Physiology Exam 2
Describe the arrangement of thick and thin filaments in a striated muscle sarcomere
in cross section, the thick filaments are arranged in a hexagonal lattice and the thin filaments occupy the centers of the triangles formed by the thick filaments.
Nerve gases
inhibit the acetylcholine esterase and cause ACh to build up at muscarinic synapses, where parasympathetic neurons inhibit cardiac pacemaker cells.
List the factors responsible for skeletal muscle fatigue.
Lack of Ca2+ and Na+ ions
Write the formula relating cardiac output, heart rate, and stroke volume; give normal values for an adult at resting.
- CO= HR x SV- An adult usually pumps 3-4 liters of blood per minute at rest- adult heart rate ranges from 60-100 beats per minute - stroke volume is the amount of blood pumped by each ventricle
What are the three factors influencing venous pressure?
- a decrease in cardiac output either due to decreased heart rate or stroke volume results in blood backed up in venous circulation, which increases CVP- an increase in total blood volume as occurs in renal failure increases venous pressure- venous constriction caused by sympathetic activation of veins decreases venous compliance
Name the two functions of arterioles.
- arterioles transport blood around the body - they are tiny branches of arteries that lead to capillaries - under control of sympathetic nervous system, and constrict and dilate to regulate blood flow- they transport blood from arteries to capillaries - main regulators of blood flow and pressure
Contrast AP in ventricular muscle cell with SA node APs.
- pacemaker potentials and APs at SA node1. Na+ enters2. Ca2+ enters (pace pot)3. Ca2+ enters (depol)4. K+ exits (repol)- ventricular muscle AP1. Na+ enters (depol)2. Trans K+ exit3. Ca2+ enters/K+ exits (plateau)4. K+ exits (repol)
Describe the effects of the sympathetic and parasympathetic nerves on heart rate. Which is dominant at rest or during exercise?
- parasympathetic are inhibitory on heart rate - sympathetic are stimulatory on heart rate and contractility (fight or flight) - At the beginning of exercise, your body releases the parasympathetic stimulation which allows your heart rate to increase- sympathetic is dominant during exercise, and parasympathetic is dominant at rest
What is the only autonomic innervation of most arterioles?
- sympathetic activation is most prominent in arterioles, since it constricts them and creates resistance vessels. this increases vascular resistance and decreases distal blood flow
Summarize the effects of the autonomic nerves on the heart.
- the medulla, which is in the brainstem above the spinal cord, is the site for autonomic nerve outflow
What are the major factors influencing the force of contraction?
- the size of muscle fibers affect strength of contraction - larger fibers contract more strongly because they contain more proteins- the number of motor units recruited affects the strength of muscle contraction - the length of time it has been contracting affects the strength of the contractions- later muscle contractions will be stronger than earlier ones because more calcium has been released
Describe the effects of the sympathetic nerves on cardiac muscle during contraction and relaxation.
- the sympathetic and parasympathetic nerves flow through the cardiac plexus at base of heart- sympathetic stimulation causes release of norepinephrine at NMJ of cardiac nerves, this shortens repol period, so speeds up rate of depol and contraction, which leads to inc in HR
What are the major sites of resistance in the systemic vascular system?
- the walls of veins are sites of resistance. when the smooth muscle constricts, and the lumen get rounded which decreases the surface area encountered by blood
What is the relationship between cardiac output and venous return in the steady state? What is the force driving venous return?
- venous return is the flow of blood back to the heart. under steady state conditions, venous return must equal cardiac output, when averaged over time the CV system is essentially a closed loop
Draw a ventricular muscle cell action potential (AP). Describe the changes in membrane permeability that underlies the potential changes.
1. voltage gated Na+ channels open2. Voltage gated Ca2+ channels open3. K+ channels open - heart possesses own pacemaker- during activity, systemic goes up
Draw a diagram of the pressure changes in the left atrium, left ventricle and aorta throughout the cardiac cycle. Show when the valves open and close, when the heart sounds occur, and the pattern of ventricular ejection.
- when chambers are relaxed (diastole), blood flows from veins and into atria, which are higher pressure - pressure rises as blood flows into atria so blood moves passively from atria to ventricles- when the muscles contract (systole) the pressure within atria rises further, pumping blood into ventricles - during ventricular systole, pressure rises in ventricles, pumping blood into pulmonary trunk from right ventricle and into aorta from left ventricle
Contrast diffusion and bulk flow. Which mechanism exchanges nutrients, oxygen, and metabolic end products across the capillary wall?
-Diffusion: net movement down a concentration gradient due to the random motion of individual molecules - Bulk Flow: movement of water and solutes together due to a pressure gradient - 2 mechanisms- fluid moves from higher pressure in cap bed to lower pressure in tissues via filtration, and movt of fluid from area of inc pressure in tissues to area of low pressure in caps is reabsorption
Draw and label a normal ECG. Relate the waves to the atrial and ventricular APs as well as the mechanical events (contraction, relaxation)
-P wave- represents depolarization, causes atrical contraction - QRS complex- represents ventricular depolarization, causes ventricular contraction - T-Wave- represents ventricular repolarization - With AV block, the p waves occur consistently, but the QRS is skipped - cardiologists use the different waves to see where the problems are
muscle cells locations
-Skeletal muscle is found between bones, and uses tendons to connect the epimysium to the periosteum -Cardiac muscle cells are located in the walls of the heart -Smooth muscle cells (myocytes) are found in the walls of hollow organs
What four variables determine the net filtration pressure across the capillary wall? Give representative values for each of them in the systemic capillaries.
-proteinuria- excessive protein in the urine, can alter net filtration pressure altering flow of fluid across the capillary wall - hydrostatic pressure- pressure generated by fluid on the walls of capillary, usually forcing water out of circulatory system- net filtration pressure- balance of four starling forces that determines net flow of fluid across capillary membrane - oncotic pressure- form of osmotic pressure exerted by proteins in a fluid that usually tends to pull water into circulatory system
Describe the conversion process of an electrical energy (action potential) to a chemical energy (neurotransmitter)?
A neuron becomes activated when there is a chemical signal that is transduced into an electrical response. When a neurotransmitter is emitted into the synaptic space and is picked up by a nearby neuron, this information needs to be converted into electrical energy (which produces an action potential): Signal transduction
Describe the source of calcium that leads to the increase in cytosolic calcium that triggers contraction in smooth muscle.
Ca2+ from ECFCa2+ from sarcoplasmic reticulum
Explain 4 major roles of ATP in muscle contraction.
ATP binds to myosin causing it to change position and attach to actin and pull, causing muscles to contract. Without ATP, muscles could not contract as one part of the muscle could not attach to the other.
Explain the effect of a pacemaker potential on a smooth muscle cell.
All cardiac muscle and some smooth muscle will contract without nerve input because these muscles contain pacemaker cells. The pacemaker cells fire APs simultaneously, and this stimulates the other cells, the contractile cells (that do not have pacemaker potentials), to contract
Describe the four steps of one cross-bridge cycle.
Binding:myosin cross bridge binds to actin molecule Power stroke:cross bridge bends, pulling thin filament inward Detachment:cross bridge detaches at end of power stroke and returns to original conformation Binding:cross bridge binds to more distal actin molecule, cycle repeats
Compare the mechanisms for muscle contractions between cardiac, skeletal and smooth muscles.
Cardiac and skeletal muscle are both striated in appearance, while smooth muscle is not. Both cardiac and smooth muscle are involuntary while skeletal muscle is voluntary. ... While skeletal muscles are arranged in regular, parallel bundles, cardiac muscleconnects at branching, irregular angles, called intercalated discs.
Contrast and compare the structure of cardiac muscle with that of skeletal and smooth muscle.
Cardiac and skeletal muscle are both striated in appearance, while smooth muscle is not. Both cardiacand smooth muscle are involuntary while skeletal muscle is voluntary. ... Cardiac muscle is also an involuntary muscle but is more akin in structure to skeletal muscle, and is found only in the heart.
Compare the mechanisms by which a rise in cytosolic calcium concentration initiates contractile activity in skeletal, smooth, and cardiac muscle cells.
Cardiac and skeletal muscle mechanisms are similar- dependent on tropioninSmooth muscle mechanism-dependent on calmodulin
Mean arterial pressure (MAP) = equation
Cardiac output (CO) x Total peripheral resistance (TPR)
Mean arterial pressure (MAP) equation
Diastolic + 1/3(Pulse pressure)
State the formula relating flow, pressure difference, and resistance, and explain the relationship between these three parameters.
F= change pressure/ resistance
Compare different types of skeletal muscle fibers.
Fast Twitch Muscle Fiber Types. The two types of skeletal muscle fibers are slow-twitch(type I) and fast-twitch (type II). Slow-twitch muscle fibers support long distance endurance activities like marathon running, while fast-twitch muscle fibers support quick, powerful movements such as sprinting or weightlifting.
explain the changes in width of band/filament during the muscle contraction.
For a muscle cell to contract, the sarcomere must shorten. However, thick and thin filaments—the components of sarcomeres—do not shorten. ... The A band stays the same width and, at full contraction, the thin filaments overlap. When a sarcomere shortens, some regions shorten whereas others stay the same length.
Draw a ventricular function curve illustrating the Frank-Starling mechanism.
Frank-Starling curves show how changes in ventricular preload lead to changes in stroke volume. This type of graphical representation, however, does not show how changes in venous return affect end-diastolic and end-systolic volumes.
List the fuel molecules that are metabolized to produce ATP during skeletal muscle activity.
Glycogen and creatine phosphate
What is the only solute that has significant concentration differences across the capillary wall? How does this difference influence water concentration?
Large plasma proteins (termed colloids) are present in relatively high concentration in the plasma and low concentration in the interstitial fluid. Since these proteins are essentially non-penetrating the water concentration in plasma is slightly less than that in interstitial fluid, inducing an osmotic flow of water from the interstitial compartment into the capillary.
Compare the neural control of smooth muscle activity with that of skeletal muscle.
Like skeletal muscle - striated appearance due to regularly repeating sarcomeres composed of myosin-containing thick filaments interdigitating with thin actin filaments; both include troponin and tropomyosin; T-tubule system and Ca2+ loaded sarcoplasmic reticulumLike smooth muscle - relatively small and generally contain single nucleus; slow action potentials; arranged in layers and surround hollow cavities; some exhibit pacemaker potentials that generate action potentials spontaneously
Write the formula relating flow through an organ to mean arterial pressure and to the resistance to flow that organ offers.
MAP = DP +1/3(SP-DP)
Describe the events that result in the relaxation of skeletal muscle fibers.
Once signal stops, opening of Ca2+ channel in the sarcoplasmic reticulum created by the ryanodine receptor, shuts down, Ca2+ pumps will reduce Ca2+ inside the muscle cell and muscle will relax
List the three types of muscle cells, the unique features for each
Skeletal Muscle 1. Multinucleate 2. Contain many mitochondria Cardiac Muscle 1. Glycogen that surrounds the nucleus 2. Intercalated discs between adjacent cells Smooth Muscle 1. Contains one nucleus per cell 2. Non-striated
List the types of stimuli that can trigger a rise in cytosolic calcium in smooth muscle cells.
Spontaneous electrical activity in plasma membrane of muscle cellNeurotransmitters released by autonomic neuronsHormonesLocally induced changes in chemical composition (paracrine factors, acidity, oxygen, osmolarity, and ion concentrations) of ECF surrounding the cell
Describe the sequential events by which an action potential in a motor neuron produces an action potential in the plasma membrane of a skeletal muscle fiber.
Stimulation of motor neurons initiate action potentialOnce action potential reaches the axon terminal the plasma membrane is depolarizedVoltage gates calcium channels are opened The release of calcium results in the release of Acetylcholine from vesicles in the axon terminal These vesicles are what binds to the receptors in the sarcolemma (membrane) The binding of the Ach with the receptors initiates end plate potential (depolarization of skeletal muscle fiber)This initiates action potential in muscle plasma membrane
Cardiac output (CO) equation
Stroke volume (SV) x Heart rate (HR)
List the structures through which blood passes from the systemic veins to the systemic arteries.
Systemic veins --> Vena cava --> Right atrium --> Right ventricle --> Pulmonary trunk and arteries --> Pulmonary capillaries of the lungs --> Pulmonary veins --> Left atrium --> Left ventricle --> Aorta --> Systemic arteries
Describe the spread of excitation from the SA node through the rest of the heart.
The initial depolarization normally arises in a small group of conducting-system cells called the sinoatrial node (SA). The action potential spreads throughout the myocardium, passing from cell to cell by way of gap junctions. It first spreads through the muscle cells of the atria, with both atria conducting at essentially at the same time. The link between atrial depolarization and ventricular depolarization is a portion of the conducting system called the atrioventricular node (AV), located at the base of the right atrium. The action potential is conducted rapidly from the SA node to the AV node through intermodal pathways. The propagation of action potentials through the AV node is relatively slow (requiring approximately .1 sec) allowing atrial contraction to occur before ventricular excitation occurs. The action potential then propagates down the interventicular septum. This pathway has a bundle of conducting fibers called the bundle of His that separates into right and left branches at the apex. The fibers in turn make contact with Purkinje fibers, large diameter conducting cells that rapidly distribute the impulse throughout the ventricles.
Compare the organization of thick and thin filaments in smooth muscle fibers versus in striated muscle fibers.
There is no regular allignment of actin and myosin filaments into the sarcomere and they are not organized into myofibrils
What are the two main functions of the arteries?
They carry oxygenated blood away from the heart and to the tissues (The aorta is connected to the left ventricle of the heart) - The pulmonary artery differs in that it is connected to the right ventricle and carries oxygen poor blood to the lungs, it then branches to arterioles and capillaries so the blood can take on oxygen before returning to the heart
Describe how a stimulus may lead to the contraction of a smooth muscle cell without a change in the plasma membrane potential.
This occurs because each muscle fiber is linked to adjacent fibers by gap junctions, through which action potentials occurring in one cell are propagated to other cells by local currents.
Describe the location, structure, and function of the sarcoplasmic reticulum (SR) in skeletal muscle fibers
This organelle is composed of two parts: The longitudinal tubules and the lateral sacs. This organelle is specialized to store Ca2+, which are critically important in the process of muscle contraction.The sarcoplasmic reticulum is homologous to the endoplasmic reticulum found in most cells. This structure forms a series of sleevelike segments around each myofibril. At the end of each segment there are two enlarged regions, known as terminal cisternae that are connected to each other by a series of smaller tubular elements.
Explain the effect of frequency of action potentials on the force of contraction in a skeletal muscle fiber.
an increase in action potential frequency increases the force of contraction of a skeletal muscle fiber
curare
deadly arrowhead poison used by indigenous peoples of south america. It binds strongly to nicotinic ACh receptors, it doesn't open their ion channels however, and acetylcholinesterase doesn't destroy it. When a receptor is occupied by curare, ACh cannot bind to the receptor. Therefore although the motor nerves still conduct normal action potentials and release ACh, there is no resulting EPP in the motor end plate and no contraction, curare poisoning can cause death by asphyxiation.
botulinum
inhibitor of neuromuscular signaling used in cosmetic procedures, the toxin is produced by the bacterium clostridium botulinum, it blocks the release of acetylcholine from nerve terminals. It is an enzyme that breaks down proteins of the SNARE complex that are required for the binding and fusion of ACh vesicles with the plasma membrane of the axon terminal. It produces the food poisoning called botulism, and is one of the most potent poisons known because of the very small amount needed to produce an effect. Application is increasingly being used for clinical/cosmetic procedures, including the inhibition of overactive extraocular muscles, prevention of excessive sweat gland activity, treatment of migraine headaches, and reduction of aging-related skin wrinkles.
Describe the cardiovascular response to the acute hemorrhage.
is biphasic, comprising an early tachycardia while blood pressure is maintained followed by a reflex bradycardia and hypotension. Injury, by contrast, leads to a tachycardia and increased blood pressure. Furthermore, injury modifies the cardiovascular response to hemorrhage.
Describe the physical state of a muscle fiber in rigor mortis and the condition that produces this state.
the gradual stiffening of skeletal muscles that begins several hours after death and reaches a maximum after about 12 hours
Describe the Length-Tension relationship in the isometric contraction in skeletal muscle fibers.
the length-tension relationship states that isometric tensiongeneration in skeletal muscle is a function of the magnitude of overlap between actin and myosin filaments. ... Experimentally, a muscle is allowed to shorten against a constant load.
When the arterial baroreceptors decrease or increase their rate of firing, what changes in autonomic outflow and cardiovascular function occur?
they are responding to a decrease in arterial pressure. The medullary cardiovascular center stimulates increased sympathetic activity to the heart, arterioles, and veins, and decreases parasympathetic activity to the heart.
