Organ of hearing, how auditory sensations are created
nervous system is responsible for receiving, conducting and analyzing neural stimuli;
receptors receive light, mechanical and chemical stimuli;
information that travels from the receptor is transferred via sensory nerves to the encephalon or spinal cord, where it is analyzed.
to describe the build and functions of elements of the outer, middle and inner ear;
to explain the connection between how an ear is build and its functions;
to explain how auditory sensations are created;
Organ of hearing
Ears have two functions: they receive sounds and they inform about the location and movements of the head. Thanks to them we can detect and localize sounds, differentiate their pitch and intensity and register the placement of the body.
Ear consists of three parts: outer ear, middle ear and inner ear. The outer earouter ear is composed of auricle and outer auditory canal. Auricle is a fold of skin stretched on the scaffolding of cartilage. Its shape and folds on the surface are the adaptation to catch sound waves, enhance them and transfer them to the outer auditory canal – a canal closed with tympanic membranetympanic membrane. The inside of the canal consists of hairs and glands that produce fatty secretion – ear wax. Hairs keep away dirt, while ear wax keeps away microbes and dust.
Middle earMiddle ear is composed of tympanic cavity filled with air in which there are 3 auditory ossiclesauditory ossicles – smallest bones of our body: malleus, incus and stapes. One end of the malleus is attached to the tympanic membrane and its other end is connected with the incus, while the incus is connected with the stapes. Auditory ossicles are connected with each other by joints.
Tympanic cavity is connected with the throat via a canal called auditory tubeauditory tube (Eustachian tube), which is responsible for evening out the pressure between the middle ear and the environment. The difference in pressure appears for example when a plane takes off and lands, during mountain climbing, while listening to music using earphones and during explosion. It may cause pressure in the ear, pain and problems with hearing. Swallowing saliva means that the outlet of the auditory tube, which is normally closed, opens. Air is exchanged between the tympanic cavity and throat, the pressure in the middle ear evens out with the pressure of the environment and the unpleasant feeling in the ear disappears.
Inner earInner ear has a complicated shape. It consists of a vestibule, colchea and 3 semicircular canals. These are spaces and canals in the bones of a cranium, separated by the membrane. They are filled with liquid (endolymph). Inside the colchea canal there is the actual organ of hearing in form of sensory hair cells. Other parts of the inner ear are the sense of balance.
Explain why inflammation inside oral cavity, e.g. untreated tooth or runny nose, can be the cause of otitis media.
In the case of dual organs, it is usual that one of them is a bit stronger than the other. Examine which ear of your schoolmates from lower grades is stronger. Put a small bead into a matchbox and ask each person to decide how many beads are in the box while shaking it. Suggest them to bring the box closer to their ear. Write down which ear the students have chosen, how many people in the class are right‑eared and how many of them are left‑eared. The ear which we automatically put things close to is the dominant one.
How auditory sensations are created
The stimulus which works on the organ of hearing is a sound wave. Outer ear directs it onto the tympanic membrane. Under the influence of the energy of the acoustic wave, the tympanic membrane starts vibrating. These vibrations are transferred to malleus that is attached to the tympanic membrane. Thanks to the movable joint connections between the auditory ossicles, the vibrations move from the malleus onto the incus and then onto the stapes, which is connected with the inner ear. Vibrations of the stapes cause the liquid in the cochlear canal to vibrate. The sensory hair cells that line the inside of the cochlear canal become irritated which causes electrical impulses. Via auditory nerve they reach the auditory centre in the cerebral cortex where they are read and interpreted.
The assessment of the pitch of the sounds depends on the speed of their vibrations (frequency expressed in hertz, Hz). Sounds with high frequency are interpreted as high, whereas those of low – as low. Sensory epithelium is responsible for differentiating the pitch of the sounds. Different parts of the membrane, depending on their location in the cochlea, receive vibrations of different frequency. The brain differentiates information coming from different groups of cells and assesses the pitch of the sounds.
Select the correct sentences.
- While listening to music on headphones, our acoustic organ receives electrical stimuli.
- Inner ear has auditory sensory epithelium with auditory receptors.
- The auditory centre is located in the inner ear and consists of the auditory nerve.
- The balance organ informs about the location of the body in space.
Summary
Ear is the organ of hearing and balance.
The actual organ of balance are the receptor cells found inside the cochlear canal.
Receptor cells of the organ of hearing receive information in form of vibrations of the fluid that fills in the inside of the cochlear canal, whereas the cells of the organ of balance – the movement of the fluid in semicircular canals.
Auditory sensations are created in the auditory centre in the cerebral cortex.
3 semicircular canals that are the part of inner ear are responsible for receiving the stimuli connected with head movement or change in body position.
Human ear reacts to sounds with the frequency of 16 Hz‑20 thousand Hz and the volume up to 130 dB.
Describe the elements of the inner, middle and outer ear and the functions they have in the process of creating the auditory sensation.
Keywords
organ of hearing, organ of balance, sound wave
Glossary
błona bębenkowa – cienka, elastyczna błona łącznotkankowa oddzielająca ucho zewnętrzne od ucha środkowego, odpowiedzialna za wzmacnianie drgań i przekazywanie ich na kosteczki słuchowe
kosteczki słuchowe – młoteczek, kowadełko, strzemiączko; najmniejsze elementy kostne organizmu połączone ze sobą stawowo; przekazują drgania z błony bębenkowej do ucha wewnętrznego
ucho środkowe – część ucha składająca się z błony bębenkowej, jamy bębenkowej i 3 kosteczek słuchowych: młoteczka, kowadełka i strzemiączka; częścią ucha środkowego jest też trąbka słuchowa, który łączy jamę bębenkową z gardłem; ucho środkowe odpowiada za wzmacnianie drgań i przekazywanie ich do ucha wewnętrznego
ucho wewnętrzne – część ucha, w której znajduje się właściwy narząd słuchu (przewód ślimakowy) oraz zmysł równowagi (kanały półkoliste i przedsionek)
ucho zewnętrzne – część ucha odpowiedzialna za wychwytywanie i przekazywanie dźwięków do ucha środkowego
trąbka słuchowa – przewód łączący jamę bębenkową z gardłem; odpowiada za wyrównywanie różnicy ciśnień między uchem zewnętrznym i środkowym