Correctly Label The Following Muscles Of The Posterior View

The posterior view of the human muscular system provides a fascinating glimpse into the intricate network of tissues responsible for movement, posture, and overall body function. Accurately identifying and understanding these muscles is fundamental for students, healthcare professionals, fitness enthusiasts, and anyone keen on delving into the mechanics of the human body. This comprehensive guide will walk you through the major muscles visible from the posterior view, offering detailed descriptions of their origins, insertions, actions, and clinical significance.

Unveiling the Muscles of the Posterior View

The posterior aspect of the body hosts a diverse array of muscles, each playing a critical role in various movements and postural maintenance. These muscles can be broadly categorized into superficial and deep layers, and understanding their arrangement is essential for accurate identification. We'll explore the major muscles from the top down, starting with the neck and moving towards the lower limbs.

Muscles of the Neck and Upper Back

1. Trapezius: The trapezius is a large, superficial muscle that spans the neck, shoulders, and upper back. It's divided into three parts: upper, middle, and lower fibers.

   • Origin: Occipital bone, ligamentum nuchae, and spinous processes of vertebrae C7-T12.
   • Insertion: Lateral third of the clavicle, acromion, and spine of the scapula.
   • Action: The upper fibers elevate the scapula, the middle fibers retract the scapula, and the lower fibers depress the scapula. Together, they can rotate the scapula upward. The trapezius also extends the neck.
   • Clinical Significance: Common site for tension and pain, often associated with poor posture or stress.

2. Levator Scapulae: As the name suggests, the levator scapulae elevates the scapula. It's located deep to the trapezius in the neck region.

   • Origin: Transverse processes of vertebrae C1-C4.
   • Insertion: Medial border of the scapula, from the superior angle to the spine.
   • Action: Elevates and rotates the scapula downward. It also assists in neck flexion.
   • Clinical Significance: Can contribute to neck pain and stiffness, especially with repetitive movements or poor posture.

3. Rhomboid Minor: Located inferior to the levator scapulae and deep to the trapezius, the rhomboid minor is a small, rectangular muscle.

   • Origin: Spinous processes of vertebrae C7-T1.
   • Insertion: Medial border of the scapula, at the level of the spine.
   • Action: Retracts and rotates the scapula downward. It also helps to fix the scapula to the thoracic wall.
   • Clinical Significance: Often works in conjunction with the rhomboid major, and both can be affected by poor posture.

4. Rhomboid Major: Larger than the rhomboid minor, the rhomboid major lies directly inferior to it and deep to the trapezius.

   • Origin: Spinous processes of vertebrae T2-T5.
   • Insertion: Medial border of the scapula, from the spine to the inferior angle.
   • Action: Retracts and rotates the scapula downward. It also helps to fix the scapula to the thoracic wall.
   • Clinical Significance: Weakness in the rhomboids can contribute to scapular winging, where the medial border of the scapula protrudes from the back.

Muscles of the Back (Intermediate and Deep Layers)

1. Latissimus Dorsi: The latissimus dorsi is a large, broad muscle that covers the lower back. It's one of the widest muscles in the body and plays a crucial role in shoulder movement.

   • Origin: Spinous processes of vertebrae T7-L5, thoracolumbar fascia, iliac crest, and lower ribs.
   • Insertion: Intertubercular groove of the humerus.
   • Action: Extends, adducts, and internally rotates the arm. It also assists in shoulder depression and can contribute to trunk extension.
   • Clinical Significance: Important for activities like swimming, rowing, and climbing. Strains and tears are common, especially in athletes.

2. Thoracolumbar Fascia: While not a muscle itself, the thoracolumbar fascia is a deep layer of connective tissue that covers the muscles of the lower back. It provides support and attachment points for several muscles, including the latissimus dorsi and the gluteus maximus.

3. Erector Spinae: The erector spinae is a group of muscles that run along the vertebral column from the sacrum to the skull. It's divided into three columns: iliocostalis, longissimus, and spinalis.

   • Iliocostalis: The most lateral column, further divided into lumborum, thoracis, and cervicis sections.

     • Origin: Iliac crest, sacrum, and ribs.
     • Insertion: Ribs and transverse processes of vertebrae.
     • Action: Extends and laterally flexes the vertebral column.

   • Longissimus: The intermediate column, also divided into thoracis, cervicis, and capitis sections.

     • Origin: Transverse processes of vertebrae.
     • Insertion: Transverse processes of vertebrae and ribs.
     • Action: Extends and laterally flexes the vertebral column.

   • Spinalis: The most medial column, divided into thoracis, cervicis, and capitis sections.

     • Origin: Spinous processes of vertebrae.
     • Insertion: Spinous processes of vertebrae.
     • Action: Extends the vertebral column.

   • Clinical Significance: Essential for maintaining posture and controlling spinal movements. Strains and spasms are common causes of back pain.

4. Serratus Posterior Superior: This thin muscle lies deep to the rhomboids and helps elevate the ribs.

   • Origin: Spinous processes of vertebrae C7-T3.
   • Insertion: Ribs 2-5.
   • Action: Elevates the ribs, assisting in inspiration.
   • Clinical Significance: Plays a minor role in respiration, but can be affected by postural imbalances.

5. Serratus Posterior Inferior: Located in the lower thoracic region, this muscle lies deep to the latissimus dorsi and helps depress the ribs.

   • Origin: Spinous processes of vertebrae T11-L2.
   • Insertion: Ribs 9-12.
   • Action: Depresses the ribs, assisting in expiration.
   • Clinical Significance: Plays a minor role in respiration and can be affected by postural imbalances.

Muscles of the Shoulder and Upper Arm

1. Deltoid: While the anterior and lateral portions of the deltoid are visible from the anterior view, the posterior portion is prominent from the back. This muscle covers the shoulder joint.

   • Origin: Spine of the scapula, acromion, and lateral third of the clavicle.
   • Insertion: Deltoid tuberosity of the humerus.
   • Action: The posterior fibers extend and externally rotate the arm. The anterior fibers flex and internally rotate the arm, and the lateral fibers abduct the arm.
   • Clinical Significance: Common site for injections. Can be affected by rotator cuff injuries.

2. Teres Major: This muscle runs from the scapula to the humerus and assists in shoulder movement.

   • Origin: Inferior angle of the scapula.
   • Insertion: Intertubercular groove of the humerus.
   • Action: Extends, adducts, and internally rotates the arm.
   • Clinical Significance: Often works in conjunction with the latissimus dorsi and can be strained with similar activities.

3. Teres Minor: One of the rotator cuff muscles, the teres minor is located superior to the teres major.

   • Origin: Lateral border of the scapula.
   • Insertion: Greater tubercle of the humerus.
   • Action: Externally rotates and adducts the arm. It also helps to stabilize the shoulder joint.
   • Clinical Significance: Part of the rotator cuff, and injuries to this muscle can contribute to shoulder pain and instability.

4. Infraspinatus: Another rotator cuff muscle, the infraspinatus occupies the infraspinous fossa of the scapula.

   • Origin: Infraspinous fossa of the scapula.
   • Insertion: Greater tubercle of the humerus.
   • Action: Externally rotates the arm and stabilizes the shoulder joint.
   • Clinical Significance: The most commonly injured rotator cuff muscle.

5. Triceps Brachii: The triceps brachii is the only muscle on the posterior aspect of the upper arm. It has three heads: long, lateral, and medial. The long head is the most visible from the posterior view.

   • Origin:
     • Long head: Infraglenoid tubercle of the scapula.
     • Lateral head: Posterior surface of the humerus, superior to the radial groove.
     • Medial head: Posterior surface of the humerus, inferior to the radial groove.
   • Insertion: Olecranon process of the ulna.
   • Action: Extends the forearm at the elbow. The long head also assists in shoulder extension and adduction.
   • Clinical Significance: Important for pushing and straightening movements. Can be strained with overuse or trauma.

Muscles of the Forearm (Posterior Compartment)

The posterior compartment of the forearm contains muscles primarily responsible for wrist and finger extension. While many of these muscles are deep and not easily visible from the surface, understanding their general location and function is crucial.

1. Brachioradialis: While primarily located in the lateral compartment, the brachioradialis can be partially seen from the posterior view as it wraps around the forearm.

   • Origin: Lateral supracondylar ridge of the humerus.
   • Insertion: Styloid process of the radius.
   • Action: Flexes the forearm at the elbow. It also assists in pronation and supination.
   • Clinical Significance: Important for stabilizing the elbow during rapid movements.

2. Extensor Carpi Radialis Longus: This muscle runs along the radial side of the posterior forearm and extends the wrist.

   • Origin: Lateral supracondylar ridge of the humerus.
   • Insertion: Base of the second metacarpal.
   • Action: Extends and abducts the wrist.
   • Clinical Significance: Can be affected by tennis elbow (lateral epicondylitis).

3. Extensor Carpi Radialis Brevis: Located next to the extensor carpi radialis longus, this muscle also extends the wrist.

   • Origin: Lateral epicondyle of the humerus.
   • Insertion: Base of the third metacarpal.
   • Action: Extends and abducts the wrist.
   • Clinical Significance: Also susceptible to tennis elbow (lateral epicondylitis).

4. Extensor Carpi Ulnaris: This muscle runs along the ulnar side of the posterior forearm and extends the wrist.

   • Origin: Lateral epicondyle of the humerus and posterior border of the ulna.
   • Insertion: Base of the fifth metacarpal.
   • Action: Extends and adducts the wrist.
   • Clinical Significance: Can be strained with repetitive wrist movements.

5. Extensor Digitorum: This muscle extends the fingers.

   • Origin: Lateral epicondyle of the humerus.
   • Insertion: Extensor hoods of the fingers (digits 2-5).
   • Action: Extends the fingers and the wrist.
   • Clinical Significance: Important for hand function and can be affected by conditions like arthritis.

6. Extensor Digiti Minimi: This muscle extends the little finger.

   • Origin: Lateral epicondyle of the humerus.
   • Insertion: Extensor hood of the little finger (digit 5).
   • Action: Extends the little finger and assists in wrist extension.
   • Clinical Significance: Works in conjunction with the extensor digitorum.

7. Anconeus: A small muscle located at the elbow that assists in forearm extension.

   • Origin: Lateral epicondyle of the humerus.
   • Insertion: Olecranon process of the ulna.
   • Action: Extends the forearm and stabilizes the elbow joint.
   • Clinical Significance: Helps the triceps brachii in extending the forearm.

Muscles of the Hip and Lower Limb

1. Gluteus Maximus: The gluteus maximus is the largest and most superficial of the gluteal muscles. It forms the bulk of the buttocks.

   • Origin: Iliac crest, sacrum, coccyx, and thoracolumbar fascia.
   • Insertion: Gluteal tuberosity of the femur and iliotibial tract (IT band).
   • Action: Extends and externally rotates the hip. It also abducts the hip and assists in maintaining an upright posture.
   • Clinical Significance: Important for activities like walking, running, and climbing stairs. Weakness can contribute to hip and back pain.

2. Gluteus Medius: Located deep to the gluteus maximus, the gluteus medius is an important hip abductor.

   • Origin: Outer surface of the ilium, between the iliac crest and the posterior gluteal line.
   • Insertion: Greater trochanter of the femur.
   • Action: Abducts the hip and stabilizes the pelvis during walking. It also internally rotates the hip.
   • Clinical Significance: Weakness can lead to Trendelenburg gait, where the pelvis drops on the side of the swing leg.

3. Gluteus Minimus: The deepest of the gluteal muscles, the gluteus minimus is located deep to the gluteus medius.

   • Origin: Outer surface of the ilium, between the anterior and inferior gluteal lines.
   • Insertion: Greater trochanter of the femur.
   • Action: Abducts and internally rotates the hip. It also stabilizes the pelvis during walking.
   • Clinical Significance: Works in conjunction with the gluteus medius.

4. Piriformis: One of the deep external rotators of the hip, the piriformis is located deep to the gluteus maximus.

   • Origin: Anterior surface of the sacrum.
   • Insertion: Greater trochanter of the femur.
   • Action: Externally rotates and abducts the hip. It also stabilizes the hip joint.
   • Clinical Significance: Can compress the sciatic nerve, leading to piriformis syndrome.

5. Hamstrings: The hamstrings are a group of three muscles located on the posterior thigh: biceps femoris, semitendinosus, and semimembranosus.

   • Biceps Femoris: Has two heads: long and short.

     • Origin:
       • Long head: Ischial tuberosity.
       • Short head: Linea aspera of the femur.
     • Insertion: Head of the fibula.
     • Action: Flexes the knee and extends the hip. It also externally rotates the hip and flexed knee.

   • Semitendinosus:

     • Origin: Ischial tuberosity.
     • Insertion: Medial surface of the tibia, near the tibial tuberosity.
     • Action: Flexes the knee and extends the hip. It also internally rotates the hip and flexed knee.

   • Semimembranosus:

     • Origin: Ischial tuberosity.
     • Insertion: Medial condyle of the tibia.
     • Action: Flexes the knee and extends the hip. It also internally rotates the hip and flexed knee.

   • Clinical Significance: Important for activities like running, jumping, and kicking. Hamstring strains are common, especially in athletes.

6. Gastrocnemius: The gastrocnemius is the most superficial muscle of the posterior calf. It has two heads: medial and lateral.

   • Origin:
     • Medial head: Medial condyle of the femur.
     • Lateral head: Lateral condyle of the femur.
   • Insertion: Calcaneus (heel bone) via the Achilles tendon.
   • Action: Plantar flexes the ankle and flexes the knee.
   • Clinical Significance: Important for walking, running, and jumping. Can be strained or torn.

7. Soleus: Located deep to the gastrocnemius, the soleus is a broad, flat muscle that plantar flexes the ankle.

   • Origin: Head and proximal shaft of the fibula and the medial border of the tibia.
   • Insertion: Calcaneus (heel bone) via the Achilles tendon.
   • Action: Plantar flexes the ankle.
   • Clinical Significance: Important for maintaining balance and posture.

8. Plantaris: A small muscle that runs along the posterior calf between the gastrocnemius and soleus. It has a long tendon.

   • Origin: Lateral condyle of the femur.
   • Insertion: Calcaneus (heel bone) via the Achilles tendon.
   • Action: Weakly assists in plantar flexion and knee flexion.
   • Clinical Significance: Often considered a vestigial muscle, and its tendon can be used for grafts in reconstructive surgery.

9. Achilles Tendon (Calcaneal Tendon): While not a muscle, the Achilles tendon is the strongest and thickest tendon in the body. It connects the gastrocnemius and soleus muscles to the calcaneus.

   • Clinical Significance: Prone to injury, especially in athletes. Rupture of the Achilles tendon can be debilitating.

10. Tibialis Posterior: Deepest of the posterior compartment of the leg.

    • Origin: Interosseous membrane, posterior surfaces of tibia and fibula.
    • Insertion: Navicular tuberosity and other tarsal bones.
    • Action: Plantar flexes and inverts the foot; supports the arch of the foot.

11. Flexor Digitorum Longus: Located medially in the posterior compartment of the leg.

    • Origin: Posterior surface of tibia.
    • Insertion: Plantar surfaces of distal phalanges of toes 2-5.
    • Action: Flexes toes 2-5 and plantar flexes the foot.

12. Flexor Hallucis Longus: Located laterally in the posterior compartment of the leg.

    • Origin: Posterior surface of fibula and interosseous membrane.
    • Insertion: Plantar surface of distal phalanx of great toe (hallux).
    • Action: Flexes the great toe and plantar flexes the foot.

Conclusion

Understanding the muscles of the posterior view is crucial for anyone studying anatomy, working in healthcare, or involved in fitness and sports. This guide provides a comprehensive overview of the major muscles visible from the back, including their origins, insertions, actions, and clinical significance. By mastering this knowledge, you'll be well-equipped to analyze movement, understand injuries, and optimize training programs. Remember to study diagrams, use anatomical models, and practice palpation to solidify your understanding of these essential structures.