physio cardiac muscle

cardiac function in body

pump blood, maintain BP, supply oxygen and nutrients to body, remove CO2 and waste from body

skeletal muscle is what type of syncytium

true syncytium

cardiac muscle is what type of syncytium

functional syncytium

similar to skeletal muscle, cardiac muscles are

striated muscles

striated muscles contract in the absence of

nerve activity (involuntary)

what is a function unit of cardiac muscles called

sarcomere

are fibers branched?

yes

how do fibers connect one another at the cardiomyocycte cell membrane

by intercalated discs

intercalated discs contain what that allows free diffusion of ions

several permeable gap junctions

why do ions move easily in intracellular fluid along longitudinal axes of cardiac muscle fibers

so action potential travel easily from one cardiac muscle cell to the next

cardiac muscle is a _________ of many heart muscle cells

syncytium

what does the cardiac muscle being a syncytium contribute to

allows action potential to spread to all heart muscle cells

where are the nuclei in cardiac muscle cells

centrally located

where are cardiac muscle cells nuclei abundant

mitochondria

sarcolemma has what kind of specialized ion channel

voltage gated Ca channel

SR less abundant than _____ muscle, but greater density than ______muscle

skeletal, smooth

what is a key feature of cardiac myocyte

intercalated disk

what is the intercalated disk composed of

adherens junction, desmosome, gap junctions

types of adherens junctions

C, alpha, beta, gamma, delta

Cadherins

family of transmembrane protein that form homodimer in Ca-dependent manner with other cadherin molecule on adjacent cell

delta-catenin

bind juxtamembrane region of cadherin

gamma-catenin

bind catenin bind region of cadherin

beta-catenin

bind cytoplasmic region of cadherin

alpha-catenin

link actin cytoskeleton to N-cadherins by binding to beta or gamma catenin

desmosomes

composed of desmosome intermediate filament complexes (DIFC)

DIFC

network of cadherin proteins, linker protein, and intermediate filaments

DIFC can be broken into 3 regions

ICS, ODP, IDP

what does extracellular core gion contain

desmoglein and desmocollin

desmoglein and desmocollin are both

cadherin family of cell adhesion proteins, have 4 extracellular domains and have Ca binding motifs

what contributes to ODP region of desmosome

plakophillin, plakoglobin, N-terminus globular domain of desmoplakin

what contribtues to IDP region of desmosome

C-terminus globular domain of desmoplakin and intermediate filament interaction region

gap junction

specialized intracellular connections that directly connect cytoplasmm of 2 cells and allow various things to pass directly through regulated gate between cells

what is 1 gap junction channel composed of

2 protein hexamers called connexons, which connect across intracellular space bridging gap between 2 cells

adherens junction overall

connects actin filaments of adjoining cardiomyocytes

desmosome overall

connects to intermediate filaments of adjoining cardiomyocytes

gap junctions overall

opening to allow flow of ions, action potential, molecules, between cardiomyocytes

2 specialized cardiac muscle cells

contractile and autorhythmic

contractile cells

99% of cardiac muscle cells, do mechanical work of pumping

autorhythmic cells

dont contract, intiiate and conduct AP responsible for contraction of working cells

electrophysiological properties of cardiac muscles

automaticity, excitabilty, conductivity, contractiliy, rhtyhmicity

automaticity

abilty to spontaneously generate electrical impulse

excitability

ability to respond to an electrical impulse

conductivity

allow transmission of electrical impulse to another cardiac cell

contractility

ability to contract after electrical impulse response

rhythmicity

ability to send electrical impulses in regular manner

excitation of heart triggered by

electrical impulse rather than neural transmitters

contraction of heart triggered by

elevation of intracellular calcium influx

reason for plateau in AP for cardiac muscle and NOT skeletal muscle

-L type Ca channel slower to open and stay open longer

-permeability of cardiac muscle membrane for K ions decreases by 5 fold

in phase 0 of cardiac AP (depolarization)

influx of Na, voltage gated ion channel open

in phase 1 of cardiac AP (inital repolarization)

Na channel close

in phase 2 of cardiac AP (plateau)

slow Ca channel open

in phase 3 of cardiac AP (rapid repolarization)

slow Ca channel close

in phase 4 of cardiac AP (resting membrane potential)

K channel close

energy for cardiac contraction

derived from catabolism of fatty acids, glucose, lactate, and ketone bodies

after fatty meal

60% from oxidation of fatty acids

starvation

breakdown of adipose tissue (ketone bodies)

cardiac performance is function of

preload, afterload, contractility, heart rate

preload

myocardial stretch at end of diastole

afterload

resistance ventricle must overcome to eject blood

heart rate

# of times heart beat in minute

rank of cardiac output in autonomic nervous system control from high to low

maximum sympathetic, normal sympathetic, zero sympathetic, parasympathetic

when end diastolic volume (EDV) increases

stretches muscle fibers, force of contraction and output per beat (SV) increase up to limit, beyond which stroke volume falls with further increase in diastolic volume

end diastolic volume (EDV)

volume of blood in left ventricle at end of ventricular filling

stroke volume (SV)

volume of blood pumped out of left ventricle of heart during each systolic cardiac contraction

cardiac output (CO)

heart rate x SV

ejection fraction (EF)

SV/EDV x 100%

regulation of heart pumping

frank sterling mechanism and autonomic nervous system

frank sterling mechanism

intrinsic cardiac regulation of pump in response to change in volume of blood flowing into heart

autonomic nervous system

control of heart rate and strength of heart pumping by parasympathic and sympathetic nerves

at rest heart pump

4-6 liter per minute

during exercise heart pump

12-35 liter per minute

how does sinoatraial node cell generate impulse for cardiac contraction for life (loop)

self excite to cause AP → recovery from AP→ hyperpolarization after AP is over → drift of resting potential to threshold (loops)

how does sinoatraial node cell generate impulse for cardiac contraction for life (step)

-high Na conc in ECF and leaky Na channel lets Na into cell

-threshold reached, L type Ca channel opens (depolarization)

-Ca channel close within 100-150 millisecond after opening

-K channel open

-K channel close, leakiness of Na channel restarts cycle

PQRST and AP trace (how it works)

if electrode place on opposite side of heart on skin, electrical potential generated by current can be recorded by electrocardiogram (ECG)

AV node impulse delay ensures

the atria empties their blood into ventricles before ventricular contraction begins

cardiac electrical activity coordinates

pumping action of the heart

P wave

atrial depolarization

QRS complex

ventricular depolarization

ST-T segment

ventricular repolarization

excitation-contraction coupling and relaxation in cardiac muscle

-AP open Ca channel in t-tubule (5x wider than skeletal)

-rely in Ca from extracellular space for contraction (95% stored in cells)

-contraction similar to skeletal muscle, Ca dependent

-SR Ca pump and Ca-Na exchanger remove Ca during relaxation

-Na transported out of cell by Na-K pump to reach resting potential

in skeletal muscle ____% of Ca is stored in t-tubule and SR

100

where do we see a plateau, in the skeletal or cardiac muscle

cardiac muscle

summary of excitation-contraction coupling in cardiac contractile cells

-Ca enter cell (depolarization) trigger release of Ca by terminal cisternae

-Ca bind to troponin C induce conformation change in troponin complex

-myosin head bind to actin, cross bridge movement (ATP hydrolysis needed) and reduction in sarcomere length

-Ca resequestered by SR by SERCA pump

-Ca removed from troponin C and myosin unbind from actin (ATP needed), allows sarcomere to resume original relaxed length