Skeletal muscles have unique names that reveal their shape, size, location, and function. These names use Latin and Greek roots to provide a wealth of information about each muscle's characteristics and role in the body.

Understanding muscle nomenclature helps identify and remember the hundreds of muscles in the human body. This naming system connects muscle structure to function, making it easier to grasp how muscles work together to produce movement and maintain posture.

Skeletal Muscle Nomenclature

Criteria for naming skeletal muscles

• Shape describes the muscle's appearance resembles a geometric shape or object
  • Deltoid muscle has a triangular shape similar to the Greek letter delta
  • Rhomboid muscle appears like a rhombus or diamond shape
  • Trapezius muscle resembles a trapezoid, a four-sided shape with parallel sides
  • Serratus muscle has a saw-toothed appearance with finger-like projections
• Size compares the muscle's dimensions to other muscles in the same group
  • Maximus indicates the largest muscle in a group (gluteus maximus)
  • Minimus denotes the smallest muscle in a group (gluteus minimus)
  • Longus signifies a muscle longer than others in the group (adductor longus)
  • Brevis specifies a muscle shorter than others in the group (extensor digitorum brevis)
• Location refers to the muscle's position in the body or its relationship to other structures
  • Pectoralis muscles are located in the chest region (pectoralis major and minor)
  • Gluteus muscles are situated in the buttocks area (gluteus maximus, medius, and minimus)
  • Brachii muscles are found in the arm, particularly the upper arm (biceps brachii, triceps brachii)
  • Femoris muscles are located in the thigh region (rectus femoris, vastus lateralis)
• Function describes the primary action or movement the muscle performs
  • Flexor muscles flex or bend a joint, decreasing the angle between bones (flexor carpi radialis)
  • Extensor muscles extend or straighten a joint, increasing the angle between bones (extensor digitorum)
  • Adductor muscles adduct or pull a limb toward the body's midline (adductor magnus)
  • Abductor muscles abduct or move a limb away from the body's midline (abductor pollicis longus)

Application of muscle naming conventions

• Combining criteria creates a more precise description of the muscle's features and actions
  • Serratus anterior is a saw-toothed muscle located on the anterior side of the body
  • Adductor longus is a long muscle responsible for adduction
  • Extensor digitorum longus is a long muscle that extends the digits (fingers or toes)
  • Flexor pollicis brevis is a short muscle that flexes the thumb (pollex)
• Directional terms indicate the muscle's orientation or direction of fibers
  • Rectus describes a straight muscle with parallel fibers (rectus abdominis)
  • Transversus specifies a muscle with fibers running transversely or horizontally (transversus abdominis)
  • Obliquus refers to a muscle with obliquely oriented fibers, running at an angle
    • Obliquus internus is the internal oblique muscle with fibers angled upward and medially
    • Obliquus externus is the external oblique muscle with fibers angled downward and medially
• Number of origins specifies the number of attachment points the muscle has at its proximal end
  • Biceps muscles have two origins or heads (biceps brachii, biceps femoris)
  • Triceps muscles have three origins or heads (triceps brachii)
  • Quadriceps muscles have four origins or heads (quadriceps femoris)

Latin and Greek roots in muscle nomenclature

• Latin roots provide information about the muscle's characteristics
  • Rectus indicates a straight muscle (rectus femoris)
  • Transversus denotes a transverse orientation of fibers (transversus abdominis)
  • Obliquus refers to an oblique or slanted direction of fibers (obliquus capitis inferior)
  • Longus signifies a long muscle compared to others in the group (peroneus longus)
  • Brevis specifies a short muscle in relation to others in the group (peroneus brevis)
  • Major denotes the larger of two similar muscles (pectoralis major)
  • Minor indicates the smaller of two similar muscles (pectoralis minor)
• Greek roots often describe the muscle's shape or resemblance to an object
  • Deltoid refers to a triangular shape, similar to the Greek letter delta (deltoid muscle)
  • Trapezius denotes a trapezoid or table-like shape (trapezius muscle)
  • Rhomboid describes a rhombus or diamond-shaped muscle (rhomboid major and minor)
  • Latissimus signifies the widest muscle in a region (latissimus dorsi)
  • Psoas refers to muscles in the loin area (psoas major and minor)
• Examples demonstrate how Latin and Greek roots are used in naming specific muscles
  • Rectus abdominis is the straight muscle of the abdomen
  • Transversus abdominis is the transverse muscle of the abdomen
  • Teres major is the larger of the two round muscles in the shoulder region
  • Teres minor is the smaller of the two round shoulder muscles
  • Latissimus dorsi is the widest muscle of the back
  • Psoas major is the larger muscle of the loin region

Muscle Attachments and Functional Relationships

• Origin refers to the more stationary attachment point of a muscle, typically proximal or closer to the body's midline
• Insertion is the more mobile attachment point of a muscle, usually distal or farther from the body's midline
• Agonist muscles are the primary movers in a specific action (e.g., biceps brachii in elbow flexion)
• Antagonist muscles oppose the action of the agonist (e.g., triceps brachii in elbow flexion)
• Synergist muscles assist the agonist in performing an action, often by stabilizing joints
• Fascicle is a bundle of muscle fibers enclosed by connective tissue, contributing to the overall muscle structure
• Myofiber, also known as a muscle fiber, is the individual contractile unit of skeletal muscle tissue