CHAPTER 9: Muscle and Muscle tissue Flashcards
Skeletal muscle
-Attaches do bone and skin
-Longest fibres, striated
-Voluntary muscle/consciously controlled
Cardiac muscle
-Bulk of the heart
-Striated
-Involuntary
Smooth muscle
-In walls of hollow organs
-Non-striated
-Involuntary
-Visceral
4 characteristics of muscle tissue
- Excitability/responsiveness: ability to receive and respond to stimuli
- Contractibility: Ability to shorten forcibly when stimulated
- Extensibility: Ability to be stretched
4.Elasticity: Ability to recoil to resting length
4 muscular functions
- Produce movement
- Maintain posture/body position
- Stabilize joints
- Generate heat as they contract
Sacrolemma
Muscle fibre plasma membrane
What is sarcoplasm and what does it contain?
Muscle fibre cytoplasm
1. Glycosomes for glycogen stores
2. Myoglobin for oxygen storage
Myofibrils
Densely packed, rodlike elements
Striations, two types of bands
Striped formed from repeating series of dark/light bands
A bands: dark regions
I bands: lighter regions
Sacromere
-Smallest contractile unit of muscle fibre
-Area between Z-discs
-Align end to end along myofibril
Myofilaments
Orderly arranged within sarcomere (actin and myosin)
Actin myofilament
-Thin filament
-Anchored to z-disc
Myosin myofilament
-Thick filament
-Connected at M line
Tropomyosin/troponin
Regulatory proteins bound to actin
Sliding filament model
Thin filaments slide past thick filaments, causing actin/myosin to overlap more
What transports action potential from neuron to muscle and how is it regulated?
Acetylcholine (ACh), regulated by chemically gated ion channels
What is the sequence of the bands/discs/zones during contraction?
- Z discs are pulled towards M lines
- I bands shorten
- Z discs become closer
- H zones disappear
- A bands move closer together
4 events for skeletal muscle contraction
- Events at neuromuscular junction
- Muscle fibre excitation
- Excitation-contraction coupling
- Cross-bridge cycling
Events at the neuromuscular junction
- Action potential arrives at the axon terminal
- Voltage-gated calcium channels open, and calcium enters the motor neuron
- Calcium entry causes ACh neurotransmitter into the synaptic cleft
- ACh diffuses across to ACh receptors on the sarcolemma
- ACh binds to receptors, opens gates, allowing Na+ to enter resulting end plate action potential
- Acetylcholinesterase degrades ACh
3 steps of action potential generation
- Generation of end plate potential
- Depolarization (charge removed)
- Repolarization (charge restored)
How can cross-bridge cycling begin?
- Voltage-sensitive proteins in T tubules change shape, causing sarcoplasmic reticulum (SR) to release Ca2+ to cytosol
- At higher intracellular Ca2+ concentrations, Ca2+ binds to troponin
- Tropinin changes shape and moves tropomyosin away from myosin binding sites
-Myosin heads are then allowed to bind to actin, forming cross-bridges
-Cycling is initiated, causing sarcomere shortening and muscle contraction
-When nervous stimulation ceases, Ca2+ is pumped back into SR, contraction ends
4 steps of the cross-bridge cycle
- Cross bridge formation: high-energy myosin heads attach to actin thin filament active site
- Working (power) stroke: Myosin heads pivot and pulls actin towards m-line
- Cross bridge detachment: ATP attaches to the myosin head, causing cross bridges to detach
- Cocking of the myosin head: The energy from hydrolysis of ATP “cocks” myosin head into high-energy state (this energy will be used for the next power stroke of the cross-bridge)
Slow oxidative fibres
Endurance (ex. marathons)
Fast oxidative fibres
sprinting/walking
