Biology Question

1. Develop a table which compares cardiac, skeletal and smooth muscle.
Page 408
2. Explain the sliding filament theory of contraction.
Page 382 – Fig 12.5
The sliding filament theory of contraction describes how a muscle contracts and how it
creates force with no movement. When the muscle is relaxed, the sarcomere naturally has the
actin and myosin slightly overlapping each other. The I band consists of only the length of actin
while the A band is the length of the myosin. When the muscle contracts, the Z disks, which are
proteins that hold the actin together, move closer creating a shorter sarcomere. Also, when in
contraction, the sarcomere’s I band, length of actin, and H zone, length of myosin, both shorten.
This describes one part of the sliding filament theory of contraction considering actin and
myosin in sarcomeres slide past each other in contraction, The second part of the theory is that
force can be created without creating movement. For example, when pushing on a wall, tension
is being created in the muscles, yet you are not moving the wall. This is different from lifting
weights, whereas you are moving the object that helps create contraction. Overall, tension
generated is directly affected by the overlapping of actin and myosin in the sarcomeres.
3. Explain the Frank-Starling law of the heart.
Page 466
It all started off with the relationship between stretch and force in the intact heart. When
talking about stretch, it refers to end-diastolic volume. This tells us the volume of blood in the
ventricle when ventricular relaxation occurs. The end-diastolic volume is determined by venous
return, which is the amount of blood that enters the heart from the venous circulation. This
measurement then determines sarcomere length. Then force is indicated by stroke volume.
Stroke volume is the amount of blood being pumped by a ventricle during contraction. Stroke
volume can be found by subtracting volume of blood before contraction by volume of blood after
contraction. This law states that as stroke volume increases, so will the end-diastolic volume.
This means that as more blood enters the heart, the heart will contract more forcefully and eject
more blood. In other words, the heart pumps all the blood that returns to it. This is important
because it shows how both the left and right ventricle maintain an output equality.
4. Describe the conductions of electrical signals through the heart.
Page 452
The main components of the cardiac conduction system are the sinoatrial (SA) node,
atrioventricular (AV) node, atrioventricular (AV) bundle, bundle branches, and Purkinje fibers.
Depolarization begins at the SA node. The SA node is autorhythmic cells in the right atrium that
serves as the main pacemaker of the heart. The depolarization wave then goes to the AV node
through the internodal pathway. The AV node is a group of autorhythmic cells near the floor of
the right atrium. As depolarization moves through the AV node, it then reaches the ventricles.
Purkinje fibers are cells that are responsible for transmitting the electrical signals rapidly down
the AV bundle. The AV bundle divides into right and left bundle branches which then the bundle
branches of fiber continue downward towards the apex of the heart where they divide into
smaller Purkinje fibers that spread out among the contractile cells.
5. Describe the parts of the electrocardiogram (ECG) and explain how these electrical events
are related to the mechanical events of the cardiac cycle.
Page 457 & 460
Electrocardiograms are recordings that show a summary of all electrical activity
generated by all cells within the heart. An electrocardiogram is divided into parts called waves,
segments, and intervals. What reflects atrial depolarization on an ECG is called the P wave and
is always the first wave. What connects the P wave to the beginning of the QRS wave is called
the P-R segment. The P-R segment is when the electrical signal is being slowed down as it
passes through the AV node and AV bundle.The next wave to appear is called the QRS
complex. This wave represents the ventricular depolarization. Yet in the R wave, atrial
repolarization occurs. After the R wave, the S wave then connects to the T wave by what is
called the S-T segment. In this segment, the ventricles contract. The final wave would be the T
wave. The last wave is the repolarization of the ventricle. One connection between electrical
events and mechanical events of the cardiac cycle is that both display how contraction and
relaxation is presented. In electrical events, contraction and relaxation is presented through
sodium-potassium pumps, while the mechanical events show it by blood volume.
6. Discuss the role of the Na+K+ pump in maintaining the membrane potential of a cell.
Na+K+ plays a huge role in maintaining the membrane potential in the cell. Specifically it
helps maintain equilibrium in the electrochemical gradient. Since the membrane is permeable,
there is a good chance that there is leakage. Not only is the Na+K+ pump essential for
membrane potential, but it still manages to maintain equilibrium when there are leaks. Basically,
to maintain equilibrium 2 K+ will be transported in while 3 Na+ will be pumped out with the help
of ATP. The reason why it’s able to do this is because of its antiport active transport.
7. Compare the terms depolarization, hyperpolarization and repolarization.
Depolarization, hyperpolarization, and repolarization are all involved in action potentials,
yet all have different roles. Depolarization is part of Phase 0 of action potentials. Depolarization
is when a cell’s membrane potential goes through electrical charge shift which results in a less
negative charge inside the cell. Depolarization occurs when voltage-gates Na2+ channels open
and lets Na2+ to enter the cell. Repolarization is when the cell’s membrane potential
experiences a decrease in electrical charge since a large amount of K+ is flowing out of the cell.
This occurs after depolarization. Phase 1 and phase 3 both involve repolarization. In pHase 1,
K+ leaving the cell allows for repolarization. Phase 3 consists of K+ permeability to increase as
Ca2+ channels close. After repolarization is hyperpolarization. Hyperpolarization is when the
cell’s membrane potential decreases even more into the negatives as compared to its original
voltage in the beginning of the resting potential. Hyperpolarization prevents action potentials
from occuring by increasing the stimulus required to move the membrane potential to the action
potential threshold.
8. Compare graded and action potentials.
Page 237 – Table 8.3
Both graded and action potentials are voltage changes across a membrane. Graded
potentials are variable-strengthened signals that travel short distances. They are mainly used
for short-distance communication. Graded potentials are usually found in the dendrites or the
cell body. The strength of the signal depends on the initial stimulus and can be summed. For
example, a large stimulus causes a strong graded potential. Yet, in order to obtain a signal, the
entry of ions, such as Na+, K+, or Ca2+, through gated channels is required for initiation. If the
graded potential is strong enough, it reaches the trigger zone that allows action potential to then
occur. Unlike graded potentials, action potentials travel long distances without losing strength.
Action potentials are referred to “all-or-nothing” because it has to reach maximum depolarization
or else nothing happens. The conduction of an action potential is often described as a domino
effect, where an electrical current travels in the direction of conduction.
9. Discuss the role of Na+ and K+ channels in generating an action potential.
Page 240
Without the sodium-potassium pump, conduction of action potentials will not be possible.
These channels are only able to open once the membrane depolarizes to the threshold. Once
depolarization occurs, Na+ and K+ channels can now open. Since Na+ channels are open, Na+
rapidly enters the cell to depolarize it. As the membrane potential’s charge starts increasing, the
Na+ channels will slowly begin to close as K+ channels start to open, but they are slow. K+ is
slowly pumped out of the cell to the extracellular fluid. As K+ channels remain open, K+ leaks
out of the cell which results in hyperpolarizing. This means that the voltage will become more
negative than it was in the resting potential phase. As time goes by, K+ channels close and less
K+ leaks occur, the cell is then able to return to resting membrane potential. Without the gain
and loss of Na+ and K+ at certain times, action potential would not even occur and would only
be in a resting potential phase. The sodium-potassium pump allows for depolarization,
hyperpolarization, and repolarization to occur, which overall conducts action potential.
10. Compare nicotinic, cholinergic, muscarinic, and adrenergic receptors.
Page 252
Cholinergic, nicotinic, muscarinic, and adrenergic are all receptors that respond to
certain neurotransmitters. Cholinergic, nicotinic, and muscarinic are receptors that respond to
acetylcholine neurotransmitters. Cholinergic are neurons that secrete acetylcholine and
receptors that bind to acetylcholine. Cholinergic receptors actually have two subtypes; nicotinic
and muscarinic. Although they share the same neurotransmitters, does not mean that they are
exact. Nicotinic is an ion channel receptor, meaning that it allows ions such as sodium and
potassium to pass through membranes. Nicotinic receptor locations are mainly found in the
central nervous system, skeleton muscles, and autonomic neurons. Muscarinic, on the other
hand, is a G protein-coupled receptor (GPCR). Muscarinic receptor locations can be found on
smooth and cardiac muscle, central nervous system, and endo/exocrine glands. Then there is
adrenergic. Just like muscarinic, it is also a G protein-coupled receptor. Adrenergic receptors
are targets of catecholamines such as norepinephrine and epinephrine. Again, adrenergic
shares the characteristic of receptor locations as muscarinic receptors, like smooth and cardiac
muscle and central nervous system. Its other receptor location are glands. Overall, all are found
within the bilayer of a phospholipid.

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