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WHERE AM I?. Online Anatomy Module 1. INTRO & TERMS. CELL. EPITHELIUM. CONNECTIVE TISSUE. MUSCLE. NERVOUS SYSTEM. AXIAL SKELETON. APPENDICULAR SKELETON. MUSCLES. EMBRYOLOGY. MUSCLE. see Marieb pp. 82-84, 153-166. MUSCLE CELL’S ROLE.

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Where am i

WHERE AM I?

Online Anatomy Module 1

INTRO & TERMS

CELL

EPITHELIUM

CONNECTIVE TISSUE

MUSCLE

NERVOUS SYSTEM

AXIAL SKELETON

APPENDICULAR SKELETON

MUSCLES

EMBRYOLOGY


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MUSCLE

see Marieb pp. 82-84, 153-166


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MUSCLE CELL’S ROLE

Muscle cell contracts along an axis to furnish force applied to what it is attached to


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MUSCLE CELL = MUSCLE FIBER

Muscle cells are often called muscle fibers.

Note the distinction with connective tissue cells, which construct extracellular fibers such as collagen.

Muscle cells are also called ‘myocytes’, e.g., cardiomyocyte


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MUSCLE ACTIONS

Visceral

Somatic

lumen

skeletal muscle

rotation around joint*

squeezing/ * constriction

Muscle cells work together as ‘muscles’ (abs. etc) or layers of heart or tubes, for a purpose

* how the force is applied


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MUSCLE CONTRACTION: Requirements

Force Generated

Applied usefully

Controlled

Energized

Sustained

Variedfor conditions


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MUSCLE CONTRACTION: Requirements

GENERATED by interactions between actin & myosin

Applied usefullyconnective tissues to tendons; visceral & cardiac muscle contract in a circle

CONTROLLED voluntary & involuntary: nervous;

& nervous + diffuse chemical control

ENERGIZED blood supply; mitochondria ; ATP; glycogen - stored form of glucose

SUSTAINED multiple muscle units; prolonged contraction (smooth muscle)

VARIED FOR CONDITIONS sub-types of muscle

The diverse requirements demand 3 three separate kinds of muscle


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MUSCLE CONTRACTION: Requirements

GENERATED by interactions between actin & myosin


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ACTIN & MYOSIN FILAMENTS IN MUSCLE

Z line/disc

thickMYOSIN filament

thinACTIN filament

In muscle, for strong shortening (contractile) force the actin filaments are stabilized and interdigitated with thicker myosin filaments, which pull them in deeper


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SKELETAL MYOFIBER IN LONGITUDINAL EM VIEW

I band

A band

I band

H zone with M line

Z line/disc

thickMYOSIN filament

thinACTIN filament

Banding pattern - I & Abands, Z lines, H zones, M lines

The regular arrangement of the filaments & their attachments yields a visible banding pattern across the fiber


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BANDING-PATTERN CHANGES IN CONTRACTION

A band

I band

I band

actin

myosin

M line but noH zone

Z line

1

Sarcomere shortens

3

A band unchanged

2

I band shortens

4

H zonedisappears


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SKELETAL MYOFIBER: Generating contraction

H zone with M line

Z line/disc

thickMYOSIN filament

thinACTIN filament

Tails of heavy (H) myosin bundle together to make the myosin filament

ACTIN filament

attached globular F actin molecules

H & L myosin heads hinge step-wise along actin filament


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Actin-myosin interaction to generate myosin’s pull on actin filament

Myosin head / Motor domain

Parts of Motor domain

Actin-binding site

ATP-catalysing site

Regulatory domain interacts with tropomyosin under control of Ca 2+--switched troponin

Thick filament- Rods of H myosin

Catalytic domain

Actin filament

myosin rods held stationary

Regulatory domain does the lever work, aided by the flexible start of the rod

2

1

Actin filament

pulled


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MUSCLE CONTRACTION: Requirements actin filament

Applied usefullyconnective tissues to tendons;


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SKELETAL MUSCLE actin filament

striated/cross-banded myofiber

capillary

sarcolemma

TENDON

endomysium CT

Myofiber in cross-section

myofibrils


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SKELETAL MUSCLE: Connective Tissue Organization actin filament

MYOCYTE

PERIMYSIUM

}

creates

FASCICLE/ bundle

endomysium

EPIMYSIUM


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SKELETAL MUSCLE actin filament

myofibrils

striated/cross-banded myofiber

capillary

sarcolemma

TENDON

endomysium CT

Myofiber in cross-section


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Myofiber in cross-section actin filament

myofibrils

Each myofibril consists of bundled myofilaments

thickMYOSIN

But, at regular intervals along the relaxed fiber, only thin or only thick filaments are found. Why?

thinACTIN


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PERIPHERAL MYOFIBRIL IN LONGITUDINAL EM VIEW actin filament

I band

A band

I band

Z line/disc

thickMYOSIN filament

thinACTIN filament

Hits thick & thin

Hit only thin


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MUSCLE CONTRACTION: Requirements actin filament

CONTROLLED voluntary & involuntary: nervous;

& nervous + diffuse chemical control


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SKELETAL MUSCLE: INNERVATION actin filament

Axons/nerve fibers to motor end-plates to cause contraction

striated/cross-banded myofiber

TENDON


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MOTOR END-PLATE or NEUROMUSCULAR/MYONEURAL JUNCTION actin filament

AXON

AXOLEMMA

SARCOLEMMA

SCHWANN CELL

SYNAPTIC VESICLES

mitochondrion

synaptic cleft

secondary/ junctional folds of

POST-SYNAPTIC MEMBRANE

SKELETAL MUSCLE FIBER/MYOCYTE


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MOTOR END-PLATE: LOCATION OF ‘TRANSMISSION’ MOLECULES actin filament

voltage-gated ion channels

SARCOLEMMA

AXOLEMMA

voltage-gated ion channels

Acetyl Choline/ACh

SYNAPTIC VESICLES

synaptic cleft

Cholinesterase

Ligand-gated ion channels

PRE-SYNAPTIC MEMBRANE

ACh receptors

POST-SYNAPTIC MEMBRANE

SKELETAL MUSCLE FIBER/MYOCYTE

Ca2+ channels


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SKELETAL MYOFIBER: Initiating contraction actin filament

motor end-plate

T/transverse tubule

sarcolemma

A-I junction

Z line

}

Sarcoplasmic reticulum wraps around myofibril and releasesCalcium ion, when stimulated viaT-tubule&feet

Triad = T-tubule + two terminal cisternae

Feet

Terminal cisterna of SR

Motor end-plate - Sarcolemma AP - T-tubule AP - Feet - SR - Ca 2+ release


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MUSCLE CONTRACTION: Requirements actin filament

CONTROLLED voluntary & involuntary: nervous;

& nervous + diffuse chemical control

ENERGIZED blood supply; mitochondria ; ATP; glycogen - stored form of glucose


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AROUND EACH MYOFIBRIL, meaning actin filamentbetween myofibrils

Glycogen granules

Sarcoplasmic reticulum

energize

control

Myofilamentsgenerate force

Mitochondria

energize

MYOFIBRIL


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THREE MAIN TYPES OF MUSCLE actin filament

SMOOTHsmall but prolongable force; diverse types, uses, & controls; controlled partly by autonomic/involuntary nervous system, partly by chemicals released from nearby cells, and by cell-to-cell connections

CARDIACstrong rhythmic contractions; controlled by own cell-to-cell connections; pace determined by autonomic innervation to a little of the cardiac muscle

SKELETALmost forceful kind, but contracts only in response to voluntary/somatic nervous system activity; applies its force via well-organized connective tissue; strength of contraction needs high internal organization within the muscle cell/fiber


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THREE MAIN TYPES OF MUSCLE I actin filament

SMOOTH

small but prolongable force;

diverse types, uses, & controls;

controlled partly by autonomic/ involuntary nervous system, partly by chemicals released from nearby cells, and by cell-to-cell connections


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THREE MAIN TYPES OF MUSCLE II actin filament

CARDIAC

strong rhythmic contractions;

controlled by own cell-to-cell connections;

pace determined by autonomic innervation to a little of the cardiac muscle


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THREE MAIN TYPES OF MUSCLE III actin filament

SKELETALmost forceful kind;

but contracts only in response to voluntary/somatic nervous system activity;

applies its force via well-organized connective tissue;

strength of contraction needs high internal organization within the muscle cell/fiber


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THREE MAIN TYPES OF MUSCLE IV actin filament

Muscle cells are often called muscle fibers. Note the distinction with connective tissue cells, which construct extracellular fibers such as collagen.

Muscle cells are also called ‘myocytes’, e.g., cardiomyocyte


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THREE MAIN TYPES OF MUSCLE: Sub-types actin filament

SMOOTHskin, cardiovascular, airway, uterine, otherreproductive, urinary, gastrointestinal (GI)

CARDIACatrial, ventricular, nodal, Purkinje

SKELETALtype I - slow, type IIa - fast oxidative, type IIb - fast glycolytic


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SKELETAL MYOFIBER: Needs determining structure actin filament

Generation

Force generation

Stabilization

Force application

Control of contraction

Energize


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CARDIAC MUSCLE actin filament

striated/cross-banded CARDIOMYOCYTES

INTERCALATED DISK

Reticular fiber

centralNUCLEUS

Capillary

branching muscle fibers

Sarcolemma & external lamina


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INTERCALATED DISC - electro-mechanical union actin filament

ID is a strong myocyte-myocyte attachment + electrical connections

Fascia adherensstrength

Maculae adherensstrength

Gap junctiontransmits contraction


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PURKINJE FIBER actin filament

ventricle

}

Endocardium

Sub-endocardium

Large, pale cell specialized for conduction, not contraction

Myofilaments

Glycogen


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SMOOTH MUSCLE actin filament

SMOOTH MUSCLE CELL has same contractile & control *machinery as skeletal myocyte, but less organized

Reticular fiber

Gap junction/Nexus

Autonomic nerve axon

Myocyte plasmalemma + glycoprotein External lamina

* There is the important difference that smooth muscle uses Myosin Light-chain Kinase (MLCK) to phosphorylate the regulatory myson light chain as the main means to provoke the actomyosin ATPase to start contraction


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SMOOTH MUSCLE actin filament

SMOOTH MUSCLE CELL has same contractile & control machinery* as skeletal myocyte, but less organized

Filaments attach to DENSE BODIES serving the role of Z-lines

CAVEOLAE for stimulus-contraction coupling serve role of T-tubule & SR system


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SMOOTH MUSCLE actin filament

* There is the important difference that smooth muscle uses Myosin Light-chain Kinase (MLCK) to phosphorylate the regulatory myosin light chain as the main means to provoke the actomyosin ATPase to start contraction


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CAVEOLA actin filament

Caveolae are plasma membrane invaginations found in most cell types of all four tissues. They are conspicuous in endothelial cells & smooth muscle.

Membrane molecules:

Caveolin - characteristic integral membrane protein

Cholesterol (lots)

Molecules related to -

Plasmalemma

Transcytosis

Endocytosis or

Signal transduction


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SMOOTH MUSCLE actin filament

View with H & E staining - solid pink mass (stained sarcoplasm)

cross-section

long.-section

Unseen are reticular and nerve fibers, plasmalemmas & external laminae

Trichromestains distinguish smooth muscle cells from collagen fibers


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SKELETAL MYOFIBER: Needs determining structure actin filament

Generation

Force generation

Stabilization

Force application

Control of contraction

Energize


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MYOFIBER: Stabilization* & Force Application materials actin filament

Dystrophin

Integrin

External lamina

Sarcolemma

M line*

Nebulin*

a-actinin*

Desmin* intermediate filaments

Z line

Titin* (“elastic”)


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SKELETAL MUSCLE: SENSORY INNERVATION actin filament

striated/cross-banded myofiber

TENDON

Golgi tendon receptor

Muscle spindle

Sensory axon & spindle receptor

The fine control of contraction in individual myofibers requires abundant sensory feedback on how the muscle as a whole is performing


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CARDIAC MUSCLE actin filament

striated/cross-banded CARDIOMYOCYTES

INTERCALATED DISK

Reticular fiber

centralNUCLEUS

Capillary

branching muscle fibers

Sarcolemma & external lamina


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CARDIAC PATHOLOGY actin filament

Enlarged, but altered and weakened muscle of Ventricular hypertrophy

More & thicker fibers of Fibrosis

Reticular fiber

Capillary

Bad gap junctions Arrythmia

altered connexin

Blocked vessels damaged heart muscle (Cardiac infarct)


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Caution how you exit. actin filament

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Unfortunately there is

no way that you can

directly reach other

topics listed here by

clicking on them. You

get there by going back

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Anatomy menu

WHERE AM I?

Online Anatomy

Module 1

You are at the End

ORIENTATION

CELL

EPITHELIUM

CONNECTIVE TISSUE

MUSCLE

NERVOUS SYSTEM

AXIAL SKELETON

APPENDICULAR SKELETON

MUSCLES

EMBRYOLOGY


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