Muscle Tissue, Nervous Tissue, and Tissue Injury and Repair Notes

Muscle Tissue Overview

• General Definition: Muscle tissue is a tissue type specialized for contraction.

• Three Categorical Types of Muscle Tissue:

  1. Skeletal Muscle: Large muscles responsible for body movement.

  2. Cardiac Muscle: Found exclusively in the heart.

  3. Smooth Muscle: Found in the walls of hollow, contracting organs.

• Comparative Histological Features:

  • Skeletal Muscle Cells: These cells possess prominent striations and have nuclei located on their periphery.

  • Smooth Muscle Cells: These cells feature a single nucleus and lack visible striations.

  • Cardiac Muscle Cells: These cells appear striated and typically have a single nucleus.

• Imaging Data (Light Micrographs):

  • Comparative view: $1600 \times$ magnification.

  • Individual skeletal muscle view: $180 \times$ magnification.

  • Individual cardiac muscle view: $450 \times$ magnification.

  • Individual smooth muscle view: $235 \times$ magnification.

Skeletal Muscle Tissue

• Cellular Structure:

  • Consists of long, thin cells called muscle fibers.

  • Each cell is long and cylindrical.

  • Each cell spans the entire length of the whole muscle.

  • Multinucleate: Cells have multiple nuclei arranged specifically on the periphery.

  • Striated: Cells exhibit visible bands or stripes.

• Functional Classification: Referred to as striated voluntary muscle.

• Growth and Repair:

  • Adult skeletal muscle cells do not divide.

  • New fibers are produced by the divisions of myosatellite cells.

• Locations: Combined with connective tissues and neural tissue within the skeletal muscles.

• Functions:

  • Moves or stabilizes the position of the skeleton.

  • Guards entrances and exits to the digestive, respiratory, and urinary tracts.

  • Generates heat.

  • Protects internal organs.

Cardiac Muscle Tissue

• Cellular Structure:

  • Cells are short and branched.

  • Cells form branching networks.

  • Intercalated Discs: Specialized regions where cells are interconnected and connected at branching points.

  • Nucleation: Usually contains one nucleus per cell, located in the center of the cell.

  • Striated: Contains visible striation patterns.

• Functional Classification: Referred to as striated involuntary muscle.

• Regulation: Regulated by pacemaker cells rather than voluntary control.

• Location: Found only in the heart.

• Functions:

  • Circulates blood through the cardiovascular system.

  • Maintains blood pressure.

Smooth Muscle Tissue

• Cellular Structure:

  • Cells are small and spindle-shaped.

  • Nonstriated: Lacks the visible stripes found in skeletal and cardiac tissue.

  • Nucleation: One single, central nucleus per cell.

• Growth and Repair: Unlike other muscle tissues, smooth muscle cells can divide and regenerate.

• Functional Classification: Referred to as nonstriated involuntary muscle.

• Locations:

  • Found in the walls of blood vessels.

  • Found in digestive, respiratory, urinary, and reproductive organs.

• Functions:

  • Moves food, urine, and reproductive tract secretions.

  • Controls the diameter of respiratory passageways.

  • Regulates the diameter of blood vessels.

Nervous Tissue

• General Definition: Specialized for conducting electrical impulses.

• Concentration: Primarily concentrated in the brain and spinal cord.

• Cell Types:

  1. Neurons: The primary functional units for signal transmission.

  2. Neuroglia (Supporting Cells): Provide support and maintenance for neurons.

• Parts of a Neuron:

  • Cell Body (Soma): Contains the nucleus, nucleolus, and major organelles like mitochondria.

  • Dendrites: Short, branching extensions from the cell body that receive incoming signals and transfer nerve impulses to the soma.

  • Axon (Nerve Fiber): A long, thin extension of the cell body that conducts information (action potentials) away to another excitable cell or destination.

• Neuroglia Functions:

  • Maintain the physical structure of nervous tissues.

  • Repair the tissue framework after an injury.

  • Perform phagocytosis to remove debris or pathogens.

  • Provide essential nutrients to neurons.

  • Regulate the composition of the interstitial fluid surrounding neurons.

• Microbiology Note: Neuron sizes and shapes vary widely; representation shown at $1600 \times$ and $872 \times$ magnification.

Tissue Injury and Repair

• Response Stages: Tissues respond to injury in two distinct, sequential stages:

  1. Inflammation (Inflammatory Response): The immediate reaction to injury.

  2. Regeneration: The process to restore normal function.

• The Inflammatory Response:

  • Triggers: Can be activated by trauma (physical injury) or infection (presence of pathogens).

  • Chemical Release from Damaged Cells: Releasing prostaglandins, proteins, and potassium ions ($K^+$).

  • Mast Cell Activation: Damaged connective tissue activates mast cells, which release chemicals including Histamine, Heparin, and Prostaglandins.

• Cardinal Signs of Inflammation:

  1. Redness.

  2. Heat (warmth).

  3. Swelling.

  4. Pain.

  5. Loss of function (sometimes).

• Physiological Process of Inflammation:

  • Increased Blood Flow: Released chemicals cause blood vessels to dilate.

  • Increased Vessel Permeability: Capillary walls become more permeable, allowing plasma to diffuse into injured tissue, causing swelling (edema).

  • Pain Sensation: Caused by abnormal tissue conditions and chemicals stimulating nerve endings.

  • Increased Local Temperature: Result of increased blood flow and permeability.

  • Enhanced Nutrient Delivery: Vessel dilation increases oxygen and nutrient supply to the area.

  • Increased Phagocytosis: Phagocytes are activated to engulf tissue debris and pathogens.

  • Removal of Toxins and Wastes: Enhanced circulation carries wastes to the kidneys (excretion) or liver (inactivation).

• Necrosis and Complications:

  • Necrosis: Tissue destruction caused by lysosomal enzymes releasing and destroying injured and surrounding cells; begins several hours after injury.

  • Pus: Accumulation of necrotic tissues and cellular debris in the wound.

  • Abscess: Pus trapped within an enclosed area.

Tissue Regeneration Capacity

• High Regeneration Ability:

  • Epithelia.

  • Connective tissues (with the notable exception of cartilage).

  • Smooth muscle.

• Poor or No Regeneration Ability:

  • Skeletal muscle.

  • Cardiac muscle.

  • Nervous tissue.

• Fibrosis: In areas where cardiac muscle is damaged, it is replaced by fibrous tissue (scarring) rather than functional muscle cells.

Development of Cancer

• Developmental markers in tissue include:

  • Changes in cell size.

  • Changes in nucleus size.

  • Changes in the overall organization of the tissue.