Muscle Tissue and Muscular System

Overview of Muscle Types

The human body contains three main types of muscle tissue, each with distinct structures and functions. Understanding these types is essential for studying the muscular system and its role in movement and physiology.

• Skeletal Muscle: Voluntary, striated muscle attached to bones; responsible for body movement.

• Cardiac Muscle: Involuntary, striated muscle found only in the heart; responsible for pumping blood.

• Smooth Muscle: Involuntary, non-striated muscle found in walls of hollow organs (e.g., intestines, blood vessels).

Example: The biceps brachii is a skeletal muscle that flexes the forearm at the elbow.

Additional info: Skeletal muscle histology reveals multinucleated fibers with cross-striations, while cardiac muscle shows intercalated discs, and smooth muscle cells are spindle-shaped without striations.

Muscle Contractions

Muscle contractions are classified based on changes in muscle length and tension.

• Isometric Contraction: Muscle tension increases, but muscle length remains unchanged (e.g., holding a weight steady).

• Isotonic Contraction: Muscle changes length while moving a load. Subtypes include:

  • Concentric: Muscle shortens as it contracts (e.g., lifting a dumbbell).

  • Eccentric: Muscle lengthens while maintaining tension (e.g., lowering a dumbbell).

Equation:

Additional info: In isometric contractions, no work is done as there is no movement, while isotonic contractions perform mechanical work.

Major Muscles of the Human Body

Muscles of the Face

Facial muscles control expressions, mastication, and movements of the mouth and eyes.

• Temporalis: Elevates and retracts the mandible.

• Buccinator: Compresses cheek; assists in chewing.

• Orbicularis Oculi: Closes eyelids.

• Orbicularis Oris: Closes and protrudes lips.

• Zygomaticus Major: Elevates corners of the mouth (smiling).

• Mentalis: Protrudes lower lip.

• Masseter: Elevates mandible; primary muscle of mastication.

Muscles of the Neck

Neck muscles facilitate head movement, swallowing, and support of the head.

• Sternocleidomastoid: Flexes and rotates the head.

• Sternohyoid: Depresses hyoid bone after swallowing.

• Thyrohyoid: Elevates thyroid, depresses hyoid.

• Mylohyoid: Elevates floor of mouth.

• Splenius Capitis: Extends and rotates head.

• Scaleni Muscles: Elevate ribs 1-2, assist in neck flexion.

Muscles of the Back and Shoulder Girdle

These muscles stabilize and move the scapula and upper limb.

• Trapezius: Elevates, retracts, and rotates scapula.

• Levator Scapulae: Elevates scapula.

• Rhomboideus Major & Minor: Retract scapula.

• Infraspinatus: Lateral rotation of arm.

• Supraspinatus: Abducts arm.

• Teres Major & Minor: Medial and lateral rotation of arm, respectively.

• Latissimus Dorsi: Extends, adducts, and medially rotates arm.

• Subscapularis: Medial rotation of arm.

Muscles of the Thorax

Thoracic muscles are involved in respiration and movement of the upper limb.

• Pectoralis Major: Flexes, adducts, and medially rotates arm.

• Pectoralis Minor: Stabilizes scapula.

• Serratus Anterior: Protracts scapula; assists in upward rotation.

• Internal & External Intercostals: Elevate and depress ribs during breathing.

• Diaphragm: Primary muscle of inspiration; separates thoracic and abdominal cavities.

Muscles of the Abdominal Wall

These muscles support abdominal organs, flex and rotate the trunk, and assist in respiration.

• External Oblique: Compresses abdomen; rotates trunk.

• Internal Oblique: Compresses abdomen; rotates trunk.

• Rectus Abdominis: Flexes vertebral column.

• Transversus Abdominis: Compresses abdominal contents.

Muscles of the Arm and Shoulder Girdle

These muscles control movements of the shoulder, arm, and forearm.

• Deltoid: Abducts arm.

• Biceps Brachii: Flexes elbow, supinates forearm.

• Triceps Brachii: Extends elbow.

• Brachialis: Flexes elbow.

• Brachioradialis: Flexes forearm at elbow.

• Flexor Carpi Radialis/Ulnaris: Flex and abduct/adduct wrist.

• Palmaris Longus: Flexes wrist.

• Pronator Teres: Pronates forearm.

• Supinator: Supinates forearm.

• Extensor Carpi Radialis/Ulnaris: Extend and abduct/adduct wrist.

• Extensor Digitorum: Extends fingers.

• Lumbricals & Interossei: Flex and extend fingers.

Muscles of the Leg

Leg muscles are responsible for movement of the hip, knee, ankle, and toes.

• Gluteus Maximus/Medias/Minimus: Extend, abduct, and medially rotate thigh.

• Tensor Fascia Latae: Abducts and medially rotates thigh.

• Biceps Femoris, Semitendinosus, Semimembranosus (Hamstrings): Flex knee, extend hip.

• Rectus Femoris, Vastus Lateralis/Medialis/Intermedius (Quadriceps): Extend knee, flex hip (rectus femoris).

• Sartorius: Flexes, abducts, and laterally rotates thigh; flexes knee.

• Gracilis: Adducts thigh, flexes knee.

• Adductor Longus/Magnus: Adduct and medially rotate thigh.

• Pectineus: Adducts and flexes thigh.

• Iliopsoas (Psoas Major/Iliacus): Flexes hip.

• Tibialis Anterior: Dorsiflexes and inverts foot.

• Extensor Digitorum Longus: Extends toes, dorsiflexes foot.

• Peroneus (Fibularis) Longus/Brevis: Everts and plantarflexes foot.

• Gastrocnemius: Plantarflexes foot, flexes knee.

• Soleus: Plantarflexes foot.

• Flexor Digitorum Longus: Flexes toes, plantarflexes foot.

• Calcaneal (Achilles) Tendon: Attaches gastrocnemius and soleus to calcaneus.

Muscles of the Eye

Extraocular muscles control eye movement.

• Superior Rectus: Elevates eye.

• Inferior Rectus: Depresses eye.

• Medial Rectus: Moves eye medially.

• Lateral Rectus: Moves eye laterally.

• Superior Oblique: Depresses and abducts eye.

• Inferior Oblique: Elevates and abducts eye.

Muscle Classification Table

The following table summarizes the three main muscle types and their characteristics:

Summary

• Muscles are classified by structure, function, and location.

• Major muscles are grouped by region: face, neck, thorax, abdomen, back, arm, and leg.

• Understanding muscle actions and attachments is essential for anatomy and physiology studies.