Exam 3 (Muscles)

Question 1

What is the M line?

Answer 1

where myosin strands bind

Question 2

What is the I band?

Answer 2

area of actin not bound to myosin

Question 3

What is the relaxation period in a muscle contraction?

Answer 3

Ca⁺⁺ is pumped back into sarcoplasmic reticulum

time varies across muscle type

Question 4

What does connective tissue do?

Answer 4

matrix for nerve and blood cells; attaches tendons to bones

Question 5

What are the features of nebulin?

Answer 5

inelastic; aligns actin

Question 6

What controls skeletal muscle?

Answer 6

neurotransmitters from somatic neuron

Question 7

What controls cardiac muscle?

Answer 7

autorhythmic; some hormones

Question 8

What controls smooth muscle?

Answer 8

Ach; epinephrine; paracrines (NO)

Question 9

What causes cramps?

Answer 9

low muscle K⁺ → Ca⁺⁺ stays out of sarcoplasmic reticulum → muscle stays contracted

Question 10

What is the latent period in a muscle contraction?

Answer 10

pause between ACh stimulus and the actual muscle contraction

standard across muscle type

Question 11

What is the muscle equivalent of the cell membrane?

Answer 11

sarcolemma

Question 12

What causes parasthesia?

Answer 12

constricted blood flow to nerve → nerve can’t respond until O₂/glucose restored

Question 13

What is the Z disc?

Answer 13

where actin strands bind

Question 14

What are the forms of troponin?

Answer 14

• TN-I: binds actin
• TN-T: binds TM
• TN-C: binds Ca⁺⁺ → TN conformational change → TM move → stronger actin/myosin bond → power stroke

Question 15

What are the factors involved in peripheral muscle fatigue?

Answer 15

• inadequate ACh synthesis
• increased local [Pi]
• calcium phosphate → Ca⁺⁺ can’t bind to TN
• reduced muscle glycogen stores

Question 16

What is the function of tropomyosin (TM)?

Answer 16

covers actin; blocks actin-myosin binding sites

Question 17

What causes benign muscle fasciculations (twitching)?

Answer 17

low blood Ca⁺⁺ → somatic motor neuron vgNa⁺ channels open easily → neuron depolarizes randomly

Question 18

What is the H zone?

Answer 18

area of myosin not bound to actin

Question 19

What are the features of titin?

Answer 19

largest protein; elastic; returns stretched muscle to resting length

Question 20

What are the steps of triggering a muscle contraction?

Answer 20

1. ACh released from neuron
2. ACh binds to lg-Na⁺ channels → Na⁺ influx
3. depolarization down t-tubule → conformational change in DHPR (protein plug)
4. RyR (protein pore) opened → Ca⁺⁺ release
5. Ca⁺⁺ binds to TN → muscle contraction

Question 21

How is muscle contraction regulated?

Answer 21

1. acetylcholinesterase hydrolyzes ACh → terminates action potential
2. Ca⁺⁺ ATPase pumps Ca⁺⁺ back into sarcoplasmic reticulum

Question 22

What happens when myosin binds to actin?

Answer 22

Pi is released; power stroke

Question 23

What does botulism do?

Answer 23

blocks ACh release

Question 24

What happens when ATP is hydrolyzed by myosin ATPase?

Answer 24

myosin cocks and binds to actin (cross-bridge)

Question 25

What are the two types of muscle fatigue?

Answer 25

central (only in brain)

peripheral (in muscle)

Question 26

What happens when ATP binds to myosin?

Answer 26

myosin dissociates from actin