BioSci E109: Skeletal and Smooth Muscle

• The study guide is for BioSci E109: Module 2 Quiz.

Skeletal Muscle

• Control is voluntary, via the somatic nervous system.
• The appearance is striated due to sarcomeres.
• Cells are multinucleated.
• There are no gap junctions.
• Optimal resting length equals maximum force production.
• Force can be increased by motor unit recruitment.
• Force can be increased by the frequency of action potentials.
• Calcium binds to troponin, which exposes myosin-binding sites on actin, initiating cross-bridge cycling.
• ATP hydrolysis drives cross-bridge cycling.
• Fatigue resistance is achieved through slow ATP hydrolysis and cross-bridge cycling.
• Relies on oxidative phosphorylation, thus many mitochondria are present.

Smooth Muscle

• Control is involuntary, via the autonomic nervous system.
• There are no sarcomeres; dense bodies organize actin and myosin.
• Gap junctions facilitate electrical coupling.
• Calcium binds to calmodulin, which activates myosin light-chain kinase (MLCK).
• Myosin phosphatase dephosphorylates myosin, leading to relaxation.
• Stretching can stimulate action potentials.
• Increased myosin phosphatase activity decreases force.
• Excitatory neurotransmitters, such as acetylcholine, increase force.

Cardiac Muscle

• Control is involuntary.
• Striated with gap junctions.
• Autorhythmic cells, specifically the SA node, set the heart rate.
• Sodium influx causes depolarization.
• Calcium influx causes the plateau phase.
• Potassium efflux causes repolarization.
• A long refractory period prevents summation.
• During atrial systole, the atria contract and the AV valves open.
• During ventricular systole, the AV valves close and the semilunar valves open.
• During isovolumetric contraction, all valves are closed, and there is no volume change.
• Stroke volume is the blood ejected during systole.
• Parasympathetic stimulation increases potassium permeability, decreasing heart rate.
• Sympathetic stimulation increases calcium and sodium permeability, increasing heart rate.

Cardiovascular System

• Flow rate (Q) = ΔP / R.
• Resistance (R) depends on vessel diameter and blood viscosity.
• Increased vessel diameter increases flow rate.
• The first heart sound ("lub") occurs when the AV valves close during ventricular contraction.
• The second heart sound ("dub") occurs when the semilunar valves close during ventricular relaxation.
• The P wave on an ECG represents atrial depolarization.
• The QRS complex on an ECG represents ventricular depolarization.
• The T wave on an ECG represents ventricular repolarization.

Key Differences Between Muscle Types

• Skeletal muscle distinctions: voluntary control, striated, no gap junctions, multinucleated, fastest contraction speed, low fatigue resistance (glycolytic fibers).
• Smooth muscle distinctions: involuntary control, non-striated, gap junctions, single nucleus, slowest contraction speed, high fatigue resistance (slow ATPase).
• Cardiac muscle distinctions: involuntary control, striated, gap junctions, single nucleus, intermediate contraction speed, high fatigue resistance (oxidative fibers).

Important Equations

• Flow Rate (Q) = ΔP / R, where ΔP is the pressure gradient and R is resistance.
• Resistance (R) = (8 * η * L) / (π * r^4), where η is blood viscosity, L is vessel length, and r is vessel radius.
• Stroke Volume (SV) = End-diastolic volume - End-systolic volume.

Key Points

• Skeletal muscle exhibits voluntary control, striations, and lacks gap junctions.
• Smooth muscle exhibits involuntary control, lacks striations, and has gap junctions.
• Cardiac muscle exhibits involuntary control, striations, and possesses gap junctions.
• Calcium is essential for contraction in all muscle types.
• Parasympathetic stimulation decreases heart rate by increasing potassium permeability.
• Flow rate increases with larger vessel diameter and a higher pressure gradient.
• ECG waves represent P (atrial depolarization), QRS (ventricular depolarization), and T (ventricular repolarization).

Study guide for BioSci E109 Module 2 Quiz, focusing on skeletal and smooth muscle. Covers control mechanisms, appearance, cellular structures, and force generation. Includes the roles of calcium and ATP in muscle function.