Comprehensive Study Guide for Human Locomotor Anatomy

 # Anatomical Study of the Lower Limb: Myology, Vasculature, and Innervation

The muscular architecture of the lower limb is characterized by specific insertion points and functional groupings. The rectus femoris muscle (recto anterior del cuádriceps) originates at the anterior inferior iliac spine ($Espina \, iliaca \, anteroinferior$). In the proximal region of the femur, the iliopsoas muscle accesses the thigh by passing laterally to the iliopectineal ligament or arch ($ligamento \, iliopectineo$). Within the femur, the linea aspera serves as a significant site for muscle attachments; however, the long head of the biceps femoris specifically does not insert on this line. For rotation and adduction of the thigh, muscles such as the quadratus femoris ($cuadrado \, crural$) act as external rotators and adductors. The pectineus muscle is notably absent from insertions on the ischiopubic rami, while the adductor brevis, obturator externus, and obturator internus do attach there.

The "Goose Foot" or pes anserinus ($pata \, de \, ganso$) is a crucial clinical landmark formed by the tendons of the sartorius, gracilis (rectus internus), and semitendinosus muscles. On the posterior aspect of the knee, the popliteal muscle ($popliteo$) is identified as the most proximal muscle in the deep plane of the posterior leg. Distally, the tibialis anterior inserts into the medial aspect of the first cuneiform and the base of the $1^{st}$ metatarsal, whereas the tibialis posterior attaches to the navicular tuberosity, the three cuneiforms, the cuboid, and the bases of the $2^{nd}$, $3^{rd}$, and $4^{th}$ metatarsals. The flexor hallicus longus (flexor largo del dedo gordo) inserts into the distal phalanx of the $1^{st}$ digit, and its tendon passes between the medial and lateral tubercles of the talus ($astrágalo$).

The vascular transition from the thigh to the leg occurs at the adductor hiatus ($hiato \, aductor$), where the femoral artery becomes the popliteal artery. Inside the popliteal fossa, the arrangement of elements from deep to superficial and medial to lateral is the popliteal artery, followed by the popliteal vein, and finally the tibial nerve. The internal saphenous vein (vena safena interna) originates at the fusion of the internal and external plantar veins. In its terminal portion, it relates to the inferior external pudendal artery and eventually penetrates the deep fascia by crossing the vastoadductor membrane ($membrana \, vastoaproximadora$). The external saphenous vein (vena safena externa) terminates in the deep veins of the popliteal fossa. Additionally, the superior articular arteries of the knee are branches of the popliteal artery, while the anterior and posterior peroneal recurrent arteries originate from the anterior tibial artery.

Innervation of the lower limb is primarily provided by the lumbar and sacral plexuses. The sciatic nerve ($nervio \, ciático$) provides motor innervation to the muscles of the posterior region of the thigh. The obturator nerve ($nervio \, obturador$) provides motor fibers to the adductor brevis and the adductor mayor (via its posterior branch). The superior gluteal nerve innervates the gluteus medius, gluteus minimus, and tensor fasciae latae, but notably not the gluteus maximus, which is supplied by the inferior gluteal nerve. The common peroneal nerve ($nervio \, peroneo \, común$) travels anteriorly by rounding the neck of the fibula; its deep branch (tibial anterior) descends between the tibialis anterior and the extensor hallicus longus in the lower leg. The superficial peroneal nerve descends applied to the lateral face of the fibula, covered by the peroneus longus.

Anatomical Study of the Upper Limb: Myology, Vasculature, and Innervation

In the shoulder region, the scapulohumeral joint is stabilized by ligaments such as the glenohumeral (superior, middle, inferior) and the coracohumeral. The coracohumeral ligament specifically inserts onto both tubercles of the superior humeral epiphysis ($troquín$ and $troquiter$). The greater tuberosity ($troquiter$) provides insertion for the supraspinatus, infraspinatus, and teres minor, while the lesser tuberosity ($troquín$) is the site for the subscapularis. The bicipital groove ($corredera \, bicipital$) hosts the tendons of the pectoralis major (lateral lip), latissimus dorsi (floor), and teres major (medial lip). The long head of the biceps originates at the supraglenoid tubercle and the superior part of the glenoid labrum. The axilla's lateral wall is formed by the coracobrachialis muscle, the short head of the biceps, and the humerus.

The forearm's anterior region is organized into planes. The superficial plane includes the pronator teres ($pronador \, redondo$), flexor radialis carpi ($palmar \, mayor$), palmaris longus ($palmar \, menor$), and flexor ulnaris carpi ($cubital \, anterior$). The flexor pollicis longus is part of the deep plane and inserts into the distal phalanx of the thumb. The median nerve reaches the forearm by passing between the two heads of the pronator teres and travels within the fascia of the flexor digitorum superficialis. The ulnar nerve passes behind the medial epicondyle and, at the wrist, passes medially to the pisiform bone. The radial nerve's terminal motor branch passes between the two heads of the supinator muscle to reach the posterior compartment.

Vascularization in the upper limb includes the formation of palmar arches. The superficial palmar arch is primarily formed by the anastomosis of the ulnar artery and the superficial palmar branch of the radial artery. The deep palmar arch results from the radial artery and the deep palmar branch of the ulnar artery. The "pulse canal" ($canal \, del \, pulso$) is a critical clinical site located between the tendons of the brachioradialis ($supinador \, largo$) and the flexor radialis carpi. The anatomical snuffbox ($tabaquera \, anatómica$) is delimited by the tendons of the abductor pollicis longus, extensor pollicis brevis, and extensor pollicis longus.

Space-specific boundaries include the quadrangular space ($cuadrilátero \, humerotricipital \, de \, Velpeau$), which is traversed by the axillary nerve ($nervio \, axilar$) and the posterior circumflex humeral artery. It is bounded by the humerus, the long head of the triceps, and the teres major and minor muscles. The triangular space ($triángulo \, omotricipital$) contains the circumflex scapular artery and is bounded by the scapula, teres major, and teres minor.

Axial Skeleton, Neck, and Abdominal Wall

The vertebral column exhibits a series of curvatures: cervical lordosis, thoracic kyphosis, lumbar lordosis, and sacral kyphosis. Intervertebral joints vary by type; zygapophyseal joints (cigoapófisis) in the cervical and thoracic regions are planar ($artrodias$), while in the lumbar region, they transition toward a cylindrical or trochoid (trocoide) shape. The atlanto-axial joint ($atlanto \, odontoidea$) is a classic trochoid joint. Significant ligaments include the posterior longitudinal ligament, which sits behind the tectorial membrane, and the nuchal ligament, which represents the cervical continuation of the supraspinous ligament. The yellow ligaments ($ligamentos \, amarillos$) are interlaminar structures extending from the axis to the sacrum.

The abdominal wall consists of the rectus abdominis, external oblique ($oblicuo \, mayor$), internal oblique ($oblicuo \, menor$), and transversus abdominis. The inferior portion of the rectus abdominis's posterior wall is covered by the transversalis fascia. The inguinal canal ($conducto \, inguinal$) is a passage in the lower abdominal wall; its anterior wall is formed by the aponeurosis of the external oblique, while its posterior wall is reinforced by the interfoveolar ligament (Hesselbach’s ligament). The "conjoint tendon" ($tendón \, conjunto$) is formed by the union of the internal oblique and transversus abdominis fibres.

In the neck, the hyoid bone is a central attachment point. The milohyoid muscle inserts into the medial portion of the hyoid body, while the thyrohyoid attaches to the greater horn ($asta \, mayor$). Scalene muscles show specific attachments: the scalenus anterior inserts onto the Lisfranc tubercle of the $1^st$ rib, and the scalenus medius and posterior attach to the costotransverse processes of $C_4$, $C_5$, and $C_6$. The phrenic nerve travels anteriorly to the scalenus anterior, whereas the subclavian artery passes between the scalenus anterior and medius.

Head Anatomy and Cranial Nerves

The trigeminal nerve ($V$) is the primary sensory nerve of the face. The second branch ($V_2$ or maxillary) includes the infraorbital and zygomatic nerves and supplies the maxillary molars via the posterior superior alveolar artery/nerve. The third branch ($V_3$ or mandibular) provides the auriculotemporal and inferior alveolar nerves and supplies the buccal mucosa (region geniana). The facial nerve ($VII$) exits the skull through the stylomastoid foramen and innervates the muscles of facial expression, the posterior belly of the digastric, and the stylohyoid muscle.

Vascular structures in the head include the facial artery, which terminates as the angular artery, and the superficial temporal and maxillary arteries, which are the terminal branches of the external carotid artery. The inferior thyroid vein typically terminates in the left brachiocephalic trunk. Lymphatic drainage of the head and neck converges into the internal jugular chain; on the right side, these form the right lymphatic duct ($gran \, vena \, linfática$), while on the left, they drain into the thoracic duct.

The retrostyloid space is a significant anatomical region containing the internal carotid artery, the internal jugular vein, and cranial nerves $IX$, $X$, $XI$ (accessory/spinal), and $XII$ (hypoglossal), as well as the superior cervical ganglion. The prestyloid space is divided into the parotid gland region (containing the facial nerve and external carotid) and the paratonsillar region.

Questions & Discussion

Q: Which muscle inserts into the anterior inferior iliac spine? A: The rectus femoris muscle ($recto \, anterior \, del \, cuádriceps$).

Q: What elements form the pes anserinus ($pata \, de \, ganso$)? A: The sartorius, gracilis (rectus internus), and semitendinosus.

Q: Where does the femoral artery become the popliteal artery? A: After crossing the adductor hiatus ($hiato \, aductor$).

Q: Which nerve innervates the gluteus maximus? A: The inferior gluteal nerve ($glúteo \, inferior$). Note that the superior gluteal nerve innervates the gluteus medius, gluteus minimus, and tensor fasciae latae.

Q: What is the relationship of the median nerve to the pronator teres? A: The median nerve enters the forearm by passing between the two heads of origin of the pronator teres.

Q: Which artery passes between the quadratus plantae and the flexor digitorum brevis? A: The external plantar artery ($arteria \, plantar \, externa$).

Q: What is the sensory innervation of the cheek (mucosa)? A: This is provided by the mandibular branch of the trigeminal nerve ($V_3$).

Q: Describe the insertions in the bicipital groove. A: From lateral to medial: Pectoralis major (lateral lip), Latissimus dorsi (floor), and Teres major (medial lip).

Q: To which joint type does the acromioclavicular joint belong? A: It is a planar synovial joint ($sinovial \, plana$ or $artrodia$).

Q: What structures pass through the quadrangular space? A: The axillary nerve and the posterior circumflex humeral artery.

Q: Is the internal saphenous vein accompanied by an artery throughout its path? A: No, the transcript clarifies it is not accompanied by the peroneal artery throughout its entire trajectory; it relates to the external pudendal at its termination and the saphenous nerve in the leg.

Q: What type of joint is the metacarpophalangeal joint of the thumb? A: It is specifically noted as a saddle joint or reciprocal engagement joint ($encaje \, recíproco$).