Exercise 14 Microscopic Anatomy, Organization, and Classification of Skeletal Muscle.

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Exercise 14Exercise 14

Microscopic 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

Figure 12.1a Microscopic anatomy of skeletal muscle.

Nuclei Fiber

Dark A band

Light I band

Microscopic Microscopic AnatomyAnatomy

Muscle FiberMuscle Fiber NucleiNuclei

Figure 12.1b Microscopic anatomy of skeletal muscle.

Myofibril

Mitochondrion

Sarcolemma

NucleusLightI band

DarkA band

Muscle Fiber Anatomy

• Sarcolemma• Sarcoplasm

Figure 12.1c Microscopic anatomy of skeletal muscle.

Thin (actin) filament

Thick (myosin) filament

Z disc H zone Z disc

M lineI bandA bandI band

• Myofibrils– Composed of myofilaments

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

Transverse tubulesTransverse tubules

Sarcoplasmic Reticulum (SR)Sarcoplasmic Reticulum (SR)– Smooth ERSmooth ER– Terminal cisternaeTerminal cisternae: enlarged portion : enlarged portion

of SR on either side of T tubuleof SR on either side of T tubule

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

Fig. 10-3

Fig. 10-6

Figure 12.3 Photomicrograph of muscle fibers, longitudinal and cross sections (800).

Nuclei of muscle fibers

Muscle fibers,longitudinalview

Muscle fibers,cross-sectionalview

Figure 12.1d Microscopic anatomy of skeletal muscle.

Z discM line

Z disc

Elastic (titin) filaments

Thin (actin) filament

Thick (myosin) filament

• Sarcomeres– Organized group of myofilaments– Contractile units, smallest functional

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

A band: DARK• Thick and

thin• M line in

middle

I band: LIGHT• midline is Z

line/disc• Thin only

MyofilamentsMyofilaments Thick filaments: myosinThick filaments: myosin

““cross-bridges”cross-bridges”

Fig. 10-7

Contraction: myosin head

changes shape & will grab onto actin…and

pull it toward M-

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

moleculesmolecules– actin actin – TropomyosinTropomyosin– TroponinTroponin

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

Connective Tissue Connective Tissue WrappingsWrappings PerimysiumPerimysium

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

compartments:compartments: Fascicle = Fascicle = bundlebundle of muscle fibers of muscle fibers

(cells)(cells)

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)

Fig. 10-1

Connective Tissues, cont.Connective Tissues, cont.

Layers continuous & interwoven Layers continuous & interwoven – blend into one another– blend into one another

Muscle’s ends: layers unite to Muscle’s ends: layers unite to form 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 bones or

other musclesother muscles

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!

Figure 12.4 Connective tissue coverings of skeletal muscle.

EpimysiumBone

Tendon

Blood vessel

Perimysium wrapping a fascicle

Epimysium

Perimysium

Endomysium

Muscle fiberwithin afascicle

Endomysium(between individualmuscle fibers)

Muscle fiber

PerimysiumFascicle

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: Contract:

DVDDVD

Neuromuscular JunctionNeuromuscular Junction

Junction of motor neuron & a muscle Junction of motor neuron & a muscle fiber fiber

MOTOR Neuron MOTOR Neuron —elongated portion = —elongated portion = axonaxon– synaptic terminalssynaptic terminals– synaptic cleftsynaptic cleft

Synaptic terminalsSynaptic terminals– synaptic vesicles synaptic vesicles

Filled with acetylcholine (ACh)Filled with acetylcholine (ACh)– Neurotransmitter Neurotransmitter – Release triggers muscle contractionRelease triggers muscle contraction

motor end plate motor end plate – Sarcolemma, has Sarcolemma, has receptorsreceptors to bind ACh to bind ACh

Fig. 10-10 “Action Potential”

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

Figure 12.5 The neuromuscular junction.

Synaptic vesiclecontaining ACh

MitochondrionSarcolemma

Axon terminal ofmotor neuron

Junctional foldsof sarcolemma

AChreceptors

Fusingsynapticvesicles

Sarcoplasmof muscle fiber

Synapticcleft

Figure 12.6 Photomicrograph of neuromuscular junctions (750).

Terminalbranch ofan axon

Axonterminal atneuromuscularjunction

Muscle fibers

Fig. 10-10

Figure 12.6 Photomicrograph of neuromuscular junctions (750).

Terminalbranch ofan axon

Axonterminal atneuromuscularjunction

Muscle fibers

Review Figure 12.1

Review Figure 12.2

Review Figure 12.3

Nucleus

Actionpotential

Junctionalfolds of thesarcolemma

Part of amyofibril

Exercise 14 Microscopic Anatomy, Organization, and Classification of Skeletal Muscle.

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