Muscles of the Head and Face

Orbicularis Oculi

The orbicularis oculi is a muscle responsible for closing the eyelids and facilitating blinking and squinting. It consists of orbital, palpebral, and lacrimal parts, each with distinct origins and insertions.

• Origin: Frontal bone, maxilla, medial palpebral ligament, lacrimal bone

• Insertion: Skin around orbit, lateral palpebral raphe, skin of eyelids

• Action: Closes eyelids, compresses lacrimal sac

• Nerve: Facial nerve (CN VII)

Orbicularis Oris

The orbicularis oris muscle encircles the mouth and is essential for movements such as puckering the lips, speaking, and eating.

• Origin: Maxilla, mandible, and skin around the mouth

• Insertion: Skin and mucous membrane of lips

• Action: Closes and protrudes lips

• Nerve: Facial nerve (CN VII)

Muscles of the Neck

Platysma

The platysma is a superficial muscle of the neck that assists in depressing the mandible and tensing the skin of the neck.

• Origin: Subcutaneous fascia of upper chest and shoulder

• Insertion: Lower border of mandible, skin and muscle at corner of mouth

• Action: Depresses and draws lower lip laterally, tenses skin of neck

• Nerve: Cervical branch of facial nerve

Sternocleidomastoideus

The sternocleidomastoid muscle is a prominent neck muscle involved in head rotation and flexion.

• Origin: Sternum and clavicle

• Insertion: Mastoid process of temporal bone, superior nuchal line of occipital bone

• Action: Rotates head, flexes neck

• Nerve: Accessory nerve (CN XI), cervical nerves

Muscles of the Chest and Shoulder

Pectoralis Major

The pectoralis major is a large chest muscle responsible for adducting and medially rotating the arm.

• Origin: Medial half of clavicle, sternum, costal cartilages

• Insertion: Lateral lip of intertubercular sulcus of humerus

• Action: Adducts and medially rotates arm

• Nerve: Medial and lateral pectoral nerves (C5–T1)

Serratus Anterior

The serratus anterior muscle stabilizes the scapula and assists in upward rotation.

• Origin: Outer surfaces and superior borders of upper eight or nine ribs

• Insertion: Anterior surface of medial border of scapula

• Action: Protracts and rotates scapula

• Nerve: Long thoracic nerve (C5–C7)

Muscles of the Abdomen

Obliquus Externus Abdominis

The external oblique muscle compresses the abdominal contents and aids in trunk rotation.

• Origin: Lower eight ribs

• Insertion: Iliac crest, abdominal aponeurosis

• Action: Compresses abdomen, rotates trunk

• Nerve: Lower six thoracic nerves

Rectus Abdominis

The rectus abdominis is a paired muscle running vertically on each side of the anterior wall of the human abdomen, important for flexing the lumbar spine.

• Origin: Crest of pubis, pubic symphysis

• Insertion: Costal cartilages of ribs 5–7, xiphoid process

• Action: Flexes vertebral column, compresses abdomen

• Nerve: Lower six thoracic nerves

Muscles of the Back

Trapezius

The trapezius muscle is a large, triangular muscle extending over the back of the neck and shoulders, responsible for moving, rotating, and stabilizing the scapula.

• Origin: Occipital bone, ligamentum nuchae, spinous processes of C7–T12

• Insertion: Lateral third of clavicle, acromion, spine of scapula

• Action: Elevates, retracts, and rotates scapula

• Nerve: Accessory nerve (CN XI), cervical nerves

Latissimus Dorsi

The latissimus dorsi is a broad, flat muscle of the back that extends, adducts, and medially rotates the arm.

• Origin: Spinous processes of T7–L5, iliac crest, lower ribs

• Insertion: Intertubercular sulcus of humerus

• Action: Extends, adducts, and medially rotates arm

• Nerve: Thoracodorsal nerve (C6–C8)

Muscles of the Shoulder and Arm

Deltoideus (Deltoid)

The deltoid muscle forms the rounded contour of the shoulder and is responsible for abduction, flexion, and extension of the arm.

• Origin: Clavicle, acromion, spine of scapula

• Insertion: Deltoid tuberosity of humerus

• Action: Abducts, flexes, and extends arm

• Nerve: Axillary nerve (C5, C6)

Biceps Brachii

The biceps brachii is a two-headed muscle of the upper arm, important for flexion and supination of the forearm.

• Origin: Scapula (long head: supraglenoid tubercle; short head: coracoid process)

• Insertion: Radial tuberosity, bicipital aponeurosis

• Action: Flexes and supinates forearm

• Nerve: Musculocutaneous nerve (C5, C6)

Triceps Brachii

The triceps brachii is a three-headed muscle of the upper arm, responsible for extension of the forearm at the elbow.

• Origin: Scapula (long head), humerus (lateral and medial heads)

• Insertion: Olecranon process of ulna

• Action: Extends forearm

• Nerve: Radial nerve (C7, C8)

Flexor Digitorum Superficialis

The flexor digitorum superficialis is a muscle of the forearm that flexes the fingers.

• Origin: Medial epicondyle of humerus, coronoid process of ulna, shaft of radius

• Insertion: Middle phalanges of fingers 2–5

• Action: Flexes middle phalanges of fingers

• Nerve: Median nerve (C7, C8, T1)

Muscles of the Hip and Thigh

Gluteus Maximus

The gluteus maximus is the largest muscle of the buttocks, responsible for extension and lateral rotation of the hip.

• Origin: Ilium, sacrum, coccyx

• Insertion: Gluteal tuberosity of femur, iliotibial tract

• Action: Extends and laterally rotates hip

• Nerve: Inferior gluteal nerve (L5, S1, S2)

Rectus Femoris

The rectus femoris is one of the four quadriceps muscles, important for knee extension and hip flexion.

• Origin: Anterior inferior iliac spine, ilium above acetabulum

• Insertion: Patella, tibial tuberosity via patellar ligament

• Action: Extends knee, flexes hip

• Nerve: Femoral nerve (L2–L4)

Vastus Medialis

The vastus medialis is another quadriceps muscle, crucial for knee extension.

• Origin: Intertrochanteric line, medial lip of linea aspera

• Insertion: Patella, tibial tuberosity via patellar ligament

• Action: Extends knee

• Nerve: Femoral nerve (L2–L4)

Vastus Intermedius

The vastus intermedius lies beneath the rectus femoris and also extends the knee.

• Origin: Anterior and lateral surfaces of femur

• Insertion: Patella, tibial tuberosity via patellar ligament

• Action: Extends knee

• Nerve: Femoral nerve (L2–L4)

Biceps Femoris

The biceps femoris is a posterior thigh muscle, part of the hamstrings, responsible for knee flexion and hip extension.

• Origin: Ischial tuberosity (long head), femur (short head)

• Insertion: Head of fibula, lateral condyle of tibia

• Action: Flexes knee, extends hip

• Nerve: Sciatic nerve (L5, S1, S2)

Semitendinosus

The semitendinosus is another hamstring muscle, aiding in knee flexion and hip extension.

• Origin: Ischial tuberosity

• Insertion: Medial surface of tibia

• Action: Flexes knee, extends hip

• Nerve: Sciatic nerve (L5, S1, S2)

Muscles of the Leg and Foot

Extensor Digitorum Longus

The extensor digitorum longus is a muscle of the anterior leg that extends the toes and dorsiflexes the foot.

• Origin: Lateral condyle of tibia, anterior surface of fibula

• Insertion: Middle and distal phalanges of toes 2–5

• Action: Extends toes, dorsiflexes foot

• Nerve: Deep peroneal nerve (L4, L5, S1)

Peroneus Longus

The peroneus longus (fibularis longus) is a lateral leg muscle that everts and plantarflexes the foot.

• Origin: Upper lateral shaft of fibula

• Insertion: Base of first metatarsal, medial cuneiform

• Action: Everts and plantarflexes foot

• Nerve: Superficial peroneal nerve (L4, L5, S1)