What causes muscle contractions?
Myosin and actin
What is the main structure for contraction?
sarcomeres (fundamental unit of myofibrils)
What are fascia?
connective tissue that covers muscle
Where is the epimysium located?
it surrounds groups of fascicles
Where is the perimysium located?
Surrounds individual fascicles
What are fascicles?
they hold muscle fibers (discrete bundle of muscle cells)
Where is endomysium?
It separates individual muscle fibers
What is the sarcolemma?
the plasma membrane of a muscle fiber
What are muscle fascicles?
bundles of muscle tissue held together by connective tissue
What are muscle fibers composed of? (x4)
myofibrils (muscle fibre contractile strucutres), sarcoplasmic reticulum (aka smooth ER, stores and sequesters calcium), t tubules and mitochondria (E)
What are t tubules?
tubular infoldings of the sarcolemma which penetrate through muscle cells and emerge on the other side
-associate with the ends of the sarcoplasmic reticulum
What composes the triad?
2 lateral sacs and the t tubule
What gives skeletal and cardiac muscles striations and what are striations composed of?
myofibrils – due to thick and thin filaments which run parallel to the long axis
What creates thick and thin filaments?
thick: myosin
thin: actin
- both contractile proteins
What are tropomyosin and troponin and what do they do?
regulatory proteins that regulate muscle cells
What are titin and nebulin and what do they do
they are accessory proteins and they anchor myosin and actin into the sarcomere
What are transverse tubules?
a system of tubules that provides channels for ion flow throughout the muscle fibers to facilitate the propagation of an action potential.
What is the H zone and what is it composed of?
H = helles = the clear band (within the A band) – made up of myosin, gets shorts during muscle contraction
What is the A band?
A = anisotropic = darkest coloured band (length stays the same) – contains myosin
What is the I band?
I = isotropic = lightest coloured band (length decreases) – contains actin
What is actin and what is the binding site for?
a contractile protein with a binding site for myosin
What regulates skeletal muscle contraction?
calcium binding to troponin
What is the Z line?
the line formed by the attachment of actin filaments between two sarcomeres of a muscle fiber in striated muscle cells (links thin filaments)
What is the M line?
supporting proteins that hold the thick filaments together in the H zone. myosin tail is toward this (links thick filaments)
What is the hinge region?
it enables the myosin head to move (thick filament where the length decreases)
What is g actin (globular)?
a globular subunit of F actin with an active site for binding a myosin head
What is f actin (filament)?
linear polymer of G actin units (G actin is single globular unit)
What is TnT?
a component of troponin that binds and attaches to tropomyosin
What is TnI?
a component of troponin that attaches to actin and inhibits binding with myosin
What is TnC?
a component of troponin that binds to calcium ions (reversibly)
What are cross bridges
aka myosin heads, they bridge the gap between thin and thick filaments
What is titin?
a long and elastic accessory protein that anchors thick filaments between the M and Z line, also provides structural support and elasticity
What is nebulin?
a protein that lies along the thin filament that attaches to a Z line but not the M line – regulates thin filament length during sarcomere assembly
What is the sliding filament theory?
a theory that actin filaments slide toward each other during muscle contraction, while the myosin filaments are still; neither thick/thin filaments shorten, filaments slide past each other
What is the cross bridge cycle?
a cyclical formation and breaking of cool bridges (how muscles generate force)
What is excitation contraction coupling?
how muscle contractions are turned on and off – a sequence of events when an AP in the sarcolemma causes contraction (requires calcium release)
What are sarcomeres?
a functional unit of muscle, spans from Z line to Z line and shortens during contraction (composed of actin and myosin)
What shortens during contraction?
I band, H zone and sarcomeres
What is rigor mortis and what causes it?
stiffness of the body that sets in several hours after death; occurs due to myosin heads being frozen in their 90 degree position
What happens in high energy form for myosin heads?
its at 90 degrees, ADP and Pi are bound to myosin and it has a high affinity for actin
What happens in low energy form for myosin heads?
its at 45 degrees, ADP is bound to myosin and it has a low affinity for actin
What is a power stroke for myosin heads?
movement of the myosin head that pushes the thin filament toward the center of the muscle, after which thick + thin filaments detach and the myosin head returns to its initial potential
What role does calcium play in contraction?
it binds to troponin, causing movement of troponin, causing movement of tropomyosin, exposing binding sites for myosin on actin
What opens calcium channels and where?
DHP receptors of t tubules in lateral sacs of sarcolemma
What is the heart?
a hollow muscular organ that pumps blood throughout the body
What does the cardiovascular system transport (x3)?
- O2 from nutrients to cells
- removes waste from tissues to liver and kidney (Co2 and urea)
- hormones, immune cells and clotting proteins to their specific target cells
What are blood vessels?
tubelike structures that carry blood throughout the body
What is blood?
a connective tissue with a fluid matrix called plasma where red and white blood cells, and platelets (cell fragments) are suspended
What are the 2 valves?
atrioventricular and semilunar
How many chambers does the heart have?
4
What is the inter ventricular septum?
it separates ventricles
Which way does the electrical signal flow through the heart?
from the apex to the base
What is the strucuture of the cardiovascular system called?
vasculature
What is the order blood flows in the heart?
heart, arteries, arterioles, capillaries, venules then veins
What are arteries?
large, branching vessels that conduct blood away from the heart
What are arterioles?
small branching vessels that conduct blood away from the heart?
What are capillaries?
sites of exchange between blood and tissue
What are venules?
small converging vessels
What are veins?
large converging vessels that conduct blood to the heart
What kinda system is the cardiovascular system?
a closed system
What are erythrocytes?
red blood cells that transport oxygen and CO2`
What are leukocytes?
white blood cells that defend the body against pathogens
What are platelets?
cell fragments that are important in blood clotting
What is plasma?
the fluid part of blood (water) + solutes (ex. carbs, minerals, lipids, vitamins, etc.)
What are the 2 ways the blood circulates?
- series flow through the cardiovascular system
2. parallel flow within the systemic or pulmonary circuit
What is the pulmonary circuit?
- supplied by the right heart
- blood vessels from the heart to the lungs and lungs to the heart
What is the systemic circuit?
- supplied by the left heart
- blood vessels from the heart to systemic tissues and tissues to the heart
What colour is oxygenated and deoxygenated blood?
oxy: red
deoxy: blue
How does blood becomes oxygenated?
When it passes through the lungs, oxygen diffuses through the tissues into the blood
Why is parallel blood flow great?
it allows for independent regulation of blood flow to organs
Where does the right atrium receive blood from (x2)?
venae cavae and coronary sinus
What is the right atrioventricular valve?
aka the tricuspid valve, blood leaving the R atrium flows into the L ventricle through it
What does the right ventricle do?
pumps deoxygenated blood to the lungs
What does the left atrium do?
receives oxygenated blood from the lungs
What does the left atrioventricular valve do?
(mitral or bicuspid valve) Blood leaving the left atrium flows into the left ventricle through this valve; most commonly replaced due to more pressure on left side of the heart
What does the left ventricle do?
pumps oxygenated blood to the body
What does the aorta do?
the large arterial trunk that carries blood from the heart to be distributed by branch arteries through the body
What is the pulmonary semilunar valve?
the heart valve opening from the right ventricle to the pulmonary artery
What is the aortic semilunar valve?
the valve located between the left ventricle and the aorta
Where is the heart located?
in the thoracic cavity
What is the phragmdia?
it separates the abdominal cavity from the thoracic cavity
What is the pericardium?
a membranous sac that surrounds the heart and lubricates it to decrease friction
What is pericarditis?
inflammation of the pericardium in cows that swallow nails
What are the 3 layers of the heart wall?
- endocardium (inner)
- myocardium (middle)
- epicardium (outer)
What is the endocardium?
inner layer of the heart wall, composed of endothelial cells
What is the myocardium?
the middle layer of the heart wall, composed of cardiac muscle
What is the epicardium?
the outer layer of the heart wall, external membrane
Which ventricle is thicker and why?
the left as it pumps bloods to the longer systemic circuit
What are intercalated disks?
structures that connect cardiac muscle cells to each other
What do gap junctions do?
they cause the heart to contract as a unit
What are desmosomes?
tough connective tissue that resist stress in the heart muscles
What does the fibrous skeleton do? (x2)
separates atria and ventricles and anchors the heart valves
What does an aerobic muscle mean?
that it uses oxygen to generate ATP
What type of growth occurs after infancy?
hypertrophy (increase in cell size, not number)
What are the majority of cardiac muscles? And what is the other tiny bit?
majority: contractile
minority (1%): autorhythmic cells (self generate APs)
What cells set the rate of heart beat?
autorhythmic cells
What generates heart pumping action?
rhythmic contraction and relaxation
What pushes blood out of the heart and into the vasculature?
contractions
When does the heart fill with blood?
during relaxation
What is a heartbeat?
a wave of contraction through cardiac muscled
What is the flow of blood and what drives it?
atria to ventricles to arteries, driven by pressure difference
What opens valves?
they open passively due to the pressure gradient (no going backwards only forwards)
What do the papillary muscles and chordae tendinae do together?
they keep the AV valves from turning outwards
What are the semilunar valves?
aortic and pulmonary
What is autorhythmicity?
the hearts ability to generate its own rhythm
What are autorhythmic cells? and what are the 2 types?
set the rate of the heartbeat – pacemaker cells and conduction fibers
What are pacemaker cells?
spontaneously depolarizing membrane potentials to generate APs – coordinate and provide rhythm to the heartbeat (fastest cells) – never rest so their potential is called “pacemaker potential” rather than resting potential
What are conduction fibers
they rapidly conduct APs initiated by pacemaker cells to the myocardium (faster than regular muscle fibers)
What is the sinoatrial node?
the pacemaker of the the heart
What is the atrioventricular node?
a specialized mass of conducting cells located at the atrioventricular junction in the heart
What are internodal pathways?
specialized conductile cells within the atria that transmit the impulse from the SA node throughout the myocardial cells of the atrium and to the AV node
What is the bundle of His?
a conduction fiber of the myocardium, modified heart muscle that transmits the cardiac impulse from the atrioventricular node to the ventricles causing them to contract
What are bundle branches?
branches of the AV bundle that divide to the right and left sides of the interventricular septum
What are purkinje fibers?
fibers in the ventricles that transmit impulses to the right and left ventricles, causing them to contract
What links cardiac cells and why?
gap junctions, used for electrical coupling
What are intercalated disks?
junctions between adjacent myocardial cells (for electrical coupling)
What are the steps of the interatrial pathway?
from sinoatrial node - to right atrium - to left atrium (rapidly) causing simultaneous contraction of the right and left atria
What is the internodal pathway?
the spread of excitation from sinoatrial node to the atrioventricular node
What is the AV node transmission pathway?
the only pathway from atria to ventricles, slow conduction where atria contract before ventricles do
What is ventricular excitation?
the spread of excitation down the bundle of His, right and left bundle branches and up the purkinje fibers
What causes spontatnous depolarization/
closing of K channels and opening of If (funny) and Ca (t-type) channels (sodium is greater than potassium)
What are L type channels
fast calcium channels that generate an action potential in pacemaker cells by depolarizing it to the threshold
What is the resting membrane potential of a contractile (myocardial cell)
-90mv
What do cardiac cells and skeletal muscle have in common?
sarcoplasmic reticulum calcium, T tubules, troponin-tropomyosin regulation
What do cardiac cells and smooth muscle have in common?
extracelular calcium and gap junctions
How does cardiac muscle relaxation occur?
through the removal of calcium from the cytosol
What is calcium ATPase?
pumps for the removal of calcium in the sarcoplasmic reticulum and plasma membrane
What is the sodium-calcium exchanger?
pumps that remove calcium from the cytosol that are present in the plasma membrane
What do troponin and tropomyosin cover?
myosin binding sites
