Hearing is one of the five senses. It is a complex process of picking
up sound and attaching meaning to it. The ability to hear is critical
to understanding the world around us.
The human ear is a fully developed part of our bodies at birth and
responds to sounds that are very faint as well as sounds that are very
loud. Even before birth, infants respond to sound.
So, how do we hear?
The ear can be divided into three parts leading up to the brain – the outer ear, middle ear and the inner ear.
The outer ear consists of the pinna, or auricle, and the ear canal (external auditory meatus).
The pinna – the part of the "ear" that we see on each side of our
heads – is made of cartilage and soft tissue so that it keeps a
particular shape but is also flexible. The pinna serves as a collector
of sound vibrations around us and guides the vibrations into the ear
canal. It helps us decide the direction and source of sound. Sound travels down the ear canal,
striking the eardrum and causing it to move or vibrate.
The middle ear is a space behind the eardrum that contains three small bones called ossicles.
This chain of tiny bones is connected to the eardrum at one end and to
an opening to the inner ear at the other end. Vibrations from the
eardrum cause the ossicles to vibrate which, in turn, creates movement
of the fluid in the inner ear.
The inner ear contains the sensory organs for hearing and balance. The cochlea is the hearing part of the inner ear. The semicircular canals in the inner ear are part of our balance system.
The cochlea is a bony structure shaped like a snail and filled with two fluids (endolymph and perilymph). The Organ of Corti is the sensory receptor inside the cochlea which holds the hair cells, the nerve receptors for hearing.
The mechanical energy from movement of the middle ear bones pushes in a membrane (the oval window)
in the cochlea. This force moves the cochlea's fluids that, in turn,
stimulate tiny hair cells. Individual hair cells respond to specific
sound frequencies (pitches) so that, depending on the pitch of the
sound, only certain hair cells are stimulated.
Signals from these hair cells are changed into nerve impulses. The
nerve impulses are sent out to the brain by the cochlear portion of the
auditory nerve. The auditory nerve carries impulses from the cochlea to a relay station in the mid-brain, the cochlear nucleus. These nerve impulses are then carried on to other brain pathways that end in the auditory cortex (hearing part) of the brain. The brain then interprets these electrical signals as sound.
Also housed within the inner ear are the semicircular canals, the utricle, and the saccule. These
structures help control one’s sense of steadiness or balance. These
balance organs share the temporal bone space with the cochlea. These
organs also share the same fluid that is in the cochlea.
Hearing is one of the five senses. It is a complex process of picking
up sound and attaching meaning to it. The ability to hear is critical
to understanding the world around us.
The human ear is a fully developed part of our bodies at birth and
responds to sounds that are very faint as well as sounds that are very
loud. Even before birth, infants respond to sound.