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Chapter: BIOLOGY (ZOOLOGY) Standard XI first year 11th text book Assignment topics question and answer Explanation Definition

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Ears (The organs of hearing) - The Sensory Organ

Ears (The organs of hearing) - The Sensory Organ
The ears are the organs of hearing and balance. They have three parts, namely external, middle and inner ears.

Ears (The organs of hearing) - The Sensory Organ

 

 

The Sensory Organs.

 

Living organism respond to several stimuli such as light, heat, sound, chemicals, pressure, touch, stretch and orientation. These stimuli are felt by specific receptors. The receptors convert the stimuli into impulses in the ner-vous systems.

 

The touch receptors in the skin are the simplest receptors. Such receptors are single nerve cells responding directly to the stimulus. Other re-ceptors are complex sense organs. On these organs the stimulus is chan-nelled into a receptive region of the organ. Among the several organs, the most important are the eyes and ears.

 

 

Ears (The organs of hearing)

 

The ears are the organs of hearing and balance. They have three parts, namely external, middle and inner ears.

 

External ear - The fleshy part outside the head is called the pinna. It is made up of elastic cartilage and skin. It is followed by the external auditorymeatus. This passage is lined with hairs and ceruminous glands. These glands produce cerumen or earwax. The hair and wax prevent foreign ob-jects from reaching the ear drum. The ear drum or tympanic membrane is a oval, three layered structure. It separates outer and middle ears.

 

Middle ear - It is an air filled cavity. It contains three auditory ossicles called the malleusincus and stapes. The handle of malleus is in contact with the inner surface of the ear drum. The head of the malleus is attached to the incus. While the stapes on one side is attached to the incus, its other side fits into theoval window. The oval window leads to the inner ear.


Inner ear - This region has tunnels and chambers inside the temporal bone called the bony labyrinth. The bony labyrinth contains three regions called the cochlea, vestibule and semicircular canals. The oval window found in between the middle and inner ears communicates with the vestibule of the inner ear. The organs of the inner ear perceive the sound.


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