Sensory organs

Touch— the skin

Touch consists of several distinct sensations communicated to the brain through specialised neurons and receptors in the skin. These include; pressure, temperature, humidity, vibration and pain.

Taste — the tongue

The receptors for taste lie in the tongue and are able to identify four types of taste: sweet, salty, bitter, sour. These taste ‘pores’ are found on papillae on the tongue and when they are stimulated by chemicals in the saliva they send impulses to the brain to be interpreted by a specific area of the cortex.

Smell — the nose

The receptors for smell are located in the top part of each nasal cavity, known as the olfactory mucosa. Sniffing helps bring more air (containing smells) over this part. Olfactory neural pathways are closely linked to the brain which means that smells or odours can vividly recall memories and arouse an emotional response.

Note: Taste and appreciation of foods is influenced by the sense of smell and the temperature and texture of foods.

Hearing and balance — the ear

The ear is divided into three main areas: the external ear; the middle ear; and the inner ear. The outer and middle ear is involved in hearing only. The inner ear functions in both balance and hearing. The external ear is composed of the pinna and the external auditory canal. In the walls of the external auditory canal are glands that secrete earwax.

Sound waves entering the external auditory canal eventually hit the eardrum or the tympanic membrane and cause it to vibrate. The eardrum separates the outer and the middle ear. The middle ear is a small space containing the Eustachian tube and three small bones called the ossicles. The eustachian tube connects the middle ear and the throat. The ossicles amplify sound received from the eardrum and transmit it to the inner ear. The inner ear consists of the semi-circular canals and the cochlea, which contains fluid. In the cochlea, fluid carries sound waves received from the middle ear to the auditory nerve. The auditory nerve carries the message to the brain. The semi-circular canals are involved in balance. They sense the head’s position and changes in position and send messages to the brain.

Vision — the eye

The eye is a hollow sphere. The accessory structures of the eye include the extrinsic eye muscles, the tear glands and ducts, the eyelids, the eyelashes and the conjunctiva. Light rays from a distant object are nearly parallel as they reach the eye and can be focused without change to the shape of the lens (convex). Diverging light rays from close objects require that the lens bulges more to focus the image on the retina. This ability of the eye to focus specifically for close objects is called accommodation.

Activity

Explore an overview of the eye and then watch the video below.