Neuromuscular Junction and Sarcomere

Question 1

Area between pre-synaptic membrane and post-synaptic membrane

Answer 1

Synaptic Cleft

Question 2

Neuromuscular junction

Answer 2

Region between neuron synaptic bulb and muscle fiber

Question 3

What do the synaptic vesicles in the terminal bulb of the neuromuscular junction contain?

Answer 3

Excitatory neurotransmitter ACh

Question 4

Where is ACh synthesized and by what molecules?

Answer 4

1) cytosol

2) Acetyl-CoA and Choline

Question 5

What happens when an AP reaches the synaptic bulb of the neuromuscular junction?

Answer 5

1) Ca+ voltage channels open, Ca+ floods into bulb
2) Causes the release of ACh via exocytosis into synaptic cleft
3) ACh that makes it to the post-synaptic cleft binds to receptors (Na+ ligand gated channels) on post-synaptic cleft, which open and allow an influx of Na+ into the cell
4) Muscle Fiber depolarized, eventually generating an AP

Question 6

What is acetylcholineesterase?

Answer 6

1) Enzyme that hydrolyzes ACh into acetyl-CoA and choline (which are recycled back into synaptic cleft to synthesize ACh)
2) Bound to surface of post-synaptic membrane

Question 7

What would happen in the absence of acetylcholineesterase?

Answer 7

1) ACh would remain in synaptic cleft and continually bind to post-synaptic membrane causing continuous AP
2) Result in prolonged muscle spasm

Question 8

EPSP

Answer 8

1) excitatory postsynaptic potential (Depolarizes, leading to an AP)
2) Increases post-synaptic Na+ permeability (to leave cell)

Question 9

IPSP

Answer 9

1) inhibitory postsynaptic potential (Hyperpolarizes, making it more difficult to generate an AP)
2) Increases post-synaptic K+ AND Cl- permeability (to enter cell)

Question 10

What happens when two axons meet?

Answer 10

They stop

Question 11

Connects muscle to bone.

Answer 11

Tendon

Question 12

Myocytes

Answer 12

Multinucleated muscle fibers

Question 13

Skeletal muscles have striations in both transverse and longitudinal directions. What causes the striations in t eh longitudinal direction?

Answer 13

Myofibrils

Question 14

What do myofibrils contain?

Answer 14

Sarcomeres with contractile units actin and myosin

Question 15

What are the contractile units in muscle fibers?

Answer 15

actin and myosin

Question 16

Describe Actin

Answer 16

1) Thin contractile unit
2) monomer subunits: G-Actin (spherical in shape)
3) G-Actin comes together to form a long string of actin
4) Has tropomysin and troponin

Question 17

What is tropomyosin?

Answer 17

protein on actin that covers up binding site for myosin heads (preventing myosin from binding)

Question 18

Troponin

Answer 18

1) Holds tropomyosin in place (causing tropomyosin to cover up myosin binding sites on actin)
2) When Ca+ is bound to, changes conformation and releases Tropomyosin from myosin binding sites (allowing myosin to bind)

Question 19

What happens to myosin when it is not bound to actin?

Answer 19

1) In a relaxed state (45 degree angle)

2) Bound to ATP (decreases Myosin’s affinity for Actin)

Question 20

Right before actin and myosin binds, what happens to the ATP on myosin heads?

Answer 20

It is hydrolyzed to Pi + ADP

Question 21

What happens during a muscle contraction in regards to actin and myosin?

Answer 21

1) ATP binds to myosin head to release actin
2) ATP hydrolyzes into Pi + ADP
3) Binding of actin and myosin causes myosin to release ADP and Pi
4) Power Stroke (myosin filaments “swivel” to pull actin filaments past it)

Question 22

What is the product of the power stroke?

Answer 22

Rigor State/Complex (after myosin pulls actin past it and the two are still bound together)

Question 23

What is needed to resolve the “rigor complex?”

Answer 23

ATP

w/o ATP, muscle remains in a state of rigor (contracting without relaxing). Thus, Myosin needs ATP to bind to its heads in order to release actin and allow the muscle to relax. As, previously state, when ATP binds to the myosin heads, it causes myosin to have a lower affinity for actin, which results in it releasing.

Question 24

Why does rigor mortis occur when people die?

Answer 24

No ATP available to relax muscles (break bond b/t actin and myosin)

Question 25

Is skeletal muscle actin or myosin based?

Answer 25

Actin based (b/c the tropomyosin on ACTIN prevents the binding of actin and myosin when Ca+ is not present to bind to Troponin)

(cardiac and smooth muscle are myosin based)

Question 26

What structure directly surround and supplies the myofibrils with Ca+?

Answer 26

Sarcoplasmic reticulum

Question 27

Sarcolemma

Answer 27

Plasma membrane of a myocyte

Question 28

Invagination of the sarcolemma (plasma membrane)

Answer 28

T-Tubules

Question 29

Why are T-tubules important?

Answer 29

When an AP reaches Post-synaptic membrane (sarcolemma), the AP spreads across the membrane and down the T-tubules, stimulating the release of Ca+ in the sarcoplasmic reticulum.

Question 30

What are three things that can vary the strength of a muscle contraction

Answer 30

1) Size and number of motor units
2) Amount of Actin and myosin in a cell (increased by weight training)
3) Concentration of ATP

Question 31

What is a motor unit?

Answer 31

A motor neuron and muscle fibers it controls (more/larger motor units, greater the strength)

Question 32

Aerobic respiration occurs in the presence of ___ and produces:

Answer 32

1) Oxygen

2) CO2, H20, ATP

Question 33

Anaerobic respiration occurs in the absence of ___ and produces:

Answer 33

1) Oxygen

2) Lactate (Glucose is metabolized to Lactate) and ATP