BIOL 273 - Unit 3.4 +3.5 Flashcards
What is the tension exerted by a muscle during a single twitch is influenced by (2)
- Muscle type (fast twitch can generate more force)
- Sarcomere length (at rest)
Describe the overlaps at rest of the thick and thin filaments
- Too little overlap - few crossbridges/little force
- Too much overlap - actin filaments start to interfere with eachother/ less force generated
- Way too much overlap - thick filaments collide with Z disks/ force rapidly decreases
How to increase single tension
increase the rate of action potentials before cell can fully release
- summate tension
What is the term of the state of a musce when it reches maximum force of contraction
Tetanus; 2 types that are dependant on rate of stimulation
What is Incomplete (unfused) tetanus
slow stimulation rate - fibre relaxes slightly between stimuli
- won’t fully relax thus it will summate and lead to tetanus
- doesn’t stay at maximum tension
What is complete (fused) tetanus
fast stimulation rate - fibre does not have time to relax
- stays at maximum tension
What is the motor unit
the basic unit of contraction in an intact skeletal muscle
- many are found in a muscle
- all muscle fibres of a motor unit are of the same type
What are the two components of the motor unit
- A group of muscle fibres
- A somatic motor neuron that controls them all
How can the contraction of the muscle vary (2)
- Changing the type of motor unit that is activated
- Changing the number of motor units that are active
describe the threshold for stimulation of slow oxidative fibres and fast glycolytic fibres
slow: have a low threshold for stimulation
fast: have a high threshold for stimulation
Describe isotonic movement
- creates force and moves a load
- the load is usually constant, and the muscle length changes
Describe isometric movement
- creates force without movement
- muscle length is constant (contracts)
- the load is usually greater than the force that can be applied
Where is smooth muscle found in the body?
- walls of hollow organs and tubes - not attached to bones of skeleton
- ex. bladder, sphinchter, intestine, walls of blood vessels
Two ways smooth muscle cells can be arranged
- Single unit - cells connected via gap junctions
- Multi unit - no connections
Single unit characteristics
- not necessary to elctricaly stimulate each individual fibre because there are gap junctions
- found on walls of internal organs ex blood vessels
Multi-unit characteristics
- each individual muscle fibre is separatley innervated
- eg. iris of eye, parts of reproductive organs
What kind neuron innervates smooth muscle
autonomic neurons (sympathetic and parasympathetic)
differentiate the contraction between smooth and skeletal muscle
- skeletal muscle changes length when contracts
- smooth muscle changes shape, not just length
Differentiate the speed of contraction between smooth and skeletal muscle
- smooth muscle develops tension musch slower than skeletal muscle
- however that contraction can be sustained for a long period of time without fatiguing
Differentiate between smooth and skeletal muscle on a cellular level
- fibres much smaller in smooth muscle than skeletal fibre
- No striations on smooth muscle / no sarcomeres
- actin and myosin arranged in long bundles around periphery of the cell
- actin anchored by dense bodies and not Z lines
- smooth muscles have caveolae instead of T-tubules in sarcolemma for cell signalling (to hold calcium)
how does smooth muscle starts the path to begin to contract, with the absence of t tubules?
“calcium dependent calcium release “
- influx of calcium that causes the release of more calcium in the SR
Differentiate between skeletal and smooth muscles on a molecular level
- less myosin per unit actin in smooth muscle
- Actin and myosin filaments are longer and overlap more in smooth muscle
- develop tension slower in smooth muscle because of slow Myosin ATPase activity
- myosin heads are located along all parts of myosin in smooth
- no troponin in smooth
What is the major difference between contraction of smooth muscle and skeletal muscles
“Role of Phosphorylation”
Signal to initiate contraction is increase in cytosolic calcium, how does calcium enter ECF? (3)
- Voltage gated channels - due to depolarizing
- Stretch activated channels - due to membrane stretch
- Chemically gated channels - due to hormones
What does calcium entry in the ECF in smooth muscle result in
release of additional calcium from the SR
Since there is no troponin for calcium to bind to in smooth muscle, what does it bind to instead? What results in this?
calmodulin in the cytosol
- leads to the activation of the enzyme “myosin light chain kinase (MLCK)”
- which will phosphorylate myosin heads
What is the role of MLCK (myosin light chain kinase)
activates myosin by phosphorylating the light chain of the myosin molecule using the inorganic phosphate from ATP
- ATPase activity depends on phosphorylation of myosin - which can then break apart ATP to initiate crossbridge cycle
How is the crossbridge cycle/contraction initiated in smooth muscles
When phosphorylated myosin interacts with actin
- MLCK uses inorganic phosphate from ATP to activate myosin (turn it on)
- but more ATP is needed to go through crossbridge cycling contraction to occur
What structure of smooth muscle and skeletal muscle determines the initiation of the crossbridge cycle
Smooth muscle: myosin is regulated via phosphorylation of myosin
Skeletal muscle: actin is regulated via troponin/tropomyosin interaction with actin
Describe relaxation in smooth muscle ; what molecules are used to remove calcium
Calcium ions is removed from the cytosol as it is pumped out of the cell or into the SR
Ca2+ - Na+ antiport (calcium out and sodium in)
Ca2+ ATPase
Decrease levels of calcium in cytosol causes calcium to unbind from calmodulin (inactivates MLCK)
Myosin light chains are dephosphorylated by protein myosin phophatase (MLCP)
Does dephosphorylation of myosin relax the smooth muscle
- does not automatically relax the muscle, smooth muscle enters latch state
- tension is maintained but with minimal ATP consumption
