Laboratory Exercise 8: Skeletal Muscle Anatomy and Action

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Laboratory Exercise 8: Skeletal Muscle Anatomy and Action
Skeletal muscles give the body its form and its ability to move. The muscle cell’s internal structure allows for the movement.
Skeletal muscle has two parts:

The fleshy, contractile part, the belly, or gaster,

The connective tissue ends which attach to bones, the tendons. When the tendon is flat sheet-like

connective tissue, it is called an aponeurosis.

The muscle spans a joint by way of the tendon to pull on a bone or body part to cause movement at that joint. The skeletal muscle never pushes a bone.
Muscle Origin   that part of a muscle attached to the more fixed, proximal (toward origin of a structure) bone.
Muscle Insertion   that part of the muscle attached to the more movable, distal (further from origin of a structure) bone. As a muscle contracts, it pulls on the insertion bone to effect movement. Example - The biceps pulls on the forearm to flex it; the triceps pulls on the forearm from the opposite side to extend it.
Muscles do not act alone to produce movement. A muscle functions as part of a group. To move a particular part of the skeleton, several muscles must be coordinated.

Within a muscle group, a muscle may act as a (an):

Agonist (Prime Mover)   the principal muscle responsible for a particular movement.
Synergist.   a muscle whose contraction enhances the effectiveness of the prime mover.
Antagonist   a muscle whose action opposes that of the prime mover. The antagonist is located opposite

the prime mover. The antagonist is relaxed during prime mover contraction, otherwise the joint would

Types of Muscle Contractions
Isotonic Contraction – a contraction is isotonic when the muscle length shortens, but the amount of tension (force) remains the same. As the muscle shortens, it pulls on its insertion bone and moves it. The muscle condenses and becomes firm to the touch. Isotonic contractions involve body movement.
Isometric Contraction – a contraction is isometric when the muscle shows no visible change in length, but an increase in tension. Isometric contractions increase force without producing movement. Isometric contractions maintain posture by supporting the bones in a fixed position or fix the bones to support the weight of an object.

A. Muscles of the Head and Neck Region

Muscles of Facial Expression


Orbicularis oris

Orbicularis oculi

Muscles that Move the Mandible
Antagonistic Muscles

Mastication Muscles

Masseter   agonist elevates mandible

Temporalis   synergist

Platysma - depresses mandible
Muscle that Moves the Neck and Head

Antagonistic Muscles

Sternocleidomastoid   flexes cervical vertebrae (neck) and draws head forward, rotates head from side to side

Trapezius – extends cervical vertebrae (neck) and extends head

B. Muscles of the Arm and Shoulder (Pectoral) Girdle
Muscles that Move the Humerus (Arm)

Antagonistic Muscles

Pectoralis major   flexes

Latissimus dorsi   extends

Deltoid   abduct

Pectoralis major   adduct

Origin Insertion
Infraspinatus   lateral rotates inferior to spine of scapula greater tubercle of humerus
Teres major   medial rotates lower tip of scapula on lesser tubercle of humerus

dorsal surface

*Isometric Contraction   bi and triceps muscles contract simultaneously; lock the elbow joint to support the weight, then the pectoralis major with the help of the deltoid flex to move the object.
Muscle that moves the Shoulder (Pectoral) Girdle

Trapezius   elevates and depresses

Muscles that Move the Forearm

Antagonistic Muscles

Biceps brachii - agonist flexes  radius

Brachioradialis – synergist 

Brachialis flexes ulna
Triceps brachii – antagonist -extends radius and ulna

Anconeus - synergist

Pronator teres – pronation -turns palm posterior

Pronator quadratus

Supinator – supination -turns palm anterior

Muscles that Move the Carpels, Metacarpals and Phalanges
Antagonistic Muscles

Flexors in the forearm   on the anterior surface

Extensors in the forearm   on the posterior surface
C. Muscles of the Abdominal Region
Muscle Actions
Origin Insertion Flexes Flexes Laterally Compresses

vertebral vertebral rotates abdomen

cartilage column column vertebral

Rectus abdominis pubic crest of 5-7 ribs A-P laterally column

pubic symphysis xiphoid X X

External oblique ribs iliac crest X X X X

linea alba

(mid line

Internal oblique iliac ribs X X X X

Transversus iliac crest xyphoid process, X

abdominis 5-10 ribs linea alba, pubic symphysis
Compression of the abdominal cavity by these muscles is used for coughing, vomiting, defection, urination, forced expiration and childbirth.

All abdominal muscles protect the abdominal organs.

D. Muscles of the Pelvis, Thigh and Leg

Muscles that Move the Femur (Thigh)
Antagonistic Muscles

Iliopsoas - agonist  flexes

*Sartorius - synergist
Gluteus maximus  extends
Gluteus medius  abduct

Adductor muscle group  adduct

Gracilis - adduct
Gluteus maximus  lateral rotates

Gluteus medius - agonist  medial rotates

Adductor muscle group - synergist
*Sartorius rotates femur laterally, crossing the leg.
Muscles that Move the Tibia and Fibula (Leg)
Antagonistic Muscles

Quadriceps femoris  extends

Hamstrings – agonist  flexes

*Sartorius - synergist

Muscles that Move the Tarsals, Metatarsals and Phalanges
Antagonistic Muscles

Gastrocnemius   agonist  extends (plantar flexion)

Soleus  synergist



Tibialis anterior - antagonist  flexes (dorsiflexion)
Gastrocnemius, Soleus and Peroneus are attached to the calcaneus (heel bone) by the Calcaneus (Achilles) tendon.
*Note the three actions of the Sartorius.
Antagonistic Muscles of the Upper Appendage
Prime Movers
Triceps brachii Biceps brachii
Location   on posterior surface of humerus Location   on anterior surface of humerus
Function (Action)   extend the forearm Function   flex the radius
Head Origin Insertion Head Origin Insertion

Long glenoid fossa Long glenoid fossa


Lateral lateral olecranon radial

proximal part process tuberosity

humerus Short coracoid process


Medial distal part

(lies anterior to of humerus Synergist

lateral head) Brachioradialis

Location   on anterior surface of humerus
Function   helps flex the radius
Origin Insertion

medial – lateral along radius

surface of distal on lateral

humerus surface


Location   lies under biceps brachii

on anterior surface of humerus

Function   flex the ulna

Origin Insertion

distal anterior proximal

surface of humerus ulna

Pronators and Supinator of the Forearm
Origin Insertion Origin Insertion
Pronator medial shaft of Supinator lateral on lateral

teres epicondyle of radius epicondyle of surface of

humerus and along mid  humerus and radius

ulna lateral proximal ulna

surface of

distal radius

Pronator distal distal

quadratus ulna radius

Function   pronators turn palm Function  supinator turns palm

posterior or down anterior or up

Muscles of the Thigh (Femur)
Hamstring group - posterior surface of femur
Lateral   Biceps femoris
Medial   Semitendinosus
Middle - Semimembranosus
Function - flex leg
Quadriceps femoris   anterior surface of femur
Parallel to mid line Rectus femoris

of femur
Lateral Vastus lateralis

Middle below Vastus intermedius

rectus femoris

Medial Vastus medialis
Function   extend leg

Muscular System

Muscles Primary Action

Head and Neck Muscles
Facial Expressions
Head Muscles

Eyebrow and Scalp Movement


Frontalis with aponeurosis fixed raises eyebrows

and wrinkles forehead

Occipitalis pulls scalp posterior

Sphincter Muscles

Sphincters are muscles that close openings

Orbicularis oris closes mouth, purses and protrude lips

Orbicularis oculi closes eyelids, allows for blinking and


Zygomatic major, minor draws angle of mouth up and backward as

in smiling and laughing

Masticatory Movements   chewing of food

Masseter raises mandible

Temporalis acts synergistically with masseter to raise


Buccinator holds food between teeth during chewing

and compresses cheeks, draws corners of

mouth lateral

Neck Muscles, Superficial
Anterior   lateral surface

Platysma lowers mandible

Sterocleidomastoid flexes vertebral column in cervical region

to draw head toward chest; contraction on

one side rotates head side to side (lateral)

Posterior surface

Trapizus raises and lowers scapula, as in shrugging

the shoulder, extend vertebral column in

cervical region to extend head
Thorax and Shoulder Muscles, Superficial   these muscles move the arm or brachium (humerus).
Arm Movement
Anterior surface

Pectoralis major flexes humerus, adducts humerus

Lateral surface

Deltoid abducts humerus

Posterior surface

Latissimus dorsi extends humerus
Infraspinatus rotates humerus lateral

Teres major rotates humerus medial

Upper Extremity Muscles
Arm or Brachium Muscles   these muscles move forearm or antebrachium (radius and ulna).
Forearm Movement

Anterior surface

Biceps brachii flexes forearm at elbow

long head lateral

short head medial
Brachioradialis – in forearm flexion synergist to biceps brachii flexes radius

insert radius

Brachialis – in forearm flexion synergist to biceps brachii flexes ulna

insert on ulna

Posterior surface

Triceps brachii extends forearm

long head

lateral head

medial head

Anconeus – synergist to triceps brachii extends forearm

Forearm or Antebrachium Muscles   these muscles move wrist, hand, fingers.
Hand Movement

Anterior surface

Flexors flex wrist, hand, and fingers

Pronator teres pronation (turns palm down)

Pronator quadratus
Posterior surface

Extensors extend wrist, hand, and fingers

Supinator supination (turns palm up)

Anterior Abdominal Wall Muscles
Trunk Movement

Abdominal. Muscles   there are four muscles.

Rectus abdominis all abdominal muscles flex and laterally External obliques rotate vertebral column in lumbar region,

Internal obliques hold abdominal organs in place,

Transverse abdominis compress abdominal contents to assist

in defecation, urination, vomiting,

parturition (childbirth)

Lower Extremity Muscles
These muscles move the thigh (femur) or upper leg.
Pelvic Muscles
Anterior Surface

Iliopsoas (Iliacus + Psoas major) flexes femur

Sartorius rotates femur lateral as in crossing the leg
Hip or Os Coxa muscles

Posterior Surface

Gluteus maximus extends femur, rotates femur lateral

Gluteus medius abducts femur, rotates femur medial

Medial Surface

Adductor muscle group adducts femur, rotates femur medial




Gracilis adducts femur, rotates femur medial

Thigh or Upper Leg Muscles - these muscles move the lower leg (tibia and fibula).
Lower Leg Movement

Anterior surface

Quadriceps femoris

Rectus femoris extends lower leg

Vastus lateralis

Vastus medialis

Vastus intermedius
Posterior surface

Hamstrings flex lower leg

Biceps femoris lateral muscle

short head lateral

long head medial

Semitendinosus medial muscle, superficial

Semimembranosus medial muscle, deep
Lower Leg Muscles   these muscles move the ankle, foot, toes.
Ankle and Foot Movement

Anterior surface

Tibialis anterior flexes foot (dorsiflexion)
Posterior surface

Gastrocnemius extends foot (plantar flexion)

lateral head inserts on the calcaneous bone by the

medial head calcaneous (Achilles) tendon

Lateral surface

Fibularis (Peroneal) muscles

Toe Movement

Extensors on anterior surface extend toes

Flexors on posterior surface flex toes

The Origins and Insertions of Selected Muscles

Muscles of Face and Neck
Origin Insertion


Frontalis cranial aponeurosis at muscles and skin of eyebrows

top of frontal bone and upper nose

Occipitalis occipital and temporal cranial aponeurosis

Orbicularis oculi frontal and maxillary skin of eyelid

bones around orbit
Orbicularis oris muscles around mouth muscles and skin at angles of mouth
Temporalis temporal fossa coronoid process of mandible
Masseter zygomatic arch and angle and ramus of mandible


Buccinator mandible and maxilla orbicularis oris and skin at

the angle of the mouth

Platysma skin and fascia of breast lower border of mandible

(pectoralis major) and face below mouth

Sternocleidomastoid sternum (manubrium) mastoid process of

and medial clavicle temporal bone

Zygomatic zygomatic bone muscles and skin angle of mouth
Muscles of the Shoulder, Chest and Back
Pectoralis major clavicle, sternum, costal greater tubercle of

cartilages of ribs 2-6, and humerus

aponeurosis of external

Deltoid lateral clavicle, acromion, lateral humerus

and spine of scapula (deltoid tuberosity)

Trapezius occipital bone, spinous lateral clavicle, spine of

processes of seventh cervical scapula, acromion

and all thoracic vertebrae

Latissimus dorsi spinous processes of T6 L5, intertubercular groove of

sacrum, iliac crest (all via humerus

lumbodorsal fascia)
Teres major dorsal surface of lower tip lesser tubercle of humerus of scapula
Infraspinatus fossa inferior to spine of greater tubercle of humerus

Muscles of the Arm

Biceps brachii

Short head 1. coracoid process of radial tuberosity


Long head 2. intertubercular groove

and within glenoid fossa

Brachioradialis lateral epicondyle lateral part of the base of styloid

of distal humerus process of radius
Brachialis distal, anterior surface coronoid process of ulna

of humerus

Triceps brachii

Long head 1. glenoid fossa olecranon process

Lateral head 2. posterior lateral surface of ulna

of humerus

Medial head 3. lower posterior humerus
Anconeus lateral epicondyle of humerus lateral aspect of

olecranon process

Muscles of the Forearm
Flexor group of forearm medial epicondyle of wrist, hand, fingers

humerus (palmar surface)

Extensor group of forearm lateral epicondyle of wrist, hand, fingers

humerus (dorsal surface)

Pronator teres medial epicondyle of distal, lateral surface

humerus and coronoid of mid-radius shaft

process of u1na
Pronator quadratus medial anterior surface of anterior lateral surface

distal ulna of distal radius

Supinator lateral epicondyle

of humerus and anterior lateral surface

proximal ulna of proximal radius

Muscle of the Abdomen
External oblique anterior surface of linea alba (ventral midline)

lower 8 ribs and iliac crest

Rectus abdominis pubic crest and xiphoid process, costal

pubic symphysis cartilages of ribs 5 7

Deep Abdominals
Internal oblique iliac crest, inguinal ligament linea alba, pubic crest and

lumbar fascia cartilages of lower four ribs


abdominis iliac crest, inguinal ligament, linea alba and pubic crest lumbar fascia, and

carti­lage of lower six ribs

Muscles of the Thigh

Gluteus maximus posterior iliac crest, gluteal tuberosity of femur

sacrum and coccyx and iliotibial tract

Gluteus medius lateral surface of ilium lateral surface of greater

Adductor muscle ramus of pubis linea asperal (gIuteal

group tuberosity) of femur

Gracilis ramus of pubis anterior surface of tibia

inferior to medial condyle

Hamstring Group ischial tuberosity lateral surface of head of

fibula and lateral condyle of

tibia (biceps femoris)

proximal medial surface of

tibia (semitendinosus and



Psoas major transverse processes lesser trochanter of femur

and bodies of lumbar


Iliacus iliac crest and fossa lesser trochanter of femur

(medial surface of ilium)

Quadriceps group femur (for vasti) and tibial tuberosity via

anterior inferior iliac quadri­ceps tendon

spine (rectus femoris) (patellar liga­ment)

Sartorius anterior superior proximal surface of medial

iliac spine surface of tibia (just below


Muscles of the Leg
Gastrocnemius medial and lateral calcaneus (via calcaneal

condyles of femur tendon or Achilles)

Soleus posterior aspect of tibia and calcaneus (via calcaneal

fibula at their proximal ends tendon)
Fibularis (Peroneal) muscles fibula inferior surface of 1st and

5th metatarsal

Tibialis anterior anterior lateral surface of inferior surface base at the of 1st

tibia (upper two thirds) metatarsal

Extensor muscle anterior surface of superior surface

group of lower leg tibia and fibula of toe phalanges

Flexor muscle posterior surface of inferior surface

group of lower leg tibia and fibula of toe phalanges

B. Muscles of Arm and Shoulder Girdle

Name of Muscle

Action of Muscle

Name of Muscle

Action of Muscle



1. Flex forearm


Flexors of wrist, hand


7. Clench fist tight

(flex wrist, hand, fingers)



2. Extend forearm

Extensors of wrist, hand, fingers

8. Extend wrist, hand, fingers


3. Abduct

humerus (arm)

Pectoralis major

9. Flex humerus

Pectoralis major

4. Adduct


Latissumus dorsi

10. Extend humerus

Teres major

5. Rotate humerus medial


11. Elevate and depresses shoulder girdle, extends neck


6. Rotate humerus lateral

Name of Muscle












Action of Muscle

Biceps brachii


Flexes of forearm (radius)

Triceps brachii


Extends of forearm



Abduct humerus (arm)

Pectoralis major


Adduct humerus

Teres major


Medial rotates humerus



Lateral rotates humerus

Flexors of wrist, hand, fingers


Flexes wrist, hand, fingers

Extensors of wrist, hand, fingers


Extends wrist, hand, fingers

Pectorlis major


Flexes humerus

Latissumus dorsi


Extends humerus



Elevates and depresses should girdle and extends neck

Antagonistic muscles acting on the humerus (arm)

Pectoralis major-flexes, Latissimus dorsi-extends

Deltoid-abduct, Pectoralis major- adduct

Teres major-medial rotates, Infraspinatus-lateral rotates
Antagonistic muscles acting on the forearm (radius)

Biceps brachii – flexes, Triceps brachii extends

Pronator teres, pronator quadratus – pronates,Supinator-supernates forearm, wrist, hand
Anatagonistic muscles acting on wrist (carpals),hand (metacarpals),fingers (phalanges).

Flexor are on anterior surface of forearm.

Extensors are on posterior surface of forearm.
Antagonistic muscles acting on the shoulder girdle, neck, head

Trapezius – elevates and depresses pectoral girdle, extends cervical vertebrae, extends head

Sternoclediomastoid – flexes cervical vertebrae, flexes head

D. Muscles of Pelvis, Thigh and Leg

Name of Muscle

Action of Muscle

Name of Muscle

Action of Muscle


1. Flex thigh (femur)

Hamstring Group

8. Flex knee (leg)



Gluteus Maximus

2. Extend thigh

Quadricep Group

9. Extend knee

Gluteus Medius

3. Abduct thigh

Gastronemius Soleus

10. Stand on tiptoes

(Plantar flex)

Adductor Group

4. Adduct thigh

Peroneus, Tibialis


11. Dorisflex

Gluteus Maximus

5. Rotate thigh lateral

Gluteus Medius

6. Rotate thigh medial

Adductor group


7. Rotate femur lateral as in

crossing the leg

Name of Muscle












Action of Muscle

Gluteus Maximus



Extends, lat. rotates

Gluteus Medius



Abducts med. rotates








Flexes lat. rotates

Adductor Group



Adduct, med. rotates




Hamstring Group





Plantar flexes







Tibialis anterior


Dorisflex (flexes)

Antagonistic muscles in terms of flex and extend femur

Iliopsoas flexes Gluteus maximus extends

Antagonistic muscles in terms of abduct and adduct femur

Gluteus medius abduct, Adductor group- adduct

Antagonistic muscles in terms of lateral and medial rotate femur

Gluteus maximus – lateral rotates, Gluteus medius and Adductor group – medially rotates

Antagonistic muscles in terms of flex and extends leg

Hamstring group – flexes, Quadricep group – extends

Antagonistic muscles in terms of flexes and extends foot

Tibialis anterior – flexes, Gastrocnemius, soleus, peronus - extends

A. Muscles of the Head and Neck Region
Name of Muscle Location Origin Insertion Function (Action)
Temporalis lat. skull temporal coronoid elevates lower

bone process, jaw

fossa ramus of




Orbicularis oris

Orbicularis oculi






B. Muscles of Arm and Shoulder Girdle
Name of Muscle Location Origin Insertion Function (Action)
Pectoralis major






Teres major

Biceps brachii



Triceps brachii

Name of Muscle Location Origin Insertion Function (Action)

Flexors of

wrist, hand, fingers

Extensors of

wrist, hand, fingers


C. Muscles of the Abdominal Region
Name of Muscle Location Origin Insertion Function (Action)
Rectus Abdominis






D. Muscles of the Pelvis, Thigh and Leg
Name of Muscle Location Origin Insertion Function (Action)
Gluteus maximus

Gluteus medius



Adductor Muscle









Fibularis (Peroneus)

Name of Muscle Location Origin Insertion Function (Action)



Extensors of

ankle, foot, toes

Flexors of

ankle, foot, toes

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