Muscles anatomy

7/28/2019 Muscles anatomy

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MUSCLES


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MUSCLES

1. Skeletal muscle

2. Cardiac muscle3. Smooth muscle


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SKELETAL MUSCLES


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Skeletal Muscle Structure

A muscle is composed of skeletalmuscle tissue, nervous tissue,blood, and connective tissue.

Individual muscles are held inplace by fascia, dense connectivetissue.

Tendons are extensions of thefascia and intertwine with thefibers in the periosteum of thebone.

Muscles are connected to musclesby sheets of connective tissuecalled aponeuroses.


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Connective Tissue Coverings

Blood vessels and nervespass through the layers ofconnective tissue.

Deep fascia surrounds andpenetrates the muscle.

Subcutaneous fascia liesbeneath the skin and formsthe subcutaneous layer.


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Connective Tissue Coverings

Epimysium: connectivetissue that surrounds askeletal muscle.

Perimysium: connective

tissue that extends inwardfrom the epimysium andseparates the muscle intobundles of muscle fibers

called fascicles. Endomysium: Connective

tissue that surrounds eachfascicle/cell


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Structure and Organization of Skeletal Muscle


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MUSCLE FIBER/CELL

Sarcolemma is themuscle cellmembrane.

Sarcoplasm is the

cytoplasm containingnuclei, mitochondria(sarcosome), andmyofibrils.

Myofibrils arecomposed of proteinfilaments, myosin andactin.


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Skeletal Muscle Fiber/Cell A skeletal muscle fiberis cylindrical

multinucleated & nucleiare peripherally located.

The cell is striated.

Consists of T-tubules &

sarcoplasmic reticulum Triad

Action voluntary


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Microscopic structure Sarcoplasmic

reticulum: network of

membranous sacssurroundingmyofibrils.

Transverse tubules

(T-tubules) extendinto the sarcoplasmand containextracellular fluid.


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Microscopic structure

Cisternae: enlargedportions of the

sarcoplasmic reticulum. These three structuresform a triad where theactin and myosin overlap.


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Striated skeletal muscle in longitudinal section (lower) and in cross section (upper). Thenuclei can be seen in the periphery of the cell, just under the cell membrane, particularly

in the cross sections of these striated fibers. H&E stain.


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Longitudinal section of skeletal muscle fibers. Note the dark-stained A bands andthe light-stained I bands, which are crossed by Z lines. Giemsa stain. Highmagnification.

Myosin: Thick filament of


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Protein Filaments

Myosin: Thick filament oftwisted protein strandswith globular ends called

cross-bridges. Actin: Thin filament

protein, also containstropomyosin and

troponin. Organization of filaments

leads to light and darkstriations seen in

skeletal muscle.

S St t


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Sarcomere Structure Striations form a repeating

pattern along the fiber calledsarcomeres.

I-bands (light bands) arecomposed of actin filamentsattached to Z lines.

A-bands (dark bands) are

composed of myosinoverlapping actin attached to Zlines.

A central region (H zone)

consists of myosin only with athick line, the M line.


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Neuromuscular Junction

Motor neuron axons join theskeletal muscle at theneuromuscular junction.

Neurotransmitters: chemicalsstored in vesicles of the motorneuron axon. Acetylcholinecontrols skeletal muscle.


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Motor end plate:specialized regionof the sarcolemmaat theneuromuscular

junction.Synaptic cleft:space between the

neuron and themotor end plate.


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Motor Unit: The Nerve-Muscle Functional Unit

PLAY InterActive Physiology :Contraction of Motor Units, pages 3-9
http://../09PPTLect-anim/IP_Muscle_FILES/9-System%20Suite/ipweb/systems/motounit_pg_03.htmlhttp://../09PPTLect-anim/IP_Muscle_FILES/9-System%20Suite/ipweb/systems/motounit_pg_03.htmlhttp://../09PPTLect-anim/IP_Muscle_FILES/9-System%20Suite/ipweb/systems/motounit_pg_03.html


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Muscle Spindles

Are composed of 3-10 intrafusal

muscle fibers that lackmyofilaments in their centralregions, are noncontractile, andserve as receptive surfaces

Muscle spindles are wrapped withtwo types of afferent endings:primary sensory endings of type Iafibers and secondary sensoryendings of type II fibers


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Muscle Spindles

These regions are innervatedby gamma () efferent fibers

Note: contractile muscle fibersare extrafusal fibers and areinnervated by alpha () efferentfibers


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Microscopic Anatomy of Heart Muscle

Cardiac muscle is striated, short, fat, branched, and interconnected

The connective tissue endomysiumacts as both tendon and insertion

Intercalated discs anchor cardiac cells together and allow free passage of ions

Heart muscle behaves as a functional syncytium

Cardiac MuscleOccurs only in the heart


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Occurs only in the heart,striated

Each cells has a single or

2 nuclei. Sarcoplasmic reticulum, T

tubules --> diad

mitochondria.

The cells are branched

Intercalated discs are gapjunctions.

Cardiac muscle isinvoluntary and self-exciting. It hasrhythmicity.


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Microscopic Anatomy of Cardiac Muscle

Smooth muscles lackstriation and transverse


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Smooth Musclestriation and transversetubules.

Cell is spindle-

shaped/elongated Each cell has a nucleus

Has dense bodies &filaments

Multiunit have fibers thatfunction as separate units.

Single-unit is sheets ofcells joined by gapjunctions. - respond

as a unit. - displaysrhythmicity


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Proportion and Organization of Myofilaments in Smooth Muscle

Innervation of Smooth Muscle


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Innervation of Smooth Muscle


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Smooth Muscle


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Smooth muscle cells in cross section (upper) and in longitudinal section (lower).Note the centrally located nuclei. In many cells the nuclei were not included inthe section.


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Structure of the 3 muscle types. The drawings at right show these muscles in crosssection. Skeletal muscle is composed of large, elongated, multinucleated fibers. Cardiacmuscle is composed of irregular branched cells bound together longitudinally by

intercalated disks. Smooth muscle is an agglomerate of fusiformcells.

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Muscles anatomy

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