Editor’s Note: Hemant Joshi and his colleagues at Tara Innovations are frequent contributors to American Pharmaceutical Review and Pharmaceutical Outsourcing magazines. Tara offers internships to students interested in science. During their internship, students learn how science is applied to real-world situations. American Pharmaceutical Review supports their efforts by publishing articles written by their interns.
Humans have five basic senses – sight, touch, hearing, smell and taste and there is a sensory organ associated with each. Thus, hearing is one of vital senses and the ear is a vital sensory organ.
Functions of the Ear
The ear has two main functions: hearing and balance.
Hearing
The ears detect sound by using the hearing process. This process begins at the auricle of our outer ear, the visible portion of the ear. The auricle collects sound waves from the outside environment and directs them into the external auditory meatus (ear canal), amplifying the sound. The sound waves then travel towards the tympanic membrane, which vibrates in response to receiving sound waves. At this stage, the process moves into the middle ear, where the vibration of the tympanic membrane leads to the vibration of the three small ossicles (the malleus, incus, and stapes) that amplify the sound further. The vibration from the stapes then travels to the cochlea: the snail-shaped, fluid-filled structure within the inner ear. Within the cochlea is an elastic partition called the basilar membrane, which splits the cochlea into upper and lower parts and serves as the base on which important hearing structures reside. When vibrations cause the cochlear fluid to ripple, a wave travels across the basilar membrane, stimulating the hair cells atop the membrane.1 Hair cells near the wider end of the cochlea detect higher-pitched sounds, while those near the center detect lower-pitched sounds. As these hair cells move up and down, microscopic projections called stereocilia on top of the hair cells bump against structures and bend, which opens up pore-like channels on the tips of the stereocilia. When these pores open, chemicals move into the cells and create an electrical signal.2 The auditory nerve then brings these signals to the brain, which translates them into understandable sounds.1
Balance
The vestibular system consists of three semicircular canals and two otolith organs and is located in the inner ear. The semicircular canals help you to feel the direction in which your head is turning when moved. Each semicircular canal detects one of three directions of movement: upwards or downwards, right or left, and side to side.3
Each canal is filled with fluid and ends with a space called the ampulla, which has small sensory hairs within it. When a person’s head turns, the sensory hairs within the canals are bent due to fluid shift, which allows chemicals to enter the cells and create nerve signals to send to the brain. When the head stops turning, the fluid then causes the hair to bend in the opposite direction, which allows us to notice acceleration or deceleration of head movement.3
The otolith organs sense changes in the speed of linear movements. One otolith organ tells the brain when the body moves forward, backward, or sideways, while the other detects upward or downward movements. The hairs of the otolith organs are suspended within a gel-like membrane that has small otoliths in it. When movement occurs, the membrane and sensory hairs also move and pass information to the brain.3
The vestibular system sends information to the brain for other organs, such as the eyes, joints, and muscles, to know the position of our body is in and how to maintain balance. Aspects such as age, infection, and contradictory messages from different sensory organs can affect how this system and our sense of balance work.3
History
In the early stages of evolution, many early aquatic vertebrates had a lateral line system, which was a mechanical sensory organ used to detect water movements and . vibrations 4 .It helped these organisms have environmental awareness within aquatic habitats. As these vertebrates began to transition to living on land, they began to require ways to detect vibrations in the air. To do so, amphibians developed structures that met these needs, which marked the beginning of hearing adaptations within terrestrials.5 In reptiles, evolution created more distinct ear structures that enhanced the ability to hear airborne vibrations, such as the tympanic membrane and one auditory ossicle known as the columella.6 In early mammals, the development of three ossicles (malleus, incus, and stapes) was seen. These three ossicles allowed for further amplified sound vibrations, which helped with having more sensitive hearing and processing higher frequencies.5 Finally, with humans, there was the development of many complex structures, such as the pinna, which allows for better direction of sound waves into the ear canal, and the cochlea, which intricately detects and processes a wide variety of sound frequencies.5
Evolutionary Adaptations in Humans
Many adaptations to human hearing have occurred over the years. Due to environmental and social influences, the pinna of the outer ear has evolved to effectively funnel sound waves into the ear canal.7 Additionally, there has also been an increase in hearing sensitivity towards different frequencies within human speech. This adaptation has strengthened the ability of humans to communicate.8 Lastly, the vestibular system within the inner ear was also an aspect of evolution that formed to help humans with balance and spatial orientation once early humans began to start walking on two legs.9
Comparison of Human Ears to Animal Ears
Many animals have different hearing adaptations from those of humans, who can hear between 31 Hz to 19 kHz, to meet their needs.10 For example, dogs have a much higher hearing range than humans and can detect frequencies between 40 Hz and 60 60kHz. This is done through their larger and more flexible pinnae, which allow them to collect sounds with a high level of precision.11 Elephants also have more wider spectrum of earing than humans and can hear many low-frequency and infrasound frequencies as low as 14 Hz. This adaptation is also due to having very large and sensitive ears, which help them to communicate and understand environmental cues over long distances.12 Some animals, such as bats and dolphins, have completely different mechanisms of hearing. Both of these animals use echolocation to navigate their surroundings and hunt for prey by tbyemitting noises and interpreting the echoes that return. A bat’s hearing system can hear frequencies up to 200 kHz, and dolphins can hear frequencies within 20 Hz to 150 kHz both underwater and in aerial surroundings 13
Diseases of the Ears
Similar to all other tissues in the body, the human hearing system does not escape from diseases and malfunctions. There are many diseases of the ears, each impacting different parts of the ear.
- Swimmer’s Ear (otitis externa): Infection of the outer tympanic membrane, caused by water remaining in the ear after swimming and making a moist environment for bacterial growth. It is seen through symptoms such as discharge, ear pain, redness, and itching.
- Cerumen Impaction: Buildup of earwax that blocks the ear canal and can lead to earache, dizziness, and hearing loss.
- Perichondritis: Infection of the tissue surrounding ear cartilage, which results from injuries or piercings. Symptoms involve swelling, pain, and redness.
- Otitis media: Infection of the middle ear; symptoms include ear pain, hearing difficulties, and fever.
- Eustachian Tube Dysfunction: Blocking and malfunctioning of the Eustachian tube; causes ear fullness, hearing issues, and popping sounds.
- Tympanic Membrane Perforation: Sometimes a hole or rupture is formed in the tympanic membrane, affectingthe the ear’s functioning.
- Sensorineural Hearing Loss: Hearing loss is caused by damage to the inner ear or auditory nerve that is often permanent and causes difficulties with hearing faint sounds and processing speech.
- Conductive Hearing Loss: Hearing loss is caused by problems in the middle or outer ear that prevent sound from being conducted to the inner ear.
- Meniere’s Disease: An inner ear disorder that causes vertigo, tinnitus, hearing loss, and fullness in the ear.
- Vertigo: Sensation of spinning or dizziness from inner ear problems that cause balance issues and nausea.
- Labyrinthitis: Inflammation of the inner ear labyrinth.
- Tinnitus: Ringing noises in the ears without an external sound source.
- Vestibular Neuritis: Inflammation of the vestibular nerve that causes vertigo and balance issues without affecting hearing.
Current Medications Used to Treat Ears
Currently, there are a variety of medications to treat different ailments of the ears in multiple drug classes. Firstly, within the antibiotics class, there are drugs such as ciprofloxacin (Cipro, Cetraxal), neomycin and polymyxin B (Casporyn HC, Oticair), amoxicillin, augmentin, cephalexin, azithromycin (Zithromax), and gentamicin that help treat bacterial infections through oral and/or ear drop form. Steroid ear drops, such as hydrocortisone (Vosol HC), fluocinolone acetonide (Dermotic, Flac), and betamethasone, treat ear inflammation. Common analgesics, such as acetaminophen (Tylenol), ibuprofen (Advil, Motrin), and aspirin, are used when treating ear pain and inflammation. Topical analgesics, such as lidocaine and benzocaine, can also be used to numb the ears and alleviate ear pain. Additionally, to treat fungal infections, there are antifungal ear drops composed of either clotrimazole, fluconazole, or miconazole. Allergy-induced symptoms of the ears are treated using decongestants and antihistamines, such as pseudoephedrine, diphenhydramine (Benadryl), loratadine (Claritin,) and cetirizine (Zyrtec). Lastly, to treat earwax, cerumenolytics such as carbamide peroxide (Debrox), hydrogen peroxide, and olive or mineral oil are used to soften and break down earwax.14
Can We Deliver Medicines to the Throat via the Tympanic Membrane?
Though it is possible to deliver medicines to the throat through the ears, it is not a standard practice within medicine due to the low level of permeability of the tympanic membrane as well as other anatomical barriers.15 As the tympanic membrane acts as a protective barrier for structures in the middle and inner ear, it is usually impermeable to most substances and would require the delivery of highly potent drugs in small quantities to gain therapeutic effects.15 However, specific situations such as inflammation of the ear could make the tympanic membrane more permeable, and make this drug delivery method more feasible.16 When throat-related conditions are involved, direct administration methods through oral, topical, or nasal routes are preferred for treatments as they are more efficient and effective.15
We recently came across a novel patent by S. Dhawan and Y. Dhawan (US patent # 12,029,814, July 9, 2024). Inventors used the ears as the route of administration to prevent and treat upper respiratory viral infections. They added eucalyptus oil to the oil-based formulation and added it to the ear. They could get the smell of eucalyptus oil in their throat. Eucalyptus oil permeated through the tympanic membrane, reaching the throat area via the eustachian tube (see Figure 1). They tested various oils for their permeability through the tympanic membrane. Their formulation contained hemin, remdesivir, and eucalyptus oil in jojoba oil. This formulation can be used to treat upper respiratory infections such as SARS-CoV-2. Hopefully, such research would generate interest in the otic route of administration.17
What Could Be Novel Advances in Ear Drug Delivery?
Zhang et al18 reviewed hurdles to the otic delivery systems to deliver drugs across the tympanic membrane. New research is being done through experimenting with aspects such as nanoparticles and liposomes, to further improve trans-tympanic drug delivery methods.19 Nanomaterials are being used to help with targeted drug delivery in the inner ear due to their ability to cross biological barriers.20 There is also experimentation related to using hydrogels, as it allows for drugs to diffuse through the barrier that makes up the tympanic membrane.19
Conclusion
The ear serves as a critical organ for hearing and balance, with complex structures that allow for precise sound detection and spatial awareness. Over time, nature’s evolution has fine-tuned these mechanisms, resulting in adaptations that enhance human communication and mobility. Compared to other animals, humans have a unique but limited hearing range, while other species have developed specialized hearing abilities to navigate their environments.
Despite the ear’s intricate design, it remains susceptible to various diseases, many of which can be treated with existing medications such as antibiotics, steroids, and analgesics. However, conventional treatments face challenges, particularly in delivering drugs effectively to the inner ear. Research into novel drug delivery systems, including nanoparticles and hydrogels, presents promising avenues for improving trans-tympanic treatments. While delivering medicine to the throat through the ear is generally not viable due to anatomical barriers, emerging technologies may offer new possibilities for targeted therapies in the future.
Continued advancements in ear drug delivery systems hold significant potential for treating auditory disorders more efficiently. Future research should focus on overcoming biological barriers and enhancing targeted treatments to improve patient outcomes. As innovation progresses, these developments could revolutionize how we address ear-related health concerns, ultimately leading to more effective and accessible medical solutions.
References
- https://www.hopkinsmedicine.org/health/conditions-and-diseases/how-the-ear works#:~:text=The%20cochlea%20is%20filled%20with,auditory%20nerve
- https://www.nidcd.nih.gov/health/how-do-we-hear
- https://www.ncbi.nlm.nih.gov/books/NBK279394/
- https://www.britannica.com/science/lateral-line-system
- https://pmc.ncbi.nlm.nih.gov/articles/PMC3918741/
- https://en.wikipedia.org/wiki/Middle_ear
- https://pmc.ncbi.nlm.nih.gov/articles/PMC524325/
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7399675/
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7054002/
- https://www.lsu.edu/deafness/HearingRange.html
- https://www.connecthearing.com/blog/hearing-loss/how-do-different-animals-hear/
- https://www.valuehearing.com.au/news/top-10-best-hearing-animals
- https://www.audicus.com/human-hearing-range/?srsltid=AfmBOorwKggiV01rqGEoRA TF_xwR_Q1WQVT5W86Dpd0ESI3XanKAyX72
- https://my.clevelandclinic.org/health/treatments/24654-ear-drops
- https://www.nature.com/articles/srep22663
- https://pmc.ncbi.nlm.nih.gov/articles/PMC7940379/
- S. Dhawan and Y. Dhawan; Formulation of ear drops and methods for delivery thereof for treating upper respiratory infections; U.S. Patent # 12,029,814; July 9, 2024.
- https://pmc.ncbi.nlm.nih.gov/articles/PMC8594847/
- https://www.tandfonline.com/doi/full/10.2217/nnm-2022-0121
- https://pmc.ncbi.nlm.nih.gov/articles/PMC8594847
Author Details
Sucheta Pansare; Sanjana Medapati; Neelam Sharma
Hemant Joshi# - www.tarainnovations.com, #hemantjoshi@tarainnovations.com
Sucheta Pansare is a senior at the Morris County School of Technology, as part of the Academy for Healthcare Sciences. She is planning on attending NJIT with an intended major in biochemistry.
Sanjana Medapati is a senior at The Academy for Mathematics, Science & Engineering. She is planning on attending Nova Southeastern University’s 4+4 Dual Admission program in Allopathic Medicine with an intended major in Biology and Public Health.
Publication Details
This article appeared in American Pharmaceutical Review:Vol. 28, No. 3
April 2025Pages: 22-25
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