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Cardiac Muscle Cells

BIOL 2130 Presentation 2013
by

Jasmeen Dhaliwal

on 16 March 2013

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Transcript of Cardiac Muscle Cells

Comparison to skeletal muscle photo (cc) Malte Sörensen @ flickr CARDIAC MUSCLE CELLS CELL BIOLOGY PRESENTATION:
Cardiac Muscle Cells Heart muscle
Myofibrils are red
Nuclei are blue CHARACTERISTICS: Only found in cardiac muscle of the heart
Make heart contractions possible through involuntary movements
Most physically energetic cell in the body, contract 3 billion times or more in a lifetime
Each cell contains myofibrils, which are made up of units called sarcomeres responsible for cell contractions
Have one nucleus
Vast amounts of mitochondria to produce ATP rapidly; prevents fatigue TWO CELL TYPES
IN THE HEART: 1. Myocardiocytes 2. Cardiac Pacemaker Cells Myocardiocytes makeup the atria (blood in) and ventricles (blood out) of the heart
Flexible cells that are able to shorten and lengthen, which is critical for heart contractions Cardiac pacemaker cells carry impulses to beat the heart
Found at the sinoatrial (SA) and atrioventricular (AV) nodes of the heart
Responsible for spontaneous generation of electrical signals sent to the heart and between cells
Need to respond to electrical impulses sent from the brain
All connected by cellular junctions called intercalated discs, allowing the cells to function as one unit
These allow Na+, K+ and Ca 2+ to pass between cells for depolarization/repolarization cycle Jasmeen Dhaliwal, Nicole Harris, Lyndsey Nabata and Eric Esslinger Cell Requirements
unlike other cells of the heart they don't use the blood of the ventricles and atria for nourishment; they use the outer coronary arteries of the heart
blockage of these coronary arteries cuts off supply to theses cells
they require a high amount of oxygen to function which means there is a high number of mitochondria in each cell Specialized structures for function
mitochondria for aerobic metabolism
intercalated disks which conduct simultaneous electric signals throughout the heart for a single contraction of all cells
intercalated disks are secured by desmosomes and linked by gap junctions
actin and myosin microfilaments found in the cytoplasm of the cell allowing contractions by sliding over each other Chemical Requirements
mostly oxygen
also require calcium, potassium and sodium
the opening and closing of potassium and sodium channels is what allows depolarization and repolarization of the cell membrane
calcium initiates "cross-bridge cycling"; the sliding of actin and myosin involved in a muscle contraction What happens when something goes wrong? heart attack
known as myocardial infarction
occurs when blood flow to the heart cells is blocked
a common cause of blocked arteries is atherosclerosis
causes portions of the heart to die
because heart cells do not easily regenerate, these cells are lost causing permanent damage
recent stem cell research however has shown it may be possible to regrow these damaged cells cardiac arrest
occurs when the heart suddenly stops beating
caused by a problem with the heart's electrical system
this prevents nutrients and oxygen from reaching organs
death can occur within minutes Structure and Functions Structure of Cardiac Muscles unlike skeletal muscle, cardiac muscles do not require commands from the CNS to contract, signals originate from within the muscle itself
therefore, the heart can beat without a brain... each cardiac myocyte is surrounded by a cell membrane called a sarcolemma and contains one nucleus
the cells are packed with mitochondria to provide a constant supply of ATP that is needed to sustain cardiac contraction Similarities:
contain contractile proteins (actin + myosin)
overall appearance

Differences:
cardiac muscle is striated - skeletal muscle is ordered
cardiac muscles are often branched, so one cell may form connections with several neighbors - skeletal muscles tend to be linear
cardiac muscle = involuntary control - skeletal muscle = voluntary control adjacent cardiac myocytes are joined by intercalated disks (complex adhering structures)
if they don't touch each other they will beat independently
also have gap junctions that allow them to work as one because they allow action potentials to spread between the cells by permitting the passage of ions (depolarization)
electronic pacemakers may be used for a patient whose heart doesn't beat in rhythm How do they connect together? a heart can survive for 4 - 6 hours outside the body Polarization and Depolarization of the Cell the cardiac action potential consists of two cycles, a rest phase and an active phase
resting potential: during this phase of the beat ions like Na+, K+ and Ca 2+ are separated
the electrical cell generates an impulse + the ions will cross the membrane causing depolarization
the movement through the Na+, K+ and Ca 2+ channels is what causes the contraction of the heart muscle.
depolarization + contraction = wave movement of the heart muscle
ions move back to repolarize + heart relaxes
electrocardiogram (ECG) measures strength of these cycles
time between is very long, so cardiac muscles don't tire as easily Steps of the cardiac action potential: 4 - the resting potential (-96 mV) is seen between contractions

0 - inward movement of Na+ (depolarization) causes a wave of movement through the heart muscle

1 - K+ moves in and Cl- out

2 - inward movement of Ca 2+ is balanced by outward movement of K+

3 - outward movement of K+ (repolarization)

4 - resting potential How does a contraction occur? calcium from the action potential binds to troponin and the actin binding sites are exposed
myosin binds to the actin filaments
movement occurs from the sliding of these filaments against each other using ATP on the globular head of myosin Each sarcomere contracts sarcomeres are repeating units that cause the striations of the cell

myosin pulls the actin filaments together shrinking the h-zone

contraction of many sarcomeres at once causes the heart to beat Let's see how quickly we can send
"cell signal impulses" between each other! Pacemaker cells send impulses between each other at a rate of 119 m/s!
Let's see how fast we can be! Now time for a little game! Thank For You Watching! One final fun fact: The heart pumps about 2000 gallons of blood every day!

That is equal to 21,000 beer cans!
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