A&P @ LCC by Dr. Prince

Ch. 10 Muscular System
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  • Study hand out given on Friday
  • Selected key terms
  • Differentiate between prime movers, antagonists, synergists, and fixators
  • Know the criteria used in naming muscles
  • Define lever system, the structural components of each type of lever, and give an example of each
  • Name and identify selected muscles along with their origin, insertion and action.
  • List 3 muscles used for intramuscular injections

What is the difference between a synergistic muscle and a fixator muscle?
A synergistic muscle is one that complements the action of a prime mover or the agonist. 
A fixator muscle is one that provides a stable base for the action of the prime mover. 
So a fixator is in fact a synergist that helps by "standing still".

Human Musculature
The Head and Neck
  • Orbucularis oculi
  • Orbicularis oris
  • Zygomaticus major
  • Platysma
  • Sternocleidomastoid

The Thorax

  • Pectoralis major
  • Serratus anterior

The Abdomen

  • External oblique
  • Rectus abdominis

The Back

  • Trapezius
  • Latissimus dorsi

The Upper Limb

  • Deltoid
  • Biceps brachii
  • Triceps brachii
  • Extensor carpi radialis longus
  • Extensor carpi ulnaris
  • Extensor digitorum
  • Flexor carpi ulnaris
  • Flexor carpi radialis
  • Flexor digitorum superficialis

The Lower Limb

  • Gluteus maximus
  • Tensor fasciae latae
  • Sartorius
  • Rectus femoris
  • Vastus lateralis
  • Vastus medialis
  • Vastus intermedius
  • Gracilis
  • Biceps femoris
  • Semitendinosus
  • Gastrocnemius
  • Soleus
  • Tibialis anterior
  • Extensor digitorum longus
  • Peronus longus

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Chapter 10

The Muscular System


Dr F Prince

Interactions of Skeletal Muscles

Skeletal muscles work together (synergists) or in opposition (antagonists)

Muscles generate force by shortening and so pull bones and tissues never push

When a muscles shortens it is the insertion that moves and the origin that usually immobile

The actions of muscles or muscle groups are apposed by other muscles or muscle groups.

Muscle Classification: Functional Groups

A prime mover is the muscle that provides the major force for producing the specific movement

Antagonists are muscles that oppose or reverse a particular movement

Synergists work in one of two ways

They add force to a movement

Reduce undesirable movement by stabilizing the joint

Fixators are synergists that immobilize a bone or a muscle’s origin

Naming Skeletal Muscles

Location, location, location! The bone or body region associated with the muscle

The shape of muscle the deltoid muscle is triangular or deltoid

Relative size compared to the other muscles, maximus (largest), minimus (smallest), longus (long)

Direction of the fibers, rectus if they run straight up and down, transversus if straight across, and oblique if fibers run at angles to a defined axis

Naming Skeletal Muscles

Number of origins like the biceps that has two origins and the triceps with three origins

Location of attachments that is its origin and/or insertion

The muscle’s action, flexor if it flexes or extensor if it extends

Arrangement of Fascicles

Parallel – fascicles run parallel to the long axis of the muscle (sartorius)

Fusiform – spindle-shaped muscles (biceps brachii)

Pennate – short fascicles that attach obliquely to a central tendon running the length of the muscle resembling a feather pen (rectus femoris)

Convergent – fascicles converge from a broad origin to a single tendon insertion (pectoralis major)

Circular – fascicles are arranged in rings (orbicularis oris)

Arrangement of Fascicles

Components of Lever Systems

Lever – a rigid bar that moves on a fulcrum, or fixed point

Effort – force applied to a lever

Load – resistance moved by the effort

Fulcrum – the pivot point

Bone-Muscle Relationships: Lever Systems

Bone-Muscle Relationships: Lever Systems

Classes of Levers

First class – the fulcrum is between the load and the effort

Second class – the load is between the fulcrum and the effort

Third class – the effort is applied between the fulcrum and the load

Lever Systems: First Class

Lever Systems: Second Class

Lever Systems: Third Class

Major Skeletal Muscles: Anterior View

The 40 superficial muscles here are divided into 10 regional areas of the body

Major Skeletal Muscles: Posterior View

The 27 superficial muscles here are divided into seven regional areas of the body

Muscles: Name, Action, and Innervation

Name and description of the muscle gives you a good description of some aspect of the muscle either its location, origin/insertion, action etc.

There is always a joint between the origin and insertion

The action of a muscle is best learned by acting out the muscle’s movement on your own body or on a volunteer (make sure they volunteer!!!)

Nerve supply is the nerve that innervates that muscle