Muscles & Skin Flashcards by Holly Grey

What are the muscular system functions?

Body movement (locomotion)
Maintenance of posture
Heart beat
Respiration 
Vasoconstriction

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What are skeletal muscles attached to?

Bones

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What are skeletal muscles responsible for?

Locomotion, facial expression, posture, respiratory movements + body movement

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What are skeletal muscles controlled by?

Somatic motor neurons

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Are skeletal muscles voluntary in action?

YES

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What are the cardiac muscles controlled by?

Involuntarily controlled by endocrine + autonomic nervous system

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Where are smooth muscles found?

Hollow organs, blood vessels, eyes, uterus + skin

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What are some functions of smooth muscles?

Propel urine, mix food in digestive tract, dilating/constricting pupils + regulating blood flow

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What are smooth muscles controlled by?

Involuntarily by endocrine + autonomic nervous systems

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What is a muscle?

Soft tissue which cells are rich in actin + myosin that slide past one another, producing contraction

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What is a syncytium?

Multinucleated cell that can result from multiple cell functions of uninuclear cells

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What is an example of a structural syncytium?

Skeletal muscle

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What is an example of a functional syncytium?

Cardiac or smooth muscle

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Describe the structure of myofiber

Membrane = sarcolemma 
T-tubules 
Multinucleated 
Myofibrils assembled into myofibers 
Fibres surrounded + bundled by connective tissue

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Describe structure of cardiomyocyte

Single centrally located nucleus 
Branching structure 
Mitochondria
Abundant reserve of myoglobin 
Each cell in contact with adjacent cells

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Why do cardiomyocytes have a large reserve of myoglobin?

To store O2

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Why do cardiomyocytes have each cell in contact with adjacent cells?

Have membrane modification to increase SA

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What are electrical coupling (intercalated discs)?

Specialised intracellular attachment of cardiac muscle cells compromising gap junctions

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What are gap junctions?

Intracellular channels that allow for direct chemical communication between adjacent cells through diffusion of ions + small molecules without contact with extracellular fluids

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What are desmosomes?

Fasteners through plasma membrane of adjacent cells by means of intermediate filaments, compassed of keratin or desmin to form dense plaque

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What is a sacromere?

Repeating functional unit of myofibrils or cardiomyocyte

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What is A-band (dark) made up of?

Thick myosin filament

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What is the I-band (light)?

From Z discs to end of thick filaments

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What is the M line?

Protein which thick filaments attach

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What is the H-zone?

Thick filaments with NO thin

What are the Z discs?

Filamentous network of protein, attaches actin filament

What are thin filaments?

Elastic chains of polypeptides

Describe myosin

Thick, fibrillar protein

Describe actin

Thin, globular protein

What colour is a slow twitch muscle?

Red

What colour is a fast twitch muscle?

White

What is the density of capillaries in slow twitch fibres?

High

What is the density of capillaries in fast twitch fibres?

Low

What is the density of mitochondria in slow twitch fibres?

High

What is the density of mitochondria in fast twitch fibres?

Low

What is the density of myoglobin in slow twitch fibres?

High

What is the density of myoglobin in fast twitch fibres?

Low

What type of energy is released in slow twitch fibres?

Aerobic (oxidative phosphorylation)

What type of energy is released in fast twitch fibres?

Anaerobic (glycolysis)

What type of fuel for slow twitch fibres?

Fats or carbohydrates

What type of fuel for fast twitch fibres?

Carbohydrates-glucose

What are the dynamics of slow twitch fibres?

Slow, lasts for long time with little fatigue

What are the dynamics of fast twitch fibres?

Fast, fatigue develops quickly

What type of force for slow twitch fibres?

Little

What type of force for fast twitch fibres?

Powerful

Describe the muscle contraction mechanism

``` ATP hydrolysed ADP + Pi bind to myosin head Ca2+ binds to troponin = exposes myosin binding site Myosin head binds to actin Power stroke occurs Sarcomere contracts ADP + Pi dissociate from myosin New ATP bind to myosin = detachment of myosin from actin Hydrolysis of ATP ----> ADP + Pi = recocks head ```

Describe what happens in contraction

``` Stimulate Na+ channel to open = stimulates Ca2+ channels to open DEPOLARIZATION Ca2+ conc + = Ca2+ release from Ryanodine receptors Ca2+ stimulate contractile apparatus ```

Describe what happens in relaxation

Ca2+ reuptake into SR Withdrawal of Ca2+ to extracellular media Active transport Exchange of Ca2+ for 3Na+ with Na+/Ca2+ exchanger Then 3Na+ exchanged for 2K+ with Na+/K+-ATPase Activation of K+ channels REPOLARIZATION

What are examples of vascular smooth muscles?

Arteries, veins + lymphatic vessels

What are examples of visceral smooth muscles?

Airways, GI tract + urinary system

What does it mean smooth muscles are strated?

No sarcomeres

Describe smooth-muscle contraction

Excitation-depolarisation = opening of voltage-gated L-type Ca2+ channels Ca2+ released from ER/SR via RYR = increases [Ca2+] Ca2+ binds to calmodulin (CaM) Ca2+-CaM complex activates myosin light chain kinase (MLCK) MLCK phosphorylates myosin head + stimulates contraction

What is importance of Ca2+?

Responsible for depolarisation + propagation of excitation Activation of contraction of muscles Ca2+ important signal molecule + 2nd messenger

What is the excitation for skeletal muscles?

Voltage-gated Na+ channels

What is the contraction for skeletal muscles?

Ca2+ release from internal stores (SR)

Why do skeletal muscles have short latent period?

Need fast response

What is the excitation for cardiac muscles?

Voltage-gated Ca2+ channels

What is the contraction for cardiac muscles?

External Ca2+ influx released from internal stores

Why are cardiac muscles latent period not as fast as skeletal muscles?

Still must be fast to push blood to circulation system

Why do cardiac muscles have long action potential?

Increases absolute refractory period | = decreases probability of arrhythmia

What is the excitation for smooth muscles?

Voltage-gated Ca2+ channels

What is the contraction for smooth muscles?

Extend Ca2+ influx + partly Ca2+ release from internal store (SR)

Why do smooth muscles have long latent period?

Slow to contract

What is latent period?

Time between stimulus + muscle contraction

What is a twitch in muscle excitation?

Single contractile action

What is a wave summation in muscle excitation?

Muscle does not relax between stimulations | Fibre re-stimulated while there is still some contractile activity

What is a incomplete tetanus in muscle excitation?

Frequency of stimulation increases, contractions fuse into total contraction with partial relaxations between events

What is a complete tetanus in muscle excitation?

Frequency of stimulation is maximal + separate events fuse into smooth, continuous contraction with no relaxation

What happens due to force of contraction rises with frequency of stimulation, in tetanus?

Increases Ca2+ around myofibril with Ca2+ ATPase are unable to manage intracellular Ca2+

What are the functions of skin?

``` Regulates body temp Stores blood Protects body Detects cutaneous sensations Excretes + absorbs substances Synthesises vitamin D ```

What is stratum basale?

Contains basale keratinocytes that form basal lamina + attach to dermis These keratinocytes proliferate + regenerate epidermis

What is stratum spinosum?

Contain suprabasal keratinocytes that differentiate + produce different types of keratin

What is the "spinous" appearance of keratinocytes caused by?

Desmosomes

What is stratum granulosum?

Keratinocytes start losing their nuclei + cytoplasm appears granular Lipids released from cells to contribute to cornified envelop

What is stratum lucidum?

Clear or translucent layer only found in palms + soles

What is stratum corneum?

Outermost layer of 10-30 flattened cells without nucleus or other organelles Cells surrounded by keratin, lipids + other crosslinked proteins forming barrier

What happens to dead cells?

Exfoliated requiring constant regeneration of epidermis

What are holocrine glands?

Secretions are released by rupture of plasma membrane, which destroys the cell + results in secretion + cell remnants into lumen

What is an example of a holocrine gland?

Sebaceous glands

What are merocrine cells?

Secretions are released by exocytosis

What is exocytosis?

Fusion of secretory vesicles with cell membrane + release of product to outside the cell

What is an example of a merocrine gland?

Sweat glands

What are apocrine glands?

Secretions released by budding off the apical portion of cells including the secreted product

What is an example of an apocrine gland?

Mammary gland

Muscles & Skin Flashcards

(84 cards)