Chapter 4: Muscular System - Medical Terminology

Overview of the Musculoskeletal System

• Systemic Interaction and Function:

  • The muscular and skeletal systems are frequently referred to collectively as the musculoskeletal system due to their integrated physiological and biomechanical functions.

  • Together, these systems provide the human body with:

    • Form: Defining anatomical shape and contour.

    • Support: Sustaining upright posture and internal organ alignment.

    • Stability: Maintaining joint integrity under mechanical load.

    • Mobility: Allowing deliberate locomotion and mechanical movement.

• Key Word Parts:

  • muscul/o: Muscle

  • skelet/o: Skeleton

Structural Components of Skeletal Muscle

• Muscle Fibers:

  • Long, slender specialized cells that constitute the functional contractile elements of muscles.

  • Each skeletal muscle is composed of organized bundles of these individual fibers bound together by protective layers of fibrous connective tissue.

• Fascia:

  • Definition: A band or sheet of fibrous connective tissue that envelops, separates, or binds together individual muscles or functional muscle groups.

  • Functional Characteristics: Possesses flexibility to accommodate muscle elongation and contraction during active body movements.

  • Related Terminology:

    • myofascial (my-oh-FASH-ee-ahl): Pertaining to both muscle tissue and its surrounding fascia.

    • Word parts breakdown: my/o (muscle) + fasci (fascia) + -al (pertaining to).

• Tendons and Aponeuroses:

  • Tendon: A narrow band of dense, nonelastic, fibrous connective tissue that securely anchors a muscle to a bone.

  • Aponeurosis: A flat, sheet-like expanse of fibrous connective tissue that resembles a broadened tendon; serves to link muscles together or attach a muscle across a broader surface of bone.

Types of Muscle Tissue

• Skeletal Muscle:

  • Control Mechanism: Voluntary muscles; they contract and relax directly in response to conscious, intentional motor thought.

  • Microscopic Appearance: Striated muscles; composed of fibers containing multiple nuclei per cell, which exhibit alternating light and dark bands of color (striations or cross-stripes) under microscopic examination.

  • Primary Function: Responsible for major voluntary body movements and skeletal locomotion.

• Smooth Muscle:

  • Control Mechanism: Involuntary muscles; operate under the regulatory control of the autonomic nervous system and cannot be moved via conscious effort.

  • Microscopic Appearance: Unstriated muscles; spindle-shaped fibers lacking the dark and light transverse bands characteristic of striated tissue; each cell possesses a single centrally located nucleus.

  • Anatomical Location and Alternate Names: Known as visceral muscles; situated within the walls of internal hollow organs and structures, including the digestive tract, blood vessels, and the urinary system.

  • Terminology: Visceral relates directly to internal body organs.

• Myocardial Muscle:

  • Alternate Names: Myocardium or cardiac muscle.

  • Control Mechanism: Involuntary; contracts autonomously under autonomic and internal cardiac conduction regulation.

  • Microscopic Appearance: Striated appearance with distinct cross-stripes; features branching, interconnected fibers with centrally positioned nuclei.

  • Function: Forms the muscular pumping wall of the heart.

Neuromuscular Innervation and Muscle Physiology

• Neuromuscular Junction:

  • Definition: The physiological contact site between terminal branches of motor neurons and the sarcolemma of individual muscle fibers.

  • Function: Facilitates rapid transmission of electrical nerve impulses (action potentials) that stimulate biochemical cascade reactions leading to muscle contraction.

  • Terminology: Neuromuscular denotes the functional relationship between nervous elements and muscular structures.

  • Word parts breakdown: neur/o (nerve) + muscul/o (muscle) + -ar (pertaining to).

• Antagonistic Muscle Pairs:

  • All skeletal muscles operate in balanced, paired arrangements designated as antagonistic pairs.

  • Antagonistic Concept: Muscles function in direct opposition to one another across a movable joint.

  • Contraction:

    • Active tensioning and tightening of the muscle.

    • Fibers shorten and thicken mechanically, resulting in enlargement of the central mass, termed the belly of the muscle.

  • Relaxation:

    • Release of contractile tension, allowing the muscle to return to resting length.

    • Fibers elongate and thin, returning the muscle belly to its baseline, un-enlarged dimensions.

  • Classical Example:

    • Arm flexion: Biceps brachii contracts (agonist) while triceps brachii relaxes (antagonist).

    • Arm extension: Triceps brachii contracts (agonist) while biceps brachii relaxes (antagonist).

Contrasting Movements of the Muscular System

• Abduction and Adduction:

  • Abduction: Movement of a limb or extremity away from the coronal midline of the body.

    • Word parts breakdown: ab- (away from) + duct (to lead) + -ion (action).

  • Adduction: Movement of a limb or extremity toward the coronal midline of the body.

    • Word parts breakdown: ad- (toward) + duct (to lead) + -ion (action).

• Flexion, Extension, and Hyperextension:

  • Flexion: Decreasing the biological angle between two articulating bones, accomplished by bending a limb at a joint.

    • Word parts breakdown: flex (to bend) + -ion (action).

  • Extension: Increasing the angle between two articulating bones, accomplished by straightening a limb out.

    • Word parts breakdown: ex- (away from) + tens (to stretch out) + -ion (action).

  • Hyperextension: Overextension or exaggerated straightening of a limb or joint beyond its normal anatomical limits.

    • Word parts breakdown: hyper- (excessive, increased).

• Elevation and Depression:

  • Elevation: The upward mechanical lifting or raising of an anatomical body part (e.g., shrugging shoulders upward).

  • Depression: The downward mechanical lowering or pulling down of an anatomical body part.

• Rotation, Circumduction, and the Rotator Cuff:

  • Rotation: Turning or pivoting a body segment circularly around its longitudinal central axis.

  • Circumduction: Circular movement of a limb that traces a cone-like path, moving circularly at the distal end while remaining fixed at the proximal joint.

  • Rotator Cuff Mechanics:

    • A rotator muscle pivots an anatomical element around its axis (e.g., the spherical head of the humerus [HYUM-er-us] rotating within the glenoid cavity of the scapula).

    • The rotator cuff comprises a specialized complex of four muscles and their associated stabilizing tendons that hold the head of the humerus securely within the shallow glenohumeral joint socket during rotational movements.

• Supination and Pronation:

  • Supination: Rotational movement of the forearm or foot such that the palmar surface faces upward or anteriorly, or the plantar aspect faces medially/upward.

  • Pronation: Rotational movement of the forearm or foot such that the palmar surface turns downward or posteriorly, or the plantar aspect tilts outward/downward.

• Dorsiflexion and Plantar Flexion:

  • Dorsiflexion: Upward mechanical flexion of the foot at the talocrural (ankle) joint, pulling toes toward the shin.

  • Plantar Flexion: Downward extension/flexion of the foot at the ankle joint, pointing the toes and plantar surface downward toward the ground.

Principles of Muscle Nomenclature

Muscles are classified and named anatomically based on specific structural, positional, or functional criteria:

• 1. Named by Origin and Insertion:

  • Origin: The anatomical anchor where a muscle tendon attaches to a stationary or relatively immovable bone.

  • Insertion: The distal site where a muscle tendon attaches to the movable bone that translates through space when the muscle contracts.

  • Sternocleidomastoid Muscle:

    • Possesses dual origins: the sternum (stern/o, breastbone) and the clavicle (cleid/o, collar bone).

    • Single insertion: the mastoid process of the temporal bone located immediately posterior to the ear.

• 2. Named by Action:

  • Designated according to the specific joint movement generated, such as flexion or extension.

  • Example - Wrist Articulators:

    • Flexor carpi muscles: Actuate wrist flexion (bending).

    • Extensor carpi muscles: Actuate wrist extension (straightening).

    • Root breakdown: carp/o denotes the wrist or carpal bones.

• 3. Named by Location:

  • Pectoralis Major: Thick, fan-shaped muscle located over the anterior thoracic chest wall (pectoral = relating to the chest).

  • Vastus Lateralis: Substantial muscle situated toward the lateral (outer) aspect of the thigh (vastus = Latin for huge; lateralis = toward the side).

  • Vastus Medialis: Muscle oriented toward the medial (inner) midline aspect of the thigh (medialis = toward the midline).

  • Both vastus muscles belong to the four-part quadriceps femoris group controlling knee flexion and extension.

• 4. Named by Fiber Direction:

  • Oblique: Fascicles oriented obliquely (slanted or at an angle relative to the body's midline).

  • Rectus: Fascicles oriented in a straight, parallel alignment along the vertical longitudinal axis of the body (e.g., rectus abdominis).

  • Transverse: Fascicles aligned perpendicularly in a horizontal, crosswise direction (e.g., transversus abdominis).

*   *Sphincter:* Circular, ring-like muscle band that constricts an internal lumen or natural body orifice (e.g., lower esophageal sphincter, pyloric sphincter of the stomach).

• 5. Named by Number of Divisions (Heads):

  • Biceps brachii: Formed from two distinct origins or heads (bi- = two; -ceps = head).

  • Triceps brachii: Formed from three distinct origins or heads (tri- = three; -ceps = head).

• 6. Named by Size or Shape:

  • Gluteus maximus: The largest muscle of the buttock (maximus = great, large).

  • Deltoid muscle: Muscular cap of the shoulder named after the inverted triangular form of the Greek capital letter delta ($\Delta$).

• 7. Named by Historical or Unique Context:

  • Hamstrings: Posterior thigh muscle group named historically from the tradition of butchers utilizing these strong exposed tendons to suspend slaughtered pigs during processing.

Medical Specialties in Musculoskeletal Health

• Exercise Physiologist:

  • A healthcare professional working under physician oversight who develops, prescribes, and implements tailored exercise regimens and conducts clinical fitness diagnostics to optimize cardiovascular and neuromuscular function.

• Occupational Therapist (OT):

  • A clinician specializing in restoring or adapting motor capability to enable patients to engage independently in Activities of Daily Living (ADLs), including dressing, bathing, work obligations, educational tasks, and social participation.

• Physical Therapist (PT):

  • A licensed provider dedicated to preventing musculoskeletal impairment and restoring joint and muscular functionality through targeted therapeutic exercises, manual manipulation, heat therapy, massage, and physical modalities.

• Sports Medicine Physician:

  • A physician specializing in clinical diagnosis, conservative management, therapeutic rehabilitation, and injury prevention involving the bones, joints, ligaments, and musculature of athletic and active populations.

Pathologies of Fibers, Fascia, and Tendons

• Fasciitis:

  • Acute or localized inflammation of a fascia sheath.

  • Etymology: fasci/o (fascia) + -itis (inflammation).

• Fibromyalgia Syndrome:

  • A chronic, non-articular systemic disorder characterized by generalized muscular pain, widespread soft-tissue tenderness, fatigue, and cognitive dysfunction without joint inflammation.

  • Etymology: fibr/o (fibrous tissue) + my/o (muscle) + -algia (pain).

• Tendonitis (Tendinitis):

  • Inflammatory irritation of a tendon provoked typically by localized overuse, repetitive traction, or acute friction trauma.

  • Etymology: tendon/o or tendin/o (tendon) + -itis (inflammation).

• Tendinosis:

  • A chronic, non-inflammatory degenerative condition of a tendon marked by micro-tearing and structural disruption resulting from chronic mechanical overuse or an improperly healed previous tendon injury.

• Myofascial Pain Syndrome:

  • A chronic regional pain disorder affecting muscles and their enclosing fascia, precipitated by sustained muscle tension or repetitive stress.

  • Trigger Points: Palpable, hyperirritable nodules that develop predominantly where fascia contacts muscle.

  • Referred Pain: Hallmark sensory phenomenon wherein stimulation of a trigger point elicits localized pain felt at a distant anatomical site.

• Plantar Fascia and Heel Pathologies:

  • Plantar Fasciitis: Inflammation along the thick fibrous plantar aponeurosis extending across the sole from the calcaneus to the metatarsals.

  • Heel Spur: Reactive calcium osteophyte deposition projecting into the plantar fascia at its calcaneal insertion site, frequently co-occurring with chronic fasciitis.

General Muscle Disorders and Pathologies

• Adhesion:

  • A band of fibrous scar tissue that binds together internal tissues or anatomical structures abnormally, frequently developing secondary to trauma, surgery, or repetitive inflammation.

• Muscle Atrophy:

  • Pathological wasting away, weakening, or reduction in cell size and mass of muscle tissue resulting from disuse, neurological denervation, or malnutrition.

  • Etymology: a- (without, not) + troph/o, -trophy (development, nourishment).

• Myalgia:

  • Tenderness, discomfort, or cramp-like pain localized to muscle tissue.

  • Etymology: my/o (muscle) + -algia (pain).

• Hernia:

  • Protrusion of an anatomical organ or internal tissue through an abnormal opening or weakened focal defect in the surrounding muscular or fascial wall.

  • Inguinal Hernia: The most prevalent clinical variety; characterized by intestinal herniation through the inguinal ring into the groin canal (inguinal = pertaining to the groin).

• Rhabdomyolysis:

  • Pronunciation: rab-doh-my-AHL-eh-sis.

  • Clinical Definition: A severe, potentially life-threatening medical syndrome precipitated by extensive direct or indirect skeletal muscle necrosis.

  • Pathophysiological Mechanism: The rapid death and dissolution of muscle fibers causes toxic intracellular proteins—most notably myoglobin—to spill into systemic circulation, causing severe downstream complications including acute renal failure.

  • Etymology: rhabdomy/o (striated muscle) + -lysis (breakdown, destruction).

• Sarcopenia:

  • Pronunciation: sar-koh-PEE-nee-ah.

  • Definition: The progressive, age-associated loss of skeletal muscle mass, contractility, strength, and physiological functional capacity.

  • Therapeutic Interventions: Structured resistance or weight-training interventions significantly stimulate hypertrophy, helping slow—though not permanently arrest—this degenerative aging process.

  • Etymology: sarc/o (flesh) + -penia (deficiency).

Neuromuscular Tone and Movement Impairments

• Alterations in Muscle Tone:

  • Hypotonia: Condition characterized by diminished, abnormally low skeletal muscle tone or flaccidity (hypo- = deficient, decreased).

  • Dystonia: A state of disordered tonicity featuring sustained, involuntary, repetitive twisting muscle contractions (dys- = bad, difficult).

  • Atonic: Entirely lacking normal muscle tone, firmness, or contractile strength (a- = without; ton/o = tension, tone).

• Ataxia:

  • Inability to coordinate voluntary muscle movements, producing unsteady gait, clumsiness, and motor inaccuracy during deliberate motor tasks.

  • Etymology: a- (without) + tax (coordination).

• Contracture:

  • Permanent, irreversible shortening and rigidity of fascia, muscles, tendons, ligaments, or cutaneous skin, occurring when normal elastic soft tissues are substituted by dense, nonelastic fibrous bands.

• Involuntary Muscle Spasms and Cramps:

  • Spasm: A sudden, abrupt, involuntary contraction of one or multiple muscles.

    • Tic: A spasmodic, involuntary, repetitive muscle twitch, predominantly presenting in the facial musculature or eyelids; exceedingly difficult or impossible to control voluntarily.

  • Cramp: A painful, prolonged, localized muscle spasm named typically for inciting circumstance or anatomical region (e.g., menstrual cramps, writer's cramp).

    • Charley Horse: Colloquial slang denoting a sudden, intensely painful cramp (most frequently in the gastrocnemius/hamstring complex), originating in baseball vernacular during the 1880s.

• Kinetic Movement Disorders:

  • Bradykinesia: Exceptional, pathological slowness of physical movement (brady- = slow; kines/o = movement).

  • Dyskinesia: Distortion, impairment, or difficulty performing voluntary movements (dys- = difficult, bad).

  • Hyperkinesia: Abnormally heightened, excessive, uncontrollable muscular activity or restlessness (hyper- = excessive, increased).

• Myasthenia Gravis:

  • Pronunciation: my-as-THEE-nee-ah GRAH-vis.

  • Definition: Chronic autoimmune disorder causing autoantibodies to block acetylcholine receptors at the neuromuscular junction, preventing nerve impulses from activating muscle cells.

  • Clinical Presentation: Severe progressive muscle weakness accompanied by rapid, abnormal muscular fatigue during exertion; targets facial, extraocular (eyelids/vision), swallowing, and throat muscles.

  • Etymology: my (muscle) + -asthenia (weakness, loss of strength); gravis is derived from the Latin word meaning grave or serious.

• Muscular Dystrophy (MD):

  • A collective category encompassing 30 distinct inherited genetic disorders.

  • Characterized by progressive, irreversible symmetric skeletal muscle wasting and generalized muscular degeneration.

  • Crucially spares the central and peripheral nervous systems, having an exclusively myogenic etiology; no curative therapy currently exists.

Repetitive Stress and Sports-Related Injuries

• Compartment Syndrome:

  • A medical emergency involving acute or chronic compression of neurovascular structures within a myofascial compartment.

  • Caused by swelling, bleeding, or fluid accumulation within the unyielding enclosed fascial envelope that separates muscle groups in the lower or upper extremities.

• Overuse Injuries and Trigger Finger:

  • Overuse Injuries: Microscopic cellular tissue damages precipitated by continuous mechanical stress and unyielding repetition without adequate rest and recovery (e.g., stress fractures).

  • Trigger Finger: Painful mechanical blockage and progressive restriction of finger excursion driven by inflammatory swelling of the tendon's surrounding synovial sheath; often exhibits an audible and palpable snapping sound during attempted movement.

• Rotator Cuff Tendinopathy:

  • Impingement Syndrome: Also designated as rotator cuff tendinitis; occurs when the supraspinatus tendon and adjacent subacromial bursa undergo mechanical friction and entrapment within the narrow coracoacromial arch during overhead movements.

  • Frequently named after inciting athletic activities (e.g., tennis shoulder, swimmer's shoulder).

• Carpal Tunnel Syndrome (CTS):

  • Pathology: Compression neuropathy caused by acute or repetitive inflammation and inflammatory edema affecting flexor tendons coursing through the unyielding carpal tunnel of the wrist.

  • Mechanism: Swelling restricts space, applying mechanical ischemic pressure to the median nerve.

  • Terminology: Carpal designates structural association with the wrist (carp/o = wrist).

• Ganglion Cyst:

  • A benign, non-neoplastic, painless fluid-filled cystic nodule that arises along joint capsules or tendon sheaths, presenting most commonly on the dorsal aspect of the wrist.

  • Originates from the Greek root ganglion, meaning a knot or localized swelling.

• Epicondylitis:

  • Pronunciation: ep-ih-kon-dih-LYE-tis.

  • Definition: Inflammation localized to the tendon origins attaching to the bony epicondyles of the distal humerus (condyle = rounded articular bony prominence).

  • Lateral Epicondylitis (Tennis Elbow): Inflammation involving common extensor tendons inserting on the lateral epicondyle, characterized by pain on the extensor/lateral aspect of the forearm.

  • Medial Epicondylitis (Golfer's Elbow): Inflammatory strain affecting common flexor tendons inserting on the medial epicondyle, marked by pain along the palmar/medial aspect of the forearm.

• Acute Athletic Injuries:

  • Sprain: Traumatic joint injury produced by forceful wrenching, stretching, or tearing of supporting ligamentous tissue.

  • Strain: Overstretching, tearing, or traumatic overuse disruption of a muscle belly or its anchoring musculo-tendinous junction.

  • Shin Splint: Painful condition occurring when the lower leg muscles (tibialis anterior or posterior) pull forcefully and tear away micro-attachments along the medial border of the tibia.

Paralysis Classifications

• Paresis versus Plegia:

  • -paresis: Designates incomplete, mild, or partial muscle paralysis and weakness.

  • -plegia: Designates total, complete motor paralysis with absolute loss of voluntary contraction.

• Hemiparesis and Hemiplegia:

  • Hemiparesis: Motor weakness or mild, incomplete paralysis localized to one lateral half of the body (hemi- = half; -paresis = incomplete paralysis).

  • Hemiplegia: Complete loss of voluntary motor function and total paralysis affecting one lateral half of the body, typical of unilateral cerebral stroke or hemisphere trauma (hemi- = half; -plegia = complete paralysis).

• Paraplegia and Quadriplegia:

  • Paraplegia: Symmetrical paralysis involving both lower extremities and varying extents of the lower torso, typically resulting from spinal cord trauma below the cervical segment.

  • Quadriplegia (Tetraplegia): Complete paralysis involving all four anatomical limbs (both arms and both legs) alongside trunk involvement, resulting from cervical spinal cord lesions.

    • Root breakdown: quadr/i (four) or tetra- (four) + -plegia (paralysis).

    • Spinal levels of injury: High cervical injuries ($\text{C1}-\text{C4}$) produce complete tetraplegia; lower cervical lesions ($\text{C5}-\text{Th1}$) retain minimal upper-limb function while paralyzing lower extremities; thoracic lesions ($\text{Th2}-\text{Th6}$ and $\text{Th7}-\text{Th12}$) result in paraplegia.

Diagnostic Procedures and Therapeutic Modalities

• Deep Tendon Reflexes (DTR):

  • Procedure: Tested utilizing a neurological reflex hammer to apply an abrupt percussion strike directly upon a tendon (e.g., patellar reflex or knee-jerk exam; Achilles reflex).

  • Diagnostic Purpose: Evaluates the functional integrity and neurological homeostasis of the spinal reflex arc between the spinal cord segment and the peripheral nervous system.

• Range-of-Motion (ROM) Testing:

  • Clinical Goal: Evaluates maximum baseline joint mobility, active flexibility, and mechanical muscle strength.

  • Goniometer: A protractor-like diagnostic instrument utilized to quantify exact degrees of angular range-of-motion across joints such as the knee or elbow (goni/o = angle).

  • Therapeutic ROM Exercises: Targeted rehabilitation routines executed to restore functional mobility, muscular tone, and joint excursion following immobilization.

• Electromyography (EMG):

  • Definition: An electrodiagnostic modality that measures and records the intrinsic electrical activity generated within muscle fibers upon stimulation by motor nerves.

  • Techniques: Performed using either noninvasive surface electrodes applied over the skin or sterile needle electrodes inserted directly into muscle bellies.

  • Etymology: electr/o (electricity) + my/o (muscle) + -graphy (the process of producing a picture or record).

• Ergonomics:

  • Pronunciation: er-goh-NOM-icks.

  • Definition: The scientific study of human structural factors, capacities, and anatomical limits governing the design, arrangement, and operation of tools, devices, and working environments.

  • Objective: Proactively optimize workplace efficiency and comfort while reducing repetitive strain injuries, musculoskeletal strain, and chronic postural fatigue.

  • Key Ergonomic Standards for Seated Workstations:

    • Monitor Viewing Distance: Kept between $18\text{--}24\text{ inches}$.

    • Desk Surface Height: Positioned within $25\text{--}30\text{ inches}$ from the floor.

    • Chair Seat Pan Height: Adjustable between $16\text{--}20\text{ inches}$ from the ground.

    • Limb Angles: Elbows supported at a $90^\circ$ angle; knees maintained at a $90^\circ$ flexion angle with thighs oriented horizontally and feet planted flat upon the floor.

    • Spinal Alignment: Shoulders relaxed, back properly supported against lumbar contour.

• Myofascial Release:

  • A manual soft-tissue therapy involving sustained, gentle mechanical pressure and stretching into myofascial tissue restrictions.

  • Indications: Alleviates localized pain and immobility associated with fibromyalgia, myofascial pain syndrome, carpal tunnel syndrome, temporomandibular joint (TMJ) disorders, and post-traumatic movement restrictions.

• Transcutaneous Electrical Nerve Stimulation (TENS):

  • Mechanism: A portable battery-operated electromedical device that delivers controlled, mild electrical impulses via cutaneous electrode pads positioned over painful muscle pathways.

  • Physiological Impact: Modulates peripheral pain pathways and stimulates motor nerve units, inducing therapeutic muscular and neurosensory changes.

  • Common Applications: Indicated for cervical pain, frozen shoulder, chronic low back pain, sciatica, carpal tunnel syndrome, post-operative knee pain, degenerative knee arthritis, and generalized lower-leg pain.