Upper and Lower Limb Muscle Compartments

• Flexion and extension compartments organize muscles by function around joints
• Muscles serve multiple purposes but specialize in one movement
• Flexion muscles bend joints and decrease angle between bones.
• Extension muscles straighten joints and increase angle between bones.
• Grouping muscles clarifies their roles in flexion and extension
• Antagonistic muscle pairs work together, one flexing and the other extending a joint
• Compartments allow muscles to perform opposite functions at the same joint
• Muscle grouping makes functional movements efficient
• Muscles have primary actions but contribute to wider actions when combined

Learning Outcomes

• Describe the muscle compartments of upper and lower limbs
• Describe the main muscle groups of the upper and lower limbs
• Actions and nerve supply of muscle groups/compartments should be described

Muscles Connecting Upper Limb to Thoracic Wall

• Several muscles on the anterior surface of the thoracic cage attach the upper limb
• Pectoralis Major actions: Flexion, adduction, and medial rotation of the humerus
• Nerve supply for the Pectoralis Major are Pectoral nerves from the brachial plexus
• Serratus Anterior is important in horizontal arm movements like punching and pushing (boxer's muscle)
• Serratus Anterior's nerve supply is the long thoracic nerve

Muscles Connecting Upper Limb to Vertebral Column

• Several muscles on the back attach the upper limb to the vertebral column
• Trapezius actions:
  • Superior fibers elevate the scapula
  • Middle fibers retract the scapula
  • Inferior fibers depress the scapula
• The trapezius fibers rotate the scapula upward and stabilize scapula
• Nerve supply to the trapezius is the spinal part of the accessory nerve
• Latissimus dorsi Actions: Extends, Adducts, and medially rotates the arm
• Nerve supply to the Latissimus dorsi is the thoracodorsal nerve

Muscle Compartments

• Limb muscles are organized into compartments separated by intramuscular septa
• Each compartment contains one main nerve supply
• Muscles in the same compartment have similar actions and blood supply
• Upper limb: Arm and forearm each have anterior and posterior compartments
• Lower limb: Gluteal region (buttock), thigh, and leg each have three compartments
• Thigh Compartments: Anterior, Posterior and Medial
• Leg Compartments: Anterior, Posterior and Lateral

Upper Limb (Arm)

• Anterior compartment muscles and nerve supply
  • Coraco-brachialis: Musculo-cutaneous nerve- Flexes the arm at the shoulder joint
  • Biceps brachii: Musculo-cutaneous nerve- Flexes the forearm at the elbow joint and supinates the forearm; also flexes the arm at the shoulder joint
  • Brachialis: Musculo-cutaneous nerve- Powerful flexor of the forearm at the elbow joint
• Posterior compartment muscles and nerve supply
  • Triceps brachii: Radial nerve- Extends the forearm at the elbow joint; Its long head extends and adducts arm at the shoulder joint

Upper Limb (Forearm)

• Anterior Compartment (Flexors of wrist and fingers)
  • Flexor digitorum superficialis (FDS): Flexes wrist and metacarpophalangeal and proximal inter-phalangeal joints of medial 4 fingers
  • Nerve supply: Median nerve
  • Flexor digitorum profundus (FDP): Flexes distal interphalangeal joints of the index, middle, ring, and little fingers
  • It can also flex metacarpophalangeal joints of the same fingers and the wrist joint
  • Nerve supply: Median and ulnar nerves
• Movements at Superior Radio-ulnar Joints
  • Supinator- Supination
  • Biceps brachii- Supination
  • Pronator quadratus- Pronation
  • Pronator teres- Pronation
  • Supinator nerve supply: Radial
  • Biceps brachii nerve supply: Musculo-cutaneous
  • Other Muscles nerve supply: Median
• Posterior Compartment of forearm: (Extensors of the wrist and fingers)
  • Extensor carpi ulnaris : Extension of wrist
  • Extensor carpi radialis longus: Extension of wrist
  • Extensor digitorum: Extension of digits
  • Nerve supply to ALL posterior group muscles: Radial nerve

Upper Limb (Hand)

• Muscles involved in controlling precise movements (threading a needle)
  • Four lumbricals assist flexion at metacarpophalangeal joint-medial two by ulnar and lateral two by median nerve
  • Three Palmer interossei adduct fingers-ulnar nerve
  • Four dorsal interossei abduct fingers from middle finger axis-ulnar nerve

Upper Limb (Thumb)

• Flexor pollicis longus (FPL) and F. P. brevis- Flexion-Medium nerve
• Extensor pollicis longus (EPL) and E. P. brevis- Extension-Radial nerve
• Abductor pollicis longus (APL) and A. P. brevis - Abduction-APL-Radial nerve, APB-Median nerve
• Adductor pollicis- Adduction-Ulnar nerve
• Opponens pollicis- Opposition-Median nerve

Lower Limb

• Gluteal Region
  • All gluteal muscles originate from the posterior surface of the ilium insert on the femur
  • Gluteus Maximus- Extends and laterally rotate hip joint-Inferior Gluteal nerve
  • Gluteus Medius and Minimus- Abducts hip joint-Superior Gluteal nerve
  • Ilio-psoas muscle: flexes the thigh at the hip joint-Flex trunk on the hip as in sitting up from the supine position:
    • ILIACUS-femoral nerve
    • PSOAS- branches from lumbar plexus
• Thigh (three compartments)
  • Anterior Compartment:
    • Sartorius
    • Ilio-psoas (psoas major and iliacus)
    • Quadriceps femoris (vastus medialis, vastus intermedius and vastus lateralis plus rectus femoris)
    • Actions: flexion at hip joint and extension at knee
    • Nerve supply: femoral nerve
  • Posterior Compartment:
    • Biceps femoris,
    • Semitendinosus
    • Semimembranosus
    • Adductor Magnus (hamstring posterior part)
    • Actions: mainly extension at the hip joint and flexion at the knee joint
    • Nerve supply: sciatic nerve
  • Medial Compartment:
    • Adductor longus
    • Adductor brevis
    • Adductor Magnus (adductor anterior part)
    • Actions: adduction at hip joint
    • Nerve supply: obturator nerve
• Leg (three compartments)
  • Anterior compartment:
    • Tibialis anterior (TA)
    • Extensor hallucis longus (EHL)
    • Extensor digitorum longus (EDL)
    • Fibularis tertius (FT)
    • Actions: Dorsiflexion at ankle joint. Extension of big toe, lateral toes. Inversion of foot, FT can also do eversion -Nerve supply: deep fibularis nerve
  • Lateral compartment:
    • Fibularis longus (FL)
    • Fibularis brevis (FB)
    • Actions: Plantar flexion at ankle joint, Eversion of foot
    • Nerve supply: superficial fibularis nerve
  • Posterior compartment:
    • Superficial group:
      • Gastrocnemius
      • Plantaris
      • Soleus
      • Actions: All do plantar-flexion at ankle joint and flexion at knee joint -Deep group:
      • Flexor hallucis longus
      • Flexor digitorum longus
      • Tibialis posterior
      • Actions: plantar-flexion at ankle joint, big toe, digits and inversion of foot.
    • Nerve supply to both groups: tibial nerve