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 Buccinator
Muscles that Move the Mandible Antagonistic Muscles
Masseter agonist elevates mandible
Platysma - depresses mandible
Muscle that Moves the Neck and Head
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)
Pectoralis major flexes
Latissimus dorsi extends
Pectoralis major adduct
OriginInsertion 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
*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
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)
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
Location on anterior surface of humerus
Function helps flex the radius
medial – lateral along radius
surface of distal on lateral
Location lies under biceps brachii
on anterior surface of humerus
Function flex the ulna
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
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
Middle - Semimembranosus
Function - flex leg
Quadriceps femoris anterior surface of femur
Parallel to mid line Rectus femoris
Lateral Vastus lateralis
Middle below Vastus intermedius
Medial Vastus medialis
Function extend leg
Head and Neck Muscles Facial Expressions
lateral head inserts on the calcaneous bone by the
medial head calcaneous (Achilles) tendon
Fibularis (Peroneal) muscles
Extensors on anterior surface extend toes
Flexors on posterior surface flex toes
The Origins and Insertions of Selected Muscles
Muscles of Face and Neck OriginInsertion
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