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