Unit 1 Topic 5

Question 1

What is the function of troponin?

Answer 1

binds calcium to allow the confromational change of tropomyosin so that myosin can bind to actin

Question 2

What is the function of tropomyosin?

Answer 2

blocks myosin binding sites on actin

Question 3

What is the function of actin?

Answer 3

binds myosin

Question 4

What is the function of titin?

Answer 4

stabilize the thick filament during contraction

Question 5

What is the function of myosin?

Answer 5

-molecule tails wind together into a filament
-myosin heads (S1 heads) protrude from the thick tails and are oriented in 2 directions
-Bind to actin

Question 6

What are the steps of skeletal muscle contraction?

Answer 6

-ACh release from the nerve terminal binds to nicotinic ACh receptors and allows opening of Na channels to initiate the action potential. Action potentials spread across the membrane to initiate contraction
-Action potential is spread to the T-tubules
-Passive calcium release from the SR elicits muscle contraction, but upon relaxation actively returned to the SR due to the closure of channels

Question 7

What are the details of smooth muscle contraction?

Answer 7

-Responses regulated by the autonomic nervous system, hormones, physical stresses, or substances released from local tissues
-Smooth muscle contraction is indirectly Ca dependent
-Receptor expression determines response and uses ACh, Epi, NE, histamine, etc.
Hormone/chemical binds to receptor
Calcium influx from extracellular domain and SER binds to calmodulin
Calmodulin/calcium complex binds to/activates myosin light chain kinase (MLCK)
Inactive myosin is converted to active myosin by MLCK and binds myosin; ATP-dependent contraction cycle starts

Question 8

What replaces Z lines in smooth muscle?

Answer 8

dense bodies

Question 9

What organelles are found in skeletal muscle?

Answer 9

multiple nuclei are pushed to the periphery

Question 10

How are myofibrils organized in skeletal muscle?

Answer 10

lie along the long axis of the fiber and have repeating patterns of protein filaments producing a striated apperance

Question 11

What organelles are in cardiac muscle?

Answer 11

-Intercalated Disk: combination of desmosomes and gap junctions that link cells anatomically and physiologically
-T Tubules: significantly larger diameter T-tubules, but SR is more sparse; cardiac T tubules align with the Z lines, therefore only 1 per sarcomere to form dyads
-Mitochondria: in rows aligned between myofibrils
-Calcium binds to troponin as in skeletal muscle

Question 12

How are myofibrils organized in cardiac muscle?

Question 13

What are the organelles in smooth muscle?

Question 14

How are myofibrils organized in Smooth muscle?

Question 15

What is the ability of skeletal muscle to regenerate?

Answer 15

can possibly regenerate and may result in hypertrophy

Question 16

What is the ability of cardiac muscle to regenerate?

Answer 16

unlikely to regenerate and hypertrophy occurs with overuse

Question 17

What is the ability of smooth muscle to regenerate?

Answer 17

can undergo mitosis to regenerate leading to hyperplasia; hypertrophy also occurs