Tissues 7: Muscle

Question 1

Name the two types of muscle contraction?

Answer 1

Isometric Contraction Isotonic Contraction

Question 2

What is Isotonic Contraction

Answer 2

muscle changes length and tension remains the same Concentric: shortening Eccentric: lengthening add pic

Question 3

What is isometric contraction

Answer 3

tension develops and muscle does NOT change length add pic

Question 4

What is the ultrastructure of Skeletal muscles?

Answer 4

Skeletal muscle consists of bundles of muscle cells known as myofibres. add pic

Question 5

Name some features of myofibres?

Answer 5

Large & Cylindrical Multinucleate Packed with myofibrils

Question 6

What doe myofibrils appear as?

Answer 6

Light & dark bands giving them a ‘striated’ appearance Add pic

Question 7

How is muscle contraction initiated?

Answer 7

Muscle contraction is initiated by an increase in the cytosolic calcium concentration

Question 8

List the steps that causes contraction of a skeletal muscle?

Answer 8

add pic

Question 9

Name some microscopic features of Myofibres

Answer 9

long, multinucleate cells, T-tubules, extensive SR

Question 10

What is the strucural and functional unit of skeletal muscle called

Answer 10

Sarcomere

Question 11

Recall the process of excitation and contraction coupling

Answer 11

AP propagates along T-tubules®– change in conformation of DHPR®– RyR opening ®– Ca2+ efflux from SR into cytoplasm

Question 12

What is a Z line in a Scarcomere

Answer 12

Defines lateral boundaries of sarcomere add pic

Question 13

What effect does Calcium have on troponin and tropomyosin.

Answer 13

add pic

Question 14

List the steps for the sliding filament theory?

Answer 14

In the presence of Ca2+ movement of troponin from tropomyosin chain Movement exposes myosin binding site on surface of actin chain ‘Charged’ myosin heads bind to exposed site on actin filament This binding & discharge of ADP causes myosin head to pivot (the ‘power stroke’)  pulling actin filament towards centre of sarcomere ATP binding  releases myosin head from actin chain ATP hydrolysis  provides energy to ‘recharge’ the myosin head add pic

Question 15

What are purkinje fibres

Answer 15

large cells that rapidly conduct electrical impulses

Question 16

What are cells of the heart known as

Answer 16

Cardiomyocytes

Question 17

What are myocytes

Answer 17

Muscle cells

Question 18

Where are pacemaker cells found

Answer 18

Atrial ventricular node and Sinotrial node add pic

Question 19

What type of muscle are cardiomyocytes

Answer 19

striated muscle

Question 20

What are intercelated discs and what features do they have to help action potentials spread rapidly around the heart?

Answer 20

Specialised regions connecting individual cardiomyocytes Contain numerous gap junctions: allow action potentials to spread rapidly from cell to cell. add pic

Question 21

What is the difference between Excitation- Contraction cupling in skeletal and cardiac E-C coupling?

Answer 21

In Skeletal muscle, Ca comes from intracellular Ca stores (via changes in receptors), whereas in Cardiac muscle, Ca entrs through VGCaCs and Ca induced Ca release (from SR) occurs.

As with skeletal muscle, contraction is initiated by an increase in the cytosolic Calcium concentration. However there are subtle differences in the way the intracellular Calcium levels rise within these two cell types:

1) The action potential propagates along the cardiomyocyte membrane and T-Tubule (same as Skeletal Muscle)
2) Depolarisation opens voltage-gated Ca2+ channels (VGCCs)  Ca2+ influx
3) This Ca2+ has three main effects: Ca2+ induced Ca2+ release
i) (CICR) by binding to RyR on SR
ii) Initiate contraction binding to troponin
iii) Further depolarisation
4) Thus depolarisation  increase in intracellular Ca2+ muscle contraction ( Same as skeletal muscle)

Question 22

What is different about the arrangement of actin and myosin in smooth muscle?

Answer 22

Do NOT contain regular arrangement of actin & myosin

Question 23

List the steps for E-C coupling in Smooth muscle

Answer 23

Depolarisation activates VGCCs (voltage gated calcium channel) which allows the influx of calcium into the cells The calcium binds to the intracellular protein Calmodulin (CaM) This Calcium-CaM complex activates myosin light chain kinase (MLCK) MLCK phosphorylates the myosin ligh chains allowing them to form cross-bridges with the actin filaments resulting in contraction