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THE MUSCULAR SYSTEM CHAPTER 5
MUSCULAR SYSTEM • Only tissue capable of shortening or
contracting
• Responsible for both powerful and graceful
movements
• Control movements of eyes, food, and heart
• Three categories of muscle fibers
• Skeletal
• Smooth
• cardiac
SKELETAL MUSCLE
• Striated muscle
• Voluntary
• Attach to bones
• Individual cell is referred
to as muscle fiber
• Genetically determined
• Growth with age
SKELETAL MUSCLE
• Highly organized
• Sarcolemma – cell membrane
• Endomysium – protective sheath
• Perimysium – strong fibrous membrane
• Fascicle – unit
• Epimysium – thick, tough connective tissue
SMOOTH MUSCLE
• Also known as visceral muscle
• Small
• Spindle shaped
• Non-striated
• Involuntary
• Single nucleus
• Found in internal organs such as: • Stomach
• Intestines
• Respiratory passageways
• bladder
SMOOTH MUSCLE
• Arranged in layers
• One layer runs lengthwise
• Other surrounds the organ in which the muscles
are contained
• Moving food through the digestive system
• Emptying the bladder
• Changing diameter of blood vessels
• Can sustain contraction for long periods of time
CARDIAC MUSCLE
• Solely in walls of heart
• Branched
• Cross-striated
• Involuntary
• Arranged in spiral shaped bundles
• Joined at structures called intercalated discs
• Enables simultaneous contractions of
neighboring cells to produce heartbeat
BEHAVIORAL PROPERTIES
• Irritability
• Ability to respond to a stimulus
• Extensibility
• Ability to be stretched
• Elasticity
• Ability to return to normal length after stretch
• Contractility
• The ability to contract or shorten
TENSION
• Contraction – implies shortening
• We usually use this term when tension has
developed in a muscle
• However, one of three actions can happen:
• Muscle can shorten
• Muscle can remain the same length
• Muscle can lengthen
TENSION • Concentric
• Shortening contraction
• Eccentric
• Lengthening contraction
• Isometric
• Contraction where no change occurs
• Agonist
• Muscle that is the prime mover
• Antagonist
• Opposing muscle group
THE MOTOR UNIT
• Muscle can’t develop tension unless stimulated
by nerves
• Motor neuron: nerve that stimulates skeletal
muscle
• Motor unit: single motor neuron and all of the
muscle cells it stimulates
• Considered to be the functional unit of the
neuromuscular system
ACTION POTENTIALS • Axon: connects the motor neuron cell body with
the muscle fibers in a motor unit
• Axon terminals: axon branches into axon
terminals which branch out to individual muscle
fibers
• Neuromuscular Junction: link between axon
terminal and muscle fiber
• Synaptic Cleft: gap between axon terminal and
muscle fiber
ACTION POTENTIALS • Acetylcholine: neurotransmitter than stimulates
muscles
• Makes sarcolemma temporarily permeable
• Channels open that allow Na+ ions to invade the
muscle fiber, as K+ ions rush out
• More Na+ enters than K+ exits = positive charge
• Depolarization: reversal of electrical charge
• Triggers opening of additional channels in fiber
membrane that only allow Na+ to enter
• This generates an electrical charge called an ACTION
POTENTIAL
• https://www.youtube.com/watch?v=WrV510gUlco
SARCOMERE CONTRACTION
• Glycogen provides the energy for creating action
potentials
• Phosphocreatine in the cell enables transfer of
energy to protein filaments actin and myosin
• Sarcomeres release Ca+ ions which results in a
contraction
SKELETAL FIBER TYPES
• Skeletal muscle fibers may play a big role in
which sports people excel in
• Slow-twitch
• Contract slowly
• Fast-twitch
• Type IIa – speed between slow and type IIb
• Type IIb – 1/7 the time required for slow twitch,
however they fatigue much faster
FIBER ARCHITECHTURE
• Way fibers are arranged within the muscle
• Two major types
• Parallel
• Pennate
PARALLEL MUSCLE FIBER
• Run largely parallel in length
• Result in 3 shapes
• Fusiform
• Bundled
• Triangular
PENNANTE FIBER
• Unipennate
• Aligned in one direction to a
central tendon
• Bipennate
• Attach to a central tendon
• Multipennate
• Attach to a central tendon in
more than two directions
STRENGTH, ENDURANCE, POWER
• Muscular Strength
• Impossible to measure
• Multiple muscle groups move a certain amount of resistance
• Amount of torque joints can make
• Muscular Power
• Force x velocity
• Based on resistance moved and speed
• Muscular Endurance
• Ability of muscle to produce tension over a period of time
DIRECTIONAL MOVEMENTS
• Origin: end of muscle
that attached to fixed
structure
• Insertion: end of muscle
that attaches to bone that
typically moves
• Ex.
• Brachialis muscle
MUSCLES OF HEAD & NECK
MUSCLES OF THE TRUNK
MUSCLES OF THE TRUNK
MUSCLES OF UPPER LIMB
MUSCLES OF LOWER LIMB
MUSCLE INJURIES
• Muscle Strain: when a muscle is stretched beyond its usual limits
• Grade I
• Mild, tightness in the muscle the day after
• Grade II
• Moderate, pain from a partial tear in the muscle
• Grade II
• Severe, tearing of the muscle, loss of function, internal bleeding, and swelling
MUSCLE INJURIES • Contusion: bruise or bleeding within the
muscle resulting from an impact
• Ex. Head injuries in football players
• Myositis Ossificans: occurs when an injured
muscle is repeatedly struck
• Involves the formation of a calcium mass within the
muscle
• After 6-7 weeks the mass is resorbed by the body
• In some cases a bony lesion can remain in the
muscle
MUSCLE INJURIES
• Tendinitis: inflammation of a tendon usually causing
pain and swelling
• Acute and overuse injuries
• Can occur with aging as elasticity decreases
• Can occur in any part of the body
• Tendinosis: degeneration of a tendon
• Caused by mircotears in the tendon
• Increases likelihood of rupture
• Recovery – months to years of minimal use
• No inflammation
MUSCLE INJURIES • Rotational injuries of the shoulder
• Repetitions of forceful overhead
motions
• Throwing, spiking a volleyball, tennis
serve
• Swimmer’s Shoulder
• Improper motion mechanics contribute
to inflammation or tears of muscle and
surrounding tendons
• Treatment: ice, rest, possible surgical
repair
MUSCLE INJURIES • Overuse injuries to the elbow:
inflammation and sometimes microtearing of muscle tendons that cross the lateral and medial side of the elbow.
• If left untreated the condition can worsen leading to swelling and scarring of the tendons near the elbow
• Tennis Elbow: lateral epicondylitis
• Little Leaguer’s Elbow: medial epicondylitis
MUSCLE INJURIES
• Shin Splints: localized pain in the
medial lower leg
• Overuse injury that typically arises from
running or dancing on a hard surface
• Believed to be microdamage to the muscle
tendons that attach to the tibia or
inflammation of the periosteum of the tibia
• Treatment
• Stop activity
• Ice
• Stretch achilles and calf
• Wear proper shoes
MUSCLE DISORDERS • Muscular Dystrophy: progressively worsening
muscle weakness and loss of muscle tissue
• May occur in childhood or adulthood
• Some forms affect a certain muscle group, others affect all muscles
• Symptoms
• Intellectual disability
• Delayed development of motor skills
• Frequent falling
• Drooling
• Drooping of eyelids
MUSCLE DISORDERS
• Hernia: balloon-like section of the
abdominal cavity lining that
protrudes through a whole or
weakened section of the muscle in
the abdomen
• Can be caused by heavy lifting or by any
activity that increase pressure inside the
abdominal cavity
• Most produce no symptoms, some cause
discomfort or pain that intensifies with
heavy lifting or other activities that
produce abdominal strain