Muscular Movement Flashcards
Muscle Structure
Organ Level
-major skeletal muscles of the body
Muscle Structure
Tissue Level
-neuromuscular junctions and fascicles
Muscle Structure
Cellular Level
-myoblasts and myofibers
Muscle Structure
Microscopic Level
-sarcomere and myofibrils
Muscle Structure
Molecular Level
-actin and myosin
From Single Cells to Fibers
- each skeletal fibre is a single skeletal muscle cell / skeletal myocyte formed from the fusion of precursor cells:
1) cell multiplication, dividing myocytes
2) multiplication ceases and cells align
3) aligned cells fuse, appearance of muscle specific proteins
4) spontaneous contractiuons begin in the muscle fiber
How do muscles grow?
- mature cells can chage in size but new cells aren’t formed when muscles grow
- more myofibril strands made of myosin and actin contractile proteins are created
Muscle Cell Properties
- lots of mitochondria for ATP / energy
- myofibrils composed of thick and thin filaments of myosin and actin
Muscle Contraction
Actin and Myosin
- actin filaments form the thin filaments
- bundles of over 200 myosin II proteins form the thick filaments
- upon activation, myosin II heads pull opposing actin filaments towards each other
Muscle Contraction
Myosin Activation
- in relaxed state, tropomyosin blocks the myosin binding sites on the actin preventing cross bridges from forming and keeping the muscle in the relaxed state
- Ca2+ binding to troponin alters the shape of the tropomyosin which uncovers the myosin binding sites and allowing muscular contraction to occur
Nerve Impulse to Muscular Movement
- motor neurons carry signal from the brain along axons from the spinal cord to muscles
- dendrites collect the sigl/nal
- the axon passes it along to the muscular fiber
Motor Neuron Junction
Steps
1) nerve impulse arrives at axon terminal
2) Ca2+ ions released into axon terminal
3) Ca2+ causes synaptic vesicles to release acetylcholine (ACh) via exocytosis
4) ACh binds to ion channels in the muscular fiber membrane allowing flow of Na+ ions into the muscles cell which reverses the membrane potential
Diffusion and Distance Equation
= 2mDt
-where D is the diffusion constant, t is the diffusion time and m is the number of dimensions
Pressure and Concentration Equation
Δp = Δc kb T
Pressure and Tension
Δp = 2λ/R
-where λ is the tension and R is the radius of the cell
Signalling into the Muscle Cell
- ACh binding to receptors in the muscle cell membrane allows the flow of Na+ in which reverses the membrane potential
- this propagates down the T (transverse) - tubules which are deep indents in the membrane into the cell through a chain reaction of voltage gated sodium channels
Calcium Cycle
- muscle cells usually maintain a low internal calcium concentration
- a small increase in this concentration leads to contraction
- to maintain the low concentration, calcium is actively pumped out of muscle cells or into organelles for storage
Oubain
- in cardiac muscle cells, an antiporter which couples extusion of Ca2+ to entry of Na+ into the cell is used
- the drug is used to treat heart failure by inhibiting activity of Na-K pumps
- this raises the intracellular concentration of sodium which reduces the activity of the Na-Ca exchanger
- the intracellular calcium concentration is therefore maintained at a higher than usual level leading to higher cardio contractility
What are most procces carried out by?
-molecular motors
What dominate behaviour at a cellular level?
- stochastic interactions
- probabilistic transitions
What do cells use when they can’t rely on probabilistic events?
-the large free energy change of the ATP - > ADP reaction can be used to drive the system form equilibrium
