Orthopedics: Muscular System - Medical Terminology Study Guide

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 examines orthopedics from the perspective of the muscular system, including its anatomy, function, diseases, diagnostic procedures, and treatments.

The Muscular System

Components of the Muscular System

The muscular system consists of muscles, tendons, and related connective tissues throughout the body. Its primary functions are to maintain body position and produce movement of the skeletal framework. Due to its close relationship with bones, it is often referred to as the musculoskeletal system.

• Muscles: Contractile tissues responsible for movement.

• Tendons: Connect muscles to bones.

• Fascia: Thin connective tissue wrapping each muscle.

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 movements; characterized by striations and multiple nuclei.

• Cardiac Muscle: Involuntary muscle found in 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 for orthopedics.

Connective Structures

• Tendon: White fibrous band attaching muscle to bone.

• Fascia: Connective tissue wrapping each muscle and merging into its tendon.

• Aponeurosis: White fibrous sheet attaching flat muscle to bone or deeper muscles.

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

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

Muscle Origins and Insertions

Muscles attach to bones at two main sites:

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

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

• Belly: The part of the muscle with the greatest mass.

Muscle Names and Terminology

Latin Naming Conventions

Muscle names are written in Latin and often describe location, shape, size, or action. Understanding word parts helps decode muscle names:

• 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 Latin '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

• Frontalis

• Orbicularis oculi

• Masseter

• Sternocleidomastoid

• Platysma

• Buccinator

• Orbicularis oris

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 movement, posture, and trunk rotation.

• Deltoid

• Trapezius

• Latissimus dorsi

• Scapula

• Aponeurosis

Muscles of the Upper Extremity

These muscles control arm, wrist, and finger movements.

• Biceps brachii

• Brachioradialis

• Triceps brachii

• Flexor and extensor muscles

• Thenar muscles

• Retinaculum

Muscles of the Forearm and Retinaculum

Extensor muscles of the forearm have long tendons held in place by the retinaculum, enabling finger extension.

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 bending, walking, and climbing.

• Sartorius

• Rectus femoris

• Vastus lateralis

• Vastus medialis

• Patella

• Tibialis anterior

• Peroneus longus

• 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

A muscle is composed of fascicles, which contain bundles of muscle fibers (cells). Each fiber contains myofibrils made of actin (thin) and myosin (thick) filaments.

• Fascicle: Bundle of muscle fibers wrapped in fascia.

• Muscle fiber: Long cell with multiple nuclei.

• Myofibril: Contains actin and myosin filaments.

Neuromuscular Junction and Contraction

Each muscle fiber connects to a nerve cell at the neuromuscular junction. The nerve releases acetylcholine, triggering calcium release and causing actin to slide between myosin, resulting in contraction.

• Acetylcholine: Neurotransmitter initiating muscle contraction.

• Calcium ions: Enable actin-myosin interaction.

• Muscle contraction: Shortening of muscle fibers.

Muscle Tone

Muscles maintain mild, partial contraction (muscle tone) due to continuous nerve impulses, keeping them firm and ready to act. Muscle tone is not under conscious control.

Types of Muscle Movement

Extension, Abduction, Pronation, Dorsiflexion

Muscle movements are classified by their action:

• Extension: Straightening a limb.

• Abduction: Moving a limb away from the midline.

• Pronation: Rotating the hand or foot downward.

• Dorsiflexion: Bending the foot upward.

Adduction, Flexion, Plantar Flexion, Rotation

• Adduction: Moving a limb toward the midline.

• Flexion: Bending a limb.

• Plantar flexion: Bending the foot downward.

• Rotation: Turning a body part around its axis.

Rotation of the Head

The head rotates right and left around the vertebral column axis.

Growth and Development Milestones

Muscle strength and coordination develop as infants reach milestones 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 abnormal, 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 inflammation of the triceps brachii tendon at the elbow joint due to repetitive motion.

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 from gripping and flexing the wrist during pitching.

Medical Procedures and Treatments

Braces

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

Deep Tendon Reflex

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 helps decrease muscle stiffness and restore function after injury or immobility.

Intramuscular Injection

Immunizations are often administered into the thigh muscles, which are the largest in infants.

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	Organs, vessels	No striations, single nucleus

Summary Table: Major Muscles and Their Actions

Muscle	Location	Action
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

Key Equations

Muscle Contraction (Sliding Filament Theory)

The process of muscle contraction can be summarized as:

$\text{Muscle Contraction} = \text{Actin slides between Myosin}$

$\text{ATP} + \text{Ca}^{2+} \rightarrow \text{Actin-Myosin Interaction}$

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.