Ch. 20 - Cardiac Muscle

Front 1

cardiac muscle

Back 1

- central nuclei
- cross-striation
- intercalated disks = fascia adherens and numerous desmosomes
- cells have Y shape
- gap junction between cells
- lots of mitochondria
- fibrils of reticular fibers
- contact between cells accomplished by interdigitation in transverse region

Front 2

Y shape fibers

Back 2

- cells often branched
- allow muscle fibers to interweave in a more complicated arrangement within fascicles
- produces efficient contraction mechanism for emptying heart

Front 3

junction specializations of intercalated disk

Back 3

- zonulae adherentes anchor actin filaments of the terminal sacromeres to plasmalemma
- desmosomes bind cells together, preventing their separation during contraction cycles
- gap junctions couple cells and provide for spread of contractile depolarization
- zonulae adherentes and desmosomes in transverse portion
- gap junctions restricted to longitudinal portions where least stress

Front 4

membrane bound granules

Back 4

- aggregated at nuclear pores
- most abundant in muscle cells of right atrium
- smaller quantities found in left atrium and ventricles
- atrial granules contain precursor of atrial natriuretic factor

Front 5

atrial natriuretic factor (ANF)

Back 5

- target cells of kidneys to bring about sodium and water loss
- opposes action of aldosterone and antidiuretic hormone

Front 6

features of cardiac muscle

Back 6

- myofibrils less dense and organized than skeletal muscle
- alternate with abundant mitochondria
- mitochondria may occupy up to 40% of cytoplasm
- heart relies on aerobic respiration
- T tubules are larger and more numerous compared to skeletal
- diads rather than triads
- SR reduced

Front 7

cardiac sacromere

Back 7

- actin, myosin, tropomyosin
- thin filaments anchored by Z-disk by cross-linking protein alpha actinin and capped by Capz
- thin filaments pointy ends terminate within A band
- capped by tropomodulin
- myosin-binding-protein C

Front 8

fatty acid

Back 8

- transported to heart by lipoproteins
- major fuel for heart
- triglycerides and glycogen stored as droplets in cytoplasm
- enter cardiac muscle cell by passive diffusion or protein-mediated transport
- glucose enters via a glucose transporters (GLUT)

Front 9

lactic acid

Back 9

- also used by heart
- generated by skeletal muscle as energy source
- convert back to pyruvic acid

Front 10

layers of connective tissue

Back 10

- wrap around cardiac muscle
- endocardium
- myocardium
- epicardium

Front 11

endocardium

Back 11

- simple squamous
- elastic fiber
- subendocaridal layer

Front 12

myocardium

Back 12

- heart muscle arranged in spiral layers
- thickest layer
- contractile fibers
- purkinje fibers

Front 13

epicardium

Back 13

- mesothelium
- thin layer of CT

Front 14

heart diagram

Back 14

Front 15

annulus fibrosis

Back 15

- contains all the heart valves
- pulmonary valve
- aortic valve
- tricuspid valve
- mitral valve

Front 16

endogenous action potentials

Back 16

- generated at periodic intervals

Front 17

intrinsic conduction system

Back 17

- consist of non contractile cardiac cells specialized to initiate and distribute impulses throughout heart
- SA node
- AV node
- bundle of HIS
- purkinje fibers

Front 18

action potential of pacemaker cells

Back 18

- auto rhythmic cell membranes show slow drift to threshold = pacemaker potential
- at rest = -55
- slow depolarization to threshold caused by a cyclical decrease in passive outward flux of K+ coupled with slow unchanging inward leak of Na+
- transient Ca (CaT) channels open along with voltage gated Na channels until threshold reached
- voltage gated Na+ channels open
- long lasting Ca channels (Ca L) open and cause plateau coupled with outward flow of K+
- K+ causes depolarization
- Calcium permeability decreases

Front 19

impulse generating and conducting system

Back 19

Front 20

senatorial node (SA)

Back 20

- located in right atrial wall just inferior to superior vena cava
- generates about 75 action potentials per minute
- hearts main pacemaker
- sinus rhythm

Front 21

atrioventricular node (AV)

Back 21

- located in inferior portion of interaertrial septum
- from the SA node depolarization wave spreads to AV via internodal system
- impulse delayed by 0.1 seconds
- depolarizes about 50 times per second

Front 22

bundle of HIS

Back 22

- atrioventricular bundle
- only electrical connection between atria and ventricles
- right and left branches
- depolarize about 30 times per second

Front 23

purkinje fibers

Back 23

- modified muscle fibers with few myofibrils
- depolarize about 30 times per second
- controls ventricles and papillary muscles
- tighten chodae tenineae
- open tricuspid and mitral valve

Front 24

contractile muscle fibers

Back 24

- bulk of heart muscle

Front 25

action potential of contractile cardiac cell

Back 25

- rest membrane potential is about -90 due to Na/K ATPase pump, Na/Ca exchanger of inward rectifying K channel
- fast Na+ channel opens—3 gates
- resting = m closed and d/j open
- depolarization = m open and and d/j closed
- Ca in slow at 25mV and all fast Na channels closed
- K permeability decreased producing plateau phase
- transient Cl- channel opens dropping potential to 20mV
- K+ permeability increases with decreasing repolarization delayed rectifying channels with inactivation of Ca++ channels

Front 26

long refractory period

Back 26

- period in which heart can't regenerate action potential
- can't go into tetany and summation
- don't want contraction until blood has pumped through heart
- can't start contraction until first contraction is complete
- heart must be empty

Front 27

control of heart rhythm

Back 27

- pacemaker generates wave of signals to contract
- signals are delayed getting to AV node
- signals pass to heart apex
- signals spread throughout ventricles

Front 28

heart beat

Back 28

- P wave is depolarization of SA node through atria
- QRS is ventricular depolarization
- covers atrial depolarization as well
- T wave is ventricular repolarization

Front 29

myocardial contraction

Back 29

- activated by a transient rise in cytosolic free calcium concentration to about 1 μM from about 0.1 μM
- bulk of this Ca required for activation of contraction originates from the sarcoplasmic reticulum (SR)
- Ca influx through L-type Ca channels interacting with Ryr receptors
- Na–Ca exchangers (NCX) making more minor contributions
- Ryr receptor is a different isoform than in skeletal muscle
- different type of DHPR in cardiac muscle

Front 30

heart controlled by nervous system

Back 30

- sympathetic nervous system increases contraction
- parasympathetic nervous system decreases contraction
- extrinsic control
- fibers of autonomic nervous system modify intrinsic control
- vagus nerve

Front 31

medulla

Back 31

- cardiac center
- nucleus tractus solitarius (NTS) of the medulla receives sensory input from different systemic and central receptors
- receives information from other brain regions

Front 32

cardioacceleratory center

Back 32

- sympathetic
- projects motor neurons in T1-T5 that synapse with neurons in cervical and upper thoracic sympathetic ganglia
- from sympathetic ganglion fibers run to the heart
- they innervate SA and AV node, heart muscle, and coronary arteries

Front 33

cardioinhibitory center

Back 33

- parasympathetic
- sends impulse via vagus nerve
- ganglia lie in heart wall and send fibers to SA and AV node

Front 34

cardiac cycle

Back 34

- movement of blood through heart
- mechanical events
- blood flows from vena cava and pulmonary veins into atria and then into ventricle through tricuspid and bicuspid valve
- brief period of atrial contraction forces all remaining blood in atria into ventricles
- ventricular contractions pump blood into pulmonary artery and aorta through semilunar valve