Muscular System Notes

Functions of the Muscular System

• Muscles hold the body erect and facilitate movement.
• Muscle movement produces almost 85% of the body's heat.
• Muscles aid in moving food via the digestive system.
• Muscle movements, like walking, assist blood flow through veins.
• Muscle action helps move fluids through ducts and tubes linked to other body systems.

Structures of the Muscular System

• Musculoskeletal system: Combination of the muscular and skeletal systems. Gives the body its form, support, stability, and ability to move.
• The body has over 600 muscles, making up about 40-45% of body weight.
• Skeletal muscles: Fibers covered with fascia, attached to bones via tendons.

Muscle Fibers

• Long, slender cells composing muscles. Muscles have groups of fibers linked by connective tissue.

Fascia

• Connective tissue band that envelops, separates, or binds muscles or muscle groups.
• It is flexible to allow muscle movements.
• Myofascial: Relating to muscle tissue and fascia.

Tendons

• Narrow bands of nonelastic, dense, fibrous connective tissue.
• They connect muscle to bone.

Examples:

• Patellar tendon: connects muscles to the bottom of the patella (kneecap).
• Achilles tendon: connects the gastrocnemius muscle (major calf muscle) to the heel bone.

Aponeurosis

• Sheet-like fibrous connective tissue resembling a flattened tendon. Connects muscles together or to bone.
• Tendons attach muscle to bone, while ligaments join bone to bone.

Types of Muscle Tissue

Skeletal Muscles

• Attached to bones and enable body motions.
• Voluntary, striated muscles.

Smooth Muscles

• Found in the walls of internal organs.
• Involuntary, unstriated, visceral muscles.

Myocardial Muscle

• Found in the walls of the heart; its constant contraction and relaxation cause the heartbeat.
• Also known as myocardium or cardiac muscle.
• Appearance similar to striated skeletal muscle but involuntary like smooth muscle.

Muscle Contraction and Relaxation

Muscle Innervation

• Stimulation of a muscle via an impulse from a motor nerve.
• When the stimulation ceases, the muscle relaxes.
• Motor nerves control voluntary muscular contractions.
• Injury or disease disrupting nerve impulses can paralyze a muscle or prevent proper contraction.
• Neuromuscular: Relating to the relationship between a nerve and muscle.

Antagonistic Muscle Pairs

• Muscles arranged in antagonistic pairs work in opposition to each other.
• When one muscle in the pair contracts, the other relaxes.
• Contrasting motions enable contraction and relaxation.
• Contraction: tightening of a muscle.
• Relaxation: muscle returning to its original form.

Contrasting Muscle Motion

Abduction and Adduction

• Abduction: Moving a limb (arm or leg) away from the body's midline. An abductor is a muscle that carries out this movement.
• Adduction: Moving a limb (arm or leg) toward the body's midline. An adductor is a muscle that carries out this movement.

Flexion and Extension

• Flexion: Reducing the angle between two bones; bending a limb at a joint. A flexor muscle bends a limb at a joint.
• Extension: Increasing the angle between two bones; straightening out a limb. An extensor muscle straightens a limb at a joint.
• Hyperextension: Extreme overextension of a limb or body part beyond its normal limit.

Elevation and Depression

• Elevation: Raising or lifting a body part. The levator anguli oris muscles raise the corners of the mouth into a smile. Levator means a muscle that raises a body part.
• Depression: Lowering a body part. The depressor anguli oris lowers the corner of the mouth into a frown. Depressor means a muscle that lowers a body part.

Rotation and Circumduction

• Rotation: Circular movement around an axis, like the shoulder joint. An axis is an imaginary line through the body's center.
• Circumduction: Circular movement at the far end of a limb.
• Rotator muscle: Turns a body part on its axis.
• Rotator cuff: Group of muscles and their tendons that hold the head of the humerus securely in place.

Supination and Pronation

• Supination: Rotating the arm or leg so the palm of the hand or sole of the foot faces forward or upward.
• Pronation: Rotating the arm or leg so the palm of the hand or sole of the foot faces downward or backward.

Dorsiflexion and Plantar Flexion

• Dorsiflexion: Bending the foot upward at the ankle, decreasing the angle between the top of the foot and the front of the leg.
• Plantar flexion: Bending the foot downward at the ankle. Plantar refers to the sole of the foot. Pointing the toes and foot downward increases the angle between the top of the foot and the front of the leg.

How Muscles Are Named

Muscles Named for Their Origin and Insertion

• Origin: Where the muscle begins, usually nearest the midline of the body or on a less movable part of the skeleton.
• Insertion: Where the muscle ends by attaching to a bone or tendon, the more movable attachment, farthest from the midline.
• Example: Sternocleidomastoid muscle: Helps bend the neck and rotate the head.

Muscles Named for Their Action

• Such as flexion or extension.
• Flexor carpi muscles and extensor carpi muscles enable flexion (bending) and extension (straightening) of the wrist.

Muscles Named for Their Location

• Location on the body or nearby organ.
• Pectoralis major: Pectoral means relating to the chest.
• Vastus lateralis: Vastus means huge; lateralis means toward the side.
• Vastus medialis: Vastus means huge; medialis means toward the midline.

Muscles Named for Their Fiber Direction

• Oblique: Slanted or at an angle (e.g., external and internal obliques).
• Rectus: Straight alignment with the vertical axis of the body (e.g., rectus abdominis and rectus femoris).
• Sphincter: Ring-like muscle that constricts an opening (e.g., anal sphincter).
• Transverse: Crosswise direction (e.g., transverse abdominis).

Muscles Named for Number of Divisions

• Biceps brachii (biceps): Formed from two divisions.
• Triceps brachii (triceps): Formed from three divisions.
• Biceps and triceps are the same in both singular and plural forms.

Muscles Named for Their Size or Shape

• Broad or narrow, or large or small.
• Gluteus maximus: Largest muscle of the buttock.
• Deltoid muscle: Shaped like an inverted triangle (Greek letter delta).
• Muscles Named for Strange Reasons: Hamstrings are named for muscles by which a butcher hangs a slaughtered pig.

Select Muscles and Their Functions

Muscles of the Head

• Frontalis (occipitofrontalis): Muscle in the forehead; raises and lowers the eyebrows.
• Temporalis muscle: Moves the lower jaw up and back to close the mouth.
• Masseter muscle: One of the strongest in the body; moves the lower jaw up to close the mouth when chewing.

Muscles of the Trunk

• Pectoralis major:
  • Male: Bulk of the chest muscles.
  • Female: Lies under the breast.
• External and internal obliques: Found in the abdomen.
• Rectus abdominis: Helps flex the trunk, assists in breathing, and supports the spine.
• Transverse abdominis: Located on the side of the abdomen; engaged when a person laughs or coughs.

Muscles of the Shoulders and Arms

• Deltoid: Forms the muscular cap of the shoulder.
• Trapezius muscle: Moves the head and shoulder blade.
• Biceps brachii: Located in the anterior upper arm; flexes the elbow.
• Triceps brachii: Located in the posterior upper arm; extends the elbow.

Muscles of the Legs

• Rectus femoris: Extends the leg at the knee and flexes the thigh at the hip joint.
• Quadriceps femoris: Made up of four muscles.
• Hamstring group: Involved in knee flexion and hip extension.
• Gastrocnemius: Calf muscle that flexes the knee and bends the foot downward (Latin for “stomach of the leg,” because of its bulging shape).

Pathology of the Muscular System

Fibers, Fascia, and Tendons

• Fasciitis: Inflammation of a fascia.
• Fibromyalgia: Debilitating chronic condition with fatigue; diffuse or specific muscle, joint, or bone pain; and a wide range of other symptoms.
• Tenosynovitis: Inflammation of the sheath surrounding a tendon.
• Tendinitis: Acute inflammation or irritation of tendons caused by excessive or unusual joint use.
• Tendinosis: Chronic condition characterized by pain caused by repetitive overuse or an unhealed injury.
• Chronic fatigue syndrome (CFS): Debilitating and complex disorder of unknown cause affecting many body systems.

Muscle Disorders

• Adhesion: Band of fibrous tissue that abnormally holds structures together. Can form in muscles or internal organs after injury or surgery.
• Atrophy: Weakness or wearing away of body tissues and structures caused by pathology or disuse of the muscle.
• Cachexia: Physical wasting away due to loss of weight and muscle mass, common in patients with advanced cancer or AIDS.
• Hernia: Tissue protruding through a weak area in the muscle normally containing it. The inguinal (groin) hernia is the most common type.
• Myalgia: Tenderness or pain in the muscles.
• Polymyositis (PM): Simultaneous inflammation and weakening of voluntary muscles in many body parts.
• Rhabdomyolysis: Death of muscle fibers releasing contents into the bloodstream, which can lead to complications like renal failure.
• Sarcopenia: Loss of muscle mass, strength, and function that comes with aging.

Muscle Tone

• Atonic: Lacking normal muscle tone or strength.
• Dystonia: Movement disorder characterized by involuntary and repetitive contraction of certain muscles.
• Hypotonia: Diminished tone of skeletal muscles, often described as floppy baby syndrome in infants.

Muscle Movement

• Ataxia: Lack of muscle coordination during voluntary movement, often resulting in shaky and unsteady movements.
• Contracture: Permanent tightening of fascia, muscles, tendons, ligaments, or skin where normally elastic connective tissues are replaced with nonelastic fibrous tissues.
• Intermittent claudication (IC): Poor circulation causes pain in the leg muscles during exercise, relieved by rest.
• Spasm: Sudden, involuntary contraction of one or more muscles. Repeated spasm, often involving the eyelids or face, is called a tic.
• Myoclonus: Quick, involuntary jerking of a muscle or group of muscles that may occur normally as a person is falling asleep or result from a neurological disorder.
• Singultus (hiccups): Myoclonus of the diaphragm.
• Cramp: Painful localized muscle spasm, often named for its cause (e.g., menstrual cramps, charley horse).
• Torticollis (wryneck): Stiff neck caused by spasmodic contraction of neck muscles pulling the head toward the affected side.
• Bradykinesia: Extreme slowness in movement.
• Dyskinesia: Fragmented or jerky motions.
• Hyperkinesia (hyperactivity): Abnormally increased muscle function or activity.

Myasthenia Gravis

• Chronic autoimmune disease affecting the neuromuscular junction.

Muscular Dystrophy (MD)

• General term for a group of over 30 genetic diseases characterized by progressive weakness and degeneration of skeletal muscles. Two common forms are Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD).

Repetitive Stress Disorders (Repetitive Motion Disorders)

• Compartment syndrome: Compression of nerves and blood vessels caused by swelling within a compartment separating groups of muscles in the arm or leg.
• Overuse injuries: Minor tissue injuries that have not been given time to heal.
• Overuse tendinitis: Inflammation of tendons caused by excessive or unusual joint use.
• Trigger finger: Painful and progressive restriction of movement caused by inflammation of a tendon’s synovial sheath.
• Myofascial pain syndrome: Chronic pain disorder affecting muscles and fascia throughout the body, with development of trigger points producing local and referred muscle pain.

Rotator Cuff Injuries

• Tendinopathy: Irritation or degeneration of a tendon in any joint.
• Impingement syndrome: Rotator cuff tendinitis; tennis shoulder or swimmer’s shoulder.
• Rotator cuff tear: Occurs as irritated tendons weaken, often resulting from a fall or injury.

Carpal Tunnel Syndrome

• Tendons that pass through the carpal tunnel are chronically overused, becoming inflamed and swollen, creating pressure on the median nerve.
• Carpal tunnel release: Surgical reduction of pressure on the median nerve.
• Ganglion cyst: Benign, fluid-filled lump usually occurring on the outer surface of the wrist or hand, generally painless and not requiring treatment.

Epicondylitis

• Inflammation of the tissues surrounding the elbow.
  • Lateral epicondylitis: Tennis elbow.
  • Medial epicondylitis: Golfer’s elbow.

Ankle and Foot Problems

• Heel spur: Calcium deposit in the plantar fascia.
• Plantar fasciitis: Inflammation of the plantar fascia on the sole of the foot.
• Morton’s neuroma: Pain on the ball of the foot caused by a swollen, inflamed nerve.
• Posterior tibial tendon dysfunction (PTTD): Fallen arches; tendon supporting the foot’s arch weakens.

Sports Injuries

• Soft tissue injury: Damage to skin, muscles, ligaments, and tendons.
  • Most sports injuries (wounds, sprains, and strains) fall into this category.
• Sprain: Wrenched or torn ligament.
• Strain: Stretched or torn muscle or tendon attachment.
• Shin splint: Tibialis anterior muscle tearing away from the shin bone.
• Hamstring injury: Strain or tear caused by muscles contracting too quickly.
• Achilles tendinitis: Painful inflammation of the Achilles tendon.
• Iliotibial band syndrome (ITBS): Iliotibial band rubbing against bone, often in the area of the knee.

Spinal Cord Injuries (SCI)

• A piece of a broken vertebra presses into the spinal cord.
• Vertebrae are pushed or pulled out of alignment.
• Brain's ability to communicate with the body below the injury level may be reduced or lost altogether.
• Type of paralysis is determined by the level of the vertebra closest to the injury.
  • Incomplete injury: Some function below the injury level, even if not normal.
  • Complete injury: Complete loss of sensation and muscle control below the injury level.

Types of Paralysis

• Myoparesis: Weakness or slight muscular paralysis.
• Hemiparesis: Weakness or slight paralysis affecting one side of the body (common effect of a stroke).
• Hemiplegia: Total paralysis affecting only one side of the body.
• Paraplegia (partial paralysis): Paralysis of both legs and the lower part of the body.
• Quadriplegia (tetraplegia): Paralysis of all four extremities.

Diagnostic Procedures of the Muscular System

• Deep tendon reflexes (DTRs): Involuntary response to a stimulus tested using a reflex hammer (e.g., knee-jerk test).
• Range-of-motion testing (ROM): Evaluates joint mobility and muscle strength.
• Electromyography (EMG): Measures electrical activity within muscle fibers.
• Muscle biopsy: Removal of a tissue plug for examination.

Treatment Procedures of the Muscular System

Medications

• Antispasmodic: Anticholinergic that suppresses smooth muscle contractions of the stomach, intestine, or bladder.
• Cortisone: Corticosteroid drug that relieves pain and inflammation in a specific joint.
• Anabolic steroids: Replace muscle loss. Sometimes illegally used by athletes for muscle mass.
• Muscle relaxant: Relaxes certain muscles to relieve stiffness, pain, and discomfort by acting on the central nervous system. May interact negatively with alcohol and antidepressants.
• Neuromuscular-blocking drugs: Cause temporary paralysis by blocking nerve stimuli transmission to muscles, used as an adjunct to anesthesia during surgery.
• Platelet-rich plasma therapy (PRP): Patient’s blood is separated to create a concentrated platelet-rich plasma, injected into a joint to promote healing and pain relief.
• Viscosupplementation: Direct injections of hyaluronic acid into the knee to increase the joint’s viscous fluid, providing temporary relief from arthritis pain (sometimes called chicken shots).

Ergonomics

• Study of human factors affecting the design and operation of tools and the work environment.

Treatment Techniques

• Myofascial release: Soft-tissue manipulation technique to ease pain.
• Occupational therapy (OT): Rehabilitation to assist patients in performing activities of daily living (ADL).
• Physical therapy (PT): Treatment to prevent disability or restore function using exercise, heat, massage, or other techniques.
• Therapeutic ultrasound: Uses high-frequency sound waves to treat muscle injuries, generating heat deep within muscle tissue to ease pain, reduce muscle spasms, and accelerate healing by increasing blood flow to target tissues.
• Transcutaneous electrical nerve stimulation (TENS): Device delivering electrical impulses through the skin, causing changes in muscles.

RICE (Rest, Ice, Compression, Elevation)

• Most common first aid treatment for soft tissue injuries.

Fascia

• Fasciotomy: Surgical incision through the fascia to relieve tension or pressure.

Tendons

• Tenodesis: Surgical suturing of the end of a tendon to a bone.
• Tenolysis: Release of a tendon from adhesions.
• Tenotomy: Surgical cutting of a tendon to provide release or allow lengthening.

Muscles

• Myorrhaphy: Surgical suturing of a muscle.
• Myotomy: Surgical incision into a muscle.

Abbreviations Related to the Muscular System

• ADL = Activities of daily living
• CTS = Carpal tunnel syndrome
• MD = Muscular dystrophy
• OT = Occupational therapy, occupational therapist
• RSD = Repetitive stress disorder
• ROM = Range-of-motion testing