Study Guide: Medical Terminology of the Muscular System (Orthopedics)

Orthopedics and the Muscular System

Overview of Orthopedics

Orthopedics is the medical specialty focused on the study and treatment of the muscular and skeletal systems. This chapter emphasizes the muscular system, its anatomy, functions, diseases, diagnostic procedures, and treatments.

• Orthopedics: Concerned with muscles, bones, tendons, and related structures.

• Practitioners use laboratory tests, diagnostic imaging, medical and surgical procedures, and drugs to treat diseases.

• The muscular system is sometimes referred to as the musculoskeletal system due to its close relationship with bones.

Anatomy of the Muscular System

Components of the Muscular System

The muscular system consists of muscles, tendons, fascia, aponeuroses, retinacula, and bursae. Its primary functions are maintaining body position and producing movement.

• Muscles: Contractile tissues responsible for movement.

• Tendons: White fibrous bands attaching muscles to bones.

• Fascia: Thin connective tissue wrapping each muscle and merging into tendons.

• Aponeurosis: Flat sheet of connective tissue attaching flat muscles to bones or deeper muscles.

• Retinaculum: Translucent band holding down tendons at the wrist and ankle.

• Bursa: Fluid-filled sac reducing friction where tendons rub against bones.

Types of Muscle Tissue

There are three types of muscle tissue in the human body, each with distinct structure and function.

• Skeletal Muscle: Voluntary muscles responsible for body movement; characterized by striations and multiple nuclei.

• Cardiac Muscle: Involuntary muscle forming the heart; has less prominent striations and a single nucleus.

• Smooth Muscle: Involuntary muscle forming a thin layer around organs; lacks striations and has a single nucleus.

• Only skeletal muscle is considered part of the muscular system in orthopedics.

Muscle Origins, Insertions, and Structure

Muscles attach to bones at specific sites called origins and insertions, and are composed of fascicles, fibers, and myofibrils.

• Origin: Site where a tendon attaches to a stationary or nearly stationary bone.

• Insertion: Site where a tendon attaches to the bone that moves during contraction.

• Belly: The thickest part of the muscle.

• Muscle fibers are long cells with multiple nuclei, containing myofibrils made of actin and myosin filaments.

Muscle Naming Conventions

Latin Roots and Word Parts

Muscle names are derived from Latin, often describing location, shape, size, or action.

• Biceps brachii: 'Biceps' means two heads; 'brachii' means of the arm.

• Brachioradialis: 'Brachi/o-' means arm; 'radi/o-' means radius bone; '-alis' means pertaining to.

• Extensor digitorum: 'Extens/o-' means straightening; '-or' means thing that produces.

• Flexor hallucis brevis: 'Flex/o-' means bending; 'hallucis' refers to the big toe; 'brevis' means short.

• Gluteus maximus: 'Gluteus' means buttocks; 'maximus' means large.

• Rectus abdominis: 'Rectus' means straight; 'abdominis' means of the abdomen.

• Temporalis: Pertains to the side of the head.

• Triceps brachii: 'Tri-' means three; '-ceps' from 'caput' (head).

Major Muscles of the Body

Muscles of the Head and Neck

These muscles are involved in facial expressions, chewing, and head movement.

• Temporalis: Above the temporal bone.

• Masseter: Jaw muscle.

• Sternocleidomastoid: Neck muscle.

• Platysma: Throat muscle.

• Frontalis: Forehead muscle.

• Orbicularis oculi: Around the eye.

• Buccinator: Cheek muscle.

• Orbicularis oris: Below the lips.

Muscles of the Shoulders and Chest

These muscles facilitate arm movement, shoulder rotation, and breathing.

• Sternocleidomastoid, Trapezius, Deltoid, Pectoralis major, Intercostal muscles

Muscles of the Shoulders and Back

These muscles are responsible for shoulder elevation, trunk rotation, and posture.

• Deltoid, Trapezius, Latissimus dorsi, Scapula, Aponeurosis

Muscles of the Upper Extremity

These muscles control arm, wrist, and finger movements.

• Biceps brachii, Brachioradialis, Flexor muscles, Extensor muscles, Thenar muscles, Triceps brachii, Retinaculum

Muscles of the Forearm and Retinaculum

Extensor muscles of the forearm have long tendons crossing the wrist, held in place by the retinaculum.

• Contraction of extensor muscles straightens and extends the fingers.

Muscles of the Abdomen

Abdominal muscles are involved in trunk rotation, flexion, and stabilization.

• External abdominal oblique, Internal abdominal oblique, Rectus abdominis, Aponeurosis

Muscles of the Lower Extremity

These muscles enable leg movement, knee flexion, walking, and climbing.

• Sartorius, Rectus femoris, Vastus lateralis, Vastus medialis, Patella, Tibialis anterior, Peroneus longus, Retinaculum, Gluteus medius, Gluteus maximus, Semitendinosus, Semimembranosus, Biceps femoris, Gastrocnemius, Achilles tendon, Calcaneus

Muscle Strength and Size

Muscle strength and size can be developed through exercise and training, as seen in bodybuilders.

Muscle Structure and Function

Microscopic Anatomy of Muscle

Muscles are composed of fascicles, fibers, and myofibrils, each with specialized structures for contraction.

• Fascicle: Bundle of muscle fibers wrapped in fascia.

• Muscle fiber: Long cell with multiple nuclei.

• Myofibril: Contains actin (thin) and myosin (thick) filaments.

Neuromuscular Junction and Muscle Contraction

Each muscle fiber is connected to a nerve cell at the neuromuscular junction. The nerve releases acetylcholine, triggering calcium release and muscle contraction.

• Acetylcholine: Neurotransmitter that initiates muscle contraction.

• Calcium ions: Cause actin to slide between myosin, shortening the muscle.

Muscle Tone

Muscles maintain a mild, partial contraction called muscle tone, which is not under conscious control and keeps muscles firm and ready to act.

Types of Muscle Movement

Common Movements

Muscles produce various types of movement, including extension, abduction, pronation, dorsiflexion, adduction, flexion, plantar flexion, and rotation.

• Extension: Straightening a limb.

• Abduction: Moving a limb away from the midline.

• Pronation: Rotating the hand or foot downward.

• Dorsiflexion: Raising the foot upward.

• Adduction: Moving a limb toward the midline.

• Flexion: Bending a limb.

• Plantar flexion: Pointing the foot downward.

• Rotation: Turning a body part around its axis.

Growth and Development Milestones

Muscle Coordination in Infancy

Infants develop muscle strength and coordination, enabling activities such as lifting the head and supporting the upper body.

Diseases of the Muscles and Related Structures

Muscle Atrophy

Muscle atrophy is the wasting and weakening of muscles, often caused by malnutrition or lack of use.

Muscle Contracture

Contractures are permanent shortening of muscles or tendons, commonly seen in patients with limited mobility.

Muscle Strain

Muscle strain is an injury caused by overexertion, resulting in pain and limited movement.

Muscular Dystrophy

Muscular dystrophy is a progressive disease causing muscle weakness and loss of mobility, especially in the legs.

Tennis Elbow

Tennis elbow is an overuse injury causing inflammation of the triceps brachii tendon at the elbow joint.

Diseases of the Bursa, Fascia, or Tendon

Dupuytren Contracture

Dupuytren contracture is a progressive disease affecting the ring and little fingers, causing them to bend inward.

Medical Epicondylitis (Pitcher's Elbow)

Pitcher's elbow is an overuse injury caused by repetitive wrist flexion and gripping, common in baseball pitchers.

Medical Procedures and Treatments

Braces

Braces provide support and stability for injured or weak muscles and joints.

Deep Tendon Reflex Testing

A percussion hammer is used to test reflexes by tapping tendons, such as below the patella, to observe involuntary muscle contraction.

Physical Therapy

Physical therapy is used to decrease muscle stiffness and improve mobility after injury or surgery.

Intramuscular Injection

Immunizations are often administered into the thigh muscles, which are the largest in a baby's body.

Summary Table: Types of Muscle Tissue

Type	Control	Location	Appearance
Skeletal	Voluntary	Attached to bones	Striated, multiple nuclei
Cardiac	Involuntary	Heart	Striated, single nucleus
Smooth	Involuntary	Walls of organs	No striations, single nucleus

Summary Table: Major Muscles and Their Functions

Muscle	Location	Function
Biceps brachii	Upper arm	Flexes forearm
Triceps brachii	Upper arm	Extends forearm
Deltoid	Shoulder	Abducts arm
Gluteus maximus	Buttocks	Extends thigh
Rectus abdominis	Abdomen	Flexes trunk
Gastrocnemius	Calf	Plantar flexes foot

Key Medical Terminology

• Atrophy: Wasting away of muscle tissue.

• Contracture: Permanent shortening of muscle or tendon.

• Dystrophy: Progressive degeneration of muscle.

• Epicondylitis: Inflammation of the tendons at the elbow.

• Fascia: Connective tissue surrounding muscles.

• Retinaculum: Band holding tendons in place.

• Bursa: Fluid-filled sac reducing friction.

Muscle Contraction Equation

The sliding filament theory describes muscle contraction:

$\text{Force} = \text{Number of cross-bridges} \times \text{Force per cross-bridge}$

Calcium ions and ATP are essential for cross-bridge formation and muscle contraction.

Abbreviations

• LUE: Left Upper Extremity

• RUE: Right Upper Extremity

• LLE: Left Lower Extremity

• RLE: Right Lower Extremity

Conclusion

The muscular system is essential for movement, posture, and overall function. Understanding its anatomy, terminology, diseases, and treatments is fundamental for medical terminology students.