ll: 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.

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