Muscular System_ Chapter 8

8.1: Introduction to the Muscular System

• Muscle Functions:

  • Muscles generate force for movement, enabling activities such as walking, breathing, pumping blood, and moving food in the digestive tract.

• Types of Muscle Tissue:

  • Skeletal Muscle: Striated, voluntary control, attached to bones.

  • Smooth Muscle: Non-striated, involuntary control, found in walls of hollow organs.

  • Cardiac Muscle: Striated, involuntary control, found only in the heart.

8.2: Structure of a Skeletal Muscle

• Skeletal Muscles Overview:

  • Over 600 skeletal muscles in the human body.

• Connective Tissue Coverings:

  • Fascia: Dense connective tissue surrounding and separating muscles.

  • Tendons: Formed from fascia and attach muscles to bones.

  • Aponeuroses: Broad sheets of connective tissue connecting muscles.

8.3: Structure of a Skeletal Muscle Fiber

• Muscle Fiber Characteristics:

  • Each fiber is a long cylindrical cell.

  • Cell Membrane: Sarcolemma.

  • Cytoplasm: Sarcoplasm containing mitochondria and many nuclei.

  • Myofibrils: Composed of thick (myosin) and thin (actin) filaments, leading to striations.

8.4: Skeletal Muscle Contraction

• Muscle Contraction Mechanism:

  • Contraction results from overlapping myosin and actin filaments (sliding filament model).

  • Cross-Bridge Formation: Myosin heads bind to actin to pull filaments and shorten the muscle.

  • Sarcomere: Functional unit of muscle that shortens during contraction.

8.5: Neuromuscular Junction

• Contraction Initiation:

  • Skeletal muscles contract when stimulated by a motor neuron at the neuromuscular junction.

  • Neurotransmitter: Acetylcholine released to trigger contraction.

  • Motor End Plate: Specialized region on the muscle cell that contains receptors for acetylcholine.

8.6: Energy Sources for Muscle Contraction

• ATP: Main source of energy for muscle contraction.

• Creatine Phosphate: Rapidly regenerates ATP from ADP.

• Glycolysis and Aerobic Respiration:

  • Glycolysis is anaerobic (yields 2 ATP), while aerobic respiration occurs in mitochondria (yields 28 ATP).

8.7: Muscle Fatigue and Oxygen Debt

• Muscle Fatigue Causes:

  • Changes in electrolyte balance, decreased ATP levels, and increased lactic acid levels.

• Oxygen Debt:

  • Refers to extra oxygen needed by liver cells to convert lactic acid back into glucose after exercise.

8.8: Types of Muscle Fibers

• Fast Fibers (White):

  • Rapid response, fatigue quickly, high anaerobic capacity.

• Slow Fibers (Red):

  • Slower, fatigue-resistant, high aerobic capacity.

8.9: Muscle Metabolism

• Types of Exercise:

  • Low to moderate exercise utilizes aerobic respiration.

  • High-intensity exercise leads to anaerobic metabolism and lactic acid production.

8.10: Major Skeletal Muscles

• Naming:

  • Based on size, shape, location, action, number of attachments, or fiber direction.

• Examples:

  • Pectoralis major, biceps brachii, deltoid, etc.

8.11: Muscle Relationships

• Muscle Actions:

  • Agonist: The primary mover.

  • Antagonist: Opposer of the primary mover.

  • Synergists: Assist the primary mover.

8.12: Muscle Fiber Organization

• Fascicle Patterns:

  • Parallel, convergent, pennate, and circular arrangements influence muscle function.

8.13: Muscles of Facial Expression

• Major Muscles:

  • Include the epicranius, orbicularis oculi, orbicularis oris, masseter, and zygomaticus.

8.14: Muscles of Mastication

• Chewing Muscles:

  • Masseter and temporalis primarily used to elevate the mandible.