TLDR;
This video provides a comprehensive overview of muscle anatomy, biomechanics, and related pathologies. It covers muscle structure from macroscopic to microscopic levels, explains the sliding filament theory of muscle contraction, and discusses the lever systems involved in muscle action. Additionally, it explores common muscle disorders and the impact of various factors on muscle function.
- Muscle structure and function
- Biomechanics of muscle action
- Common muscle disorders
Muscle Structure [0:10]
The video begins by explaining the structure of a muscle, using the biceps brachii as an example. The muscle consists of an active part called the venter (belly) and a passive, tendinous part called the tendo (tendon). On a cross-section, the muscle is covered by a dense connective tissue sheath called the epimysium, which extends to form the tendon. Connective tissue partitions extend from the epimysium, dividing the muscle into fascicles (muscle bundles). These fascicles are covered by the perimysium, another dense connective tissue sheath containing blood vessels and nerves.
Muscle Fibres and Myofibrils [1:52]
A closer look at a muscle fascicle reveals that it is composed of muscle fibres (muscle cells), each covered by the endomysium. Muscle fibres range from 1 to 40 mm in length and 10 to 100 μm in thickness. Each muscle fibre is enclosed by the sarcolemma, which contains nuclei, mitochondria, and myoglobin. Within the muscle fibres are myofibrils, the contractile units of the muscle. The endomysium is also a connective tissue sheath, while the perimysium and epimysium transition into the tendon.
Sarcomere Structure [4:04]
The myofibril is composed of segments called sarcomeres. Sarcomeres consist of thick myosin filaments and thin actin filaments. Myosin filaments have bodies, cross-bridges, and heads, while actin filaments are thin strands. The M-line (or mesophragma) in the middle of the sarcomere holds the thick myosin filaments in place, and the Z-line (or telophragma) holds the thin actin filaments. Elastic filaments, made of connectin or titin, maintain muscle elasticity. The M-line and Z-line are composed of various proteins, including creatine phosphate in the M-line, which stores ATP for energy during physical activity.
H-band, A-band and I-band [6:17]
The sarcomere also features distinct bands: the H-band, which contains only myosin filaments; the A-band, which contains both myosin and actin filaments (and appears dark or anisotropic); and the I-band, which contains only actin filaments. The Z-membrane and M-line are also key structures within the sarcomere, each responsible for maintaining the structural integrity and function of the contractile unit.
Muscle Contraction [7:24]
Muscle contraction occurs when actin interacts with myosin. Tropomyosin, a protein, prevents actin from interacting with myosin. Troponin, another protein, changes the conformation of tropomyosin, allowing actin to bind to myosin. This process is calcium-dependent; calcium interacts with troponin, forming a troponin-calcium complex that moves tropomyosin, exposing the binding sites on actin. ATP is then split, providing energy for muscle contraction. Each muscle fibre contains 2,000 to 3,000 mitochondria, reflecting its high energy demands.
Actin-Myosin Interaction and Energy [8:36]
During contraction, actin interacts with myosin, forming an actomyosin complex. ATP breaks down, releasing energy that causes the filaments to slide closer together, resulting in muscle shortening. Relaxation requires energy to detach actin from myosin. Contraction requires more energy than relaxation. Key proteins involved include troponin, tropomyosin, actin, and myosin. Actin and myosin are responsible for muscle contraction, while troponin and tropomyosin regulate the contraction and relaxation processes.
Muscle Tension and Movement [9:35]
When myofibrils contract, muscle fibres shorten, creating tension in the endomysium, perimysium, and epimysium. This tension is transmitted to the tendon, which pulls on the bone, causing movement around the joints. The active part of the muscle acts on the passive tendon, resulting in bone movement.
Myofascial Pain Syndrome [10:23]
Myofascial pain syndrome, a common muscle pathology, involves pain in the muscles. Muscle fibres are innervated by the somatic nervous system, which releases acetylcholine, a neurotransmitter that interacts with nicotinic receptors, causing muscle contraction. Prolonged, awkward positions, trauma, inflammation, or overexertion can increase acetylcholine release, leading to strong muscle contractions and the formation of knots or nodules in the muscle.
Trigger Points and Ischemia [12:01]
These nodules, known as trigger points, are not scar tissue or tumours but chronic contractions of muscle fibres. They compress capillaries, reducing blood flow and causing ischemia (lack of blood supply). Ischemia leads to damage and the release of inflammatory mediators, such as prostaglandins and bradykinin, causing pain. Local anaesthetics can temporarily relieve the pain, but treatment requires breaking down the nodule to restore blood flow.
ATP and Muscle Relaxation [13:49]
Ischemia reduces ATP production, which is necessary for muscle relaxation. Breaking down the nodule increases blood flow, providing nutrients and ATP. This ATP is used to reduce calcium levels, allowing the muscle to relax. Trigger points are not scar tissue or tumours but nodules formed due to prolonged muscle contraction.
Muscle Biomechanics: Lever Systems [15:14]
Muscles operate on the principle of levers, involving a fulcrum (point A), a point of force application (point B), and a point of resistance (point V). There are three types of levers. First-class levers (levers of equilibrium) have the fulcrum between the force and resistance, such as the atlanto-occipital joint, which balances and stabilises the head. Second-class levers (levers of force) have the resistance between the fulcrum and force, such as the metatarsophalangeal joint, providing a mechanical advantage for lifting heavy loads with less energy. Third-class levers (levers of speed) have the force between the fulcrum and resistance, such as the elbow joint, providing speed and range of motion but requiring more muscle force.
Lever Types and Muscle Function [17:29]
The video explains the mechanical advantages of each lever system. Second-class levers allow muscles to lift heavy objects with less energy, while third-class levers provide speed and amplitude of movement but require more muscle force. Most muscles in the limbs operate as third-class levers. The video uses the example of a sledgehammer to illustrate how the position of the hand (force) relative to the hammerhead (resistance) affects the energy required to lift and swing the tool.
Accessory Muscle Structures: Tendons and Fascia [20:26]
Accessory structures, such as tendons, fascia, synovial sheaths, sesamoid bones, synovial bursae, aponeuroses, muscle retainers, and muscle blocks, support muscle function. These structures do not contract but help muscles perform movements efficiently, reduce friction, and protect against injury. Tendons, dense cords of collagen fibres, connect muscles to bones and are a continuation of the epimysium, perimysium, and endomysium.
Tendons, Fascia and Their Functions [21:58]
Tendons transmit the force of muscle contraction to bones, enabling movements such as flexion, extension, abduction, adduction, and rotation. Tendon pathologies include tendinitis (inflammation), tendinosis (degeneration), and rupture, often affecting the Achilles tendon. Fascia, dense fibrous connective tissue, forms sheaths for muscles, muscle groups, neurovascular bundles, and internal organs. It consists of collagen and elastic fibres and includes superficial fascia (beneath the skin) and deep fascia (surrounding muscles).
Anatomical and Clinical Significance of Fascia [23:50]
Deep fascia forms compartments for muscles and neurovascular bundles, separating muscle groups and reducing friction between adjacent muscles. It also helps maintain muscle position and ensures proper direction of muscle contraction. Clinically, fascia limits the spread of infection and serves as a surgical landmark. It is used in plastic surgery due to its density and rapid recovery. Fascial planes are used for nerve blocks, such as transverse abdominis plane (TAP) blocks, and prevent vein collapse.
Fascia Pathologies and Synovial Sheaths [26:19]
Fascia pathologies include fasciitis (inflammation), fasciomyositis (inflammation of fascia and muscle), and compartment syndrome (increased pressure within a fascial compartment). Compartment syndrome can lead to ischemia and necrosis of muscles and nerves. Synovial sheaths, such as vagina synovialis tendinum, form sheaths around muscle tendons, consisting of visceral and parietal layers. The mesotendon contains blood vessels and nerves, and the synovial cavity contains synovial fluid, reducing friction during movement.
Synovial Sheaths, Sesamoid Bones and Synovial Bursae [28:34]
Synovial sheaths are essentially synovial membranes in the form of a sheath around tendons, located under retainers. Pathologies include tenosynovitis (inflammation of the tendon and synovial sheath) and hygroma (cyst filled with serous fluid). Sesamoid bones, such as the patella, are located within tendons near joints, increasing muscle leverage, strengthening joints, distributing pressure, and directing tendon movement. Sesamoid bone pathologies include dislocations and fractures of the patella and sesamoiditis (inflammation). Synovial bursae, small closed sacs lined with synovial membrane and filled with synovial fluid, reduce friction between muscles, tendons, and bones.
Synovial Bursae, Aponeuroses and Muscle Retainers [31:21]
Synovial bursae, such as the prepatellar and infrapatellar bursae, consist of an outer fibrous sheath and an inner synovial membrane that produces synovial fluid. They reduce friction, soften pressure during movement, ensure tendon gliding, and prevent tissue trauma. Pathologies include bursitis (inflammation) and calcifying bursitis (calcium deposits). Aponeuroses, broad, flat, dense connective tissue sheets, are part of a muscle's tendon, acting as a wide tendon. They are located in the anterior abdominal wall, head, palm, sole, and back.
Aponeuroses Functions and Muscle Retainers [34:27]
Aponeuroses provide mechanical protection, support and fix organs, transmit muscle contraction force, participate in breathing, and ensure intra-abdominal pressure. Examples include the anterior abdominal aponeurosis, epicranial aponeurosis, palmar aponeurosis, and plantar aponeurosis. Pathologies include abdominal hernias, scalp wounds, Dupuytren's contracture, and plantar fasciitis. Muscle retainers (retinacula musculorum) are dense fibrous thickenings of fascia located near joints, mainly in the foot and wrist, but also in the knee.
Muscle Retainers and Muscle Functions [37:44]
Muscle retainers fix tendons, preventing displacement during contraction, directing movement, and transmitting forces. Damage to retainers can cause tendon displacement. Key muscle functions include locomotion (motor-driven), static (maintaining posture), protective (protecting internal organs), and participation in vital functions (breathing, swallowing). Muscles also act as venous pumps, promoting venous and lymphatic flow, regulating intra-cavity pressure, and contributing to thermogenesis.
External and Internal Factors Affecting Muscles [41:02]
External factors affecting muscles include physical activity (training increases muscle mass, bed rest causes atrophy), temperature (cold causes shivering, heat causes weakness), hypoxia (causes fatigue), trauma (causes rupture and myositis), nutrition (proteins, B vitamins, vitamin D, E, calcium, magnesium, potassium), and medications (botulinum toxin disrupts neuromuscular transmission). Internal factors include nerve regulation (central nervous system control, stroke, spinal cord injury, peripheral nerve diseases cause paresis and paralysis), blood circulation (insufficient circulation reduces muscle trophism), metabolism (hypoglycaemia causes weakness, acidosis causes fatigue), hormonal regulation (thyroxine provides energy, testosterone promotes growth, cortisol promotes breakdown), age (muscle mass decreases), and genetics (predisposition to muscle diseases).
Muscle Classification by Form and Function [44:00]
Muscles are classified by form (fusiform, square, triangular, trapezoidal, serrated, biceps, triceps, quadriceps), fibre direction (longitudinal, oblique, transverse, circular), relation to joints (monoarticular, biarticular, multiarticular, non-articular), topography (superficial, deep, medial, lateral, external, internal, anterior, posterior), body region (face, neck, back, chest), and function (flexors, extensors, abductors, adductors, rotators, elevators, depressors, sphincters, dilators).
Muscle Terminology and Types [46:31]
Muscle terminology often reflects function (e.g., levator scapulae, levator labii superioris). Muscles are also classified by structure and origin into skeletal, cardiac, and smooth muscle. Skeletal muscle is innervated by the somatic nervous system and is voluntary. Cardiac muscle, a type of striated muscle, is autonomous and controlled by the autonomic nervous system. Smooth muscle is also controlled by the autonomic nervous system and is found in blood vessels and internal organs.
Facial Muscles: Mimetic Muscles [48:29]
Facial muscles are divided into mimetic (facial expression) and masticatory (chewing) muscles. Mimetic muscles originate on bones and insert into the skin, moving the skin of the face and scalp but not acting on joints. They lack or have weakly expressed fascia, which facilitates the spread of inflammation. They are innervated by the facial nerve (seventh cranial nerve), and their tone decreases with age, leading to wrinkles and ptosis.
Functions and Groups of Mimetic Muscles [49:47]
Mimetic muscles give the face expression, assist in chewing, articulate speech, protect the eyes, nose, and mouth, facilitate mucus outflow, aid in breathing, and ease venous drainage from the face and head. They are grouped into muscles of the cranial vault, auricular muscles, muscles surrounding the orbital fissure, muscles surrounding the nasal openings, and muscles surrounding the oral fissure.
Muscles of the Cranial Vault and Auricular Muscles [52:17]
The occipitofrontalis muscle (epicranius) consists of two bellies: the occipital belly, which originates from the highest nuchal line and attaches to the epicranial aponeurosis, and the frontal belly, which originates from the aponeurosis and inserts into the skin of the eyebrow. The occipital belly retracts the aponeurosis, while the frontal belly raises the eyebrows, forming transverse wrinkles on the forehead. Auricular muscles include the anterior, superior, and posterior auricular muscles, which are rudimentary in humans.
Muscles Surrounding the Orbital Fissure [56:52]
Muscles surrounding the orbital fissure include the orbicularis oculi (which has orbital, palpebral, and lacrimal parts), the corrugator supercilii (which wrinkles the brow), the depressor supercilii (which lowers the brow), and the procerus (which creates transverse wrinkles on the glabella). The orbicularis oculi closes the eyelids, protecting the eye from bright light and dust. The corrugator supercilii draws the eyebrows towards the midline, creating vertical wrinkles, while the depressor supercilii pulls the skin of the brow and forehead down, creating transverse wrinkles. The procerus, an antagonist to the frontalis, pulls the skin of the forehead down, creating transverse wrinkles on the glabella.
Muscles Surrounding the Nasal and Oral Openings [1:03:33]
Muscles surrounding the nasal openings include the nasalis (which has transverse and alar parts) and the depressor septi nasi. The transverse part of the nasalis narrows the nostrils, while the alar part widens them. The depressor septi nasi lowers the nasal septum. Muscles surrounding the oral fissure include the orbicularis oris (which has labial and marginal parts), the levator labii superioris alaeque nasi (which raises the upper lip and ala of the nose), the levator labii superioris (which raises the upper lip), the levator anguli oris (which raises the corner of the mouth), the zygomaticus minor and major (which pull the corner of the mouth up and laterally), the depressor anguli oris (which lowers the corner of the mouth), the depressor labii inferioris (which lowers the lower lip), the mentalis (which raises the skin of the chin), the buccinator (which pulls the corner of the mouth laterally and presses the cheek against the teeth), and the risorius (which pulls the corner of the mouth laterally).
Masticatory Muscles: Temporalis and Masseter [1:17:43]
Masticatory muscles include the temporalis, masseter, lateral pterygoid, and medial pterygoid. These muscles originate on the bones of the skull and insert into the mandible, acting on the temporomandibular joint. They have dense fascia and are innervated by the mandibular branch of the trigeminal nerve (fifth cranial nerve). Their functions include closing the mouth, moving the mandible forward, backward, and side to side, and participating in speech articulation. The temporalis muscle originates from the temporal fossa and inserts into the coronoid process of the mandible, pulling the mandible up and back. The masseter muscle originates from the zygomatic arch and inserts into the masseteric tuberosity of the mandible, moving the mandible up and forward.
Pterygoid Muscles and Masticatory Muscle Pathologies [1:22:07]
The lateral pterygoid muscle has two heads: the superior head originates from the infratemporal surface and crest of the sphenoid bone and inserts into the joint capsule and disc of the temporomandibular joint, while the inferior head originates from the lateral plate of the pterygoid process and inserts into the pterygoid fovea of the mandible. This muscle protracts the mandible and facilitates lateral movements. The medial pterygoid muscle originates from the pterygoid fossa of the sphenoid bone and inserts into the pterygoid tuberosity of the mandible, elevating the mandible. Pathologies of the masticatory muscles include bruxism (involuntary contraction), trismus (spasm), myositis (inflammation), paralysis (due to trigeminal nerve damage), and myofascial pain syndrome.
Accessory and Mimetic Masticatory Muscles and Cellular Spaces of the Head [1:26:48]
Accessory masticatory muscles include the geniohyoid, mylohyoid, and digastric muscles, as well as mimetic muscles. Cellular spaces of the head are located between fascia and muscles, containing loose adipose tissue and neurovascular bundles. These spaces serve as pathways for infection and are richly vascularised, facilitating the spread of oedema and haematomas. Key cellular spaces include the subaponeurotic space of the cranial vault, the subaponeurotic temporal space, the interaponeurotic space, the interpterygoid space, the pterygomandibular space, and the masseteric-mandibular space.
Fascia and Cellular Spaces of the Head [1:27:55]
The fascia of the head includes the fascia of the masticatory muscles (masseteric, temporal, lateral pterygoid, and medial pterygoid), the buccal fascia, and the parotid fascia. Cellular spaces are formed between these fascial layers and muscles, containing loose adipose tissue and neurovascular bundles. These spaces are interconnected and can facilitate the spread of infection. They also have connections to the cellular spaces of the neck.
Superficial Neck Muscles: Platysma and Sternocleidomastoid [1:32:07]
Neck muscles are divided into superficial, middle, and deep groups. The middle group is further divided into suprahyoid and infrahyoid muscles, and the deep group into lateral and prevertebral muscles. Superficial neck muscles include the platysma and sternocleidomastoid. The platysma, originating from the pectoral and deltoid fascia, inserts into the lower border of the mandible, skin of the angle of the mouth, and parotid masseteric fascia. It facilitates venous return from the head and neck, depresses the mandible, and draws the skin of the angle of the mouth downwards and outwards.
Sternocleidomastoid Muscle and Middle Neck Muscles [1:35:19]
The sternocleidomastoid muscle originates from the anterior surface of the manubrium of the sternum and the sternal end of the clavicle, inserting into the mastoid process of the temporal bone and the superior nuchal line. Bilateral contraction extends the head or lifts the head and neck, while unilateral contraction rotates the head to the opposite side. Middle neck muscles are divided into suprahyoid and infrahyoid muscles. Suprahyoid muscles (mylohyoid, geniohyoid, stylohyoid, and digastric) elevate the hyoid bone and form the floor of the mouth. Infrahyoid muscles (sternohyoid, sternothyroid, thyrohyoid, and omohyoid) depress the hyoid bone.
Suprahyoid and Infrahyoid Muscles [1:37:59]
The mylohyoid and geniohyoid muscles form the diaphragm of the mouth. The mylohyoid originates from the mylohyoid line of the mandible and inserts into the hyoid bone. The geniohyoid originates from the mental spine of the mandible and inserts into the hyoid bone. The stylohyoid originates from the styloid process of the temporal bone and inserts into the hyoid bone. The digastric muscle has anterior and posterior bellies, originating from the mastoid notch of the temporal bone and the digastric fossa of the mandible, with its tendon fixed to the hyoid bone.
Infrahyoid Muscles and Deep Neck Muscles [1:47:23]
Infrahyoid muscles include the sternohyoid, sternothyroid, thyrohyoid, and omohyoid. The sternohyoid originates from the internal surface of the manubrium of the sternum and the sternal end of the clavicle, inserting into the hyoid bone. The sternothyroid originates from the internal surface of the manubrium of the sternum and the cartilage of the first rib, inserting into the oblique line of the thyroid cartilage. The thyrohyoid originates from the oblique line of the thyroid cartilage and inserts into the hyoid bone. The omohyoid has superior and inferior bellies, originating from the superior border of the scapula and inserting into the hyoid bone. Deep neck muscles are divided into lateral and prevertebral groups.
Lateral and Prevertebral Neck Muscles [1:52:19]
Lateral deep neck muscles include the anterior, middle, and posterior scalene muscles. The anterior scalene originates from the transverse processes of the third to sixth cervical vertebrae and inserts into the first rib. The middle scalene originates from the transverse processes of the second to seventh cervical vertebrae and inserts into the first rib. The posterior scalene originates from the transverse processes of the fourth to sixth cervical vertebrae and inserts into the second rib. These muscles laterally flex the head, flex the head forward, and elevate the upper ribs during inspiration. Prevertebral deep neck muscles include the longus colli, longus capitis, rectus capitis anterior, and rectus capitis lateralis.
Prevertebral Neck Muscles and Cervical Fascia [1:56:46]
The longus colli muscle has vertical, inferior oblique, and superior oblique parts, originating from the bodies and transverse processes of the cervical and thoracic vertebrae and inserting into the bodies and anterior tubercle of the atlas. The longus capitis originates from the transverse processes of the third to sixth cervical vertebrae and inserts into the basilar part of the occipital bone. The rectus capitis anterior originates from the lateral mass of the atlas and inserts into the basilar part of the occipital bone. The rectus capitis lateralis originates from the transverse process of the atlas and inserts into the jugular process of the occipital bone. These muscles flex and rotate the head. Cervical fascia, as classified by Shevkunenko, includes superficial fascia, superficial layer of the deep fascia, deep layer of the deep fascia, pretracheal fascia, and prevertebral fascia.
Cervical Fascia Layers and Cellular Spaces [2:05:03]
The superficial cervical fascia lies beneath the skin and forms a sheath for the platysma muscle. The superficial layer of the deep cervical fascia forms sheaths for the trapezius and sternocleidomastoid muscles and the submandibular salivary gland. The deep layer of the deep cervical fascia forms sheaths for the omohyoid, sternohyoid, sternothyroid, and thyrohyoid muscles. The pretracheal fascia surrounds the organs of the neck (thyroid gland, trachea, oesophagus) and forms a carotid sheath for the common carotid artery, internal jugular vein, and vagus nerve. The prevertebral fascia covers the prevertebral muscles and the sympathetic trunk. Cellular spaces of the neck include the suprasternal space, the retropharyngeal space, and the prevertebral space.
Cellular Spaces and Triangles of the Neck [2:13:01]
Cellular spaces of the neck are divided into closed (non-communicating) and communicating spaces. Closed spaces include the suprasternal space, the blind space of Gruber, the sheath of the sternocleidomastoid muscle, the space of the submandibular gland, and the prevertebral space. Communicating spaces include the pre-visceral space (communicating with the anterior mediastinum) and the retrovisceral space (communicating with the posterior mediastinum). Triangles of the neck are used to define anatomical regions.
Submandibular and Submental Triangles [2:22:49]
The submandibular triangle is bounded by the lower border of the mandible, the anterior belly of the digastric muscle, and the posterior belly of the digastric muscle. It contains the submandibular gland, facial artery and vein, and submandibular lymph nodes. The submental triangle is bounded by the anterior bellies of the digastric muscles and the hyoid bone. It contains submental lymph nodes.
Carotid Triangle and Omohyoid Triangle [2:34:49]
The carotid triangle is bounded by the anterior border of the sternocleidomastoid muscle, the posterior belly of the digastric muscle, and the superior belly of the omohyoid muscle. It contains the common carotid artery, internal and external carotid arteries, internal jugular vein, vagus nerve, hypoglossal nerve, and branches of the cervical plexus. The omohyoid (or omotracheal) triangle is bounded by the superior belly of the omohyoid muscle, the sternocleidomastoid muscle, and the midline of the neck. It contains the thyroid gland, trachea, and oesophagus.
Omohyoid-Tracheal Triangle and Lateral Neck Region [2:46:49]
The omohyoid-tracheal triangle is bounded by the superior belly of the omohyoid muscle, the sternocleidomastoid muscle, and the midline of the neck. It contains the thyroid gland, trachea, and oesophagus. The lateral region of the neck is bounded by the sternocleidomastoid muscle, the trapezius muscle, and the clavicle. It contains the spinal accessory nerve, branches of the cervical plexus, and the subclavian artery and vein.
Muscles of the Back: Superficial Layer [2:54:30]
Muscles of the back are divided into superficial, intermediate, and deep layers. The superficial layer includes the trapezius, latissimus dorsi, rhomboid major and minor, and levator scapulae muscles. These muscles primarily control the movement of the upper limbs. The trapezius muscle originates from the occipital bone, nuchal ligament, and spinous processes of the cervical and thoracic vertebrae, inserting into the acromion and spine of the scapula and the lateral third of the clavicle. It elevates, retracts, and rotates the scapula.
Muscles of the Back: Intermediate and Deep Layers [3:26:40]
The intermediate layer of the back muscles includes the serratus posterior superior and serratus posterior inferior muscles, which assist in respiration. The deep layer of the back muscles is divided into superficial, intermediate, and deep layers. The superficial layer includes the splenius capitis and splenius cervicis muscles, which extend and rotate the head and neck. The intermediate layer includes the erector spinae muscles (iliocostalis, longissimus, and spinalis), which extend and laterally flex the vertebral column. The deep layer includes the transversospinalis muscles (semispinalis, multifidus, and rotatores), which stabilise and rotate the vertebral column.
Transversospinalis Muscles and Suboccipital Muscles [3:39:29]
The transversospinalis muscles originate from the transverse processes of the vertebrae and insert into the spinous processes of the vertebrae above, spanning several segments. The deep layer also includes the interspinales and intertransversarii muscles, which assist in extension and lateral flexion of the vertebral column. The suboccipital muscles (rectus capitis posterior major and minor, obliquus capitis superior and inferior) are located in the suboccipital triangle and control head movements.
Fascia of the Back and Muscles of the Chest [3:48:43]
The fascia of the back includes the superficial fascia, the thoracolumbar fascia, and the nuchal fascia. The thoracolumbar fascia is divided into superficial, middle, and deep layers. Muscles of the chest are divided into superficial, deep, and diaphragmatic muscles. Superficial chest muscles include the pectoralis major and minor, subclavius, and serratus anterior.
Superficial Chest Muscles: Pectoralis Major and Minor [3:52:56]
The pectoralis major originates from the clavicle, sternum, costal cartilages, and aponeurosis of the external oblique muscle, inserting into the crest of the greater tubercle of the humerus. It adducts, flexes, and medially rotates the arm. The pectoralis minor originates from the ribs 3-5 and inserts into the coracoid process of the scapula, depressing and protracting the scapula.
Subclavius and Serratus Anterior Muscles [3:54:50]
The subclavius originates from the first rib and inserts into the inferior surface of the clavicle, depressing the clavicle. The serratus anterior originates from the upper eight or nine ribs and inserts along the medial border of the scapula, protracting and rotating the scapula upward.
Muscles of the Abdomen: Rectus Abdominis and Obliques [4:01:10]
Muscles of the abdomen are divided into anterior, lateral, and posterior groups. The anterior group includes the rectus abdominis and pyramidalis muscles. The lateral group includes the external oblique, internal oblique, and transversus abdominis muscles. The posterior group includes the quadratus lumborum muscle. The rectus abdominis originates from the pubic crest and symphysis and inserts into the xiphoid process and costal cartilages of ribs 5-7, flexing the vertebral column and compressing the abdomen.
Pyramidalis and Oblique Muscles of the Abdomen [4:20:45]
The pyramidalis muscle originates from the pubic crest and inserts into the linea alba, tensing the linea alba.
