module 5

Question 1

endomysium

Answer 1

 Connective tissue surrounding individual muscle fibers

Question 2

epimysium

Answer 2

 Dense connective tissue surrounding the whole muscle

Question 3

perimysium

Answer 3

 Connective tissue surrounding each muscle fascicle (bundle of muscle fibers)

Question 4

Neuromuscular junction

Answer 4

o NMJ made of the terminal part of a motor neuron axon (presynaptic) and the thickened part of the sarcolemma (motor plate)
o Importance of acetylcholine
 Space between two neurons is called the synaptic cleft
 When nerve impulse arrives at the terminal end of the motor neuron ACh is released
 ACh is the key neurotransmitter at all neuromuscular junctions
 ACh binds to its nicotinic receptors on the sarcolemma
o Chemicals and drugs that impacts muscle contraction

Question 5

ATP in contraction

Answer 5

• Myosin binds to ATP molecules before contraction
• ATPase on the myosin head cleaves ATP into ADP and phosphate (Pi) and energy is released for energizing the myosin head
• Action potential causes the release of calcium SR
• Calcium binds to troponin C, causing tropomyosin molecules to uncover the myosin head binding sites on the G-actin molecule
• Myosin heads bind to its binding sites on G-actin molecule
• Conformational change in myosin head cause actin to slide toward the center of the sarcomere
• ADP and Pi are released from myosin, and a new molecule of ATP binds, and the myosin head detaches
• Binding of ATP triggers detachment of myosin head from actin filament and the cycle is repeated

Question 6

ATP in relaxation

Answer 6

• ATP is used by the muscle fiber to pump Ca++ back into the sarcoplasmic reticulum after contraction
• ATP is needed during the recovery of the membrane after depolarization
  o Needed during repolarization for the activity of the sodium-potassium pump, which is actively transporting sodium outside the cell and bringing potassium back inside the cell to restore the RMP

Question 7

actin and myosin

Answer 7

o Each myofibril (organelle of muscle cell) contains thick myosin and thin actin filaments
o Actin and myosin are contractile proteins of the myofibril
o The linking of myosin and actin during muscle contraction (works with the action of calcium on the troponin C on Actin
 Excitation-contraction coupling

Question 8

Function of transverse tubules (T-system)

Answer 8

 T-tubules are continuous with the sarcolemma and extend into the interior of the cell at right angles to the contractile elements in sarcoplasmic reticulum
 Tubules transmit action potentials from sarcolemma into the interior of the cell to initiate contraction of myofibril
 Where t-tubules pass through sarcomere, longitudinal tubules adjoin them, which bulge to form two lateral sacs on either side of tubule
 These structures form triad (sarcomere, right angle tubules and longitudinal tubules)

Question 9

acetylcholinesterase

Answer 9

degrades ACh

Question 10

white muscle, fast twitch

Answer 10

White muscle fibers contain low myoglobin and rely on glycolytic processes for energy metabolism. This is type II muscle with fast twitch

 Fast twitch muscles are used in situations that require short, powerful bursts of speed energy.
 Fast twitch muscles fatigue easily

Question 11

red muscle, slow twitch

Answer 11

 Red muscle fibers contain high myoglobin (muscular form of hemoglobin) and uses oxidative phosphorylation for metabolism. This type I muscle is slow twitch

function in situations that require prolonged and constant muscle contraction

Question 12

drugs and chemicals that effect contraction

Answer 12

o Organophosphates: inhibit action of acetylcholinesterase, causes ACh buildup resulting in muscular spasm and asphyxiation
o Curariform Drugs: act like curare (deadly poison), which binds to motor end plate receptors so ACh cannot bind, and contraction cant occur. Causes asphyxiation.
o Botulism toxin: created by bacterium Clostridium botulinum, which blocks the release of ACh from terminal bulb, no action potentials produced for contraction, results in deadly paralysis

Question 13

what happens during contraction

Answer 13

 Skeletal muscle contracts in response to motor nerve stimulation
 The contractile process is almost the same across muscle types, however strength and duration of contraction differs
 Striated muscle contraction is triggered by the generation of an action potential on the sarcolemma

 Bonding of ACh leads to the opening of membrane sodium channels and production of an action potential-> causes muscle contraction

Question 14

muscle relaxation

Answer 14

contraction continues as long as there is an excess of calcium ions present in the sarcoplasm(cytoplasm of muscle)

relaxation occurs with the decrease calcium content

-effect of AP ends, calcium ions are pumped back (active transport) into sarcoplasmic reticulum
-accomplished by SERCA, a transport protein that uses ATP to pump calcium back into SR
-calsequestrin protein helps stack calcium inside SR

Question 15

importance of ACh

Answer 15

 Ach (acetylcholine), released when a nerve impulse arrives at the terminal end of the motor neuron
 ACh is a key neurotransmitter at all neuromuscular junctions
 Binds to its nicotinic receptors on sarcolemma
 Continues to stimulate receptors in synaptic cleft as long as its there (a few millisecond’s)
 Then it is degrades by acetylcholinesterase, found in s.cleft

 ACh released in the result of motor nerve depolarization
 Synthesized in cytoplasm of nerve ending and stored in vesicles at terminal end of nerve fiber
 Prolonged contraction occurs if there is a decrease in degradation of ACh

Question 16

Myasthenia gravis (MG)

Answer 16

an autoimmune disease where the body produces antibodies against its own ACh receptors on the motor end plate of skeletal muscle -> leads to muscle weakness and paralysis
* Treated with drugs that destroy acetylcholinesterase

Question 17

sarcoplasmic reticulum

Answer 17

 Network of tubules within the sarcoplasm and is where calcium is stored
 Calcium very important for muscle contraction

Question 18

skeletal muscle

Answer 18

– voluntary and striated
* Attached to skeleton and contract In response to motor nerve stimulation

Question 19

cardiac muscle

Answer 19

involuntary and striated
* Responsible for heart contraction

Question 20

smooth

Answer 20

– involuntary (no striation)
* Responsible for functions of visceral organs, such as peristalsis of the gastrointestinal tract