our muscles in action!!!!!
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8/7/2019 Our Muscles in Action!!!!!
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Skeletal Muscle Actions
The muscular system consists of skeletal muscles and their associated connective tissues. It
does not include cardiac muscle or smooth muscle, which are associated with the systems in
which they are found, such as the cardiovascular, digestive, urinary, or other organ systems.
A skeletal muscle may attach a bone to another bone (often across a joint) or a bone to another
structure, such as skin. When the muscle contracts, one of the structures usually remains
stationary, while the other moves. The following terms refer to this characteristic of muscle
contraction.
y The origin of the muscle is the muscle end that attaches to the stationary structure,usually bone.
y The insertion of the muscle is the muscle end that attaches to the moving structure.y The belly of the muscle is that part of the muscle between the origin and insertion.
Several muscles usually influence a particular body movement:
y The prime mover is the muscle that is most responsible for the movement.y Synergists are other muscles that assist the prime mover. Synergists may stabilize nearby
bones or refine the movement of the prime mover.
y Antagonists are muscles that cause a movement opposite to that of the prime mover. Ifthe prime mover raises an arm, then its antagonist pulls the arm down. An antagonist is
generally attached to the opposite side of the joint to which the prime mover is attached.
Names of Skeletal Muscles
Skeletal muscles are often named after the following characteristics:
y Number of origins. Biceps, triceps, and quadriceps indicate two, three, and four origins,respectively.
y Location of origin or insertion. The sternocleidomastoid names the sternum (sterno) andclavicle (cleido) as its origins and the mastoid process of the temporal bone as its
insertion.
y Location. In addition to its origin or insertion, a muscle name may indicate a nearby boneor body region. For example, the temporalis muscle covers the temporal bone.
y Shape. The deltoid (triangular), trapezius (trapezoid), serratus (sawtoothed) andrhomboideus major (rhomboid) muscles have names that describe their shapes.
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y Direction of muscle fibers. The terms rectus (parallel), transverse (perpendicular), andoblique (at an angle) in muscle names refer to the direction of the muscle fibers with
respect to the midline of the body.
y Size. Maximus (largest), minimus (smallest), longus (longest), and brevis (shortest) arecommon suffixes added to muscle names.
y Action. Terms such as flexor, extensor, abductor, and adductor are added as prefixes tomuscle names to indicate the kind of movement generated by the muscle.
Muscle Size and Fascicles
The size of a muscle influences its capabilities. When a muscle fiber (cell) contracts, it can
shorten to nearly half its relaxed length. The longer a muscle fiber, then the greater range of
movement it can generate. In contrast, an increase in the number of muscle fibers increases the
strength of the contraction.
Muscle fibers are grouped into fascicles, which are, in turn, grouped together to form a muscle.
The size (length) and number of fascicles determine the strength and range of movement of a
muscle. Common fascicle patterns follow:
y Parallel fascicles have their long axes parallel to each other. Parallel fascicles can be flat,or straplike, or they can bulge at their bellies and be spindle shaped, or fusiform.
yCircular fascicles are arranged in concentric rings. Muscles with this pattern form sphinctermuscles that control the opening and closing of orifices.
y Pennate fascicles are short and attach obliquely to a long tendon that extends across theentire muscle. In a unipennate pattern, the muscle resembles one half of a feather (the
tendon is represented by the shaft of the feather). A bipennate pattern resembles a
complete feather, with fascicles attached to both sides of a central tendon. A multipennate
pattern of fascicles resembles three or more feathers attached at their bases.
Major Skeletal Muscles
The major skeletal muscles are described in following tables and figures.
TABLE 1 Muscles of the Head and Neck
Muscle Origin/Insertion Action
Epicranius:frontalis O: galea aponeurotica I: skin around eyes raises eyebrows; surprised
Epicranius:occiptalis O: occipital bone I : galea aponeurotica pulls scalp back; surprised
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Orbicularis oculi O: maxillary & frontal bones I: eyelids closes eyelids; blinking
Orbicularis oris O: muscle fibers around mouth I: skin around mouth closes lips; kissing
Buccinator O: maxilla & mandible I: orbicularis oris compresses cheek; whistling
Platysma O: fascia in upper chest I: mandible & corner of mouth lowers mandible; opens mouth
Mentalis O: mandible I: skin of chin protrudes lower lip; pouting
Risorius O: fascia on masseter muscle I: skin at corner of mouth lateral movement of lips; grimacing
Zygomaticus O: zygomatic bone I: skin around mouth raises edges of mouth; smiling
Levator labi superioris O: infroarbital margin of maxilla I: skin of upper lip raises upper lip; as in disgust
Depressor labi inferioris O: mandible I: skin of lower lip lowers lower lip
Temporalis O: parietal bone I: mandible raises mandible; closes mouth
Masseter O: zygomatic arch I: mandible raises mandible; closes mouth
Medial pterygoid O: sphenoid & maxilla I: mandible raises mandible; side-to-side mouth motion
Lateral pterygoid O: sphenoid & maxilla I: mandible raises mandible; side-to side mouth motion
Sternocleidomastoid O: ternum & clavicle I: temporal bone flexes & rotates head
Splenius capitis O: cervical & thoracic vertebrae I: temporal bone rotates, bends, or extends head
Semispinalis capitis O: cervical & thoracic vertebrae I: occipital bone rotates or extends head
Longissimus O: cervical & thoracic vertebrae I: temporal bone rotates, bends, or extends head
Omohyoid O: scapula I: hyoid bone depresses hyoid bone
Sternohyoid O: sternum & clavicle I: hyoid bone depresses hyoid bone
TABLE 2 Muscles of the Neck, Shoulder, Thorax, and Abdominal Wall
Muscle Origin/Insertion Action
Semispinalis capitis O: cervical & thoracic vertebrae I: occipital bone extends & rotates head
Splenius capitis O: c & t vertebrae I : occipital & temporal bone extends and rotates head
Deltoid O: clavicle & scapula I: humerus abducts, flexes, extends, & rotatesarm
Pectoralis major O: clavicle, sternum, ribs I: humerus flexes, adducts, & rotates arm
Infraspinatus O: scapula I: humerus rotates arm
Teres major O: scapula I: humerus extends, rotates arm
Latissimus dorsi O: vertebrae, ribs, ilium I : humerus extends, adducts, rotates arm
Levator scapulae O: cervical vertebrae I: scapula elevates scapula
Pectoralis minor O: ribs I: scapula stabilizes scapula, elevates ribs
Serratus anterior O: ribs I: scapula stabilizes scapula, elevates ribs
Trapezius O: occipital bone & c & t vertebrae; I : scapula &
clavicle
elevates, adducts, & rotates scapula
Rhomboideous major/Rhomboideusminor
O: c & t vertebrae I: scapula adducts & rotates scapula
Rectus abdominis O: pubic crest & symphysis I: xiphoid process &
ribs
flexes vertebral column, compresses
abdomen
External oblique O: ribs I : linea alba, ilium compresses abdomen, rotates trunk
Transverse abdominis O: ilium, ribs I: linea alba, xiphoid process compresses abdomen
External intercostals O: lower border of rib above I: upper border of rib elevates ribs, aids inspiration
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below
Internal intercostals O: upper border of rib below I: lower border ofrib above
pulls ribs together, aids expiration
Diaphragm O: lower ribs, sternum I: central tendon aids inspiration
Spinalis O: lumbar & thoracic vertebrae I: thoracic &cervical vertebrae
extends vertebral column
Longissimus O: lumbar & cervical vertebrae I : temporal bone,
vertebrae
extends vertebral column
Iliocostalis O: ilium, ribs I: ribs extends vertebral column
TABLE 3 Muscles of the Arm and Forearm
Muscle Origin/Insertion Action
Coracobrachiolis O: scapula I: humerus flexes & adducts arm
Biceps brachii O: scapula, glenoid cavity I: radius flexes arm, flexes forearm, & rotates hand
Brachialis O: humerus I: ulna flexes forearm
Brachioradialis O: humerus I: radius flexes forearmTriceps brachii O: humerus I: ulna extends forearm
Anconeus O: humerus I: ulna extends forearm
Pronator teres O: humerus, ulna I: radius rotatesforearm
Pronator quadratus O: ulna I: radius rotates forearm
Supinator O: ulna I: radius rotates forearm
Flexor carpi radialis O: humerus I : metacarpals flexes & abducts wrist
Flexor carpi ulnaris O : humerus, ulna I : carpals, metacarpals flexes & abducts wrist
Flexor digitorum superficialis O: humerus, ulna, radius I: phalanges flexes finger 25
Flexor digitorum profundus O: ulna I: phalanges flexes distal fingers 25
Palmaris longus O: humerus I : flexor retinaculum flexes wrist
Extensor carpi radialis longus O : humerus I : second metacarpal extends & abducts wrist
Extensor carpi ulnaris O: humerus, ulna I: fifth metacarpal extends & adducts wrist
Extensor digitorum O: humerus I: distal phalanges extends fingers 25
Extensor pollicis brevis O: radius I: phalanx of thumb thumb extends
Extensor pollicis longus O: radius I: phalanx of thumb extends thumb
Extensor indicis O: ulna I: index finger extends index finger
Abductor pollicis longus O: radius & thumb I: first metacarpal abducts & extends thumb
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Figure 1 The major skeletal musclesanterior superficial view.
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Figure 2 The major skeletal musclesposterior superficial view.
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Figure 3The major skeletal muscleslateral view.
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Figure 4 The major skeletal musclesanterior superficial view, anterior deep view, posterior superficial view, and posteriordeep view.
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Figure 5 The major skeletal musclesanterior superficial view, anterior deep view, posterior superficial view, and posteriordeep view.
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Figure 6 The major skeletal musclesanterior superficial view, anterior deep view, posterior superficial view, and posteriordeep view.
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