lecture 16a physiology

Lecture Overview

• Instructor: Dr. Suzanne Gray

• Course: BIO 1220 Human Physiology

• Lecture: Muscle Function - Lecture 16A

• Term: Winter 2025

1. Types and Structure of Muscle

• Three types of muscle tissues:

  • Skeletal Muscle

  • Cardiac Muscle

  • Smooth Muscle

2. Skeletal Muscle Contraction

• Muscles contract using the sliding filament mechanism through actin and myosin interactions.

• Contractile speed and strength vary among muscle fibers.

  • Key Terms:

    • Twitch: A single contraction.

    • Peak Force: Maximum force exerted by muscle fibers.

3. Stimulation and Strength of Contraction

• Influenced by muscle fiber diameter (larger diameter = stronger contractions).

• Variability in contraction speed due to muscle fiber types (slow vs. fast twitch).

  • Fibers vary in speed and peak force achievement.

4. Types of Skeletal Muscle Fibers

a) Slow and Fast Twitch Fibers

• Slow Twitch Fibers:

  • Take longer to reach peak tension.

  • Example: Soleus muscle (mostly slow twitch).

• Fast Twitch Fibers:

  • Rapid contraction;

  • Example: Extraocular muscles (mainly fast twitch).

• Mixed Fibers:

  • Example: Gastrocnemius (equal slow and fast twitch).

b) Glycolytic and Oxidative Fibers

• Classification based on metabolic properties:

  • Glycolytic Fibers: Use anaerobic glycolysis, less efficient ATP production, faster fatigue.

  • Oxidative Fibers: Use aerobic respiration, more mitochondria, efficient ATP production.

5. Muscle Fiber Characteristics

Comparison of Fiber Types

Slow Twitch (SO) Fibers:

• Efficient in using oxygen.

• Delayed muscle firing.

• Resistant to fatigue.

Fast Twitch (FG) Fibers:

• Quick to fire, support explosive movements.

• Do not utilize oxygen for energy production.

• Fatigue quickly.

Metabolic Pathways

• Oxidative Metabolism:

  • Complete breakdown of glucose using oxygen, yielding high ATP per glucose molecule.

• Glycolytic Metabolism:

  • Breakdown of glucose without oxygen (glycolysis), yielding lower ATP.

Detailed Characteristics of Fiber Types

6. Cardiac and Smooth Muscle

a) Cardiac Muscle

• Similarities to skeletal muscle:

  • Striated, contains actin and myosin in sarcomeres.

• Differences:

  • Branched and interconnected cells.

  • Contain gap junctions, behaving as a single functional unit.

  • Rich in mitochondria for ATP production, preventing fatigue.

b) Smooth Muscle

• Found in walls of internal organs (blood vessels, digestive tract, etc.).

• Lacks sarcomeres but contains actin and myosin.

• Allows considerable stretching (e.g., uterus during pregnancy).

• Innervated by autonomic neurons instead of motor neurons.

• Controlled differently (excitation vs. inhibition).

Smooth Muscle Types

• Single-unit:

  • Extensively linked by gap junctions, contracts as a unit (e.g., gastrointestinal tract).

• Multi-unit:

  • Fewer gap junctions, precise contraction control (e.g., large airways, arteries).

Summary of Key Concepts

1. Categories of Muscle: Knowledge of muscle types, structure, and functions.

2. Skeletal Muscle Contraction: Mechanisms of muscle contraction.

3. Control of Muscle Contractions: The role of neurotransmitters.

4. Muscle Fiber Types: Characteristics of slow vs. fast twitch; glycolytic vs. oxidative fibers.

5. Cardiac and Smooth Muscle: Functions and locations of these muscle types.

Lecture Recap

• Today covered muscle function and types.

• Next class will focus on the cardiovascular system.