Lecture 4

Question 1

Functions of cardiac skeleton (3)

Answer 1

• electrphysiological discontinuity(allow for total filling/ insulation)
• attachments for atrial and ventricular myocardium
• strong yet flexible support for vavular openings

Question 2

Cardiac skeleton

Answer 2

fibrous plate- 3 triangular areas- trigones

reinforced by cartilage or bone- ox (2 bones), sheep (1 bone- os cordis), cat, dog pig, horse (cartilage)

Question 3

The heart wall- 3 layers

Answer 3

• endocardium (inside)- endothelium
  -myocardium (largest and thickest)- bundles of cardiac muscle cells
  -epicardium (outside)- mesothelial cells of visceral pericardium
  THERE IS FAT ON THE OUTSIDE (under epicardium)

Question 4

What is special about cardiac myocytes? 2

Answer 4

• Abundant mitochondria

- dependent on aerobic respiration- no rest periods-no o2 debt possible

Question 5

cardiac muscle has (4)

Answer 5

intercalated discs
central nuclei (usually 1) with perinuclear space
good blood supply
branched fibers

Question 6

intercalated discs (2)

Answer 6

structurally attached at desmosomes

electrically connected at gap juncitons

Question 7

what are t tubules

Answer 7

cell membrane invaginations to get AP closer to SR

Question 8

what are purkinje fibers and histo look

Answer 8

specialized conducting cells, 
pale staining (lots of glycogen) large cells

Question 9

What links AP and contraction

Answer 9

all about Ca

• Ca enters vell in respose to AP, stimulates release of Ca from SR-> contraction
• Ca sensitive Ca release
• 20% of rise in intracellualr Ca thorugh VO channels
• 80% from SR

Question 10

Excititation- contraction coupling

Answer 10

AP conducted across myocyte membrane and down t tubule->

• opening of VO Ca channels
• entry of Ca into cell
• inc in intracellular Ca that:
• stimulates release of Ca from SR (ryanodine receptor channels)->initiates contraction

Question 11

generation of tension- regulatory protein complex

Answer 11

tropomyosin
troponin
these prevent interaction betwen actin and myosin

Question 12

generation of tension- ca switch

Answer 12

in intracellualr Ca
Ca causes tropomyosin to move aside
myosin-actin crossbridges from: contraction

Question 13

generation of tension- contraction

Answer 13

(powerstroke)

energy supplied by ATP bound to myosin

Question 14

generation of tension- Ca release from SR

Answer 14

contributes to the plateau phase of the AP (phase 2) and therefor to the refractory period

Question 15

Relaxation (4)

Answer 15

Active pumps return Ca to: -SR - extracelluar fluid
Ca exchanged for extracellular Na
intracellular Ca [ ] falls
myocyte relaxes

Question 16

Generation of tension round 2 (3)

• amount of Ca release (and therefor force of contraction) depends on…
• -tension generally directly related to…
• tension generated also depends on…

Answer 16

amount of Ca release (and therefor force of contraction) depends on how much Ca stored in SR and #of release channels activated

• tension generally directly related to intrcellular Ca levels
• tension generated also depends on length of myocyte prior to contraction

Question 17

Isotonic contraction

Answer 17

(muscle gets shorter)
activating an unrestrained muscle causes it to shorten without force development (maximal velocity)(like when valves open)

Question 18

isometric contraction

Answer 18

(stays same length but creates tension)
measure of the muscles maximal ability to create tension
-like cardiac contraction before the valves open

Question 19

Effect of cell length (2)

Answer 19

cell length determines overlap of thick and thin filaments

length of relaxed cells is determined by amount of blood in ventricle

Question 20

optimal and normal cell length

Answer 20

normal cell length is less than maximal

Question 21

length tension relationship

Answer 21

tension (CO) inc as length (EDV) inc. to a point and then plateau

Question 22

contractility

Answer 22

the amount of tension that can be developed at any given stretch of cardiac muscle

Question 23

inotropes

Answer 23

agents that alter contractility

Question 24

contractility is inc by…

Answer 24

and inc in intracellular Ca[ ]

Question 25

intracelluar Ca can be modualted by… (2)

Answer 25

receptor operated Ca chanels on cell membrane

ryanodine channels on SR

Question 26

2 ways to inc strength of contraction

Answer 26

inc length by inc cardiac filling

agent (inotrope) that inc excitation of a cell