Question

Draw a neat and labeled diagram of the human ear. With the help of this diagram, explain the construction and working of the human ear.

Answer 1

• The ear is a sensitive organ of the human body. It’s all about the identification, amplification, and detection of sound. A further essential feature of the human ear is to maintain a sense of balance. The human ear is composed of three parts
• Internal ear
• External ear
• Middle ear
• ​
• External Ear-The outer ear is further divided into the following parts
• Auricle-The auricle consists of a thin base of elastic cartilage surrounded by a skin layer.
• External Auditory Meatus -It is a slightly curved canal that is protected by bone in its inner part and cartilage in the outer part. Lined with stratified epithelium and wax glands is the meatus or canal.
• Tympanic Membrane-This membrane separates the middle ear and the outer ear. This portion receives the sound waves and intensifies them. The center portion is known as the umbo.
• Middle ear -
• Ossicles are the three tiny bones connected to each other that transmit sound waves to the inner ear. These three tiny bones are stapes, malleus, and incus.
• Eustachian Tube is a tube that connects the middle ear to the back of the nose. It helps to maintain equal pressure in the middle ear which facilitates the proper transmission of sound waves.
• Internal ear
• It comprises two parts: Bony labyrinth and Membranous labyrinth

Bony Labyrinth

• The bony labyrinth comprises a vestibule, three semi-circular canals, and a spirally coiled cochlea. It is filled with perilymph.
  

Membranous labyrinth

• The bony labyrinth surrounds the membranous labyrinth. It comprises sensory receptors responsible for balance and hearing. The membranous labyrinth is filled with endolymph and comprises three semi-circular ducts, cochlear duct, saccule, and utricle. The sensory receptors include cristae, an organ of Corti, and ampullaris maculae.
  

• Working of Ear-
• Ears perform two main functions, hearing and equilibrium maintenance.
• The organ of the Corti (Cochlea) is responsible for hearing function.
• Maculae (Saccule and Utricle) are responsible for static equilibrium.
• Cristae (semicircular canals) are responsible for dynamic equilibrium.
• Mechanism of Hearing
• The pinna receives the sound waves and it reaches the tympanic membrane through the meatus.
• The eardrum vibrates and these vibrations get transmitted to the three ossicles present in the middle ear.
• Malleus, incus and stapes amplify the sound waves.
• These vibrations then reach the perilymph (scala vestibuli) through the oval window.
• Then the pressure waves get transferred to the endolymph of scala media and reach basilar membrane and then to the perilymph of scala tympani. This movement of fluid is facilitated by the round window present at the end of scala tympani.
• The basilar membrane movement causes rubbing of stereocilia against the tectorial membrane.
• Stereocilia are bent resulting in the opening of ion channels in the plasma membrane of hair cells. Glutamate, a neurotransmitter, is released due to Ca++ ion movement inside the cell.
• These neurotransmitters bind to the receptors of afferent neurons, which synapse with hair cells causing depolarisation of neurons. A nerve impulse is generated and transmitted to the auditory cortex of the brain through the auditory nerve (cranial nerve VIII).
• The brain analyses the impulses and we hear the sound. The brain not only recognises the sound but also judges the direction, loudness and pitch of the sound.