WHERE AM I? Online Anatomy Module 1

APPENDICULAR SKELETON

CELL

INTRO & TERMS

EPITHELIUM

CONNECTIVE TISSUE

MUSCLE

NERVOUS SYSTEM

AXIAL SKELETON

MUSCLES

EMBRYOLOGY

MUSCLE

see Marieb pp. 82-84, 153-166

MUSCLE CELL’S ROLE

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

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

MUSCLE CELL = MUSCLE FIBER

MUSCLE ACTIONS

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

Somatic skeletal muscle

rotation around joint*

Visceral

squeezing/ * constriction

lumen

* how the force is applied

MUSCLE CONTRACTION: Requirements

Force Generated

Applied usefully

Controlled

Energized

Sustained

Varied for conditions

MUSCLE CONTRACTION: Requirements

GENERATED by interactions between actin & myosin

Applied usefully connective 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

MUSCLE CONTRACTION: Requirements

GENERATED by interactions between actin & myosin

ACTIN & MYOSIN FILAMENTS IN MUSCLE

Z line/disc thick MYOSIN filament thin ACTIN filament

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

SKELETAL MYOFIBER IN LONGITUDINAL EM VIEW

Z line/disc

I band A band I band

H zone with M line

thick MYOSIN filament thin ACTIN filament

Banding pattern - I & A bands, Z lines, H zones, M lines

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

BANDING-PATTERN CHANGES IN CONTRACTION

Z line

I band A band I band

M line but no H zone

myosinactin

Sarcomere shortens

I band shortens

A band unchanged

H zone disappears

1

4

32

SKELETAL MYOFIBER: Generating contraction

Z line/disc H zone with M line

thick MYOSIN filament thin ACTIN filament

ACTIN filament

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

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

attached globular F actin molecules

Regulatory domain interacts with tropomyosin under control of Ca 2+--switched troponinThick filament - Rods of H myosin

ATP-catalysing siteActin-binding site

Catalytic domainActin filament

Myosin head / Motor domain

Parts of Motor domain

Actin filament

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

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

12

pulled

myosin rods held stationary

MUSCLE CONTRACTION: Requirements

Applied usefully connective tissues to tendons;

SKELETAL MUSCLE

endomysium CT

striated/cross-banded myofiber sarcolemma

TENDON

capillary

Myofiber in cross-section myofibrils

SKELETAL MUSCLE: Connective Tissue Organization

}FASCICLE/ bundle

PERIMYSIUM

EPIMYSIUM

endomysium

creates

MYOCYTE

SKELETAL MUSCLE

endomysium CT

striated/cross-banded myofiber sarcolemma

TENDON

capillary

Myofiber in cross-section myofibrils

Myofiber in cross-section

myofibrils

Each myofibril consists of bundled myofilaments

thick MYOSIN

thin ACTIN

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

PERIPHERAL MYOFIBRIL IN LONGITUDINAL EM VIEW

Z line/disc

I band A band I band

thick MYOSIN filament thin ACTIN filament

Hit only thinHits thick & thin

MUSCLE CONTRACTION: Requirements

CONTROLLED voluntary & involuntary: nervous;

& nervous + diffuse chemical control

SKELETAL MUSCLE: INNERVATION

striated/cross-banded myofiber

TENDON

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

MOTOR END-PLATE or NEUROMUSCULAR/MYONEURAL JUNCTION

AXON

SCHWANN CELL

SARCOLEMMA

SKELETAL MUSCLE FIBER/MYOCYTE

synaptic cleft

secondary/ junctional folds of

POST-SYNAPTIC MEMBRANE

AXOLEMMA

SYNAPTIC VESICLES

mitochondrion

MOTOR END-PLATE: LOCATION OF ‘TRANSMISSION’ MOLECULES

SARCOLEMMA

SKELETAL MUSCLE FIBER/MYOCYTE

synaptic cleft

POST-SYNAPTIC MEMBRANE

AXOLEMMA

SYNAPTIC VESICLES

voltage-gated ion channels

voltage-gated ion channels

ACh receptors

Ligand-gated ion channels

Cholinesterase

Acetyl Choline/ACh

PRE-SYNAPTIC MEMBRANE

Ca2+ channels

SKELETAL MYOFIBER: Initiating contraction

Z line

motor end-plate

sarcolemmaT/transverse tubule

Sarcoplasmic reticulum wraps around myofibril and releases Calcium ion, when stimulated via T-tubule & feet

Feet

Terminal cisterna of SR

Triad = T-tubule + two terminal cisternae

}

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

A-I junction

MUSCLE CONTRACTION: Requirements

CONTROLLED voluntary & involuntary: nervous;

& nervous + diffuse chemical control

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

MYOFIBRIL

AROUND EACH MYOFIBRIL, meaning between myofibrils

Glycogen granules Sarcoplasmic reticulum

Mitochondria

energize

energize

control

Myofilaments generate force

THREE MAIN TYPES OF MUSCLE

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

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

SKELETAL most 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

THREE MAIN TYPES OF MUSCLE I

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

THREE MAIN TYPES OF MUSCLE II

CARDIAC

strong rhythmic contractions;

controlled by own cell-to-cell connections;

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

THREE MAIN TYPES OF MUSCLE III

SKELETAL most 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

THREE MAIN TYPES OF MUSCLE IV

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

THREE MAIN TYPES OF MUSCLE: Sub-types

SMOOTH skin, cardiovascular, airway, uterine, other reproductive, urinary, gastrointestinal (GI)CARDIAC atrial, ventricular, nodal, PurkinjeSKELETAL type I - slow, type IIa - fast oxidative, type IIb - fast glycolytic

SKELETAL MYOFIBER: Needs determining structure

Generation

Force generation

Stabilization

Force application

Control of contraction

Energize

CARDIAC MUSCLE

striated/cross-banded CARDIOMYOCYTES

Capillary

INTERCALATED DISK

central NUCLEUS

branching muscle fibersSarcolemma & external lamina

Reticular fiber

INTERCALATED DISC - electro-mechanical union

ID is a strong myocyte-myocyte attachment + electrical connections

Fascia adherens strength

Maculae adherens strength

Gap junction transmits contraction

PURKINJE FIBER

} Endocardium

Sub-endocardium

Large, pale cell specialized for conduction, not contraction

Myofilaments

Glycogen

ventricle

SMOOTH MUSCLE

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

Reticular fiber

Gap junction/NexusAutonomic 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

SMOOTH MUSCLE

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

SMOOTH MUSCLE

* 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

CAVEOLA

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 - Transcytosis

Endocytosis or

Signal transduction

Plasmalemma

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

cross-section

long.-section

Unseen are reticular and nerve fibers, plasmalemmas & external laminae

Trichrome stains distinguish smooth muscle cells from collagen fibers

SKELETAL MYOFIBER: Needs determining structure

Generation

Force generation

Stabilization

Force application

Control of contraction

Energize

MYOFIBER: Stabilization* & Force Application materials

Z line

M line*

a-actinin*

Sarcolemma External lamina

Nebulin*

Titin* (“elastic”)

Dystrophin

Desmin* intermediate filaments

Integrin

SKELETAL MUSCLE: SENSORY INNERVATION

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

CARDIAC MUSCLE

striated/cross-banded CARDIOMYOCYTES

Capillary

INTERCALATED DISK

central NUCLEUS

branching muscle fibersSarcolemma & external lamina

Reticular fiber

CARDIAC PATHOLOGY

Enlarged, but altered and weakened muscle of Ventricular hypertrophy

Capillary

Reticular fiber

Blocked vessels damaged heart muscle (Cardiac infarct)

More & thicker fibers of Fibrosis

Bad gap junctions Arrythmiaaltered connexin

WHERE AM I? Online Anatomy Module 1

APPENDICULAR SKELETON

CELL

ORIENTATION

EPITHELIUM

CONNECTIVE TISSUE

MUSCLE

NERVOUS SYSTEM

AXIAL SKELETON

MUSCLES

EMBRYOLOGY

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