Lecture 4: Membranes, Muscle & Nervous Tissue – Study Notes

Tissue Membranes

Overview of Tissue Membranes

Tissue membranes are physical barriers that line or cover body surfaces, providing protection and compartmentalization. They are essential for maintaining the integrity and function of organs and body cavities.

• Mucous membranes: Line body cavities open to the exterior (digestive, respiratory, urinary, reproductive tracts).

• Serous membranes: Line closed ventral body cavities (peritoneal, pleural, pericardial).

• Cutaneous membrane: The skin, covering the outer surface of the body.

• Synovial membranes: Line joint cavities and produce synovial fluid.

Mucous Membrane

Mucous membranes are coated with secretions from mucous glands and mucus-secreting cells. They protect and lubricate surfaces exposed to the external environment.

• Structure: Composed of epithelium and underlying lamina propria (areolar connective tissue).

• Function: Trap pathogens and particles, facilitate absorption and secretion.

• Location: Digestive, respiratory, urinary, and reproductive tracts.

Serous Membrane

Serous membranes line the ventral body cavities and secrete serous fluid to reduce friction between organs.

• Structure: Mesothelium (simple squamous epithelium) over areolar tissue.

• Function: Produce serous fluid for lubrication.

• Location: Peritoneal, pleural, and pericardial cavities.

Cutaneous Membrane

The cutaneous membrane, or skin, is the body's largest organ and serves as a protective barrier.

• Structure: Stratified epithelium, areolar tissue, and dense irregular connective tissue.

• Function: Protection, sensation, thermoregulation.

• Location: External surface of the body.

Synovial Membrane

Synovial membranes line joint cavities and produce synovial fluid, which lubricates and nourishes articular cartilage.

• Structure: Areolar tissue, epithelium, adipocytes, capillaries.

• Function: Reduce friction, facilitate movement in joints.

• Location: Synovial joints (e.g., knee, elbow).

Connective Tissue Framework

Support and Organization

Connective tissue layers surround and support organs in the ventral body cavity, maintaining their positions and providing strength and stability.

• Functions:

  • Maintain relative positions of internal organs

  • Provide strength and stability

  • Route for distribution of blood vessels

Fascia

Fascia is a thin connective tissue casing that surrounds and holds every blood vessel, organ, bone, muscle, and nerve fiber in place.

• Superficial fascia: Subcutaneous layer (hypodermis), adipose & areolar connective tissue.

• Deep fascia: Dense connective tissue, bound to ligaments, tendons, capsules.

• Subserous fascia: Areolar tissue between serous membranes and deep fascia.

Type	Location	Main Components
Superficial Fascia	Between skin and underlying organs	Areolar tissue, adipose tissue
Deep Fascia	Internal framework, bound to capsules, tendons, ligaments	Dense connective tissue
Subserous Fascia	Between serous membranes and deep fascia	Areolar tissue

Muscle Tissue

General Functions

Muscle tissue is specialized for contraction, enabling movement, posture, joint stabilization, and heat generation.

• Movement: Bones, digestive tract, blood vessels.

• Posture: Maintains body position.

• Joint stabilization: Supports and stabilizes joints.

• Heat generation: Muscle contractions produce heat.

Types of Muscle Tissue

There are three main types of muscle tissue, each with distinct structure and function.

• Skeletal muscle: Large, long, slender cells (muscle fibers); voluntary control.

• Cardiac muscle: Found only in the heart; involuntary control.

• Smooth muscle: Located in walls of visceral organs; involuntary control.

Type	Location	Control	Striations	Nuclei
Skeletal	Skeletal muscles	Voluntary	Present	Multinucleated, peripheral
Cardiac	Heart	Involuntary	Present	One (sometimes two), central
Smooth	Visceral organs	Involuntary	Absent	One, central

Common Properties of Muscle Tissue

• Vascular: Rich blood supply.

• Contractile: Generates pulling forces (muscles only pull).

• Excitable: Responds to nerve signals, causing contraction.

Skeletal Muscle Tissue

Skeletal muscle tissue is responsible for voluntary movements and is characterized by its striated appearance and multinucleated cells.

• Cells: Thick, long, cylindrical, multinucleated, parallel orientation.

• Nuclei: Located at the periphery of the cell.

• Striations: Due to arrangement of actin and myosin filaments.

• Control: Voluntary, via nervous system stimulation.

Skeletal Muscle Organization

Skeletal muscle is organized hierarchically and surrounded by connective tissue sheaths at multiple levels.

• Muscle cell (fiber) → Fascicle (group of fibers) → Muscle (group of fascicles)

• Endomysium: Surrounds individual muscle cells.

• Perimysium: Surrounds fascicles.

• Epimysium: Surrounds entire muscle.

Cardiac Muscle Tissue

Cardiac muscle tissue is found only in the heart and is specialized for rhythmic, involuntary contractions.

• Cells: Cardioctyes, smaller than skeletal muscle cells, usually one central nucleus.

• Striations: Present.

• Intercalated discs: Specialized connections for coordinated contraction; contain gap junctions for ion/electrical impulse transmission.

• Control: Involuntary; pacemaker cells establish contraction rate.

Smooth Muscle Tissue

Smooth muscle tissue is found in the walls of visceral organs and blood vessels, enabling involuntary movements such as peristalsis and vasoconstriction.

• Cells: Spindle-shaped, shorter, no striations, more closely packed than cardiac muscle.

• Nuclei: Centrally located, one per cell, larger than in skeletal muscle.

• Control: Involuntary; can contract independently via gap junctions.

• Regeneration: Capable of cell division and repair after injury.

Nervous Tissue

Overview of Nervous Tissue

Nervous tissue is specialized for communication through electrical and chemical signals, forming the basis of the nervous system.

• Neurons: Main nerve cells responsible for transmitting signals.

• Dendrites: Extensions that receive information.

• Axons: Extensions that conduct information to other cells.

• Neuroglia: Support cells (glial cells) that maintain, protect, and nourish neurons.

Neuron Structure and Function

• Cell body (soma): Contains nucleus and organelles; size varies from 5 to 140 μm.

• Dendrites: Extensively branch from the cell body; transmit signals toward the cell body.

• Axon: Only one per neuron; impulse generator and conductor; transmits impulses away from the cell body.

Neuroglia (Supporting Cells)

• Functions:

  • Maintain physical structure of tissues

  • Repair tissue framework after injury

  • Perform phagocytosis

  • Provide nutrients to neurons

  • Regulate composition of interstitial fluid

Tissue Injury and Inflammation

Inflammatory Response

Inflammation is a protective response to tissue injury caused by impact, abrasion, distortion, chemical irritation, infection, or extreme temperatures.

• Functions:

  • Isolates injured tissue

  • Removes damaged cells, tissue components, and microorganisms

Inflammation Step	Description
Mast Cell Activation	Release of histamine, heparin, and prostaglandins
Increased Blood Flow	Vasodilation brings more blood to the area
Increased Vessel Permeability	Allows immune cells and proteins to enter tissue
Pain	Caused by chemical mediators and tissue swelling

Tissue Regeneration and Aging

Regeneration

The ability of tissues to regenerate varies by tissue type.

• Good regeneration: Epithelial, connective, and smooth muscle tissues.

• Poor regeneration: Other muscle tissues, neural tissue, some cartilage.

• Necrosis: Tissue destruction after injury and trauma.

Aging and Tissue Repair

• Repair declines with age: Epithelia thins, connective tissue becomes fragile.

• Maintenance slows: Reduced efficiency in tissue repair and maintenance.

• Cancer rates increase: Higher risk of abnormal cell growth with age.