Chapter 43: Musculoskeletal Systems

Question 1

What is the final outcome of the action potential in muscles?

Answer 1

Movement

Question 2

Explain the neural pathway for muscle movement

Answer 2

o There are sensory neurons and motor neurons
 Sensory neurons fire action potential to the brain and the spinal cord
 Motor neurons fire action potential to the muscles
• Causes the muscles to move
 Receptors and Effectors

Question 3

What kind of tissue are muscles?

Answer 3

Contractile tissues

Question 4

Classifications of Skeletal, Smooth, and Cardiac muscles

Answer 4

-Skeletal (voluntary)
-Smooth (involuntary)
Found around the organs
-Cardiac (involuntary)
Muscles of the heart

Question 5

Levels of Organization (4) in muscles

Answer 5

1. Muscle
2. Fascicle
3. Muscle Fiber
4. Sarcomere

Question 6

What are muscles made up of?

Answer 6

Fascicles

Question 7

What are fascicles made of?

Answer 7

Muscle fibers

Question 8

What are muscle fibers made up of?

Answer 8

myofibrils (contractile tissue)

Question 9

What are sarcomeres?

Answer 9

Defined patterns that make up myofibrils. Connected via Z lines
• Contains alternating proteins (thin/think filaments)
o Thick filament are contain myosin
o Thin filaments contain a contractile protein (actin) and two regulatory proteins (troponin) and (tropomyosin)

Question 10

What are Z lines?

Answer 10

Interconnecting structural proteins that serve as structural support for sarcomeres

Question 11

Whatt attaches the think filament to the z line?

Answer 11

Tytin attaches the thick filament to the Z line

Question 12

What does the thick filament contain?

Answer 12

myosin (motor protein)

Question 13

What does the thin filament contain?

Answer 13

Actin (Contractile protein), Troponin (regulatory protein), and tropomyosin (regulatory protein)

Question 14

Describe myosin

Answer 14

o Has the 2 myosin head and the 2 myosin tail
 The myosin head (cross bridge) is where the electrical activity occurs
• Has two bind sites
o Actin binding site
o ATP binding site
 Muscle contraction requires energy

Question 15

what is the Sliding Filament Mechanism?

Answer 15

When the muscle contracts, the overlap between the thick and thin filaments increases. Sarcomere shortens

Question 16

Describe Actin

Answer 16

Actin is a globular protein that polymerizes to form an intertwined helix
• Has a binding site for myosin
• Polymerization:
o Regulatory proteins sit on top of the actin
 In the relaxed state the regulatory proteins cover the myosin binding site
 Regulate interaction of actin and myosin

Question 17

Describe tropomyosin

Answer 17

Tropomyosin is arranged like a ribbon that binds the myosin binding site on the actin
• Won’t let myosin bind
• On top of the tropomyosin is troponin

Question 18

Describe Troponin

Answer 18

Troponin has three binding sites
•	Actin binding site
•	Tropomyosin binding site
•	Calcium binding site
      o Signal to contract

Question 19

What happens to the sarcomere during muscle contraction?

Answer 19

The sarcomere beocomes shorter

Question 20

What does muscle contraction require?

Answer 20

ATP and Calcium
o ATP comes from the mitochondria (which muscles are full of)
o Calcium is stored inside the cell at low levels
 Calcium rises during electrical activities
 Is tightly regulated by the Sarcoplasmic Reticulum (Modified Smooth ER)
•Found on the myofibrils
•The lateral sacs are at the end segments that release calcium upon stimulation

Question 21

Name of plasma membrane for muscle cells

Answer 21

Sarcolemma

Question 22

What is the sarcolemma?

Answer 22

-Modified plasma membrane for muscle cells
-Sarcolemma has extensions (invaginations) that dip into the cytoplasm
Invaginations are known as T-tubules
• Are arranged passing close to the sarcoplasmic reticulum
•Contain dihydropyridine receptors (DHPR)
•Ryanodine receptors (foot proteins) are located on the lateral sacs of the Sarcoplasmic reticulum

Question 23

what are dihydropyridine receptors (DHPR)?

Answer 23

-Voltage sensitive proteins
-When they open, they don’t permeate a lot of calcium
They are voltage sensors: proteins that sense voltage
Steps: Neuronmuscular junction will tell muscle to contract. Release acetylcholine and action potentials will cause DHPR to release calcium

Question 24

What are ryanodine receptors?

Answer 24

-(foot proteins) are located on the lateral sacs of the Sarcoplasmic reticulum
oAllows calcium out of the SR

Question 25

Neuromuscular junction

Answer 25

-Neurotransmitter is called acetylcholine
-Skeletal command is under the nervous system
Brain to Spinal cord, Spinal cord to the muscles

Question 26

Steps for muscle contraction

Answer 26

• Steps for Muscle contraction
o Action potential at the axon terminal causes the release of acetylcholine
 Ach binds and cause the release of sodium
o Sodium influx causes depolarization (End plate potential aka graded potential)
 “Motor end plate” =Neuromuscular junction
o The action potential propagates/travels along the sarcolemma
 On the surface and in the T-Tubules (sense voltage change coming from the action potential
• Reaches the core of the muscle
 Dihydropyandine receptors are activated once action potential reaches T Tubules
• Sense the voltage change from action potential
o “Touches” ryanodine receptors, and they are activated
 Ryanodine receptors are calcium channels that open up
• Calcium is released into the cell cytochine
o Located in the lateral sacs of the sarcoplasmic reticulum (high concentration) and in low concentration in the cytosol
 Now the muscle has a higher concentration of calcium
o THE CALCIUM IS NOT COMING THE OUTSIDE. IT IS LOCATED IN THE ER AND IS RELEASED INTO THE CYTOSOL
o Calcium binds to troponin
 A regulatory protein that moves troponin/tropomyosin out of the way
• Sliding filament theory
 Now myosin (high energy state since it already broke down ATP) can bind and interact with the actin

Question 27

What happens in the crossbridge cycle?

Answer 27

• Cross Bridge Cycle (Attachment, power stroke, detachment) [CONTINUATION OF MUSCLE CONTRACTION]
o When myosin is at rest, there is ADP and P bound to it
 High energy state (when ATP is hydolized)of the myosin occurs when it is ready to interact with the actin
• Called this because it use the ATP when it’s ready
o When actin is exposed, myosin binds to the actin
 Actin and myosin are protein made of a sequence of amino acids
• When binded, the change shapes
o Loses affinity for inorganic phosphate
 Pi unbinds from the myosin head and is released
o The myosin had angle changes (145 to 90)
 The power stroke (bends)
• The bending of the myosin causes the sarcomere to shorten
o Muscle stiffens
• Where force production occurs (when myosin folds on the actin)
o When the myosin goes into the power stroke, it changes conformations again
 Loses affinity for ADP and the ADP dissociates
• The myosin head is now vacant and attracts a new ATP that binds to the myosin on its binding site
o Myosin dissociates from the actin
o ATP is hydrolyzed and myosin is ready for the next cycle
 Keeps continuing as long as actin is available (which is determined by the availability of calcium
• Ryanodine receptors are the channels that promote the release of calcium (caused by DHPR)
o Calcium Is taken back via the calcium pumps (active transport) to the cell cytosol

Question 28

What stops the crossbridge cycle? (2)

Answer 28

-Removal of acetylcholine
Via acetylcholine esterase -
-Removal of calcium
Via calcium pumps that take it back to Sarcoplasmic Reticulum

Question 29

Where do muscles get their energy from?

Answer 29

• Muscles get glucose and oxygen to produce energy

- Limited source of ATP (switch to another source)

Question 30

Alternate sources of energy for muscles:

Answer 30

-Creatine phosphate 
   o Immediate source (limited) of energy: PHOSPHOGENS
      Provide Pi to ADP to create ATP
   o Creatinekinase found in vertebrates
      Arginine phosphate for invertebrates
-Cellular respiration
   o Long term energy source 
   o Oxygen dependent (aerobic)
-Glycolysis Fermentation (anaerobic)
   o Emergency source
   o Replenish the oxygen

Question 31

What causes fatigue?

Answer 31

• Local increase of inorganic phosphate (ATP)
• Buildup of acid
• Depletion of energy

Question 32

Do creatine supplements work?

Answer 32

no

Question 33

What is tetnus?

Answer 33

-Clostridium tetani
-Is a toxin produced by an anaerobic bacteria
• Acts on the inhibitory neurons
o Removal causes over excitation
•Over excitation of the neurons
-Symptom: muscle stiffness
• Muscles are working more than normal

Question 34

What is Botox?

Answer 34

-Clostridium botulinum
•Inhibits neurotransmitter release
-Used to prevent wrinkles
•Wrinkles are over-active neurons