Module 9.1 Overview of Skeletal Muscles

Structure of a Skeletal Muscle

Skeletal muscles are defined by the shape, size, placement, and arrangement of their fibers, all of which contribute to their function. Understanding how muscles are named and classified is essential for studying their anatomy and physiology.

• Naming Muscles: Muscles are named based on appearance, size, position, or function. Some names are derived from historical or descriptive terms. Common naming conventions include:

  • Location: Muscles may be named for their anatomical position (e.g., rectus abdominis).

  • Attachment: Some are named for the bones or structures to which they attach (e.g., sternocleidomastoid).

  • Action: Muscles may be named for their action, such as flexors, extensors, adductors, and abductors.

Functions of Skeletal Muscles

Skeletal muscles perform more than just movement; they are involved in various physiological processes.

• Movement and Other Functions:

  • Muscle contractions generate heat, helping maintain body temperature.

  • The diaphragm's contraction is essential for respiration.

  • Facial muscles allow for expression by moving the skin.

  • Sphincter muscles control the opening and closing of body orifices.

Muscle Actions and Roles

Muscles work in groups to perform movements, with each muscle playing a specific role:

• Agonists (Prime Movers): Provide most of the force for a movement.

• Antagonists: Oppose the action of agonists, allowing for controlled movement.

• Synergists: Assist agonists by stabilizing joints or adding extra force.

• Fixators: Stabilize the origin of the agonist muscle to increase efficiency and prevent unwanted movement.

Muscle Origin and Insertion

Muscles attach to bones at two main points:

• Origin: The fixed attachment point, usually proximal.

• Insertion: The movable attachment, usually distal, where movement occurs.

Module 9.2 Muscles of the Head, Neck, and Vertebral Column

Muscles of Facial Expression

These muscles insert into the skin and connective tissue of the face, allowing for subtle changes in facial structure and expression.

• Epicranius aponeurosis: Connects the frontalis and occipitalis muscles, raising the eyebrows and skin of the forehead.

• Orbicularis oculi: Closes the eyelids.

• Zygomaticus major/minor, levator labii superioris, risorius: Elevate and retract the lips and mouth.

• Orbicularis oris: Closes and protrudes the lips, important for speech and eating.

• Depressor anguli oris, depressor labii inferioris, mentalis: Involved in frowning and other negative facial expressions.

• Buccinator: Compresses the cheeks, aiding in chewing.

• Platysma: Tenses the skin of the neck and helps depress the mandible.

Muscles of the Head and Neck

• Muscles of Chewing (Mastication):

  • Masseter, temporalis: Elevate the mandible for biting and chewing.

  • Medial pterygoid: Assists in elevation and side-to-side movement.

  • Lateral pterygoid: Protracts the mandible and assists in side-to-side movement.

• Muscles of Swallowing: Move food from the mouth to the pharynx and esophagus.

  • Digastric, stylohyoid, mylohyoid, geniohyoid: Elevate the hyoid and move food toward the pharynx.

  • Genioglossus, hyoglossus, styloglossus: Manipulate the tongue for swallowing.

• Pharyngeal constrictor muscles: Initiate swallowing.

• Sternocleidomastoid, scalenes, splenius capitis: Move the head and neck.

Module 9.3 Muscles of the Trunk and Pelvic Floor

Muscles of the Trunk

• Muscles of Respiration: Diaphragm, internal intercostals, external intercostals are essential for breathing.

• Abdominal Muscles: Rectus abdominis, external obliques, internal obliques, transversus abdominis support trunk movement and protect internal organs.

  • Rectus sheath: Connective tissue covering the rectus abdominis.

  • Linea alba: Midline connective tissue separating left and right rectus abdominis.

Module 9.4 Muscles of the Pectoral Girdle and Upper Limbs

Muscles of the Shoulder and Arm

• Muscles that move the scapula: Serratus anterior, pectoralis minor, trapezius, levator scapulae, rhomboid major, rhomboid minor.

• Muscles that move the humerus: Pectoralis major, latissimus dorsi, teres major, coracobrachialis, teres minor, supraspinatus, infraspinatus, subscapularis.

• Muscles that abduct the arm: Deltoid.

Muscles of the Arm, Forearm, and Hand

• Anterior forearm muscles: Flexor carpi radialis, palmaris longus, flexor carpi ulnaris.

• Superficial flexors: Flexor digitorum superficialis, flexor digitorum profundus, flexor pollicis longus.

• Pronators: Pronator teres, pronator quadratus.

• Supinator: Rotates the forearm laterally.

• Wrist extensors: Extensor carpi radialis longus, extensor carpi radialis brevis, extensor carpi ulnaris.

• Hand muscles: Abductor pollicis brevis, lumbricals, palmar interossei, dorsal interossei.

Module 9.5 Muscles of the Hip and Lower Limb

Muscles That Move the Thigh and Knee

• Anterior thigh muscles: Iliopsoas, sartorius.

• Medial thigh muscles: Adductor magnus, adductor longus, adductor brevis, pectineus, gracilis.

• Quadriceps femoris group: Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius.

• Gluteal muscles: Gluteus maximus, gluteus medius, gluteus minimus.

• Deep posterior muscles: Piriformis, obturator internus, gemelli, quadratus femoris, obturator externus.

• Posterior thigh muscles (hamstrings): Biceps femoris, semitendinosus, semimembranosus.

Muscles That Move the Ankle and Foot

• Anterior leg muscles: Tibialis anterior, extensor digitorum longus, extensor hallucis longus (dorsiflex the foot).

• Posterior leg muscles (triceps surae): Soleus, gastrocnemius, plantaris (plantarflex the foot).

• Lateral leg muscles: Fibularis longus, fibularis brevis (evert the foot).

• Deep posterior muscles: Tibialis posterior, flexor hallucis longus, flexor digitorum longus (invert and flex the foot and toes).

• Intrinsic foot muscles: Flexor digitorum brevis, lumbricals, plantar interossei, dorsal interossei.

Summary Table: Major Muscle Groups and Their Functions

Additional info: The above notes expand on the outline by providing definitions, examples, and a summary table for clarity. All muscle names are italicized as per anatomical convention, and key terms are bolded for emphasis.