unit 5 – muscular system alireza ashraf, m.d. professor of physical medicine & rehabilitation...

UNIT 5 – MUSCULAR SYSTEMUNIT 5 – MUSCULAR SYSTEM

Alireza Ashraf, M.D.Professor of Physical Medicine & Rehabilitation

Shiraz Medical school

MUSCLE TYPESMUSCLE TYPES

Cardiac muscleCardiac muscle – found only in the – found only in the heart, striated, involuntary, heart, striated, involuntary, arranged in figure-8 shaped arranged in figure-8 shaped bundles (for contraction), bundles (for contraction), intercalated disksintercalated disks

Smooth muscleSmooth muscle – visceral (hollow – visceral (hollow organs), non-striated, involuntary, organs), non-striated, involuntary, arranged in sheets or layers arranged in sheets or layers (contract – change shape of (contract – change shape of organ)organ)

Skeletal muscleSkeletal muscle – where muscle – where muscle connects to bone for movement, connects to bone for movement, striated, voluntarystriated, voluntary

SKELETAL MUSCLE ANATOMYSKELETAL MUSCLE ANATOMY

EndomysiumEndomysium – delicate – delicate connective tissue sheeth that connective tissue sheeth that encloses each muscle fiberencloses each muscle fiber

FasciculusFasciculus – bundle of muscle – bundle of muscle fibers covered by fibers covered by perimysiumperimysium (coarser fibrous membrane)(coarser fibrous membrane)

EpimysiumEpimysium – covers bundle of – covers bundle of fasciculi (entire muscle); fasciculi (entire muscle); blends into either:blends into either:– TendonTendon – cord of dense, – cord of dense,

fibrous tissue attaching a fibrous tissue attaching a muscle to a bonemuscle to a bone

– AponeurosisAponeurosis – fibrous or – fibrous or membranous sheet membranous sheet connecting a muscle and connecting a muscle and the part is moves (usually the part is moves (usually found on torso)found on torso)

MUSCLE FUNCTIONSMUSCLE FUNCTIONS

Produce movementProduce movement Maintains postureMaintains posture Stabilizes jointsStabilizes joints Generates heatGenerates heat

MICROSCOPIC ANATOMY OF SKELETAL MUSCLEMICROSCOPIC ANATOMY OF SKELETAL MUSCLE

Sarcolemma Sarcolemma – plasma membrane of muscle fiber (cell); – plasma membrane of muscle fiber (cell); under the under the endomysiumendomysium

Peripheral nucleiPeripheral nuclei – nuclei are pushed aside by long ribbon-like – nuclei are pushed aside by long ribbon-like organelles called myofibrils – contain trains of tiny contractile organelles called myofibrils – contain trains of tiny contractile units called units called sarcomeressarcomeres

2 types of myofilaments in the sarcomeres:2 types of myofilaments in the sarcomeres:– 1. 1. myosinmyosin filaments – thick filaments – thick– 2. 2. actinactin filaments – thin filaments – thin– Their arrangement produces a banding pattern, or Their arrangement produces a banding pattern, or striationsstriations

SKELETAL MUSCLE ACTIVITYSKELETAL MUSCLE ACTIVITY Stimulation and contraction of single skeletal muscle cells:Stimulation and contraction of single skeletal muscle cells:

– IrritabilityIrritability – the ability to receive and respond to a stimulus – the ability to receive and respond to a stimulus– ContractilityContractility – the ability to shorten (forcibly) when an adequate – the ability to shorten (forcibly) when an adequate

stimulus is receivedstimulus is received– Nerve stimulus and action potential – one motor neuron may Nerve stimulus and action potential – one motor neuron may

stimulate a few muscle cells or hundreds of them, depending on stimulate a few muscle cells or hundreds of them, depending on the particular muscle and the work it does (gross motor vs. fine the particular muscle and the work it does (gross motor vs. fine motor)motor)

Motor unitMotor unit – one neuron and all the skeletal muscle cells it – one neuron and all the skeletal muscle cells it stimulatesstimulates

Neuromuscular junctionNeuromuscular junction – where the axon terminals for – where the axon terminals for junctions with the sarcolemmajunctions with the sarcolemma

When the nerve impulse reaches the axon terminals, a When the nerve impulse reaches the axon terminals, a neurotransmitterneurotransmitter is released, which travels across the is released, which travels across the synaptic cleftsynaptic cleft (gap between nerve & muscle); (gap between nerve & muscle); acetylcholine acetylcholine (Ach)(Ach) – neurotransmitter that stimulates skeletal muscle – neurotransmitter that stimulates skeletal muscle

Ach attaches to receptors which makes the membrane more Ach attaches to receptors which makes the membrane more permeable to permeable to NaNa++

NaNa+ + diffuses in and Kdiffuses in and K+ + rushes out, generating an rushes out, generating an action action potentialpotential (electrical impulse), which travels over the entire (electrical impulse), which travels over the entire surface of the sarcolemmasurface of the sarcolemma

Muscle cell contractsMuscle cell contracts ACH is removed by ACH is removed by acetylcholinesteraseacetylcholinesterase to stop contraction to stop contraction

SKELETAL MUSCLE ACTIVITYSKELETAL MUSCLE ACTIVITY

steps of the action potential Mechanism of muscle contraction: Mechanism of muscle contraction: Sliding Filament TheorySliding Filament Theory

– AP travels down AP travels down T-tubulesT-tubules, which causes , which causes Ca2+Ca2+ to be released to be released from the lateral sacs of the from the lateral sacs of the sarcoplasmic reticulumsarcoplasmic reticulum

– Ca2+ binds to Ca2+ binds to tropinintropinin, causing , causing tropomyosintropomyosin to move out of to move out of the way – exposing the the way – exposing the active siteactive site on the actin filament on the actin filament

– Myosin heads swing back and attach to the active site on actin, Myosin heads swing back and attach to the active site on actin, forming forming cross-bridgescross-bridges

– Myosin heads perform a Myosin heads perform a power strokepower stroke – move toward the – move toward the center of the center of the sarcomeresarcomere

– Pulling actin filaments towards the center of the Pulling actin filaments towards the center of the sarcomeresarcomere– ATP is broken down to provide energy for the myosin heads to ATP is broken down to provide energy for the myosin heads to

releaserelease the active site; leftover energy is stored for the next the active site; leftover energy is stored for the next power strokepower stroke

– Myosin heads grab further & further back each timeMyosin heads grab further & further back each time– Whole muscle shortensWhole muscle shortens– Whole series of events takes few thousands of a secondWhole series of events takes few thousands of a second

SKELETAL MUSCLE ACTIVITYSKELETAL MUSCLE ACTIVITY

muscle contraction video Contraction of skeletal muscle as a wholeContraction of skeletal muscle as a whole

– Graded responsesGraded responses All-or-none law – All-or-none law – a muscle cell will contract to its fullest a muscle cell will contract to its fullest

extent when it is stimulated adequately; it never partially extent when it is stimulated adequately; it never partially contracts; is true of muscle cells only (not whole muscle)contracts; is true of muscle cells only (not whole muscle)

Muscle cells react to stimuli with graded responses or Muscle cells react to stimuli with graded responses or different degrees of shorteningdifferent degrees of shortening

Can be produced 2 ways:Can be produced 2 ways:– 1. 1. By changing frequency of muscle stimulationBy changing frequency of muscle stimulation

A single, brief, jerky contraction – A single, brief, jerky contraction – muscle twitchmuscle twitch Nerve impulses are delivered to the muscle at a Nerve impulses are delivered to the muscle at a

very rapid rate, so rapid that muscle does not get a very rapid rate, so rapid that muscle does not get a chance to relax completely between stimuli; as a chance to relax completely between stimuli; as a result, the effects of the successive contractions result, the effects of the successive contractions are “are “summedsummed” (added) together and contraction ” (added) together and contraction gets “gets “stronger and smootherstronger and smoother,” with no evidence to ,” with no evidence to relaxation seen – muscle is in relaxation seen – muscle is in fusedfused, or , or completecomplete, , tetanustetanus, or , or tetanic contractionstetanic contractions (tetanus is normal (tetanus is normal and desirable, not to be confused with and desirable, not to be confused with tetanus/lockjaw, which is caused by bacterium)tetanus/lockjaw, which is caused by bacterium)

SKELETAL MUSCLE ACTIVITY (CONT.)SKELETAL MUSCLE ACTIVITY (CONT.)

– 2. by changing number of muscle cells being stimulated2. by changing number of muscle cells being stimulated How forcefully a muscle contracts depends largely on How forcefully a muscle contracts depends largely on

the number of muscle cells stimulated; when only a the number of muscle cells stimulated; when only a few cells are stimulated, contractions will be few cells are stimulated, contractions will be slightslight; ; when all cells are stimulated, contraction is when all cells are stimulated, contraction is strongstrong

– Providing energy for muscle contraction – as muscle contracts, Providing energy for muscle contraction – as muscle contracts, ATP is broken down for energy; muscles stre a limited supply (4-ATP is broken down for energy; muscles stre a limited supply (4-6 seconds worth), so it must be regenerated continuously. 6 seconds worth), so it must be regenerated continuously. Working muscles use 3 pathways for ATP regeneration:Working muscles use 3 pathways for ATP regeneration:

1. Direct phosphorylation of ADP by creatine phosphate:1. Direct phosphorylation of ADP by creatine phosphate: a a phosphate group transfers from CP to ADP, regenerating phosphate group transfers from CP to ADP, regenerating more ATP; CP supplies exhaust in about 20 secondsmore ATP; CP supplies exhaust in about 20 seconds

2. Aerobic respiration:2. Aerobic respiration: provides 95% of ATP at rest and provides 95% of ATP at rest and during light exercise; occurs in mitochondria & involves a during light exercise; occurs in mitochondria & involves a series of metabolic pathways that use oxygen – called series of metabolic pathways that use oxygen – called oxidative phosphorylation; glucose is broken down into CO2 oxidative phosphorylation; glucose is broken down into CO2 & H2O; some released energy is captured in ATP bonds (get & H2O; some released energy is captured in ATP bonds (get 36ATP/1 glucose)36ATP/1 glucose)

3. Anaerobic glycolysis and lactic acid formation:3. Anaerobic glycolysis and lactic acid formation: initial steps initial steps of glucose breakdown occur via of glucose breakdown occur via glycolysisglycolysis which is anaerobic. which is anaerobic.

– Glucose Glucose pyruvic acid with energy captured in ATP pyruvic acid with energy captured in ATP bonds (2ATP/ 1 glucose)bonds (2ATP/ 1 glucose)


– If enough oxygen is present, If enough oxygen is present, pyruvic acid enters pyruvic acid enters aerobic pathways that occur within mitochondriaaerobic pathways that occur within mitochondria

– If there is not enough oxygen present (i.e. – intense If there is not enough oxygen present (i.e. – intense muscle activity), or if oxygen or glucose delivery is muscle activity), or if oxygen or glucose delivery is inadequate, inadequate, pyruvic acid is converted to lactic acid in a pyruvic acid is converted to lactic acid in a process called anaerobic glycolysisprocess called anaerobic glycolysis

Lactic acidLactic acid - causes muscle soreness and fatigue - causes muscle soreness and fatigue (muscle fatigue occurs when the muscle can no (muscle fatigue occurs when the muscle can no longer contract despite still being stimulated). longer contract despite still being stimulated). It It results from oxygen debt which must be “paid results from oxygen debt which must be “paid back” (taking deep breaths)back” (taking deep breaths)

– Isotonic vs. isometric contraction:Isotonic vs. isometric contraction: Isotonic contractions – Isotonic contractions – when myofilaments are successful in when myofilaments are successful in

sliding movements so muscle shortens during contraction; sliding movements so muscle shortens during contraction; most familiar type (i.e. – smiling, bending at knee)most familiar type (i.e. – smiling, bending at knee)

Isometric contractions – Isometric contractions – when muscles do not shorten b/c when muscles do not shorten b/c muscles are pitted against some more or less immovable muscles are pitted against some more or less immovable object, but tension keeps building (i.e. – lifting a dresser, object, but tension keeps building (i.e. – lifting a dresser, pushing arms against a wall)pushing arms against a wall)

– Muscle tone – Muscle tone – state of continuous partial contractionstate of continuous partial contraction


Effect of Exercise on Muscles:Effect of Exercise on Muscles:– Aerobic or endurance exerciseAerobic or endurance exercise

Examples – biking, jogging, swimming lapsExamples – biking, jogging, swimming laps Results in stronger more flexible muscles with greater Results in stronger more flexible muscles with greater

resistance to fatigue resistance to fatigue blood supply increases blood supply increases individual muscle cells form more mitochondria and store individual muscle cells form more mitochondria and store

more oxygen (makes overall body metabolism more more oxygen (makes overall body metabolism more efficientefficient

Improves digestion and elimination of wastesImproves digestion and elimination of wastes Enhances neuromuscular coordinationEnhances neuromuscular coordination Makes the skeleton strongerMakes the skeleton stronger Heart enlargesHeart enlarges Fat deposits are cleared from blood vessel wallsFat deposits are cleared from blood vessel walls Lungs become more efficient at gas exchangeLungs become more efficient at gas exchange Does Does NOTNOT cause muscles to increase in size cause muscles to increase in size


Effects of Exercise on Muscles:Effects of Exercise on Muscles:– Resistance or isometric exerciseResistance or isometric exercise

Examples – weightlifting, theraband or medicine ball Examples – weightlifting, theraband or medicine ball training, bodyweight exercises like push-ups or pull-ups, training, bodyweight exercises like push-ups or pull-ups, plyometricsplyometrics

Key is that muscles are being forced to contract with as Key is that muscles are being forced to contract with as much force as possible or as quickly as possiblemuch force as possible or as quickly as possible

Muscles increase in size and strengthMuscles increase in size and strength– Due to enlargement of individual muscle cells (more Due to enlargement of individual muscle cells (more

contractile filaments), not because more muscle fibers contractile filaments), not because more muscle fibers are madeare made

– Size of reinforcing connective tissue also increases to Size of reinforcing connective tissue also increases to support increased muscle sizesupport increased muscle size

SKELETAL MUSCLE ACTIVITY (CONT.)SKELETAL MUSCLE ACTIVITY (CONT.) Attached Parts of a Muscle:Attached Parts of a Muscle:

– OriginOrigin – part of the muscle – part of the muscle attached to the immovable or attached to the immovable or less movable boneless movable bone

– InsertionInsertion – part attached to – part attached to the movable bone; insertion the movable bone; insertion moves toward the originmoves toward the origin

Types of Muscle Movement:Types of Muscle Movement:– FlexionFlexion – decrease angle of a – decrease angle of a

joint (hinge joints – knee & joint (hinge joints – knee & elbow)elbow)

– ExtensionExtension – increases angle of – increases angle of a joint (straighten knee or a joint (straighten knee or elbow)elbow)

– RotationRotation – movement of a – movement of a bone around its longitudinal bone around its longitudinal axis (ball & socket joints – axis (ball & socket joints – shaking your head “no”)shaking your head “no”)


– AbductionAbduction – moving a limb – moving a limb away from the midline away from the midline (raising arm or leg out to (raising arm or leg out to the side)the side)

– AdductionAdduction – moving a limb – moving a limb toward the midline toward the midline (lowering arm or leg from (lowering arm or leg from the side back down to the the side back down to the body)body)

– CircumductionCircumduction – proximal – proximal end of a limb is stationary, end of a limb is stationary, distal end moves in a distal end moves in a circle, combination of circle, combination of flexion, extension, flexion, extension, abduction, & adduction)abduction, & adduction)

– DorsiflexionDorsiflexion – lifting the – lifting the foot so that its superior foot so that its superior surface approaches the surface approaches the shinshin

– Plantar flexionPlantar flexion – – depressing the toes (point depressing the toes (point the foot)the foot)


– InversionInversion – turn the – turn the sole medially (most sole medially (most common type of ankle common type of ankle sprain)sprain)

– EversionEversion – turn the sole – turn the sole laterallylaterally

– SupinationSupination – forearm – forearm rotates laterally so rotates laterally so palm faces anteriorly; palm faces anteriorly; radius & ulna are radius & ulna are parallelparallel

– PronationPronation – forearm – forearm rotates medially so rotates medially so palm faces posteriorly; palm faces posteriorly; radius & ulna form an radius & ulna form an “X”“X”

– OppositionOpposition – movement – movement of thumb when of thumb when touching tips of other touching tips of other fingers on same handfingers on same hand

INTERACTIONS OF SKELETAL MUSCLES IN THE BODYINTERACTIONS OF SKELETAL MUSCLES IN THE BODY

Prime moverPrime mover – muscle that has the major responsibility for – muscle that has the major responsibility for causing a particular movementcausing a particular movement

AntagonistAntagonist – muscles that oppose or reverse a movement – muscles that oppose or reverse a movement SynergistsSynergists – help prime movers by producing same – help prime movers by producing same

movementsmovements FixatorsFixators – hold a bone still or stabilize the origin of a prime – hold a bone still or stabilize the origin of a prime

mover so all the tension can be used to move the insertion mover so all the tension can be used to move the insertion bone (i.e. – postural muscles that stabilize the vertebrae)bone (i.e. – postural muscles that stabilize the vertebrae)

NAMING SKELETAL MUSCLESNAMING SKELETAL MUSCLES Direction of the muscle fibersDirection of the muscle fibers – usually a reference to a – usually a reference to a

midline or long axis of a limb (i.e. – rectus = straight; midline or long axis of a limb (i.e. – rectus = straight; oblique = at a slant to)oblique = at a slant to)

Relative size of the muscleRelative size of the muscle – maximus, minimus, longus – maximus, minimus, longus Location of the muscleLocation of the muscle – named for bone associated with – named for bone associated with

the muscle (i.e. – temporalis, tibialis)the muscle (i.e. – temporalis, tibialis) Number of originsNumber of origins – biceps brachii, triceps brachii – biceps brachii, triceps brachii Location of muscle’s origin & insertionLocation of muscle’s origin & insertion – –

sternocleidomastoid (originates on sternum & clavicle, sternocleidomastoid (originates on sternum & clavicle, inserts on mastoid process of temporal bone)inserts on mastoid process of temporal bone)

Shape of the muscleShape of the muscle – deltoid means triangular – deltoid means triangular Action of the muscleAction of the muscle – flexor, extensor, adductor, etc. – flexor, extensor, adductor, etc. website tutorial

ARRANGEMENT OF FASCICLESARRANGEMENT OF FASCICLES

CircularCircular – concentric – concentric circles around outside circles around outside body opening (sphincters – body opening (sphincters – eye & mouth)eye & mouth)

ConvergentConvergent – fascicles – fascicles converge to single tendon converge to single tendon (pectoralis major)(pectoralis major)

ParallelParallel – length of fascicle – length of fascicle runs parallel to long axis runs parallel to long axis of muscleof muscle– FusiformFusiform – spindle- – spindle-

shaped muscle with shaped muscle with expanded belly (biceps expanded belly (biceps brachii)brachii)

PinnatePinnate – short fascicles – short fascicles attach obliquely to central attach obliquely to central tendon (uni-, bi-, or tendon (uni-, bi-, or mulit-)mulit-)

GROSS ANATOMY OF SKELETAL MUSCLESGROSS ANATOMY OF SKELETAL MUSCLES

Practical 1 – head & neckPractical 1 – head & neck Facial MusclesFacial Muscles

– FrontalisFrontalis– Orbicularis oculiOrbicularis oculi– Orbicularis orisOrbicularis oris– BuccinatorBuccinator– ZygomaticusZygomaticus

Chewing MusclesChewing Muscles– MasseterMasseter– TemporalisTemporalis

Neck MusclesNeck Muscles– PlatysmaPlatysma– SternocleidomastoidSternocleidomastoid

GROSS ANATOMY OF SKELETAL MUSCLESGROSS ANATOMY OF SKELETAL MUSCLESPractical 2 – trunk musclesPractical 2 – trunk muscles AnteriorAnterior

– Pectoralis majorPectoralis major– Intercostals (internal & external)Intercostals (internal & external)– Muscles of the abdominal girdle:Muscles of the abdominal girdle:

Rectus abdominusRectus abdominus External obliqueExternal oblique Internal obliqueInternal oblique Transversus abdominusTransversus abdominus


Practical 2 – trunk musclesPractical 2 – trunk muscles PosteriorPosterior

– TrapeziusTrapezius– Latissimus dorsiLatissimus dorsi– Erector spinaeErector spinae– DeltoidDeltoid

unit 5 – muscular system alireza ashraf, m.d. professor of physical medicine & rehabilitation...

Documents

particular muscle

nerve muscle acetylcholine

shape of organskeletal

actin filamentmyosin

skeletal muscleach

fibrous tissue

power strokemyosin heads

active site leftover