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Humans have vestigial ear muscles that activate when listening closely to something, even though people lost the ability to move their ears about 25 million years ago. These muscles, which once helped our distant ancestors move their ears to improve hearing quality, are classified as extrinsic and intrinsic. The extrinsic muscles position the ear in place and the intrinsic muscles play a role in positioning and formation of the folds we can feel on our ears. While these muscles are generally considered to be of little functional significance, they are still activated when people listen hard.
| Characteristics | Values |
|---|---|
| Ear muscles in humans | Vestigial |
| Ear muscles in animals | Functional |
| Function of ear muscles | Positioning and formation of folds in the ear |
| Ear muscles | Auricularis superior, anterior and posterior |
| Ear muscles | Intrinsic and extrinsic |
| Ear muscles | Activate when listening intently |
| Ear muscles | Activate when trying to locate the source of a sound |
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What You'll Learn
Humans lost the ability to move their ears 25 million years ago
Humans lost the ability to move their ears around 25 million years ago. Our evolutionary ancestors used to be able to move their ears to funnel sound and improve hearing quality. However, as they became more reliant on vision and complex vocal communication, the muscles responsible for ear movement, known as the auricular muscles, became vestigial.
The auricular muscles are classified as vestigial, meaning that while humans have retained the muscle structure, the function has been lost through evolution. These muscles are no longer necessary for human survival, but they refuse to go silent, twitching invisibly whenever we strain to hear. This vestigial auriculomotor system is a "neural fossil", a leftover trait from our evolutionary past that our brains retain but that no longer serves a practical purpose.
In a recent study, researchers from Saarland University in Germany found that these vestigial muscles in our ears still react when we focus on competing sounds, especially in noisy environments. They recorded electrical signals in two different ear muscles: the superior auricular muscle, which raises the ears, and the posterior auricular muscle, which pulls the ear back. As the listening task got more challenging, they observed increased activity in these muscles as if participants were trying to prick up their ears like a dog or cat.
The study's lead author, Andreas Schröer, noted that while the muscle activity may not improve hearing, it could provide an objective measure of listening effort. This information could be useful for diagnosing hearing difficulties or designing better hearing aids. Further research could explore the role of these muscles in people with hearing impairments and how they interact with other aspects of auditory processing.
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Vestigial ear muscles activate when listening intently
Human ears cannot move like those of dogs, cats, and horses. However, people have certain muscles around the ear that are vestigial, meaning they have lost their function through evolution, but the structure has been retained. These vestigial muscles, which once helped our distant ancestors move their ears to improve hearing quality, activate when we listen intently, even though people lost the ability to move their ears about 25 million years ago.
In a study, researchers examined the function of these vestigial muscles by asking participants to listen closely to an audiobook while wearing electrodes. The audiobook was engaging and full of fun trivia, but other sounds and distracting podcasts at different volumes were also played at times. The researchers found that the more difficult it was for participants to hear the audiobook, the more the superior auricular muscles activated, as if participants were trying to prick up their ears like animals. When sounds came from behind a participant, the posterior auricular muscles contracted, as if attempting to point the ears in that direction.
The researchers observed that the auricular muscles, particularly the superior auricular muscle, exhibited increased activity during effortful listening tasks. This suggests that these muscles are engaged not merely as a reflex but potentially as part of an attentional effort mechanism, especially in challenging auditory environments. Previous research had already linked activity in the posterior and superior auricular muscles to attentive listening, indicating that our primate ancestors used them to move their ears and funnel sound.
The findings of this study shed light on a vestigial part of our bodies and a once-useful ability lost to evolution. They also offer new insights into human auditory evolution and could potentially lead to improvements in hearing aids. By monitoring activity in these vestigial muscles, hearing aids could get information about how a person is experiencing the act of listening and make adjustments accordingly.
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Intrinsic and extrinsic ear muscles
The mammalian external ear houses extrinsic and intrinsic auricular muscles. The extrinsic muscles are those that originate elsewhere and insert onto the surfaces of the ear. The intrinsic muscles, on the other hand, originate and insert within the external ear.
There are three extrinsic auricular muscles: the posterior, superior, and anterior auricular muscles. These muscles are classified as vestigial, meaning that humans have lost their function through evolution, although the structure has been retained. Some people can still voluntarily contract these muscles to move their ears. The extrinsic muscles are innervated by the facial nerve and are important for localising the ear.
There are six intrinsic auricular muscles: the helicis major and minor, tragicus, anti-tragicus, transverse, and oblique muscles. These muscles play a role in the positioning and formation of the folds of the cartilaginous auricle, contributing to the overall topography of the human ear. They are also involved in modifying the shape of the auricle. The intrinsic muscles are considered vestigial in humans, but they may have been important for protection in our evolutionary past.
The neural connections of the auricular muscles with the brainstem and other deep brain structures are intact. This accessibility makes them valuable for therapeutic and diagnostic wearable devices, as well as for controlling neuroprosthetics. The functionality and significance of these muscles are still not fully understood and require further research.
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Auricularis superior, anterior and posterior
The auricularis superior, anterior, and posterior are extrinsic muscles of the ear. They position the ear in place. These muscles are classified as vestigial, meaning they have lost their function through evolution, although their structure has been retained. Some people can still voluntarily move their ears by contracting these muscles.
The anterior auricular muscle is the smallest of the three auricular muscles. It is thin and fan-shaped, with pale and indistinct fibres. It arises from the lateral edge of the epicranial aponeurosis and inserts into a projection on the front of the helix. The anterior auricular muscle draws the auricle of the outer ear upwards and forwards, a very subtle movement in most people. However, some people can wiggle their ears.
The auricularis anterior muscle is the most frequently missing of the three auricular muscles. It originates from the lateral margin of the epicranial aponeurosis. Its fibres converge and attach to the spine of the helix.
The auricularis superior and posterior muscles have been associated with hypermobility of the ear.
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The auricular muscles' role in facial paralysis
The auricular muscles are thin, fan-shaped muscles that connect the auricle to the scalp and move the auricle to a certain extent. They are classified as intrinsic and extrinsic muscles. Intrinsic muscles contribute to defining the shape of the auricle by passing between its cartilaginous parts. On the other hand, extrinsic muscles play a role in positioning the auricle, originating from the skull and attaching within the auricle itself. These muscles are classified as vestigial, meaning that through evolution, humans have lost their function, but the structure has been retained.
Facial paralysis is a condition where the facial nerve is damaged, resulting in the inability to control the facial muscles on the affected side. This can be caused by various factors such as inflammation, stroke, petrous bone fracture, or tumors. The auricular muscles play a crucial role in facial paralysis as they can help in the recovery process. During the flaccid stage of recovery, the facial muscles on the affected side exhibit weakness and immobility, leading to a loss of facial expression. However, in the paretic stage, muscle tone returns, and the face appears more symmetrical at rest, with movement gradually coming back.
Synkinesis, a specific symptom of facial paralysis, causes the affected muscle to be held in a shortened position for extended periods, resulting in tightness and pain. This occurs due to overstimulation from the recovering facial nerve, which has lost its ability to differentiate between activity and rest. Relaxation techniques and auricular stretches can help alleviate this issue. Additionally, the posterior auricular branches of the facial nerve supply all the muscles of the external ear/auricle, and their electrical activity can be monitored to understand a person's listening experience and adjust hearing aids accordingly.
In conclusion, while the auricular muscles may have a limited role in everyday life, they can be crucial in the context of facial paralysis. Their electrical activity provides insights into listening efforts, and their tightness and relaxation directly impact the recovery process for those suffering from facial paralysis. Further research and practical applications based on these findings may lead to improved hearing aid technologies and enhanced understanding of facial paralysis.
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Frequently asked questions
Ear muscles are a group of muscles located around the ear, including extrinsic and intrinsic muscles. They are generally considered to be of little functional significance as humans lost the ability to move their ears about 25 million years ago.
While ear muscles are considered vestigial, they are still activated when people listen intently. The auricular muscles, which helped our distant ancestors move their ears to improve hearing quality, are activated when people try to listen to competing sounds.
Vestigial organs, such as wisdom teeth in humans, are those that have become functionless through evolution. However, vestigial ear muscles may be linked to the fear of being wounded or dying. They also continue to have a significant influence on the body through reflexogenic connections.
