Muscles & Skin Flashcards
What are the muscular system functions?
Body movement (locomotion) Maintenance of posture Heart beat Respiration Vasoconstriction
What are skeletal muscles attached to?
Bones
What are skeletal muscles responsible for?
Locomotion, facial expression, posture, respiratory movements + body movement
What are skeletal muscles controlled by?
Somatic motor neurons
Are skeletal muscles voluntary in action?
YES
What are the cardiac muscles controlled by?
Involuntarily controlled by endocrine + autonomic nervous system
Where are smooth muscles found?
Hollow organs, blood vessels, eyes, uterus + skin
What are some functions of smooth muscles?
Propel urine, mix food in digestive tract, dilating/constricting pupils + regulating blood flow
What are smooth muscles controlled by?
Involuntarily by endocrine + autonomic nervous systems
What is a muscle?
Soft tissue which cells are rich in actin + myosin that slide past one another, producing contraction
What is a syncytium?
Multinucleated cell that can result from multiple cell functions of uninuclear cells
What is an example of a structural syncytium?
Skeletal muscle
What is an example of a functional syncytium?
Cardiac or smooth muscle
Describe the structure of myofiber
Membrane = sarcolemma T-tubules Multinucleated Myofibrils assembled into myofibers Fibres surrounded + bundled by connective tissue
Describe structure of cardiomyocyte
Single centrally located nucleus Branching structure Mitochondria Abundant reserve of myoglobin Each cell in contact with adjacent cells
Why do cardiomyocytes have a large reserve of myoglobin?
To store O2
Why do cardiomyocytes have each cell in contact with adjacent cells?
Have membrane modification to increase SA
What are electrical coupling (intercalated discs)?
Specialised intracellular attachment of cardiac muscle cells compromising gap junctions
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
What are desmosomes?
Fasteners through plasma membrane of adjacent cells by means of intermediate filaments, compassed of keratin or desmin to form dense plaque
What is a sacromere?
Repeating functional unit of myofibrils or cardiomyocyte
What is A-band (dark) made up of?
Thick myosin filament
What is the I-band (light)?
From Z discs to end of thick filaments
What is the M line?
Protein which thick filaments attach
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