Excitation Contraction Coupling

Question 1

What property of muscle refers to its ability to shorten and generate force?

Answer 1

Contractility

Question 2

What property of muscle refers to its ability to receive an electrical stimulus and generate an action potential from its resting potential?

Answer 2

Excitability

Question 3

What property of muscle refers to its ability to return to its resting length after being stretched?

Answer 3

Elasticity

Question 4

What property of muscle refers to its ability to be stretched back to its resting length?

Answer 4

Extensibility

Question 5

What type of muscle makes up 40% of body weight, attaches to bones, and is under voluntary control via somatic motor neurons?

Answer 5

Skeletal muscle

Question 6

What type of muscle is involuntary, auto-rhythmic but influenced by autonomic nervous system?

Answer 6

Cardiac muscle

Question 7

What type of muscle lines the walls of hollow organs, blood vessels, eyes, glands, uterus, and skin, is involuntary with endocrine and autonomic nervous system inputs?

Answer 7

Smooth muscle

Question 8

________ neurons stimulate muscle fibers to contract, axons branch so each muscle fiber is innervated, and form a neuromuscular junction

Answer 8

Motor

Question 9

_______ is the plasma membrane of the muscle cell, which has invaginations of sarcolemma through the muscle fibers called ___________

The _______ _______ is the calcium storage site for the muscle cell.

Answer 9

Sarcolemma; T-tubules

Sarcoplasmic reticulum

Question 10

______ is a sarcomere structure that serves as the attachment for thin filaments

Answer 10

Z-disk

Question 11

______ is a sarcomere structure that serves as the attachment for thick filaments

Answer 11

M-line

Question 12

Which part of the myosin has ATPase activity?

Answer 12

Heavy chain

Question 13

What are the 3 subunits of troponin?

Answer 13

Troponin T - binds tropomyosin

Troponin C - binds calcium

Troponin I - inhibits actin binding to myosin

Question 14

______ covers the myosin binding sites until troponin binds calcium and removes it so that actin can bind

Answer 14

Tropomyosin

Question 15

If the heavy chain of myosin has the ATPase activity, what does the light chain do?

Answer 15

Regulatory activity

Question 16

______ is the elastic protein responsible for binding myosin to the Z-discs

Answer 16

Titin

Question 17

______ is the protein that serves as a scaffold for actin in the sarcomere

Answer 17

Nebulin

Question 18

What part of the sarcomere serves as the attachment site for actin? How does this area change during sarcomere shortening?

Answer 18

Z-disc - the z-discs move closer together during contraction of the sarcomere

Question 19

What part of the sarcomere serves as the attachment site for myosin?

Answer 19

M-line

Question 20

What part of the sarcomere is made up of mostly myosin? Does this part change length during contraction of the sarcomere?

Answer 20

A-band - does NOT change length!

Question 21

What part of the sarcomere is made up of actin only? Does this part change during contraction?

Answer 21

I-band; YES it shrinks during contraction of the sarcomere because actin filaments are pulled closer together

Question 22

What part of the sarcomere is composed of myosin only and changes length during contraction?

Answer 22

H band (center of sarcomere, shrinks when actin filaments get closer together)

Question 23

Briefly describe the events leading up to a depolarization at the sarcolemma

Answer 23

Action potential travels from motor neuron to muscle fiber at the neuromuscular junction

ACh is secreted into synaptic cleft and binds to nicotinic ACh receptors, increasing sarcolemma permeability to Na+, which opens the voltage gated sodium channels, initiating depolarization on the sarcolemma

Question 24

Once a depolarization/AP occurs on the sarcolemma, what events follow?

Answer 24

Calcium from the EC space enters through the voltage gated calcium channels (DHP receptors), which lie in close proximity to the ryanodine receptors on the sarcoplasmic reticulum.

Calcium exits the SR through the RyR into the cytosol, helping to initiate contraction in the sarcomere.

The action potential ends, and calcium is pumped out of the cytosol via SERCA and the Na+/Ca++ exchanger

Question 25

What is another term for the voltage gated calcium channels in the sarcolemma?

Answer 25

DHP receptors

Question 26

What are the 2 ways that calcium is pumped out the cytosol after an action potential at the sarcolemma ends?

Answer 26

SERCA is an ATPase that takes calcium into the SR

Na+/Ca++ exchanger removes 1 calcium for every 3 sodium exchanged

Question 27

What are the events of the actin-myosin power stroke?

Answer 27

1. ATP binds myosin head, causes dissociation of actin-myosin complex
2. ATP is hydrolyzed, myosin heads return to the resting “cocked” conformation
3. Cross bridge is formed and myosin head binds to new position on actin
4. Phosphate is released
5. Conformational change in myosin causes power stroke, ADP is released

Question 28

What are the 2 major muscle fiber types and what is their ratio of distribution in the human body?

Answer 28

Slow twitch = type I

Fast twitch = type II

Humans have 50/50

Question 29

Describe slow twitch muscle fibers

Answer 29

Type I 
Slow contraction
Slow to fatigue
Highly oxidative
Many mitochondria
Capillary dense
Appear red

Question 30

Describe fast twitch muscle fibers

Answer 30

Type II
Fast contraction
Fast to fatigue
Low oxidative capacity
Few mitochondria
Not capillar dense
Appear white