wk 4-7

In general, what type of control does the somatic nervous system provide?

Conscious (voluntary) control of skeletal muscle.

Which neurotransmitter deficit can cause weak or absent skeletal muscle contraction?

Acetylcholine (ACh).

Which receptor subtype is affected in Myasthenia gravis?

Nicotinic cholinergic receptors (N1) on the motor end plate.

How many motor neurons extend from the CNS to the effector in the somatic nervous system?

One single, heavily myelinated motor neuron.

Which statement is NOT a characteristic of a reflex?

Reflexes are only visceral; reflexes can be somatic or visceral.

Which pair describing reflex classifications is incorrect?

None; all listed classifications are correct.

What type of reflex occurs when a learned response causes someone to retract from intense heat?

A learned (conditioned) reflex.

Which spinal cord structure controls skeletal muscle and causes weakness when damaged?

The anterior (ventral) horn.

What is reciprocal inhibition?

The agonist contracts while the antagonist muscle on the same side relaxes.

Which statement about the crossed extensor reflex is true?

It maintains balance, flexes one limb, extends the opposite limb, and is polysynaptic.

Which tissue is affected in Lambert-Eaton myasthenic syndrome?

Skeletal muscle.

How is the somatic nervous system functionally characterized?

Excitatory only; it controls voluntary actions and subconscious reflexes.

What spinal structure is damaged when hand weakness occurs but touch and pain remain intact?

The ventral (anterior) horn.

What is the specialized sarcolemma region where motor neuron terminals bind?

The motor end plate.

Which ions primarily maintain the resting membrane potential of the sarcolemma?

Sodium (Na+) and potassium (K+).

Which channels trigger ACh release from the presynaptic terminal?

Voltage-gated calcium (Ca2+) channels.

Where are the receptors that initiate an action potential in skeletal muscle?

On the sarcolemma, specifically at the motor end plate.

What are bundles of contractile and elastic proteins inside muscle fibers called?

Myofibrils.

What are the thin and thick filaments of a sarcomere?

Actin is thin; myosin is thick.

What does the H-band contain?

Myosin, or thick filaments, without actin.

What region does the A-band cover?

The full length of the thick filaments, including areas of overlap.

What does the I-band contain?

Actin, or thin filaments, without thick filaments.

What factors contribute to skeletal muscle fatigue?

Lactic acid, inorganic phosphate, H+ accumulation, and glycogen depletion.

What happens when an action potential reaches the motor neuron bouton?

Ca2+ enters and triggers ACh release into the motor end plate.

What happens when ACh binds nicotinic receptors?

Na+ channels open, causing Na+ influx and a graded MEPP.

Where does a motor end plate potential travel to trigger Ca2+ release?

It travels down T-tubules, activating DHP receptors and then RyR channels.

What does Ca2+ bind during skeletal muscle contraction?

Ca2+ binds troponin, moving tropomyosin and exposing actin binding sites.

What three events terminate skeletal muscle contraction?

ACh is degraded, Ca2+ is resequestered into the SR, and ATP binds myosin.

Which factor does NOT contribute to skeletal muscle fatigue?

An increase in cytoplasmic Ca2+; elevated Ca2+ promotes contraction.

Why do H+ and inorganic phosphate accumulate during heavy exercise?

H+ comes from metabolism, while Pi is released from myosin during the power stroke.

What are the key functions of myoglobin?

It carries oxygen, is a red pigment, is abundant in slow-twitch fibers, and supports aerobic respiration.

Why do overly shortened and stretched sarcomeres produce less tension?

There is an optimal length L0; short sarcomeres have less sliding space and long ones have fewer cross-bridges.

Are muscle fibers within one motor unit the same or different?

They are the same physiological fiber type.

What mechanism recruits additional motor units to increase force?

Spatial summation, or motor unit recruitment.

What is the correct sequence of excitation-contraction coupling?

ACh release → ACh binding → T-tubule AP → SR Ca2+ release → troponin binding → exposed actin sites.

What is asynchronous motor unit recruitment?

Motor units activate at different times to maintain force and prevent whole-muscle fatigue.

What is the relationship between the biceps and triceps during elbow movement?

They are antagonistic; biceps flexes and triceps extends the elbow.

What is the brief period between ACh release and mechanical contraction called?

The latent period.

How do arteries and veins differ in blood flow direction?

Arteries carry blood away from the heart; veins carry blood toward the heart.

Which statement about heart chambers is false?

Atria push blood out to the body; they actually push blood into the ventricles.

What are the functions of the fibrous skeleton of the heart?

It attaches valves, maintains shape, prevents collapse, and electrically insulates atria from ventricles.

What is mitral valve stenosis?

Narrowing of the mitral (bicuspid) valve opening.

What happens when the pulmonary semilunar valve fails to open properly?

Ventricular ejection is impaired during the second phase of ventricular systole.

What percentage of healthy heart cells are autorhythmic pacemaker cells?

Approximately 1%.

Why can an isolated heart continue beating outside the body?

Funny channels (If) in pacemaker cells spontaneously generate electrical impulses.

How does an action potential spread between cardiac cells?

Through gap junctions within intercalated discs.

What percentage of cardiac contraction Ca2+ comes directly from the SR?

Approximately 90%; about 10% enters from extracellular fluid.

What removes Ca2+ from cardiac cells during relaxation?

Ca2+-ATPase pumps return it to the SR and the Na+/Ca2+ exchanger removes it from the cell.

What determines the number of active cross-bridges in cardiac muscle?

The amount of Ca2+ in the cytosol.

What mechanical stimulus increases cardiac contraction force?

Stretching of cardiac muscle from increased venous return, via the Frank-Starling mechanism.

Which ion causes Phase 0 depolarization in cardiac contractile cells?

Na+ entering through fast voltage-gated Na+ channels.

Which ion causes the rapid upstroke in cardiac pacemaker cells?

Ca2+ entering through voltage-gated Ca2+ channels.

What is the correct cardiac conduction pathway?

SA node → AV node → Bundle of His → bundle branches → Purkinje fibers.

Which valves are open during late ventricular diastole?

The AV valves: tricuspid and mitral valves.

Which ECG wave represents atrial depolarization?

The P wave.

What happens to heart rate if SA node cells become more permeable to K+?

Heart rate decreases because the cells become hyperpolarized.

What creates the first and second heart sounds?

Blood turbulence caused by cardiac valves closing.

What happens to intraventricular pressure during isovolumetric contraction?

It increases while ventricular volume remains constant.

Why do the semilunar valves close after ventricular ejection?

Ventricular pressure falls below arterial pressure.

How is stroke volume defined?

The amount of blood pumped by one ventricle per contraction; SV = EDV − ESV.

Why does ventricular fibrillation severely impair circulation?

Chaotic contractions prevent effective ventricular pumping and adequate blood flow.

How does the parasympathetic nervous system affect heart rate?

ACh activates muscarinic receptors and decreases heart rate.

How does the sympathetic nervous system affect heart rate?

Norepinephrine activates β1 receptors and increases heart rate.

What shape adaptation improves gas exchange in red blood cells?

A biconcave shape.

What is the leukocyte abundance order from least to most common?

Basophils → eosinophils → monocytes → lymphocytes → neutrophils.

What property of hemoglobin increases its affinity for additional oxygen?

Cooperativity.

Which white blood cells respond to allergies and parasitic infections?

Eosinophils.

Which cardiac parameter best indicates venous return?

End-diastolic volume (EDV).

What mechanisms enhance venous return?

Skeletal muscle pump, respiratory pump, and sympathetic venoconstriction.

What is NOT an effect of norepinephrine on cardiac contractile cells?

Increasing the length of contraction; norepinephrine shortens contraction duration.

What does phosphorylated phospholamban do?

It increases Ca2+ reuptake into the SR, allowing stronger and shorter contractions.

How do liquids and gases move along pressure gradients?

From areas of higher pressure to areas of lower pressure.

What happens to blood pressure farther from the heart?

It decreases.

Which parameter does NOT directly affect vascular resistance inside the vessel lumen?

Vessel wall thickness.

What is the primary driving force for cardiovascular blood flow?

A pressure gradient (ΔP).

What happens to resistance when a vessel's radius doubles?

Resistance decreases to 1/16 of its original value.

What is cardiogenic shock?

Failure of the heart to provide enough driving force for blood flow.

Which drug class can lower blood pressure by blocking sympathetic vasoconstriction?

Alpha-1 blockers (α1-adrenergic antagonists).

Which hormone is a powerful systemic vasoconstrictor?

Angiotensin II.

Why is the long plateau phase of cardiac action potentials important?

It prolongs the refractory period and prevents tetanus.

Why is mean arterial pressure (MAP) important?

It represents the main driving pressure for blood flow and accounts for the longer duration of diastole.