Muscle Interactions and Classification

Interactions of Skeletal Muscles

• Muscles work in pairs, either together or in opposition
• Muscles can only pull, not push
• When muscles contract, the insertion moves toward the origin
• For every muscle action, there is a counteraction

Muscle Classification: Functional Groups

• Prime movers produce the major force for a specific movement
• Antagonists oppose or reverse a movement
• Synergists add force to a movement and reduce unwanted movement
• Fixators stabilize a bone or muscle's origin

Naming Skeletal Muscles

• Location: Muscles are named based on the bone or body region they're associated with.
• Shape: For example, the deltoid muscle is named after its triangular shape.
• Relative Size: Maximus means largest, minimus means smallest, longus means long.
• Direction of Fibers: Rectus indicates straight fibers, transversus and oblique indicate fibers running at angles.
• Number of Origins: Biceps have two origins, triceps have three.
• Location of Attachments: Named based on the point of origin or insertion.
• Action: Muscles are named based on their actions, like flexors and extensors.

Arrangement of Fascicles

• Parallel: Fascicles run parallel to the muscle's long axis (e.g., sartorius)
• Fusiform: Spindle-shaped muscles (e.g., biceps brachii).
• Pennate: Short fascicles attach obliquely to a central tendon (e.g., rectus femoris).
• Convergent: Fascicles converge from a broad origin (e.g., pectoralis major).
• Circular: Fascicles arranged in concentric rings (e.g., orbicularis oris).

Bone-Muscle Relationships: Lever Systems

• A lever is a rigid bar that moves around a fixed point (fulcrum).
• The force applied is the effort.
• The resistance moved is the load.

Lever Systems: Classes

• First Class: The fulcrum is located between the load and the effort.
• Second Class: The load is located between the fulcrum and the effort.
• Third Class: The effort is applied between the fulcrum and the load.

Major Skeletal Muscles: Anterior View

• This view shows 40 superficial muscles divided into 10 regional areas.

Major Skeletal Muscles: Posterior View

• This view shows 27 superficial muscles divided into 7 regional areas.

Muscles: Name, and Action

• Focus on the information provided in the muscle's name.
• Remember that there is always a joint between the origin and insertion.
• Learn a muscle's action by imitating the movement on your own body.

Muscles of the Scalp

• The epicranius (occipitofrontalis) consists of:
  • Frontalis
  • Occipitalis
  • Cra

Interactions of Skeletal Muscles

• Muscles work together or in opposition
• Muscles can only pull, never push
• The insertion of a muscle moves towards its origin as the muscle shortens
• For every muscle action, there is an opposing muscle action

Muscle Classification: Functional Groups

• Prime movers are the main muscles responsible for a specific movement
• Antagonists oppose or reverse a particular movement
• Synergists work together to add force to a movement, reduce undesirable or unnecessary movement
• Fixators immobilize a bone or muscle's origin to help other muscles work more efficiently

Naming Skeletal Muscles

• Muscles are named based on their location, shape, size, fiber direction, number of origins, location of attachments, and action.
• Some examples:
  • Location: Pectoralis (chest)
  • Shape: Deltoid (triangle)
  • Relative Size: Maximus (largest), Minimus (smallest), Longus (long)
  • Direction of Fibers: Rectus (fibers run straight), Transverse, Oblique (fibers run at angles)
  • Number of Origins: Biceps (two origins), Triceps (three origins)
  • Location of Attachments: Named according to point of origin or insertion
  • Action: Flexor or extensor, depending on the movement they produce

Arrangement of Fascicles

• Parallel: Fascicles run parallel to the long axis of the muscle (example: sartorius)
• Fusiform: Spindle-shaped muscles (example: biceps brachii)
• Pennate: Short fascicles attach obliquely to a central tendon (example: rectus femoris)
• Convergent: Fascicles converge from a broad origin to a single tendon insertion (example: pectoralis major)
• Circular: Fascicles arranged in concentric rings (example: orbicularis oris)

Bone-Muscle Relationships: Lever Systems

• Lever: A rigid bar that moves on a fixed point called a fulcrum
• Effort: Force applied to a lever
• Load: Resistance moved by the effort

Lever Systems: Classes

• First Class: 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

Major Skeletal Muscles: Anterior View

• The diagram includes 40 superficial muscles on the anterior view of the body
• They are divided into 10 regional areas of the body

Major Skeletal Muscles: Posterior View

• The diagram includes 27 superficial muscles on the posterior view of the body
• They are divided into seven regional areas of the body

Muscles: Name, and Action

• When studying muscles, remember to note the name, description, origin and insertion, and action.
• There is always a joint between the origin and insertion of a muscle
• Action can be learned by acting out the muscle movement on your own body

Muscles of the Scalp

• Epicranius (occipitofrontalis): Consists of:
  • Frontalis
  • Occipitalis
  • Cra