Muscular systemMuscle actionsTypes of musclesLever systemsNaming MusclesListing of Major Skeletal Muscles

Fascicular arrangement and muscle types

Lever systems and examples

Attachments and Actions of Skeletal Muscles

Actions depend largely on what the muscles are attached toAttachment sites

– Origin – an attachment site for a less movable bone

– Insertion – an attachment site for a more moveable bone

Attachments and Actions (cont.)

Movement usually produced by a group of musclesPrime mover – muscle responsible for most of the movementSynergists – muscles that help the prime mover by stabilizing jointsAntagonist (agonist) – produces movement opposite to prime mover

Relaxes when prime mover contracts

Attachments and Actions Body Movements

Flexion – bending a body part

Extension – straightening a body part

Hyperextension – extending a body part past the normal anatomical position

Dorsiflexion – pointing the toes up

Plantar flexion – pointing the toes down

Abduction – moving a body part away from the anatomical position

Adduction – moving a body part toward the anatomical position

Circumduction – moving a body part in a circle

Pronation – turning the palm of the hand down

Supination – turning the palm of the hand up

Inversion – turning the sole of the foot medially

Eversion – turning the sole of the foot laterally

Retraction – moving a body part posteriorly

Protraction – moving a body part anteriorly

Attachments and Actions: Body Movements

Elevation – lifting a body part; for example, elevating the shoulders as in a shrugging expression

Depression – lowering a body part; for example, lowering the shoulders

Attachments and Actions: Body Movements (cont.)

Major Skeletal Muscles

The muscle name indicates LocationSizeActionShape

ORNumber of attachments of the muscle

As you study muscles, you will find it easier to remember them if you think about what the name describes.

Major Skeletal Muscles: The Head

Sternocleidomastoid Pulls the head to oneside Pulls the head to the chest

Frontalis Raises the eyebrows

Splenius capitisRotates the head Allows it to bend to the side

Orbicularis oris Allows the lips to pucker

Major Skeletal Muscles: The Head (cont.)

Orbicularis oculi Allows the eyes to close

Zygomaticus Pulls the corners of the mouth up

Platysma Pulls the corners of the mouth down

Masseter and temporalis

Close the jaw

Major Skeletal Muscles: Upper Arm

Pectoralis major Pulls the arm across the chest Rotates and adducts the arms

Latissimus dorsi Extends and adducts the arm and rotates the arm inwardly

Major Skeletal Muscles: Upper Arm (cont.)

DeltoidAbducts and extends the arm at the shoulder

Subscapularis Rotates the arm medially

Infraspinatus Rotates the arm laterally

Major Skeletal Muscles: Forearm

• Biceps brachii – Flexes the arm at the elbow – Rotates the hand laterally

• Brachialis – Flexes the arm at the elbow

• Brachioradialis – Flexes the forearm at the

elbow

Major Skeletal Muscles: Forearm (cont.)

Triceps brachii Extends the arm at the elbow

Supinator Rotates the forearm laterally (supination)

Pronator teres Rotates the forearm medially (pronation)

Major Skeletal Muscles: Wrist, Hand, and Fingers

Flexor carpi radialis and flexor carpi ulnaris

Flex and abduct the wristPalmaris longus

Flexes the wristFlexor digitorum profundus

Flexes the distal joints of the fingers, but not the thumb

Extensor carpi radialis longus and brevis

Extend the wrist and abduct the hand

Extensor carpi ulnaris Extends the wrist

Extensor digitorum Extends the fingers, but not the thumb

Major Skeletal Muscles: Wrist, Hand, and Fingers (cont.)

Major Skeletal Muscles: Respiratory

Diaphragm Separates the thoracic cavity from the abdominal cavityIts contraction causes inspiration

External and internal intercostals

Expand and lower the ribs during breathing

Major Skeletal Muscles: Abdominal

External and internal obliques Compress the abdominal wall

Transverse abdominis Also compresses the abdominal wall

Rectus abdominisFlexes the vertebral columnCompresses the abdominal wall

Click for View of Abdominal Muscles

Major Skeletal Muscles: Pectoral Girdle

Trapezius Raises the arms Pulls the shoulders downward

Pectoralis minor Pulls the scapula downwardRaises the ribs Click for View of

Pectoral Girdle Muscles

Major Skeletal Muscles: LegPsoas major and iliacus

Flexes the thigh

Gluteus maximus Extends the thigh

Gluteus medius and minimus

Abduct the thighs Rotate them medially

Major Skeletal Muscles: Leg (cont.)Adductor longus and magnus

Adduct the thighs Rotate them laterally

Biceps femoris, semitendinosus, and semimembranosus

Known as the hamstring groupFlex the leg at the knee Extend the leg at the thigh

• Rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius – Extend the leg at the knee

• Sartorius – Flexes the leg at the knee and thigh – Abducts the thigh, rotating the thigh

laterally but rotating the lower leg medially

Major Skeletal Muscles: Leg (cont.)

Major Skeletal Muscles: Ankle, Foot, and Toes

Tibialis anterior Inverts the foot and point the foot up (dorsiflexion)

Extensor digitorum longus Extends the toes and point the foot up

GastrocnemiusFlexes the foot and flexes the leg at the knee

Soleus Flexes the foot

Flexor digitorum longus

Flexes the foot and toes

Major Skeletal Muscles: Ankle, Foot, and Toes (cont.)

Diseases and Disorders of the Muscular System

Disease DescriptionBotulism Affects the gastrointestinal tract and various

muscle groups

Fibromyalgia Fairly common condition that causes chronic pain primarily in joints, muscles, and tendons

Muscular Dystrophy

Inherited disorder characterized by muscle weakness and a loss of muscle tissue

Myasthenia gravis Autoimmune condition in which patients experience muscle weakness

Diseases and Disorders of the Muscular System (cont.)

Disease Description

Rhabdomyolysis A condition in which the kidneys become damaged after serious muscle injuries

Tendonitis Painful inflammation of a tendon and the tendon-muscle attachment to a bone

Torticollis (wryneck)

Acquired or congenital; spasm or shortening of the sternocleidomastoid muscle; head bends to affected side and chin rotates to opposite side

Trichinosis An infection caused by parasites (worms)