*Week 1: Naming Skeletal Muscles

Introduction to Naming Skeletal Muscles

• Discusses how skeletal muscles are named.

• Identifies functional muscle groups and compartments.

• Muscle naming criteria include:

  • Directions of fascicles

  • Size

  • Shape

  • Action

  • Number of origins

  • Location of the muscle

  • Sites of origins and insertions

• Muscle action: movement produced by muscle contraction.

How Skeletal Muscles Are Named

• Clues about muscle features can be inferred from their names.

• Muscle names typically combine a root word with distinctive features based on the following factors:

  • Fascicle Direction: Relation to midline of the body.

  • Size: Relative dimensions of muscles.

  • Shape: Physical form of the muscle.

  • Action: Function of the muscle during activity.

  • Number of Origins: Count of muscle attachment points.

  • Body Regions: Where the muscle is located.

• Fascicle Orientation affects appearance and function.

  • Rectus: Parallel to midline (e.g., Rectus abdominis).

  • Transverse: Perpendicular to midline (e.g., Transverse abdominis).

  • Oblique: Diagonal to midline (e.g., External oblique).

Naming Muscles Based on Size

• Muscles can be named according to their size:

  • Maximus: Largest (e.g., Gluteus maximus)

  • Minimus: Smallest (e.g., Gluteus minimus)

  • Longus: Long (e.g., Adductor longus)

  • Brevis: Short (e.g., Adductor brevis)

  • Latissimus: Widest (e.g., Latissimus dorsi)

  • Longissimus: Longest (e.g., Longissimus capitis)

  • Magnus: Large (e.g., Adductor magnus)

  • Major / Minor: Larger / smaller (e.g., Pectoralis major/minor)

  • Vastus: Huge (e.g., Vastus lateralis).

Naming Muscles Based on Shape

• Shape influences naming:

  • Deltoid: Triangular (e.g., Deltoid muscle)

  • Trapezius: Trapezoid (e.g., Trapezius muscle)

  • Serratus: Saw-toothed (e.g., Serratus anterior)

  • Rhomboid: Diamond-shaped (e.g., Rhomboid major)

  • Orbicularis: Circular (e.g., Orbicularis oculi)

  • Gracilis: Slender (e.g., Gracilis muscle).

Naming Muscles Based on Action

• Muscle naming often reflects principal action:

  • Flexor: Decreases joint angle (e.g., Flexor carpi radialis).

  • Extensor: Increases joint angle (e.g., Extensor carpi ulnaris).

  • Abductor: Moves bone away from midline (e.g., Abductor pollicis longus).

  • Adductor: Moves bone closer to midline (e.g., Adductor longus).

  • Levator: Elevates body part (e.g., Levator scapulae).

  • Depressor: Lowers body part (e.g., Depressor labii inferioris).

  • Supinator / Pronator: Turns palm anteriorly/posteriorly.

  • Rotator: Rotates bone around longitudinal axis.

Functional Groups of Muscles

• Muscles can also be categorized by their number of origins:

  • Biceps: Two origins (e.g., Biceps brachii).

  • Triceps: Three origins (e.g., Triceps brachii).

  • Quadriceps: Four origins (e.g., Quadriceps femoris).

Muscle Action Details

• Muscle movements characterized by:

  • Origin: Attachment to stationary bone.

  • Insertion: Attachment to moving bone.

  • Agonist: Prime mover producing force.

  • Synergist: Assists the prime mover.

  • Antagonist: Opposes the action of the agonist.

  • Fixator: Stabilizes the bone during action.

Muscle Compartments

• Muscles grouped into compartments by function, with fascia maintaining position.

• Compartment syndrome: Painful condition caused by increased pressure around muscles, limiting blood flow.

Scalp Muscles Overview

• Occipitofrontalis: Draws scalp anteriorly and posteriorly.

Muscles of Facial Expression

• Includes Orbicularis oris (closes/protrudes lips), Zygomaticus major/minor (smiling), and others associated with facial expressions.

Extrinsic Muscles of the Eye

• Muscles involved in moving the eye around:

  • Superior/Inferior Rectus: Moves eyeball superiorly/inferiorly.

  • Lateral/Medial Rectus: Abducts/adducts the eye.

  • Superior/Inferior Oblique: Rotates the eyeball.

Neck Muscles

• Examples include:

  • Platysma: Elevates neck, creates wrinkling appearance.

  • Sternocleidomastoid: Flexes cervical spine, rotates head.

Abdominal Muscles

• Major muscles include:

  • Rectus abdominis: Flexes vertebral column, assists in exhalation.

  • External/Internal oblique and Transverse abdominis: Assist with flexion of the vertebral column.

Muscles of the Thorax

• Key muscles for ventilation include:

  • Diaphragm: Main muscle of inhalation.

  • Intercostals: Assist with inhalation and forced exhalation.

Scapular Muscles

• Muscles that move the humerus like Deltoid (abducts arm) and Subscapularis (medially rotates arm).

Arm Muscles

• Key arm muscles:

  • Biceps brachii: Flexes forearm and shoulder.

  • Triceps brachii: Extends forearm and shoulder.

Muscles of Lower Extremities

• Includes hip joint movers such as Tensor Fascia Lata and Gluteus Maximus.

Muscles of Anterior Thigh (Quadriceps Femoris)

• Group with common tendon for knee extension.

Hamstrings (Posterior Thigh)

• Include Biceps femoris, Semitendinosus, Semimembranosus: flex knee, extend hip joint.

Muscles of the Leg

• Involves posterior (e.g., Gastrocnemius) and anterior (e.g., Tibialis anterior) muscle actions.