Function of the muscular system
Movement
Muscles are classified into 3 groups based on
Characteristics and function
Smooth, cardiac, skeletal
Term for a single cell
Muscle fiber
Skeletal muscle
Moving muscle
Smooth muscle
Moving components, usually within a tube
Controlled by brain
Cardiac muscle
Pumping blood
Thick filaments are made up of
Myosin
Polypeptide chains form
Two globular heads and a tail
Crossbridge
Area that exerts force on the thin filament
Heads contain
ATP binding sites and actin binding sites
Thin filaments are made up of
Actin and troponin and tropomyosin
Thin filaments have an important role in
Regulating contractions
Tropomyosin
Overlaps binding sites blocking cross bridges
Troponin
Ca2+ binding to troponin regulates skeletal muscle contraction
Moves tropomyosin away and allows myosin to interact with the actin
Excitation-contraction coupling occurs
At axon terminal of neuron
Motor end plate is
ESPS on muscle fiber
Ca2+ enables…
ACh to be released across the space between axon terminal and motor end plate
ACh binds to
Nicotininc ACh (muscle fibers) receptors
Nervous system stimulates
Muscle fibers
Action potential in muscle fibers
Contract
Action potential starts in
Muscle cell
T-tubule voltage gated calcium channel
Open when membrane is depolarized
Relaxation occurs as
Ca2+ is pumped into Sarcoplasmic reticulum when an action potential stops
Cross bridge cycle is initiated when
Excitation contraction coupling increases Ca2+ and binding sites on actin are exposed
Each cross bridge goes through its cycle ____ of other cycles
Independently
Step 1 in cross bridge cycle
The active site on actin is exposed as Ca2+ binds to troponin
Step 2 in cross bridge cycle
Myosin head forms a cross bridge with actin
Step 3 in cross bridge cycle
During the power stroke, myosin head bends and adp and phosphate is released
Step 4 in cross bridge cycle
A new molecule of atp attaches to the myosin head causing the cross bridge to detach
Step 5 in cross bridge cycle
ATP hydrolyzes to adp and phosphate, which returns the myosin to the cocked position
The myosin head serves as a….
Myosin ATPase enzyme
What is happening in step one and two of the cross bridge cycle
Energy present excitement, ca2+ concentration needs to increase and bind troponin and tropomyosin to move to bind myosin and actin
Release of phosphate upon binding creases a change on myosin head to produce a
Power stroke
What is happening in step three and four of cross bridge cycle
Binding actin and myosin creates a release of phosphate
After the power stroke….
Adp is released and a new atp binds, to make myosin release actin
What is happening in step five and six of cross bridge cycle
“Resetting”
Filaments do not change length but they….
Slide
Smooth muscle
Undergo changes in volume with accompanying changes in lengths of the smooth muscle fibers
Examples of smooth muscle
Stomach, intestine, blood vessels
Smooth muscle cells have a ___ nucleus
Single
Nerves are part of the ____ division instead of somatic
Autonomic
In smooth muscle….
Thick and thin filaments are not organized into myofibrils
In smooth muscles, calcium binds to….
Calmodulin
Pacemaker cells
Action potential spontaneously in absence of neuronal or hormonal input
Depolarization opens
Voltage gated ca2+ channels
Prolonged stimulation holding ca2+ concentrations is called
Latch state
Latch state
Muscles hold tension for long periods
Ex. Sphincter muscles of GI tract
Two sources of Ca2+ that contribute to the rise of cytosol in ca2+ in smooth muscle
Sarcoplasmic reticulum
Extracellular ca2+ enters the cell through plasma membrane
To relax….
Ca2+ has to be removed using Ca-ATPase pump
Cellular structure of cardiac muscle
Striated using sliding filament mechanism
Arranged like smooth muscle
Myocardium
Contracts fully every time its stimulated
Cells are linked by
Gap junctions
Gap junctions
Spread currents quickly
Autonomic nervous system hormones and neurotransmitters modulate
Amount of ca2+ released
Heart cannot exhibit
Summation and tetanus due to refractory period and fulling heart
Three main functions of the cardiovascular system
Transportation, circulation, protection
Transportation
O2 and co2, products of digestion, waste
Regulation
Hormones, temperature (cycling blood through deep to surface vessels)
Protection
Clotting and immune system
Cells of cardio
Myocardial cells, node (pacemaker) cells, erythrocytes, endothelial cells
Circulatory system is impacted by which systems
Endocrine, nervous, respiratory, Kidneys
Arteries
Away
Veins
In
Systemic
Arteries carry oxygenated blood and veins carry deoxygenated blood
Pulmonary
Carry deoxygenated blood to the lungs and the pulmonary veins vary oxygenated blood to the heart
Atari empty into _____
Ventricles
Atrioventricular valve (AV)
Permits blood flow from atrium to ventricles but not backwards
Left AV/mitral
Bicuspid
Right AV
Tricuspid
Pulmonary valve
Right ventricle to pulmonary trunk
Aortic valve
Left ventricle to aorta
Conducting system
Special cells in electrical contact with cardiac muscle cells via gap junction
Conducting system functions
Initiated heartbeat and spreads action potential
Signal starts in the
SA node
SA node is located in
Right atrium
Discharge rate of the SA node determines
Heart rate
Action potential jumps from cell to cell via
Gap junctions
Action potential passage through AV node is
Slow
After AV node is excited…
Action potential moves down the septum to the bundle of His
AV node and bundle of his
Separates atrial and ventricular contraction
Purkinji fibers
Spread the potential quickly throughout the ventricles causing them to depolarize together
Slow predictable depolarization is called
Pacemaker potential
K+ channels
Gradually closing from previous action potential
HCN channels
Open in response to hyperpolarization and Na+ enters causing spontaneous depolarization
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