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


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


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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