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Study Guide 4: Chapters 12, 13, 14 & 15 Flashcards
Skeletal Muscles
Responsible for voluntary movements and body posture.
Attached to bones via tendons (connective tissue).
Composed of muscle fibers (cells) which are elongated and cylindrical.
Exhibit striations due to the arrangement of actin and myosin filaments.
Transverse Tubules (T-Tubules)
Invaginations of the sarcolemma (muscle cell membrane).
Transmit action potentials deep into the muscle fiber, ensuring rapid and uniform contraction.
Ensures coordinated muscle contraction by allowing simultaneous activation of all parts of the muscle fiber.
Sarcomere
The basic functional unit of a muscle fiber; responsible for muscle contraction.
Located between two Z discs (Z lines), which define its boundaries.
Contains:
A band: Contains both actin and myosin filaments. It is the dark region of the sarcomere. Its length remains constant during contraction, representing the length of the myosin filaments.
I band: Contains only actin filaments. It is the light region of the sarcomere. This band narrows during contraction as the actin filaments slide over the myosin filaments.
H zone: Contains only myosin filaments. This zone narrows during contraction as the actin filaments slide toward the center of the sarcomere.
M line: The midline of the sarcomere to which myosin filaments are anchored. It helps maintain the alignment of myosin filaments.
Z disc: The boundary of each sarcomere, serving as an anchor for actin filaments.
Latent Period
The time between the arrival of the stimulus (action potential) and the start of muscle contraction.
Involves excitation-contraction coupling, including the release of calcium ions (Ca^{2+}) and binding to troponin.
Motor Units
A motor neuron and all the muscle fibers it innervates; the functional unit of motor control.
Smaller motor units (fewer muscle fibers per neuron) allow for fine motor control, such as in the fingers and eyes.
Larger motor units (more muscle fibers per neuron) are found in muscles responsible for gross motor movements, such as in the legs.
Effectors in a Reflex
The muscles or glands that carry out the response in a reflex arc, producing a specific action.
The effector's response helps to maintain homeostasis or protect the body from harm.
Reflex Arc and Integration Centers
Reflex arc: The neural pathway involved in a reflex action; typically includes a sensory receptor, sensory neuron, integration center, motor neuron, and effector.
Components: sensory receptor (responds to stimulus), sensory neuron (transmits afferent impulses to the CNS), integration center (processes information), motor neuron (transmits efferent impulses from the CNS), effector (muscle or gland that responds).
Integration centers: Sites within the CNS (spinal cord or brain) where sensory information is processed and motor commands are generated. These centers determine the appropriate response to a stimulus.
Crossed Extensor Reflex
A contralateral reflex that occurs in conjunction with the flexor (withdrawal) reflex.
Involves a flexor reflex on one side (e.g., stepping on a tack) and an extensor reflex on the opposite side to maintain balance.
Maintains balance during withdrawal reflexes by shifting weight and preventing falls.
Intercalated Discs
Specialized junctions between cardiac muscle cells, facilitating coordinated contraction.
Contain:
Gap junctions: Allow for rapid spread of electrical signals (ions) between cells, enabling synchronized contraction.
Desmosomes: Provide strong adhesion between cells, preventing separation during contraction.
End-Diastolic Volume (EDV)
The volume of blood in the ventricle at the end of diastole (filling); represents the maximum amount of blood the ventricle will contain during that cycle.
EDV is a critical factor affecting stroke volume and cardiac output.
Cardiac Output (CO)
The amount of blood pumped by each ventricle per minute; a key indicator of cardiac performance.
CO = Stroke : Volume (SV) x Heart : Rate (HR)
Factors affecting CO include heart rate, contractility, preload (EDV), and afterload (resistance).
Starling's Law of the Heart
The greater the EDV (preload), the greater the force of contraction, and the greater the stroke volume.
Due to increased stretch of cardiac muscle fibers, leading to increased sensitivity to Ca^{2+} (calcium ions), which enhances cross-bridge formation and force generation.
Metarterioles
Small blood vessels that link arterioles and capillaries, playing a crucial role in regulating blood flow to tissues.
Contain precapillary sphincters (rings of smooth muscle) that regulate blood flow into capillaries based on tissue needs.
Angiogenesis
The formation of new blood vessels from pre-existing ones; a complex process involving endothelial cell proliferation and migration.
Important in development, wound healing, and tumor growth, providing oxygen and nutrients to tissues.
Mean Arterial Pressure (MAP)
The average arterial pressure throughout one cardiac cycle; represents the driving force for blood flow to organs.
MAP = Diastolic : Pressure + RAC{1}{3}(Pulse : Pressure)
Maintained through a balance of cardiac output and systemic vascular resistance.
Pulse Pressure
The difference between systolic and diastolic pressure; reflects the elasticity and compliance of arteries.
Pulse : Pressure = Systolic : Pressure - Diastolic : Pressure
Increased pulse pressure may indicate arterial stiffness, while decreased pulse pressure may indicate heart failure.
Osmotic, Oncotic, Colloid Pressure
Osmotic pressure: Pressure exerted by solutes in a solution, pulling water into the solution; determined by the concentration of solutes.
Oncotic pressure: Osmotic pressure specifically due to proteins (e.g., albumin) in the blood; a major determinant of fluid balance between blood and tissues.
Favors movement of fluid into the capillary due to the presence of plasma proteins that cannot easily cross the capillary membrane.
Also known as colloid osmotic pressure.
Baroreceptors (Cardiac Reflexes)
Pressure-sensitive receptors located in the aortic arch and carotid sinuses; play a critical role in short-term blood pressure regulation.
Detect changes in blood pressure and trigger reflexes to maintain blood pressure homeostasis by adjusting heart rate and vascular resistance.
Cardiac reflexes: Baroreceptors initiate cardiac reflexes via the autonomic nervous system to manage blood pressure through heart rate and contractility adjustments.
Excitation-Contraction Coupling
The sequence of events linking the action potential in the muscle fiber membrane to muscle contraction, ensuring coordinated muscle activation.
Action potential arrives at the axon terminal of motor neuron
Voltage-gated Ca^{2+} channels open and Ca^{2+} enters the axon terminal moving down its electrochemical gradient
Ca^{2+} entry causes ACh (a neurotransmitter) to be released by exocytosis
ACh diffuses across the synaptic cleft and binds to ACh receptors on the sarcolemma
ACh binding opens chemically (ligand) gated ion channels that allow simultaneous passage of Na^{+} into the muscle fiber and K^{+} out of the muscle fiber. More Na^{+} ions enter than K^{+} ions exit which produces a local change in the membrane potential called the end plate potential
ACh effects are terminated by its breakdown in the synaptic cleft by acetylcholinesterase and diffusion away from the junction
End plate potential (local depolarization) ignites an action potential in the sarcolemma
Action potential propagates along the sarcolemma and down the T tubules
The action potential opens voltage-sensitive proteins which are mechanically linked to Ca^{2+} channels in the SR. Ca^{2+} release channels in the SR open and Ca^{2+} floods into the cytosol
Ca^{2+} binds to troponin removing the blocking action of tropomyosin. When Ca^{2+} levels are high enough, the blocking action is removed and the myosin-binding sites on actin are exposed.
Myosin heads bind to actin forming cross bridges. Contraction begins (Sliding filament theory)
When the action potential ends, voltage-sensitive tubule proteins return to their original shape closing the Ca^{2+} release channels in the SR.Ca^{2+} levels in the sarcoplasm fall as Ca^{2+} is actively transported back into the SR
Tropomyosin blockage restored, blocking myosin-binding sites on actin. Myosin-actin interaction is prevented, and relaxation occurs.
Sliding Filament Theory (Contraction Cycle)
The mechanism of muscle contraction based on the sliding of actin and myosin filaments past each other, leading to sarcomere shortening and muscle contraction.
Crossbridge Formation: Myosin head attaches to the actin filament forming a crossbridge, initiating the contraction cycle.
The Power (working) Stroke: The myosin head pivots and bends, pulling the actin filament toward the M line, shortening the sarcomere.
Crossbridge detachment: ATP attaches to myosin. The link between myosin and actin weakens, and the myosin head detaches (the cross bridge breaks), allowing the cycle to repeat.
Cocking of the myosin head: As myosin hydrolyzes ATP to ADP and Pi, the myosin head returns to its prestroke high-energy, or "cocked" position, ready to form another crossbridge.
Muscle Fatigue (Causes)
A decline in muscle force production due to prolonged activity; multifactorial, involving both peripheral and central mechanisms.
Causes:
ATP depletion: Insufficient ATP to power muscle contraction and relaxation, leading to impaired cross-bridge cycling.
Lactic acid accumulation: Decreases muscle pH, affecting enzyme activity and impairing muscle function.
Electrolyte imbalances: Disrupts muscle cell membrane potential, affecting muscle excitability and contraction.
Central fatigue: Psychological factors affecting motivation and perception of effort, reducing voluntary muscle activation.
Isotonic vs Isometric Muscle Contraction
Isotonic contraction: Muscle changes in length while tension remains constant; involves movement and work.
Concentric: Muscle shortens, overcoming resistance (e.g., lifting a weight).
Eccentric: Muscle lengthens, resisting the force of gravity (e.g., lowering a weight).
Isometric contraction: Muscle length remains constant while tension increases; involves no movement, but still requires energy.
Example: pushing against a wall; muscle generates force but does not change length.
Differences Between Three Types of Muscles
Skeletal muscle: Striated, voluntary, multinucleated, responsible for movement and posture.
Smooth muscle: Non-striated, involuntary, uninucleated, found in the walls of internal organs and blood vessels, responsible for regulating internal processes.
Cardiac muscle: Striated, involuntary, uninucleated, intercalated discs, found only in the heart, responsible for pumping blood.
Refer to muscle type table in textbook for a detailed comparison of structure, function, and control.
Autonomic Reflexes vs Somatic Reflexes
Autonomic reflexes: Involve smooth muscle, cardiac muscle, or glands; regulate involuntary functions.
Regulate functions like blood pressure, digestion, and heart rate; controlled by the autonomic nervous system.
Somatic reflexes: Involve skeletal muscles; control voluntary movements and posture.
Mediated by the somatic nervous system, allowing conscious control over muscle actions.
Relationship Between Blood Volume, Blood Vessel Diameter, Blood Flow, and Blood Pressure
Blood volume: Increased blood volume leads to increased blood pressure, provided other factors remain constant; influenced by fluid intake and loss.
Blood vessel diameter: Vasoconstriction (decreased diameter) increases blood pressure and decreases blood flow; controlled by smooth muscle in vessel walls.
Vasodilation (increased diameter) decreases blood pressure and increases blood flow; regulated by local and systemic factors.
Blood flow: Directly proportional to the pressure gradient and inversely proportional to resistance; critical for tissue perfusion and oxygen delivery.
Blood : Flow = RAC{Pressure : Gradient}{Resistance}
Resistance is affected mostly by the blood vessel diameter, with smaller diameters increasing resistance and reducing flow.
Three Waves of ECG
P wave: Atrial depolarization, representing the electrical activity associated with atrial contraction.
QRS complex: Ventricular depolarization (and atrial repolarization), indicating the spread of electrical activity through the ventricles.
T wave: Ventricular repolarization, reflecting the return of the ventricles to their resting electrical state.
Heart Sounds
S1 (lub): Closure of the AV valves (tricuspid and mitral) at the beginning of ventricular systole; indicates the start of ventricular contraction.
S2 (dub): Closure of the semilunar valves (aortic and pulmonic) at the beginning of ventricular diastole; indicates the end of ventricular contraction and the start of ventricular filling.
Events at Isovolumic Contraction (Ventricular Systole)
Ventricles begin to contract, increasing pressure inside the ventricles.
All heart valves are closed, preventing blood flow into or out of the ventricles.
Ventricular pressure increases rapidly, but volume remains constant as the ventricles generate force.
Phases of the Cardiac Cycle
Ventricular filling: AV valves are open, blood flows passively from the atria into the ventricles; occurs during diastole.
Isovolumetric contraction: Ventricles contract, increasing pressure, but all valves are closed, so there is no change in volume.
Ventricular ejection: Semilunar valves open, blood is ejected into the aorta and pulmonary artery; occurs during systole.
Isovolumetric relaxation: Ventricles relax, decreasing pressure, but all valves are closed, so there is no change in volume.
Local Vasodilators and Vasoconstrictors
Refer to textbook figure for a comprehensive list of substances that regulate blood vessel diameter locally.
Vasodilators: substances that cause blood vessel dilation (e.g., nitric oxide, adenosine), increasing blood flow to tissues.
Vasoconstrictors: substances that cause blood vessel constriction (e.g., endothelin, angiotensin II), decreasing blood flow to tissues.
How to Calculate MAP
Mean Arterial Pressure (MAP) is calculated using diastolic and pulse pressures.
MAP = Diastolic : Pressure + RAC{1}{3}(Pulse : Pressure)
Where Pulse : Pressure = Systolic : Pressure - Diastolic : Pressure
Active vs Reactive Hyperemia
Active hyperemia: Increased blood flow to a tissue due to increased metabolic activity; a normal physiological response to increased demand.