Muscle TissueMuscle Tissue

• A primary tissue type, divided into:A primary tissue type, divided into:– skeletalskeletal muscle muscle– cardiaccardiac muscle muscle– smoothsmooth muscle muscle

Skeletal MusclesSkeletal Muscles

• Are attached to the skeletal systemAre attached to the skeletal system

• Allow us to moveAllow us to move

The Muscular SystemThe Muscular System

• Includes only skeletal musclesIncludes only skeletal muscles

Skeletal Muscle StructuresSkeletal Muscle Structures

• Muscle tissue (muscle cells or Muscle tissue (muscle cells or fibersfibers))

• Connective tissuesConnective tissues

• NervesNerves

• Blood vesselsBlood vessels

Functions of Skeletal Functions of Skeletal MusclesMuscles

1.1. Produce skeletal movementProduce skeletal movement

2.2. Maintain body positionMaintain body position

3.3. Support soft tissuesSupport soft tissues

4.4. Guard body openingsGuard body openings

5.5. Maintain body temperatureMaintain body temperature

Organization of Connective Organization of Connective TissuesTissues

Figure 10–1

EpimysiumEpimysium

• Exterior collagen layerExterior collagen layer

• Connected to deep fasciaConnected to deep fascia

• Separates muscle from surrounding Separates muscle from surrounding tissuestissues

PerimysiumPerimysium

• Surrounds muscle fiber bundles Surrounds muscle fiber bundles ((fasciclesfascicles))

• Contains blood vessel and nerve Contains blood vessel and nerve supply to fasciclessupply to fascicles

EndomysiumEndomysium

• Surrounds individual muscle cells Surrounds individual muscle cells (muscle (muscle fibersfibers))

• Contains capillaries and nerve fibers Contains capillaries and nerve fibers contacting muscle cellscontacting muscle cells

• Contains Contains satellite cellssatellite cells (stem cells) (stem cells) that repair damagethat repair damage

Muscle AttachmentsMuscle Attachments

• Endomysium, perimysium, and Endomysium, perimysium, and epimysium come together:epimysium come together:– at ends of musclesat ends of muscles– to form connective tissue attachment to to form connective tissue attachment to

bone matrixbone matrix– i.e.,i.e., tendontendon (bundle) or (bundle) or aponeurosisaponeurosis

(sheet)(sheet)

NervesNerves

• Skeletal muscles are voluntary Skeletal muscles are voluntary muscles, controlled by nerves of the muscles, controlled by nerves of the central nervous systemcentral nervous system

Blood Vessels Blood Vessels

• Muscles have extensive vascular Muscles have extensive vascular systems that:systems that:– supply large amounts of oxygensupply large amounts of oxygen– supply nutrientssupply nutrients– carry away wastescarry away wastes

Formation of Formation of Skeletal Muscle FibersSkeletal Muscle Fibers

• Skeletal muscle cells are called Skeletal muscle cells are called fibersfibers

Figure 10–2

Skeletal Muscle FibersSkeletal Muscle Fibers

• Are very long Are very long

• Develop through fusion of Develop through fusion of mesodermal cells (mesodermal cells (myoblastsmyoblasts))

• Become very large Become very large

• Contain hundreds of nuclei Contain hundreds of nuclei

Organization ofOrganization of Skeletal Muscle Fibers Skeletal Muscle Fibers

Figure 10–3

The SarcolemmaThe Sarcolemma

• The cell membrane of a muscle cell The cell membrane of a muscle cell

• Surrounds the Surrounds the sarcoplasmsarcoplasm (cytoplasm of muscle fiber)(cytoplasm of muscle fiber)

• A change in transmembrane A change in transmembrane potential begins contractionspotential begins contractions

Transverse Tubules (Transverse Tubules (T T tubulestubules))

• Transmit Transmit action potentialaction potential through cell through cell

• Allow entire muscle fiber to contract Allow entire muscle fiber to contract simulataneouslysimulataneously

• Have same properties as Have same properties as sarcolemmasarcolemma

MyofibrilsMyofibrils

• Lengthwise subdivisions within Lengthwise subdivisions within muscle fibermuscle fiber

• Made up of bundles of protein Made up of bundles of protein filaments (filaments (myofilamentsmyofilaments))

• Myofilaments are responsible for Myofilaments are responsible for muscle contraction muscle contraction

Types of Myofilaments Types of Myofilaments

• Thin filamentsThin filaments: : – made of the protein actinmade of the protein actin

• Thick filamentsThick filaments: : – made of the protein myosinmade of the protein myosin

Sarcoplasmic ReticulumSarcoplasmic Reticulum

• A membranous structure surrounding A membranous structure surrounding each myofibril each myofibril

• Helps transmit Helps transmit action potentialaction potential to to myofibrilmyofibril

• Similar in structure to smooth Similar in structure to smooth endoplasmic reticulumendoplasmic reticulum

• Forms chambers (Forms chambers (terminal cisternaeterminal cisternae) ) attached to T tubules attached to T tubules

A A TriadTriad

• Is formed by 1 Is formed by 1 T tubuleT tubule and 2 and 2 terminal cisternaeterminal cisternae

CisternaeCisternae

• Concentrate CaConcentrate Ca2+2+ ( (viavia ion pumps) ion pumps)

• Release CaRelease Ca2+2+ into into sarcomeressarcomeres to to begin muscle contractionbegin muscle contraction

SarcomeresSarcomeres

Figure 10–4

SarcomeresSarcomeres

• The contractile units of muscleThe contractile units of muscle

• Structural units of Structural units of myofibrilsmyofibrils

• Form visible patterns within Form visible patterns within myofibrilsmyofibrils

Muscle StriationsMuscle Striations

• A striped or A striped or striatedstriated pattern within pattern within myofibrils:myofibrils:– alternating dark, alternating dark, thick filamentsthick filaments (A (A

bands)bands) and light, and light, thin filamentsthin filaments (I bands)(I bands)

M LinesM Lines and and Z LinesZ Lines

• M lineM line::– the center of the the center of the A bandA band– at midline of sarcomereat midline of sarcomere

• Z linesZ lines::– the centers of the the centers of the I bandsI bands– at 2 ends of sarcomereat 2 ends of sarcomere

Zone of OverlapZone of Overlap

• The densest, darkest area on a light The densest, darkest area on a light micrograph micrograph

• Where thick and thin filaments Where thick and thin filaments overlapoverlap

The The H ZoneH Zone

• The area around the The area around the M lineM line

• Has thick filaments but no thin Has thick filaments but no thin filaments filaments

TitinTitin

• Are strands of protein Are strands of protein

• Reach from tips of thick filaments to Reach from tips of thick filaments to the the Z lineZ line

• Stabilize the filamentsStabilize the filaments

Sarcomere StructureSarcomere Structure

Figure 10–5

Sarcomere FunctionSarcomere Function

• Transverse tubulesTransverse tubules encircle the encircle the sarcomere near sarcomere near zones of overlapzones of overlap

• CaCa2+2+ released by released by SRSR causes thin and causes thin and thick filaments to interact thick filaments to interact

Figure 10–6 (1 of 5)

Level 1: Skeletal MuscleLevel 1: Skeletal Muscle

Level 2: Muscle FascicleLevel 2: Muscle Fascicle

Figure 10–6 (2 of 5)

Level 3: Muscle FiberLevel 3: Muscle Fiber

Figure 10–6 (3 of 5)

Level 4: MyofibrilLevel 4: Myofibril

Figure 10–6 (4 of 5)

Level 5: SarcomereLevel 5: Sarcomere

Figure 10–6 (5 of 5)

A Thin FilamentA Thin Filament

Figure 10–7a

4 Thin Filament Proteins4 Thin Filament Proteins

1.1. F actinF actin::– is 2 twisted rows of globular is 2 twisted rows of globular G actinG actin– the the active sitesactive sites on G actin strands bind on G actin strands bind

to to myosinmyosin

4 Thin Filament Proteins4 Thin Filament Proteins

2.2. NebulinNebulin::– holds holds F actinF actin strands together strands together

4 Thin Filament Proteins4 Thin Filament Proteins

3.3. TropomyosinTropomyosin::– is a double strandis a double strand– prevents prevents actin–myosinactin–myosin interaction interaction

4 Thin Filament Proteins4 Thin Filament Proteins

4.4. TroponinTroponin::– a globular proteina globular protein– binds binds tropomyosintropomyosin to to G actinG actin– controlled by Cacontrolled by Ca2+2+

Troponin and TropomyosinTroponin and Tropomyosin

Figure 10–7b

Initiating ContractionInitiating Contraction

• CaCa2+2+ binds to receptor on binds to receptor on troponintroponin moleculemolecule

• Troponin–tropomyosin complexTroponin–tropomyosin complex changeschanges

• Exposes Exposes active siteactive site of of F actinF actin

A Thick FilamentA Thick Filament

Figure 10–7c

Thick Filaments Thick Filaments

• Contain twisted Contain twisted myosinmyosin subunits subunits

• Contain Contain titintitin strands that recoil after strands that recoil after stretchingstretching

The Mysosin MoleculeThe Mysosin Molecule

Figure 10–7d

The Mysosin MoleculeThe Mysosin Molecule

• TailTail::– binds to other myosin molecules binds to other myosin molecules

• HeadHead::– made of 2 globular protein subunitsmade of 2 globular protein subunits– reaches the nearest thin filamentreaches the nearest thin filament

Mysosin ActionMysosin Action

• During contraction, During contraction, myosin headsmyosin heads::– interact with interact with actinactin filaments, forming filaments, forming

cross-bridgescross-bridges – pivot, producing motion pivot, producing motion

Sliding Filaments Sliding Filaments

Figure 10–8

Skeletal Muscle ContractionSkeletal Muscle Contraction

• Sliding filament theorySliding filament theory::– thin filamentsthin filaments of sarcomere slide toward of sarcomere slide toward

M lineM line– between between thick filamentsthick filaments– the width of A zone stays the samethe width of A zone stays the same– Z lines move closer togetherZ lines move closer together

InterActive Physiology: Sliding Filament TheoryPLAYPLAY

Skeletal Muscle ContractionSkeletal Muscle Contraction

Figure 10–9 (Navigator)

Skeletal Muscle InnervationSkeletal Muscle Innervation

Figure 10–10a, b (Navigator)

Skeletal Muscle InnervationSkeletal Muscle Innervation

Figure 10–10c

The Neuromuscular JunctionThe Neuromuscular Junction

• Is the location of neural stimulationIs the location of neural stimulation

• Action potentialAction potential (electrical signal): (electrical signal):– travels along nerve axontravels along nerve axon– ends at ends at synaptic terminalsynaptic terminal

Synaptic TerminalSynaptic Terminal

• Releases neurotransmitter Releases neurotransmitter ((acetylcholineacetylcholine or or AChACh))

• Into the Into the synaptic cleftsynaptic cleft (gap between (gap between synaptic terminalsynaptic terminal and and motor end motor end plateplate))

The NeurotransmitterThe Neurotransmitter

• AcetylcholineAcetylcholine or or AChACh::– travels across the travels across the synaptic cleftsynaptic cleft – binds to membrane receptors on binds to membrane receptors on

sarcolemma (sarcolemma (motor end platemotor end plate))– causes sodium–ion rush into sarcoplasmcauses sodium–ion rush into sarcoplasm– is quickly broken down by enzyme is quickly broken down by enzyme

((acetylcholinesteraseacetylcholinesterase or or AChEAChE))

Action PotentialAction Potential

• Generated by increase in sodium Generated by increase in sodium ions in sarcolemmaions in sarcolemma

• Travels along the T tubulesTravels along the T tubules

• Leads to Leads to excitation–contractionexcitation–contraction couplingcoupling