinal cord and brain. These receptor organs are not equally distributed in the skin.From a numbe of studies,it is noted that pain spots are generally most numerous.Next most numerous are the pressure spots.A much smaller number of spots for cold have been found,while the least numerous are the warmth spots.

Another finding is that sensitive spots do not seem to be stable.There is difficulty encountered in stimulating exactly the same small spot that was touched before the second time.it could be included that different areas of the skin have different sensitivities to the four basic qualities of pain,pressure,cold,and warmth.
Our cutaneous senses are said to be our reality senses such that when we feel something with our skin,we are convinced that something is really there.