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THE MUSCULAR SYSTEM

THE MUSCULAR SYSTEM. INTERACTIONS OF SKELETAL MUSCLES IN THE BODY. Muscles only pull; they are not capable of pushing Generally as a muscle shortens, its insertion (attachment on the movable bone) moves toward its origin (its fixed or immovable point of attachment)

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THE MUSCULAR SYSTEM

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  1. THE MUSCULAR SYSTEM

  2. INTERACTIONS OF SKELETAL MUSCLES IN THE BODY • Muscles only pull; they are not capable of pushing • Generally as a muscle shortens, its insertion (attachment on the movable bone) moves toward its origin (its fixed or immovable point of attachment) • Muscles can be classified into four functional groups: • 1.Prime Movers: • The muscle that provides the major force for the specific movement is called the prime mover or the agonist, of that movement • The biceps brachii muscle, which fleshes out the anterior arm (and inserts on the radius), is a prime mover of elbow flexion • 2.Antagonists: • Muscles that oppose or reverse a particular movement • When a prime mover is active, the antagonist muscles are often stretched and may be relaxed • Can also help to regulate the action of a prime mover by contracting to provide some resistance, thus helping to prevent overshoot or to slow or stop the movement • Prime mover and its antagonist are located on opposite sides of the joint across which they act • Antagonists can also be prime movers in their own right • Example: flexion of the forearm by the biceps brachii muscle of the arm is antagonized by the triceps brachii, the prime mover for extending the forearm

  3. INTERACTIONS OF SKELETAL MUSCLES IN THE BODY • 3.Synergists: • Help the prime movers by: • Adding a little extra force to the same movement • Or reducing undesirable or unnecessary movements that might occur as the prime mover contracts • When a muscle crosses two or more joints, its contraction causes movement at all of the spanned joints unless other muscles act as joint stabilizers • Example: the finger flexor muscles cross both the wrist and the phalangeal joints, but you can make a fist without bending your wrist because synergistic muscles stabilize the wrist • As some flexors act, undesirable rotation movements occur • Synergists can prevent this, allowing all of the prime mover’s force to be exerted in the desired direction

  4. INTERACTIONS OF SKELETAL MUSCLES IN THE BODY • 4.Fixators: when synergists immobilize a bone, or a muscle’s origin, they are more specifically called fixators • Examples: • Scapula is held to the axial skeleton only by muscles and is quite freely movable • The fixator muscles that run from the axial skeleton to the scapula can immobilize the scapula so that only the desired movements occur at the mobile shoulder joint • Muscles that help to maintain upright posture

  5. INTERACTIONS OF SKELETAL MUSCLES IN THE BODY • Although prime movers seem to get all the credit for causing certain movements, antagonistic and synergistic muscles are also important in producing smooth, coordinated, and precise movements • A muscle may act as a prime mover in one movement, an antagonist for another movement, a synergist for a third movement, and so on

  6. NAMING SKELETAL MUSCLES • 1. Location of the muscle: Some muscle names indicate the bone or body region with which the muscle is associated • Example: • Temporalis muscle overlies the temporal bone • Intercostal muscles run between the ribs • 2. Shape of the muscle: Some muscles are named for their shape • Example: • Deltoid muscle is roughly triangular • Together the right and left trapezius muscles form a trapezoid • 3. Relative size of the muscle: Terms such as maximus (largest), minimus (smallest), longus (long), and brevis (short) are often used in muscle names to indicate relative size of the muscle • Example: • Gluteus maximus • Gluteus minimus

  7. NAMING SKELETAL MUSCLES • 4. Direction of muscle fibers: The names of some muscles indicate the direction in which their fibers (and fascicles) run in reference to some imaginary line, usually the midline of the body or the longitudinal axis of a limb bone • Examples: • Rectus (straight): fibers run parallel to that imaginary line (axis) • Rectus femoris: straight muscle of the thigh, or femur) • Transversus (right angle): muscle fibers run at right angles • Transversus abdominis: transverse muscle of the abdomen • Oblique (oblique angle): muscle fibers run at oblique angles • External oblique: oblique muscle of the abdomen

  8. NAMING SKELETAL MUSCLES • 5. Number of origins: The number of origins a muscle has may be indicated by the word biceps, triceps, or quadriceps • Example: • Biceps brachii: muscle of the arm has two origins (heads)

  9. NAMING SKELETAL MUSCLES • 6. Location of the attachments: Some muscles are named according to the location of their origin and insertion • Origin is always named first • Example: • Sternocleidomastoid: muscle of the neck • Has a dual origin on the sternum (sterno) and clavicle (cleido), and it inserts on the mastoid process of the temporal bone

  10. NAMING SKELETAL MUSCLES • 7. Action: A muscle may be named for its action by using such words as flexor (flex), extensor (extend), adductor (brought toward), or supinate (bend backward) in its name • Example: • Adductor longus: located in the medial thigh • Brings about thigh adduction (toward the main axis of the body or a limb) • Supinator muscle: • Supinates the forearm: • Turn the forearm or hand so that the palm faces upward • Supinates the leg and foot: • To rotate the foot and leg outward

  11. NAMING SKELETAL MUSCLES • Several criteria are combined in the naming of some muscles • Example: extensor carpi radialis longus • Action of the muscle: the muscles action (extensor) • Location of attachment: joint it acts on (carpi = wrist) • Location of muscle: lies close to the radius of the forearm (radialis) • Relative size of muscle: relative to other wrist extensor muscles (longus) • Unfortunately, not all muscle names are this descriptive

  12. MUSCLE MECHANICS:IMPORTANCE OF FASCICLE ARRANGEMENT AND LEVERAGE • In skeletal muscles the common arrangement of the fascicles varies, resulting in muscles with different shapes and functional capabilities

  13. Arrangement of Fascicles • Fascicle: bundle of nerve or muscle fibers (cells) bound together by connective tissue • All skeletal muscles consist of fascicles, but fascicle arrangement vary, resulting in muscles with different shapes and functional capabilities

  14. SKELETAL MUSCLE

  15. Arrangement of Fascicles • (a): Circular pattern: • Fascicles arranged in concentric rings • Muscles with this arrangement surround external openings, which they close by contracting • General term for these muscles is sphincters (squeezers) • Examples: • Orbicularis muscles surrounding the eyes (Orbicularis oculi) and the mouth (Orbicularis oris)

  16. Arrangement of Fascicles • (b): Convergent pattern: • Muscle has a broad origin, and its fascicles converge toward a single tendon of insertion • Such a muscle is triangular or fan shaped like the pectoralis major muscle of the anterior thorax

  17. Arrangement of Fascicles • (c)(f): Parallel pattern: • The long axes of the fascicles run parallel to the long axis of the muscle • Such muscles are either: • straplike (c: parallel) • spindle (f: fusiform) • shaped with an expanded belly (midsection) • Examples: • Sartorius of thigh (c) • Biceps brachii muscle of the arm (f)

  18. Arrangement of Fascicles • (d)(e)(g): Pennate pattern: • In a pennate (feather) pattern of arrangement the fascicles are short and attach obliquely to a central tendon that runs the length of the muscle • Types: • Unipennate: d • Fascicles insert into only one side of the tendon • Example: extensor digitorum muscle of the leg • Bipennate: g • Fascicles insert into the tendon from opposite sides (muscle grains resemble a feather) • Example: rectus femoris muscle of the thigh • Multipennate: e • Arrangement looks like many feathers situated side by side, with all their quills inserted into one large tendon • Example: deltoid muscle, which forms the roundness of the shoulder

  19. FASCICLE ARRANGEMENT TO MUSCLE STRUCTURE

  20. MUSCLE MECHANICS:IMPORTANCE OF FASCICLE ARRANGEMENT AND LEVERAGE • The operation of most skeletal muscles involves the use ofleverage and lever systems, partnerships between the muscular and skeletal systems • A lever is a rigid bar that moves on a fixed point, or a fulcrum, when a force is applied to it • The applied force, or effort is used to move a resistance or load • In your body, your joints act as the fulcrums, the bones as the levers, and the muscle contraction as the effort (force) • Load (resistance) is the bone itself, along with overlying tissues and anything else you are trying to move with that lever

  21. Lever Systems • A lever allows a given effort (force) to lift a heavier load (resistance), or to move a load (resistance) farther or faster, than it otherwise could • (a):First-Class: the load is close to the fulcrum and the effort is applied far from the fulcrum • A small effort exerted over a relatively large distance can be used to move a large load over a small distance • Such a lever is said to operate at a mechanical advantage and is commonly called a power lever

  22. Lever Systems • (b): Third-Class: • Load is far from the fulcrum and the effort is applied near the fulcrum, the force exerted by the muscle must be greater than the load moved or supported • This lever system operates at a mechanical disadvantage and is a speed lever • These levers are useful because they provide rapid contractions with a wide range of motion

  23. MUSCLE LEVERAGE

  24. Lever Systems • All levers follow the same basic principle: • Effort farther than load from fulcrum = mechanical advantage • Effort nearer than load to fulcrum = mechanical disadvantage • Lever systems that operate at a mechanical disadvantage (speed levers),force is lost but speed and range of movement are gained, and this can be a distinct benefit • Lever systems that operate at a mechanical advantage (power levers) are slower, more stable, and used where strength is a priority

  25. Lever Systems • There are three types of levers: • First-class • Second-class • Third-class

  26. Lever SystemsFirst-Class Levers • (a): Effort is applied at one end of the lever and the load is at the other, with the fulcrum somewhere between • Examples: • Seesaws • Scissors • Lift your head off your chest • Some operate at a mechanical advantage • Others operate at a mechanical disadvantage • Action of the triceps muscle in extending the forearm against resistance (pushing)

  27. Lever SystemsSecond-Class Levers • (b): Effort is applied at one end of the lever and the fulcrum is located at the other, with the load between them • All second-class levers in the body work at a mechanical advantage because the muscle insertion (effort) is always farther from the fulcrum than is the load to be moved • Levers of strength, but speed and range are sacrificed for that strength • Examples: • Wheelbarrow • Uncommon in the human body • Best example is the act of standing on your toes

  28. Lever SystemsThird-Class Levers • (c): Effort is applied between the load and the fulcrum • Operate with great speed and always at a mechanical disadvantage • Most skeletal muscles of the body • Tend to be thicker and more powerful • Permits a muscle to be inserted very close to the joint across which movement occurs • Allows rapid, extensive movements with relatively little shortening of the muscle • Examples: • Tweezers (forceps) • biceps

  29. MUSCLE LEVERAGE

  30. Skeletal Muscles • Over 600 • Book only list approximately 125 pairs of them

  31. ANTERIOR SUPERFICIAL MUSCLES

  32. DIAGRAMMATIC VIEW OF ANTERIOR MUSCLES

  33. POSTERIOR VIEWOF SUPERFICIAL MUSCLES

  34. DIAGRAMMATIC VIEW OF POSTERIOR MUSCLES

  35. Facial Muscles • Muscles of the Head: Facial Expression • Muscles of the scalp include the epicranius consisting of the frontalis and the occipitalis • Muscles of the face include corrugator supercilii, orbicularis oculi, zygomaticus, risorius, levator labii superioris, depressor labii inferioris, depressor anguli oris, orbicularis oris, mentalis, buccinator, and platysma

  36. MAJOR SKELETAL MUSCLES OF THE FACE • Frontalis:cranial (facial nerve) VII • Raises the eyebrows (as in surprise) • Wrinkles forehead skin horixzontally • Cranial nerve VII • Orbicularis oculi:cranial (facial nerve) VII • Protects eyes from intense light and injury • Produces blinking, squinting • Draws the eyebrows inferiorly • Orbicularis oris:cranial (facial nerve) VII • Closes lips • Purses (pucker) and protrudes (stick out) lips • Kissing and whistling muscle

  37. HEAD MUSCLES

  38. Muscles of the Head • Mastication and Tongue Movement: • Muscles of mastication include the masseter, temporalis, medial pterygoid, lateral pterygoid, and the buccinator • Muscles promoting tongue movement are the genioglossus, hypoglossus, and the styloglossus

  39. Mastication Muscles • Masseter:Temporalis:cranial (trigeminal) nerve V • Prime mover of jaw closure • Elevates mandible • Temporalis:cranial (trigeminal) nerve V • Closes jaw • Elevates and retracts mandible • Buccinator:cranial (facial) nerve VII • Trampoline-like action • Keeps food between grinding surfaces of teeth during chewing

  40. Mastication Muscles

  41. HEAD MUSCLES

  42. Mastication Muscles

  43. Tongue Muscles • Genioglossus:cranial (hypoglossal) nerve XII • Primarily protrudes tongue, but in concert with other extrinsic muscles to retract tongue

  44. TONGUE MUSCLES

  45. MAJOR SKELETAL MUSCLES OF THE BODY • Muscles of the Anterior Neck and Throat: Swallowing • Suprahyoid muscles include digastric, stylohyoid, mylohyoid, and geniohyoid • Infrahyoid muscles include sternohyoid, sternothyroid, omohyoid, thyrohyoid, and the pharyngeal constrictor muscles (superior, middle, and inferior)

  46. Neck and Throat Muscles • Mylohyoid:cranial (trigeminal) nerve V • Elevates hyoid bone and floor of mouth • Enables the tongue to exert backward and upward pressure that forces food bolus into pharynx

  47. Neck and Throat Muscles • Pharyngeal constrictor muscles (superior, middle, and inferior):cranial (vagus) nerve X • Working as a group and in sequence, all constrict pharynx during swallowing • Propels food bolus to esophagus • peristalsis

  48. NECK MUSCLES

  49. NECK MUSCLES

  50. MAJOR SKELETAL MUSCLES OF THE BODY • Muscles of the Neck and Vertebral Column: Head and Trunk Movement • Anterolateral neck muscles include the sternocleidomastoid, and scalenes (anterior, middle, and posterior) • Intrinsic muscles of the back include splenius capitis, erector spinae or sacrospinalis, iliocostals, longissimus, spinalis, semispinalis, and the quadratus lumborum

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