Human Biological Processes - Muscle Tissue

Course Information

  • Course Title: Human Biological Processes

  • Instructor: Dr. Shona McQuilken

Course Aims

  • Outline the properties of muscle tissue.

  • Describe the types of muscle cells and how they differ in location, function, and histology.

  • Describe how each muscle type is stimulated to contract.

  • Describe the organization of skeletal muscle.

  • Describe some examples of diseases of muscle.

Properties of Muscle Tissue

  • Muscle is a very abundant tissue, making up 40-50% of body weight.

Functions of Muscle

  • Movement: Facilitates locomotion and mobility.

  • Posture and Joint Stability: Maintains body position against gravity.

  • Protein Supply: Serves as a reservoir for amino acids.

  • Regulation of Organ Volume: Controls the volume of hollow organs such as the bladder and stomach.

  • Propulsion of Fluids/Food: Aids in digestion and circulation through contraction (e.g., smooth muscle in intestines and cardiac muscle in heart).

  • Heat Generation: Produces heat during contraction, aiding thermoregulation.

Muscle Properties

  • Excitability: Ability to receive and respond to stimuli.

  • Close Relationship with Surrounding Connective Tissue (CT): Facilitates the transfer of forces.

  • Contractility: Ability to contract forcefully when stimulated.

  • Extensibility: Ability to stretch without damage.

  • Elasticity: Ability to return to original shape after being stretched.

Types of Muscle

  • There are 3 types of muscle:    - Cardiac Muscle
       - Smooth Muscle
       - Skeletal Muscle

  • These muscle types differ in:   - Location   - Function   - Histology   - Control

Comparative Features of Muscle Types

Feature

Cardiac

Smooth

Skeletal

Shape

Branched (Y-shaped)

Spindle-shaped

Long cylindrical

Nuclei

1-2 centrally located

1 centrally located

Multiple, peripherally located

Striations

Yes

No

Yes

Location

Heart wall

Walls of hollow organs

Attached to bones

Fibre Diameter

Medium

Small

Large

Fibre Length

Medium

Short

Long

Cardiac Muscle

  • Location: Most of the heart wall.

  • Contraction and Relaxation: Involuntary control.

  • Autorhythmicity: Built-in pacemaker cells regulate heartbeat.

  • Control of Contraction Strength and Speed: Influenced by hormones and neurotransmitters.

Smooth Muscle

  • Characteristics: Non-striated, includes actin and myosin.

  • Action: Involuntary; some areas exhibit autorhythmicity (e.g., GI tract).

  • Regulation: Controlled by the autonomic nervous system (ANS) and endocrine system.

Skeletal Muscle

  • Composition: Surrounded by connective tissues such as fascia, which separates individual muscles or muscle groups.

  • Organization: Includes several layers of connective tissue comprising:   - Epimysium: Surrounds entire muscle.   - Perimysium: Surrounds fascicles (bundles of muscle fibers).   - Endomysium: Surrounds individual muscle fibers.

Question

  • What are the functions of the fascia?
      - Supports and protects muscles, provides a pathway for nerves and blood vessels.   - Helps to compartmentalize muscles, enhancing coordinated movement.

Skeletal Muscle Structure

  • Muscle Fiber: Individual muscle cells with multiple nuclei located along the periphery just under the sarcolemma.

  • Development: Muscle fibers develop through the fusion of myoblasts.

  • Mitochondria: Abundant to support high energy demands.

  • Sarcoplasmic Reticulum (SR): Specialized smooth endoplasmic reticulum that stores calcium ions.

Skeletal Muscle Myofibrils

  • Structure: Cylindrical structures within muscle fibers that perform contractions and are responsible for the striations seen in skeletal muscle.

  • Dimensions: 1-2 μm in diameter, composed of functional units called sarcomeres.

  • Sarcomeres Composition:   - Light Bands (I band): Contain thin filaments.   - Dark Bands (A band): Contain thick filaments.

Sarcomere Structure

  • I band: Contains only thin filaments.

  • A band: Contains thick filaments with overlapping thin filaments.

  • Z line: Defines the boundaries of a sarcomere.

  • N line: Holds the thick filaments in place (midpoint of A band).

Muscle Diseases

  • Myopathy: An abnormal condition or disease affecting muscle tissue.

  • Dystrophy: Muscle degenerating diseases leading to progressive degeneration of muscle fibers (e.g., Duchenne’s muscular dystrophy).

  • Neuromuscular Disorders: Include conditions affecting any component of the motor unit (motor neurons, neuromuscular junction, muscle fibers).

Causes of Myopathy

  • ATP Metabolism Defects: Any defect in muscle ATP metabolism can lead to myopathy, often presenting in childhood or teenage years.

  • Examples: Glycogen storage diseases, mitochondrial myopathies.

  • Symptoms include:
      - Fatigue
      - Muscle weakness
      - Cramps and pains.

Inflammatory Myopathies

  • Characteristics: Chronic muscle inflammation and weakness; often idiopathic and autoimmune in nature.

  • Progression: Progressive weakness typically presents as proximal weakness that advances to distal.

Further Reading

  • Netter’s Essential Histology (Chapter 4)

  • Martini Fundamentals of Anatomy and Physiology (Chapter 10)

  • Reference by Leif Saul.