Ch. 10 - Muscular Tissue Flashcards
C/C the appearances of skeletal, cardiac, and smooth muscle tissues
SK - multi-nucleated, striated
C - one nucleus, striated, intercalated discs
SM - one nucleus, no striations
What are 5 functions of muscle tissue?
- movement
- stabilization
- regulating organ volumes
- movement of substances w/i bodies (smooth, cardiac)
- generating heat (involuntary contraction of skeletal muscles)
What are 4 properties of muscle tissue?
- electrical excitability
- contractility
- extensibility
- elasticity
What are skeletal muscles formed of?
thousands of myocytes (muscle fibres!)
3 layers of CT; subcutaneous (adipose, areolar), fascia
blood cells, nerves
What is fascia?
dense sheets of irregular CT that supports and surrounds muscles
What are the 3 layers to help organize muscles?
- endomysium: separates individual myocytes from each other
- perimysium - surrounds fasciles (10-100 myocytes)
- epimysium - surrounds whole muscle
What is the difference between a tendon and aponeurosis?
T - CT layers extending beyond muscle bully, attaching to periosteum
A - extends as broad flat sheet
What are the sarcoplasm, sarcolemma, and sarcoplasmic reticulum??
sarcoplasm = cytoplasm
sarcolemma = plasma membrane
SR = smooth ER; stores Ca2+ ions and encircles each myofibril
What are transverse tubules?
invaginations of sarcolemma that spread the action potential to all parts of myocyte
What are myofibrils?
consist of thick and thin filaments; contractile structures
What causes the striation pattern in skeletal muscle cells?
the arrangement (overlap)of thick and thin filaments; filaments do not change length!
What are the 3 kinds of proteins that make up myofibrils?
contractile - myosin, actin
regulatory - troponin, tropomyosin
structural - titin, myomesin
Describe composition and shape of thick filaments
- made of myosin
- resembles 2 golf clubs twisted together, myosin heads extend towards thin F
- held in place by M line (myomesin)
Describe composition and shape of thin filaments
- made of actin, with some trop/tropomyosin
- actin filaments bind to myosin
- held in place by Z discs
What occurs prior to a contraction cycle?
- myosin binding sites on actin are covered by tropomyosin
- onset of contraction: SR releases Ca2+ into sarcoplasm
- Ca2+ bind to troponin and cause trop-tropom compolexes to move away from m-binding sites on actin
- once binding sites are free, contraction cycle begins
What are the steps of the contraction cycle?
- ATP binds to myosin head hydrolyzes atp
- attachment of activated M to A, forming crossbridge
- powerstroke (movement of thin F to M line via myosin head pivoting)
- ATP binds to myosin head, detachment of myosin from actin
What is rigor mortis?
rigidity of muscles after death bc muscle cant contract/stretch due to lack of ATP synthesis
- after death, calcium leaks out of SR, allowing binding of M heads to actin, but myosin cannot detach from actin due to lack of ATP
What causes the Ca2+ to be released? What is this phenomenon?
muscle action potential - rapid change in membrane potential that involves depolarization followed by repolarization
What is excitation-contraction coupling?
excitation - muscle action potential along sarcolemma, into T tubules
contraction - sliding of filaments
How does a muscle contraction begin?
motor neurons send NT acetylcholine to trigger an action potential in muscle sarcolemma
What is a neuromuscular junction (NMJ)?
a type of synapse where communication occurs bt neuron and muscle cell
What are the components of a NMJ?
- synaptic end bulbs (end of axon terminal) containing synaptic vesicles filled with ACh
- motor end plate membrane (part of muscle cell) containing ACh receptors
What is the process of a neuron action potential?
- ACh is released from synpatic vesicle (in axon)
- ACh binds to ACh receptor (on muscle cell)
- Muscle action potential is produced
- AChE breaks down ACh on receptors on motor end plate, causing action potential to cease, and muscle cell to relax
What role do muscle proteins play in muscle contractions?
contractile prot (myosin and actin)
What is a motor unit made of?
motor neuron and muscle fibers it innervates
What do motor units produce?
smooth muscle contraction; delays muscle fatigue so contraction can be sustained
Do precise movements require smaller or larger contraction?
smaller (fewer fibers per neuron)
e.g. 10-20 for eye movements, 2000-3000 in biceps brachii
Which motor units are required first? What is the purpose of this?
weaker ones, then progressively stronger ones if tasks requires more force
saves energy, allows precision/control to movements
What is muscle tone?
involuntary contraction of a small number of muscle fibers (active and inactive muscle fibers)
What does muscle tone accomplish?
- keeps muscles firm while relaxed; does not produce movement
- essential for maintaining posture and BP
What does the strength of contraction of a muscle fiber depend on?
- frequency of stimulation
- amount muscle fiber has been stretched before contraction
- availability of nutrients and O2 to fuel rxns; make ATP
Why does frequency of stimulation matter and not the strength?
strength is always the same bc action potential is all-or-nothing; rather depends on number of action potentials it receives per second
What is twitch contraction?
brief contraction of all fibers in a motor unit in response to a single action potential in its motor neuron
What are the 4 stages of a twitch contraction?
- latent period: Ca2+ released from SR
- contraction period: filaments slide past each other
- relaxation period: active transport of Ca2+ back into SR
- refractory period: muscle fiber cannot respond and has lost its excitability (cant be stimulated by another AP)
What is wave summation?
if 2nd AP is applied after the refractory period but before complete M relaxation is complete, the force of 2nd contraction is stronger than first
What is the length-tension relationship?
indicates how the forcefulness of sk muscle contraction depends on length of sarcomeres before contraction begins
What determines sarcomere length?
overlap of thick and thin filaments
What is the difference between isotonic and isometric contractions?
isotonic: tension remains constant while muscle changes in length
isometric: tension generated is insufficient to exceed resistance of object to be moved; does not change in length; no movement
What are 2 types of isotonic contractions?
concentric: muscle shortens to produce force/movement
eccentric: muscle lengthens while maintaining force/movement
When a muscle fiber is active for more than a few seconds, what are the 3 processes to generate ATP?
- from creatine phosphate
- glycolysis
- aerobic cellular resp
What is creatine?
small organic molec produced by liver, kidneys, and pancreas and then transported to muscles
How is ATP generated from creatine phosphate?
- when muscle is relaxed, more ATP that it needs is produced
- excess ATP is used to make creatine phosphate (creatine kinase adds P group to creatine)
- When ATP reserves are exhausted (after few sec of contraction), P group is transferred from creatine phosphate to ADP, to form ATP
What is glycolysis?
glucose breakdown into pyruvic acid
How does glycolysis generate ATP?
if no O2 is present, pyruvic acid is converted into lactic acid, which diffuses into blood
- liver can convert lactic acid back to glucose
How does aerobic cellular respiration generate ATP?
- if sufficient O2 is available, pyruvic acid (amino acid and FA too) enter mitochondria to generate ATP, water, heat
- only source for activity lasting over 2 mins
What are the 3 groups of skeletal muscle fibers?
- slow-oxidative fibers
- fast oxidative-glycolytic fibers
- fast glycolytic fibers
What are SO fibers made of? Describe its function and speed of contraction.
- many mitochondria, BV, high [myoglobin] (dark red)
- smallest diameter, weakest type
- resistant to fatigue; sustained contraction for many hours
How do SO fibers produce ATP?
aerobic cellular resp
What are FOG fibers made of? Describe its function and speed of contraction.
- many mitochondria, myoglobin, BV (red/pink colour)
- hydrolyse ATP at fast rate; fast speed and of contraction
How do FOG fibers generate ATP?
aerobic cellular resp, glycolysis
What are FG fibers made of? Describe its function and speed of contraction.
- few mitochondria and capillaries, low [myoglobin] (white colour)
- largest diameter, strongest type
- hydroylze ATP very rapidly; strong and quick contractions
- fatigue easily
How do FG fibers generate ATP?
glycolysis
What kind of activities are each of these muscle fibers normally used for?
- SO: sustained/prolonged activities (e.g. maintaining posture, endurance activities)
- FOG: some endurance, speed (e.g. walking, sprinting)
- intense anaerobic movements for short duration (e.g. weight-lifting)
The proportions of different type of muscle fibers are related to…
…the function of each muscle
*proportions will vary bt genetics, training
All muscle fibers within a motor unit are of the same type or different type?
same; different motor units are recruited in a specific order
What are some properties of cardiac muscle that differ from skeletal muscle?
- longer release of Ca2+ into SR, causing longer contractions
- cells connected by intercalated discs with gap junctions
- more and larger mitochondria (depends on aerobic resp)
- contract when stimulated by autorhythmic fibers (opposed to ACh triggers)
What are the 2 types of smooth muscle?
visceral (single-unit) and multi-unit
How do the 2 types of smooth muscle differ?
Visceral - found in walls of hollow viscera, small BV; autorhytmic and gap junctions cause fibers to contract in unison
Multi-unit - found in larger arteries, large airways, eye muscles, arrector pili muscles individual fibers each with their own motor neuron ending
Describe smooth muscle and how it differs from skeletal and cardiac muscles
not striated; thick and thin myofilaments not arranged in adjacent sarcomeres
- thin F attached to dense bodies (similar function to Z discs)
- dense bodies attached to intermediate F and to sarcolemma
How do smooth muscles contract and how does it differ from skeletal/cardiac MT?
contracts and twists into a helix as it shortens; relaxes by untwisting
How does contraction of smooth muscle differ from skeletal muscle?
smooth - contraction starts slowly and lasts longer; lacks T tubules and has little SR for Ca2+ storage
- Ca2+ takes longer to reach troponin on thin F; takes longer to leave which accounts for delayed relaxation
- increased tone!
