Human Anatomy - A Course of Lectures - Kostylenko Yu.P. 2015

General Myology. Structural Features of the Muscles of the Head

Lecture Plan:

3.1 General characteristics of the human muscular system.

3.2 Concept of a Muscle as an organ.

3.3 Classification of Muscles.

3.4 Accessory apparatus of muscles.

3.5 Structural Features of the Muscles of the HEAD.

3.6 Characteristics of fascial spaces of the head.

3.1 General CHARACTERISTICS OF THE human muscular system

The Musculoskeletal System consists of passive and active parts. The passive part is formed by the Skeleton and bone joints, while the active part consists of the muscles.

The Study of the muscular system is called Myology (from the Greek Myos - muscle), hence muscle inflammation is called myositis, a muscle tumor is called myoma, and so on.

There are approximately 637 muscles in The Human Body, 316 of which are paired and 5 are unpaired. The Great Medical Encyclopedia lists 1108 muscle names, including synonyms.

There are 3 types of Muscle tissue:

1. Cytology/cytology/32.html">Smooth muscle tissue. It is found in the walls of Internal Organs and Blood Vessels. It is composed of smooth muscle Cells characterized by high extensibility but slow contraction. That is why a snail or an earthworm, which possess only smooth musculature, crawl slowly.

2. Striated muscle tissue

2.a Striated Skeletal Muscle tissue. This muscle tissue is capable of rapid contraction. Contraction of this muscle tissue is under voluntary control. These muscles attach to the skeleton.

2.b. Striated cardiac muscle tissue.

Functions of skeletal muscles:

1. Muscles perform the function of external and internal movement.

2. Muscles account for 35-45% of human body mass and therefore play a major role in METABOLISM. The basal metabolic rate depends on them.

3. Muscles participate in heat production.

4. Muscles participate in Blood Circulation. There is a theory according to which muscles act as pumps, or a peripheral Heart, returning blood to The Heart (During Muscle contraction).

5. Muscles are organs of proprioceptive sensitivity, or muscle sense. Muscle sense allows spatial orientation. Together with bones, muscles form the body contour.

3.2 Structure of a muscle as an organ

Each skeletal muscle is an organ that has its own muscular part (active, body, or belly) and tendinous (passive) part, as well as a system of Connective Tissue sheaths, and is supplied with blood Vessels and nerves. The specific tissue element of a muscle is the striated muscle fiber. Muscle fibers are elongated, with their length ranging from a few millimeters to 10-15 cm. Fiber thickness varies with age and differs among muscles. In an adult, it is 38-61 (up to 70) µm, while in individuals who systematically engage in sports, especially weightlifting, it reaches 100 µm. Striated muscle fibers are multinucleated formations. A single fiber may contain up to 120 nuclei. A muscle fiber is surrounded by a thin sheath called the sarcolemma. Inside the fiber is the sarcoplasm, which contains myofibrils, the specialized contractile structures of the fiber. A single muscle fiber contains from 100 to 1000 myofibrils aligned along the axis of the fiber.

About three hundred years ago, differences in the coloration of muscle fibers were noticed, and red and white fibers were distinguished. Later, differences in the Chemical Composition and metabolic processes of both types of fibers were discovered. It was established that white fibers contain relatively less sarcoplasm and more myofibrils. White fibers are characterized by faster contraction. Red muscle fibers are somewhat thinner, characterized by a high sarcoplasm content, but contain fewer myofibrils; therefore, they exhibit a lower contraction speed but a greater contraction force. The content of red and white fibers in different Introduction/39.html">Muscles and their distribution within muscles are related to the Functional Properties of the latter.

Striated muscles feature a system of connective tissue sheaths. Individual fibers are surrounded by a loose connective tissue known as the endomysium. Adjacent fibers group together into primary bundles, which in turn form larger secondary bundles, which make up even larger tertiary bundles. The connective tissue surrounding bundles of all orders constitutes the perimysium. The perimysium houses the branches of blood vessels and nerves that supply the muscle. The layer of connective tissue covering the muscle externally is called the epimysium.

A tendon consists of Collagen fibers, which also make up ligaments. Tendinous fibers penetrate the muscle sheath and are tightly bound to the muscle fibers. The endo-, peri-, and epimysium continue into the tendon, transforming into the endo-, peri-, and epitendineum. Therefore, a tendon cannot be separated from a muscle without damaging the muscle belly. In most muscles, especially in the limbs, tendons take the form of elongated cylindrical cords. On the trunk, some muscles form flat tendinous expansions called aponeuroses.

THE ORIGIN OF a muscle is termed origo, and its insertion is insertio. Conventionally, in the limbs, the origin of a muscle lies proximally, while the insertion lies distally. On the trunk, the origin lies medially, and the insertion laterally. These muscle attachment sites are fixed and do not change positions.

During muscle contraction, one of its ends remains stationary, which is the punctum fixum. The other end moves along with the bone to which it attaches, known as the punctum mobile. The mobile point is always drawn toward the fixed one. Unlike the origin and insertion of a muscle, these points can interchange. The exact same end of a muscle can be either fixed or mobile. For instance, the rectus abdominis muscle attaches to the pubic bones at one end, while its origin is on the rib cage bones. When bending forward, the punctum mobile is on the BONES OF THE rib cage, whereas during a pull-up on a bar, the opposite is true.

3.3 Muscle Classification

There is no single unified Classification of Skeletal muscles. Muscles are categorized according to their anatomical position in the human body, shape, direction of muscle fibers, function, and their relationship to joints.

1. By structure or number of heads: fusiform (spindle-shaped) muscles are the most common. They clearly exhibit a belly, a head, and a tail. A muscle may have 2, 3, or 4 heads, or even 2 bellies.

2. By shape: quadrilateral, triangular, circular.

3. By length: long, short, and broad (flat).

4. By the direction of muscle fibers: parallel fibers (rectus abdominis); oblique fibers (pennate): unipennate — flexor pollicis longus; bipennate — rectus femoris; multipennate — fan-shaped, such as the deltoid and temporal muscles (Fig. 3.1). Muscles with parallel fibers can shorten by up to 40%, whereas pennate muscles exhibit a lesser range of shortening but greater force.

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Fig. 3.1 Muscle shapes:

A — fusiform;

B — biceps;

C — digastric;

D — muscle with tendinous intersections;

E — bipennate;

F — unipennate;

1, 3 — tendons;

2 — belly;

4 — tendinous intersection;

5 — tendinous arch.

5. By function: flexors and extensors, abductors and adductors, supinators and pronators, sphincters, tensors, levators and depressors.

6. By attachment sites, such as the sternocleidomastoid muscle.

7. Depending on their relationship to the joints they span, muscles are classified as mono-, bi-, or polyarticular. Being longer, polyarticular muscles are typically located more superficially relative to monoarticular ones.

8. By position: superficial and deep, external and internal, lateral and medial muscles.

According to their origin, muscles are divided into 3 groups:

1. Some muscles that develop in the trunk remain in place, forming local or autochthonous musculature. Based on innervation, autochthonous musculature can always be distinguished from migrant muscles. This is of great clinical significance. The Abdominal muscles, for example, are autochthonous.

2. Another group of muscles migrates from the trunk to the limb. Such muscles are called trunkofugal (running from the trunk). One end of these muscles attaches to the trunk or Skull, and the other to the limb (Major and minor rhomboid, serratus anterior, and subclavius muscles).

3. A third group of muscles migrates from the limbs to the trunk. These are trunkopetal muscles, meaning they are derivatives of the limb mesoderm. They attach similarly to trunkofugal muscles (pectoralis major and minor, latissimus dorsi).

Outline for studying a muscle:

1) name the muscle (in Ukrainian and Latin);

2) trace the origin and insertion of the muscle on the skeleton;

3) demonstrate the muscle on a cadaver;

4) explain the function of the muscle (demonstrate on the skeleton and on a living person (on oneself) what movements and in which joints this muscle performs), and find its antagonists and synergists.

3.4 Accessory Apparatus of Muscles

The accessory apparatus of muscles includes fasciae, synovial bursae, fibrous and synovial tendon sheaths, muscle pulleys, and sesamoid bones.

Fasciae are sheaths formed by loose or dense Fibrous connective tissue that cover muscles, form sheaths for blood vessels and nerves, and surround various organs. Fasciae are divided into superficial and deep.

The superficial fascia is located beneath the Skin and is connected to it by connective tissue strands. The structure of the superficial fascia and the degree of its prominence vary across different body regions. A direct correlation has been noted between the thickness of the fascia, the number of layers forming it, and the degree of development of subcutaneous fat deposits. The superficial fascia is well-developed in the anterior abdominal wall, chest, arm, and thigh. In areas where the skin experiences higher external pressure, the superficial fascia fuses with the underlying Tissues and is difficult to separate from the deep fascia. This occurs on the palm, sole, in the elbow and knee regions, and the posterior forearm.

The deep fascia covers specific PARTS OF THE body and is named after these regions: Cervical fascia, thoracic fascia, axillary fascia, etc. The deep fascia forms sheaths for individual muscles and muscle groups. Fasciae perform an important supportive function. Together with adipose tissue, they form the so-called soft Skeleton of the body. Fasciae serve as sites of origin and insertion for many skeletal muscles. In certain areas, under The Influence of lateral tendon pressure, fasciae thicken and form retinacula, under which tendons pass. Flexor and extensor retinacula are present in the wrist and ankle regions.

Under the combined action of pressure and stretching forces, fasciae become dense, forming aponeuroses—palmar and plantar. The iliotibial tract is structured similarly to an aponeurosis, representing the thickened lateral part of the fascia lata of the thigh.

The anatomy of fasciae is closely related to the pathways of spread for A number of pathological processes. In some cases, fasciae act as a barrier in their path, while in other cases, conversely, they serve as channels for their spread.

Synovial bursae are small cavities lined with a synovial membrane and containing synovial fluid. They can be unilocular or multilocular. Several types of synovial bursae are distinguished based on their Location.

1. Subcutaneous bursae are located in the subcutaneous tissue between the skin and bone, usually over bony prominences (above the acromion, olecranon, etc.).

2. Subfascial bursae are similar to subcutaneous ones (anterior to the Patella).

3. Submuscular bursae form where muscles pass over bony prominences (between the gluteus maximus muscle and the greater trochanter of the Femur).

4. Subtendinous bursae are located between muscle tendons and bones, or between adjacent tendons.

Tendon sheaths can be fibrous or synovial. Fibrous tendon sheaths are channels bounded by thickened fascia through which tendons pass. Fibrous tendon sheaths are well-developed in the hand and FOOT. Synovial tendon sheaths have a more complex structure. They are double-walled sleeves placed over tendons. The outer and tendinous (inner) parts of the sheath are lined with a synovial layer, and a cavity containing synovial fluid is located between them. The tendinous part of the synovial sheath is fused with the tendon. It is connected to the outer part by a special fold called the mesotendon (mesotendineum). Blood vessels and nerves supplying the tendon pass through the mesotendon.

Synovial sheaths are located in the hand and foot, in areas where the tendons of several muscles run closely together. Synovial sheaths are easily involved in inflammatory processes.

Muscle pulleys are located where tendons change direction. For example, the passage of the tendon of the fibularis (peroneus) longus muscle beneath the trochlear process of the calcaneus.

Sesamoid bones, which are embedded within muscle tendons, increase the angle at which a tendon attaches to a bone, thereby enhancing the leverage and pulling force of that muscle.

3.5 Structural Features of the Muscles of the Head

The muscles of the head are divided into masticatory and facial muscles. The masticatory muscles, which move the Mandible, include the masseter muscle (musculus masseter), temporal muscle (musculus temporalis), medial pterygoid muscle (musculus pterygoideus medialis), and lateral pterygoid muscle (musculus pterygoideus lateralis).

The facial muscles include the epicranial muscle (musculus epicranius), auricular muscles (musculi auriculares anterior, posterior et superior), procerus muscle (musculus procerus), orbicularis oculi muscle (musculus orbicularis oculi), corrugator supercilii muscle (musculus corrugator supercilii), levator labii superioris muscle (musculus levator labii superioris), zygomaticus minor muscle (musculus zygomaticus minor), zygomaticus major muscle (musculus zygomaticus major), risorius muscle (musculus risorius), orbicularis oris muscle (musculus orbicularis oris), levator anguli oris muscle (musculus levator anguli oris), depressor anguli oris muscle (musculus depressor anguli oris), depressor labii inferioris muscle (musculus depressor labii inferioris), mentalis muscle (musculus mentalis), buccinator muscle (musculus buccinator), and nasal muscle (musculus nasalis).

Facial muscles possess several distinct characteristics:

✵ they attach directly to the skin;

✵ they are responsible for facial expressions (skin movements);

✵ they lack fascial coverings;

✵ they are innervated by the Facial Nerve;

✵ they develop from the second pharyngeal (branchial) arch;

✵ they are arranged circularly or radially around the natural orifices of the head.

3.6 Characteristics of the Facial and Cranial Fascial Spaces

The fascial spaces of the head serve as sites for the onset and spread of inflammatory processes; therefore, a thorough knowledge of their topography is essential for dental practitioners. In the fronto-parieto-occipital region, loose connective tissue forms the subaponeurotic space, located between the epicranial aponeurosis (galea aponeurotica) and the periosteum of the cranial vault, extending from the supraorbital margins to the superior nuchal line, as well as the subperiosteal spaces between the cranial bones and their periosteum, bounded by the cranial sutures and areas where the periosteum fuses with the bone.

In the temporal region, there are three fascial clefts:

1. The suprazygomatic interaponeurotic space, bounded by the two layers of the temporal fascia and the zygomatic arch;

2. The subaponeurotic space, situated between the superficial surface of the temporal muscle and the temporal fascia;

3. The deep temporal space, which separates the deep surface of the muscle from the periosteum.

In the lateral facial region, the parotid fascia encloses the parotid space, which contains not only the salivary gland but also major blood vessels, nerves, Lymph Nodes, and a considerable amount of loose connective tissue that communicates with the parapharyngeal space and the cellular tissue on the Medial surface of the mandible (in the infratemporal fossa).

The anterior part of the infratemporal fossa is occupied by the buccal fat pad (particularly well-developed in children), which adjoins the anterior borders of the masseter and temporal muscles and sends extensions into the subaponeurotic space of the temporal region, the pterygopalatine fossa, and the pterygomandibular space. The latter is located in the posterior part of the infratemporal fossa, bounded superiorly by the lateral pterygoid muscle, medially by the medial pterygoid muscle, and laterally by the mandibular ramus. Superiorly, it continues into the temporopterygoid and interpterygoid spaces. The temporopterygoid space lies between the lateral pterygoid and temporal muscles, extending upward into the deep temporal space. The interpterygoid space is situated on the medial surface of the lateral pterygoid muscle.