Exercise 14Exercise 14Microscopic Microscopic Anatomy, Anatomy,

Organization, and Organization, and Classification of Classification of Skeletal MuscleSkeletal Muscle

SKELETAL MUSCLESKELETAL MUSCLE Voluntary or involuntary?Voluntary or involuntary? Striated or not?Striated or not? Multinucleate or Multinucleate or

uninucleate?uninucleate?

““Myo-” or “-Mys-” = muscleMyo-” or “-Mys-” = muscle ““Sarco-” = fleshSarco-” = flesh

TerminologyTerminology

Microscopic Microscopic AnatomyAnatomy

Muscle Fiber = Muscle Fiber = long, slender, long, slender, cylindrical, cylindrical, MULTInucleate MULTInucleate cellcell

Nuclei located Nuclei located just under just under sarcolemma (cell sarcolemma (cell membrane)membrane)

Fig. 10-2

Muscle Fiber AnatomyMuscle Fiber Anatomy SarcolemmaSarcolemma

– Plasma membrane of muscle fiberPlasma membrane of muscle fiber– Trans-membrane potential: charge Trans-membrane potential: charge

differences on either sidedifferences on either side SarcoplasmSarcoplasm

– Cytoplasm of muscle fiberCytoplasm of muscle fiber– Stored glycogen, mitochondria, Stored glycogen, mitochondria,

myoglobin, actin, myosinmyoglobin, actin, myosin

Fig. 10-3

Transverse tubulesTransverse tubules– T tubulesT tubules– Narrow tubes, continuous with Narrow tubes, continuous with

sarcolemmasarcolemma– Extend into sarcoplasm, fluid-filledExtend into sarcoplasm, fluid-filled

MyofibrilsMyofibrils– Parallel, extend length of muscle fiberParallel, extend length of muscle fiber– Each muscle fiber contains 100s-1000sEach muscle fiber contains 100s-1000s– Composed of myofilamentsComposed of myofilaments

Actin (thin filaments) & myosin (thick Actin (thin filaments) & myosin (thick filaments)filaments)

Fig. 10-3

Sarcoplasmic Reticulum (SR)Sarcoplasmic Reticulum (SR)– Smooth ERSmooth ER– Tubular network around each myofibrilTubular network around each myofibril– Terminal cisternaeTerminal cisternae: enlarged portion : enlarged portion

of SR on either side of T tubuleof SR on either side of T tubule– Storage/release of CaStorage/release of Ca

Triad = T tubule + 2 terminal Triad = T tubule + 2 terminal cisternaecisternae

Fig. 10-3

Muscle contraction begins when Muscle contraction begins when Calcium ions are released Calcium ions are released – from the terminal cisternaefrom the terminal cisternae– Into the sarcoplasmInto the sarcoplasm

– ADAM cd-romADAM cd-rom

SarcomeresSarcomeres– Organized group of myofilamentsOrganized group of myofilaments– Contractile units, smallest functional Contractile units, smallest functional

unit of muscle fiberunit of muscle fiber– Z-line to Z-lineZ-line to Z-line

Fig. 10-4

SarcomeresSarcomeres

– A band: DARKA band: DARK Thick and thin Thick and thin

filamentsfilaments M lineM line is in is in

the middle of the middle of the the sarcomere/A sarcomere/A bandband

– I band: LIGHTI band: LIGHT midline is midline is Z Z

line/discline/disc Thin filaments Thin filaments

onlyonly

Fig. 10-4

MyofilamentsMyofilaments Thick filaments: myosinThick filaments: myosin

– Rod-like tail bound to other myosinRod-like tail bound to other myosin– Head projects outwardHead projects outward

has binding sites for actin (thin filaments), has binding sites for actin (thin filaments), ATPATP

““cross-bridges”cross-bridges”

Fig. 10-7

Contraction: The myosin

head changes

shape & will grab onto the actin…and pull it toward the

M-line

MyofilamentsMyofilaments Thin filaments: 3 types of protein Thin filaments: 3 types of protein

moleculesmolecules– actin actin

Double helix (2 strands) coil around each other Double helix (2 strands) coil around each other has binding sites for myosinhas binding sites for myosin

– Site is blocked by troponin-tropomyosin complex Site is blocked by troponin-tropomyosin complex when muscle’s when muscle’s NOT contractingNOT contracting

– TropomyosinTropomyosin Rod-like, coils around actin to stiffen itRod-like, coils around actin to stiffen it Covers binding sitesCovers binding sites

– TroponinTroponin 3 protein-complex3 protein-complex One of each binds to: actin, tropomyosin, calcium ions One of each binds to: actin, tropomyosin, calcium ions

(this one’s empty in a resting cell…see ADAM cd)(this one’s empty in a resting cell…see ADAM cd)

Fig. 10-7

Connective Tissue Connective Tissue Wrappings:Wrappings:

3 Layers3 Layers Epimysium = outerEpimysium = outer Perimysium = centralPerimysium = central Endomysium = innerEndomysium = inner

Connective Tissue Connective Tissue WrappingsWrappings

EpimysiumEpimysium– Epi = on (outside layer)Epi = on (outside layer)– Surrounds entire muscleSurrounds entire muscle– Dense layer of collagen fibers, Dense layer of collagen fibers,

connected to connected to deep fasciadeep fascia– Separates muscle from other Separates muscle from other

tissues/organstissues/organs

Fig. 10-1

Connective Tissue Connective Tissue WrappingsWrappings PerimysiumPerimysium

– Peri = around (central layer)Peri = around (central layer)– Divides muscle into compartments:Divides muscle into compartments:

Fascicle = Fascicle = bundlebundle of muscle fibers (cells) of muscle fibers (cells)– Collagen, elastic fibersCollagen, elastic fibers– Blood vessels, nerves to each fascicleBlood vessels, nerves to each fascicle

Fig. 10-1

Connective Tissue Connective Tissue WrappingsWrappings EndomysiumEndomysium

– Endo = inside (inner layer)Endo = inside (inner layer)– Surrounds individual skeletal Surrounds individual skeletal

muscle cells (fibers)muscle cells (fibers)– Interconnects adjacent muscle Interconnects adjacent muscle

fibersfibers– Capillary networks to supply blood Capillary networks to supply blood

to cells, nerve fibers to control to cells, nerve fibers to control musclemuscle

Fig. 10-1

Connective Tissues, cont.Connective Tissues, cont. Layers are continuous & interwoven Layers are continuous & interwoven

– blend into one another– blend into one another Muscle’s ends: layers unite to form Muscle’s ends: layers unite to form

– Bundle: Bundle: TENDONTENDON Attach skeletal muscles to Attach skeletal muscles to bonesbones Contraction pulls the bone(s)Contraction pulls the bone(s)

– Broad sheet: Broad sheet: APONEUROSISAPONEUROSIS Attach skeletal muscles to Attach skeletal muscles to bones or other bones or other

musclesmuscles

Muscle—covered by epimysiumMuscle—covered by epimysium Fascicles—covered by perimysiumFascicles—covered by perimysium Fiber (cell)—covered by Fiber (cell)—covered by

endomysiumendomysium Myofibril—covered by Myofibril—covered by

sarcoplasmic reticulumsarcoplasmic reticulum Sarcomere—contains thick and Sarcomere—contains thick and

thin filamentsthin filaments

Connective tissue layers!

Fig. 10-6

Blood & Nerve SupplyBlood & Nerve Supply Muscles need lots of energy, lots of Muscles need lots of energy, lots of

oxygenoxygen

Blood vessels supply theseBlood vessels supply these– Each fiber (cell) has capillary blood supplyEach fiber (cell) has capillary blood supply

Contraction stimulated by nerve Contraction stimulated by nerve impulsesimpulses– Axons (nerve fibers) penetrate connective Axons (nerve fibers) penetrate connective

tissue layers, & innervate individual tissue layers, & innervate individual muscle fibers (cells)muscle fibers (cells)

How Muscles How Muscles Contract: ADAM cd-Contract: ADAM cd-

romrom

Neuromuscular JunctionNeuromuscular Junction Junction of motor neuron & a muscle Junction of motor neuron & a muscle

fiber fiber – Motor neuron sends a signal to cause a Motor neuron sends a signal to cause a

movement of a skeletal musclemovement of a skeletal muscle

Neuron—elongated portion = axonNeuron—elongated portion = axon– Ends in expanded branches (synaptic Ends in expanded branches (synaptic

terminals) terminals) – synaptic cleft: space between synaptic synaptic cleft: space between synaptic

terminal & muscle fiber’s sarcolemmaterminal & muscle fiber’s sarcolemma

Neuromuscular JunctionNeuromuscular Junction Synaptic terminalsSynaptic terminals

– Contain synaptic vesicles Contain synaptic vesicles Filled with acetylcholine (ACh)Filled with acetylcholine (ACh)

– Neurotransmitter: chemical Neurotransmitter: chemical released by neuronreleased by neuron

Release of ACh triggers muscle Release of ACh triggers muscle contractioncontraction

Sarcolemma of motor end plate Sarcolemma of motor end plate has has receptorsreceptors to bind ACh to bind ACh

Neuromuscular JunctionNeuromuscular Junction““Motor end plate”Motor end plate”

Sarcolemma highly Sarcolemma highly foldedfolded Increases surface Increases surface

areaarea Sites of ACh Sites of ACh

bindingbinding

Fig. 10-10 “Action Potential”

Neuromuscular JunctionNeuromuscular Junction Motor unit = A single motor Motor unit = A single motor

neuron & ALL the muscle fibers it neuron & ALL the muscle fibers it controlscontrols

Fig. 10-17

Fig. 10-10

Fig. 10-10