Muscular System

Functions of muscular system

Stability and postural tone: Fight gravity, upright position, Body form and shape

Purposeful movement: Both voluntary and involuntary, Every move is a muscle contraction, Most muscles move in groups

Generate body heat: Takes energy to move muscles, some energy is lost as heat

Protect internal organs: Along with skeletal system

muscles

40-50 % of body weight

Voluntary

skeletal muscles

Contains nerves under voluntary control

Bundles of muscle cells that are multinucleate, striations of light and dark bands

Contract quickly, fatigue easily, lack the ability to remain contracted for prolonged periods

Ex. blinking, talking, dancing, eating, writing

Involuntary

smooth and cardiac muscles

Controlled by autonomic nervous system

Non-striated, small and spindle shaped, contain one nucleus at the center of each cell

Unattached to bones, they act slowly, don’t tire easily, and can remain contracted for long periods of time

Smooth muscle

involuntary, non-striated

In walls of hollow organs, not the heart

Cannot be voluntarily controlled

Controls respiration, urination

Digestion, blood vessels

Ex. esophagus

Cardiac muscle

involuntary, striated and branched

Muscles of the heart (myocardium)

Controls the contractions of the heart

Specialized striated muscle found only in the heart

Ex. atria and ventricles

sphincter

• Special circular muscles between openings
• Esophagus and stomach, stomach and small intestine
• Walls of anus, urethra 

skeletal muscle

Muscle: bundles of cells called fibers

Muscle fiber: units of myofibrils

Sarcomeres: functional unit of each muscle cell

Myosin filaments (thick)

Actin filaments (thin)

Skeletal muscle movement is the result of the contracting and relaxing of opposing muscles

agonist

muscle contracting

antagonist

muscle relaxing

muscles you need to know

• Head and neck: 4
• Upper extremities: 7
• Trunk: 4
• Lower extremities: 9
• Total: 24 muscles 

muscle contracting

• Impulse sent from a motor neuron
• Chemical changes in cell cause Ca+ to be released
• Calcium forms bridges between protein filaments
• Assists in myosin and actin sliding together
• Shortened filaments cause muscle to shorten (contract)

characteristics of muscles

Excitability: The ability to respond to certain stimuli by producing electrical signals called impulses

Contractility:

• When a muscle shortens or contracts, it bring the attached points closer together
• No other body tissue has this quality

Extensibility: A muscle’s ability to be stretched

Elasticity: The muscle’s ability to return to its original length when relaxing

Aerobic

• Oxygen is needed for glucose to be converted into energy

• Slow twitch fibers: fatigue resistant, muscles for endurance

• Ex. jogging

Anaerobic

• During periods of vigorous exercise, blood is unable to transport enough oxygen
• Switch to anaerobic mode
• Fast twitch fibers: easily fatigued
• Ex. weightlifting, sprinting 

glycogen

extra glucose stored in cells, and stored in liver and muscles

ATP

adenosine triphosphate, compound found in muscle cell, need oxygen and glucose to make ATP

ADP

adenosine diphosphate: stored chemical potential energy

lactic acid

• by product of cell metabolism, build up causes muscle fatigue and cramps

• Rest, oxygen will change this back to glucose

• Increase resting rate until O2 debt is paid back

sprains

a stretch, tear or rip in the ligament or joint capsule

strains

a stretch, tear or rip in the muscle belly or tendon

Tendonitis

• Acutely inflamed without microscopic tears. Often related to chronic overuse, repetitive motion, or untreated acute injuries
• Some tendons prone to tendonitis (a degenerative breakdown, scarring or tear of the tendons): Rotator cuff, Achilles tendon, Tibialis posterior tendon, Tendons of the lateral elbow

tennis elbow

inflammation and wearing of the tendon that connects the extensor muscle to the lateral elbow

rotator cuff

inflammation of the groups of tendons that fuse together and surround the shoulder joint

shin splints

• Pulling and tugging of muscles and connective tissue at the insertion site on the tibia
• Can be treated with rest, reduction of exercise intensity, ice, anti-inflammatory medication, and modification of footwear
• Avoid running up hills and on hard surfaces

contractures

• Permanent tightening of muscle, tendons, ligaments or skin that prevents normal movement of the body part
• May also be due to atrophy of muscle, disease process, stroke, burns, dehydration, electrolyte imbalance
• Diagnosis: physical exam, patient history, blood tests, imaging
• Can cause deformity

Tetanus

• Caused by a wound infection with clostridium tetani (lives in the soil)
• Also known as “lockjaw” because symptoms usually begin in the jaw, progresses over time
• Rigid paralysis, stiffness, pain
• Diaphragm may become paralyzed
• Prevention is by vaccination, can give IV tetanus antitoxin
• May have long term problems

Hernia

• An organ protruding through a weak muscle
• Abdominal: weakened abdominal muscle wall, intestine protrudes
• Inguinal: protrusions of abdominal cavity through the inguinal canal
• Hiatal: stomach pushes through the diaphragm

myasthenia gravis

• “Grave Muscle Weakness” 
• Autoimmune disease, no cure
• Antibodies destroy the connection between the nerve cell and muscle cell
• Effects skeletal muscles, begins from the head and neck and progresses down
• Characterized by periods of exacerbation and remission

muscle dystrophy

• Group of inherited disease (30 types)
• Mutations in genes interfere with the production of proteins needed to form healthy muscle
• Cause progressive weakness and disability (most forms begin in childhood)
• Muscles atrophy (atrophy mean waste away)
• May result in disability and death, may include trouble breathing or swallowing

muscles of the head and neck

Control human facial expression

Frontalis: forehead

Orbicularis oculi: surround eye orbits

Orbicularis oris: surrounds mouth 

Sternocleidomastoid: down sides of neck

muscles of upper extremities

• Help move shoulder, arm, forearm, wrist, hand, and fingers 
• Trapezius, Deltoid, Pectoralis major, Biceps brachii, Triceps brachii, Brachioradialis, Extensor carpi radialis longus

muscles of the trunk

• Control breathing and movement of the abdomen and pelvis
• Teres major, Latissimus dorsi, External abdominal obliques, Rectus abdominis

muscles of the lower extremities

• Assist in the movement of thigh, leg, ankle, foot, and toes
• Gluteus maximus, Gracilis, Biceps femoris, Tensor fascia lata, Pectineus, Sartorius, Rectus femoris, Tibialis anterior, Gastrocnemius