Comprehensive Study Guide: Major Muscles of the Human Body (BIO 141)

Muscles of the Head and Neck

Overview

The muscles of the head and neck are responsible for facial expressions, mastication (chewing), and movements of the head and neck. Many of these muscles have specific origins and insertions on the skull and cervical vertebrae.

• Occipitofrontalis (Frontalis and Occipitalis): Raises eyebrows and wrinkles forehead; connected by the epicranial aponeurosis.

• Temporoparietalis: Tenses scalp and moves auricle of ear.

• Temporalis: Elevates and retracts mandible; important in chewing.

• Zygomaticus major: Elevates corner of mouth (smiling).

• Orbicularis oculi: Closes eyelids (blinking, squinting).

• Orbicularis oris: Closes and protrudes lips (kissing muscle).

• Masseter: Elevates mandible; primary muscle of mastication.

• Platysma: Tenses skin of neck and depresses mandible.

• Sternocleidomastoid: Flexes neck; rotates head to opposite side.

• Buccinator: Compresses cheek (whistling, blowing).

• Nasalis: Compresses bridge and depresses tip of nose; elevates corners of nostrils.

• Medial and Lateral Pterygoid: Move mandible side to side; assist in chewing.

• Digastric: Depresses mandible; elevates hyoid during swallowing.

• Omohyoid: Depresses hyoid bone and larynx.

Oblique and Rectus Muscles

Overview

These muscles form the walls of the thorax and abdomen, aiding in respiration, trunk movement, and protection of internal organs.

• Rectus abdominis: Flexes vertebral column; compresses abdomen.

• External oblique: Compresses abdomen; laterally flexes and rotates vertebral column.

• Internal oblique: Same as external oblique but deeper.

• Transversus abdominis: Compresses abdominal contents.

• Diaphragm: Primary muscle of respiration; flattens to enlarge thoracic cavity.

• Scalenes: Elevate first two ribs; assist in neck flexion.

• External and Internal intercostals: Elevate (external) or depress (internal) ribs during breathing.

• Transversus thoracis: Depresses ribs.

• Serratus posterior (superior and inferior): Elevate (superior) or depress (inferior) ribs.

Muscles of the Vertebral Column

Overview

These muscles stabilize, extend, and rotate the vertebral column, maintaining posture and allowing trunk movement.

• Splenius: Extends, rotates, and laterally flexes the head and neck.

• Erector spinae: Group of muscles (iliocostalis, longissimus, spinalis) that extend and laterally flex the vertebral column.

Muscles That Position the Pectoral Girdle

Overview

These muscles stabilize and move the scapula and clavicle, allowing for shoulder movement.

• Trapezius: Elevates, retracts, and rotates scapula; extends neck.

• Pectoralis minor: Depresses and protracts scapula.

• Rhomboid major and minor: Retract and rotate scapula downward.

• Serratus anterior: Protracts scapula; holds it against thoracic wall.

Muscles That Move the Arm

Overview

These muscles originate on the axial skeleton or pectoral girdle and insert on the humerus, producing movements at the shoulder joint.

• Deltoid: Abducts, flexes, and extends arm.

• Latissimus dorsi: Extends, adducts, and medially rotates arm.

• Pectoralis major: Flexes, adducts, and medially rotates arm.

• Supraspinatus: Abducts arm (part of rotator cuff).

• Infraspinatus: Laterally rotates arm (rotator cuff).

• Subscapularis: Medially rotates arm (rotator cuff).

• Teres major: Extends, adducts, and medially rotates arm.

• Teres minor: Laterally rotates arm (rotator cuff).

Muscles That Move the Forearm and Hand

Overview

These muscles control movements at the elbow, wrist, and fingers. They are divided into flexors and extensors, with some acting as pronators or supinators.

• Biceps brachii: Flexes elbow; supinates forearm.

• Brachialis: Primary flexor of elbow.

• Brachioradialis: Flexes elbow, especially when forearm is mid-pronated.

• Triceps brachii: Extends elbow.

• Supinator: Supinates forearm.

• Flexor carpi radialis: Flexes and abducts wrist.

• Flexor carpi ulnaris: Flexes and adducts wrist.

• Palmaris longus: Flexes wrist.

• Extensor carpi radialis longus and brevis: Extend and abduct wrist.

• Extensor carpi ulnaris: Extends and adducts wrist.

Muscles That Move the Hand and Fingers

Overview

These muscles are responsible for fine motor movements of the hand and fingers, including flexion, extension, abduction, and adduction.

• Extensor digitorum: Extends fingers and hand at wrist.

• Extensor digiti minimi: Extends little finger.

• Flexor digitorum superficialis: Flexes middle phalanges of fingers.

• Flexor digitorum profundus: Flexes distal phalanges of fingers.

• Extensor retinaculum: Band of connective tissue holding extensor tendons in place.

• Flexor retinaculum: Band of connective tissue holding flexor tendons in place.

Muscles That Move the Thigh

Overview

These muscles originate on the pelvis or vertebral column and insert on the femur, producing movements at the hip joint.

• Gluteus maximus: Extends and laterally rotates thigh.

• Gluteus medius: Abducts and medially rotates thigh.

• Gluteus minimus: Abducts and medially rotates thigh.

• Gracilis: Adducts thigh; flexes and medially rotates leg.

• Tensor fasciae latae: Abducts and medially rotates thigh; tenses iliotibial tract.

• Iliotibial tract (IT Band): Band of collagen fibers; stabilizes lateral thigh.

• Adductor longus, brevis, magnus: Adduct, flex, and medially rotate thigh.

• Pectineus: Adducts and flexes thigh.

• Iliopsoas (Iliacus and Psoas major): Flexes thigh at hip joint.

Muscles That Move the Leg

Overview

These muscles act on the knee joint, producing flexion and extension of the leg.

• Biceps femoris: Flexes leg; extends thigh (part of hamstrings).

• Semitendinosus: Flexes leg; extends thigh (hamstrings).

• Semimembranosus: Flexes leg; extends thigh (hamstrings).

• Sartorius: Flexes, abducts, and laterally rotates thigh; flexes leg.

• Rectus femoris: Extends leg; flexes thigh (part of quadriceps).

• Vastus lateralis, medialis, intermedius: Extend leg at knee (quadriceps group).

Muscles That Move the Foot and Toes

Overview

These muscles control movements at the ankle and toes, including dorsiflexion, plantarflexion, inversion, and eversion.

• Gastrocnemius: Plantarflexes foot; flexes leg at knee.

• Soleus: Plantarflexes foot.

• Tibialis anterior: Dorsiflexes and inverts foot.

• Fibularis (Peroneus) longus: Everts and plantarflexes foot.

• Tibialis posterior: Plantarflexes and inverts foot.

• Calcaneal tendon (Achilles tendon): Connects gastrocnemius and soleus to calcaneus.

Muscles of the Pelvic Floor

Overview

These muscles support pelvic organs and control the openings of the urethra and anus.

• Bulbospongiosus: Compresses base of penis/clitoris; stiffens organ.

• External urethral sphincter: Closes urethra; controls urination.

• Levator ani: Supports pelvic viscera; raises pelvic floor.

• External anal sphincter: Closes anal opening.

Summary Table: Major Muscle Groups and Functions

Muscle Group	Main Muscles	Primary Actions
Head & Neck	Occipitofrontalis, Masseter, Sternocleidomastoid, etc.	Facial expression, mastication, head movement
Abdomen & Thorax	Rectus abdominis, Obliques, Diaphragm	Trunk flexion, rotation, respiration
Pectoral Girdle	Trapezius, Rhomboids, Serratus anterior	Scapular movement and stabilization
Arm	Deltoid, Pectoralis major, Latissimus dorsi	Shoulder movement
Forearm & Hand	Biceps brachii, Triceps brachii, Flexors/Extensors	Elbow, wrist, and finger movement
Thigh	Gluteals, Adductors, Iliopsoas	Hip movement
Leg	Quadriceps, Hamstrings, Sartorius	Knee movement
Foot & Toes	Gastrocnemius, Soleus, Tibialis anterior	Ankle and toe movement
Pelvic Floor	Levator ani, Sphincters	Support pelvic organs, control openings

Key Terms and Definitions

• Origin: The fixed attachment point of a muscle.

• Insertion: The movable attachment point of a muscle.

• Action: The movement produced when a muscle contracts.

• Flexion: Decreasing the angle between two bones.

• Extension: Increasing the angle between two bones.

• Abduction: Movement away from the midline.

• Adduction: Movement toward the midline.

• Rotation: Movement around an axis.

Additional info:

• For each muscle, students should be able to identify its origin (where it starts), insertion (where it attaches), and action (what movement it produces).

• Some structures listed (e.g., iliotibial tract, retinacula, calcaneal tendon) are not muscles but are important connective tissues associated with muscle function.

• Muscles are often grouped by their location and primary function (e.g., muscles that move the arm vs. those that move the leg).

• Understanding muscle actions is essential for clinical applications, such as diagnosing injuries or planning rehabilitation.