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The human head is home to numerous muscles, each with its own unique function and purpose. These muscles are essential for various facial expressions, chewing, speaking, and even protecting the eyes and ears. The muscles in the head can be broadly categorized into four groups: the tongue, muscles of facial expression, extra-ocular muscles, and muscles of mastication. The tongue, for example, is made up of both intrinsic and extrinsic muscles and is responsible for taste and sensation. The masseter muscles, on the other hand, are involved in the chewing process, helping to close the jaw when contracted. Understanding the intricacies of these head muscles and their functions can provide valuable insights into disorders or conditions that may arise when they are not working in harmony.
| Characteristics | Values |
|---|---|
| Number of muscles in the head | Several |
| Muscle groups | 3 |
| Muscle functions | Control of eyeball movement, opening and closing the jaw, facial expressions, hearing |
| Major muscles | Sternocleidomastoid, Trapezius, Splenius, Tensor Tympani, Lateral Pterygoid, Corrugator Supercilii |
| Nerves | Oculomotor, Trochlear, Abducens, Mandibular, Hypoglossal, Facial, Cervical Plexus, Occipital, Auricular, Trigerminal |
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What You'll Learn
The head is balanced, moved, and rotated by the neck muscles
The head is a heavy weight for the neck to balance, move and rotate, and it is the neck muscles that are responsible for these actions. The neck muscles can be sub-categorised into anterior, lateral (prevertebral), and posterior. The cervical spine is composed of seven vertebrae, with the top two, C1 and C2, being "atypical" due to their unique bony structures designed to support and move the skull. The primary motions of the OA joint between the skull and C1 are flexion and extension.
The major muscle that laterally flexes and rotates the head is the sternocleidomastoid. This muscle also divides the neck into anterior and posterior triangles when viewed from the side. The splenius muscles originate at the midline and run laterally and superiorly to their insertions. From the sides and the back of the neck, the splenius capitis inserts onto the head region, and the splenius cervicis extends onto the cervical region. These muscles can extend the head, laterally flex it, and rotate it.
The back muscles stabilise and move the vertebral column and are grouped according to the lengths and direction of fascicles. The erector spinae group forms the majority of the muscle mass of the back and is the primary extensor of the vertebral column. It controls flexion, lateral flexion, and rotation of the vertebral column, and maintains the lumbar curve. The segmental muscle group, including the interspinales and intertransversarii muscles, is important in the stabilisation of the vertebral column.
The scalene muscles (anterior, middle, and posterior) also work together to flex, laterally flex, and rotate the head. They also contribute to deep inhalation.
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The tongue is made up of intrinsic and extrinsic muscles
The human tongue is made up of eight muscles, comprising four intrinsic and four extrinsic muscles. The tongue is an organ composed entirely of muscle and is known as a muscular hydrostat. The intrinsic muscles are responsible for altering the shape of the tongue, while the extrinsic muscles are in charge of moving it in different directions.
The four intrinsic muscles are the superior longitudinal muscle, the inferior longitudinal muscle, the vertical muscle, and the transverse muscle. These muscles originate and insert within the tongue, running along its length. They change the shape of the tongue by lengthening and shortening it, curling and uncurling its apex and edges, and flattening and rounding its surface. This shape alteration is essential for speech production, as different vowels and consonants are articulated by changing the tongue's position and height. The intrinsic muscles also facilitate swallowing and eating.
The four extrinsic muscles are the genioglossus, the hyoglossus (sometimes including the chondroglossus), the styloglossus, and the palatoglossus. These muscles originate from bone and extend to the tongue, anchoring to the tongue and allowing for its movement. The genioglossus arises from the mandible and protrudes the tongue forward, earning the nickname the "safety muscle". The hyoglossus arises from the hyoid bone and is responsible for tongue retraction and depression. The styloglossus and palatoglossus also contribute to tongue movement. The palatoglossus, innervated by the vagus nerve, elevates the posterior portion of the tongue, aiding in swallowing and preventing saliva spillage.
The tongue plays a crucial role in various functions, including digestion, taste perception, speech, and breathing. It is attached to the hyoid bone, mandible, styloid process, soft palate, and pharynx via the extrinsic muscles. The tongue's flexibility and mobility are made possible by the coordinated actions of its intrinsic and extrinsic muscles.
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The lateral pterygoid is the muscle that opens the jaw
The human head contains several muscles, including those that control eyeball movements, facial expressions, and the tongue. One of these muscles is the lateral pterygoid, which is responsible for opening the jaw.
The lateral pterygoid is a craniomandibular muscle that plays a crucial role in the inferior temporal region. It is one of the four muscles of mastication, along with the medial pterygoid, masseter, and temporalis muscles. These muscles act on the temporomandibular joint (TMJ) to enable chewing and biting. The lateral pterygoid is particularly active during speaking, singing, and clenching.
The lateral pterygoid muscle has two heads or bellies, with the inferior belly being three times larger than the superior belly. The fibres of both heads merge and insert into the pterygoid fovea on the neck of the mandible. The origin of both bellies is medial to their insertions, which can cause distortion in the transverse plane when the mandible is widely opened.
The lateral pterygoid muscle depresses the mandible and opens the mouth when assisted by the anterior belly of the digastric muscle and the mylohyoid muscle. It is the only muscle among the four muscles of mastication that participates in depressing the mandible. The unilateral contraction of the lateral pterygoid muscle with the ipsilateral medial pterygoid muscle results in lateral mandibular movement to the contralateral side, which is observable during chewing, masticating, and clenching.
The lateral pterygoid muscle also plays a crucial role in controlling the function of the jaw and temporomandibular joint. It helps generate the horizontal forces required during mastication and parafunctional activities. Additionally, some fibres of the superior head of the lateral pterygoid muscle become active during clenching, preventing the mandibular condyle from being displaced posteriorly and avoiding pressure on sensitive postcondylar structures.
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The tensor tympani is a tiny muscle that tightens the eardrum
The tensor tympani is a small muscle in the middle ear that is responsible for tightening the eardrum. It is located in the bony canal above the bony part of the auditory tube, also known as the pharyngotympanic or Eustachian tube. This muscle plays a crucial role in the tympanic reflex, an evolutionary adaptation that protects the inner ear from excessively loud noises and aids in speech coordination.
The tensor tympani muscle works in conjunction with the stapedius muscle, and they both belong to the group of intratympanic muscles. The tensor tympani muscle attaches to the malleus, one of the three auditory ossicles, allowing it to tighten the tympanic membrane or eardrum. This tightening action reduces the vibration amplitude, thereby lessening sound transmission into the inner ear and reducing the perceived amplitude of sounds.
The tensor tympani muscle is innervated by the nerve to the tensor tympani, which originates from the mandibular division of the trigeminal nerve. It receives blood from the middle meningeal artery via the superior tympanic branch. The muscle's contraction can be triggered by the perception or anticipation of loud sounds, a condition known as tonic tensor tympani syndrome (TTTS).
In some individuals, the tensor tympani muscle can contract voluntarily, although this ability is considered extremely rare. This voluntary contraction can produce a rumbling sound and is often observed during deep yawning or shouting. The tympanic reflex, with a response time of approximately 40 milliseconds, helps prevent damage to the inner ear by muffling low-frequency vibrations transmitted to the oval window.
While the tensor tympani muscle plays a role in dampening loud sounds, its reaction time is not fast enough to protect against sudden loud noises like explosions or gunshots. The primary purpose of this muscle is still debated, with researchers questioning its exact function, particularly in auditory and non-auditory reflexes and sound damping.
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The levator palpebrae superioris elevates the upper eyelid
The levator palpebrae superioris is a muscle in the orbit that elevates the upper eyelid. It originates from the inferior surface of the lesser wing of the sphenoid bone, just above the optic foramen. It is a skeletal muscle, not a smooth muscle. The levator palpebrae superioris receives its blood supply from branches of the ophthalmic artery, specifically the lacrimal, supratrochlear, supraorbital, and muscular branches. These vessels connect to the superior peripheral arcade, providing circulation to the upper eyelid's superior aspect.
The levator palpebrae superioris is one of the six extraocular muscles in the orbit. These muscles facilitate movements of the eye by elevating and retracting the upper eyelid and allowing an unhindered upward gaze. The levator palpebrae superioris is also involved in facial expressions, as the upper lid elevation contributes to expressing feelings of fear, anger, and shock.
The main actions of the levator palpebrae superioris muscle are the retraction and elevation of the superior eyelid and the widening of the palpebral fissure. These actions are limited by several anatomical features of the muscle, such as the lateral and medial attachments of the muscle's aponeurosis, which prevent further elevation of the eyelid once they are stretched maximally. The orbital septum, a fibrous part of the eyelid that when compressed maximally, also prevents further retraction of the eyelid.
Damage to the levator palpebrae superioris muscle or its innervation can cause ptosis, or drooping of the eyelid. Ptosis can also result from damage to the adjoining superior tarsal muscle or its sympathetic innervation. This condition is known as Horner's syndrome and presents as partial ptosis. Treatment for congenital ptosis may include a Müllerectomy procedure, which involves resecting the conjunctiva and the Müller muscle, or the attachment of weights to the upper eyelids to counter the action of the levator palpebrae superioris muscle.
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Frequently asked questions
Yes, there are muscles in the head.
The muscles in the head include the tongue, muscles of facial expression, extra-ocular muscles, and muscles of mastication.
Extra-ocular muscles are the muscles involved in eyeball movements. There are six muscles that control eyeball movements: superior, inferior, medial and lateral recti muscles, as well as the superior and inferior oblique muscles.
The four muscles of mastication are masseters, temporalis, medial pterygoid, and lateral pterygoid. These muscles are associated with jaw movements.
When the muscles in the head don't work in harmony, it can lead to conditions like temporomandibular joint disorder (TMD), resulting in painful symptoms such as jaw pain, frequent headaches, and ear and neck pain.
