Introduction to Myology

• Myology is the study of the muscular system

Types of Muscle

• Skeletal muscle is one type of muscle
• Smooth muscle is the second type
• Cardiac muscle is the third type

Skeletal Muscles

• There are approximately 600 skeletal muscles in the human body
• Skeletal muscles are attached to bones
• Skeletal muscles make up about 40% of body weight
• Skeletal muscle functions to produce movement, maintain posture, stabilize joints, and generate heat
• Action of skeletal muscles are voluntary and controlled by somatic motor neurons

Morphology of Skeletal Muscle

• Muscle belly refers to the fleshy part of the muscle
• Tendons are a strong bundle of collagen at each end of a muscle
• Aponeurosis is a broad, flat tendonous sheath

Classification of Muscles

• Long muscles are classified by their shape
• Short muscles are classified by their shape
• Broad muscles are classified by their shape
• Orbicular muscles are classified by their shape
• Unipennate muscles are classified by their shape
• Bipennate muscles are classified by their shape
• Multipennate muscles are classified by their shape

Muscle Attachments

• Origin refers to the fixed attachment in the start/end of a muscle
• Insertion refers to the movable attachment at the opposite end of the muscle
• Proximal and distal attachments are better terms to use, since some muscles may act in both directions in different situations

Action or Movement

• Prime mover/agonist muscles actively contract to produce the desired movement
• Antagonist muscles oppose the action of the prime mover
• Synergists are more than one muscle performing an action collectively
• Fixators bring stability to the proximal part of a limb if the distal part is moving
• Under different conditions, a muscle may act as a prime mover, antagonist, synergist, or fixator

Muscle Naming

• Muscles are named by their shape, size, location, action, direction, number of parts, and points of attachment
• Examples include trapezius & rhomboid which are named for shape
• Levator scapulae is named for action
• Gluteus maximus, medius, & minimus are named for size
• Sternocleidomastoid is named for location
• Quadriceps femoris, Biceps & triceps are named for the number of heads or parts

Descriptive muscle names

• Names that identify body regions i.e. temporalis muscle indicate Location in the body
• Names that describe orgin and insertion of muscles i.e. genioglossus muscle indicate Origin and insertion
• Names of muscle that describe the fascicle orientation i.e. rectus mean straight or transversus mean oblique indicate Fascicle organization
• Names of muscle that are visible at body surface i.e. Externus (superficialis) indicate Relative position
• Names that refect how many tendons muscle have. For example bi means 2 and tri means 3 indicate Structural characteristics

Muscle Size

• Longus = long
• Longissimus = longest
• Teres = long and round
• Brevis = short
• Magnus = large
• Major = larger
• Maximus = largest
• Minor = small
• Minimus = smallest

Supplementary Structures

• Fascia is a connective tissue sheath
• Superficial fascia is immediately under the skin mixed with underlying fats, and thicker in the scalp, palm, and sole
• Deep fascia lies underneath the superficial fascia, being a much more densely packed and strong layer that covers the muscles in connective tissue aggregations, helping to keep them divided and protected
• Synovial Bursa is often found between tendon & ligaments close to bones for the freedom of movements
• Tendinous sheath is a double layer synovial sheath that envelops the tendons, mostly seen in hand & foot and has two layers
• Synovial layer is internal with loose attachment to tendons
• Fibrous layer is external & stronger
• Synovial fluid is between both layers
• Where a nerve or blood vessel is near the tendon, the structure is called mesotendon
• Sesamoid bones are developed inside the tendon

Division of the Muscular System

• Axial muscles position the head and spinal column and move the rib cage, accounting for 60% of skeletal muscles.
• Appendicular muscles support the pectoral and pelvic girdles, and limbs, accounting for 40% of skeletal muscles.