Chapter 5 Notes: Nervous and Muscular Tissue; Tissue Growth, Repair, and Regeneration
Nervous tissue and muscle overview
Nervous tissue is specialized for communication by electrical and chemical signals; it consists of neurons (nerve cells) and neuroglia (glial cells) which protect and assist neurons (housekeepers of the nervous system).
Main functions: exitability (voltage changes in response to stimuli) and rapid transmission of signals to other cells; neuronal signaling leads to rapid responses; muscle tissue contracts to produce movement.
Anatomy referenced for nerves: nuclei, axon, dendrite/dentrite, neuroma; neurosoma discussed as part of chapter 12.
Key terms introduced for later chapters: neural tissue and neurosoma/dentures (dentures appears to be a transcription artifact).
Chapter 12 will revisit detailed nervous tissue anatomy and function.
Muscular tissue and muscle types
Muscular tissue is specialized to contract and respond to stimulation, generating movement and heat.
Muscle types in the body:
Skeletal muscle: voluntary control; striated fibers; multi-nucleated; long, cylindrical fibers; attached to bone (with exceptions like tongue, upper esophagus, facial muscles).
Cardiac muscle: involuntary control; found in the heart; branched, shorter fibers; central nuclei; intercalated discs provide electrical/mechanical connection; lacks conscious control.
Smooth muscle: involuntary control; non-striated fibers; found in walls of digestive, respiratory, urinary tracts and blood vessels; regulates diameter of vessels and organ contents.
Diaphragm is skeletal muscle (not smooth). Deep breath: contraction of the diaphragm demonstrates voluntary control.
Sphincters and “fentor” (ring-like, cuff muscles that open/close passages) concept:
Internal sphincters are smooth muscle (involuntary control).
External sphincters are skeletal muscle (voluntary control).
Urinary system context:
Internal urethral sphincter: smooth muscle; involuntary control; prevents leakage when not urinating.
External urethral sphincter: skeletal muscle; voluntary control; allows conscious urine control.
Detrusor muscle: the thickened detrusor muscle in the bladder wall composed of smooth muscle; contracts to expel urine during micturition.
Male urethra is roughly longer than the female urethra, affecting urinary tract infection risk (UTIs are more common in women due to shorter urethra).
Urethral anatomy summary:
Internal urethral sphincter: smooth muscle (involuntary).
External urethral sphincter: skeletal muscle (voluntary).
Urethra passes through the urogenital diaphragm; the external sphincter surrounds the urethra externally.
Pathophysiology:
Weak sphincter muscles can lead to incontinence; treatment is individualized by cause and severity.
Cardiac muscle details:
Cardiac muscle cells (myocytes) are shorter, branched, with one centrally located nucleus; intercalated discs provide electrical and mechanical connections; they are involuntary.
Smooth muscle details:
Lack of striations; involuntary; lines digestive, respiratory, urinary tracts; propels content through organs and regulates vessel diameter.
Summary on muscle coordination:
Skeletal muscle: voluntary, somatic motor control; responds to brain/spinal cord signals.
Cardiac muscle: involuntary; intrinsic pacemaker activity and autonomic regulation.
Smooth muscle: involuntary; regulated by autonomic nerves and local factors; numerous functional roles in organ systems.
Detailed anatomy and physiology: sphincters, and urinary system integration
Fentor (ring-like) muscles can be composed of either smooth or skeletal muscle depending on location; control varies (involuntary vs voluntary).
Internal urethral sphincter:
Smooth muscle; involuntary control; part of urinary continence mechanism.
External urethral sphincter:
Skeletal muscle; voluntary control; allows conscious control of urination.
Urinary system overview:
Organs: kidneys, ureters, bladder, urethra.
Ureters enter the urinary bladder posterolaterally; detrusor muscle (a smooth muscle layer) contracts during urination to expel urine.
Bladder base narrows to a constricted neck continuous with the urethra.
Male urethra ~ longer than female; longer urethra offers protection against UTIs in males.
The internal urethral sphincter forms near the bladder neck (involuntary).
The external urethral sphincter encircles the urethra within the urogenital diaphragm (voluntary).
Clinical connection:
Incontinence may result from weakened basal sphincters; treatment depends on severity and cause.
Cell junctions and tissue connections
Intercellular junctions connect cells and mediate communication:
Tight junctions: form a seal and encircle each cell near the apical pole; prevent paracellular passage of substances; crucial in urinary bladder, stomach, skin to prevent water loss.
Desmosomes: strong junctions that resist mechanical stress; connect cells via desmosomal plaques and transmembrane cadherins.
Hemidesmosomes: “half desmosomes” that anchor epithelial cells to the basement membrane.
Gap junctions: formed by a ring-like arrangement of six connexin proteins forming a pore; allow direct passage of ions, glucose, amino acids, and other small molecules between neighboring cells.
Each junction type serves specific functions in tissue integrity, electrical coupling, and selective barrier properties.
Glands and glandular tissue
Gland basics:
Glands are organs that secrete substances for use elsewhere or elimination from the body; composed of epithelial tissue and connective tissue framework; may be exocrine or endocrine.
Exocrine glands:
Maintain a duct that conducts secretions to a surface (e.g., sweat glands, mammary glands, tear glands).
Endocrine glands:
Do not have ducts; secrete hormones directly into the bloodstream (e.g., thyroid, adrenal, pituitary, pancreas as both an endocrine and exocrine organ).
Unicellular glands:
Such as goblet cells in the epithelium of stomach and small intestine; mucus-secreting cells.
Glandular structures:
Parenchyma: the functional glandular cells (epithelium-derived).
Stroma: the connective tissue framework, including capsule and septa/trabeculae.
Duct structures can be unbranched or branched; shapes can be tubular, acinar, or tubular-acinar.
Secretions types and cell products:
Serous glands: produce thin, watery secretions (e.g., tears, digestive juice);
Mucous glands: produce mucus (glycoproteins); goblet cells are mucus-secreting unicellular glands;
Mixed glands: contain both serous and mucous components.
Cytogenicity and secretion modes:
Cytogenic (cytogenicity) relates to cell origin and secretion; some glands release whole cells; sperm and eggs are cytogenic cells—participate in reproduction.
Merocrine glands release secretions via vesicles without cell loss (e.g., many glands like pancreas).
Apocrine glands accumulate product at the apical portion then release a portion with the secretory material (cell fragments remain; e.g., mammary glands, some glands of ocular region).
Special membranes and membranes in body cavities:
Cutaneous membrane: skin—largest organ; epidermis (stratified squamous epithelium) and dermis; relatively dry protective layer.
Mucous membranes: line open passages; mucus traps particles; cilia help move mucus; epithelium often pseudostratified or simple columnar with goblet cells; lamina propria and muscularis mucosae are underlying layers.
Serous membranes: include serosa; line closed body cavities and cover organs; produce lubricating serous fluid.
Synovial membranes line joint cavities and secrete synovial fluid; primarily connective tissue without an epithelial layer.
Tissue growth, development, repair, and degeneration
Growth and development concepts:
Hyperplasia: increase in cell number; example: uterus during pregnancy via smooth muscle hyperplasia.
Hypertrophy: increase in cell size; examples include skeletal and cardiac muscle growth with exercise; liver growth via hypertrophy when regenerating after injury.
Atrophy: decrease in cell size or number; e.g., cast immobilization leads to muscle atrophy in the casted limb; astronauts experience muscle mass loss due to disuse.
Neoplasia: abnormal, uncontrolled growth forming tumors; can be benign or malignant; disordered tissue growth.
Metaplasia: change from one mature tissue type to another; can be normal (e.g., vagina tissue changes after puberty) or abnormal (e.g., smoker’s bronchial epithelium changing from pseudostratified columnar to stratified squamous).
Differentiation: specialization of embryonic cells into mature tissue types.
Stem cells and developmental potential:
Embryonic stem cells: totipotent (potential to form all cell types, including extraembryonic tissues) or pluripotent (can form any cell in the embryo).
Adult stem cells: multipotent (produce several cell types within a lineage), unipotent (produce only one cell type); bone marrow is an example producing several blood cell types (multipotent).
Regeneration: replacement of dead/damaged cells by the same type of cells, restoring function (e.g., liver, skin).
Fibrosis: replacement of damaged tissue with scar tissue; may impair function (e.g., pulmonary fibrosis, scar formation after injury).
Tissue engineering and clinical implications:
Engineering tissues in the lab (biomaterials + cells) to replace damaged tissues or organs (e.g., skin grafts, heart valves, corneas, bone, liver, cartilage, bladder wall).
Embryonic stem cells provide a powerful tool for regenerative medicine, but raise ethical controversies; adult stem cells offer alternative sources with fewer ethical concerns.
Practical implications for clinical anatomy/physiology:
Normal healing involves inflammation, tissue repair, and remodeling; excessive fibrosis can impede function.
In tissue injury, macrophages and neutrophils clear debris; fibroblasts lay down collagen; granulation tissue forms; maturation/remodeling can last weeks to years.
Cellular injury and death: necrosis vs apoptosis
Necrosis:
Premature, pathological death of tissue due to trauma, toxin, infection, or lack of blood supply; causes inflammation and tissue damage.
Infarction is tissue death due to ischemia (e.g., myocardial infarction).
Gangrene types: dry (ischemic, often in diabetics or poor perfusion) and gas gangrene (anaerobic bacterial infection).
Apoptosis:
Programmed cell death; controlled and non-inflammatory; cellular components are neatly packaged and removed without harming surrounding tissue.
Triggered by intrinsic or extrinsic signals; extracellular signals bind receptors; caspases are activated to fragment DNA and proteins.
Distinguishing features:
Necrosis: uncontrolled, usually associated with injury; inflammation often present.
Apoptosis: orderly, cell actively participates in its own demise; minimal inflammation.
Illustrative analogy used in lecture:
Pregnancy uterus expansion: hypertrophy and hyperplasia; post-delivery, regression via apoptosis rather than necrosis to remove excess cells without injury.
Tissue engineering, stem cells, and clinical prospects
Tissue engineering: creating functional tissue in vitro and implanting it in vivo; often uses collagen-based scaffolds or biodegradable polymers seeded with human cells.
Examples of engineered tissues:
Skin grafts; heart valves; coronary arteries; bone; liver; tendon; scaffolds for bladder wall.
Stem cell research and controversies:
Embryonic stem cells offer high developmental potential but raise ethical concerns.
Adult stem cells offer therapeutic potential with fewer ethical issues but may have limited differentiation capacity.
Ongoing research aims to improve regeneration, reduce fibrosis, and develop safer, more effective therapies.
Quick cross-links and study cues
Three muscle types to remember: skeletal (voluntary), cardiac (involuntary), smooth (involuntary).
The diaphragm is skeletal muscle—remember via the act of taking a deep breath and holding it.
The uro-genital and digestive systems rely on precise control of internal vs external sphincters based on whether the muscle is smooth or skeletal.
Tight junctions, desmosomes, hemidesmosomes, and gap junctions each play distinct roles in tissue integrity, barrier function, and intercellular communication.
Glands can be endocrine or exocrine; note that some organs (like the pancreas) perform both roles.
Membranes in the body include cutaneous, mucous, serous, and synovial membranes with distinct functions and locations.
Tissue growth pathways (hyperplasia, hypertrophy, neoplasia, metaplasia) have important diagnostic and therapeutic implications.
Regeneration vs fibrosis determines functional outcomes after injury; fibrosis often reduces function.
Neoplasia and metaplasia are important for understanding pathology and cancer risk.
Tissue engineering and stem cell therapy represent a frontier with clinical potential and ethical considerations.
Summary of key definitions and terms (quick reference)
Detrusor muscle: smooth muscle layer of the bladder wall that contracts during urination.
Internal urethral sphincter: smooth muscle; involuntary control.
External urethral sphincter: skeletal muscle; voluntary control.
Tight junction: seals adjacent cells to prevent paracellular passage.
Desmosome: strong cell–cell junction resisting shear forces.
Hemidesmosome: anchors epithelial cells to basement membrane.
Gap junction: cytoplasmic channels allowing direct cell-to-cell exchange.
Hyperplasia: increase in cell number.
Hypertrophy: increase in cell size.
Atrophy: decrease in cell size or number.
Neoplasia: abnormal, uncontrolled tissue growth forming a tumor.
Metaplasia: change from one mature tissue type to another.
Differentiation: maturation of cells into specialized types.
Totipotent: potential to form all cell types including extraembryonic tissues.
Pluripotent: potential to form any cell type in the embryo.
Multipotent: potential to form several cell types within a lineage.
Unipotent: potential to form only one cell type.
Regeneration: replacement of cells by the same type to restore function.
Fibrosis: replacement of tissue by scar tissue; often reduces function.
Necrosis: uncontrolled, pathological cell death with inflammation.
Apoptosis: programmed, controlled cell death with minimal inflammation.
Quick cross-links and study cues
Three muscle types to remember: skeletal (voluntary), cardiac (involuntary), smooth (involuntary).
The diaphragm is skeletal muscle—remember via the act of taking a deep breath and holding it.
The uro-genital and digestive systems rely on precise control of internal vs external sphincters based on whether the muscle is smooth or skeletal.
Tight junctions, desmosomes, hemidesmosomes, and gap junctions each play distinct roles in tissue integrity, barrier function, and intercellular communication.
Glands can be endocrine or exocrine; note that some organs (like the pancreas) perform both roles.
Membranes in the body include cutaneous, mucous, serous, and synovial membranes with distinct functions and locations.
Tissue growth pathways (hyperplasia, hypertrophy, neoplasia, metaplasia) have important diagnostic and therapeutic implications.
Regeneration vs fibrosis determines functional outcomes after injury; fibrosis often reduces function.
Neoplasia and metaplasia are important for understanding pathology and cancer risk.
Tissue engineering and stem cell therapy represent a frontier with clinical potential and ethical considerations.
Summary of key definitions and terms (quick reference)
Detrusor muscle: smooth muscle layer of the bladder wall that contracts during urination.
Internal urethral sphincter: smooth muscle; involuntary control.
External urethral sphincter: skeletal muscle; voluntary control.
Tight junction: seals adjacent cells to prevent paracellular passage.
Desmosome: strong cell–cell junction resisting shear forces.
Hemidesmosome: anchors epithelial cells to basement membrane.
Gap junction: cytoplasmic channels allowing direct cell-to-cell exchange.
Hyperplasia: increase in cell number.
Hypertrophy: increase in cell size.
Atrophy: decrease in cell size or number.
Neoplasia: abnormal, uncontrolled tissue growth forming a tumor.
Metaplasia: change from one mature tissue type to another.
Differentiation: maturation of cells into specialized types.
Totipotent: potential to form all cell types including extraembryonic tissues.
Pluripotent: potential to form any cell type in the embryo.
Multipotent: potential to form several cell types within a lineage.
Unipotent: potential to form only one cell type.
Regeneration: replacement of cells by the same type to restore function.
Fibrosis: replacement of tissue by scar tissue; often reduces function.
Necrosis: uncontrolled, pathological cell death with inflammation.
Apoptosis: programmed, controlled cell death with minimal inflammation.
Quick cross-links and study cues
Three muscle types to remember: skeletal (voluntary), cardiac (involuntary), smooth (involuntary).
The diaphragm is skeletal muscle—remember via the act of taking a deep breath and holding it.
The uro-genital and digestive systems rely on precise control of internal vs external sphincters based on whether the muscle is smooth or skeletal.
Tight junctions, desmosomes, hemidesmosomes, and gap junctions each play distinct roles in tissue integrity, barrier function, and intercellular communication.
Glands can be endocrine or exocrine; note that some organs (like the pancreas) perform both roles.
Membranes in the body include cutaneous, mucous, serous, and synovial membranes with distinct functions and locations.
Tissue growth pathways (hyperplasia, hypertrophy, neoplasia, metaplasia) have important diagnostic and therapeutic implications.
Regeneration vs fibrosis determines functional outcomes after injury; fibrosis often reduces function.
Neoplasia and metaplasia are important for understanding pathology and cancer risk.
Tissue engineering and stem cell therapy represent a frontier with clinical potential and ethical considerations.
Summary of key definitions and terms (quick reference)
Detrusor muscle: smooth muscle layer of the bladder wall that contracts during urination.
Internal urethral sphincter: smooth muscle; involuntary control.
External urethral sphincter: skeletal muscle; voluntary control.
Tight junction: seals adjacent cells to prevent paracellular passage.
Desmosome: strong cell–cell junction resisting shear forces.
Hemidesmosome: anchors epithelial cells to basement membrane.
Gap junction: cytoplasmic channels allowing direct cell-to-cell exchange.
Hyperplasia: increase in cell number.
Hypertrophy: increase in cell size.
Atrophy: decrease in cell size or number.
Neoplasia: abnormal, uncontrolled tissue growth forming a tumor.
Metaplasia: change from one mature tissue type to another.
Differentiation: maturation of cells into specialized types.
Totipotent: potential to form all cell types including extraembryonic tissues.
Pluripotent: potential to form any cell type in the embryo.
Multipotent: potential to form several cell types within a lineage.
Unipotent: potential to form only one cell type.
Regeneration: replacement of cells by the same type to restore function.
Fibrosis: replacement of tissue by scar tissue; often reduces function.
Necrosis: uncontrolled, pathological cell death with inflammation.
Apoptosis: programmed, controlled cell death with minimal inflammation.
Quick cross-links and study cues
Three muscle types to remember: skeletal (voluntary), cardiac (involuntary), smooth (involuntary).
The diaphragm is skeletal muscle—remember via the act of taking a deep breath and holding it.
The uro-genital and digestive systems rely on precise control of internal vs external sphincters based on whether the muscle is smooth or skeletal.
Tight junctions, desmosomes, hemidesmosomes, and gap junctions each play distinct roles in tissue integrity, barrier function, and intercellular communication.
Glands can be endocrine or exocrine; note that some organs (like the pancreas) perform both roles.
Membranes in the body include cutaneous, mucous, serous, and synovial membranes with distinct functions and locations.
Tissue growth pathways (hyperplasia, hypertrophy, neoplasia, metaplasia) have important diagnostic and therapeutic implications.
Regeneration vs fibrosis determines functional outcomes after injury; fibrosis often reduces function.
Neoplasia and metaplasia are important for understanding pathology and cancer risk.
Tissue engineering and stem cell therapy represent a frontier with clinical potential and ethical considerations.
Summary of key definitions and terms (quick reference)
Detrusor muscle: smooth muscle layer of the bladder wall that contracts during urination.
Internal urethral sphincter: smooth muscle; involuntary control.
External urethral sphincter: skeletal muscle; voluntary control.
Tight junction: seals adjacent cells to prevent paracellular passage.
Desmosome: strong cell–cell junction resisting shear forces.
Hemidesmosome: anchors epithelial cells to basement membrane.
Gap junction: cytoplasmic channels allowing direct cell-to-cell exchange.
Hyperplasia: increase in cell number.
Hypertrophy: increase in cell size.
Atrophy: decrease in cell size or number.
Neoplasia: abnormal, uncontrolled tissue growth forming a tumor.
Metaplasia: change from one mature tissue type to another.
Differentiation: maturation of cells into specialized types.
Totipotent: potential to form all cell types including extraembryonic tissues.
Pluripotent: potential to form any cell type in the embryo.
Multipotent: potential to form several cell types within a lineage.
Unipotent: potential to form only one cell type.
Regeneration: replacement of cells by the same type to restore function.
Fibrosis: replacement of tissue by scar tissue; often reduces function.
Necrosis: uncontrolled, pathological cell death with inflammation.
Apoptosis: programmed, controlled cell death with minimal inflammation.