Tissue Level of Organization PDF

Tissue Level of Organization BIOL 1190: Ch4 – Dr. Katelyn Janzen Outline  Introduction to tissue (4.1-4.3)  Epithelial Tissue (4.4)  Connective Tissue (4.5)  Membranes (4.6)  Muscular and Nervous Tissues (4.7,4.8) Learning Outcomes  Name and describe the four types of tissues, and the inte...

Tissue Level of Organization BIOL 1190: Ch4 – Dr. Katelyn Janzen Outline  Introduction to tissue (4.1-4.3)  Epithelial Tissue (4.4)  Connective Tissue (4.5)  Membranes (4.6)  Muscular and Nervous Tissues (4.7,4.8) Learning Outcomes  Name and describe the four types of tissues, and the intercellular junctions (4.1 – 4.3).  Epithelial Tissue (4.4):  Recognize and describe the types of cell layers and cell shapes in epithelia  List the function and location of different types of epithelial tissues  Recognize and explain exocrine and endocrine glandular epithelia  Connective Tissue (4.5):  Describe the structure and function of connective tissue  List, recognize and define different types of connective tissues  Membranes: name and describe the different membranes and their function (4.6)  Muscular and Nervous Tissues (4.7 – 4.8):  List and recognize the classes of muscular tissue  List the cell types of nervous tissue and broadly describe the function of nervous tissue  The Tissue Level of Organization  Tissue level  Cells plus surrounding structures  Epithelial, connective, muscle, nervous tissues Introduction to Tissues Tissues  Tissue – an integrated group of similar ______ cells that usually have a similar _______________ embryological origin and are _____________ specialized for a specific function  Tissues combine to form organs  There are 4 main types of tissues  Epithelial tissue (a) Epithelial tissue (b) Connective tissue  Connective tissues  Muscular tissues  Nervous tissues (c) Muscular tissue (d) Nervous tissue Cell junctions  Cells are often ____________ attached together or to basement membranes or to connective tissue  Cell junctions are the point of contact between adjacent cells  Cell junctions have three functions: 1. _________ Anchor cell together or to extracellular material  E.g., Adherens junctions, desmosomes, hemidesmosomes 2. Form fluid-tight ______ seals between cells  E.g., Tight junctions 3. Act as __________ channels that allow ions and molecules to pass from cell to cell  E.g., gap junctions  Cell Adhesion Molecules Cell adhesion molecules (CAMs) are Desmosome transmembrane proteins that bind to each other and to the cytoskeleton Adjacent plasma membranes  Adherens junctions  Function: holds cells together  E.g., joins epithelial cells together  Transmembrane integral membrane proteins are attached to _________________ microfilaments (cytoskeleton) and to the ___________ integral membrane proteins of the other cell  Structural components:  Plaque: dense layer of proteins inside the cell membrane  Integral membrane proteins (cadherin): connect cell to cell  Microfilaments: In each cell, anchors the cadherins  Forms adhesion belts  Desmosomes  Function: prevents separation of cells  E.g., prevents separation of epidermal cells and cardiac muscle cells under tension  Similar in structure to adherens junctions, except transmembrane proteins (cadherins) are anchored by _____________________________ intermediate filaments which cross the cytoplasm from one side of the cell to the other  Hemidesmosome  Function: connect cells to the _________________________ basement membrane  E.g., Stratum basale of the epidermis is anchored to the basement membrane of the ____________ dermis  Half a desmosome  Transmembrane proteins are attached to intermediate filaments (keratin)(cytoskeleton)  Anchor protein, integrin, links to protein laminin in the basement membrane Basement membrane or basal lamina, is a complex structure produced by the basal surface of the epithelium and the underlaying connective tissue  Tight junctions  At a tight junction, the two plasma membranes are tightly bound (fused) together by interlocking membrane proteins  Prevents passage of _______ fluids across a tissue layer (including water!)  Common between cells that line the GI tract and the bladder  Gap junctions  Function: allow for the passage of **connexins combine to form connexons** ions and small molecule between cells  Formed by channel proteins called ___________ connexins that span the membranes of two cells  E.g., muscle and nerve impulses spread from cell to cell  Found in the heart and smooth muscle of the gut  Enables cells to communicate  Cardiac muscle cells have gap junctions, which allow them to beat in sync  Tiny space between plasma membranes of two cells Epithelial Tissue Epithelial Tissue Two different general purposes 1. Covers and lines surfaces  Provides ____________________for selective barriers movement of material  E.g., barrier between the body and the environment (skin; gut)  E.g., barrier between different structures (blood vessels)  Provides protection from ___________________ damage/abrasion  Absorbs nutrients (gut) 2. Forms secretion portion of glands  Produces mucus, ____________________, hormones and enzymes Structure of Epithelial Tissue  Closely packed cells with little intracellular space  “Sheets” of cells held tightly together with ___________________ cell junctions  Cells sit on basement membrane – thin layer of connective tissue that provides ______________ attachment and ________________ support  Apical surface = “free” surface  Basal surface = adheres to the basement membrane  Epithelial tissue  Has a high rate of cell turnover (cell regeneration)  Has its own nerve supply  Good nerve supply  _____________ Avascular – relies on diffusion from blood vessels within connective tissue for removal of waste and nutrient delivery  Good nerve supply  Epithelial tissues: Basement membrane  Basement membrane is a thin layer of **basal membrane is acellular** _______________ connective tissue tissue underlying epithelial tissue  All epithelia are attached to a basement membrane  Function: provides ____________ attachment and ____________ support for epithelial tissue  Is a thin a cellular extracellular membrane composed of two layers:  Basal lamina  Secreted by epithelial cells  Composed of collagen fibers, laminin, various glycoproteins, and proteoglycans  Reticular lamina  Secreted by the connective tissue cells  Composed of reticular fibers  Basic Features of Epithelial Cells ____________ Microvilli to increase surface area: Cilia are found in digestive, urinary, and portions of the reproductive tracts. respiratory and reproductive tracts. The _________ apical surface is the region of the cell exposed to the space inside the organ or tube (called the lumen). The ________ basal surface, attaches to underlying epithelial cells or deeper tissues.  Types of Epithelia  Covering and lining epithelia are classified according to: 1. Number of cell layers 2. Shape of the cells  Simple epithelia have a single layer of cells  Pseudostratified epithelia have a single layer, but irregular cell shape and nucleus position  Stratified epithelia have at least two layers  Basal cells replicate by “Scale like” mitosis and replace the more superficial layers Types of Epithelial: possible combinations The name of the specific type of stratified epithelial tissue depends on the shape of the ______ apical cells Epithelial Tissue  The ___________ structure of each kind of epithelium fits its ____________ function  Material exchange (A)  Secretion and absorption of material (B, and C)  Protection (D, and E)  Simple Squamous Epithelium  _____________of Single layer flat cells  Very thin → adapted for ________ diffusion (lungs, blood, and lymph vessels) and __________ filtration (kidneys)  Can have a specific name in some organs  Endothelium lines blood vessels  Endocardium lines the chambers of the heart  Mesothelium lines serous membranes Stratified Squamous Epithelum  Two or more layers of cells  Apical cells are flat  Non-keratinized  Lines _________ moist surfaces (mouth, esophagus, part of the epiglottis, part of the pharynx, and vagina) Stratified Squamous Epithelum  Two or more layers of cells  Apical cells are flat  Keratinized  Keratin = tough, fibrous intracellular protein  Superficial layer of skin Simple Cuboidal Epithelium  One layer of ____________________ cube shaped cells  Nucleus appear very round and centered  Adapted for ___________ absorption or ____________ secretion  lines kidney tubules, thyroid gland Stratified Cuboidal Epithelium  Two or more layer of cells  Cells in the apical layer are cube-shaped  Found in some _________ ducts (e.g., sweat glands, male urethra, esophageal ducts) Simple Columnar Epithelium: Non-ciliated  Single layer of column-shaped cells  Oval nuclei usually located near the base of the cells  Non-ciliated  Contain _____________ microvilli at the apical surface and goblet cells  Goblet cells secrete mucus  Function in ____________ secretion and _______________ absorption  Mucus secretion to lubricate GI, respiratory, reproductive and urinary systems Simple Columnar Epithelium: Ciliated  Single layer of column-shaped cells with cilia on the apical surface  Oval nuclei are usually located near the base of the cells  Ciliated  Usually contain interspersed Goblet cells  Cilia ________ beat in unison  Move fluid, mucus, and/or foreign particles  Line bronchioles, uterine tubes, paranasal sinuses, central canal of the spinal cord, brain ventricles  Pseudostratified Columnar Epithelium: Non-Ciliated  Single layer of columnar cells; appears layered because nuclei are at different levels  All cells are attached to the basement membrane; not all cells reach apical layer  Non-ciliated  Lacks Goblet cells; cells do not have _______ cilia  Lines epididymis, ducts of larger glands, and parts of the male urethra  Functions: ______________ absorption and ___________________ secretion Pseudostratified Columnar Epithelium: Ciliated  Single layer of columnar cells; appears layered because nuclei are at different levels  All cells are attached to the basement membrane; not all cells reach apical layer  Ciliated  Contains cells that bear cilia or secrete mucus (Goblet cells)  Lines airways of the upper respiratory tract  What is its function? —secrete mucus and sweep away for elimination. Stratified Columnar Epithelium  Has at least two layers of cells  The __________ apical layer has column shaped cells; cells in other layers can be short or irregularly shaped  Lines part of the urethra, esophageal and salivary gland ducts  Function: _____________ protection and _________________ secretion  Transitional Epithelium  Variable (transitional) appearance  In ________________, relaxed looks like stratified cuboidal epithelium, except it have large and round apical cells  In stretched state looks like stratified squamous epithelium, as cells flatten  Lines the urinary bladder and portions of ureters and urethra  Functions: protection and ability to stretch within The Glandular Epithelium: Exocrine glands  Exocrine Glands  Cells that secrete a product (mucous, sweat, ear wax, saliva, digestive enzymes, etc.) onto the _________ apical surface of the epithelial layer  Often connected to the surface by ducts (tubes)  Examples: Goblet cells, sudoriferous, sebaceous, or salivary glands The Glandular Epithelium: Endocrine glands  Endocrine glands  Secrete __________ hormones into the interstitial fluid followed by diffusion to the __________________ bloodstream  Do not have ducts  Examples: Pituitary, adrenal, and thyroid glands  Some glands have both exocrine and endocrine tissues  E.g., Pancreas, ovaries, testes  Endocrine vs Exocrine Glands Which is endocrine? Which is exocrine? How do you know? exocrine endocrine  Structural classification of Exocrine Glands  Unicellular glands – How many cells do you think these are made up of?  E.g., Goblet cells made up of 1 individual cell  Multicellular glands  Composed of many cells that form a distinctive microscopic structure or macroscopic organ  E.g., Sweat glands, oil (sebaceous) glands, salivary glands  Functional Classification of Exocrine Glands  There are three methods of glandular secretion:  ________crine Mero Glands  ________crine Apo Glands  ________crine Holo Glands What kind of transport do you see here?  Methods of Glandular Secretion: Merocrine Glands  Merocrine glands  Mero= “part”  Most exocrine glands are merocrine glands  Discharge secretory product by ___________________ exocytosis  E.g., Salivary glands, pancreas glands, digestive enzymes, sweat glands  Methods of Glandular Secretion: Apocrine Glands  Apocrine glands  Apo=“________________” away from  _______________ Accumulate secretory product at the apical surface  The apical portion of the cell ___________________from pinches off the cell to form the secretion  The remaining part of the cell repairs itself and the process repeats  E.g., Mammary glands  Methods of Glandular Secretion: Holocrine Glands  Holocrine glands  Holo = “entire”  Cells accumulate products, _____, dies and _________ ruptures to release products  Dead cells are replaced by new ones  E.g., Sebaceous glands Review: Epithelial tissue Simple Squamous Simple Epithelium Squamous Simple Cuboidal Simple Cuboidal Epithelium Simple Non-ciliated Simple Simple Columnar- Simpleepithelium Epithelium Columnar Epithelium Ciliated CiliatedColumnar Simple Simple Columnar Epithelium Non-Ciliated Pseudostratified Pseudostratified Covering/Lining Columnar Epithelium Columnar Epithelium Stratified Squamous Stratified Epithelium Squamous Stratified Cuboidal Stratified Epithelial Tissue Epithelium Cuboidal Stratified Stratified Epithelium epithelium Stratified Columnar Stratified Epithelium Columnar Endocrine Gland Endocrine Transitional Transitional Glandular Epithelium Epithelium Epithelium Exocrine Exocrine Gland Connective Tissue  Connective Tissue  There are several types of connective tissue  Made up of _____ cells scattered in an ______-cellular extra matrix (ECM)  Cells rarely touch each other due to the _________ matrix  ECM is composed of _________fibers protein and __________ ground substance secreted by the connective tissue cells  The structure of the ECM determines the tissues’ characteristics  E.g., can be solid, liquid, or somewhere in between (gel)  E.g., Can be hard (like bone) or firm and pliable (cartilage)  General characteristics of connective tissue:  Very abundant and widely distributed  Many different forms  Good nerve and blood supply, except in __________ cartilage and ______________ tendons  No free surfaces Connective Tissue  All connective tissue cells originate from ____________, mesenchyme an embryonic connective tissue composed of mesenchymal cells Connective Tissue: Constituent Cells  -Blast: ________ immature cells that retain the ability to _______ divide and produce ______________ matrix  E.g., Fibroblast, chondroblast, osteoblast  -Cyte: _____________cells mature that cannot divide or produce matrix  Maintain the tissue and matrix  E.g., Chrondrocyte, osteocyte Connective Tissue: Constituent cells  Fibroblasts  Based on their name, what do you think that they do?  Large flat cells  Move through tissue secreting _________ fibres and _____________________ ground substance Fibroblasts  Connective Tissue: Constituent cells  Macrophages – develop from monocytes  Engulf microorganisms and cell debris by ___________________ phagocytosis  Based on the root words, what does phagocytosis mean?  Plasma cells – develop from B lymphocytes  Produce antibodies that fight against foreign substances Macrophages Plasma cells Connective Tissue: Constituent cells  Neutrophils and eosinophils: specialized leukocytes  Not common in normal connective tissue  _________phils Netro migrate to the sites of bacterial invasion  __________phils Eosino migrate to the site of parasitic invasion  Both neutrophils and eosinophils contain toxic molecules and enzymes to fight off invaders Eosinophils Neutrophils are white blood cells that migrate are white blood cells that migrate to to sites of parasitic infection and sites of infection and destroy microbes allergic responses. by phagocytosis.  Connective Tissue: Constituent cells  Mast cells – found along blood vessels in connective tissue  Produce ____________that hisatmine causes dilation of small blood vessels  Adipocytes – found ______________ subcutaneously and around organs  Fat storage and protection What does adipocyte mean? What does subcutaneous mean? Mast cells are abundant along blood vessels. They produce histamine, which dilates small blood vessels during inflammation and kills bacteria. Adipocytes or fat cells store fats. They are found below the skin and around organs (heart, kidney). Review  There are three major components found in connective tissue 1. Cells 2. Fibers 3. Ground Substance _______________________ Extracellular matrix  The protein fibers in the ECM provide strength and support to a tissue  There are 3 types of fibers  Collagen fibers  Reticular fibers Made up of proteins  Elastic fibers  Connective Tissue: Fibers  Collagen fibers  Made from the protein __________ collagen  Found in most connective tissue  Often occurs in ____________________________ parallel bundles  Collagen fibers are very strong, but are still flexible (i.e., not stiff nor brittle)  E.g., Bone, cartilage, tendons, and ligaments Connective Tissue: Fibers  Reticular fibers  _______, Thin branched fibers of ____________ collagen in fine bundles, with a coating of glycoprotein  Function: provides support for blood vessels and soft organs  E.g., spleen, lymph nodes  Also form part of the basement membrane Lymph node Connective Tissue: Fibers  Elastic Fibers Smaller diameter fibers made of the protein _____________, elastin surrounded by glycoprotein fibrillin Branch and join to form networks of fibers Can stretch up to 150% of relaxed length, and then return to its original shape (i.e., elasticity!)  E.g., Lungs, blood vessels, skin Connective Tissue: Ground Substance  Ground substance: Material ________ between cells and fibers Determines the ___________________ consistency of the connective tissue  Can be fluid, semifluid gelatinous, or calcified Supports cells, holds cells together, stores water, and allows ________ for migration, transport of molecules and chemical reactions Contains water and large organic molecules (combinations of proteins and polysaccharides)  List the 3 components of connective tissue 1. Cells Review 2. Fibres 3.Ground substance List the 3 types of fibers found in connective tissue 1. Collagen 2. Reticular 3. Elastic  Label the components of this image Reticular fiber(stain the Practice same color as Collagen Collagen fiber fibers becaus of same Collagen fiber (parallel bundles) constituents) Elastic fiber (thin) Elastic fiber Reticular fiber Fibroblast Mast cell Fibroblasts Mast Cells (the histamine vessicles make them appear big) Types of Connective Tissue Classification of connective tissues  Connective tissue proper  Supporting connective tissue  Loose connective tissue  Cartilage  Areolar  Hyaline cartilage  Adipose  Fibrous cartilage  Reticular  Elastic cartilage  Dense connective tissue  Bone Tissue  Dense regular  Compact bone  Dense irregular  Spongy bone  Elastic  Liquid connective tissue  Blood  Lymph plasma Types of connective tissue  Loose Connective tissue: Areolar  Most generalized type of connective tissue  _____________distributed Widely – in and around nearly every body structure  The “packing material” of the body  _______________ Subcutaneous layer of skin, dermis of skin, lamina propria of mucous membranes; around blood vessels, nerves, and body organs  Consists of:  Fibers: __________arranged Randomly collagen, elastic, reticular  Cells: fibroblasts, adipocytes, white blood cells  _____________________: Ground substance gelatinous (semifluid)  Functions: strength, elasticity, support Loose Connective tissue: Areolar Loose Connective tissue: Adipose  Contains ________________ adipocytes – derived from fibroblasts  Cells specialized for triglyceride storage; stored as one large, centrally located droplet (cytoplasm and nucleus are pushed to the cell periphery)  Functions: reduces ________________, heat loss energy reserve, supports and protects organs Adipose tissue Loose Connective tissue: Reticular  Network of reticular fibers and _______________________ reticular cells  Forms stroma (framework) of organs  E.g., Liver, spleen, lymph nodes, bone marrow  Ties cells of smooth muscles together  Reticular fibers can act as ______________ filters  E.g., in spleen, filters the blood to remove worn out red blood cells  E.g., in lymph node, filters the lymph to remove microbes Reticular connective tissue Dense Connective Tissue  Dense connective tissue contains more _____________________, numerous fibers and ________________ cells than loose connective tissue  The fibers present are thicker, and denser fibers than in loose connective tissue  There are 3 types of dense connective tissue  Dense regular connective tissue  Dense irregular connective tissue  Elastic connective tissue Dense Connective Tissue: Regular  Dense regular connective tissue:  Collagen fibers regularly arranged in parallel bundles with ____________ fibroblasts cells in between  Found in _____________ tendons and ligaments  Provides great tensile strength along the fiber axis  Strong attachment  Note: Collagen is not living, so tissue does not heal quickly Dense regular connective tissue Dense Connective Tissue: Irregular  Dense irregular connective tissue  Collagen fibers are ______________ irregularly arranged, with a few fibroblasts  Tissue can resist tension from any direction  Makes for very “tough tissues”  White of the eyeball, dermis, membranes surrounding the heart, cartilage and bones  Often occurs as sheets, such as fasciae (tissue beneath skin and around muscles and organs Dense irregular connective tissue Elastic Connective Tissue  Composed of ____________fibers elastic and fibroblasts  Can stretch and return to its original shape → very strong  Found in lung tissue, vocal cords, ligaments between vertebrae, and blood vessels Elastic connective tissue  Cartilage  Cartilage: supporting connective tissue that consists of a dense network of __________ collagen fibers and _________ elastic fibers embedded in chondroitin sulfate (rubbery matrix)  Collagen fibers make cartilage ______________ strong  The chondroitin sulfate makes the cartilage ______________ resilient  Does not have nerves or blood vessels (unlike other connective tissues)  Secretes anti-angiogenesis factor, which prevents blood vessel growth  Produced by ___________________________; chondroblasts mature cartilage contains chondrocytes (cartilage cells) **chondro- cartilage  Surrounded by a dense irregular connective tissue membrane called the perichondrium  3 types of cartilage:  Hyaline cartilage  Fibrocartilage  Elastic cartilage Classification of connective tissues Classification of connective tissues  Connective tissue proper  Supporting connective tissue  Loose connective tissue  Cartilage  Areolar  Hyaline cartilage  Adipose  Fibrous cartilage  Reticular  Elastic cartilage  Dense connective tissue  Bone Tissue  Dense regular  Compact bone  Dense irregular  Spongy bone  Elastic  Liquid connective tissue  Blood  Lymph plasma  Hyaline Cartilage (“glassy”)  The most abundant, but the weakest type of cartilage  Thin, fine _______________(not collagen fibres visible)  Abundant chondrocytes in ______________ lacunae (small spaces = “little lakes”) surrounded by perichondrium  Ground substances is a resilient gel  Reduces friction and absorbs shock in joints Fibrocartilage  Many more collagen fibers causes rigidity and stiffness  Chondrocytes scattered among clearly visible, thick bundles of collagen fibers  ____________ Lacks perichondrium  Is the strongest type of cartilage  E.g., intervertebral discs Cartilage lacuna containing chondrocyte Fibrous cartilage Elastic Cartilage  Chondrocytes are located within a threadlike matrix of ______________ elastic fibres  The perichondrium is present  Provides shape and elasticity → maintains shape after deformations  Found in ear, nose, vocal cartilages, epiglottis Bone tissue  ____________ Mineralized extracellular matrix  Calcium and phosphate → hardness  Interwoven collagen fibers → strength  Lacunae contain _____________ osteocytes (mature bone cells)  Can be classified as compact or spongy, depending on the __________________ arrangement of cells and matrix **contains-concentric circles Liquid connective tissue  _________ Liquid extracellular matrix  Two types of liquid connective tissue  Blood  Lymph Blood  Connective tissue with a liquid matrix (i.e., blood plasma)  Cell types include  Erythrocytes (red blood cells)  Leukocytes (white blood cells)  Platelets (cells fragments)  Found within blood vessels and heart chambers  Functions include clotting, immune functions, transport of O2, and CO2, nutrients and wastes Membranes Membranes  Membranes are flat sheets of pliable tissue that cover or line a part of the body  Types of Membranes  Epithelial membranes consist of an epithelial layer and an __________________________________tissue underlying layer  Mucous membranes  Serous membranes  Cutaneous membranes  __________________________line Synovial joints  Contain connective tissue but no epithelium Mucous Membranes  Mucous membranes (i.e., mucosa) consists of epithelium over a layer of ______________connective areolar tissue  Line body cavities that open directly onto the exterior (outside) of the body  Digestive, reproductive, respiratory, and most of the urinary tract  The epithelial layer acts as a barriers to microbes  Connected by ____________ tight junctions  Goblet cells secrete mucus onto the surface, preventing it from drying out  Also lubricates and traps pathogens  Epithelium is underlined with areolar connective tissue (lamina propria) Serous Membranes  Lines body cavities that do NOT open to the exterior  E.g. Abdominal and thoracic cavities  Consist of _________ parietal and ____________ visceral layers, with _____________in serous fluid between  Pleura covers the lungs, pericardium covers the heart, and the peritoneum covers the visceral organs  Membrane layers consists of mesothelium (simple squamous epithelium) underlined with areolar connective tissue  Cutaneous membranes  Cutaneous membranes (i.e., the skin) covers the body surface  Consists of:  _________________: Epidermis keratinized stratified squamous epithelium  ____________: Dermis areolar and irregular dense connective tissue Chapter 5 Synovial Membranes  Synovial Membranes line the joint ____________ cavities of all moveable joints  Contains connective tissue, but no epithelium (no epithelial cells)  Discontinuous layer of cells called synoviocytes  Produce synovial fluid (to lubricate joints) Muscular and Nervous Tissues Muscular Tissue  Consists of long cells called _______________________ muscle fibres  Each cell contains many contractile proteins composed of actin and _____________ myosin  Use ATP to create force and movement → motion, posture, and heat  3 types of muscle tissue 1. __________muscle Skeletal tissue – attaches to bones with tendons to promote voluntary movement 2. ___________ Cardiac muscle tissue – branched, interconnecting at specialized junctions for rapid delay *relay 3. _________muscle Smooth tissue – contracts slowly; involuntary control; found in internal organs Skeletal Muscle  Consists of long, cylindrical, striated fibers (cells)  Cells are ______ long and ___________ cylindrical with many peripheral ___________ nuclei  Has visible light and dark banding  Responsible for voluntary contraction/relaxation Chapter 10  Attached to bones by tendons  Functions: motion, posture, heat production, protection Skeletal muscle Longitudinal section Cross-section Cardiac Muscle  Forms most of the wall of the heart → pumps blood to all parts of the body  Cells are _________ branched striated cylinders with ______ one central nucleus  Cells are attached together and communicate with each other by intercalated discs (thickenings of plasma membrane that contain gap junctions and desmosomes) Chapter 20 Smooth Muscle  Spindle-shaped cells with a single central nucleus  Lack striations (smooth)  Cells are often connected by gap junctions. Why?  Found in walls of hollow organs (blood vessels, GI tract, bladder, etc.)  Involuntary contraction/relaxation Nervous Tissue  Two main cell types  __________ Neurons – functions cells of the nervous system that conduct electrical impulses  Composed of: Dendrites – receives information and conducts signals towards the cell body Cell body – contains the nucleus Axons – conducts signals away from the cell body  ______________cells Neuroglial – supportive cells  Insulate axons for faster conduction, nourish, and regulate neuronal function