The Muscular System The Muscular System

Anatomy & Physiology IChapter 8

Types of MuscleTypes of Muscle

SmoothCardiacSkeletal

Smooth MuscleSmooth MuscleMakes up walls of hollow body organs (digestive tract, blood vessel wall), respiratory passageways, uterus, irisInvoluntary movementCell structure

◦Tapered ends

◦Single, central nucleus

◦No visible bands (striations)

Stimulated by nerve impulses, hormones, stretching

Cardiac MuscleCardiac MuscleMakes up wall of heartInvoluntary movementCell structure

◦Branching interconnections◦Single, central nucleus◦Striated◦Membranes are intercalated disks

Stimulated by electrical impulses, nervous stimuli, hormones

Skeletal MuscleSkeletal MuscleAttached to bones, muscles, or skinVoluntary movementCell structure

◦Long and cylindrical◦Multiple nuclei per cell◦Heavily striated

Stimulated by nervous systemNumber of individual skeletal muscles in the body: 600+

The Muscular SystemThe Muscular System

Skeletal muscle has three primary functions Skeletal movement Posture maintenance

◦ muscles provided a steady partial contraction (muscle tone) of muscles of the thigh, abdomin, back, neck and shoulders

Heat generation ◦ heat is a natural by-product of muscle cell metabolism

Structure of a MuscleStructure of a MuscleMuscle Fiber - one muscle cellFascicles - bundles of muscle fibers

Structure of a Muscle: Structure of a Muscle: Connective Tissue Connective Tissue ComponentsComponentsEndomysium – deep layer of connective tissue surrounding indvidual muscle fibersPerimysium – connective tissue surrounding each fascicleEpimysium (deep fascia) – connective tissue sheath enclosing an entire musclethe endomysium, perimysium and epimysium merge to form tendonsTendon – the band of connective tissue that connect muscle to bone

SarcoplasmSarcolemma

Openings intotransverse tubules

Sarcoplasmicreticulum

Mitochondria

Myofibrils

Myofilaments

A band

I band

Z disc

Nucleus

Triad:Terminal cisternaeTransverse tubule

Musclefiber

Structure of a Skeletal Structure of a Skeletal Muscle FiberMuscle Fiber

(A)Structure of a muscle showing the tendon that attaches it to a bone.

(B)Muscle tissue seen under a microscope. Portions of several fascicles are shown with connective tissue coverings.

ZOOMING IN • What is the innermost layer of connective tissue in a muscle? • What layer of connective tissue surrounds a fascicle of muscle fibers?

Structure Of A Skeletal MuscleStructure Of A Skeletal Muscle

Muscle Cells in ActionMuscle Cells in ActionMotor unit is a single neuron and all the muscle fibers it

Skeletal muscle contraction requires stimulation by a neuron

◦Paralysis occurs when the damaged nervous system can’t get a signal to the muscles

Neuromuscular junction (NMJ) – the point of contact between a nerve fiber (axon) and a muscle fiber.

Neuromuscular Junction Neuromuscular Junction (NMJ)(NMJ)Neurotransmitter – chemical released

from neurons◦ Acetylcholine (Ach) is the neurotransmitter

released at the NMJ Synaptic cleft – tiny space between

two cells involved in a synapseReceptors – specialized structures

(on the muscle cell membranes) that can be excited by a stimulus

Motor end plate – muscle cell membrane that contains receptors

(A)The branched end of a motor neuron makes contact with the membrane of a muscle fiber (cell).

(B)Enlarged view of the NMJ showing release of neurotransmitter acetylcholine (Ach) into the synaptic cleft.

(C)Acetylcholine attaches to receptors in the motor end plate, whose folds increase surface area.

(D)Electron microscope photograph of the neuromuscular junction.

Neuromuscular Junction Neuromuscular Junction (NMJ)(NMJ)

Properties of Muscle TissueProperties of Muscle TissueExcitability (ability to respond to stimuli)

◦Action potential – spreading wave of electrical current

Contractility (ability to shorten when stimulated)

◦Actin – thin protein filament in muscle cells (light)

◦Myosin – thick protein filament in muscle cells (dark) Striations result from the alternating bundles of actin

(light) and myosin (dark) filaments Crossbridge – attachment between myosin head and

actin

◦Sarcomere – contracting subunit of skeletal muscle

(A)Muscle is relaxed and there is no contact between the actin and myosin filaments.

(B)Cross-bridges form and the actin filaments are moved closer together as the muscle fiber contracts.

(C)The cross-bridges return to their original position and attach to new sites to prepare for another pull on the actin filaments and further contraction. 

 ZOOMING IN • Do the actin or myosin filaments change in length as contraction proceeds?

Sliding Filament Mechanism of Sliding Filament Mechanism of Skeletal Muscle ContractionSkeletal Muscle Contraction

The Role of CalciumThe Role of CalciumCalcium

Is released when nerve fiber stimulates muscle cell

Attaches to proteins blocking receptor sites

Allows cross-bridges to form between actin and myosin

Returns to endoplasmic reticulum (ER), which is called “sarcoplasmic reticulum” in muscle cells.

Energy SourcesEnergy SourcesMuscle contraction requires energy (ATP), oxidized in muscle cells fromOxygenGlucose or other usable nutrient

Compounds in muscle cells that store oxygen, energy, or nutrients Myoglobin – stores oxygenGlycogen – stores glucoseCreatine phosphate – stores energy; can be used to make ATP

Oxygen ConsumptionOxygen ConsumptionAerobic glucose metabolism – cellular production of ATP in the presence of adequate oxygenAnaerobic glucose metabolism – cellular production of ATP in the presence of low, inadequate oxygen

◦Inefficient production of ATP◦Lactic acid accumulation◦Oxygen debt – rapid breathing after

exercise; replenishes oxygen stores; rid cells of lactic acid

◦Recovery oxygen consumption – the period after exercise when extra oxygen is needed

Effects of ExerciseEffects of ExerciseImproved balance, joint flexibilityIncrease in muscle size (hypertrophy)Improvements in muscle tissueVasodilationStrengthened heart muscleImproved breathing and respiratory efficiencyWeight controlStronger bones

Types of Muscle Types of Muscle ContractionsContractions

Muscle Tone (Tonus) – the normal state of balanced tension or partial contraction while a muscle is in a passive state; constant state of readiness for actionIsotonic ◦No change in tension ◦Muscle length shortens ◦Movement

Isometric◦Great increase in tension◦Muscle length unchanged◦No movement

Muscle shortens,tension remains

constant

Movement

Movement

Muscle developstension but does

not shorten

No movement

Muscle lengthenswhile maintaining

tension

(a) Isometric contraction (b) Isotonic concentric contraction (c) Isotonic eccentric contraction

Isometric and Isotonic ContractionsIsometric and Isotonic Contractions

The Mechanics of Muscle The Mechanics of Muscle MovementMovement

Tendons attach muscles to bonesOrigin—attached to more fixed part of skeletonInsertion—attached to more moveable part of skeleton

Muscle Origins and Muscle Origins and InsertionsInsertions

Origin◦ bony attachment at

stationary end of muscle

Belly◦ thicker, middle region

of muscle between origin and insertion

Insertion◦ bony attachment to

mobile end of muscle

Scapula

Bellies

RadiusInsertion

Humerus

UlnaInsertion

Origins Origins

Long head

Extensors:

Lateral head

Flexors:Biceps brachii

Brachialis

Triceps brachii

action – the effects produced by a muscle

◦to produce or prevent movement prime mover (agonist) - muscle that

produces most of force during a joint actionsynergist - muscle that aids the prime

mover

◦stabilizes the nearby joint

◦modifies the direction of movement antagonist - opposes the prime mover

◦preventing excessive movement and injury

Muscles Work TogetherMuscles Work TogetherMuscles Work TogetherMuscles Work Together

Muscle Actions Across Muscle Actions Across ElbowElbow

prime mover

- brachialissynergist

- biceps brachii

antagonist - triceps brachii

Scapula

Bellies

RadiusInsertion

Humerus

UlnaInsertion

Origins Origins

Extensors:

Lateral head

Flexors:Biceps brachii

BrachialisLong headTriceps brachii

Skeletal Muscle GroupsSkeletal Muscle Groups

Characteristics for naming muscles (often combined)LocationSizeShapeDirection of fibersNumber of heads (attachment points)Action

Associated structure is labeled in parentheses.

Superficial Muscles Superficial Muscles (anterior view)(anterior view)

Associated structures are labeled in parentheses.

Superficial Muscles (posterior Superficial Muscles (posterior view)view)

Muscles of the HeadMuscles of the Head

Facial expression (orbicularis) muscles◦Orbicularis oculi◦Orbicularis oris◦Levator palpebrae superioris◦Buccinator

Mastication (chewing) muscles◦Temporalis ◦Masseter ◦Intrinsic ◦Extrinsic

Associated structure is labeled in parentheses.  ZOOMING IN • Which of the muscles in this illustration is named for a bone it is near?

Muscles of the Muscles of the Head Head

Muscles of the NeckMuscles of the Neck

Are ribbonlikeExtend up, down, or obliquelyExtend in several layers in a complex mannerMost common is sternocleidomastoid

Muscles of the Upper Muscles of the Upper ExtremitiesExtremitiesPosition the shoulderMove the armMove the forearm and hand

Muscles That Move the Muscles That Move the Shoulder and ArmShoulder and Arm

TrapeziusLatissimus dorsiPectoralis majorSerratus anteriorDeltoidRotator cuff

◦Supraspinatus◦Infraspinatus◦Teres minor◦Subscapularis

Muscles That Move the Muscles That Move the Forearm and HandForearm and HandBrachialisBiceps brachiiBrachioradialisTriceps brachiiFlexor carpiExtensor carpiFlexor digitorumExtensor digitorum

Muscles That Move The Forearm & HandMuscles That Move The Forearm & Hand

Muscles of the TrunkMuscles of the Trunk

Breathing muscles

Abdominal muscles

Pelvic floor muscles

Deep back muscles

Muscles of RespirationMuscles of Respiration

DiaphragmIntercostal muscles

Associated structures are also shown.

Muscles of Muscles of Respiration Respiration

Muscles of the Abdomen Muscles of the Abdomen and Pelvisand Pelvis

External obliqueInternal obliqueTransversus abdominisRectus abdominisLevator ani

Surface tissue is removed on the right side to show deeper muscles.

Associated structures are labeled in parentheses.

Muscles of the abdominal Muscles of the abdominal wallwall

Associated structures are labeled in parentheses.

Muscles of the female perineum (pelvic floor)Muscles of the female perineum (pelvic floor)

Deep Muscles of the BackDeep Muscles of the Back

Erector spinaeDeeper muscles in the lumbar area

Muscles of the Lower Muscles of the Lower ExtremitiesExtremities

Among the longest and strongest in the bodySpecialized for locomotion and balance

Muscles That Move the Thigh Muscles That Move the Thigh and Legand Leg

Gluteus maximusGluteus mediusIliopsoasAdductorsSartoriusIliotibial (IT) tractHamstrings

Associated structures are labeled in parentheses.

Muscles of the ThighMuscles of the Thigh

Muscles That Move the Muscles That Move the FootFootGastrocnemius

Achilles tendon

Soleus

Tibialis anterior

Peroneus longus

Flexor and extensor muscles

Associated structures are labeled in parentheses

Muscles That Move The FootMuscles That Move The Foot

Effects of Aging on MusclesEffects of Aging on Muscles

Beginning at about age 40

Gradual loss of muscle cells

Loss of power

Tendency to flex hips and knees

Decrease in height

Muscular DisordersMuscular Disorders

Spasms

◦Colic

◦Seizure or convulsion

Cramps

Strains

Sprains

Atrophy

Diseases of MusclesDiseases of MusclesMuscular dystrophy

Myasthenia gravis

Myalgia

Myositis

Fibrositis

Fibromyositis

Fibromyalgia syndrome (FMS)

Disorders of Associated Disorders of Associated StructuresStructuresBursitis – inflammation of a bursa

Bunions - unnatural, bony hump that forms at the base of the big toe

Tendinitis - inflammation in or around a tendon

Tenosynovitis – inflammation of the lubricating sheath surrounding tendons.

Shin Splints – pain most likely caused by repeated stress on the shin bone (tibia) and the tissue that connects the muscle to the tibia.

Carpal tunnel syndrome - caused by compression of peripheral nerves affecting one or both hands. C

haracterized by a sensation of numbness, tingling, burning and/or pain in the hand and wrist

End of PresentationEnd of Presentation