Human Anatomy: Muscles of the Thorax, Abdomen, Vertebral Column, and Arm

Flashcards covering the origin, insertion, innervation, and action of various human muscles as detailed in the lecture transcript.

External Intercostal Muscles

Superficial thoracic muscles originating from the inferior border of the rib and inserting into the superior border of the rib below; they raise ribs during inhalation and increase thoracic diameter with fibers passing downward and forward.

Internal Intercostal Muscles

Intermediate thoracic muscles originating from the inferior border of the rib and inserting into the superior border of the rib below; they lower ribs during exhalation with fibers passing downward and backward.

Innermost Intercostal Muscles

The deepest, incomplete layer of thoracic muscles that assists the external and internal intercostals and stabilizes the ribs; they connect adjacent ribs and are innervated by intercostal nerves.

Diaphragm

The most important muscle for respiration that originates from the xiphoid process, lower $6$ costal cartilages, and first $3$ lumbar vertebrae; it increases the vertical diameter of the thorax by pulling down the central tendon.

Levatores Costarum

Inspiratory muscles that raise the ribs; they originate from the tips of the transverse processes of $C7$ and $T1-11$ and insert into the rib below.

Serratus posterior superior

An inspiratory muscle originating from the lower cervical and upper thoracic spines and inserting into the upper ribs; it functions to raise the ribs.

Serratus posterior inferior

An expiratory muscle originating from the upper lumbar and lower thoracic spines and inserting into the lower ribs; it functions to lower the ribs.

External Oblique

Anterior abdominal muscle originating from the lower $8$ ribs; it compresses abdominal contents and assists in trunk flexion, rotation, forced expiration, mictruition, defecation, and vomiting.

Internal Oblique

Anterior abdominal muscle originating from the lumbar fascia, iliac crest, and lateral $\frac{2}{3}$ of the inguinal ligament; it performs compression of abdominal contents and trunk rotation.

Transversus Abdominis

Anterior abdominal muscle originating from the lower $6$ costal cartilages, lumbar fascia, iliac crest, and lateral $3rd$ of the inguinal ligament; its primary action is compressing abdominal contents.

Rectus Abdominis

Anterior abdominal muscle originating from the symphysis pubis and pubic crest; it flexes the vertebral column, compresses abdominal contents, and acts as an accessory muscle of expiration.

Pyramidalis

A small muscle originating from the anterior surface of the pubis and inserting into the linea alba; it tenses the linea alba if present and is innervated by the $12th$ thoracic nerve.

Erector spinae (Iliocostalis, Longissimus, Spinalis)

Muscles that extend and laterally bend the vertebral column and head; they share a common origin including the posterior sacrum, iliac crest, and spinous processes of lower lumbar vertebrae.

Semispinalis

A transverospinalis muscle originating from the transverse processes of $C4-T12$ and inserting into cervical and thoracic spinous processes; it extends the head, neck, and thorax and rotates them to the opposite side.

Multifidus

A transverospinalis muscle spanning $2-4$ segments that originates from the sacrum, ilium, and transverse processes ($T1-12$); its primary action is to stabilize the spine.

Rotatores

Transverospinalis muscles spanning $1-2$ segments; they stabilize, extend, and rotate the spine, originating from transverse processes and inserting into the lamina and transverse process above.

Interspinales

Deep vertebral muscles that connect adjacent spinous processes to extend the vertebral column; innervated by the posterior rami of spinal nerves.

Intertransversarii

Deep vertebral muscles located between adjacent transverse processes that produce lateral flexion of the vertebral column.

Splenius capitis

Muscle originating from the nuchal ligament and spinous processes of $C7-T3$; it extends the head and rotates the face to the same side.

Splenius cervicis

Muscle originating from the spinous processes of $T3-T6$ and inserting into the transverse processes of $C1-C3$; it extends the neck and rotates it toward the same side.

Pectoralis major

Pectoral muscle originating from the clavicle, sternum, and upper $6$ costal cartilages; it adducts and medially rotates the arm, with clavicular fibers flexing the arm.

Pectoralis minor

Pectoral muscle originating from ribs $3, 4, 5$ and inserting into the coracoid process of the scapula; it depresses the shoulder or elevates the ribs if the scapula is fixed.

Subclavius

Muscle originating from the $1st$ costal cartilage and inserting into the clavicle; it functions to depress the clavicle.

Serratus anterior

Muscle originating from the upper $8$ ribs and inserting into the medial border of the scapula; it draws the scapula forward and rotates it, innervated by the long thoracic nerve.

Trapezius

Large muscle originating from the occipital bone to $T12$; upper fibers elevate the scapulae, middle fibers pull them medially, and lower fibers pull the medial border downward.

Latissimus dorsi

Muscle originating from the iliac crest, lumbar fascia, and lower thoracic spines; it extends, adducts, and medially rotates the arm, innervated by the thoracodorsal nerve.

Levator scapulae

Muscle originating from the transverse processes of $C1-C4$; it functions to raise the medial border of the scapula.

Rhomboid minor and major

Muscles originating from the ligamentum nuchae and thoracic spines ($C7-T5$) that raise the medial border of the scapula upward and medially.

Deltoid

Muscle originating from the clavicle, acromion, and spine of the scapula; it abducts the arm, while anterior fibers flex and posterior fibers extend the arm.

Supraspinatus

Muscle of the rotator cuff originating from the supraspinous fossa; it abducts the arm and stabilizes the shoulder joint.

Infraspinatus

Muscle originating from the infraspinous fossa of the scapula; it laterally rotates the arm and stabilizes the shoulder joint.

Teres major

Muscle originating from the lower $3rd$ of the lateral border of the scapula; it medially rotates and adducts the arm.

Teres minor

Muscle originating from the upper $\frac{2}{3}$ of the lateral border of the scapula; it laterally rotates the arm and stabilizes the shoulder joint, innervated by the axillary nerve.

Subscapularis

Rotator cuff muscle originating from the subscapular fossa and inserting into the lesser tuberosity of the humerus; it medially rotates the arm.

Biceps brachii

Anterior arm muscle with two heads (supraglenoid tubercle and coracoid process); acts as a supinator of the forearm and flexor of the elbow and shoulder joints.

Coracobrachialis

Anterior arm muscle originating from the coracoid process; it flexes the arm and acts as a weak adductor.

Brachialis

Anterior arm muscle originating from the lower half of the humerus; it is the primary flexor of the elbow joint.

Triceps

Posterior compartment arm muscle with three heads (long, lateral, medial); it serves as the principal extensor of the elbow joint and is innervated by the radial nerve.