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I'm sorry, I don't understand your request. Could you please clarify what you mean by muscle heads?
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What You'll Learn
Muscles of mastication
The muscles of mastication are a group of muscles responsible for chewing movements of the mandible at the temporomandibular joint (TMJ). These muscles enhance the process of eating by assisting in grinding food and approximating the teeth. The four main muscles of mastication are the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles. They attach to the rami of the mandible and facilitate various movements of the jaw, including elevation, depression, protrusion, retraction, and side-to-side movement.
The masseter muscle is the most powerful muscle of mastication. It has a rectangular shape with three layers: superficial, deep, and intermediate. The muscle originates from the zygomatic bone and inserts onto the mandibular ramus and coronoid process. Its primary function is to elevate the mandible and approximate the teeth.
The temporalis muscle is fan-shaped and originates from the temporal fossa of the skull, attaching to the coronoid process of the mandible. It assists in elevating and retracting the mandible. The medial pterygoid muscle has a quadrangular shape with two heads: deep and superficial. It is located inferiorly to the lateral pterygoid muscle and assists in mandibular movements.
The lateral pterygoid muscle has a triangular shape with superior and inferior heads. It originates from the sphenoid bone and inserts onto the neck of the mandible. This muscle is the sole muscle responsible for causing depression of the mandible, although it also assists with protrusion and side-to-side movement. The muscles of mastication receive their arterial supply from the maxillary artery, a branch of the external carotid artery. They are innervated by the anterior trunk of the mandibular nerve (CN V3), which is a branch of the trigeminal nerve.
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Muscles of facial expression
The muscles of facial expression, also known as mimetic muscles, are a group of about 20 flat skeletal muscles that lie underneath the skin of the face and scalp. They are responsible for two major tasks: chewing (or masticating) and making facial expressions such as smiling, pouting, frowning, or raising eyebrows in surprise. These muscles are unique because they originate from bones and insert in the dermis, manipulating the skin and soft tissues. They are located within the subcutaneous tissue of the face and can be broadly categorised into three groups: orbital, nasal, and oral.
The orbital group of facial muscles contains two muscles associated with the eye socket. If the facial nerve becomes damaged, the orbital muscles will cease to function, which can have serious clinical consequences. The eye cannot shut, causing the cornea to dry out (exposure keratitis), the lower eyelid droops (ectropion), and the lacrimal fluid pools in the lower eyelid. The test for facial nerve palsy involves raising the eyebrows and closing the eyelids.
The nasal muscles of facial expression include the procerus, which is the most superior of the nasal muscles. It lies superficially to the other muscles of facial expression and pulls the eyebrows downward to produce transverse wrinkles over the nose (associated with frowning). The depressor septi nasi muscle assists the alar part of the nasalis in opening the nostrils.
The oral muscles of facial expression are responsible for the movements of the mouth and lips. The buccolabial group of muscles forms a functional compound that controls the shape and movements of the mouth and lips. There are 11 of these muscles, including the orbicularis oris, which produces movements of the lips, and the buccinator muscle, which forms the muscular basis of the cheek. If the facial nerve is dysfunctional, the oral muscles can become paralysed, causing difficulty eating, with food collecting between the teeth and cheeks.
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Extra-ocular muscles
The actions of the six muscles responsible for eye movement depend on the position of the eye at the time of muscle contraction. The extra-ocular muscles receive motor innervation from the oculomotor nerve, except for the superior oblique, which is innervated by the trochlear nerve, and the lateral rectus muscle, which is innervated by the abducens nerve. The primary blood supply for the extra-ocular muscles is the muscular branches of the ophthalmic artery, the lacrimal artery, and the infraorbital artery.
The extra-ocular muscles have a large ratio of nerve fibres to skeletal muscle fibres compared to other skeletal muscles. They are also a specialised skeletal muscle form, with various fibre types, including slow tonic types that resist fatigue and saccadic (rapid) muscle fibres. The movements of the extra-ocular muscles take place under the influence of a system of extra-ocular muscle pulleys, soft tissue pulleys in the orbit, which is fundamental to the movement of the eye muscles and ensuring conformity to Listing's law.
The extra-ocular muscles develop along with Tenon's capsule (part of the ligaments) and the fatty tissue of the eye socket (orbit). There are three centres of growth associated with the development of the eye, and each is connected to a nerve, resulting in the subsequent nerve supply (innervation) of the eye muscles coming from three cranial nerves.
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Infrahyoid muscles
- Sternohyoid
- Omohyoid
- Sternothyroid
- Thyrohyoid
The sternohyoid muscle is the most superficial of all the infrahyoid muscles and is located in the superficial plane of the neck, along with the omohyoid muscle. It originates from the sternum and sternoclavicular joint and ascends to insert onto the hyoid bone. The omohyoid muscle is found deep in the sternocleidomastoid and consists of two bellies (superior and inferior) united by an intermediate tendon. The thyrohyoid muscle is a short band of muscle, thought to be a continuation of the sternothyroid muscle. The sternothyroid muscle is a wide muscle, located underneath the sternohyoid in the deep plane of the neck.
The infrahyoid muscles, along with the suprahyoid muscle group, are important for several functions related to speech, swallowing and the movement of the larynx, by controlling the positioning of the hyoid bone. They receive arterial supply via the superior and inferior thyroid arteries, with venous drainage via the corresponding veins. The infrahyoid muscles are innervated by the ansa cervicalis, and damage to this nerve can result in paresis or paralysis of the infrahyoid muscles, leading to difficulties in swallowing, hoarseness in the voice, and throat tightness.
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Sternocleidomastoid muscle
The sternocleidomastoid muscle, often abbreviated as SCM, is one of the largest and most superficial cervical muscles in the human body. The SCM is a powerful neck muscle that allows for the bending of the neck and the rotation or tilting of the head. The SCM is innervated by the accessory nerve, which is responsible for initiating the contraction of the SCM. The SCM is also associated with the common carotid artery and the brachial plexus.
The name sternocleidomastoid is derived from the muscle's origin and insertion points. Specifically, the SCM originates at the manubrium of the sternum (sterno-) and the clavicle (cleido-) and inserts at the mastoid process of the temporal bone of the skull (mastoid). The mastoid process is a section of bone located at the base of the skull behind the ears. The SCM is thick and narrow at its centre, broadening and thinning at either end.
The SCM has multiple functions beyond its primary role as a lateral neck flexor. It aids in respiration by acting as an accessory muscle during breathing, along with the scalene muscles of the neck. Additionally, the SCM helps to stabilise the neck and maintain posture, even when the body is at rest. It also plays a role in chewing by supporting the temporomandibular joint (TMJ), which connects the jaw to the skull and enables the opening and closing of the mouth.
Injuries, tension, sprains, strains, atrophy, and tumours can all damage the SCM, leading to pain, stiffness, and neck issues. Treatments for SCM issues include massage, osteopathic manipulation, physical therapy, and surgery in severe cases. Proper care for the SCM involves managing stress, maintaining good posture, and getting sufficient rest.
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Frequently asked questions
Muscle heads, or muscleheads, is a slang term for people who are very muscular, often due to bodybuilding.
People can become muscle heads through dedicated strength training and proper nutrition.
Muscle heads often prioritize their physical appearance and may spend a significant amount of time at the gym. They may also follow strict diets to support their muscle growth.
While there are health benefits to building muscle, excessive focus on physical appearance or extreme behaviors to achieve muscularity can be unhealthy. Balance and a healthy relationship with food and exercise are important.
