Excitation Contraction Coupling Flashcards Preview

physiology IV > Excitation Contraction Coupling > Flashcards

Flashcards in Excitation Contraction Coupling Deck (46):
1

How does the NEURONAL AP travel down the motor neuron?

In a saltatory fashion
-skips over nodes of ranvier

2

What occurs once the neuronal AP reaches the bouton?

It depolarizes the bouton
-Voltage gated ca2+ channels in the plasma membrane open
-ca2+ rushes into the bouton

3

What is caused by an elevated level of ca2+ in the bouton?

Vesicles of ACh fuse with the membrane

4

After ACh is dumped into the synaptic terminal, what channels are able to open?

ACh binds to receptors on MUSCLE --motor end plate
-allows Na+ to rush in and depolarize

5

The rushing in of Na+ ions at the motor endplate creates what?

-an Endplate action potential
-propagates along the muscle fiber

6

What is the result of the endplate potential?

-nearby voltage gated Na+ in MUSCLE membrane open leading to a MUSCLE AP

7

What inactivates ACh in the synaptic cleft?

Acetylcholinesterase on the motor end plate

8

What is myasthenia gravis?

Antibodies created to nicotinic ACh receptors at the neuromuscular junction
-muscle fatigability
-reduced excitation

9

What are some possible sites for blocking neuromuscular transmission in skeletal muscle?

Nerves
1. Motor neuron disease
2. Demyelinating disease
Muscle
1. Neuromuscular junction disease
2. Muscle disease
3. Sarcomere disease

10

What is ALS?

-Motor neuron death in the spinal cord
-loss of neuronal action potential
- reduced excitation

11

What is guillan barre syndrome?

autoimmune response against myelin
-impaired neuronal AP
- reduced excitation

12

What is muscular dystrophy?

-reduced attachment of muscle to ensheathing membrane
-reduced contraction

13

What is malignant hyperthermia?

-Mutation in Ryr1 - excessive ca2+ release in muscle
-triggered by inhaled anesthetics
-excessive contraction

14

What occurs as the muscle action potential travels down the T-tubules?

-opens ca2+ channels -ryanodine receptors in SR
-Ca2+ floods sarcoplasm

15

Can skeletal muscle contract in the absence of calcium extracellularly?

YES - calcium comes from the SR in muscle contraction (cycling is intracellular)

16

What is calcium's role in the sarcoplasm?

It allows actin to interact with myosin cross-bridges -- development of tension

17

What is the skeletal muscle triad?

1-Tubule surrounded by 2 sarcoplasmic reticulum cisternae

18

How are the tubules and cisternae attached?

-Direct coupling
-L type ca2+ channels in T tubule
-Ryanodine receptors in cisternae of SR

19

What are the three steps of ca2+ release at the skeletal muscle triad?

1. Membrane depolarization opens L-type ca2+ channel or DHP receptors (t-tub)
2. Coupling causes ca2+ release channel in SR to open (ryanodine receptors)
3. Ca2+ exits SR and activates troponin C → muscle contraction

20

What is calcium induced calcium release?

In addition to being stimulated by DHP receptors, ryanodine receptors are also triggered by the presence of ca2+ in the cytoplasm (released by other ryanodine receptors)

21

What is the major mechanism of skeletal muscle relaxation?

SERCA pumps
-hydrolyze ATP to pump ca2+ into SR

22

What are the two minor methods of skeletal muscle relaxation?

-PMCA - pumps 1 ca2+ out of cell in exchange for 1 ATP

-NCX - Lets 3 Na2+ into cell to pump 1 ca2+ out of the cell

23

What is the temporal relationship between AP, ca2+ release and tension in skeletal muscle?

-NA+ dependent AP is <5 msec - rapid
-triggers transient inc in ca2+
-leads to slower development of tension

24

What is the result of a single action potential?

-twitch

25

What is the result of high frequency APs with oscillation?

-Unfused tetanus

26

What is the result of high frequency APs without oscillation?

-Fused tetanus

27

What is the term for an increase in muscle tension from successive action potentials?

Summation

28

What is the term for mantained contraction in response to repetitive stimulation?

Tetanus

29

What two things control the strength of contraction in skeletal muscle?

1) rate coding - frequency of stimulation
2) recruitment of additional motor units

30

What is treppe?

The steady increase in tension in successive twitches

31

Is treppe the same thing as summation?

NO - each twitch relaxes to zero tension before the next twitch initiates

32

How does treppe occur?

-repeated stimulation of the muscle at low frequency
-ca2+ release from previous twitches exceeds ca2+ uptake

-Increases the number of crossbridges formed
-May warm up the muscle - inc enzymatic rate

33

What is a motor unit?

A somatic motor neuron and all the myofibers it innervates

34

Why is tetanus able to occur?

the functional refractory period of the AP in a twitch is much shorter than contraction time

35

How does recruitment occur?

Large motor units are recruited after small
-as more force is required

36

What is involved in fine motor control?

Small motor units

37

What is the energy source of slow twitch fibers?

Oxidative

38

What is the energy source of Fast twitch type IIa fibers?

Oxidative

39

What is the energy source of fast twitch type IIb fibers?

Glycolytic (anaerobic metabolism of glucose)

40

List in order the energy sources for contraction (5)

1. ATP
2. Phosphocreatine
3. Anaerobic metabolism of glucose
4. Oxidative metabolism of glucose
5. Oxidative metabolism of fats, carbs, proteins

41

What is muscle pain or burn?

Lactic acid build up
-anaerobic glycolysis (Fast twitch IIb)

42

What is Delayed onset muscle soreness?

-not correlated with lactic acid
-muscle damage, inflammatory response

43

What is Muscle Fatigue

-decline in muscle tension as result of previous contractile activity

-dec shortening velocity
-slower rate or relaxation

44

What causes muscle fatigue? Is there a correlation with ATP?

build up of lactic acid and inorganic phosphates
-NOT due to low ATP (has high levels)

45

What is high frequency fatigue?

-high intensity, short duration exercises
-failure of AP to conduct down T-tubule
-fast recovery

46

What is low frequency fatigue?

- Low intensity, long duration exercises
-build up of lactic acid and phosphates
-changes the conformation of muscle proteins
-slow recovery