Interactions of Skeletal Muscles

in the Body

     *Since muscles only contract, they can only pull, but not push.

     *Therefore, every muscle action has another muscle that reverses that action.

     *Because of all this, muscles therefore must work in groups 

The muscle that has the major responsibility for causing a particular movement.

The muscle that reverses the movement of the prime mover.

     EX:Flexion-Biceps- Contracted=Prime mover            Triceps- Relaxed= Antagonist

     EX:Triceps- Contracted= Prime mover

  Biceps- Relaxed= Antagonist

Helps the prime mover, by reducing undesirable movements. The synergists usually are muscles that cross 2 or more joints.

EX:Finger- Flexor muscles also cross the wrist, but you can still flex your fingers without flexing your wrist, due to synergists keeping your wrist stable

Hold the bones still. Stabilize the origin of the prime mover, putting all the tension to move the bone.

EX: Postural muscles of vertebral column.

EX: Muscles that stabilize the scapula.

Muscle found on frontal bone.

 Origin= Cranial aponeurosis

Insertion= In the eyebrows

    Function: Allows you to raise your eyebrows and wrinkle your forehead.

Circular muscles that surround your eyes.

Function: Blink, close eyes, wink, squint

Round muscle around the mouth.

Function: Close mouth, called "kissing muscle."

Goes horizontally across your cheek.

 Origin= Mandible

 Insertion= Orbicularis oris

Function: Flattens cheeks

Diagonal muscle.

 Origin= Cheekbone (zygomatic bone)

 Insertion= Orbicularis oris

Function: Smiling muscle

Runs down cheek.

 Origin= Zygomatic process

 Insertion= Mandible

Function: Closes mouth

Temporalis

Goes from skull and inserts into mandible.

Function: Synergist for masseter.

    *Found on temporal bone

Flat sheet-like muscle that covers the front of the neck and sides of the mouth.

 Origin= Connective tissue of chest muscles.

 Insertion= Synergist for masseter.

Function: Pulls corners of mouth downward.

1 on each side of neck- a 2 headed muscle.

 Origin= Sternum and clavicle

 Insertion= Matoid process of skull.

Function: Flex your neck= Praying muscles.

Pectoralis Major

Upper part of chest, convergent muscle originates at sternum and inserts on proximal end of humerus.

Action: Adducts the arms.

In between ribs- Most deep muscle of abdominal wall.

2 sections:

1. External Intercostal Muscles (lateral)- Helps you breath in, by raising the ribcage.

2. Internal Intercostal Muscles (Medial)- Helps you breathe out by depressing the ribcage.

Muscles of the

Abdominal Girth 

   *Purpose- Protect internal organs and bones.

   *Reinforce and stabilize your trunk.

Paired, strap-like, fibers are vertical.

 Origin= Pubis

 Insertion= Ribcage

*Action- Flexes your vertebral column. Also main muscles used by women in childbirth, and by all in excretion.

  *Fibers (diagonal) run downward from lateral to medial.

 Origin= Ribs

 Insertion= Ilium

*Action- Helps to flex vertebral column and also rotates the abdomen laterally, and to bend laterally.

Fibers run diagonally, paired, go upwards from lateral to medial- are perpendicular to extend obliques.

 Origin= Iliac Crest

 Insertion= Last as 2 ribs

*Action- Same as external obliques.