INTRODUCTION TO CELLS

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INTRODUCTION TO CELLS TISSUESByVijay Kapal
Graduate Studies Course CMM 5001 The Pathological
Basis Of Disease
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Fertilization
Fertilization of egg by the sperm Egg
Sperm (23 Chromo) (23
Chromo) Fertilized egg (Zygote)
(46 Chromosomes) Human body
Sperm
Ovum (Egg) Sperm
Zygote
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Implantation
Zygote
Blastocyst
Uterus Uterine glands Maternal blood vessels
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3-layered Flat Embryo
Ectoderm (1) Mesoderm (3) Endoderm (2)
Fertilized egg or Zygote (Single cell) 3-layers
of cells All Tissues Organs of Human body
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Human Genome
Nucleus Cytoplasm Cell membrane
Cell
Each cell has 46 chromosomes Form 23 homologous
pairs Each parent contributes 23 Autosomes
44 Sex chromosomes 2 (Male XY, Female XX)
Chromosomes (2N 46)
Each autosome of a homologous pair look alike But
each sex chromosome do not look alike
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Cell Cycle
Paclitaxel Vincristine Vinblastine Colchicine
Nondividing cells (Fixed postmitotics)
M
Resting cells (Reverting postmitotics)
G0
G1
G2
Bleomycin Etoposide
S
Methotrexate
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Mitosis Meiosis
A Homologous Pair (2 Chromosomes)
1 2 46
1 pair 23 pair
1st Division
2nd Division
Daughter Somatic Cells (2) Gametes (4)
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Meiosis
Takes place only in testes and ovaries Is a
reductional division Main purpose is to reduce
the number of chromosomes from 2N to 1N in sperms
eggs (Chromosomes of each homologous pair will
separate from each other) Homologous pair 1
chromosome from each parent (at fertilization) 2N
46 chromosomes (2 sets) 1N 23 chromosomes
(1set) So Sperm 1N chromosomes (23) Egg
1N chromosomes (23) Fertilization restores
chromosome number again to 2N 46 chromosomes (2
sets)
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Human Body
Cells Tissues Organs Human body
Cell
Tissue
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Cell Organelles

• Nucleus Chomatin, Transcription
• Rough ER Protein synthesis Segregation
• Smooth ER Fat Steroid synthesis
  Detoxification
• Golgi Complex Concentrating, Modifying
  Packaging of secretory products
• Lysosomes Intracellular digestion
• Peroxisomes Contain oxidative enzymes Use
  catalase to degrade H2O2 H2O O2
• Mitochondria Oxydative phosphorylation ATP
  production
• Cell Membrane Lipid bilayer layer with
  intramembranous proteins
• Cell cytoskeleton Actin filaments, Microtubules,
  intermediate filaments

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Cell Organelles
Mitochondria Lysozome Golgi Nucleus Rough ER
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Cells, Tissues Various Topics Of Research

• Subcellular localisation trafficking of
  molecules and oganelles
• Cell-cell and cell-extracellular matrix
  interactions
• Cell cytoskeleton and receptor dynamics and
  functions
• Cell and tissue differentiation and remodelling
• Genetically engineered cells and tissues
• Three-dimensional reconstructions, particularly
  of expression patterns over time
• Cell cycle and cell lineage analysis involving
  gene expression profiles
• Apoptosis
• Gene expression analysis from histological
  preparations
• Functional genomics proteomics
• Techniques used in molecular histology

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Epithelial Tissue
Outer layer of skin Inner lining of
trachea Inner lining of ducts of sweat glands
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General Features

• Diversity
• Metaplasia
• Lining and Covering
• Basal Lamina
• Renewal
• Avascularity
• Cell Packing
• Derivation

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Classifying Principles

• 1. Number of cell layers
• 1. Simple epithelia
• 2. Stratified epithelia
• 3. Pseudostratified epithelia
• 2. Shape of the surface cells
• 1. Squamous cells
• 2. Cuboidal cells
• 3. Columnar cells
• 3. Luminal surface modifications
• 1. Microvilli (Brush border)
• 2. Cilia
• 3. Stereocilia

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Specific Epithelial Types

• Simple squamous epithelium
• Simple cuboidal epithelium
• Simple columnar epithelium
• Pseudostratified epithelium
• Stratified Squamous epithelium
• a) Keratinized
• b) Nonkeratinized
• Stratified cuboidal epithelium
• Stratified columnar epithelium
• Transitional epithelium

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Types of Epithelia
Simple squamous Stratified squamous
Transitional
Simple cuboidal stratified cuboidal
Full Empty Bladder
Simple columnar Pseudostratified
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Kidney (Epithelium)
Simple squamous Simple cuboidal
Kidney Tubules
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Small Intestine (Simple Columnar)
Absorptive cells Nucleus Brush border Lamina
propria Lumen of gut
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Esophagus (Stratified Squamous)
Epithelium Lamina propria
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Skin (Stratified Squamous)
Epidermis (Epithelium) Dermis (Connective
tissue)
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Trachea (Pseudostratified Epithelium)
Epithelium Cilia Ciliated cells Goblet
cells Basal lamina Lamina propria
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Ureter (Transitional Epithelium)
Epithelium Lumen Basal lamina Lamina propria
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Basal Lamina

• Next to epithelia an acellular sheet like
  structure is the Basal Lamina.
• Component Layers Constinuent Macromolecules
• A. Component Layers
• Lamina lucida
• Lamina densa
• B. Constituent Macromolecules
• Lamina lucida (Laminin that binds to cell
  surface integrins, collagen IV)
• Lamina densa (Type IV Collagen)
• Basement Membrane
• Basal lamina accompanied by reticular lamina
  (Type III Collagen) is called the basement
  membrane.
• Functions
• Forms sieve-like selective barrier between the
  epithelia connective tissue.
• Aids in cell organization, cell adhesion
  maintainence of cell shape.
• Has a role in maintaining specific cell
  function.
• Helps guide migrations of cells during
  development and regeneration of injured tissue

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Polarity Specialization of Epithelial Cells

• Specialization of the Apical Surface
• 1. Microvilli (Enterocytes Proximal convoluted
  tubule cells))
• 2. Cilia (Trachea, Bronchus etc.)
• 3. Stereocilia (Epididymis)
• 4. Flagella
• Specialization of the Lateral Surfaces
• 1. Zonula occludens (Tight junctions)
• 2. Zonula adherens (Intermediate junctions)
• 3. Macula adherens (Desmosomes)
• 4. Gap junction (Nexus)
• Specialization of the Basal Surface
• 1. Basal lamina
• 2. Hemidesmosome
• 3. Sodium-potassium ATPase
• D. Intracellular Polarity

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Cell Junctions
Microvilli Zonula occludens Zonula
adherens Terminal web Macula adherens Gap
junction Nucleus Hemidesmosome
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Mucous Membranes

• Components of Mucous Membrane
• 1. Epithelium
• 2. Basement membrane
• 3. Lamina propria

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Mucous Membrane
Epithelium Basal lamina Lamina propria
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Serous Membranes

• Components of Serous Membrane
• 1. Epithelium called mesothelium
• 2. Basement membrane
• 3. Submesothelial connective tissue layer

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Functions of Epithelia

• 1. Protection from
• Mechanical trauma
• Dehydration
• Pathogens
• Secretion of
• Hormones, milk, sweat etc.
• Enzymes, HCl, glycoproteins,
• Mucous serous products
• Lubrication of
• Contents of GI tract
• Fetus in birth canal
• Joints
• 4. Filtration of wastes (Urine)
• Absorption of food (Aminoacids, Glucose, Fatty
  acids)
• Neuroepithelium (Taste, Smell, Hearing)
• Reproduction (Germ cells)

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Major Types of Epithelial Cells

• Epithelial Cells Specialized for Transport
• 1. Ion-transporting cells (Kidney tubules, Gall
  bladder etc.)
• 2. Cells that transport by pinocytosis
  (Endothelial cells of blood capillaries
• Absorption (Enterocytes, Proximal convoluted
  tubule cells)
• Secretion
• 1. Protein-secreting cells (Acinar cells of
  pancreas, Hepatocytes)
• 2. Polypeptide-secreting cells (APUD cells)
• 3. Mucous cells (Goblet cells)
• 4. Serous cells (Acinar cells of pancreas
  secretory cells of parotid salivary glands.
• 5. Steroid-secreting cells (Adrenal cortex,
  Leydig cells etc.)
• D. Contractile Epithelial Cells (Myoepithelial
  cells of glands)

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GLANDS

• Exocrine Endocrine Glands
• Classification of Exocrine Glands
• 1. By structure
• a) Number of cells
• b) Duct system
• c) Secretory portion
• 2. By secretory product
• a) Mucous secretion
• b) Serous secretion
• c) Seromucous secretion
• 3. By mode of secretion
• a) Merocrine
• b) Apocrine
• c) Holocrine

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Unicellular Multicellular Simple tubular
Coiled tubular Branched
Simple branched Simple acinar Compound
tubular
Compound tubulo-alveolar
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Salivary Glands
Mucous acini Serous acini
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Mode of Secretion
Active transport Merocrine Apocrine
Holocrine Endocrine
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Connective Tissue
Fat Fat cells Tanden Fibroblasts Bone Osteocyt
es
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Connective Tissue

• Is one of the 4 basic tissues of the body.
• Structurally it is made up of cells and large
  amount of intercellular space containing
  extracellular matrix.
• Matrix is the dominating component of this
  tissue.
• It forms framework, connecting, supporting and
  packing tissue of the body.
• It also plays a dynamic role in the development,
  growth and homeostasis of other tissue types.

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Connective Tissue
Loose connective tissue Dense connective tissue
Fibroblasts Extracellular matrix
Epithelial tissue
Mammary Glands
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Composition

• Cells
• Extracellular matrix

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Types of Cells in Loose Connective Tissue

• Residents
• Fibroblasts
• Macrophages
• Reticular cells
• Mesenchymal cells
• Visitants
• Mast cells
• Plasma cells
• Leukocytes
• Fat cells
• Melanocytes

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Loose Connective Tissue
Elastic fibers Capillary Neutrophil Plasma
cell Fibroblast Collagen fibers
Macrophage Adipocyte Mast cell Lymphocyte
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Fibroblast (Ultrastructure)
Nucleus Rough ER Collagen Extracellular
matrix
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Collagen Producing Cells

1. Fibroblast-More than one type of collagen
2. Chondroblast- Type II collagen
3. Osteoblast-Type I
4. Reticular cell- Type III
5. Smooth muscle-Type I III

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Extracellular Matrix

• Extracellular matrix (Fibers Ground substance)
  is synthesized and secreted mainly by the
  fibroblasts the fibers are assembled in the
  extracellular space.
• Fibers
• Prime function is support plays strengthing
  role in
• Ground substance
• Functions are
• 1. Acts as a molecular sieve stops the spread
  of noxious substances
• 2. Plays very important role in cellular
  nutrition waste removal
• 3. Plays a vital role in aging. Its amount
  diminishes with age and wrinkles start
  appearing.

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Fiberous Components

• Connective tissue fibers are long, slender
  protein polymers
• that are present in variable proportions in
  different types of
• connective tissue.
• In many cases the predominant fiber type is
  responsible for
• conferring specific properties on the tissue.
• Collagen Fibers
• Elastic Fibers
• Reticular Fibers

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Collagen Fibers

• Collagen Fibers
• Most abundant protein in the body.
• Synthesis assembly
• Collagen types-
• Type I- most abundant occurs in loose and
  dense connective tissue bone.
• Type II- occurs in cartilage.
• Type III- occurs in hematopoitic tissues.
• Type IV- occurs in basal laminae does not form
  fibers or fibrils.
• Type V- in placental basement membranes blood
  vessels.
• Type X- around hypertrophic, degenerating
  chondrocytes of the growth plate where bone
  formation is to occur.

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Synthesis of Collagen
Collagens main amino acids
Glycine (34) Proline (12) Hydroxyproline (10)

• Fibroblast
• Procollagen (Triple-helical units)
• Procollagen peptidase
• Tropocollagen
• Collagen fibril
• Collagen fiber

Intracellular
Extracellular
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Ground Substance

• Proteoglycans
• They are made up of a core protein to which
  glycosoaminoglycans (GAGs) are attached. GAGs are
  polysacharides that contain aminosugars.
• GAGs-Chondroitin sulphate, Dermatan sulphate,
  Keratan sulphate Heparin sulphate.
• Hyaluronic acid is a GAG but do not form
  proteoglycans.
• Matrix viscosity and rigidity are determined by
  the amount and types of GAGs, their association
  with the core protein to form proteoglycans,
  GAG-fiber association, and GAG-GAG associations.
• Glycoproteins
• Fibronectin-mediates the attachment of cells to
  the extracellular matrix.
• Laminin-a component of basal laminae that
  mediates the attachment of epithelial cells.
• Tissue fluids
• Salts

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Connective Tissue Types

• A. Connective Tissue Proper
• 1. Loose connective tissue
• 2. Dense connective tissue
• a) Dense regular connective tissue
• b) Dense irregular connective tissue
• Reticular connective tissue
• Elastic connective tissue
• Mucous connective tissue

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Connective Tissue Proper

• A. Connective Tissue Proper
• 1. Loose connective tissue (lamina propria)
• 2. Dense connective tissue
• a) Dense regular connective tissue (Tendon,
  ligament)
• b) Dense irregular connective tissue (Dermis,
  organ capsule)

Loose CT Dense CT
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Elastic Connective tissue

• Elastic fibers consist of an amorphous protein
  called elastin and numerous protein microfibrils
  embedded in it.
• Diameter range 0.1-10um.
• Elastic fibers are collected in thick, wavy,
  parallel bundles seperated by loose collagenous
  tissue with fibroblasts.
• Ground substance is sparse.
• Elastic connective tissue provides flexible
  support.
• Predominates in the ligamentum flava of the
  vertebral column the suspensory ligament of the
  penis.

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Reticular Connective Tissue

• These fibers look very similar to collagen but
  are thinner than them (0.1-1.5um).
• More highly glycosylated.
• Form delicate silver-staining network instead of
  thick bundles.
• Composed mainly of type III collagen and some
  glycoprotein.
• These fibers are covered by long processes of
  the reticular cells.
• There is very little ground substance.
• Reticular connective tissue supports motile
  cells filters body fluids.
• It is found mainly in hematopoietic tissue (bone
  marrow, spleen and lymph nodes).

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Reticular Connective Tissue
Reticular cell Nu
Reticular fibers Lymphocyte
Reticular cells
Lymph Node
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Mesenchyme

• Mesenchyme is embryonic connective tissue.
• Its stellate and fusiform cells (mesenchymal
• cells) are derived from mesoderm.
• They give rise to all the connective tissue of
• of the body.
• These are multipotential cells and persist in
• adults to give rise to new generations of
  connective
• tissue cells especially during wound healing,
  bone
• repair and tissue fibrosis.

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Mesenchymal Tissue (Embryo)
Neural tube Mesenchyme Somite Notochord
Neural tube Extracellular matrix Mesenchymal cells
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Histophysiology

• A. Functions
• 1. Support.
• 2. Defense.
• a) Physical
• b) Immunologic
• 3. Repair.
• 4. Storage.
• 5. Transport
• Edema
• Hormonal Effects
• Nutritional Factors
• Collagen Renewal

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Special Types of Connective Tissues

• Adipose tissue
• Blood lymph
• Cartilage
• Bone

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Blood
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White Blood Cells (Granulocytes)
Neutrophil Eosinophil Basophils
Functions- Neutrophils act as first line of
defense in infections. Eosinophils respond to
allergic states parasitic infection Basophils
release heparin histamine
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Defense System
ADAPTIVE DEFENSES (Requires immunization)
INNATE DEFENSES (Do not require
immunization)
Physical barriers Chemical barriers Soluble
factors
(Skin, mucous membranes)
Directly kill infected cells T lymphocytes B
lymphocytes
(Low pH, Mucous)
Cytotoxic
(Lysosomes, Interferons,
Acute phase proteins,
Complements)
Help
Facilitates
CELLS (Macrophages,
Granulocytes)
ANTIBODIES
Facilitate
Delayed response Highly flexible Highly
specific Memory, lasting immunity
Fast response Limited Flexibility Non-specific No
memory
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Mast Cells
Mast cells
Functions- Produce heparin, an
anticoagulant Produce histamine to render blood
vessels permeable
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Monocytes
Nucleus Cytoplasm Phagocytized RBC Nucleus
Nucleus Cytoplasm RBC
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LYMPHOCYTES
B Lymphocytes deliver antibodies-mediated immune
response T lymphocytes deliver cell-mediated
immune response Natural killer cells kill tumor
nonself cells
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Plasma Cells
Plasma cells
Lymphocyte
Plasma cells produce antibodies to fight the
infections Immunoglobulins IgG, IgA, IgM, IgE
IgD
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Macrophage
Macrophage
Functions- Phagocytose, process present
antigens to lymphocytes Act as scavengers etc.
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Unilocular Adipose Tissue
Adipocytes Nucleus
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Multilocular Adipose Tissue
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Cartilage
Perichondrium Chondroblasts Chondrocytes Lacuna Ca
rtilage matrix Isogenous group of chondrocytes
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Primary Bone
Periosteum Osteoblasts Osteocytes Bone
matrix Bone trabecula
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Nervous Tissue
Cerebellum Cortical neurons Spinal cord Motor
neurons Spinal ganglion Sensory neurons
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Divisions of the Nervous System

• Central Nervous System (CNS)
• Peripheral Nervous System (PNS)
• Autonomic Nervous System (ANS)

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Nervous System
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General Features

• Two Classes of Cells
• 1. Neurons
• 2. Supporting cells
• Impulse Conduction
• Synapses
• Divisions of the Nervous System
• Embryonic Development of Nervous Tissue
• Aging and Repair
• Meninges
• Blood-Brain barrier

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Cells of the Nervous Tissue

• Two Classes of Cells
• 1. Neurons.
• 2. Supporting, neuroglial or glial cells.

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Neurons

• Cell Body
• Dendrites
• Axon
• Classification of Neurons

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Neuron
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Neuromuscular Junction
Skeletal muscles Motor end plate
Axon
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Neuron
Blood capillary Glial cells Dendrites Nissl
bodies Axon hillock Nucleus Nucleolus Myelinated
axons
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Neuron (Cell body)

• Cell Body
• -It is also called soma or perikaryon
• -It is the synthetic trophic center of cell
  
• -It can receive signals from axons of other
• neurons through synaptic contacts on its
• cell membrane and relay them to its axon
• -Nucleus usually large, central, spherical
• and euchromatic
• -Nucleus with prominent nucleolus
• -Cytoplasm contains many organelles like
• mitochondia, lysosomes etc.
• -Cytoplasm has abundant free polyribosomes
• rough endoplasmic reticulum, appears
• as basophilic purplish-blue clumps called
• Nissl bodies
• -Well developed Golgi to pack often
  glycosylates
• neurotransmitters in neurosecretory, or
  synaptic vesicles
• -Abundant neurotubules (microtubules)
  neurofilaments
• (intermediate filaments) in soma, dendrites
  axon

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Neuron (Dendrites)

• Dendrites
• -Extensions of cell body, specialized to
• increase the surface area for incoming
• signals
• -Synaptic contacts are made on them
• -Some synaptic sites on them look like
• sharp projections called dendritic spines
• gemmules
• -Proximal ends has some Nissl bodies

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Neuron (Axon)

• Axon
• -One axon per neuron, its cytoplasm called
  axoplasm its plasma
• membrane, the axolemma.
• -A complex cell process (uniform diameter)
  carries impulses away
• from the soma.
• -The part of the cell body where axon exits the
  soma is called the axon
• hillock and it lacks Nissl bodies.
• -Axon can be myelinated or unmyelinated.
• -Myelin sheath in CNS is provided by the
  oligodendrocyte , while in
• PNS by the Schwann cell
• -Axon diameter myelin thickness determines the
  speed of nerve
• impulse. Internode (Myelin covered) Node
  (without myelin)
  -Some axons have branches called collaterals.
• -Terminal branching of axon is called terminal
  arborization.
• -Each branch ends as a bulb-like sac called
  terminal bouton,
• each bouton contains many mitochondria
  neurosecretory vesicles.
• Specialized region of plasma membrane of
  bouton that take part in
• the formation of synapse is called as
  presynaptic membrane.

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Nerve (Myelinated axons)
Perineurium Endoneurium Nodes of
Ranvier Axon Myelin Axon
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Myelinated Axon (E.M.)
Neurilemma Myelin Axoplasm
Node of Ranvier
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Synapses (Chemical)

• Synapses are specialized junctions by which a
  stimulus is transmitted from a neuron to its
  target cell.
• 1. Presynaptic Membrane
• This is part of plasma membrane of terminal
  bouton.
• 2. Synaptic Cleft
• Fluid-filled space between pre and post
  synaptic membranes.
• 3. Postsynaptic Membrane
• This is part of plasma membrane of the target
  cell. It is thicker
• than presynaptic membrane due to the presence
  of receptors for
• neurotransmitters. When enough receptors are
  occupied,
• hydrophilic channels open, resulting in
  depolarization of the
• postsynaptic membrane. Neurontransmitter like
  acetylcholine
• that remains in the synaptic cleft is degraded
  by acetylcholinesterase.
• This removal of extra acetylcholine allows
  postsynaptic mambrane to reestablish its resting
  potential and prevents continuous firing of the
  postsynaptic neuron in response to a single
  stimulus.

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Types of Synapses

• Axodendritic (Between an axon a dendrite)
• Axosomatic (Between an axon a cell body)
• Dendrodendritic (Between dendrites)
• Axoaxonic (Between axons)

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Neuron (Types)

• Based upon Configuration of cell processeses
• Multipolar (Motor neurons of spinal cord)
• Bipolar (Retina, olfactry mucosa)
• Unipolar (Photoreceptors, rods cones of
  retina)
• Pseudounipolar (Sensory neurons of dorsal root
  ganglia)
• Based upon Cell size
• Golgi type I (Motor neurons of spinal cord)
• Golgi type II (Interneurons of spinal cord)
• Based upon Function
• Motor neurons (Multipolar neurons of ventral
  horn etc.)
• Sensory neurons (Pseudounipolar neurons of
  dorsal root ganglia)
• Interneurons (Golgi type II neurons)
• Based upon Neurotransmitter released
• Cholinergic neurons (Most somatic motor neurons)
• Adrenergic noradrenergic neurons
  (Postganglionic sympathatic neurons)
• Dopaminergic (Some neurons of hypothalamus)
• GABAergic (Some neurons of the brain)

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Types of Neurons
Unipolar Bipolar
Pseudounipolar Multipolar
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Supporting Cells

• Provide structural and functional support to
  neurons.
• Take part in the formation of blood-brain
  barrier, thus monitoring the passage of materials
  from blood to neurons.

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Supporting cells of CNS

• 1. Astrocytes- (Blood-Brain Barrier)
• a) Protoplasmic astrocytes
• b) Fibrous astrocytes
• Oligodendrocytes- (Myelin to axons in CNS)
• Ependymal cells- (Produce the CSF)
• Microglial cells- (Macrophages of the nervous
  system)

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Supporting Cells of PNS

• Schwann cells
• A Schwann cell may envelop segments of several
  unmyelinated axons or provide a segment of a
  single myelinated axon with its myelin sheath.
  Each mylinated axon segment (internode) is
  wrapped around by layers of a Schwann cell
  process with most of its cytoplasm squeezed out.
  This multilayered Schwann cell plasma membrane
  (mainly of phospholipids) is called myelin. The
  gaps between myelin sheath segments are the nodes
  of Ranvier.
• Satellite cells
• Each neuron outside the CNS is surrounded by a
  single layer of cells, called satellite cells.

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Aging and Repair

• A neuron is a terminally differentiated cell.
• And is incapable of undergoing mitosis.
• Aging neurons accumulate more of lipofuscin
  pigment.
• Neurons lost through injury or surgery cannot be
  replaced.
• If the cell body remains intact, the injured axon
  can regenerate itself.
• If stimulated by injury, supporting cells, unlike
  neurons, can divide.

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Blood-Brain Barrier

• Components of the barrier
• 1. Endothelial cells of continuous type
  capillaries (Tight junctions)
• 2. Basal lamina
• 3. Cytoplasmic processes of astrocytes.

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Blood-brain Barrier
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Peripheral nerve
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Peripheral Nerve (Fascicle)
Perineurium Endoneurium Myelinated axons
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Response of Nerve Tissue to Injury

• Damage to the Cell Body
• A neuron is a terminally differentiated cell
  is unable to divide. So damaged or dead neurons
  cant be replaced.
• B. Damage to the Axon
• 1. Degenaration- Distal to the site of
  injury, axon myelin degenerate. Within 2-3
  days, they are removed these clear endoneurial
  channels are occupied by Schwann cells. Proximal
  to the site of injury, retrograde degeneration
  of axon goes up to 2 internodes, then injured
  axon is sealed. Cell body also undergoes
  changes in response to the injury. The Nissl
  bodies disappear (chromatolysis) nucleus moves
  to the periphery. (2 Weeks)
• 2. Regeneration- Begins at 3rd week, Nissl
  bodies reappear, protein synthesis starts.
  Axons proximal stump gives off a number of
  small processes called neurites. One of these
  enters and grows in an endoneurial channel and
  synaptic contacts are remade with the target
  cell. The target cell or organ deprived of
  innervation often atrophy.

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Nerve Injury Recovery
A B C
D E
Cell body Nissl bodies Axon Schwann
cells Motor end plate Muscle
Before injury 2 weeks 3 weeks
3 months No healing
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Muscle Tissue
Cardiac muscle Skeletal muscle Visceral
muscle
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Basic Properties of Muscle Tissue

1. Excitability- ability to respond to a stimulus
2. Conductivity- ability to propagate a limited
   response
3. Contractility- ability to shorten
4. Relaxability- ability to relax (return to
   original shape after contraction)

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IC Disc
Nucleus
Cardiomyocyte in Longitudinal Section
Endomysium
Capillary
Nucleus
Myofibrils
Cardiomyocyte
Purkinje Cell
In Cross Section
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Smooth Muscle
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Skeletal Muscle
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Cardiomyocyte (Long. Section)
Endomysium Cardiomyocytes Nucleus
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Cardiomyocytes (Cross section)
Cardiomyocytes Nucleus Myofibrils Endomysium Capil
laries
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Comparison Of Types Of Muscles
Property Skeletal Muscle Cardiac
Muscle Smooth Muscle
Location Cell size/shape Nuclei Striations
Z lines T tubules Sarcoplasmic reticulum
Cell junctions
Muscles of skeleton Long cylindrical Many
peripherally located Yes
Yes Triads at A-I junctions None
Heart Short, branched Single centrally
located Yes Yes Diads at Z
line Intercalated disks
(Adherens, occludens nexi)
Visceral organs Variable, fusiform Single
central No
Dense bodies Caveolae replace T
tubules sparse Nexi (Gapjunctions)
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EM of Cardiac muscle (IC disc)
Macula adherens
Gap junction
Fascia adherens
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EM of Skeletal muscle
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