Muscular System Part II

Muscular System Overview

Major Muscle Groups

  • Muscles of Upper Limb:

    • Brachialis
    • Triceps
    • Biceps
    • Flexor carpi ulnaris
    • Palmaris longus
    • Flexor carpi radialis
    • Teres major
    • Latissimus dorsi
    • Serratus anterior
    • External oblique
    • Rectus abdominis
    • Internal oblique

  • Muscles of Lower Limb:

    • Tensor fasciae latae
    • Iliopsoas (psoas major)
    • Pectineus
    • Adductor longus
    • Gracilis
    • Sartorius
    • Rectus femoris
    • Vastus intermedius
    • Quadriceps (Vastus lateralis, Vastus medialis)
    • Gastrocnemius
    • Peroneus longus
    • Peroneus brevis
    • Soleus

Anatomy of Skeletal Muscle

  • Attachment Points:
    • Origin: attachment at the stationary end of the muscle.
    • Insertion: attachment at the moveable end, usually crosses a joint.
  • Belly/Gaster: thick middle part of the muscle.

Fascicle Orientation Types

  • Fusiform: thick in the middle, tapering at the ends (e.g., biceps brachii).
  • Parallel: long and straplike (e.g., rectus abdominis).
  • Convergent: fan-shaped with a broad origin and narrow insertion (e.g., pectoralis major).
  • Pennate: feather-like arrangement of fascicles:
    • Unipennate: fascicles on one side of tendon.
    • Bipennate: fascicles on both sides of tendon (e.g., rectus femoris).
    • Multipennate: multiple tendons with fascicles in between.
  • Circular: fascicles arranged in a ring form (e.g., orbicularis oris).

Coordination of Muscle Actions

  • Muscle Actions:
    • Prime Mover (Agonist): muscle that produces most movement (e.g., biceps brachii when flexing elbow).
    • Synergist: assists the prime mover (e.g., brachialis).
    • Antagonist: opposes the prime mover (e.g., triceps brachii during elbow flexion).
    • Fixator: stabilizes a bone during movement (e.g., muscles stabilizing scapula when biceps brachii contracts).

Naming Muscles

  • Size: major, minor, minimus, maximus, longus, brevis.
  • Shape: trapezoidal (trapezius), triangular (deltoid).
  • Location: indicates body regions (e.g., pectoralis, femoris).
  • Number of Origins: biceps, triceps, quadriceps.
  • Orientation: rectus, transverse, oblique.
  • Action: adductor, abductor, extensor, flexor, etc.
  • Origin/Insertion: e.g., sternocleidomastoid.

Muscles of Facial Expression

  • Occipitofrontalis: connected by galea aponeurotica (epicranius).
    • Occipitalis: retracts scalp.
    • Frontalis: raises eyebrows and draws scalp forward.
  • Orbicularis oculi: closes the eye.
  • Levator palpebrae superioris: opens the eye, raises eyelid.
  • Orbicularis oris: protrudes lips (kissing) and aids in speech.
  • Zygomaticus major and minor: lift corners of the mouth (smiling).
  • Mentalis: elevates and protrudes lower lip (pouting).
  • Buccinator: compresses cheek; aids with suction (blowing and sucking).
  • Platysma: depresses mandible, opens mouth, tenses neck skin.

Muscles of Chewing and Swallowing

  • Extrinsic Tongue Muscles:
    • Genioglossus: moves tongue forward.
    • Hypoglossus: moves tongue down.
    • Styloglossus: retracts and elevates tongue.
    • Palatoglossus: elevates back of tongue.
  • Masseter: elevates mandible for biting and chewing.
  • Temporalis: also elevates mandible for biting and chewing.

Muscles that Move the Head and Vertebral Column

  • Sternocleidomastoid: rotates and tilts the head.
  • Splenius capitis: keeps head erect.
  • Semispinalis capitis: extends and rotates head.
  • Erector spinae: maintains an upright posture of the vertebral column.
  • Trapezius: abducts and extends the neck.

Muscles of Respiration

  • Diaphragm: increases thoracic cavity volume for inhalation.
  • External intercostals: lift ribs, inflating lungs.
  • Internal intercostals: pull ribs down, aiding in exhalation.

Muscles of the Abdomen

  • Rectus abdominis: flexes waist and supports abdominal viscera.
  • External oblique: flexes and rotates vertebral column.
  • Internal oblique: similar function to external oblique.
  • Transverse abdominis: compresses the abdomen and stabilizes the core.

Muscles of the Back

  • Erector spinae group: primary muscle for spinal extension; consists of:
    • Iliocostalis: cervical region.
    • Longissimus: thoracic region.
    • Spinalis: lumbar region.
  • Semispinalis: provides support in neck and back.

Muscles that Move the Pectoral Girdle (Scapula)

  • Trapezius: elevates/rotates scapula.
  • Levator scapulae: elevates scapula.
  • Rhomboid major/minor: retracts and elevates scapula.
  • Serratus anterior: protracts and rotates scapula; essential in pushing movements.
  • Pectoralis minor: protracts and depresses scapula.

Muscles that Move the Arm (Humerus)

  • Pectoralis major: adducts, rotates, and flexes humerus; assists in various movements.
  • Latissimus dorsi: adducts, medially rotates, and extends the arm.
  • Deltoid: abducts, flexes, extends, and rotates the humerus based on fiber orientation.
  • Teres major: adducts and medially rotates the humerus.

Rotator Cuff Muscles (Shoulder Stability)

  • Infraspinatus: laterally rotates the humerus.
  • Supraspinatus: abducts humerus; stabilizes during loading.
  • Subscapularis: medially rotates the humerus.
  • Teres minor: laterally rotates and adducts humerus.

Muscles that Move the Forearm

  • Biceps brachii: flexes and supinates forearm.
  • Brachialis: primary elbow flexor.
  • Triceps brachii: extends forearm at the elbow.
  • Pronator teres and Pronator quadratus: pronate the forearm.
  • Supinator: supinates the forearm.

Muscles that Move the Wrist and Hand

  • Posterior Compartment (Extensors):

    • Extensor carpi radialis longus: extends and abducts hand.
    • Extensor carpi radialis brevis: extends and abducts hand, stabilizes during flexion of fingers.
    • Extensor carpi ulnaris: extends and adducts hand.
    • Extensor digitorum: extends fingers II-V.

  • Anterior Compartment (Flexors):

    • Flexor carpi radialis: flexes and abducts hand.
    • Flexor carpi ulnaris: flexes and adducts hand.
    • Palmaris longus: weak flexor of wrist.
    • Flexor digitorum superficialis: flexes fingers II-V and wrist.

Muscles that Move the Hip and Femur

  • Iliacus: flexes femur.
  • Psoas major: flexes femur.
  • Tensor fasciae latae: flexes, abducts, and medially rotates femur.
  • Gluteus maximus: extends and laterally rotates femur, key for movements like climbing.
  • Adductor muscles: (longus, brevis, magnus) adduct and rotate femur; assist in flexing hip.
  • Gracilis: adducts femur and flexes leg at knee.
  • Pectineus: adducts and flexes hip.

Muscles that Move the Knee

  • Quadriceps femoris: extends leg at knee (comprising Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius).
  • Sartorius: flexes and rotates thigh, often used to cross legs.
  • Hamstrings: includes:
    • Biceps femoris: flexes knee, extends thigh.
    • Semitendinosus: flexes knee, extends thigh.
    • Semimembranosus: flexes knee, medially rotates tibia.

Muscles that Move the Foot

  • Extensor digitorum longus: extends toes II-V; dorsiflexes and everts foot.

  • Peroneus tertius: assists in dorsiflexion and eversion of foot.

  • Tibialis anterior: dorsiflexes and inverts foot.

  • Gastrocnemius: flexes knee and plantar flexes foot.

  • Soleus: primarily plantar flexes foot.

  • Flexor digitorum longus: flexes toes II-V and assists in plantar flexion and inversion.

  • Fibularis (peroneus) longus: plantar flexes and everts the foot.

Muscles that Move the Eyeball

  • Superior oblique: moves eyeball inferiorly and laterally; rotates eye medially.
  • Inferior oblique: moves eyeball superiorly and laterally; rotates eye laterally.
  • Medial rectus: moves eyeball medially.
  • Lateral rectus: moves eyeball laterally.
  • Superior rectus: moves eyeball superiorly.
  • Inferior rectus: moves eyeball inferiorly.

Common Muscle Injuries

  • Hamstring pull: strain or partial tear in hamstrings, often at semitendinosus region.
  • Tennis elbow: inflammation at the lateral epicondyle due to overuse of extensor carpi muscles.
  • Pulled groin: strain in the adductors of the thigh.
  • Charley horse: tear or spasm in muscle, common in quadriceps due to trauma.
  • RICE: Rest, Ice, Compression, Elevation for treatment of muscle injuries.
  • Carpal tunnel syndrome: results from repetitive motions leading to compression of the median nerve in the wrist.

Intramuscular Injections

  • Recommended maximum volume of an intramuscular injection:
    • Deltoid: up to 2 ml.
    • Gluteus medius: for amounts over 2 ml.
    • Vastus lateralis: often used in children or infants where other sites are underdeveloped.