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

Fiber Type

Glycolytic

Oxidative

Glycolytic Enzymes

High

Low

Mitochondria

Few

Rich

Diameter

Larger

Smaller

Capillaries

Fewer

Lots

Myoglobin

No

Yes (red muscle)

ATP Production

Less efficient

More efficient

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.