spring pnb - heart two

other name for contractile muscle cells

cardiac myocytes

cardiac muscle fibers

how are cardiac myocytes similar to skeletal muscle

both use the sliding filament model

what creates the pumping action in the heart

when fibers are arranged to wrap around the chambers, so when they contract they squeeze on the chambers of the heart and reduce there volume.

what muscle bifurcate or branch out

cardiac muscle

muscle cells have to be highly what?

interconnected

what does muscle cells being interconnected mean

means that there contractions should be able to be coordinated at the organ level

cardiac muscle cells are held together by what

intercellular junctions

where are intercellular junctions located in cardiac muscle cells

intercalated disk

what are the two types of proteins that make up the intercalated disk

desmosomes and GAP junctions

desmosomes

button-like; physical connection between adjacent cardiac monocytes. important for physically coupling the cells together, but allow them to bend and twist while contracting and relaxing the heart

gap junctions

create electrical and chemical connections between cardiac myocytes. allows cardiac myocyte to share ions and signaling molecules with helps it know what going on electrically with its neighbor

what creates the Atrial and Ventricular Syncytia

desmosome and gap junctions

syncytium

a lot of things that are so interconnected that they behave as a single thing

what must happen to have muscle contract

have to have an action potential of an alpha motor neuron

what is cardiac muscle innervated by

nervous system and autonomic neurons

what is different between cardiac and skeletal muscle regarding contraction

cardiac muscle can create its own action potential unlike skeletal.

how can cardiac muscle creates its own AP

due to it being an auto rythmic tissues

what is the job of the ANS for the heart

to turn the process up or turn the process down, like a controller

what happens when cardiac myocytes fire there AP

creates a depolarization (positive change in membrane potential) that spreads along the plasma membrane and eventually reaches the T tubule

what is inside the T tubule

voltage gated calcium channel called the - L-type calcium channel (LTCC)

what does depolarization do

causes the L-type channel to open which allows calcium to flow down its concentration gradient into the cytosol.

the T tubule membrane is close to what

the sarcoplasmic reticulum (500 nanometers)

what can calcium do when it comes in through the L-type calcium channel

create a small depolarization with its positive charge, which can be felt by another calcium channel that is found on the sarcoplasmic reticulum.

what is the calcium channel found on the sarcoplasmic reticulum

ryanodine receptor

what happens when the ryanodine receptor opens

calcium flood out of the SR down its gradient (higher in SR) and moves into the cytoplasm.

key differences between cardiac and skeletal muscle contraction

there is entry of extracellular calcium for the cardiac muscle contraction

what two places does extraceullar calcium enter the cardiac muscle

L-type calcium channels (from outside) and ryanodine receptor (from SR)

why is extracellular calcium needed for cardiac muscle

in order to release the calcium stores from the SR

calcium-induced calcium release

essential for cardiac muscle contraction, releases calcium stoes from the SR

what is the one rule that applies to all muscle

calcium is required to initiate contraction

why is calcium important for cardiac muscle

determines the strength of the contraction

what is the strength of contraction determined by in cardiac muscle

number of cross bridges that form between actin and myosin, which is determined by the calcium that gets released into the the cytosol.

when more calcium gets released what does that do to contraction

an increase of contractions of the cardiac myoctyes and more filaments sliding, which makes a more compressed or contracted cell

what happens to the calcium that is brought into the cytoplasm after the heart contracts

It has to get removed so the heart can relax.

what is the tip with calcium

it always goes back to where it came from

where does most calcium come from

sarcoplasmic reticulum through the ryanondine receptor

where does calcium go after contraction

back into the sarcoplasmic reticulum, through the transporter SERCA

SERCA

primary active transporter and located on the membrane of the sarcoplasmic reticulum

SERCA purpose

consumed ATP so that it can move calcium against its gradient

sodium calcium exchanger (NCX)

secondary active transporter (energetically unfavorable), antiporter which allows for sodium to flow down its gradient into the cell which allows us to use that energy to transport calcium out of the cell

what is required for the sodium calcium exchanger to work

the sodium inside the cell has to be kept low

what helps the sodium calcium exchanger to work

the sodium potassium pump working which helps continuously move sodium out of the cell

excitation contraction for cardiac muscles process

AP isnide of the cardiac myoctyes, which travels down plasma membrane into the T-tubule, depolarization opens up the L-type calcium thats going to allow a small amount of calcium to enter the cell, which is known as calcium-induced calcium release. Once calcium enter the cytosol it leads to a contraction and filament slide. To relax we need to use pumps to get calcium back into the SR and the interstitial fluid. We do that through SERCA (to SR), sodium calcium exchanger, and the sodium potassium pump located on the plasma membrane on the sarcolemma

where is the sodium potassium pump and sodium calcium exchanger located

on the plasma membrane on the sarcolemma

majority of the atria and ventricle is made up of what type of cells

contractile cells

contractile cells

have to contract to create the pumping action that allows for blood to move from place to place within the heart and also to get out into the vasculature in the vessel.

1% of the myocardium cells are called what

non-contractile cells called pacemakers

what are the SA nodes, AV nodes, and Pukinje fibers made up of

pacemaker cells

where is the sinoatrial node located

upper right portion of the heart

why are pacemaker cells called that name

they set the pace of electrical activity for the entire heart

what cells are autorythmic

pacemaker cells

autoryhtmic

can generate there own action potentials

autorhytmic rhythm can happen how many times

80-100 spikes/min

pace maker activity can be made to happen due to one specific ion channel which is?

the HCN channel (hyperpolrization gated cyclic nucleotide activated channel)

HCN channels

opens during hyper polarization and its regulated by cyclic nucleotides like cyclic AMP

is HCN and cation or anion channel

cation, selective for (+) charges like sodium and potassium

what happens when we have a cation channel

see a lot more sodium coming in than we do potassium coming out

why is HCN primarily used

to bring sodium inside the cell

major effect of HCN channel

create a depolarization of membrane potential

what is depolarization referring to the HCN channel called

funny current

funny current

produce a depolarizing current in response to a negative stimulus. Which means the HCN channel activates when membrane potential is hyper polarized.

what makes the pacemaker AP unique

lack of stable resting membrane potential (no steady state for SA NODE)

what is the hallmark of a pacemaker cell

lack of steady state or flat line

why is there no steady state for the SA node for pacemaker cells

due to HCN channel

how is pacemaker action potential created

from the HCN channel from two types of calcium channels (T and L type calcium channel) also from voltage gated potassium channels

what are the two types of calcium channels

T and L type channels

the depolarization that starts at the SA node spreads where

the atria of the heart through the internodal pathways

what happens when the depolarization spreads throughout the atria

it spreads into the cotnractile cells that are found in the atria

internodal pathways

located between two nodes (SA node and AV node)

where is the AV node located

between right atrium and right ventricle in the wall of the heart known as the inner atrial septum

what is the difference between pacemaker cell in the AV and SA nodes

the pacemaker cells in the AV node develop more slowly than the pacemakers in the SA node

pacemaker cells can create depolarization for how long in the AV node

60 times per minute

what node can conduct electricity the fastest

SA node and can essentially electrocute all the other cells, forcing them to do whatever the SA node is doing

what does the AV contain regarding tissue

non-conductive connective tissue

what does non-conductive connective tissue do to the AV node

creates a brief delay in the conduction through the AV node, due to the lack of electrical activity

what does the pause (delay) that occurs in the AV node do

buys the atria time to finish contracting before the depolarization spreads down into the ventricles

where are vessels located

at the base of the heart

where does contraction have to start in the heart

at the apex because we want o send blood up towards the base of the heart, if not blood wouldn’t leave the heart (high pressure at bottom, low pressure towards the top)

what helps prevent the depolarization from traveling into the upper portion of the ventricle

cardiac skeleton

cardiac skeleton

creates separate between the atria up top and the ventricles down low, which forces the depolorizing current from the AV nodes to use the other parts of the conduction system to make it down itnto the lower portions of the heart and finish the cycle

inter ventricular septum

separates the left and right ventricle

what happens when depolarization occurs at the apex

going to spread simultaneously through both sides and spreads through cells known as purkinje fibers

what happens to depolarization for the AV node

demoralization spread down the inter ventricular septum, which travels first throguh the AV bundle, which then separates into left and right bundle branches. Which carries the depolarization down the septum all the way to the apex or bottom of the heart

purkinje fibers

deliver the depolarizing current to the contractile cells of the ventricle and we start with the ones closest to the apex and end with the ones that are closest to the atria

where does contraction have to start in the heart

at the bottom

are the purkinje fibers autorhytmic true or false

true

what produces pace maker actions potentials very slowly

Purkinje fibers, 20 x per minute

what node begins the whole conducting system

SA node

whole conduction system summary

deprivation begins with pacemaker cells in the SA node, Travel into the internodal pathways and into the contractile cells of the atria. Then goes to AV node where there is a brief pause and then travels down the septum of the heart through the AV bundle and the left and right bundle branches. Which takes us to the apex of the heart where the pukinje fibers will pick up the signal and spread it int the contractile cells of the ventricles.

what are the most important pacemaker cells

the ones from the SA node because they fire the fastest

Failsafe

if the SA,node fails to work properly you have a type of safe system because the AV node can take over until surgery or a pacemaker is inserted

why is failure of the AV node problematic

because you only have purkinje fibers to pick up the signal which only depolarize 20 x per minute

contractile cardiac myoctyes make up what percent of cells in the heart

99%

what does it mean that contractile cardiac myoctyes are also excitable cells

they can produce an AP

why is the graph for the contractile and pacemaker cells different

they used different ion channels and therefore have a different AP than pacemakers

is it in the pacemaker or contractile cells that we have a steady line on the graph

contractile

the depolarization stage of the contractile cells is due to

fast voltage-gated sodium channels

voltage gated sodium channels

they inactivate at the peak of the AP which creates the refractory period

refractory period

time where we cannot star another AP, have to get back down to resting membrane potential first

why is the refractory period important for cardiac myocytes

allow for the cell to go through the contraction during the plateu phase of the AP. So we can finish the contraction before we repolarize and start the process of relaxation. Which is important for the coordination of the heartbeats