Gross Anatomy Of The Muscular System Exercise 13

The muscular system, a marvel of biological engineering, allows for movement, posture maintenance, and vital physiological functions. Gross anatomy, the study of anatomical structures visible to the naked eye, provides a foundation for understanding how muscles are organized and contribute to overall body function. This article delves into the gross anatomy of the muscular system, highlighting key muscles, their origins, insertions, actions, and innervation, particularly relevant to Exercise 13 in many anatomy curricula.

Introduction to the Muscular System

The muscular system is composed of over 600 skeletal muscles, each acting as an organ. These muscles work in coordination to produce a wide array of movements, from subtle facial expressions to powerful locomotive actions. Beyond movement, muscles contribute to maintaining posture, stabilizing joints, generating heat, and protecting internal organs.

Key Concepts in Muscle Anatomy:

• Origin: The attachment point of a muscle that remains relatively fixed during contraction.
• Insertion: The attachment point of a muscle that moves during contraction.
• Action: The specific movement a muscle produces.
• Innervation: The nerve that supplies a muscle, controlling its function.

Understanding these concepts is crucial for appreciating the complexity and efficiency of the muscular system.

Muscles of the Head and Neck

The head and neck contain a diverse array of muscles responsible for facial expression, mastication (chewing), and head movements.

Muscles of Facial Expression

These muscles are unique as they insert into the skin, allowing for subtle and nuanced expressions.

• Frontalis:
  • Origin: Galea aponeurotica (a fibrous sheet connecting the frontalis and occipitalis muscles)
  • Insertion: Skin of the eyebrows and nose
  • Action: Raises eyebrows, wrinkles forehead
  • Innervation: Facial nerve (CN VII)
• Orbicularis Oculi:
  • Origin: Medial orbital margin
  • Insertion: Skin around the eyelids
  • Action: Closes eyelids, squints
  • Innervation: Facial nerve (CN VII)
• Zygomaticus Major:
  • Origin: Zygomatic bone
  • Insertion: Corner of the mouth (modiolus)
  • Action: Elevates and abducts the corner of the mouth (smiling)
  • Innervation: Facial nerve (CN VII)
• Orbicularis Oris:
  • Origin: Mandible and maxilla
  • Insertion: Skin and muscle around the mouth
  • Action: Closes and protrudes lips (kissing, whistling)
  • Innervation: Facial nerve (CN VII)
• Buccinator:
  • Origin: Maxilla and mandible
  • Insertion: Orbicularis oris
  • Action: Compresses cheek, holds food between teeth during chewing
  • Innervation: Facial nerve (CN VII)

Muscles of Mastication

These powerful muscles facilitate chewing.

• Masseter:
  • Origin: Zygomatic arch
  • Insertion: Mandibular ramus
  • Action: Elevates mandible (closes jaw)
  • Innervation: Mandibular branch of trigeminal nerve (CN V3)
• Temporalis:
  • Origin: Temporal fossa
  • Insertion: Coronoid process of mandible
  • Action: Elevates and retracts mandible
  • Innervation: Mandibular branch of trigeminal nerve (CN V3)
• Medial Pterygoid:
  • Origin: Pterygoid plates of sphenoid bone
  • Insertion: Medial surface of mandibular ramus
  • Action: Elevates and protrudes mandible
  • Innervation: Mandibular branch of trigeminal nerve (CN V3)
• Lateral Pterygoid:
  • Origin: Lateral pterygoid plate of sphenoid bone
  • Insertion: Condyle of mandible
  • Action: Protrudes and depresses mandible, moves mandible side to side
  • Innervation: Mandibular branch of trigeminal nerve (CN V3)

Muscles of the Anterior Neck

These muscles are primarily involved in swallowing and speech.

• Sternocleidomastoid (SCM):
  • Origin: Sternum and clavicle
  • Insertion: Mastoid process of temporal bone
  • Action: Flexes neck (bilaterally), rotates head to opposite side (unilaterally)
  • Innervation: Accessory nerve (CN XI)
• Platysma:
  • Origin: Pectoral and deltoid fascia
  • Insertion: Mandible and skin of lower face
  • Action: Tenses skin of neck, depresses mandible
  • Innervation: Facial nerve (CN VII)

Muscles of the Posterior Neck

These muscles primarily extend, rotate, and laterally flex the neck.

• Trapezius (Superior Fibers):
  • Origin: Occipital bone, ligamentum nuchae
  • Insertion: Clavicle and acromion process of scapula
  • Action: Elevates scapula, extends neck
  • Innervation: Accessory nerve (CN XI)
• Splenius Capitis:
  • Origin: Spinous processes of C7-T3 vertebrae
  • Insertion: Occipital bone and mastoid process of temporal bone
  • Action: Extends, rotates, and laterally flexes head
  • Innervation: Cervical spinal nerves

Muscles of the Trunk

The muscles of the trunk are essential for maintaining posture, protecting internal organs, and facilitating respiration.

Muscles of the Thorax

These muscles are crucial for breathing.

• Diaphragm:
  • Origin: Xiphoid process, costal cartilages of ribs 7-12, lumbar vertebrae
  • Insertion: Central tendon
  • Action: Primary muscle of inspiration; flattens to increase thoracic volume
  • Innervation: Phrenic nerve (C3-C5)
• External Intercostals:
  • Origin: Inferior border of rib above
  • Insertion: Superior border of rib below
  • Action: Elevates ribs during inspiration
  • Innervation: Intercostal nerves
• Internal Intercostals:
  • Origin: Superior border of rib below
  • Insertion: Inferior border of rib above
  • Action: Depresses ribs during forced expiration
  • Innervation: Intercostal nerves

Muscles of the Abdomen

These muscles protect abdominal organs and facilitate trunk movements.

• Rectus Abdominis:
  • Origin: Pubic crest and symphysis
  • Insertion: Costal cartilages of ribs 5-7 and xiphoid process
  • Action: Flexes vertebral column, compresses abdomen
  • Innervation: Intercostal nerves
• External Oblique:
  • Origin: Ribs 5-12
  • Insertion: Iliac crest and linea alba
  • Action: Flexes and rotates vertebral column, compresses abdomen
  • Innervation: Intercostal nerves
• Internal Oblique:
  • Origin: Iliac crest, inguinal ligament, and thoracolumbar fascia
  • Insertion: Ribs 10-12 and linea alba
  • Action: Flexes and rotates vertebral column, compresses abdomen
  • Innervation: Intercostal nerves
• Transversus Abdominis:
  • Origin: Ribs 7-12, iliac crest, inguinal ligament, and thoracolumbar fascia
  • Insertion: Linea alba and pubic crest
  • Action: Compresses abdomen
  • Innervation: Intercostal nerves

Muscles of the Back

These muscles maintain posture and facilitate back movements.

• Erector Spinae Group (Iliocostalis, Longissimus, Spinalis):
  • Origin: Sacrum, iliac crest, and lumbar vertebrae
  • Insertion: Ribs, thoracic and cervical vertebrae, and occipital bone
  • Action: Extends vertebral column, maintains posture
  • Innervation: Spinal nerves
• Quadratus Lumborum:
  • Origin: Iliac crest and iliolumbar ligament
  • Insertion: Rib 12 and lumbar vertebrae
  • Action: Laterally flexes vertebral column, stabilizes rib 12
  • Innervation: Lumbar spinal nerves
• Latissimus Dorsi:
  • Origin: Thoracolumbar fascia, iliac crest, ribs 9-12
  • Insertion: Intertubercular groove of humerus
  • Action: Extends, adducts, and medially rotates arm
  • Innervation: Thoracodorsal nerve

Muscles of the Upper Limb

The muscles of the upper limb allow for a wide range of movements, from fine motor skills to powerful lifting actions.

Muscles of the Shoulder

These muscles stabilize the shoulder joint and facilitate arm movements.

• Deltoid:
  • Origin: Clavicle, acromion, and spine of scapula
  • Insertion: Deltoid tuberosity of humerus
  • Action: Abducts, flexes, and extends arm
  • Innervation: Axillary nerve
• Pectoralis Major:
  • Origin: Clavicle, sternum, and costal cartilages of ribs 1-6
  • Insertion: Intertubercular groove of humerus
  • Action: Adducts, flexes, and medially rotates arm
  • Innervation: Pectoral nerves
• Teres Major:
  • Origin: Inferior angle of scapula
  • Insertion: Intertubercular groove of humerus
  • Action: Extends, adducts, and medially rotates arm
  • Innervation: Lower subscapular nerve
• Rotator Cuff Muscles (Supraspinatus, Infraspinatus, Teres Minor, Subscapularis):
  • Supraspinatus: Abducts arm
  • Infraspinatus: Laterally rotates arm
  • Teres Minor: Laterally rotates and adducts arm
  • Subscapularis: Medially rotates arm
  • Innervation: Suprascapular nerve (Supraspinatus and Infraspinatus), Axillary nerve (Teres Minor), Upper and Lower Subscapular nerves (Subscapularis)

Muscles of the Arm

These muscles primarily flex and extend the elbow.

• Biceps Brachii:
  • Origin: Short head - Coracoid process of scapula; Long head - Supraglenoid tubercle of scapula
  • Insertion: Radial tuberosity
  • Action: Flexes elbow, supinates forearm
  • Innervation: Musculocutaneous nerve
• Brachialis:
  • Origin: Anterior humerus
  • Insertion: Ulnar tuberosity
  • Action: Flexes elbow
  • Innervation: Musculocutaneous nerve
• Triceps Brachii:
  • Origin: Long head - Infraglenoid tubercle of scapula; Lateral head - Posterior humerus above radial groove; Medial head - Posterior humerus below radial groove
  • Insertion: Olecranon process of ulna
  • Action: Extends elbow
  • Innervation: Radial nerve

Muscles of the Forearm

These muscles facilitate wrist and finger movements.

• Pronator Teres:
  • Origin: Medial epicondyle of humerus and coronoid process of ulna
  • Insertion: Lateral radius
  • Action: Pronates forearm, flexes elbow
  • Innervation: Median nerve
• Flexor Carpi Radialis:
  • Origin: Medial epicondyle of humerus
  • Insertion: Base of second and third metacarpals
  • Action: Flexes and abducts wrist
  • Innervation: Median nerve
• Palmaris Longus:
  • Origin: Medial epicondyle of humerus
  • Insertion: Palmar aponeurosis
  • Action: Flexes wrist, tenses palmar aponeurosis
  • Innervation: Median nerve
• Flexor Carpi Ulnaris:
  • Origin: Medial epicondyle of humerus and olecranon process of ulna
  • Insertion: Pisiform bone and hamate bone
  • Action: Flexes and adducts wrist
  • Innervation: Ulnar nerve
• Extensor Carpi Radialis Longus:
  • Origin: Lateral epicondyle of humerus
  • Insertion: Base of second metacarpal
  • Action: Extends and abducts wrist
  • Innervation: Radial nerve
• Extensor Carpi Radialis Brevis:
  • Origin: Lateral epicondyle of humerus
  • Insertion: Base of third metacarpal
  • Action: Extends and abducts wrist
  • Innervation: Radial nerve
• Extensor Carpi Ulnaris:
  • Origin: Lateral epicondyle of humerus and ulna
  • Insertion: Base of fifth metacarpal
  • Action: Extends and adducts wrist
  • Innervation: Radial nerve

Muscles of the Lower Limb

The muscles of the lower limb are responsible for locomotion, balance, and weight-bearing.

Muscles of the Hip

These muscles facilitate hip movements.

• Gluteus Maximus:
  • Origin: Iliac crest, sacrum, and coccyx
  • Insertion: Gluteal tuberosity of femur and iliotibial tract
  • Action: Extends and laterally rotates hip
  • Innervation: Inferior gluteal nerve
• Gluteus Medius:
  • Origin: Iliac crest
  • Insertion: Greater trochanter of femur
  • Action: Abducts and medially rotates hip
  • Innervation: Superior gluteal nerve
• Gluteus Minimus:
  • Origin: Ilium
  • Insertion: Greater trochanter of femur
  • Action: Abducts and medially rotates hip
  • Innervation: Superior gluteal nerve
• Iliopsoas (Iliacus and Psoas Major):
  • Origin: Iliac fossa (Iliacus), Lumbar vertebrae (Psoas Major)
  • Insertion: Lesser trochanter of femur
  • Action: Flexes hip
  • Innervation: Femoral nerve (Iliacus), Lumbar spinal nerves (Psoas Major)
• Hamstrings (Biceps Femoris, Semitendinosus, Semimembranosus):
  • Origin: Ischial tuberosity
  • Insertion: Tibia and fibula
  • Action: Extends hip and flexes knee
  • Innervation: Sciatic nerve

Muscles of the Thigh

These muscles primarily extend the knee and adduct the thigh.

• Quadriceps Femoris (Rectus Femoris, Vastus Lateralis, Vastus Medialis, Vastus Intermedius):
  • Origin: Anterior inferior iliac spine (Rectus Femoris), Femur (Vastus muscles)
  • Insertion: Tibial tuberosity via patellar tendon
  • Action: Extends knee, flexes hip (Rectus Femoris)
  • Innervation: Femoral nerve
• Sartorius:
  • Origin: Anterior superior iliac spine
  • Insertion: Medial tibia (pes anserinus)
  • Action: Flexes, abducts, and laterally rotates hip; flexes knee
  • Innervation: Femoral nerve
• Adductor Group (Adductor Longus, Adductor Brevis, Adductor Magnus, Gracilis, Pectineus):
  • Origin: Pubis and ischium
  • Insertion: Femur
  • Action: Adducts thigh
  • Innervation: Obturator nerve (Adductor Longus, Adductor Brevis, Gracilis), Obturator and Sciatic nerves (Adductor Magnus), Femoral nerve (Pectineus)

Muscles of the Leg

These muscles facilitate ankle and toe movements.

• Gastrocnemius:
  • Origin: Medial and lateral condyles of femur
  • Insertion: Calcaneus via Achilles tendon
  • Action: Plantar flexes ankle, flexes knee
  • Innervation: Tibial nerve
• Soleus:
  • Origin: Tibia and fibula
  • Insertion: Calcaneus via Achilles tendon
  • Action: Plantar flexes ankle
  • Innervation: Tibial nerve
• Tibialis Anterior:
  • Origin: Tibia
  • Insertion: Medial cuneiform and first metatarsal
  • Action: Dorsiflexes and inverts ankle
  • Innervation: Deep fibular nerve
• Fibularis Longus (Peroneus Longus):
  • Origin: Fibula
  • Insertion: First metatarsal and medial cuneiform
  • Action: Plantar flexes and everts ankle
  • Innervation: Superficial fibular nerve
• Fibularis Brevis (Peroneus Brevis):
  • Origin: Fibula
  • Insertion: Base of fifth metatarsal
  • Action: Plantar flexes and everts ankle
  • Innervation: Superficial fibular nerve

Clinical Significance

Understanding the gross anatomy of the muscular system is essential for diagnosing and treating various musculoskeletal conditions. Injuries, such as strains, sprains, and tears, can affect muscles and their associated tendons and ligaments. Nerve damage can lead to muscle weakness or paralysis, impacting movement and function. Furthermore, understanding muscle attachments and actions is crucial for rehabilitation and physical therapy interventions.

Conclusion

The gross anatomy of the muscular system provides a comprehensive understanding of the organization, function, and innervation of muscles throughout the body. This knowledge is fundamental for healthcare professionals, athletes, and anyone interested in the mechanics of human movement. By studying the origins, insertions, actions, and innervations of individual muscles, we gain a deeper appreciation for the intricate workings of this vital system. Mastering the content related to Exercise 13, and indeed the entire muscular system, is a rewarding endeavor that unlocks a wealth of knowledge about the human body's capabilities.