Muscle Tissue

Types of Muscle Tissue

Muscle tissue is a specialized tissue found throughout the human body, responsible for movement, posture, and vital bodily functions. There are three main types of muscle tissue, each with distinct structure and function.

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

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

• Smooth Muscle: Involuntary, non-striated muscle found in walls of hollow organs (e.g., intestines, blood vessels); controls movement of substances within these organs.

Dense Regular Connective Tissue: A type of connective tissue with tightly packed collagen fibers, providing strength and resistance to pulling forces; commonly found in tendons and ligaments.

• Neuromuscular Junction: The synapse or connection point between a motor neuron and a skeletal muscle fiber, where nerve impulses trigger muscle contraction.

Muscle Terminology

Key Terms in Muscle Anatomy

Understanding muscle anatomy requires familiarity with specific terminology describing muscle structure and attachment.

• Tendon: A strong, fibrous connective tissue that attaches muscle to bone.

• Aponeurosis: A broad, flat sheet of connective tissue that connects muscles to each other or to bone.

• Origin: The fixed attachment point of a muscle, typically proximal or closer to the center of the body.

• Insertion: The movable attachment point of a muscle, typically distal or farther from the center of the body.

Human Muscles

Overview of Major Muscle Groups

The human body contains over 600 muscles, organized into groups based on location and function. The following sections summarize key muscles and their primary actions.

Face & Neck Muscles

• Frontalis: Elevates eyebrows, wrinkles skin of forehead.

• Occipitalis: Pulls scalp posteriorly.

• Orbicularis oculi: Closes eyes, produces winking and blinking.

• Zygomaticus (major & minor): Raises corners of mouth (smiling).

• Orbicularis oris: Closes lips, protrudes lips (kissing).

• Masseter: Raises and protrudes mandible to close the mouth.

• Temporalis: Raises and protrudes lower lips as in doubt or disdain.

• Platysma: Depresses mandible, tenses skin of neck.

• Sternocleidomastoid: Flexes and rotates head.

Thorax & Abdomen Muscles

• External intercostals: Elevate ribs during inspiration.

• Internal intercostals: Depress ribs during forced expiration.

• Diaphragm: Increases vertical length of thoracic cavity during inspiration.

• Rectus abdominis: Flexes vertebral column.

• External oblique: Compresses abdomen.

• Internal oblique: Compresses abdomen.

• Transversus abdominis: Compresses abdomen.

• Linea alba: Fusion of aponeuroses of external oblique and transversus abdominis.

Back & Shoulder Muscles

• Trapezius: Elevates scapula, extends head.

• Levator scapulae: Elevates scapula.

• Rhomboids (major & minor): Adduct and stabilize scapula.

• Supraspinatus: Assists deltoid to abduct arm.

• Infraspinatus: Laterally rotates arm.

• Subscapularis: Medially rotates arm.

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

• Teres minor: Laterally rotates arm.

• Latissimus dorsi: Medially rotates, extends, and adducts arm; draws down shoulder.

• Deltoid: Abducts arm.

Upper Arm Muscles

• Biceps brachii: Flexes forearm and arm.

• Brachialis: Flexes forearm.

• Triceps brachii: Extends forearm.

• Anconeus: Extends forearm.

Forearm Muscles

Anterior, Ventral or Palmar View

• Brachioradialis: Flexes arm.

• Flexor carpi radialis: Flexes and abducts wrist.

• Palmaris longus: Flexes wrist.

Posterior or Dorsal View

• Flexor carpi ulnaris: Flexes and adducts wrist.

• Extensor carpi ulnaris: Extends and adducts wrist.

• Extensor digiti minimi: Abducts little finger.

• Extensor digitorum communis: Extends wrist.

Thigh Muscles

Anterior or Ventral View

• Iliotibial tract (band) (aponeurosis): Band of fascia that connects to tensor fascia lata m.

• Tensor fascia lata: Tenses the iliotibial tract.

• Sartorius: Flexes and laterally rotates thigh.

• Iliopsoas (Psoas major): Flexes thigh.

• Pectineus: Flexes, adducts, and laterally rotates thigh.

• Adductor longus: Flexes, adducts, and laterally rotates thigh.

• Gracilis: Adducts thigh and flexes leg.

Quadriceps Group

• Rectus femoris: Flexes thigh, extends leg.

• Vastus lateralis: Flexes thigh, extends leg.

• Vastus intermedius: Flexes thigh, extends leg.

• Vastus medialis: Flexes thigh, extends leg.

Posterior or Dorsal View

• Gluteus maximus: Extends thigh.

• Gluteus medius: Abducts and medially rotates thigh.

Hamstring Group

• Biceps femoris: Laterally rotates leg when knee is flexed; flexes leg; extends thigh.

• Semitendinosus: Medially rotates leg when knee is flexed; flexes leg; extends thigh.

• Semimembranosus: Medially rotates leg when knee is flexed; flexes leg; extends thigh.

Leg Muscles

Anterior or Ventral View

• Extensor digitorum longus: Dorsiflexes foot; extends toes.

• Tibialis anterior: Dorsiflexes foot; inversion.

• Soleus: Plantar flexes foot; inversion.

• Fibularis (Peroneus) longus & brevis: Plantar flexes foot; eversion.

Posterior or Dorsal View

• Soleus: Plantar flexes foot; inversion.

• Plantaris: Plantar flexes foot; flexes leg.

• Gastrocnemius: Plantar flexes foot; flexes leg.

• Achilles (calcaneal) tendon: Tendon for gastrocnemius and soleus.

Table: Major Muscle Groups and Their Actions

Note: Muscles marked with an asterisk (*) are common sites for intramuscular injection.

Additional info: The above content expands on the original notes by providing definitions, grouping muscles by region, and clarifying muscle actions for study purposes.