C6: Cardiac Innervation Flashcards
What are the two MAIN types of cardiac cells? Do both cells work together to form a single contraction?
conduction cells
muscle/myocardial cells (most numerous)
yes
How are these two cells joined together?
by gap junctions
what are gap junctions and what do gap junctions allow?
they are electrical connection between cells
allows electrical impulse to pass from 1 cell to another
how are the branches of cardiac cells joined together?
by intercalated discs that contain gap junctions
describe the 4 types of cardiac cells and their functions.
myocardial/muscle cells: for contraction
conduction cells: thin tracks through the muscle cells that initiate or conduct electricity
avascular valvular tissue: composed of interstitial cells
Endocardial cells: line all of the blood/tissue interfaces (including valves) and allow blood to side easily over the surface of the endocardium
what must occur in order for myocardial cells to contract?
they must be stimulated by an electrical current (pacemaker) or an action potential
where specifically are myocardial cells located?
in the thin atrial walls and myocardial layer of the ventricles
describe the microscopic anatomy of myocardial cells
myocardial cells are made up of many myofibrils arranged in a row… myofibrils are the elements responsible for contraction
also contain sarcomeres which are a segment of a myofibril that are arranged in several layers on top of one another
what are the 2 components that make up the myofibrils and what are there functions?
Myosin and actin… they’re contractile proteins that slide over one another
describe the movement of myosin and actin during contraction and relaxation
contraction: actin and myosin slide past eachother and overlap
relax: actin and myosin side apart and are only overlapped at their ends
what are 2 things that can effect the amount of overlap of myosin and actin before and after contraction?
preload and afterload
How does increased preload effect over lap of M&A?
How does increased afterload effect M&A?
Preload: increased preload stretches M&A apart and the amount of contraction is increased
Afterload: increased afterload lease to less overlapping of M&A and contraction is decreased
how does an action potential stimulate contraction? (in general)
it causes a change in the ion levels in and outside the cell
can muscle cells stimulate themselves?
yes but it will result in a slower HR than if stimulated by conduction cells
how do impulses travel through conduction cells?
whats another name for conduction cells?
through gap junctions (from atria to ventricles)
auto-arrhythmic cells
are conduction cells completely independent of outside stimulation?
no
what is influx?
ions entering the cell through channels in the membrane
what is efflux?
ions exiting the cell through channels in the membrane
define stimulus
strong electrical signal that can be conducted through the heart
what is automaticity and what is it based on?
ability of a cell to produce its own impulse… based on the steepness of each cells phase 4 slope
define excitability
ability of a cell to accept an impulse and transmit it to surrounding cells
define refractory/refraction. what is it based on?
ability of a cell to respond to a stimulus
based on which stage of the action potential the cell is currently in
what is electrical mechanical coupling or excitation coupling?
a series of events that connected the elec. stimulation to a mechanical event
whats action potential (AP) and what does it include? what must occur in order for the AP to get through to the cell?
a wave of electrical discharge that travels along the outer membrane of a cell
it includes a cycle of elec. depolarization and repolarization thats repeated ever HB
it must reach a certain threshold
do muscle and conduction cells both have an AP?
yes
how is AP generated in conduction cells?
conduction/specialized cells are self stimulated or stimulated from an outside source
what are the 5 sequences of electrical events that every cell must go through for every HB?
- depolarization
- early repolarization
- plateau or contraction
- repolarization
- resting state
whats the value of the AP at resting state and at depolarization?
-90mV
+50mV
whats happens during depolarization?
the cell is stimulated and prepares for contraction… then the cell fires from threshold to its maximum + state and sodium enters the cell
is the cell refractory during depolarization?
yes
whats happens during early repolarization?
is the cell refractory during repolarization?
very short time interval where the cell moves to a slightly less positive state in preparation for plateau phase… K+ exits the cell
Yes
whats happens during plateau stage?
is the cell refractory during plateau?
excitation coupling occurs which leads to contraction and Ca2+ enters the cell while K+ leaves
which ion is responsible for contraction?
calcium (entering the cell)
whats happens during repolarization?
is the cell refractory during repolarization?
‘post contraction’ or the downward slop on the AP
the cell returns to a resting state and K+ leaves the cell
the cell can be stimulated with a strong stimulus
whats happens during resting state?
cell is ‘waiting’ for another stimulus
how does the steepness of the slope in the resting state effect HR?
steep: fast intrinsic HR
flat: slow HR
do conduction cells have a plateau stage?
how do the graphs of the AP of these cells look?
No
they’re more rounded and have a steeper phase 4 slope
when is a cell immune to stimulus?
during the refractory period
what is the absolute refractory period?
when does this occur?
period where no external stimulus will make the HB
From phase 0 to the end of stage 2 and into stage 3
what is the relative refractory period?
when does this occur?
period where only a strong external stimulus will make the HB
stage 3
whats the cardiac conduction system?
network specialized cardiac fibres that provide a path for each cycle of cardiac excitation
whats the importance of electrolytes in the body?
they’re responsible for the AP…. (Na, K and Ca)
not enough= poor function of heart
too much= hyper function
whats the function of intrinsic innervation and where it it located?
controls the base HR and the HR of individual parts of the conduction system
found inside the heart
whats the function of extrinsic innervation and where it it located?
give the heart signals to change rhythm
located in the sympathetic and parasympathetic nervous system
wheres the cardiac centre in the brain?
medulla oblongata
where the Symp sys. located? how does it stimulate the heart and what does it stimulate?
how does it effect HR?
from medulla to thoracic spine
stimulates through fibres which send impulses to the SA and AV nodes and myocardium
increases it
where the parasymp sys. located? how does it stimulate the heart and what does it stimulate?
how does it effect HR?
from medulla to heart
stimulated through the vague nerve which stimulate the SA and AV nodes only
decreases it
when is the symp sys. activated? what does it release and what does it increase?
in times of stress…. releases nor-epinephrine
increases ion exchange, increases HR and force of contraction
when is the parasymp sys. activated? what does it release and what does it decrease?
in times of rest… releases acetylcholine
HR
what type of controls are the symp. and parasympathetic NS?
extrinsic
the symp. and parasympathetic NS are capable of effecting what 4 things?
chronotropy/HR
inotropy/contractility
preload/ventricle filling volume
afterload
what controls arterial pressure?
baroreceptors in the carotid bulb and AO arch
what happens with carotid bulb massage?
increases press to brain which slows HR
what are the 6 parts of the intrinsic conduction pathway?
- SA node
- LA/RA (intermodal tracts)
- AV node
- bundle of His
- R & L bundle branches
- purkinje fibers in LV
describe the location and function of the SA node
located near the superior wall of the RA, near entry of SVC
pacemaker of the heart, HB starts in the SA node
how many pulses per min does the SA node generate? what mechanism slows it down?
100 pulses per min
parasympathetic tone reduces it to 60-100
what demographic has high parasympathetic tone?
athletes
how does stimulation in the atria travel?
from the SA node along the internal atrial conduction paths and ends at the AV node
whats the location of the AV node?
found in the right side of the IAS above the annulus of the TV and near the opening of the coronary sinuses
whats the function of the AV node?
delays the impulses to allow for atrial contraction and ventricle filling… also so that the atria can contract before the ventricles
what is the AV groove?
insulates the pulses so that they only travel in the pathway of specialized cells
how many pulses per min can the Av node generate? and when would it generate pulses?
40-60… called a junctional rhythm
only if the SA node fails
where is the Av bundle located? what is its main function?
sightly distal to the AV node
only electrical pathway between the atria and ventricles (like a ‘major highway’) and protects the ventricles from fast atrial rhythms
what occurs to the impulse when it travels through the bundle branches?
it speeds up again
Through what pathway does the impulse travel along the bundle branches?
they travel along the IVS towards the apex of the heart and then turn superiorly towards the base on the lateral sides of the heart
what happens to the impulse in a left bundle branch block?
it will slow the conduction through the ventricles and lead to the longer QRS complex
which septum is stimulated first from the bundle branches?
RV septum, then L
when does ventricular depolarization occur?
as the wave of stimulation travels along the bundle branch pathway
whats causes the QRS complex on the EKG?
ventricle depolarization.
where are the purkinje fibres located? describe their appearance
through the IVS and into the ventricles/apex
they’re more elaborate on the left side due to thicken muscle (like small roads going through neighbourhoods)
whats the function of the purkinjie fibres?
deliver impulses to the individual muscle cells
help the AV valves function by stimulating the pap muscles before the rest of the cells
what happens as the stimulation is going through the purkinjie fibres?
contraction is completed and the ventricle start to repolarize
how many pulses per min and the perkinjies produce?
30-40 (would require a pacemaker)
where does contraction being?
apex, helps with the ejection of blood
whats responsible for the t wave of the ECG
Repolarization of ventri
how long does it take for repolarization to occur in the SA node?
200 ms
when the atria are repolarizing, what are the ventricles doing?
depolarizing… they will always be opposite
like which conducting pathways will take over if the SA node fails
AV node
bundle of his
LV/RV muscle cells
How many pulses per minute can the LV and RV produce?
20-30
What part of the conduction path way is malfunctioning when a person has a heart arrhythmia?
The AV node
what is the HR generated by the AV node called?
junctional rhythm
What’s another term for electrical mechanical coupling?
Excitation coupling
How long should the AP last from phase 0 to the beginning of phase 4?
200ms
What are the 3 ions are most responsible for AP and depolarization?
Sodium, calcium, potassium
