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The smallest muscle in the human body is the stapedius muscle, which is just over one millimeter in length. The stapedius muscle is located in the middle ear and is connected to the stapes bone, which is the smallest bone in the human body. The purpose of the stapedius muscle is to stabilize the stapes bone and protect the inner ear from loud noises.
| Characteristics | Values |
|---|---|
| Name | Stapedius |
| Length | 9-11mm |
| Tendon Length | 2mm |
| Breadth | 1-3mm |
| Shape | Sickle |
| Purpose | Stabilises the stapes bone |
| Location | Middle ear |
| Contraction | In response to sounds of a particular volume |
| Nerve | Facial nerve |
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What You'll Learn
The smallest skeletal muscle
The stapedius muscle is supplied by the nerve to stapedius, a branch of the facial nerve, and it plays a crucial role in the acoustic reflex. This reflex is an involuntary muscle contraction that occurs in response to high-intensity sound stimuli. By contracting, the stapedius muscle dampens the vibrations of the stapes bone, helping to control the amplitude of sound waves reaching the inner ear from the external environment. This protective mechanism shields the inner ear from loud noises, preventing potential damage.
Issues with the stapedius muscle can lead to conditions such as hyperacusis, characterised by an increased sensitivity to sound. Individuals with hyperacusis may perceive normal sounds as excessively loud due to heightened reaction of the auditory ossicles to sound vibration. Bell's palsy, a condition causing unilateral paralysis of the facial nerve, can also result in paralysis of the stapedius muscle and subsequent hyperacusis.
The stapedius muscle shares an evolutionary history with other vertebrate structures. In other tetrapods, such as bony fish and sharks, equivalent muscles were involved in jaw movement. However, in mammals, the function of jaw opening was transferred to the digastric muscle, while the stapedius muscle specialised in stabilising the stapes bone and controlling sound conduction to the inner ear.
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The stapedius muscle
A healthy individual with normal hearing typically has a sound threshold of approximately 85 decibels. When exposed to loud sounds, the stapedius muscle contracts, rotating the base of the stapes bone and closing the vestibular window. This contraction attenuates further vibrations passed to the cochlea, protecting the hearing apparatus.
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The stapedius stabilises the stapes
The stapedius muscle is the smallest skeletal muscle in the human body. It is approximately 6mm in length and is located in the middle ear. The stapedius muscle originates in the stapedius muscle fossa, within the petrous part of the temporal bone in the tympanic cavity of the middle ear.
The stapedius muscle stabilises the stapes bone, also known as the stirrup bone, by dampening excessive sound vibrations that pass through the oval window to the cochlea. This helps to reduce the loudness of sounds and protect the hearing apparatus when exposed to loud noises. When the incoming sound is loud enough to stimulate the receptor cells in the inner ear, signals are sent to the brainstem, triggering contractions of the stapedius muscle. This contraction applies tension to the stapes bone, causing it to rotate posteriorly and place the base of the stapes into the vestibular window, closing it.
The stapedius muscle is innervated by the stapedial branch of the facial nerve (CN VII), also known as the nerve to stapedius. This nerve arises from the facial canal and supplies the muscle. When the facial nerve is stimulated by loud sounds, it sends efferent signals to the stapedius muscle, triggering its contraction.
The stapedius muscle plays a crucial role in protecting the hearing apparatus when exposed to loud sounds. Paralysis of the stapedius muscle can lead to a condition known as hyperacusis, where normal sounds are perceived as very loud. This can be a sign of hearing loss or damage to the facial nerve.
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The stapedius is 1mm long
The stapedius muscle is the smallest skeletal muscle in the human body. It is just over 1mm in length, though one source states it is approximately 6mm long. The stapedius muscle has an important role in hearing and sound transmission. It stabilises the stapes, or stirrup bone, of the middle ear, which is the smallest bone in the body. The stapedius emerges from a small opening in the apex of the pyramidal eminence, a hollow, cone-shaped prominence in the posterior wall of the tympanic cavity. It then inserts into the neck of the stapes.
The stapedius muscle is innervated by the stapedial branch of the facial nerve, also known as the nerve to stapedius muscle. This nerve passes posterior to the pyramidal process to innervate the stapedius. The stapedius dampens the vibrations of the stapes by pulling on the neck of the bone. It is one of the muscles involved in the acoustic reflex, which prevents excess movement of the stapes. This helps to control the amplitude of sound waves from the external environment to the inner ear.
If the stapedius muscle is paralysed, the stapes will oscillate more widely, resulting in a heightened reaction of the auditory ossicles to sound vibration. This can cause a condition known as hyperacusis, where normal sounds are perceived as very loud. Hyperacusis can also result from Bell's palsy, a unilateral paralysis of the facial nerve.
The stapedius muscle is not the only muscle involved in the acoustic reflex. The tensor tympani, located in the middle ear, also has a protective function against excessive sound.
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Other small muscles
The smallest muscle in the human body is the stapedius, which is just over one millimetre in length. This muscle is located in the middle ear and stabilises the stapes (stirrup) bone, the smallest bone in the body. The stapedius muscle is a vital part of the acoustic reflex, helping to control the amplitude of sound waves entering the inner ear.
The masseter muscles, located on either side of the jaw, are responsible for mastication (chewing). Working alongside the temporalis, lateral pterygoid, and medial pterygoid muscles, they enable a bite force of up to 200 pounds on the molars and 55 pounds on the incisors.
The sartorius muscle, while not as small as the stapedius, is referred to as the longest muscle in the human body. Spinal muscles are also tiny, connecting to the spinous and transverse processes of the vertebral column.
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Frequently asked questions
The smallest muscle in the human body is the stapedius muscle, which is located in the middle ear.
The stapedius muscle measures about 1mm in size, or 1/26 of an inch.
The stapedius muscle has the important job of stabilising the stapes, the smallest bone in the body, to keep it from vibrating too violently and protect the inner ear from loud noises.
If the stapedius muscle is paralysed, it can cause a condition called hyperacusis, where normal sounds are perceived as very loud.
