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.
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).
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).
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).
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.
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 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.
Muscles grouped into compartments by function, with fascia maintaining position.
Compartment syndrome: Painful condition caused by increased pressure around muscles, limiting blood flow.
Occipitofrontalis: Draws scalp anteriorly and posteriorly.
Includes Orbicularis oris (closes/protrudes lips), Zygomaticus major/minor (smiling), and others associated with facial expressions.
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.
Examples include:
Platysma: Elevates neck, creates wrinkling appearance.
Sternocleidomastoid: Flexes cervical spine, rotates head.
Major muscles include:
Rectus abdominis: Flexes vertebral column, assists in exhalation.
External/Internal oblique and Transverse abdominis: Assist with flexion of the vertebral column.
Key muscles for ventilation include:
Diaphragm: Main muscle of inhalation.
Intercostals: Assist with inhalation and forced exhalation.
Muscles that move the humerus like Deltoid (abducts arm) and Subscapularis (medially rotates arm).
Key arm muscles:
Biceps brachii: Flexes forearm and shoulder.
Triceps brachii: Extends forearm and shoulder.
Includes hip joint movers such as Tensor Fascia Lata and Gluteus Maximus.
Group with common tendon for knee extension.
Include Biceps femoris, Semitendinosus, Semimembranosus: flex knee, extend hip joint.
Involves posterior (e.g., Gastrocnemius) and anterior (e.g., Tibialis anterior) muscle actions.