Muscle II Flashcards
Does skeletal muscle have cell junctions?
No
Smooth muscle has more myosin than skeletal. t/f
False
Smooth muscle has more actin than skeletal. t/f
True
Smooth muscle has sarcomeres , t/f
False
How are myosins in smooth?
They are longer than skeletal and are covered entirely in heads.
How are contractile fibres organised in smooth?
Actins are bound to dense bodies which are then connected to each other by a network of intermediate filaments
Where do the calcium ions for contraction come in the smooth?
From the extracellular fluid as well as from the sarcoplasmic reticulum
What direction can the myosin heads go to?
Both
What are single-unit smooth muscle cells?
Cells connected by gap junctions. A few neurones control a large area
What are multi-unit smooth muscle cells?
Cells with no gap junctions between each other. they need more neuronal wiring and allow finer contractions
Describe process of contraction in smooth
- Calcium enters the cell and is released from SR
- Calcium binds to Calmodulin
- Calmodulin-Ca++ complex activates Myosin Light Chain Kinase (MLCK)
- MLCK phosphorylates myosin heads leading to contraction
Describe process of relaxation in smooth
- Calcium ions are pumped out of the cell and inside sr.
- Calcium ions unbind from calmodulin
- Decreased MLCK activity
- Increased Myosin Light Chain phosphatase (MLCP) activity that decreases tension
What happens to myosins when levels of MLCP are high
Myosin heads become sensitized so low levels of calcium are enough for contraction to happen
What happens with high levels of MLCP activity?
Myosins become desensitised so even high concentrations of calcium cannot start contractions
What does IP3 do?
It triggers release of Calcium ions by the sarcoplasmic reticulum
Can smooth muscles be autorhythmic ?
Yes
Is troponin present in smooth muscles ?
No
Is sarcoplasmic reticulum present in smooth?
Yes
Is calmodulin present in skeletal muscles ?
No
What is the name of the toxin that causes tetanus?
Tetanospasmin
What bacterium releases tetanus toxin?
Clostridium Tetani
What does tetanospasmin do?
It enters the motor neurons and is transported into the spinal cord. Here it stops the release of neurotransmitters by the inhibitory interneurons.
How can tetanospasmin cause spasms?
It stops inhibitory interneurons from firing, so the muscles are never relaxed and keep on contracting until they start spasming uncontrollably
What is inheritance pattern of distal Arthrogryposis ?
Autosomal dominant
What genes are mutated in Distal Arthrogryposis ?
TPM2 (TroPoMyosin 2)
MYBPC1 (Myosin Binding Protein C )
What is the inheritance pattern of Muscular dystrophies ?
Xlinked recessive
What the worst between Duchenne and Becker?
Duchenne (no dystrophin at all)
Whereas Becker is defective dystrophin
What happens in muscular dystrophies?
Dystrophin is defective or absent. It is a protein that links cytoskeletal actin to extracellular matrix; the cell is therefore weak and cannot withstand the stress of contraction leading to leaking of components like creatine kinase(goes out) and calcium (in). This leads to muscle cell death
Does smooth muscle have sarcomeres?
No
Does smooth muscle have t tubules?
No
Does smooth muscle have t sarcoplasmic reticulum?
Yes
Can hormones influence skeletal muscles?
No
How can smooth muscle initiate contraction?
Stretch, chemical signal, autorhythmic.
Does smooth muscle have troponin?
No
Smooth muscle has more myosin than skeletal. T or F
False
Smooth muscle has more actin than skeletal. T or F
True
Are myosins different in smooth? How?
They are longer, with more heads
How are actins and myosisns organised in smooth ?
Actin is attached to dense bodies, which are then connected to each other by intermediate filaments
In what direction can myosins in smooth travel?
Both
What are single-unit smooth cells?
Smooth muscle cells that are connected by gap junctions so only a few neurons are needed to activate simultaneously a big area.
What are multi-unit smooth cells?
Smooth muscle cells not connected by gap junctions and therefore need wiring by neurons. Allows finer control of contraction
Describe process of smooth muscle contraction
- Calcium enters the cell
- Calcium released from sr as well
- Calcium binds to calmodulin
- Ca2+-Calmodulin complex activates Myosin Light chain Kinase (MLCK)
- MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
- Activated myosin cross bridges along actin creating muscle tension
Describe relaxation process of smooth muscles
- Free Calcium decreases when it is pumped out of the cell or back into sr
- Calcium unbinds from calmodulin. MLCK activity decreases
- Myosin Light chain Phosphatase removes phosphate from myosin light chains, decreasing its ATPase activity
- Less ATPase activity results in decreased muscle tension
What happens to myosin with low concentrations of phosphatase?
Myosin becomes sensitised so low levels of calcium are enough for tension to occur
What happens to myosin with high concentrations of phosphatase?
Myosin becomes desensitised so even high levels of calcium are not enough for tension to occur
What does IP3 do?
It increases Sarcoplasmic reticulum release of calcium
What is the toxin from clostridium tetani’
Tetanospasmin
Where is tetanospasmin taken up to?
Transported by motor neurons to the spinal cord
What does tetanospasmin do?
It inhibits release of neurotransmitter from inhibitory interneurons. Therefore disrupts normal balance of motor neuron excitation and inhibition, leading to excessive excitation and muscle spasm.
What is the inheritance pattern of distal Arthrogryposis ?
Autosomal dominant
What is the inheritance pattern of muscular dystrophies ?
Xlinked recessove
What happens in muscular dystrophia ?
Defects in dystrophin that links cytoskeletal actin to extracellular matrix. This leads to weaker muscular cells that cannot withstand the contraction and therefore leak important molecules like calcium, thus leading to muscle cell death and its replacement with connective tissue
