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. Understanding their origins, insertions, and actions is essential for comprehending their roles in human physiology.

• Buccinator: Compresses cheeks (as in blowing or sucking).

• Frontalis: Elevates the eyebrows, creating expressions such as surprise.

• Masseter: Elevates the mandible; the primary muscle involved in chewing.

• Temporalis: Elevates and retracts the mandible, assisting in chewing.

• Orbicularis oculi: Closes the eyelids (blinking, winking).

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

• Platysma: Depresses the mandible and tenses the skin of the neck (expression of fright or horror).

• Sternocleidomastoid: Flexes the neck and rotates the head toward the opposite side. Origin: Manubrium of sternum and medial portion of clavicle. Insertion: Mastoid process of temporal bone.

• Zygomaticus major: Elevates the corner of the mouth (smiling). Origin: Zygomatic bone. Insertion: Skin at the angle of the mouth.

• Zygomaticus minor: Assists in elevating the upper lip.

Muscles of the Upper Arm and Pectoral Girdle

Overview

These muscles are involved in movements of the shoulder and upper arm, including abduction, adduction, flexion, and rotation.

• Deltoid: Abducts the arm (prime mover). Origin: Acromion process and spine of scapula. Insertion: Deltoid tuberosity of humerus.

• Pectoralis major: Flexes, adducts, and medially rotates the arm. Origin: Clavicle, sternum, cartilage of ribs 1-6. Insertion: Intertubercular sulcus of humerus.

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

• Trapezius: Elevates, retracts, and rotates the scapula.

• Serratus anterior: Protracts and holds the scapula against the thoracic wall.

• Teres major: Extends, adducts, and medially rotates the arm. Origin: Inferior angle of scapula. Insertion: Lesser tubercle of humerus.

• Infraspinatus: Laterally rotates the arm.

Tendons of what muscles make up the rotator cuff? Answer: Subscapularis, supraspinatus, infraspinatus, teres minor.

Muscles of the Forearm

Overview

These muscles control movements of the forearm and hand, including flexion, extension, pronation, and supination.

• Biceps brachii: Flexes the forearm at the elbow (prime mover).

• Brachialis: Flexes the forearm at the elbow.

• Brachioradialis: Flexes the forearm at the elbow.

• Triceps brachii: Extends the forearm at the elbow.

Muscles of the Wrist

Overview

These muscles are responsible for flexion, extension, abduction, and adduction of the wrist and hand.

• Flexor carpi radialis: Flexes the wrist and abducts the hand.

• Palmaris longus: Flexes the wrist.

• Flexor carpi ulnaris: Flexes the wrist and adducts the hand.

What muscles extend the hand/wrist? Answer: Extensor carpi radialis longus, extensor carpi ulnaris, extensor digitorum (not listed above, but commonly included).

Respiratory & Abdominal Muscles

Overview

These muscles are involved in breathing and movements of the trunk, including flexion, rotation, and compression of the abdominal cavity.

• External oblique: Compresses the abdomen, flexes, and rotates the vertebral column.

• Internal oblique: Compresses the abdomen, flexes, and rotates the vertebral column.

• Rectus abdominis: Compresses the abdomen and flexes the vertebral column.

• Transverse abdominis: Compresses the abdomen.

What muscles are used for breathing? What are their actions?

• Diaphragm: Expands the thoracic cavity, causing inspiration.

• External intercostals: Elevate the ribs, expanding the rib cage during inspiration.

Muscles that Move the Leg

Overview

These muscles are responsible for movements at the hip and knee, including extension, flexion, abduction, and rotation.

• Biceps femoris: Extends the knee and laterally rotates the hip. Origin: Ischial tuberosity of ischium. Insertion: Head of fibula.

• Semitendinosus: Extends the knee and medially rotates the hip.

• Semimembranosus: Extends the knee and medially rotates the hip.

• Sartorius: Flexes the knee, abducts, and laterally rotates the thigh at the hip.

• Gracilis: Adducts the thigh at the hip and flexes the leg at the knee.

• Gluteus maximus: Extends the thigh at the hip and laterally rotates the thigh.

What muscles make up the hamstring group? Answer: Semitendinosus, semimembranosus, biceps femoris.

What muscles make up the quadriceps group? What is their action? Answer: Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius. Action: Extend the knee.

Muscles of the Foot

Overview

These muscles control movements of the ankle and toes, including dorsiflexion, plantar flexion, inversion, and eversion.

• Tibialis anterior: Inverts and dorsiflexes the foot at the ankle. Origin: Proximal tibia. Insertion: First metatarsal and medial cuneiform bone.

• Gastrocnemius: Flexes the knee and plantar flexes the ankle. Origin: Medial and lateral condyles of femur. Insertion: Calcaneus via calcaneal (Achilles) tendon.

• Soleus: Plantar flexes the foot at the ankle.

Muscle Tissue Types

Overview

There are three main types of muscle tissue in the human body, each with distinct structural and functional characteristics.

• Skeletal muscle: Voluntary, striated muscle attached to bones; responsible for body movement.

• Smooth muscle: Involuntary, non-striated muscle found in the walls of internal organs (e.g., intestines, blood vessels).

• Cardiac muscle: Involuntary, striated muscle found only in the heart; responsible for pumping blood.

Microscopic features: Skeletal muscle: Multinucleated, striated fibers. Smooth muscle: Spindle-shaped, single nucleus, no striations. Cardiac muscle: Branched fibers, single nucleus, intercalated discs, striations.

Summary Table: Major Muscle Groups and Actions

Key Definitions

• Origin: The fixed attachment point of a muscle.

• Insertion: The movable attachment point of a muscle.

• Prime mover (agonist): The main muscle responsible for a specific movement.

• Antagonist: A muscle that opposes the action of the prime mover.

• Synergist: A muscle that assists the prime mover.

• Fixator: A muscle that stabilizes the origin of the prime mover.

Additional info:

• Some muscle origins and insertions were expanded for clarity.

• Muscle actions and groupings were clarified based on standard anatomical knowledge.

• Examples of muscles extending the wrist and the quadriceps group were added for completeness.