Comprehensive Atlas of Muscular Origins, Insertions, Actions, and Innervations

Superficial and Deep Muscles of the Neck and Thorax

The Platysma is a superficial muscle originating from the Pectoral fascia. It inserts into the inferior border of the mandible and the adjacent muscles, specifically the Anguli Oris and Depressor Inferious. Its primary actions are to tense the skin of the neck and depress the mandible. It is innervated by the Cervical branch of the facial nerve.

The Subclavius originates from the Superior surface of the chondral end of the 1st rib and inserts into the inferior surface of the middle 1/3 of the clavicle. Its primary function is to stabilize the clavicle. It receives its innervation from the nerve to subclavius, encompassing nerve roots $C5$ and $C6$.

The Pectoralis major consists of two distinct heads. The Clavicular head originates from the anterior aspect of the medial clavical, while the Sternal head is the largest portion and originates from the manubrium, Sternum, true ribs, and costal cartilages. Both heads insert into the crest of the greater tuberosity of the humerus. Collectively, they produce shoulder adduction, Flexion, and internal rotation. The clavicular head specifically facilitates horizontal adduction, while the sternal head assists with shoulder extension. The muscle is innervated by the medial and lateral Pectoral nerves, covering roots $C5-T1$.

The Pectoralis minor originates from the anterior aspect of ribs 3-5 and inserts into the coracoid process of the scapula. Its actions include protraction and downward rotation of the Shoulder girdle at the AC and SC joints. It also serves as an accessory muscle of inspiration. It is innervated by the medial pectoral nerve ($C5-T1$).

The Serratus anterior originates from the external surfaces of ribs 1-9 and inserts along the medial border of the scapula. It acts to protract and upwardly rotate the scapula. It is innervated by the long thoracic nerve, specifically roots $C5-C7$.

Muscles of the Posterior Trunk, Respiration, and neck

The Serratus Posterior Superior originates from the nuchal ligament and the spinous processes of $C7-T3$. It inserts onto the external surfaces of ribs 2-5. Although noted to have no elevation action in some contexts, it is associated with rib positioning. It is innervated by the ventral rami of $T2-T5$.

The Serratus Posterior inferior originates from the spinous processes of $T11-L2$ and inserts onto the external surfaces of ribs 9-12. Its action is rib depression. The innervation is identified as the ventral rami $59-512$.

Intercostal muscles originate from the inferior borders of ribs 1-11 and insert into the superior border of the ribs immediately below the origin. Their actions include rib elevation and providing structural support for the thoracic cage. They are innervated by the intercostal nerves, which are the ventral ramus of the thoracic nerves. The neurovascular bundle (Intercostal Vein, Artery, and Nerve) is located within the Costal groove, positioned between the internal intercostal and innermost intercostal layers.

The Sternocleidomastoid has a Sternal head originating from the anterior surface of the manubrium and a Clavicular head originating from the medial 1/3 of the clavicle. It inserts into the mastoid process of the temporal bone and the superior nuchal line of the occipital bone. Unilaterally, it produces ipsilateral neck flexion and contralateral neck rotation; bilaterally, it results in neck flexion. It is innervated by the accessory nerve ($CN XI$) and the ventral rami of $C2-C4$.

Prevertebral and Scalene Muscles

The longus colli originates from the anterior tubercle of the transverse processes of $C3-C5$, the anterior vertebral bodies of $C5-T3$, and the anterior aspects of $T1-T3$. It inserts into the anterior arch of $C1$, the anterior vertebral bodies of $C2-4$, and the anterior tubercle of the transverse processes of $C5-6$. Bilaterally, it produces cervical flexion; unilaterally, it produces rotation. Innervation is provided by the ventral rami of $C2-C6$.

The longus capitis originates from the anterior tubercle of the transverse processes of $C3-C6$ and inserts into the Occipital bone. Its primary action is head flexion, and it is innervated by the ventral rami of $C1-3$.

The rectus capitis anterior originates from the lateral mass and transverse process of $C1$ (atlas) and inserts into the occipital bone. It facilitates head flexion and is innervated by the ventral rami of $C1-2$.

The anterior scalene originates from the anterior tubercle of the transverse processes of $C3-C6$ and inserts into the scalene tubercle of the 1st rib. Bilaterally, it produces cervical flexion. Unilaterally, it produces ipsilateral lateral flexion, contralateral rotation, and elevation of the 1st rib. It is innervated by the ventral rami of $C4-C6$.

The middle scalene originates from the transverse processes of $C2-C7$ and inserts into the superior surface of the 1st rib. It performs lateral flexion of the neck and elevation of the 1st rib. It is innervated by the ventral rami of $C3-C8$.

The posterior scalene originates from the posterior tubercle of the transverse process of $C4-6$ and inserts into the external surface of the 2nd rib. Its action is lateral flexion of the neck and elevation of the 2nd rib. It is innervated by the ventral rami of $C4-6$.

Abdominal Wall and Pelvic Floor Anatomy

The external abdominal oblique originates from the external surfaces and inferior borders of ribs 5-12. Its insertion points include the ASIS, the anterior half of the iliac crest, the Pubic crest, the Pubic tubercle, and the linea alba. Bilaterally, it produces trunk flexion, compression, and support of abdominal structures; unilaterally, it produces ipsilateral lateral flexion of the trunk and contralateral trunk rotation. It is innervated by the ventral rami of $T7-T12$.

The internal abdominal oblique originates from the thoracolumbar fascia, the iliac crest, and the inguinal ligament. It inserts into the inferior margin of ribs 10-12 and adjacent costal cartilages, the linea alba, and the pecten pubis. Bilaterally, it results in trunk flexion, compression, and support; unilaterally, it produces ipsilateral lateral flexion and ipsilateral trunk rotation. Innervation is via the ventral rami of $T7-T12$, the iliohypogastric nerve, and the ilioinguinal nerve.

Transversus abdominis originates from the costal cartilages of ribs 7-12, the thoracolumbar fascia, the iliac crest, and the inguinal ligament. It inserts onto the linea alba, the Pubic crest, and the Pecten Pubis. Its action is the compression and support of abdominal structures. It is innervated by the ventral rami of $T7-T12$, the iliohypogastric nerve, and the ilioinguinal nerve.

The rectus abdominis originates from the Pubic crest and symphysis and inserts onto the Xiphoid Process and the costal cartilages of ribs 5-7. It facilitates trunk flexion, compression, and support of abdominal structures. Innervation is from the ventral rami of $T6-T12$.

The Pyramidalis originates from the body of the Pubis and the anterior pubic ligament, inserting into the linea alba. Its action is to tense the linea alba. Innervation comes from the ventral rami of $T12$, the iliohypogastric nerve, and the ilioinguinal nerve.

In the pelvic floor, the Puborectalis originates from the posterior aspect of the body of the Pubis and its fibers surround the posterior aspect of the anorectal junction to provide structural support and facilitate fecal continence. The Pubococcygeus originates from the posterior aspect of the Pubis body and the tendinous arch of the levator ani, inserting into the coccyx, Perineal body, and lateral wall of the vagina or Prostate to support pelvic structures and urinary/fecal continence. The iliococcygeus originates from the ischial and tendinous arch of the levator ani and inserts into the Coccyx, iliococcygeal raphe, and anococcygeal ligament. These are innervated by the nerve to levatator ani ($S3-4$) and the Pudendal nerve. The Coccygeus (ischiococcygeus) originates from the ischial spine and inserts into the anterolateral aspect of the sacrum and coccyx, providing structural support; it is innervated by the ventral rami of $S4-5$.

Gluteal and Deep Hip Muscles

The gluteus maximus originates posterior to the posterior gluteal line of the ilium, the posterior aspect of the sacrum and coccyx, and the sacrotuberous ligament. It inserts onto the iliotibial band and the gluteal tuberosity of the femur. Its actions are hip extension, external rotation, and abduction. It is innervated by the inferior gluteal nerve ($L5, S1, S2$).

The gluteus medius originates from the ilium between the anterior and posterior gluteal lines and inserts into the lateral aspect of the greater trochanter. It performs hip abduction, with anterior fibers performing internal rotation and posterior fibers performing external rotation. It is innervated by the superior gluteal nerve ($L4, L5, S1$).

The gluteus minimus originates from the ilium between the anterior and inferior gluteal lines and inserts into the anterior aspect of the greater trochanter. Its actions are hip abduction and internal rotation, innervated by the superior gluteal nerve ($L4, L5, S1$).

The tensor fasciae latae originates from the ASIS and outer lip of the iliac crest, inserting into Gerdy's tubercle via the iliotibial band. It performs hip abduction, flexion, and internal rotation. It is also innervated by the superior gluteal nerve ($L4, L5, S1$).

Deep lateral rotators of the hip include the Piriformis, which originates from the pelvic surface of the sacrum and the sacrotuberous ligament and inserts into the superior border of the greater trochanter. It performs external rotation and transverse abduction of the hip and is innervated by the nerve to Piriformis ($L5-S2$ or $S1-S2$). The Obturator internus originates from the internal surface of the obturator membrane and adjacent bones, inserting into the medial aspect of the greater trochanter ($innervated by nerve to obturator internus, L5-S2$). The Obturator externus originates on the external surface of the obturator membrane and inserts into the trochanteric fossa of the femur; it is innervated by the obturator nerve ($L2-L4$ ventral rami). The Superior gemellus ($L5-S2$) and Inferior gemellus ($L5-S2$) likewise assist in hip external rotation and transverse abduction. The Quadratus femoris originates from the lateral margin of the ischial tuberosity, inserts onto the quadrate tubercle of the femur, and performs external rotation ($innervated by nerve to quadratus femoris, L5-S2$).

Deep Back and Suboccipital Muscles

The Trapezius is divided into three parts: the upper originates from the external occipital protuberance and superior nuchal line, nuchal ligament, and spinous process of $C7$. The middle originates from the spinous processes of $C7-T4$, and the lower from $T5-T12$. They insert into the lateral 1/3 of the clavicle, acromion, and the spine of the scapula. Actions include scapular elevation, upward rotation, retraction (adduction), and depression. Innervation is from the accessory nerve ($CN XI$) and ventral rami of $C3-C4$.

The Latissimus dorsi originates from the spinous processes of $T7-T12, L1-L5$ (via thoracolumbar fascia), ribs 9-12, and the iliac crest. It inserts into the floor of the intertubercular groove of the humerus and performs shoulder adduction, internal rotation, and extension. It is innervated by the thoracodorsal nerve ($C6-C8$).

The Levator Scapulae originates from the transverse processes of $C1-4$ and inserts into the superior angle and medial border of the scapula. It acts in elevation and downward rotation of the scapula, innervated by the dorsal scapular nerve ($C5$) and ventral rami of $C3-4$.

Rhomboid major and minor originate from the spinous processes of $T2-5$ and the nuchal ligament/$C7-T1$, respectively. They insert onto the medial border of the scapula and act in retraction of the scapula ($innervated by dorsal scapular nerve, C5$).

Suboccipital muscles include the rectus capitis posterior major (ipsilateral rotation, head extension; innervated by suboccipital nerve $C1$), rectus capitis posterior minor (head extension; $C1$), obliquus capitis superior (unilateral lateral flexion, bilateral extension; $C1$), and obliquus capitis inferior (unilateral lateral flexion, bilateral extension; $C1$). The Splenius capitis and cervicis facilitate bilateral extension and unilateral flexion/rotation ($innervated by dorsal rami$). The Erector spinae group—consisting of Iliocostalis, Longissimus, and Spinalis—governs extension and lateral flexion. The Transversospinalis group—consisting of Semispinalis, Multifidus, and Rotatores—governs extension and contralateral rotation. These are all innervated by the dorsal primary rami.

Muscles of the Thigh and Leg

The Hamstring muscles consist of the Semimembranosus, Semitendinosus, and Biceps femoris. The Semimembranosus originating from the ischial tuberosity and inserting at the medial tibial condyle produces nee ink. rot., Flex., and hip extension. The Semitendinosus also originating from the ischial tuberosity and inserting at the medial aspect of the proximate condyle produces Knu flex, int rot, and hip extension. The Biceps femoris has a long head ($ischial tuberosity$) and a short head ($linea aspera, lateral supracondylar line$), inserting into the fibular head to produce nee flexion, ext rot, and hip extension (long head only). All are innervated by the sciatic nerve ($L4-S3$).

The Adductor magnus has an adductor part (origin: inferior pubic ramus, ischial ramus; innervated by obturator nerve $L2, L3, L4$) and a hamstring part (origin: ischial tuberosity; innervated by sciatic nerve $L4-S3$). It facilitates hip adduction, flexion (adductor part), and extension (hamstring part).

The Popliteus originates from the lateral femoral condyle and joint capsule and inserts on the posterior surface of the tibia. It acts to internally rotate the knee to unlock it at the beginning of knee flexion ($innervated by tibial nerve$).

Posterior leg muscles include the Flexor digitorum longus (origin: posterior tibia; insertion: distal phalanges 2-5; action: DIP, IP, MTP, and ankle plantarflexion), the Flexor hallicus longus (origin: posterior fibula/interosseous membrane; insertion: distal phalanx of the great toe; action: great toe IP, MCP Flex, Onicic Plantarflex), and the Posterior tibialis (origin: posterior tibia/fibula/interosseous membrane; insertion: navicular tuberosity, cuneiforms, metatarsals 2-4; action: ankle inversion and plantarflexion). The Gastrocnemius originates from the lateral and medial femoral condyles and inserts into the calcaneus via the achilles tendon to produce ankle plantarflexion and knee flexion. The Soleus originates from the fibular head, posterior fibula, soleal line, and medial border of the tibia, inserting into the calcaneus for plantarflexion and standing support. All are innervated by the tibial nerve ($L4-S3$).