Ganong 23e chapter 5 - Excitable Tissue: Muscle (1)

Question 0

Along which section of the sarcomere does the T-tubule system run in cardiac muscle cells? And in skeletal muscle cells?

Answer 0

Cardiac myocytes: Z-lines

Skeletal muscle cells: Along the junction of the A-band and I-band

Question 1

Along which section of the sarcomere does the T-tubule system run in skeletal muscle cells?

Answer 1

Between the A and I bands

Question 2

In the sarcomere, what are the outermost lines called?

Answer 2

Z-discs

Question 3

In the sarcomere of a RELAXED muscle cell, what runs down the middle of the A-band? Describe what is found here.

Answer 3

The M-line (and also the H-band). This section contains myosin filaments, without any overlapping actin filaments.

Question 4

In order to allow myosin-actin cross-linkages, what does calcium bind to?

Answer 4

Troponin C

Question 5

How long is the action potential in skeletal muscle cells and neurons?

Answer 5

2-4 milliseconds

Question 6

How long is the action potential in cardiac myocytes?

Answer 6

250-300 milliseconds

Question 7

What are the key structural differences of the contractile mechanisms in smooth muscle compared to skeletal muscle?

Answer 7

Smooth muscle lacks striations. Actin and myosin are present, but not arranged in regular arrays. Instead of Z-lines, there are dense bodies, which are attached to the cell membrane.

Question 8

How does smooth muscle contract?

Answer 8

There is no troponin in smooth muscle. Acetylcholine causes calcium influx, which binds to calmodulin. This complex triggers myosin phosphorylation, and contraction ensues.

Question 9

Where does the calcium come from to produce skeletal muscle contraction? Where does it come from to produce smooth muscle contraction?

Answer 9

Skeletal muscle: release from intracellular stores (from sarcoplasmic reticulum)

Smooth muscle: influx from ECF

Question 10

In the sarcomere, there is myosin, tropomyosin and troponin. What is the function of each subunit of troponin?

Answer 10

Troponin I: inhibits the interaction between actin and myosin.

Troponin C: binds calcium during contraction.

Troponin T: binds to tropomyosin.

Question 11

Discuss the resting membrane potential of smooth muscle.

Answer 11

There is no true RMP. The membrane potential is unstable. There are continuous, irregular contractions, independant of the nerve supply.

Question 12

What are some triggers of smooth muscle contraction?

Answer 12

Stretch alone will trigger contraction.

Acetylcholine and parasympathetic stimulation causes calcium influx and thus contraction.

Question 13

Name a broad physiological response that causes inhibition of smooth muscle contraction?

Answer 13

Noradrenaline, adrenaline, sympathetic stimulation. These cause hyperpolarization of the membrane.

Question 14

What are the other names for Type I, Type IIa and Type IIb muscle fibres?

Answer 14

Type I: slow, oxidative

Type IIa: fast, oxidative, glycolytic

Type IIb: fast glycolytic

Question 15

What is the duration of one action potential (including the funny current) in a cardiac pacemaker cell (i.e. the length of time between one depolarisation and the next) in a normal healthy person?

Answer 15

Approx 800msec (assuming HR 75)

(See chapter 29)