Muscles of the Head: Facial Expression

Overview

The muscles of facial expression are responsible for movements that convey emotions and assist in nonverbal communication. These muscles are generally attached to the skin, allowing for subtle changes in facial appearance.

• Frontalis: Draws scalp anteriorly, raises eyebrows, and wrinkles skin of forehead horizontally.

• Occipitalis: Draws scalp posteriorly.

• Epicranius (Occipitofrontalis): Formed by the frontalis and occipitalis, connected by an aponeurosis.

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

• Zygomaticus major: Draws angle of mouth superiorly and laterally (smiling).

• Buccinator: Presses cheeks against teeth and lips (whistling, blowing, sucking).

• Platysma: Draws lower lip inferiorly and posteriorly (pouting), depresses mandible.

• Orbicularis oculi: Closes eye.

• Corrugator supercilii: Draws eyebrow inferiorly, wrinkles forehead vertically (frowning).

Example:

Smiling involves the coordinated action of the zygomaticus major and orbicularis oris.

Muscles That Move the Mandible and Assist in Mastication

Overview

These muscles are essential for chewing and speaking, controlling movements of the jaw.

• Masseter: Elevates mandible (closes mouth).

• Temporalis: Elevates and retracts mandible.

Example:

The masseter is one of the strongest muscles relative to its size, crucial for biting.

Muscles of the Anterior Neck: Deglutition and Speech

Overview

These muscles assist in swallowing and speech by moving the hyoid bone and mandible.

• Digastric: Elevates hyoid bone and depresses mandible.

Muscles of the Neck: Head Movement

Overview

Neck muscles control the movement and posture of the head.

• Sternocleidomastoid: Flexes cervical vertebral column and head when acting together.

Muscles of the Neck and Back: Vertebral Column Movement (Erector Spinae)

Overview

The erector spinae group maintains posture and extends the vertebral column.

• Iliocostalis (lateral group): Extends and maintains erect posture of vertebral column.

• Longissimus (intermediate group): Extends head and vertebral column.

• Spinalis (medial group): Extends vertebral column.

Example:

Standing upright after bending forward uses the erector spinae muscles.

Muscles of the Thorax: Breathing

Overview

These muscles facilitate respiration by changing the volume of the thoracic cavity.

• Diaphragm: Contraction flattens diaphragm, increasing thoracic cavity size (inhalation); relaxation moves it superiorly (exhalation).

• External intercostals: Expand ribcage, increasing thoracic cavity size (inhalation).

• Internal intercostals: Draw ribs together, decreasing thoracic cavity size (exhalation).

Example:

Normal breathing involves rhythmic contraction and relaxation of the diaphragm and intercostal muscles.

Muscles of the Abdomen

Overview

Abdominal muscles support trunk movement, protect internal organs, and assist in respiration.

• Rectus abdominis: Flexes vertebral column, compresses abdomen.

• External oblique: Compresses abdomen.

• Internal oblique: Compresses abdomen.

• Transversus abdominis: Compresses abdomen.

Example:

Performing a sit-up primarily engages the rectus abdominis.

Muscles of the Thorax: Pectoral Girdle Movement

Overview

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

• Pectoralis minor: Fixator of scapula.

• Serratus anterior: Fixator of scapula.

• Trapezius: Fixator of scapula.

• Levator scapulae: Fixator of scapula.

• Rhomboid major: Fixator of scapula.

• Rhomboid minor: Fixator of scapula.

Muscles of the Thorax and Shoulder: Humerus Movement

Overview

These muscles control movements of the upper arm, including rotation, abduction, and adduction.

• Pectoralis major: Adducts and medially rotates arm.

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

• Deltoid: Abducts arm.

• Supraspinatus: Assists deltoid in abducting arm.

• Infraspinatus: Laterally rotates arm.

• Subscapularis: Medially rotates arm.

Example:

Throwing a ball involves coordinated action of the deltoid, pectoralis major, and latissimus dorsi.

Muscles of the Arm: Forearm Movement

Overview

These muscles allow for flexion, extension, pronation, and supination of the forearm.

• Biceps brachii: Flexes forearm.

• Brachialis: Flexes forearm.

• Brachioradialis: Flexes forearm.

• Triceps brachii: Extends forearm.

• Pronator teres: Pronates forearm.

• Supinator: Supinates forearm.

Example:

Turning a doorknob uses the supinator and pronator teres muscles.

Muscles of the Forearm: Hand Movement

Overview

These muscles control wrist and finger movements, allowing for gripping and manipulation.

• Palmaris longus: Flexes hand at wrist.

• Flexor carpi radialis: Flexes and abducts hand at wrist (radial deviation).

• Flexor carpi ulnaris: Flexes and adducts hand at wrist (ulnar deviation).

• Extensor digitorum: Extends hand at wrist.

• Extensor carpi radialis longus: Extends and abducts hand at wrist (radial deviation).

• Extensor carpi ulnaris: Extends and adducts hand at wrist (ulnar deviation).

Muscles of the Hip: Femur Movement

Overview

Hip muscles move the thigh, enabling walking, running, and jumping.

• Psoas major (Iliopsoas): Flexes thigh.

• Iliacus (Iliopsoas): Flexes thigh.

• Gluteus maximus: Extends thigh.

• Gluteus medius: Abducts thigh.

• Tensor fascia latae: Abducts thigh.

• Adductor longus: Adducts thigh.

• Adductor magnus: Adducts thigh.

• Gracilis: Adducts thigh.

Example:

Climbing stairs uses the gluteus maximus and iliopsoas muscles.

Muscles of the Thigh: Leg Movement

Overview

Thigh muscles extend and flex the leg at the knee joint, crucial for locomotion.

• Quadriceps femoris (Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius): Extend leg.

• Sartorius: Flexes leg.

• Biceps femoris: Flexes leg.

• Semitendinosus: Flexes leg.

• Semimembranosus: Flexes leg.

The hamstrings are composed of the biceps femoris, semitendinosus, and semimembranosus.

Example:

Running involves rapid extension and flexion of the leg by the quadriceps and hamstrings.

Muscles of the Leg: Foot Movement

Overview

Leg muscles control movements of the foot, including dorsiflexion and plantar flexion, essential for walking and balance.

• Tibialis anterior: Dorsiflexes foot.

• Extensor digitorum longus: Dorsiflexes foot.

• Tibialis posterior: Plantar flexes foot.

• Fibularis longus: Plantar flexes foot.

• Fibularis brevis: Plantar flexes foot.

• Gastrocnemius: Plantar flexes foot.

• Soleus: Plantar flexes foot.

• Flexor hallucis longus: Dorsiflexes big toe.

Example:

Standing on tiptoe uses the gastrocnemius and soleus muscles.

Tendons and Bands

Overview

Tendons connect muscles to bones, transmitting force for movement. Bands such as the IT band provide structural support.

• Patellar tendon: Connects quadriceps to tibia.

• Calcaneal (Achilles) tendon: Connects calf muscles to heel bone.

• IT Band (Iliotibial band): Stabilizes lateral thigh and knee.

Summary Table: Major Muscle Groups and Actions

Additional info: The actions listed are the primary movements; many muscles also assist in stabilization and secondary actions. Understanding muscle groupings and their functions is essential for clinical assessment and movement analysis.