Anatomy and Physiology of Human Ear
The area of biology known as anatomy is dedicated to the study of the composition and organization of living things. The structural organization of living things is the focus of the natural science field of anatomy. It is an old science with roots in the Paleolithic era. Given that these are the processes via which anatomy is produced, whether over short- and long-term timescales, comparative anatomy, evolutionary biology, and phylogeny are intrinsically linked to anatomy. A common pairing of related disciplines is anatomy and physiology, which examine the structure and operation of organisms and their components, respectively. One of the fundamental basic disciplines used in medicine is human anatomy.
The human ear is an organ of equilibrium and hearing that analyses and detects sound via transduction (or the conversion of sound waves into electrochemical impulses) and keeps the body balanced (equilibrium). Similar to other mammals, humans have sensory organs in their ears that perform two very distinct tasks: hearing and maintaining balance and coordination of head and eye movements. The outer, middle, and inner ear are the three distinct anatomical components of the ear. The auricle, also known as the pinna, protrudes from the side of the head, and the short external auditory canal—whose inner end is closed by the tympanic membrane, also known as the eardrum—makes up the outer ear. The outer ear’s job is to gather sound waves and direct them toward the tympanic membrane. A small, air-filled hollow in the temporal bone houses the middle ear. The auditory ossicles, also known as the malleus, incus, and stapes, are a chain of three minuscule bones that span them. The inner ear also referred to as the labyrinth since Galen’s time (2nd century CE), receives sound from the tympanic membrane through the ossicular chain. It is a complex network of caverns and fluid-filled channels buried deep within the temporal bone’s petrous rock. The vestibular apparatus, which consists of the vestibule and semicircular canals and includes the sensory organs of postural equilibrium, and the snail-shell-like cochlea, which contains the sensory organ of hearing, make up the two functional units that make up the inner ear. The eighth cranial nerve, often known as the vestibulocochlear nerve, has extremely specialized terminals that make up these sensory organs.
The auricle, which is the outermost portion of the ear, has a structure that distinguishes the human ear from the ears of other mammals most noticeably. The auricle in humans is a nearly primitive, usually immovable shell that is located close to the side of the head. It is made up of a delicate plate of yellow elastic cartilage that is tightly adhered to the skin. A shallow irregular funnel is created by the cartilage’s well-defined hollows, ridges, and furrows. The concha is the largest depression that immediately connects to the acoustic meatus or external auditory canal. Two tiny projections, the tongue-like tragus in front and the antitragus in back, partially cover it. The helix, a noticeable ridge rising from the concha’s floor and continuing as the upper portion of the auricle’s incurved rim, is visible above the tragus. The concha is surrounded by an inner, concentric ridge known as the antihelix, which is separated from the helix by a furrow known as the scapha, also known as the helix’s fossa. The Darwin’s tubercle, a little elevation that can be observed in some ears along the top, posterior part of the helix, is a remnant of the folded-over point of an ancient human ancestor’s ear. The only portion of the outer ear that is cartilage-free is the lobule, the fleshy lower portion of the auricle. The auricle is attached to the skull and scalp by a number of tiny, primitive muscles. Most people lack the ability to use these muscles, while some people can deliberately contract them to make little motions. A tube-shaped structure called the external auditory canal extends inward from the concha’s floor and ends blindly at the tympanic membrane. The canal’s wall is made up of bone for its inner two-thirds and cartilage for its outer third. Skin lines the passage’s whole length (24 mm, or roughly 1 inch), and it also covers the tympanic membrane’s outer surface. The canal is lined with tiny hairs that are pointed outward and modified sweat glands that create cerumen, or earwax, which deters insects from entering it.
Tympanic Membrane and Middle Ear
The external canal’s end is crossed obliquely by the eardrum, a thin, semitransparent membrane that serves as the division between the middle and outer ear. It has a diameter of 8–10 mm (0.3–0.4 inch), a flattened cone form, and an inward-pointing tip. Its exterior hence has a concave shape. The membrane’s border is thickened and linked to a groove in the tympanic annulus, a gap in an incomplete ring of bone that almost completely encircles and stabilizes the membrane. The pars flaccida, the very topmost small piece of the membrane where the ring is open, is lax, but the pars tensa, the vast majority of it, is tightly stretched. The tympanic membrane’s appearance and movement play a significant role in the diagnosis of middle ear illness, which is particularly prevalent in young children. The healthy membrane appears translucent and pearl-gray when viewed via an otoscope, occasionally with a pinkish or yellowish hue. There are three layers in the tympanic membrane as a whole. The external canal and the skin’s outer layers are one and the same. The middle ear’s tympanic cavity’s lining and the inner layer of the mucous membrane are one continuous layer. The membrane’s stiffness and tension are provided by a layer of fibrous tissue between these two layers, which is made up of circular and radial fibers. The membrane is densely populated with sensory nerve fibers and blood arteries, making it extremely sensitive to pain.
The middle ear’s cavity is a tiny, air-filled area. It is divided into an upper and a lower chamber, the epitympanum above and the tympanum (tympanic cavity) proper below, by a minor constriction. The terms “atrium” and “attic,” respectively, are also used to describe these spaces. An approximately rectangular room with four walls, a floor, and a ceiling describes the middle-ear space. The tympanic membrane creates the outside (lateral) wall of the middle-ear space. The middle ear cavity is separated from the cranial cavity and brain above the ceiling (superior wall), a thin bone plate. A thin bony plate known as the floor (inferior wall) separates the middle ear chamber from the jugular vein and the carotid artery below. The mastoid antrum, located behind the external auditory canal and the auricle, and the small air cells of the mastoid process are both accessible through an opening in the back (posterior) wall, which also partially divides the middle-ear cavity from another cavity. The Eustachian tube, also known as the auditory tube, which connects the middle ear with the nasopharynx, has its entrance in the front (anterior) wall. The bone otic capsule of the inner ear includes the inner (medial) wall, often known as the labyrinth, which divides the middle ear from the inner ear. Two tiny apertures, called fenestrae, are located one above the other. The oval window in the upper one is covered by the stapes’ footplate. The round window, which is on the lower one, is protected by a thin membrane.
The short ossicular chain, made up of three small bones, crosses the middle ear cavity and connects the oval window and inner ear with the tympanic membrane. They are the malleus (hammer), incus (anvil), and stapes (from the outside in) (stirrup). The incus looks more like an anvil than incus, and the malleus more closely resembles a club than a hammer. Ligaments that support these bones allow them to move freely as they transport sound from the tympanic membrane to the inner ear.
The handle and the head make up the malleus. From the middle (umbo) to the upper edge, the handle is securely fastened to the tympanic membrane. Three tiny ligaments hold the head of the malleus to the walls and roof of the epitympanum, where it is hanging in the space between the malleus and incus right above the upper rim of the tympanic annulus. Another tiny ligament anchors the incus’ short process (crus) in the fossa incudis, a shallow depression in the cavity’s back wall. Near its terminus, the lengthy incus process bends and bears a tiny bony knob that joins the head of the stapes in a loose ligament-enclosed joint. The smallest bone in the body is the stapes. It is only 3 mg in weight and around 3 mm (0.1 inch) length (0.0001 ounce). It is approximately horizontal and is at an angle to the incus process. Although the elastic annular ligament surrounds its base, or footplate, which is free to vibrate in order to transport sound to the labyrinth, it fits neatly in the oval window.
The middle ear has two extremely small muscles. The lengthier muscle, known as the tensor tympani, emerges from a bony canal right above the opening of the eustachian tube and switches direction by running backward and then outward as it crosses a bone projection that resembles a pulley. The upper portion of the malleus’ handle is where this muscle’s tendon is joined. Tympanic membrane tension is maintained or increased when the tensor tympani contracts, pulling the malleus inward. The back wall of the middle ear cavity gives rise to the shorter, stouter stapedius muscle, which extends forward and joins to the neck of the stapes’ head. The stapes tend to tip backward during its reflex contractions as if trying to drag it out of the oval window. As a result, it specifically lowers the volume of sounds entering the inner ear, particularly those with lower frequency.
The facial nerve, the seventh cranial nerve, travels from the brainstem to the muscles of the face, taking a somewhat circuitous route through the facial canal in the petrous part of the temporal bone. The chorda tympani nerve, a small but significant branch, passes between the long process of the incus and the handle of the malleus as it emerges from the canal into the middle-ear cavity. It then proceeds along the inner surface of the pars tensa of the membrane. It looks to be relatively naked since it is now just covered by the tympanic mucous membrane. After that, it continues through the anterior bony wall, supplying the anterior two-thirds of the tongue with taste-related sensory fibers and the salivary glands with parasympathetic secretory fibers.
The Eustachian tube, which is between 31 and 38 millimeters (1.2 and 1.5 inches) in length, extends downward and inward from the tympanum to the nasopharynx, the area above the soft palate that is behind and continuous with the nasal passages. The tube is small and bone-enclosed at its top end. It widens and turns cartilaginous as it gets closer to the pharynx. The mucous lining of the tympanum, which continues into the middle ear, is coated in cilia, tiny hairlike projections whose coordinated rhythmical sweeping motions facilitate the rapid drainage of mucous secretions to the pharynx.
In order to keep the air pressure on either side of the tympanic membrane equal, the eustachian tube aids in middle ear ventilation. When at rest, the tube is closed; nevertheless, it opens during swallowing to allow for unconscious pressure adjustment of small variances. The tube might stay completely closed during an airplane takeoff or underwater dive. By performing a forced expiration while tightly closing your mouth and nose, you can typically get rid of the discomfort that comes with the increase in external pressure. The Valsalva manoeuvre is what causes the tube to open by increasing the air pressure in the pharynx.
The membrane labyrinth is located inside the bone labyrinth, and there are actually two labyrinths inside the inner ear. The vestibule, the three semicircular canals, and the spirally coiled cochlea make up the bone labyrinth’s central chamber. A corresponding portion of the membranous labyrinth is contained within each structure, taking up only a small portion of the available space: the vestibule houses the utricle and saccule, each semicircular canal houses its corresponding semicircular duct, and the cochlea houses its corresponding cochlear duct. The watery fluid known as perilymph surrounds the membranous labyrinth and fills the remaining area. The cerebrospinal fluid of the brain and the aqueous humour of eye are similar, but not identical, to this blood plasma-derived substance. The membranous labyrinth is lined with epithelium, like most hollow organs (a sheet of specialized cells that covers internal and external body surfaces). Endolymph, the substance that fills it up, has a significantly different ionic composition than perilymph. The endolymph and perilymph do not mingle because the membrane labyrinth is a closed system.
Cochlea (Auditory organ)
- The cochlea is a tortuous part of the membranous labyrinth that looks like a snail.
- The cochlea is composed of three tubes, the superior vestibular duct or scala vestibular, the middle cochlear duct or scala media, and the inferior tympanic or scala tympani, separated by thin membranes.
- The scala vestibule is filled with perilymph and ends with an oval window.
- The scala tympani is also filled with perilymph and ends with the opening of the middle ear – the round window.
- The Reissner’s membrane separates the scala mesogastric and the scala vestibular. The middle floor is filled with endolymph and contains the organ of Corti, the organ of hearing.
- Each organ of Corti contains approximately 18,000 hair cells. Hair cells reside in the basement membrane that separates the scala tympani from the scala tympani.
- Stereocilia project from the hair cells and extend to the cochlea. Above the hair cells is another membrane called the tectorial membrane. Hair cells in the cochlea detect pressure waves, and at the base of the hair, cells are sensory receptors (afferent nerves) that send signals to the brain.
Vestibular Apparatus (Equilibrium organ)
- The vestibule of the ear is balanced and lies above the cochlea. It resides in the membranous labyrinth. He has three semicircular canals and two sac-like chambers called the sac and utricle.
- The saccule and utricle have a macula, which is a prominent crest. The macula contains sensory hair cells. Stereocilia protrude from the hair cells.
- The stereocilia are covered by a gelatinous ampullary shell in which otoliths are embedded.
- Otoliths are calcium otoliths that push stereocilia against gravity and play an important role in spatial orientation.
- Each semicircular canal is filled with endolymph and connects at right angles to the utricle. The base of the duct is swollen and known as the ampulla. Crystaampullaris is present in each ampulla and serves to detect angular rotation. have hair cells.
- The cristae, such as the macula of the sac and utricle, lack otoliths, and the stereocilia of the hair cells are stimulated by endolymphatic movement within the ducts.
The inner ear component responsible for balance is known as the vestibular system. It is made up of the vestibule and the semicircular canals, two bony labyrinth structures, as well as the structures of the membrane labyrinth that are housed inside of them.
The otolith organs are the two membrane sacs that make up the vestibule, the utricle, and the saccule. They are also known as gravity receptors because of how they react to gravitational forces. A single macula, or patch of sensory cells, with a diameter of around 2 mm (0.08 inch), can be found on the inner surface of each sac. The macula keeps track of the head’s angle with respect to the vertical. The macula in the utricle protrudes from the tubular sac’s anterior wall and mostly resides in the horizontal plane. The bone of the vestibule’s inner wall is directly overlain by the macula, which is located in the saccule’s vertical plane. Its elongated shape is similar to the letter J. The neuroepithelium, a layer made up of supporting and sensory cells, a basement membrane, nerve fibers, and nerve endings, and underlying connective tissue are all components of each macula. Due to the hair-like cilia—stiff, nonmotile stereocilia and flexible, motile kinocilia—that extend from the apical ends of the sensory cells, they are known as hair cells. The vestibulocochlear nerve’s superior or vestibular, division is where the nerve fibers originate. Depending on the type of hair cell, they puncture the basement membrane and either terminate on the basal end of the cell or create a calyx, or cuplike structure, that encircles it.
The vestibular organs’ hair cells are each topped by a hair bundle, which is made up of one motile kinocilium and roughly 100 fine, nonmotile stereocilia of varying lengths. At the apex of the cell, a thick cuticular plate serves as the anchor for the stereocilia. One side of the cuticular plate has a noncuticular region of the cell membrane from which the solitary kinocilium, which is longer and larger than the stereocilia, rises. The stereocilia that are closest to the kinocilium are the longest; those that are farther away from the kinocilium shorten gradually. Small filamentous strands connect the tips and shafts of adjacent stereocilia. The otolithic, or statolithic, membrane, a thin acellular structure, covers the whole macula. This membrane has a fibrillar appearance yet is occasionally described as gelatinous. Otoconia or statoconia, which are rhombohedral calcium carbonate crystals in the form of calcite, are a layer of crystals that cover the membrane’s surface. These crystalline particles, which range in size from 1 to 20 m (1 m = 0.000039 inch), are significantly denser than the membrane and so add mass to it. Their specific gravity is almost three times greater than that of the membrane and the endolymph.
Physiology of Hearing
The process of hearing is how the ear converts external sound vibrations into nerve impulses sent to the brain, which are translated into sounds. When an item vibrates, such as a guitar string being plucked, pressure pulses of vibrating air molecules—better known as sound waves—are created. By identifying and evaluating various physical qualities of the waves, the ear can differentiate between various subjective components of a sound, such as its volume and pitch. Pitch, or the number of wavelengths that pass a particular place in a unit of time, is the impression of the frequency of sound waves. The unit of measurement for frequency is hertz or cycles per second. The full hearing range of sounds extends from around 20 to 20,000 hertz, at least for typical young ears. The human ear is most sensitive to and easily perceives frequencies of 1,000 to 4,000 hertz. Although other mammals can hear them, ultrasonic sound waves have an even higher frequency. Loudness is the perception of a sound’s loudness or the force that sound waves apply to the tympanic membrane. The pressure or intensity of the sound will increase with its amplitude or strength, which will also increase the volume of the sound. Decibels (dB), a measurement that describes the relative amplitude of a sound on a logarithmic scale, are used to measure and quantify sound intensity. In other words, a decibel is a unit for comparing the intensity of any given sound with a reference sound that is barely audible to the average human ear at a frequency within the range of the ear’s most sensitivity. The range of human hearing, measured in decibels, ranges from 0 dB, or a level that is almost inaudible, to about 130 dB, or the point at which sound becomes painful. The energy of a sound must go through three modifications before it can reach the central nervous system. The tympanic membrane and middle ear ossicles first vibrate as a result of the air vibrations. These then cause the fluid in the cochlea to vibrate. Last but not least, the fluid vibrations create waves that pass down the basilar membrane and excite the organ of Corti’s hair cells. These cells transform the sound waves into nerve impulses that are then transmitted by the cochlear nerve fibers to the brainstem, where they are relayed after undergoing considerable processing to the primary auditory area of the cerebral cortex, the brain’s hearing center. The listener doesn’t actually hear the sound until the nerve impulses get here.
Mechanism of Maintaining Equilibrium
The vestibular system is a sensory organ in the inner ear that helps the body maintain postural balance. Information from the vestibular system is also essential for coordinating head posture and eye movements. The inner ear or labyrinth has two sets of end organs. A semicircular canal that responds to rotational motion (angular acceleration). The utricle and saccule in the vestibule respond to changes in head position relative to gravity (linear acceleration). The information provided by these organs is proprioceptive relative to internal events, not extra-receptive to external events, as is the case for the cochlear response to sound. Functionally, these organs are closely related to the cerebellum and reflex centers in the spinal cord and brainstem that control movements of the eyes, neck, and limbs.
Detection of Angular Acceleration: Dynamic Equilibrium
The three semicircular canals—the superior, posterior, and horizontal semicircular canals—are orthogonal to each other, allowing us to perceive motion in three-dimensional space. When the head begins to rotate in either direction, the inertia of the endolymph lags the head and exerts pressure to bend the cupula in the opposite direction. This distraction stimulates hair cells by bending stereocilia in the opposite direction. German physiologist Friedrich Goltz formulated the “hydrostatic concept” in 1870 to explain how semicircular canals work. He hypothesized that the canal would be stimulated by the weight of the liquid it contained and that the pressure would vary with the position of the head. In 1873, the Austrian scientists Ernst Mach and Josef Breuer and the Scottish chemist Krum Brown suggested that head movements caused endolymphatic flow in the ducts, which were stimulated by fluid movements and changes. He proposed his own concept of hydrodynamics. with pressure. German physiologist J.R. Ewald showed that squeezing the pigeon’s horizontal canal with a small pneumatic hammer causes the endolymph to migrate toward the cristae, causing the head and eyes to rotate in opposite directions. Decompression reverses both the direction of endolymph movement and the rotation of the head and eyes. The hydrodynamic concept was validated by researchers after tracing the path of oil droplets injected into the semicircular canals of living fish. At the beginning of the rotation in the plane of the canal, the cupula deflected in the direction opposite to the movement and then slowly returned to the rest position. At the end of the spin, it flexed again, this time in the same direction as the spin, and then returned to an upright resting position. These deflections are due to endolymph inertia. The endolymph lags at the onset of rotation and continues after the head rotation stops. The slow return is a function of the elasticity of the cupula itself.
Detection of Linear Acceleration: Static Equilibrium
The gravitational receptors that respond to linear acceleration of the head are the macula of the utricle and saccule. The left and right utricle spots lie in the same approximately horizontal plane. Because of this position they help provide information about the position of the head and its lateral tilt when the person is in an upright position. It lies in parallel vertical planes and may be more responsive to head tilts fore and aft. Both pairs of the macula are stimulated by shear forces between the otolithic membrane and the underlying hair cell cilia. The otolithic membrane is covered with clusters of small calcite crystals (otoconia). This adds weight to the membrane and increases the shear forces produced in response to small displacements when the head is tilted. The tufts of macular hair cells are arranged in specific patterns, either toward the curved midline (within the utricle) or away from the curved midline (within the bulbar), giving rise to possible All head positions can be detected. These sensory organs, especially the utricle, play an important role in the upright reflex and reflex control of the leg, trunk, and neck muscles that keep the body in an upright position. The role of the sac is not fully understood. Some researchers suggest that it responds to both head vibration and linear acceleration in the sagittal plane (anterior and posterior). Of the two receptors, the utricle appears to be the dominant partner. There is evidence that mammalian vesicles may even retain traces of sound sensitivity inherited from their auditory organs, fish.
FAQs on Human Ear
Question 1: What is the Human Ear?
There are three distinct components to the human ear: The outer ear is responsible for gathering ambient sound. Middle ear: It makes the vibrations louder. It transforms sound into electrical signals in the inner ear.
Question 2: What is the function of the Human Ear?
The “hearing complex” is made up of numerous intricate components that support various operations. The middle ear receives sound waves through the eardrum after being assembled by the outer ear and channeled into the skull’s resonating temporal bone. The middle ear is made up of three microscopic mechanisms that filter and magnify sound before being sent to the brain via nerve signals by the neurological hub.
Question 3: Which bones are the most delicate bones in your body called?
The most delicate bones in our body are Ossicles. The tiniest bones in the body, the malleus, incus, and stapes, are located in the middle ear between the inner ear and the ear drum.
Question 4: What is a decent way to take care of our ears?
The delicate structure of the ear is easily and permanently injured. Therefore, protecting your ears by using earplugs and avoiding the insertion of foreign items like cotton buds is a smart idea.
Question 5: What splits the middle ear from the outer ear?
The delicate and important eardrum prevents debris, infections, and other items from entering the ear. As a result, it divides the middle from the outer ear.
Question 6: What part of your ear allows the ‘popping’ that happens when you fly?
When the pressure inside and outside of the middle ear are balanced, it pops in your ears, which typically provides significant relief and improves hearing. The middle ear and the back of your nose are connected by the Eustachian tube, which allows for pressure relief and fluid drainage.
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