muscle types

Question 1

what makes up a muscle

Answer 1

muscle
fascicles
muscle fibers
myofibrils
thick and thin filaments(sarcomere)

Question 2

what is a motor unit

Answer 2

a motor neuron and a muscle fiber

Question 3

features of the neuromuscular junctions

Answer 3

a motor nerve
which axon goes towards a muscle fiber
here there is a axon terminal
in this axon terminal there are Schwann cells and vesicles containing ACH
there is then the synapetic cleft

Question 4

pathway of action potential

Answer 4

1. Motor neuron’s action potential arrives at
   the axon terminal
   ↓
   Depolarizes plasma membrane
2. Opening Ca2+ channels
   ↓
   Ca2+ions diffuse into axon terminal
   ↓
   Ca2+binds to proteins
3. Synaptic vesicles release Ach
4. Ach diffuses from axon terminal to motor
   end plate, binding to nicotinic receptors
   5.Binding of Ach opens an ion channel
   ↓
   Na+ and K+ can pass through these
   channels (electrochemical gradient across
   plasma membrane means more Na+ moves
   in than K+ out)
5. local depolarization of the motor
   end plate
6. Muscle fibre action potential
   initiated
7. Propagation (end plate potential)

Question 5

what produces a action potential in muscle fibers

Answer 5

Every action potential in a motor neuron normally
produces an action potential in each muscle fiber in its
motor unit.

Question 6

what is a excitation contraction coupling

Answer 6

The sequence of events by which an action potential in the plasma membrane
activate the force-generating mechanisms.

• An action potential in a skeletal
  muscle fibre lasts 1 to 2 ms and
  is over before signs of
  mechanical activity begin
• Mechanical activity following an
  action potential may last 100 ms
  or more

Question 7

excitation contraction coupling in a relaxed muscle

Answer 7

Low Ca2+
Cross-bridge cannot bind with Actin
because Tropomyosin is covering the
binding site (Troponin holds tropomyosin
over binding site)

Question 8

excitation contraction coupling in an active muscle

Answer 8

High Ca2+
Ca2+ binds to troponin → tropomyosin
moves away from cross-bridge binding
site → Actin binds to cross-bridge

Question 9

how a muscle contractions with the help of calcium

Answer 9

the action potential propagated along the muscle cell membrane and goes into the transverse tubule

calcium is then release at the terminal cisternae via the Dihydropyridine(DHP) receptor
(Membrane)
– Ryanodine receptor
(sarcoplasmic reticulum)

calcium then binds to troponin removing blocking action of tropomyosin

cross bridges then bind and start to rotate and generate force

calcium is then transported back into the sarcoplasmic reticulum via the calcium ATPase pump, this removal from cytosol requires energy

the removal of calcium from troponin restores the blocking action of the tropomyosin

Question 10

what is the sliding filament mechanism

Answer 10

Shortening of the muscle is the result of certain parts of the actin
and myosin filament interacting with each other.

Question 11

what is the 4 stages of the cross bridge cycle

Answer 11

1. Energized myosin cross bridges on the thick filaments bind to actin
2. Cross bridge binding triggers release of ATP hydrolysis products from myosin, producing angular movement
3. ATP bound to myosin, breaking link between actin and myosin → cross bridge dissociate
4. ATP bound to myosin, is split, energizing the myosin cross bridge

ATPase: an enzyme which determines the speed of ATP hydrolysis and resulting
sarcomere shortening velocity