Human Phys Mid 4

Muscle Tension and Responses

Tension Overview

  • Single Twitches: Muscle completely relaxes between stimuli.

  • Summation: Closer stimuli lead to incomplete relaxation.

    • Unfused Tetanus: Muscles relax slightly between stimuli.

    • Complete Tetanus: Muscle maintains steady tension without relaxation.

Effects of Fatigue

  • Continual stimulation leads to muscle fatigue, resulting in decreased tension.

  • Fatigue is defined as the muscle’s inability to maintain required force despite ongoing stimuli.

Action Potential and Tension

  • Time (msec) determines duration and intensity of muscle tension responses.

Motor Unit Recruitment

Increasing Force of Contraction

  • Force may be augmented by:

    • Changing the type of active motor units.

    • Increasing the number of motor units activated.

Skeletal Muscle Types

Muscle Fiber Classification

  • Type I Fibers: Slow twitch, slow oxidative fibers.

  • Type IIa Fibers: Intermediate, fast oxidative fibers.

  • Type IIx Fibers: Fast twitch, fast glycolytic fibers.

  • Each type contributes differently based on physical demands (e.g., endurance vs. sprinting).

Characteristics of Muscle Fibers

  • Type I: More myoglobin, numerous mitochondria, fatigue resistant.

  • Type II: Larger diameter, faster contraction, easily fatigued.

  • Fiber color relates to oxidative capacity — darker fibers indicate more myoglobin and aerobic metabolism.

Athletic Performance Implications

  • Different sports favor different muscle fiber compositions, influencing training specificity.

  • Typical fiber compositions for various athletes: 70-80% slow fibers (Type I) for distance runners, higher percentages of fast fibers (Type II) for sprinters.

Cardiac Muscle Characteristics

Heart Muscle Cells

  • Autorhythmic Cells: Pacemakers; initiate contractions, lack sarcomeres.

  • Contractile Cells: Striated, organized fibers forming functional units.

Action Potentials in Cardiac Muscle

  • Length of Action Potential: Cardiac muscle holds a prolonged action potential (over 200 ms) preventing tetanus, allowing proper filling during diastole.

  • Skeletal muscle fibers have much shorter action potentials (1-5 ms).

Ionic Mechanisms

  • Pacemaker potential influenced by fluctuating membrane permeability to Na+ and K+ ions.

  • L-type and T-type calcium channels regulate depolarization phases in cardiac muscle.

Cardiac Control Mechanisms

  • Heart rate can be modulated by:

    • Parasympathetic Control: Reduces heart rate through acetylcholine (ACh) and hyperpolarized states.

    • Sympathetic Control: Increases heart rate via epinephrine; affecting force of contraction and contraction duration.

Smooth Muscle Features

Smooth Muscle Functionality

  • Characterized by slow contraction and relaxation capabilities; can sustain contraction without fatigue.

  • Distinct differences from striated muscle in organization and control (actin and myosin arrangements without sarcomeres).

Types of Smooth Muscle

  • Single-Unit Smooth Muscle: Electrically coupled, contracts as a unit (e.g., gastrointestinal tract).

  • Multi-Unit Smooth Muscle: Requires individual stimulation (e.g., eye muscles).

Contraction Mechanism

  • Initiation via Ca2+ from extracellular fluid and sarcoplasmic reticulum, triggering phosphorylation processes.

Respiratory Physiology

Respiratory System Functions

  • Gas exchange, pH regulation, protection against pathogens, vocalization.

Anatomy of the Respiratory System

  • Structured into upper (nose, pharynx) and lower (trachea, lungs) regions, facilitating airflow and gas exchange.

Lung Functionality

  • Alveoli: Primary sites for gas exchange, aiding in oxygen uptake and carbon dioxide release.

  • Alveolar disorders (e.g., cystic fibrosis) can severely hinder proper function through disrupted saline secretion processes.

Gas Exchange Mechanism

  • Diffusion: Oxygen and CO2 transfer across the alveolar-capillary interface; efficiency relies on surface area, concentration gradients, and barrier permeability.

Impacts on Gas Exchange

  • Factors such as alveolar ventilation rate and blood flow significantly affect overall gas exchange efficacy.

Lung Volumes and Capacities

  • Determined using spirometry; key measurements include Tidal Volume (VT), Expiratory Reserve Volume (ERV), and Total Lung Capacity.

Factors Affecting Ventilation

  • Compliance and resistance play integral roles in effective airflow; abnormal lung conditions influence these parameters.

Importance of Surfactant

  • Reduces surface tension in the lungs, preventing collapse of smaller alveolar units; critical for healthy lung function, especially in newborns.