physio exam 3 AI generated - test 2

What are the three types of muscle tissue?

Skeletal muscle (voluntary, attached to bones), cardiac muscle (heart, involuntary, striated), and smooth muscle (involuntary, non-striated, found in organs).

What is a muscle fiber?

A single muscle cell that contains many myofibrils and is specialized for contraction.

What are myofibrils composed of?

Repeating units called sarcomeres, which contain contractile proteins.

What is a sarcomere?

The basic contractile unit of muscle, made of thick (myosin) and thin (actin) filaments, separated by Z lines.

What is the function of the sarcoplasmic reticulum?

A specialized smooth ER that stores and releases Ca²⁺ for muscle contraction.

What are terminal cisternae?

Enlarged regions of the sarcoplasmic reticulum that store large amounts of Ca²⁺ near T-tubules.

What are T-tubules?

Invaginations of the muscle cell membrane that help transmit action potentials deep into the muscle fiber.

What is a motor unit?

A motor neuron and all the muscle fibers it innervates.

How is muscle contraction strength regulated?

By increasing firing frequency of motor neurons and recruiting more motor units.

What is the neuromuscular junction (NMJ)?

The synapse between a motor neuron and a muscle fiber where signals are transmitted.

What neurotransmitter is released at the NMJ?

Acetylcholine (ACh), which initiates muscle contraction.

How does ACh cause muscle depolarization?

It binds nicotinic receptors, opening ligand-gated Na⁺ channels, allowing Na⁺ influx.

How is the ACh signal terminated?

By acetylcholinesterase, which breaks down ACh in the synapse.

What is excitation-contraction coupling?

The process linking an action potential to muscle contraction via Ca²⁺ release.

How does Ca²⁺ trigger contraction?

Ca²⁺ binds to troponin, causing tropomyosin to move and expose myosin-binding sites on actin.

What is the cross-bridge cycle?

The process where myosin binds actin, performs a power stroke, and detaches using ATP.

What role does ATP play in contraction?

ATP is required for myosin detachment, re-cocking, and powering Ca²⁺ pumps.

What happens if ATP is depleted?

Myosin cannot detach from actin, causing rigor mortis (permanent contraction).

What is muscle relaxation?

The process of reducing cytosolic Ca²⁺ by pumping it back into the sarcoplasmic reticulum.

Why is there a latent period in contraction?

Time is needed for Ca²⁺ release, binding to troponin, and initiation of cross-bridge cycling.

What is a muscle twitch?

The mechanical response of a muscle fiber to a single action potential.

What are the three phases of a twitch?

Latent period (delay), contraction phase (tension increases), and relaxation phase (tension decreases).

What is isotonic contraction?

A contraction where muscle length changes while producing tension.

What is concentric contraction?

Muscle shortens as it generates force (e.g., lifting a weight).

What is eccentric contraction?

Muscle lengthens while under tension (e.g., lowering a weight).

What is isometric contraction?

Muscle produces tension without changing length.

What determines whether a muscle shortens?

Cross-bridge force must exceed the opposing load.

What is the length-tension relationship?

The force a muscle generates depends on initial sarcomere length and filament overlap.

What is titin?

A protein that provides passive elasticity and helps return muscle to resting length.

What are the three main ways muscle produces ATP?

Glycolysis (fast, low yield), oxidative phosphorylation (slow, high yield), and creatine phosphate (fastest).

What is glycolysis in muscle?

A fast, anaerobic process that produces small amounts of ATP and lactic acid.

What is oxidative phosphorylation?

A slower, oxygen-dependent process that produces large amounts of ATP.

What is the creatine phosphate system?

A rapid system that regenerates ATP by transferring a phosphate to ADP.

What is muscle fatigue?

A decrease in muscle’s ability to generate force after repeated activity.

What causes muscle fatigue?

Ion imbalances, lactic acid buildup, ATP depletion, and impaired Ca²⁺ handling.

What is conduction failure?

Failure of action potentials to propagate along T-tubules due to ion buildup.

How does lactic acid affect muscle?

It lowers pH, impairing enzyme function and Ca²⁺ handling.

What are slow oxidative fibers?

Type I fibers that are fatigue-resistant and rely on aerobic metabolism.

What are fast glycolytic fibers?

Type IIb fibers that fatigue quickly and rely on anaerobic metabolism.

What is motor unit recruitment order?

Slow fibers are recruited first, then intermediate, then fast fibers for stronger contractions.

What is myasthenia gravis?

An autoimmune disease where antibodies destroy ACh receptors, impairing muscle contraction.

How is myasthenia gravis treated?

With acetylcholinesterase inhibitors and immunosuppressants.

What is smooth muscle structure?

Spindle-shaped cells with a single nucleus and no sarcomeres.

How does smooth muscle contract?

Ca²⁺ binds calmodulin, activating MLCK, which phosphorylates myosin.

How is smooth muscle relaxation achieved?

By myosin light chain phosphatase removing phosphate from myosin.

What makes smooth muscle unique?

It can contract spontaneously, respond to hormones, and use extracellular Ca²⁺.

What is cardiac muscle structure?

Striated, branched cells connected by intercalated discs.

What are intercalated discs?

Specialized junctions with desmosomes and gap junctions for mechanical and electrical coupling.

What is the sinoatrial (SA) node?

The SA node is the heart’s natural pacemaker that spontaneously generates action potentials due to leak ion channels, setting the baseline heart rate.

Why do SA node cells depolarize spontaneously?

They have “leaky” ion channels that allow positive ions to slowly enter, causing gradual depolarization without external signals.

What is the role of the atrioventricular (AV) node?

The AV node delays the electrical signal, allowing the ventricles time to fill with blood after atrial contraction.

What is the pathway of electrical conduction in the heart?

SA node → AV node → bundle of His → Purkinje fibers, which spread the signal through ventricles for coordinated contraction.

Why does ventricular contraction start at the bottom of the heart?

Purkinje fibers conduct signals upward, ensuring blood is pushed efficiently out of the ventricles.

What are arrhythmias?

Irregular or uncoordinated contractions of the heart caused by disruptions in the electrical conduction system.

What is fibrillation?

A severe arrhythmia with rapid, irregular contractions independent of the SA node, which reduces effective blood pumping.

Why is ventricular fibrillation more dangerous?

It prevents effective blood circulation, leading to rapid loss of oxygen delivery to tissues.

How is fibrillation treated?

With defibrillation, which applies an electrical shock to reset pacemaker activity and restore normal rhythm.

What is heart block?

A condition where electrical signals cannot properly travel through the heart, often between the SA and AV nodes.

What is an ECG?

An electrocardiogram that records the electrical activity of the heart to detect abnormalities in rhythm and conduction.

What do the P wave, QRS complex, and T wave represent?

P wave = atrial depolarization, QRS complex = ventricular depolarization, T wave = ventricular repolarization.

What is cardiac output (CO)?

The amount of blood pumped by each ventricle per minute.

How is cardiac output calculated?

CO = heart rate (HR) × stroke volume (SV).

What is stroke volume?

The amount of blood pumped by a ventricle with each heartbeat.

What factors affect cardiac output?

Heart rate, stroke volume, hormones, nervous system input, blood volume, and vascular resistance.

How do hormones affect heart rate?

Hormones like epinephrine and thyroid hormone increase depolarization rate of SA node cells, increasing heart rate.

How does the parasympathetic nervous system affect heart rate?

It releases acetylcholine, which slows depolarization of SA node cells and decreases heart rate.

What is end-diastolic volume (EDV)?

The amount of blood in the ventricle after filling, before contraction.

What is end-systolic volume (ESV)?

The amount of blood remaining in the ventricle after contraction.

What determines stroke volume?

Stroke volume depends on EDV, ESV, preload, afterload, and contractility.

What is preload?

The amount of blood returning to the heart, which stretches the ventricles and increases contraction strength.

What is afterload?

The resistance the heart must overcome to eject blood, often due to arterial pressure.

How does increased resistance affect stroke volume?

Higher resistance (afterload) decreases stroke volume because the heart must work harder to pump blood.

What are capillaries specialized for?

Exchange of gases, nutrients, and wastes due to their thin, permeable walls.

What controls blood flow into capillaries?

Precapillary sphincters regulate flow into capillary beds.

What forces drive fluid movement in capillaries?

Hydrostatic pressure pushes fluid out, while colloid osmotic pressure pulls fluid in.

How are veins different from arteries?

Veins have thinner walls, larger diameters, and act as blood reservoirs with greater compliance.

How does blood return to the heart through veins?

Via skeletal muscle contractions, smooth muscle activity, valves preventing backflow, and the respiratory pump.

What is the respiratory pump?

Breathing movements that change pressure in the chest and abdomen to help push blood toward the heart.

What are varicose veins?

Veins with leaky or damaged valves that allow blood to pool.

What is the arterial baroreceptor reflex?

A feedback system that maintains blood pressure homeostasis by adjusting heart rate and vessel diameter.

What effectors are involved in the baroreceptor reflex?

Smooth muscle in vessels, cardiac muscle, arterioles, and the SA node.

What is hemoglobin?

A protein in red blood cells made of four subunits, each containing a heme group that binds oxygen.

What is cooperative binding in hemoglobin?

Binding of one O₂ increases the affinity for additional O₂, making subsequent binding easier.

What is the oxygen-hemoglobin dissociation curve?

A graph showing how hemoglobin saturation changes with oxygen pressure.

What causes a right shift in the dissociation curve?

Increased temperature or decreased pH lowers hemoglobin’s affinity for oxygen, promoting oxygen release.

What causes a left shift in the dissociation curve?

Increased affinity for oxygen, meaning hemoglobin holds onto oxygen more tightly.

How is CO₂ transported in the blood?

Primarily as bicarbonate ions, but also dissolved and bound to hemoglobin.

How does hemoglobin help buffer pH?

Deoxygenated hemoglobin binds H⁺, helping stabilize blood pH.

What is ventilation?

The process of moving air in and out of the lungs.

What are the steps of respiration?

Ventilation, gas exchange in lungs, transport in blood, gas exchange in tissues, and cellular respiration.

What is the conducting zone?

Airways (like trachea) that conduct air and are supported by cartilage to prevent collapse.

What is the respiratory zone?

Includes alveoli where gas exchange with capillaries occurs.

What is tidal volume?

The amount of air moved in or out of the lungs during a normal breath.

What is alveolar ventilation rate?

The amount of fresh air reaching alveoli for gas exchange per minute.

What is dead space?

Air that does not participate in gas exchange, such as air in conducting airways.

Why does a snorkel increase breathing difficulty?

It increases dead space, requiring deeper breaths to maintain effective gas exchange.

What determines gas movement in the lungs?

Differences in partial pressure drive diffusion of O₂ and CO₂.

What is hypoventilation?

Reduced ventilation relative to metabolism, leading to increased CO₂ and decreased blood pH.

What is hyperventilation?

Excess ventilation that removes too much CO₂, increasing blood pH.

Why can hyperventilation be dangerous?

Low CO₂ reduces carbonic acid and H⁺, raising blood pH and disrupting homeostasis.