Ear - Hearing and Balance

The human ear can detect a wide range of frequencies, from the low rumbles of distant thunder to the high-pitched whine of a mosquito. The sensory cells that detect these sounds are called hair cells, named for the hair-like strands that cluster on their tops. Hair cells are spread across a flat surface called the basilar membrane, which is rolled like a carpet and tucked into a snail shell-shaped structure in the inner ear called the cochlea. Each of our roughly 16,000 hair cells is dedicated to a narrow frequency range. These cells are ordered along the basilar membrane according to the frequencies they detect.

The amplitude is the SI unit of the pitch of the sound. So, the correct option is "Amplitude".

The Cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.5 turns around its axis, the modiolus.
Thus, the correct answer is option C.

The standard range of human hearing is generally cited as 20 Hz to 20,000 Hz. Option C (50 Hz to 15,000 Hz) is the closest acceptable range provided in the options.

The inner ear consists of two systems of canals which are namely cochlea and vestibular apparatus. The vestibular apparatus consists of three semicircular canals, cristae and two sacs called as saccule and utricle. Cochlea is the organ of hearing which contain mechanoreceptors for hearing. This makes option B incorrect. The three semicircular canals lie at right angle to each other in vestibular apparatus of inner ear and are filled with endolymph; this arrangement senses the change in movement (acceleration or deceleration) or position and maintain equilibrium. The mechanism includes movement of cupula in response to movement of endolymph within the canal causing the bending of cilia to generate the nerve impulse. This makes option A correct. Hammer is the one of the three ossicles of the middle ear which is concerned with amplification of air pressure while passing it from the inner surface of tympanic membrane via incus to stapes. This makes option C incorrect. The eustachian tube extends from each middle ear to nasopharynx and permits the equalization of air pressure. This makes option D incorrect. Correct answer is A. 

Receptors that sense the change in atmospheric pressure are classified under mechanoreceptors. Three pressure receptors are namely Pacinian corpuscles, Ruffini endings and Krause end bulbs which are located in skin. This makes option A incorrect. The three semicircular canals lie at right angle to each other in vestibular apparatus of inner ear and are filled with endolymph; this arrangement senses the change in movement (acceleration or deceleration) or position. The mechanism includes movement of cupula in response to movement of endolymph within the canal causing the bending of cilia to generate the nerve impulse. This makes option C correct and option D incorrect. Migratory birds and animals have receptors in their brain which are activated by direction of sunlight and orient their body at certain angle in relation to sun. This makes option B incorrect. Correct answer is C. 

Receptors that sense the change in atmospheric pressure are classified under mechanoreceptors. Three pressure receptors are namely Pacinian corpuscles, Ruffini endings and Krause end bulbs which are located in skin. This makes option A incorrect. The three semicircular canals lie at right angle to each other in vestibular apparatus of inner ear and are filled with endolymph; this arrangement senses the change in movement (acceleration or deceleration) or position. The mechanism includes movement of cupula in response to movement of endolymph within the canal causing the bending of cilia to generate the nerve impulse. Migratory birds and animals have receptors in their brain which are activated by direction of sunlight and orient their body at certain angle in relation to sun. Thus, the correct answer is option C.

The olfactory nerve is the second cranial nerve which transmits the nerve impulses from olfactory receptors, receptors of sense the smell that are located in nasal epithelium of roof of the nasal cavity, to the brain.

Statoreceptors are the receptors for sense of balance and equilibrium. They are present in vestibular apparatus of inner ear. 

The inner ear consists of two systems of canals which are namely cochlea and vestibular apparatus. The vestibular apparatus consists of three semicircular canals, cristae and two sacs called as saccule and utricle. The cochlea is the organ of hearing which contains mechanoreceptors for hearing. This makes option B incorrect. The three semicircular canals lie at the right angle to each other in vestibular apparatus of the inner ear and are filled with endolymph; this arrangement senses the change in movement (acceleration or deceleration) or position. The mechanism includes movement of cupula in response to movement of endolymph within the canal causing the bending of cilia to generate the nerve impulse. Hammer is one of the three ossicles of the middle ear which is concerned with amplification of air pressure while passing it from the inner surface of tympanic membrane via incus to stapes. The eustachian tube extends from each middle ear to nasopharynx and permits the equalization of air pressure. Thus, the correct answer is option A.

The human ear can generally hear sounds with frequencies between 20 Hz and 20 kHz. Although hearing requires an intact and functioning auditory portion of the central nervous system as well as a working ear, human deafness most commonly occurs because of abnormalities of the inner ear, rather than in the nerves or tracts of the central auditory system. Sound below 20 Hz is considered infrasonic, which the ear cannot process. Therefore, the correct answer is option A.

Ear of frog consists of only two parts - middle and internal ear but no external ear. In the rabbit, ear has three regions which are external, middle and internal. External ears consist of the pinna (auricle) and auditory canal (external auditory meatus). Pinna is provided with voluntary muscle and is supported by elastic fibrocartilage. Pinna helps in collecting the sound waves. So, hearing in the rabbit is better than the frog.

The semicircular canals are three canals used to provide information to the brain on directional balance and equilibrium. Each canal is lined with cilia and filled with a fluid called endolymph. As the head and body move, the fluid moves and pushes the cilia back and forth to create a motion sensor.

The auditory cortex, which processes sound information, is located in the temporal lobes of the brain.

• The outermost part of human ear is called pinna (external ear).
• Pinna is followed by auditory canal. It is a tube by which pinna is connected to middle ear.
• The auditory canal extends from pinna to tympanic membrane (ear drum).
• Tympanic membrane is followed by three ear ossicles, malleus, incus and stapes.
• Stapes is attached to oval window of cochlea and transfers the vibrations to the fluid of cochlea. Cochlea is a part of inner ear.
• Inner ear contains vestibular apparatus and auditory nerve along with cochlea.

• When sound waves from the environment enter the external ear, they are directed to ear drum (tympanic membrane). 
• The ear drum vibrates on receiving sound waves and the vibrations are sent to oval window through ear ossicles which are malleus, incus and stapes. 
• From the oval window, these vibrations are passed onto fluid of cochlea where waves are generated into lymph due to these vibrations. 
• These waves generate vibrations in the basilar membrane which bend the hair cells and press them against the tectorial membrane.
• This results in the generation of nerve impulses in afferent neurons which are transmitted by afferent fibres to auditory cortex of brain. 
• The impulses are analysed and recognised in brain.

• Sound waves from the environment enter the external ear and are directed to ear drum (tympanic membrane). 
• The ear drum vibrates on receiving sound waves and the vibrations are sent to oval window through ear ossicles which are malleus, incus and stapes. 
• From the oval window, these vibrations are passed onto fluid of cochlea where waves are generated into lymph due to these vibrations. 
• These waves generate vibrations in the basilar membrane which bend the hair cells and press them against the tectorial membrane.

Maculae are the specialized mechanoreceptors within the utricle and saccule for the detection of static equilibrium, they make use of the hair cells to detect the movements of the otolithic membrane, the nerve impulses thus generated and transmitted along the vestibular branch of the cranial nerve to the central nervous system.

The vestibular system, which is responsible for balance, consists of the semicircular canals and the otolith organs, which include the utriculus and sacculus.

The structures responsible for balance, specifically the vestibular system (semicircular canals and otolith organs), are located within the inner ear.

Maculae detect changes in the body with respect to gravity (static equilibrium) and in the movement in one direction (linear acceleration). So, the correct answer is (A).

The functional components of the membranous labyrinth involved in the sensations of static and dynamic equilibrium are a system of thin walled, intercommunicating tubes and ducts situated within the petrous part of the temporal bone at the base of the skull. There are five vestibular structures, each containing a specialized mechanoreceptor, (maculae), within the utricle and saccule, and cristae within the ampulla of the superior, horizontal, and posterior semicircular canals.

Within the bony labyrinth, is the membranous labyrinth; filled with the fluid called as endolymph. The membranous labyrinth within the cochlea contains the organ of Corti containing the inner and outer hair cells, that generate the nerve impulses required for hearing. Nerve impulses generated in the inner ear travel along the vestibulocochlear nerve (cranial nerve VIII) to the brain.

Ear acts as the dual receptor in the following ways:

The semicircular canals are three canals used to provide information to the brain on directional balance. Each canal is lined with cilia and filled with fluid, called as endolymph. As the head and body move, the fluid moves and pushes the cilia back and forth to create a motion sensor. The three main parts of the semicircular canals are the horizontal, posterior and superior. The superior is responsible for head rotation, the posterior canal detects movement and rotation on the sagittal plane, and the horizontal senses on a vertical basis.

The first part of the ear to develop is the inner ear. Its appearance occurs around the 22$^{nd}$ day of the embryo's development, originating from the ectoderm germinative layer.

• Semicircular canals are three tiny fluid-filled tube in our inner ear that helps to keep our balance.
  
• Cochlea transforms the sound or vibration of cochlear liquid into neural signals.
  
• Utriculus and Sacculus are part of balancing apparatus of ear located within the vestibule of the bony labyrinth which respond to change in the position of the head with respect to gravity (linear acceleration).
  

The cupula is a structure in the vestibular system, providing the sense of spatial orientation. The cupula is located within the ampullae of each of the three semicircular canals. Part of the crista ampullaris, the cupula has embedded hair cells that have several stereocilia associated with each kinocilium. The cupula itself is the gelatinous component of the crista ampullaris that extends from the crista to the roof of the ampullae. When the head rotates, the endolymph filling the semicircular ducts initially lags behind due to inertia. As a result, the cupula is deflected opposite the direction of head movement. As the endolymph pushes the cupula, the stereocilia are bent as well, stimulating the hair cells within the crista ampullaris. After a short time of continual rotation, however, the endolymphs acceleration normalizes with the rate of rotation of the semicircular ducts. As a result, the cupula returns to its resting position and the hair cells cease to be stimulated. This continues until the head stops rotating which simultaneously halts semicircular duct rotation.

A semicircular canal or a semicircular duct is one of three semicircular, interconnected tubes located inside each ear. The three canals are the horizontal semicircular canal (also known as the lateral semicircular canal),     superior semicircular canal (also known as the anterior semicircular canal)     and the posterior semicircular canal (also known as the inferior semicircular canal).
It helps in regulating body balance. Endolymph, which is present in the ear plays a major role in regulating body balance.

The ear not only detects sound but also notes its direction, judges its loudness and determines is pitch.Auditory impulse form through different steps: