Muscular Movement

Question 1

Muscle Structure

Organ Level

Answer 1

-major skeletal muscles of the body

Question 2

Muscle Structure

Tissue Level

Answer 2

-neuromuscular junctions and fascicles

Question 3

Muscle Structure

Cellular Level

Answer 3

-myoblasts and myofibers

Question 4

Muscle Structure

Microscopic Level

Answer 4

-sarcomere and myofibrils

Question 5

Muscle Structure

Molecular Level

Answer 5

-actin and myosin

Question 6

From Single Cells to Fibers

Answer 6

• 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

Question 7

How do muscles grow?

Answer 7

• 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

Question 8

Muscle Cell Properties

Answer 8

• lots of mitochondria for ATP / energy

- myofibrils composed of thick and thin filaments of myosin and actin

Question 9

Muscle Contraction

Actin and Myosin

Answer 9

• 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

Question 10

Muscle Contraction

Myosin Activation

Answer 10

• 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

Question 11

Nerve Impulse to Muscular Movement

Answer 11

• 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

Question 12

Motor Neuron Junction

Steps

Answer 12

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

Question 13

Diffusion and Distance Equation

Answer 13

= 2mDt

-where D is the diffusion constant, t is the diffusion time and m is the number of dimensions

Question 14

Pressure and Concentration Equation

Answer 14

Δp = Δc kb T

Question 15

Pressure and Tension

Answer 15

Δp = 2λ/R

-where λ is the tension and R is the radius of the cell

Question 16

Signalling into the Muscle Cell

Answer 16

• 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

Question 17

Calcium Cycle

Answer 17

• 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

Question 18

Oubain

Answer 18

• 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

Question 19

What are most procces carried out by?

Answer 19

-molecular motors

Question 20

What dominate behaviour at a cellular level?

Answer 20

• stochastic interactions

- probabilistic transitions

Question 21

What do cells use when they can’t rely on probabilistic events?

Answer 21

-the large free energy change of the ATP - > ADP reaction can be used to drive the system form equilibrium