Heart pt 2 Flashcards
How many nuclei does a myocardial cell have?
one
How many nuclei do myocardium cells have?
One.
Do heart muscle cells have sarcomeres? T-tubules? Sarcoplasmic reticulum?
Yes. T tubules and SR to a lesser extent than skeletal muscle.
Do myocardial cells have sarcomeres? t-tubules? sarcoplasmic reticulum?
yes, yes, yes. T-tubules and SR is less extensive than in muscles.
What are intercalated discs? How are they connected (2 things)?
Attachment sites between cardiac cells.
Desmosomes (adhering junctions) that transmit contraction forces and hold tissue together.
Gap Junctions permit electronic communication between cells, forming a syncytium (cell network for coordinated contraction). This is important for AP conduction.
What stimulates myocardial contraction?
Action Potentials
What are the two kinds of myocardial action potentials?
Contraction AP (myocardial cells) Conduction AP (pacemaker cells)
What triggers myocardial contraction?
Where are contraction APs produced?
Long duration AP
Atria, ventricles, purkinje fibers
Muscle contraction occurs in the same time frame as ______________.
Action Potentials
Where are conduction APs found?
SA and AV nodes
What does autorhythmic and what type of AP does this term describe?
Authrhythmic means something (the heart) generates its own action potentials.
conduction APs originate from pacemaker cells, which are autorhythmic.
What ion starts cardiac (contraction) AP but then inactivates?
Na+
What type of channel produces long duration AP with plateau?
Slow L types Ca channels
What ion assists slow L type channels to produce long duration AP and what direction does it flow?
K+
Out of the cell
What ion depolarizes membrane of cardiac cells?
Ca+
Calcium blocker block this type of channel to reduce cardiac contractility. What are examples of Ca blockers?
L type channels
Nifedipine, verapamil
What is the net result of incoming Ca+ via slow channels?
prolonged depolarization
How is the AP from SA node conveyed through myocardium?
gap junctions
What does the AP open in myocardial cells?
L-type Ca channels in T-tubules
What does the inward Ca flux bind to when it enters the cell?
Ryr
What does the Ryr open in the cardiac cell?
Opens SR Ca channel in terminal cisternae
What is trigger Ca?
The Ca that binds to the Ryr to open the SR. This Ca is in an amount too small to initiate contraction.
In both skeletal and cardiac muscle it is the ____ that initiates release of Ca from the SR.
Action potential
What does Ca from the SR inititate?
actin-myosin contraction
What reabsorbs Ca back into the SR?
SERCA (sarcoendoplasmic reticulum calcium ATP-ase)
What stopes CA release from the SR?
Cessation of the AP
What does the Na/Ca exchanger do?
Helps the muscle relax by moving (1)Ca out of the cell. (3)Na is brought into the cell by the exchanger due to the concentration gradient created by the Na pump (different than exchanger).
What is the affect of hyperkalemia?
Excess extracellular K lowers Ca entry and causes weakness of the heart.
Decreased membrane potential = diminished AP amplitude
Less depolarizing current = less SR release of Ca = weakening of the heart
Autonomic activity is only the most ________ aspect of CNS control of visceral structures.
Peripheral
For three parts of the brain form a hierarchical control over the preganglionic and postganglionic neurons of the sympathetic and parasympathetic portions of the ANS?
Cerebral cortex
Limbic system (amygdala)
Hypothalamus
What innervates the upper sympathetic chain ganlia?
preganglionics (T1-5)
Where do postganlionics from upper ganglia project and via what?
projects to the heart
via the cardiac plexus
why types of receptors do the sympathetic ganglionics stimulate?
beta receptors in nodes and myocardium
Where do the preganglionics and postganlgions project in the parasympathetic system?
Preganglionics: from brain stem to heart via cardiac plexus
postganglionics: neurons in myocardium stimulate muscarinic receptors in nodes
What nerve makes up the parasympathetic system and from where does it exit the skull? What is its path from there?
Vagus nerve
jugular foramen
descends neck and gives off branches including the cardiac plexus
What chemicals are used by the sympathetic ns in cardiac contraction? What receptors do they use?
NE from sympathetic neurons
EPI from adrenal medulla
Beta 1 receptors
What second messenger is used by the sympathetic ns? Does the sympathetic system activate or inhibit it?
cAMP
activates
What does cAMP do?
enhances opening of L-type CA channels
What is the effect of more Ca entering the cell?
More Ca released from SR to bind to troponin = more forceful contraction
Parasympathetic activity mostly affects what phase of the cardiac cycle?
atrial contraction (decreases)
What chemical does the parasympathetic ns use?
ACh
what receptors does the ACh use?
muscarinic
Does the parasympathetic system (ACh) increase or decrease cAMP activity?
decreases
What affect does less cAMP have on the L-type Ca channels? on the SR?
Less Ca entering the cell
Less Ca released by the SR
Why is the primary affect of the parasympathetic ns on the atrium?
Fewer parasympathetic nerves in the ventricles
Where is the SA node found?
In the junction of SVC and R atrium
What is the role of the SA node?
Primary pacemaker of the heart, generates auto-rhythmic impulses
What do APs from the SA node trigger?
atrial contraction
Where is the AV node found?
base of the right atrium
What is the role of the AV node?
regulator of conduction into ventricles
What does the Bundle of His branch into?
Left and right bundle branches (to left and right ventricles)
what can interrupt conduction through the Bundles of His?
necrosis caused by coronary artery occlusion
Where does the AV node send fibers? what do these form?
through the CT right surrounding the tricuspid valve
Bundles of His
What do the CT rings in the heart surround?
AV and semilunar valves
What is the only conduction pathway between the atria and ventricles?
Bundle of HIs
Where is the Bundle of His located, specifically?
endocardium of the interventricular septum
What does the bundle of his form part of in the right ventricle? What does this send conduction to?
moderator band
papillary muscles
What are purkinje fibers? what do they do?
modified cardiac cells that generate and conduct AP
large fibers with high conduction velocity located in the endocardium.
Form the bundle of his and extend into myocardium
trigger synchronous contraction of myocardial cells
At what rate do purkinje fibers conduct AP?
2-4 m/sec. about the same as unmyelinated neurons
What makes up the endocardium?
inner layer- endothelium and subendothelial CT
Middle layer- smooth muscle
Deep subendo cardial CT layer containing purkinje fibers
Most AP conduction is ____________ (speed)
rapid
AV conduction velocity is ___________ (fastest/slowest). Due to what?
Slowest
fewer gap junctions
Where is the delay in AP between? what does this give time for?
atrial and ventricular contraction
filling
What two landmarks have autorhymicity?
SA and AV node
What produces the initial depolarization in SA and AV nodes?
Fast T-type Ca channels
What is absent in conduction APs?
voltage gated Na channels
Are Ca channels inhibited by Ca blockers during conduction AP?
NO
What do slow L types C channels do during conduction AP?
prolong AP, but with less of a plateau than contraction AP
What repolarizes the cell during conduction AP?
opening of K channels
What do Funny Na channels produce?
slow diastolic depolarization that spontaneously generates the next AP
What opens Funny Na channels?
effects of hyperpolarization and K flux
