Dominic Stone
The human ear is a complex organ that is responsible for the sense of hearing. While the ear is not a muscle, it does contain muscles. The middle ear, which lies within the temporal bone and extends from the tympanic membrane to the lateral wall of the inner ear, contains two muscles: the tensor tympani and the stapedius. These muscles, along with the bones of the middle ear, play a crucial role in transmitting sound vibrations to the inner ear. The tensor tympani and stapedius muscles also serve a protective function by contracting in response to loud noises, thus reducing the transmission of sound to the inner ear and protecting it from potential damage.
| Characteristics | Values |
|---|---|
| Parts of the ear | The ear can be split into two parts: the tympanic cavity and epitympanic recess |
| Middle ear | The middle ear lies within the temporal bone, and extends from the tympanic membrane to the lateral wall of the inner ear |
| Main function of the middle ear | To transmit vibrations from the tympanic membrane to the inner ear via the auditory ossicles |
| Middle ear muscles | The two inner ear muscles are the tensor tympani and the stapedius |
| Tensor tympani muscle | A muscle within the middle ear that connects to the malleus bone |
| Stapedius muscle | A muscle that attaches to the stapes |
| Tensor tympani function | To dampen loud sounds, such as those produced from chewing, shouting, or thunder |
| Stapedius function | To reduce sound transmission through the middle ear at high levels |
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What You'll Learn
The ear has two muscles: the tensor tympani and the stapedius
The ear is not a muscle, but it does contain two muscles: the tensor tympani and the stapedius. These muscles are located in the middle ear and serve a protective function. The tensor tympani muscle is located in the bony canal above the bony part of the auditory tube and connects to the malleus bone. It arises from the cartilaginous part of the pharyngotympanic tube and inserts on the manubrium of the malleus. The tensor tympani muscle is innervated by the trigeminal nerve, specifically the mandibular division.
The stapedius muscle, on the other hand, is innervated by the facial nerve. It attaches to the stapes bone. Both muscles contract in response to loud noises, inhibiting the vibrations of the malleus, incus, and stapes, and reducing the transmission of sound to the inner ear. This action is known as the acoustic reflex. The reaction time of these muscles is not fast enough to protect against sudden loud noises such as explosions or gunshots. However, they can help to dampen the sound of chewing, shouting, or thunder.
The tensor tympani muscle is also associated with the phenomenon of a rumbling sound that can be heard when the neck or jaw muscles are highly tensed, such as during a deep yawn. This has been known since at least 1884. In some cases, individuals may have voluntary control over the tensor tympani muscle, contracting it to produce a rumbling sound. However, according to the National Institute of Health, voluntary control of this muscle is extremely rare.
The exact function of the tensor tympani muscle is still debated, with questions surrounding its role in auditory and non-auditory reflexes and sound damping. Some studies suggest that it contracts in response to non-auditory stimulation such as facial or head movements, while others suggest that it is triggered by auditory stimulation from the cochlear nucleus. Despite the ongoing debate about its specific functions, the tensor tympani muscle is structurally important in the middle ear and plays a role in protecting the inner ear from loud sounds or desensitizing the ear to self-generated sounds.
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Tensor tympani pulls the malleus inwards
The ear is not a muscle, but it does contain muscles. One of these muscles is the tensor tympani, which is located in the middle ear. The tensor tympani muscle is one of two muscles in the tympanic cavity, the other being the stapedius. The tensor tympani is a tiny, long, paired muscle that connects to the malleus bone.
The tensor tympani muscle develops from mesodermal tissue in the first pharyngeal arch. It arises from the cartilaginous part of the auditory tube and the adjacent great wing of the sphenoid. It then passes through its own canal and ends in the tympanic cavity as a slim tendon that connects to the handle of the malleus. The tensor tympani receives blood from the middle meningeal artery via the superior tympanic branch. It is supplied by the tensor tympani nerve, a branch of the mandibular branch of the trigeminal nerve.
When the tensor tympani muscle contracts, it pulls the manubrium of the malleus inwards and tightens it. This tightening reduces the amplitude of the tympanic membrane oscillations, thereby reducing sound transmission into the inner ear. This is known as the tympanic reflex, which is believed to be an evolutionary adaptation to protect the inner ear from excessively loud noises and to aid in speech coordination. The tensor tympani, along with the stapedius muscle, coordinates speech with hearing. Without this action, loud sounds, such as a person's own voice, could hinder the ability to hear other sounds or even damage the cochlea.
The tensor tympani muscle also plays a role in dampening loud sounds, such as those produced from chewing, shouting, or thunder. However, because its reaction time is not fast enough, the tensor tympani muscle cannot protect against hearing damage caused by sudden loud noises, like explosions or gunshots. Some individuals have voluntary control over the tensor tympani muscle and may tense it preemptively.
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Stapedius pulls the stapes inwards
The ear is comprised of various muscles, one of which is the stapedius muscle. This muscle is the smallest skeletal muscle in the human body, measuring just over one millimeter in length. The stapedius muscle arises from the back wall of the middle ear cavity and extends forward, attaching itself to the neck of the head of the stapes bone, also known as the stirrup bone of the middle ear.
The stapedius muscle plays a crucial role in stabilizing the stapes bone, which is the smallest bone in the human body. By contracting, the stapedius muscle pulls the stapes bone inwards, dampening its vibrations. This action is part of the acoustic reflex, which helps to control the amplitude of sound waves entering the inner ear from the external environment. The stapedius muscle prevents excess movement of the stapes bone, ensuring that sound waves are transmitted at a safe volume to the inner ear.
The contraction of the stapedius muscle typically occurs in response to high-level sounds. When exposed to loud noises, the stapedius muscle contracts, pulling the stapes bone inwards and reducing its vibrations. This reflex mechanism is designed to protect the inner ear from potential damage caused by excessive sound vibrations. The stapedius reflex time is relatively quick, taking approximately 20 milliseconds to activate.
It is important to note that the stapedius muscle works in conjunction with another muscle in the middle ear called the tensor tympani muscle. The tensor tympani muscle also contributes to dampening loud sounds by pulling the malleus bone, which is connected to the stapes bone, inwards and tightening it. Together, the stapedius and tensor tympani muscles help regulate the volume of sound vibrations reaching the inner ear, ensuring that sounds are perceived at a comfortable and safe level.
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Tensor tympani is supplied by the tensor tympani nerve
The ear is a complex organ that enables humans to hear and perceive sound. While the outer part of the ear that we see is made of skin and cartilage, the inner parts are more intricate. The ear is not a muscle, but it does contain muscles, including the tensor tympani and the stapedius muscle.
The tensor tympani is a small muscle located in the middle ear, which is the section of the ear located behind the eardrum. It is a long, thin muscle that passes through a bony canal above the bony part of the auditory tube and ends in the tympanic cavity as a tendon that connects to the malleus bone. The tensor tympani is supplied by the tensor tympani nerve, which is a branch of the mandibular branch of the trigeminal nerve. The trigeminal nerve is the fifth cranial nerve and is responsible for providing sensory input to the face and motor functions like biting and chewing.
The tensor tympani muscle has an important role in dampening loud sounds. When this muscle is contracted, it pulls the malleus bone inwards and tightens the tympanic membrane, reducing the vibration and the amplitude of sounds. This action helps to protect the inner ear from damage caused by excessively loud noises. The tensor tympani is activated by the perception or anticipation of loud sounds, and this reflex is known as the tonic tensor tympani syndrome (TTTS) or the startle response.
In rare cases, individuals may have voluntary control over the tensor tympani muscle, and they can tense it at will. This phenomenon has been observed in some patients with tinnitus, where they voluntarily contract the tensor tympani muscles in both ears simultaneously. Additionally, some people with hyperacusis exhibit increased activity in the tensor tympani muscle as part of their startle response to certain sounds.
The tensor tympani plays a crucial role in various auditory processes, including the regulation of the eustachian tube and the stiffening of the tympanic membrane to control sound transmission. This muscle is also believed to decrease the intensity of sound during activities like chewing and swallowing.
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Stapedius is innervated by the facial nerve
The ear is a complex organ that enables humans to hear and interpret sound. While the outer part of the ear that we see is mostly made of skin and cartilage, the inner parts of the ear are intricate and fascinating. The ear is not a muscle, but it does contain some muscles, including the stapedius muscle and the tensor tympani muscle.
The stapedius muscle is a tiny muscle in the middle ear. It is one of the smallest in the human body and is attached to the stapes bone, also known as the stirrup bone, which is one of the three bones in the middle ear. The stapedius muscle, along with the tensor tympani muscle, is part of the middle-ear reflex arc, which also includes the spiral ganglion neurons, the auditory nerve, cochlear nucleus, the superior olive, the facial nerve nucleus, the facial nerve, and the two middle-ear muscles.
The stapedius muscle is innervated by the facial nerve, also known as CN VII, which is the seventh paired cranial nerve. The facial nerve carries both motor and sensory fibres and is responsible for innervating many of the muscles within the head and neck. The facial nerve has two roots, a large motor root and a smaller nervus intermedius, which emerge from the lower border of the pons and enter the petrous part of the temporal bone, travelling through the internal auditory meatus before entering the facial canal. Within the facial canal, the two roots fuse to form the facial nerve, which then gives rise to the geniculate ganglion.
The nerve to the stapedius muscle, or the stapedius nerve, is a branch of the facial nerve that arises within the facial canal. It passes through the pyramidal eminence to supply the stapedius muscle in the middle ear. The stapedius muscle plays a role in the auditory system by dampening sound transmission and stabilising the stapes, preventing excessive movement in response to loud sounds. This reflex is important for protecting the cochlea and controlling the dynamic range of the auditory system.
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Frequently asked questions
No, the ear is not a muscle, but there are muscles in the ear. The middle ear contains two muscles, the tensor tympani and the stapedius.
The tensor tympani is a muscle within the middle ear that connects to the malleus bone. It acts to dampen loud sounds, such as those produced from chewing, shouting, or thunder.
The stapedius is a muscle in the middle ear that attaches to the stapes. It contracts in response to intense low-frequency acoustic stimuli, reducing the intensity of sound energy reaching the inner ear.
The main function of the muscles in the middle ear is to protect the ear from loud noises and control the dynamic range of the auditory system. They contract in response to loud noises, inhibiting the vibrations of the malleus, incus, and stapes, and reducing the transmission of sound to the inner ear.
