This document provides information about the four basic types of tissues in the body: epithelial, connective, muscle, and nervous tissue. It focuses primarily on epithelial tissue, describing the classification, functions, characteristics, and examples of different epithelial tissues like squamous, cuboidal, columnar, transitional, and glandular epithelium. In 3 sentences: The document defines tissue and describes the four basic types. It focuses on epithelial tissue, classifying it based on cell shape and layers, and describing the structure, location and functions of different epithelial tissues like squamous, cuboidal, columnar, and glandular epithelium. The document provides an overview of the key epithelial tissues in the body.

1. Tissues
Presented By :
Dr. Dushyantsinh Vala
Guided By :
Dr. Rajat V
Dr. Neha Gandhi
Dr. Vinayak Mantu
1

2. • Perichondrium separates cartilage from surrounding tissues
Functions:
• It supports soft tissues, coz it is smooth surface and resilient.
• Acts as a shock absorber and sliding area for joints and
facilitates bone movements.
2

3. Contents
• Introduction & definition ………………………………………..
• Epithelial Tissue ………………………………………………………
Origin…………………………………………………………………............
Function………………………………………………………………………
Special Characteristics of epi………………………………….......
• Classification ………………………………………………………….
Simple Squamous epi………………………….……………………..
Simple Cuboidal epi………………………………………………………
Simple Columnar epi……………………………………………….......
Pseudostratified Ciliated ………………………………………………
Stratified Cuboidal …………………………………………………….…
Stratified Columnar……………………………………………………...
Transitional Epithelium…………………………………………………
Glandular Epithelium ……………………………………………….....
Exocrine Gland………………………………………………..……
Endocrine Gland…………………………………..………………
Specialized Epithelium………………………………………………..… 3

4. • Connective Tissue…………………………………………………….
Classification………………………………………………………………
Origin……………………………………………………………………..…
Connective tissue proper………………………………………....
Adipose Tissue………………………………………………………....
Reticular Connective Tissue……………………………………...
Dense Connective Tissue………………….………………………
Dense Regular CT………………………………………….…
Dense Irregular CT………………………………………....
Cartilage………………………………………………………….
Hyaline Cartilage……………………………………………
Elastic Cartilage………………………………………..……
Fibro Cartilage………………………………………………..
Bone……………………………………………………………….…
Blood………………………………………………………………...
Function………………………………………………………….
Composition……………………………………………………
4

5. • Muscle Tissue…………………………………………………..
Skeletal Muscle ………………………………………………….
Cardiac Muscle……………………………………………………
Smooth Muscle…………………………………………………..
• Nervous Tissue…..…………………………………………….
Function……………………………………………………………..
Histology of Nervous Tissue………………………………..
• Reference…………………………………………………….…..
5

6. • Introduction & Definition:
Tissue can be defined as a group of
closely associated cells that perform related functions
and are similar in structure.
• Between cells: Nonliving extracellular material
• Four basic types of tissue…function
1) Epithelium…covering
2) Connective tissue…support
3) Muscle tissue…movement
4) Nervous tissue…control
6

7. EpithElial tissuE
• Epithelium: The outer surface of the body & the luminal
surfaces of cavities within the body are lined by one or more
layers of cells that completely cover them. Such layers of
cells are called epithelial tissue.
• Roles: as interfaces and as boundaries
7

8. ORIGIN OF EPITHELIUM
• Fertilized ovum or zygote undergoes a series of divizon that
leads to the development of a solid spherical mass of cells
termed Morula.
8

9. • When continuing mitosis
cause the morula to enlarge,
it develops the central cavity
and becomes a hollow sphere
called as Blastocyst.
• At this stage implantation in
uterine wall occurs.
Trophoblast
Inner Cell Mass
9

10. • Prior to implantation blastocyst develops an inner cell mass
that will give rise to embryo and a thin outer shell of cells
called as Trophoblast. That contribute to the placenta.
• The inner cell mass or embryoblast forms embryo proper.
• Embryoblast differentiates into two layered germ disc -
ectoderm and endoderm.
10

11. • Amniotic cavity appears between ectodermal cells and
overlying trophoblast.
• Secondary yolk sac appears below endodermal cells.
• A small enlargement of ectoderm and endoderm cells is
seen at one circular area near the margin of disc, this area is
known as prochordal plate
11

12. •Some ectodermal cells along the central axis near the tail end of
the disc proliferate to form an elevation called primitive streak
that bulges into amniotic cavity.
•The cells of ectoderm along primitive streak start proliferating
and pass between the ectodermal and endodermal layers to form
mesoderm.
12

13. • Stage of formation of trilaminar emryonic disk which is made
up of three germ layers and process is known as Gastrulation.
13

14. 14

15. Functions of Epithelial Tissue
• Protection
• Epithelial cells from the skin protect underlying tissue from
mechanical injury, harmful chemicals, invading bacteria and
from excessive loss of water.
• Sensation
• Sensory stimuli penetrate specialized epithelial cells.
Specialized epithelial tissue containing sensory nerve endings
is found in the skin, eyes, ears, nose and on the tongue.
• Secretion
• In glands, epithelial tissue is specialized to secrete specific
chemical substances such as enzymes, hormones and
lubricating fluids. 15

16. • Absorption
• Certain epithelial cells lining the small intestine absorb
nutrients from the digestion of food.
• Excretion
• Epithelial tissues in the kidney excrete waste products from
the body and reabsorb needed materials from the urine.
Sweat is also excreted from the body by epithelial cells in the
sweat glands.
• Diffusion
• Simple epithelium promotes the diffusion of gases, liquids and
nutrients. Because they form such a thin lining, they are ideal
for the diffusion of gases (eg. walls of capillaries and lungs).
16

17. • Cleaning
• Ciliated epithelium assists in removing dust particles and
foreign bodies which have entered the air passages.
• Reduces Friction
• The smooth, tightly-interlocking, epithelial cells that line the
entire circulatory system reduce friction between the blood
and the walls of the blood vessels.
17

18. Special characteristics of epithelia
• Cellularity
• Specialized contacts
• Polarity
– Free upper (apical) surface
– Lower (basal) surface contributing basal lamina to
basement membrane
• Support by connective tissue
• Avascular but innervated
– Without vessels
– With nerve endings
• Regeneration
18

19. Classification of epithelia
19

20. Surface Epithelium
Epithelium
Simple (Unilayered / Unilaminar ) Stratified (Multilayered / Multilaminar))
Simple squamous Simple cuboidal fdfdfsfdgsgdSimple columnar Pseudostratified columnar
Transitional (Urothelium)Stratified cuboidalStratified columnarStratified squamous
Keratinized Nonkeratinized
20

21. Classification of epithelia
• According to thickness
– “simple” - one cell layer
– “stratified” – more than one layer of cells (which are
named according to the shape of the cells in the apical
layer)
21

22. • According to shape
– “squamous” – wider
than tall
– “cuboidal” – as tall
as wide
– “columnar” - taller
than wide
22

23. Simple Squamous Epithelium
• Cells are flattened, their height being very little as compared to
their width.
• Cytoplasm of cells forms only a thin layer ( 0.1µm )
• Nuclei produce bulging of cell surface
• Surface view: cells have polygonal or irregular wavy outline
23

24. • Location:
• lines serous membrane of body cavities ( pleura,
pericardium, peritoneum ) & surface of viscera -
mesothelium, lung alveoli, renal tubules, internal ear, blood
vessels, lymphatic – endothelium
• Functions :
• Simple squamous epithelial cells are well suit to facilitate
exchange (diffusion osmosis ) across the epithelium.
24

25. Simple Squamous Epithelium
25

26. Simple Cuboidal Epithelium
• Length & width of cells are nearly equal
• Nuclei – rounded
• Surface view: epithelium appear as hexagonal
polygons
• Vertical section: sheet of cells appear as a row of
square or rectangular
• Location:- Follicles of thyroid gland
- ducts of exocrine gland
- choronoid plexuses
- pigmented epithelium of retina
- with a prominent brush border – seen in
the proximal convoluted tubules of kidney
26

27. FUNCTION:-
• Simple cuboidal cells also facilitates exchange, but are more
involved in active mechanism that requires extensive
organelles and membrane system which necessitate greater
cell volume.
27

28. Simple Cuboidal Epithelium
28

29. Simple Columnar Epithelium
• Height of cells is much greater than their width
• Nuclei – oval, elongated & lie in lower half of cells
• Vertical section: cells appear tall, slender, standing upright like
columns or fence polling.
29

30. FUNCTION:-
• Principle function is to protect wet body surfaces.
• It is important for active mechanism of exchange where large
volume of organelles are required.
• Taller nature of columnar cells may also provide a greater
degree of protection
30

31. Types
Acc. to nature of free surface of cells
•1) Simple columnar epithelium: cell surface has no particular
specialization
e.g. mucous membrane of stomach & large intestine
•2) Ciliated columnar epithelium: cell surface bears cilia
e.g. most of the respiratory tract, uterus, uterine tube, parts of
middle ear & auditory tubes
•3) Cell surface is covered with microvilli visible with electron
microscope with light microscope region of microvilli is seen as a
striated border ( when microvilli are arranged regularly e.g. 31

32. Simple Columnar Epithelium
32

33. Pseudo-stratified Ciliated Epithelium
• All the cells are in contact with basement membrane but not
all of them reach the surface.
• Some have broad attachment at base, narrow rapidly &
extend upward through only a fraction of the thickness of
epithelium. Other extend throughout the thickness of
the epithelium, but are widest near the free surface.
• Since nucleus lie in widest portion of the cell, nuclei are
found aligned at two or more levels in this type of
epithelial giving a false
appearance of stratification , so it is called pseudostratified
columnar epithelium. 33

34. Location:-
• large excretory ducts of parotid and other glands
- some parts of auditory tube
- ciliated- trachea & bronchi
34

35. Pseudo-stratified Ciliated Epithelium
35

36. Stratified: Regenerate From Below
36

37. Stratified Cuboidal Epithelium
• Two or more layers of cell
- cells of superficial layers are cuboidal in shape
• Location:-seminiferous tubules
-ovarian follicles
-ducts of sweat glands & mammary gland
37

38. Stratified Cuboidal Epithelium
38

39. • Two or more layers of cells
- Deeper layer consists of small irregularly polyhedral cells
• Cells of superficial layer are prismatic columnar
• Location:- fornix of conjuctiva
- Cavernous urethra
- Pharynx, epiglottis, nasal surface of soft palate
Stratified Columnar Epithelium
39

40. Stratified Columnar Epithelium
40

41. Transitional Epithelium
Urothelium
• 5-6 layers of cells- varies greatly in appearance depending
upon the conditions under which it is fixed
• Found lining hollow organs which are subjected to great
changes due to contraction & distention
• In contracted condition: it consists of many cell layers, the
deepest cells are columnar or cuboidal, above there are several
layers of irregular polyhedral cells.
• Superficial layer consists of large cells with a characteristic
rounded free surface like an umbrella.
41

42. • In stretched condition: the interrelation of cells change to
accommodate to the distention of the organ & usually
• only two layers can be distinguished: a superficial layer of
large squamous cells over a layer of more or less cuboidal
cells.
• e.g. excretory passages of urinary system from the
renal calyces to the urethra
• With the E. M., cells are firmly connected to one another by
numerous desmosomes. So cell retain their relative
position when the epithelium is stretched.
42

43. • At the surface of epithelium, the plasma membrane are
embedded in the lipid layer of membrane, these are
glycoprotein.
• It is believed that these glycoproteins make the membrane
impervious & resistant to toxic effects of substance present
in urine.
( Urinary bladder H. & E. ) 43

44. Transitional Epithelium
44

45. 45

46. Endothelium
A simple squamous
epithelium that lines
the interior of the
circulatory vessels
and heart.
Mesothelium
Simple squamous
epithelium that lines the
peritoneal, pleural and
pericardial cavities and
covers the viscera.
46

47. Glandular EpitheliumGlandular Epithelium
• Some epithelial cells are specialized to perform secretory
function called glands
• may be
• 1) Unicellular:- Consists of a single cell distributed among
non secretory cells.
e.g. goblet cell
• 2) Multicellular:- Formed when the epithelial layer
invaginates in deeper tissue to form a
diverticulum
-Proximal part of diverticulae forms duct
while the distal part forms the secretory
units. 47

48. Exocrine glands
unicellular or multicellular
Unicellular: Goblet cell
scattered within epithelial
lining of intestines and
respiratory tubes.
Product: mucin
mucus is mucin & water
48

49. Multicellular exocrine glands
Epithelium walled : duct and a secretory unit
49

50. Examples of exocrine gland products:
• Many types of mucus secreting glands
• Sweat glands of skin
• Oil glands of skin(sabeceous glands)
• Salivary glands of mouth
• Liver (bile)
• Pancreas (digestive enzymes)
• Mammary glands (milk)
50

51. Endocrine glands
• Ductless glands
• Release hormones into extracellular space
– Hormones are messenger molecules
• Hormones enter blood and travel to specific target organs
51

52. Specialized EpitheliumSpecialized Epithelium
• Seminiferous Epithelium:
• Specialized tissue found in testis.
• Consist of a heterogeneous population of cells forming the
lineage of the spermatozoa together with supporting cells.
52

53. Oral Epithelium :
• Derived from Embryonic Ectoderm
• It is a stratified squamous epithelium
• Depending on the location & functional requirements has a
layer that is keratinised, non-keratinised or parakeratinised.
• Maintains its structural integrity by a process of continuous
cell renewal in which cells produced by mitotic divisions in the
deepest layers, migrate to the surface to replace those that
are shed off.
53

54. • So the cells of oral epithelium considered to be consists of
two functional population.
1) Progenitor population – To divide & provide new cells.
2) Maturing population – Cells continually undergo a process
of differentiation or maturation to form a protective surface
layer.
54

55. Types:
a) Keratinized epithelium:
- Masticatory mucosa
-Gingiva & hard palate
- Vermilion border of lip
b) Nonkeratinized epithelium:
-Lining mucosa: lip, cheeck, vestibular fornix, alveolar mucosa,
soft palate, ventral surface of tongue, floor of oral cavity
- Specialized mucosa: dorsal surface of the tongue
55

56. STRATIFICATIONS OF ORAL EPITHELIUM
1] Keratinizing oral epithelium:
a) Basal layer ( Stratum Basale ) :
•Layer of cuboidal or columnar cells adjacent to basement
membrane
•Occasionally term proliferative or germinative layer is used to
describe the cells in basal region that are capable of division.
56

57. b) Prickle cell layer ( Stratum Spinosum ) :
•Above basal layer , there are several rows of larger elliptical or
spherical cells, called prickle cell layer.
•Cells exhibit short cytoplasmic processes which form
intercellular bridges or desmosomes with adjacent cells. This
alignment gives cells a spiny or prickle line profile.
57

58. c) Granular layer ( Stratum granulosum ) :
•Large flattened cells stacked in 3-5 layers of cells.
•Contains small granules that stain intensely with acid dyes such
as hematoxylin. ( i.e. they are basophilic )
•Granules are called keratohyalin granules.
58

59. d) Surface layer / Keratinized layer ( Stratum Corneum ) :
•Composed of flat ( squamous ) cells, stain bright pink with the
histologic dye eosin ( appear eosinophilic ) & do not contain any
nuclei
•Pattern of maturation of these cells is termed
orthokeratinization
•The gingiva and palate are keratinized as they are associated
with masticatory function.
59

60. PARAKERATINISED ORAL EPITHELIUM
• In parakeratinized epithelium, the surface layer contains dark
pyknotic nuclei & cytoplasm contains little keratin filaments.
• Stratum granulosum is generally absent
• Present in masticatory mucosa.
• Parakeratinization is a normal event in oral epithelium but not
true for epidermis where parakeratinization may be
associated with disease such as psoriasis
60

61. A- Orthokeratinization – narrow,
darkly staining granular layer
B- Parakeratinization – pyknotic
nucleai, few scattered granules
61

62. NONKERATINIZED ORAL EPITHELIUM
• cells retain their nuclei
• cytoplasm does not contain keratin filaments
• stratum corneum & stratum granulosum are absent
• consists of 3 layers : stratum basale , stratum intermedium
and stratum superficiale .
• Basal layer is similar to one seen in keratinized epithelium.
• Stratum intermedium has large cells that do not exhibit the
prickle appearance.
62

63. C- Nonkeratinization – no
clear division of strata,
nucleai appear in surface
layer
• The cells of stratum intermedium are close to one another
and are attached to one another by desmosomes and
other junctions.
• The superficial layer contains nucleated cells with no
signs of keratinization.
• This type of epithelium is seen lining the cheeks.
63

64. Basal surface of Epithelia ( Basement membrane )
• Extracellular supporting layer between an epithelium & the
underlying connective tissue
• Divided into two layers: 1) Basal lamina
2) Reticular lamina
64

65. • Basal lamina is divided into:
a) Lamina lucida- lies beneath epithelium
b) Lamina Densa - lies between lamina lucida & connective
tissue
• Main constituents of basal lamina are – type IV collagen
adhesive glycoprotein laminin heparan sulfate proteoglycan
• Basal lamina is a product of overlying epithelium.
65

66. Epithelial surface features
• Lateral surface
– Adhesion proteins
– Cell junctions
• Basal surface
– Basal lamina: noncellular sheet of protein together with
reticular fibers form basement membrane
• Apical surface
66

67. Cell Junctions
• When cells come into contact with one another, and sometimes with the
extracellular matrix, specialized junctions may form at specific sites on the
contacting cell membranes.
• These specialized junctions may be classified into several different
categories :
• 1) OCCLUDING JUNCTIONS
• 2) ADHESIVE JUNCTIONS
67

68. • A) cell-to-cell : adherens junctions
desmosome
• B) cell-to-matrix : focal adhesion
hemi desmosomes
3) COMMUNICATING(GAP) JUNCTIONS
1)1) OCCLUDING(TIGHT) JUNCTION:OCCLUDING(TIGHT) JUNCTION:
• Unique to epithelium
• Opposing cell membrane are held in contact by the presence
of transmembrane adhesive proteins arranged in
anastomosing strands that encircles the cell 68

69. • Intercellular space obliterated Cytoplasmic adapter proteins:
 Cell polarity related proteins
 Vesicular transport related proteins
 Tumor supressor proteins Transcription factor
• Cytoskeletal filament : actin filament
Functions :
 control the passage of material through intercellular spaces
 A fence to define & maintain the 2 major domains of cell
membranes, apical & basolateral surface
69

70. Cell Junctions
• Tight junctionsTight junctions
– So close that are
sometimes impermeable
• Adherens junctionsAdherens junctions
– Transmembrane linker
proteins
• DesmosomesDesmosomes
– Anchoring junctions
– Filaments anchor to the
opposite side
• Gap junctionsGap junctions
– Allow small molecules to
move between cells 70

71. 2 )2 ) ADHESIVE JUNCTIONS :ADHESIVE JUNCTIONS :
• Hold cells together or anchor cells to the extracellular matrix
• Intercellular space – 20nm
• Epidermis, cardiac muscle as well
Functions :
 Important in cellular signaling .
 Their cytoplasmic components may interact with the
cytoskeleton, triggering changes in cell shape or motility.
 They may act as nuclear transcription factor or co-activators
71

72. a) Cell-to-cell adhesive junctions :
•Principle transmembrane adhesive proteins – members of
cadherin family.
•Cytoplasmic adapter proteins – members of catenin family
which interact with the cytoplasmic domain of transmembrane
cadherin molecule, with the cytoskeleton and with other
proteins
b) Cell-to-matrix junctions :
•Structural organization similar to cell to cell adhesive junctions,
but they use different molecular components & attach the cell to
the extracellular matrix
72

73. 3)3) GAP JUNCTIONS :GAP JUNCTIONS :
•Gap junctions electrically couple cells & allow for a coordinated
response to a stimulus by the cells that are inter connected
•Enables ions and small molecules including amino acids, sugars,
nucleotides and steroids to pass directly from one cell to another
•Also sensitive to pH changes
73

74. Cell Junctions
74

75.  Four basic types of tissue
Epithelium
Connective tissue
 Connective tissue proper (examples: fat
tissue, fibrous tissue of ligaments)
 Cartilage
 Bone
 Blood
Muscle tissue
Nervous tissue
75

76. ConneCtive tissue
• Originate from embryonic tissue called mesenchyme
• Most diverse and abundant type of tissue
• Many subclasses
• Function: to protect, support and bind together other tissues
– Bones, ligaments, tendons
– Areolar cushions; adipose insulates and is food source
– Blood cells replenished; body tissues repaired
• Cells separated from one another by large amount of nonliving
extracellular matrix
76

77. Extracellular Matrix
• Nonliving material between cells
• Produced by the cells and then extruded
• Responsible for the strength
• Two components
1. Ground substance
 Of fluid, adhesion proteins, proteoglycans
 Liquid, semisolid, gel-like or very hard
1. Fibers: collagen, elastic or reticular
77

78. Basic functions of connective tissue
• Support and binding of other tissues
• Holding body fluids
• Defending the body against infection
– macrophages, plasma cells, mast cells, WBCs
• Storing nutrients as fat
78

79. Movement of fluid through CT
• There is a decrease in hydrostatic pressure and an increase in
osmotic pressure from the arterial to the venous ends of
blood capilaries.
• Fluid leaves the capillary through its arterial end and
repenetrates the blood at the venous end.
79
• Some fluid is drained by the lymphatic capillaries.

80. Classification of Connective Tissues
80

81. Embryonic Connective Tissue
81

82. Embryonic Connective Tissue
82

83. Connective tissue proper:
• 2 classes –
– Loose CT
– Dense CT
• Loose CT - Supports many structures that are normally under
pressure and low friction is a very common type of CT.
• It fills spaces between groups of muscle cells, supports
epithelial tissue and forms a layer that sheaths the lymphatic
and blood vessels.
83

84. Origin:
• Desired directly / indirectly from embryonic mesenchymal
cells.
• They lie embedded in a gelatinous amorphous ground
substance, that begins to contain very fine intercellular fibres
as development proceeds.
84

85. Site of location:
– Papillary layer of dermis.
– Hypodermis.
– Serosal linings of peritoneal and pleural cavities.
– In glands and mucous membranes. Supporting the
epithelial cells.
85

86. Cells and fibers of connective tissue
86

87. Connective Tissue Proper: Loose Connective Tissue
- Areolar
87

88. Adipose Tissue
– Matrix similar to areolar connective tissue with closely
packed adipocytes
– Reserves food stores, insulates against heat loss, and
supports and protects
– Found under skin, around kidneys, within abdomen, and in
breasts
– Local fat deposits serve nutrient needs of highly active
organs
88

89. Histogenesis of unilocular
adipose tissue:
• Mesenchymal origin.
• 30th
week of gestation.
Multilocular adipose tissue
(brown fat)
• 1st
month of postnatal life.
• Function is to produce heat.
89

90. Adipose Tissue
90

91. Reticular Connective Tissue
– Loose ground substance with reticular fibers
– Reticular cells lie in a fiber network
– Forms a soft internal skeleton, or stroma, that supports
other cell types
– Found in lymph nodes, bone marrow, and the spleen
91

92. Reticular Connective Tissue
92

93. Dense Connective Tissue:
• It is adapted to offer resistance and protection.
• Same components as that of loose CT.
• It is less flexible and far more resistant to stress than loose
CT.
93

94. • Dense regular CT – arranged in definite pattern with linear
orientation of fibroblast.
• They offer great resistance to traction forces e.g. tendons.
94

95. Dense Regular Connective Tissue
95

96. • Dense irregular CT when the collagen fibers are arranged in
bundles without a definite orientation.
• They provide resistance to stress from all directions e.g. seen
in dermis.
• Irregularly arranged collagen fibers with some elastic fibers
96

97. • Major cell type is fibroblasts
• Withstands tension in many directions providing structural
strength
• Found in the dermis, submucosa of the digestive tract, and
fibrous organ capsules
97

98. Dense Irregular Connective Tissue
98

99. Supporting connective tissues
• Cartilage and bone support the rest of the body
• Cartilage - is a specialized form of CT in which the firm
consistency of E.C.M. allows the tissue to bear mechanical
stresses without permanent distortion.
99

100. CARTILAGE :
• Grows via interstitial and appositional growth
• Matrix is a firm gel containing chondroitin sulfate
• Cartilage – cells called chondrocytes and extensive ECM
composed of fibers and ground substance.
• Chondrocytes synthesize and secretes the ECM and cells
themselves are located in cavities called lacunae.
100

101. • Essential for growth and development of long bones both
before and after birth.
• Forerunner of bone in developing embryos
101

102. 102

103. As a consequence of various functional requirements
3 forms of cartilage have evolved exhibiting variations in matrix
composition
– Hyaline cartilage
– Elastic cartilage
– Fibrocartilage
103

104. Hyaline Cartilage
104

105. Histogenesis of hyaline cartilage
• During hyaline cartilage development, mesenchymal cells
retract their cytoplasmic extensions and assume a rounded
shape, becoming more tightly packed and forming a
mesenchymal condensation, or pre-cartilage condensation.
105

106. • The increased cell to cell contact stimulates commitment to
cartilage differentiation, which progresses from the center
outward.
• Cell at the condensation's core are the first to become
chondroblasts and secrete cartilage matrix.
• After it is surrounded by cartilage matrix, a chondroblast is
termed a chondrocyte.
• Peripheral mesenchyme condenses around the developing
cartilage mass to form the fibroblast-containing, dense
regular connective tissue of the perichondrium.
106

107. Elastic Cartilage
107

108. Cartilage
108

109. • A mold containing human cartilage cells was
implanted on the back of a hairless mouse
without an immune system.
109

110. Fibro Cartilage
110

111. Bone :
• Bone is essentially a highly vascular, lining, constantly
changing mineralized CT.
• It is remarkable for its hardness, resiliency and regenerative
capacity as well as its characteristic growth mechanisms.
111

112. Bone : Cross Sectional View
112

113. General Features:
• All mature bone tissue contains cells (osteocytes, osteoblasts
and osteoclasts), fibers (type 1 collagen), and ground
substance.
• It differs froom other connective tissues primarily having
large inorganic salt deposits in its matrix, which account for
its hardness.
• Types of Bone Tissue: Bone tissue is classified by its
architecture as spongy or compact by its fine structure as
primary(woven) or secondary (lamellar).
113

114. • All bone tissue begins as primary bone, but nearly all is
eventually replaced by secondary bone.
• The distinction between intramembranous and endochondral
bone is based on histogenesis but is not microscopically
detectable in mature bone.
• Shape: Bones are classified by their shape (eg. Long bones, flat
bones) and the process by which they form (endochondral
bones, membrane bones).
• Most exhibit protuberances that serve as attachment sites for
muscle, tendons, and ligaments.
114

115. Microscopic structure
• The bone tissue consists of bone cells present in a bone
matrix.
• The bone matrix or the intercellular substance is made of
collagen fibers and ground substance i.e. complex
mucopolysaccharides.
• The inorganic or crystalline part of the bone comprises of
hydroxyppatite crystals.
• The bone cells are called osteocytes and are found occupying
small spaces in the matrix called LACUNAE.
• The lacunae are connected to one another by a system of
canals called CANALICULI.
• Some of the canaliculi open into certain canals that contain
capillaries.
115

116. • This system of connected bone cells is the means by which
nutrients are distributed throughout the bone tissue.
• Mature bone is formed in thin layers called lamellae. The
lamellae are arranged in concentric circles called HAVERSIAN
SYSTEM.
• The haversian system consist of concentric lamellae around a
canal called HAVERSIAN CANAL which contain capillary blood
vessels.
• Haversian system consists of a central canal surrounded by
concentric circles of bony lamellae.
• The lamellae in turn are made of osteocytes found within
empty spaces called LACUNAE.
• A number of canaliculi are found radiating from the lacunae.
• Three distinct type of bony lamellae are found.
116

117. 117

118. 1. Circumferential lamellae
2. Concentric lamellae
3. Interstitial lamellae
• Circumferential Lamellae: They are bony lamellae that
surrounds the entire bone, forming its outer perimeter.
• Concentric lamellae: They form the bulk of the bone and
form the basic metabolic unit of the bone called osteon.
• The osteon is a cylinder of bone found oriented along the
long axis of the bone.
• Interstitial lamellae: They are lamellae that are found
between adjacent concentric lamellae.
• They are thus fillers that fill the space between the
concentric lamellae.
118

119. • A number of canals are found in bone, containing blood
vessels that pass into the bone from the outside or from the
bone marrow cavity. These canals are called VOLKMANN’S
CANALS.
• Branches of blood vessels from these canal may enter the
smaller haversian canals.
• BONE MARROW is found occupying the center of the bone. It
can be of two types.
• RED BONE MARROW and YELLOW BONE MARROW
• Red bone marrow:
• They are found in most of the bones in young individuals.
• They help in formation of R.B.C.’s and W.B.C.’s.
• In adult most of the red bone marrow gets converted into
yellow marrow.
119

120. • YELLOW BONE MARROW:
• It is a fatty marrow that does not produce red and white blood
cells.
• Bone Cells:
• Three type of cells have been described in association with
bone.
• They are osteoblasts, osteoclasts and the osteocytes.
120

121. • Osteoblasts, the major bone forming cells, are cuboidal; each
possesses a large, round nucleus and a basophilic cytoplasm.
• These cells form one cell thick sheets resembling simple
cuboidal epithelium on surfaces where new bone is
deposited.
• Osteoblasts exhibit high alkaline-phosphatase activity and
have the well developed gogi complex typical of protein
secreating cells.
• Osteocytes are terminally differentiated bone cells found in
cavities in the bone matrix called lacunae.
121

122. • Their long, thin cytoplasmic processes, called filopodia, radiate
from the cell body in fine extensions of the lacunar cavity
called canaliculi.
• Osteoclasts are bone-resorbing cells lying on bony surfaces in
shallow depressions termed Howship’s lacunae.
• They are large and multinucleated ( 2- 50 per cells), with an
acidophilic cytoplasm.
122

123. Histogenesis
• The process of bone formation is called osteogenesis. Bone
formation takes place in two ways.
1. Endochondral bone formation
2. Intramembranous bone formation
• Endochondral Bone formation:
• In this type of osteogenesis, the bone formation is preceded
by formation of a cartilaginous model which is subsequently
replaced by bone.
• Mesenchymal cells become condensed at the site of bone
formation.
• Some mesenchymal cells differentiate into chondroblasts and
lay down hyaline cartilage.
123

124. • The cartilage is surrounded by membrane called
perichondrium.
• This is highly vascular and contains osteogenic cells.
• The intercellular substance surrounding the cartilage cells
becomes calcified due to the influence of enzyme alkaline
phosphatase secreted by the cartilage cells.
• Thus the nutrition to the cartilage cells is cut off leading to
their death. This results in formation of empty spaces called
primary areolae.
• The blood vessels and osteogenic cells from the
perichondrium invade the calcified cartilaginous matrix which
is now reduced to bars or walls due to eating away of the
calcified matrix.
• This leaves large empty spaces between the walls called
secondary areolae.
124

125. 125
Cartilage cells
Formation of primary areolae
Formation of secondary areolae
Endochondral bone formation

126. 126
Osteogenic cells arrange around the bars of calcified matrix
Laying down of osteoid
Osteoid converted into mature bone

127. • The osteogenic cells from the perichondrium become
osteoblasts and arrange themselves along the surface of
these bars of calcified matrix.
• The osteoblasts lay down osteoid which later becomes
calcified to form a lamella of bone.
• Now another layer of osteoid is secreted and this goes on
and on.
• Thus the calcified matrix of cartilage acts as a support for
bone formation.
127

128. • Intramembranous bone formation:
• In this type of ossification, the formation of bone is not
preceded by formation of a cartilaginous model.
• Instead bone is laid down directly in a fibrous membrane.
• The intra-membranous bone is formed in the following
manner:
• At the site of bone formation, mesenchymal cells become
aggregated.
• Some mesenchymal cells lay down bundle of collagen fibers.
• These osteoblasts secrete a gelatinous matrix called osteoid
around the collagen fibers.
• They deposit calcium salts into the osteoid leading to
conversion of osteoid into bone lamella.
128

129. 129
Loose mesenchymal tissue
Condensation of mesenchymal tissue
Collagen fibers laid down between
mesenchymal cells
Some mesenchymal cells
differentiate into odontoblasts

130. • Now the osteoblasts move away from the lamellae and a
new layer of osteoid is secreted which also gets calcified.
• Some of the osteoblasts get entrapped between two
lamellae.
• They are called OSTEOCYTES.
130
Osteoid secreted around the collagen fibers
Calcium secreted into the osteoid by the
osteoblasts. Osteoid is converted into lamellus of
bone
Osteoblasts move away and secrete another layer
of osteoid

131. Blood:
• Blood cells represent category of free connective tissue cells
that are not attached to other cells but held in position by
intercellular substance.
• It is propelled mainly by rhythmic contraction of heart.
131

132. Functions of Blood
132
• Transporting gases
(oxygen & carbon
dioxide)
• Transporting waste
products
• Transporting
nutrients
• Helping remove
toxins from the body

133. General Features:
• Two components: Human have total blood volume of 5L
(depending on body size).
• Blood divisible into two parts: the formed elements, which
include blood cells and platelets, and the plasma, or liquid
phase, in which the formed elements are suspended and in
which a variety of important proteins, hormones, and other
substances are disolved.
B) Basic cell type: There are two basic blood cell types: the
erythrocytes, or red blood cells, and leukocytes, or white
blood cells.
Differential cell count: Blood is also studied by spreading a drop
on a slide to produce a single layer of cells (blood smear).
133

134. • The cells are stained, differentiated by type, and
counted to reveal dieses-related changes in their
relative numbers.
• The smears are usually stained with Romanowsky-
type dye mixtures containing eosin and
methylene blue.
• Composition:
A) Water : Plasma contains 90% water by volume.
B) Solutes: Plasma contains many soluble
proteins(7% by volume). Albumin is the most
abudant plasma protein (3.5 – 5.0 g/DL of blood )
and is mainly responsible for maintain blood’s
osmotic pressure.
• Water-insoluble substances (eg. Lipids) are caried
in plasma associated with albumin.
• Alpha, beta, and gama globulins are globular
proteins dissolved in plasma.
134

135. • Other organic compounds. Other organic molecules in plasma
(2.1 % by volume) include nutrients such as amino acids and
glucose, vitamins and a variety of regulatory peptides, steroid
hormones, and lipids.
• In-organic salts. Inorganic salts in plasma(0.9% by volume)
include blood electrolytes such as sodium, potassium, and
calcium salts.
FORMED ELEMENTS :
A) Erythrocytes: Erythrocytes also called red blood cells, or RBCs,
are the most abudant formed elelments in blood(4-6 * 106
/
micro L) .
135

136. Formed Elements of the Blood
136

137. • Their presence in most tissues and organs makes them useful
in estimating the size of other structures.
• LEUKOCYTES: Leukocytes, or white blood cells, are nucleated
and are larger and less numerous (6000 to 10,000/ micro L )
than erythrocytes.
• Leukocytes can be divided into 2 main groups, Granulocytes
and Agranulocytes, according to their granule content.
• Each group can be further divided based on size, nuclear
morhology , N:C ratio volume and staining properties.
 Agranulocytes : have segmented nuclei. These mononuclear
leukocytes lck specific granules but contain azurphilic
granules (0.05 micro m in diameter)
137

138. • Lymphocytes : constitute a diverse class of cells; they have
similar morphogenic characteristics but a variety of highly
specific functions.
• They normally account for 20 to 25% of adult white blood
cells but are characterized by a broad range of normal
variation (20 to 45 %).
A) B-lymphocytes differentiate into plasma cells, which secrete
antigen-binding molecules that circulate in the blood and
lymph and serve as a major component of humoral immunity.
B) T-lymphocytes derivatives serve as the major cells of the
cellular immune response. They produce a variety of
cytokines (eg. Interferon) that influence the activities of
macrophages and other leukocytes involved in an immune
response.
138

139. • Helper T cells enhance the activity of some B cells and other T
cells.
• Suppressor T cells inhibit the activity of some B cells and
other T cells.
• B) monocytes : are often confused with large lymphocytes.
They are large and constitute only 3 to 8 % of the white blood
cells in healthy adults.
• Monocytes occur only in the blood, but remain in circulation
for less than a week before migrating through capillary walls
to enter other tissues or to become incorporated in the lining
of sinuses.
• The mononuclear phagocyte system consist of monocyte-
derived phagocytic cells throughout the body.(eg. Liver’s
Kupffer cells and some connective tissue macrophages.)
139

140.  Granulocytes : have segmented nuclei and are described as
polymorphonuclear leukocytes. Depending on the cell type,
the mature nucleus may have two to seven lobes connected
by thin strands of nucleoplasm.
 Granulocytes types are distinguished by their size and staining
properties.
 Neutrophils are the most abundant circulating leukocytes.
• they constitute 60 to 70 % of the white blood cells, and are
characterized by a limited range of normal variation( 50 to
70%)
• They are also found outside the blood stream, especially in
loose connective tissue.
• Neutrophils are the first line of cellular defense against
bacterial invasion.
140

141.  Eosinophils constitute only 1 to 4 % of the circulating
leukocytes in healthy adults.
• They are capable of limited phagocytosis, with a preferance
for antigen-anti-parasitic infection and rapidly decreases
during corticosteroid treatment.
 Basophils are the least numerous circulating leukocytes,
constituting 0 to 1% in healthy adults.
• Basophils may exit the circulation but are capable of only
limited ameboid movememnt and phagocytosis.
 Platelets: Platelets or thrombocytes the smallest formed
elements, are dislike cell fragments that vary in diameter
from 2 to 5 micro meter.
• In human they lack nuclei and originate by budding from large
cells in the bone marrow called megakaryocytes.
141

142. • They range in number from 1,50,000 to 3,00,000/micro L of
blood and have a life span of approximately 8 days.
• In blood smear they apear in clumps.
• Each platelet has a peripheral hyalomere that stains a faint
blue and a dense central granulomere containing a few
mitochondria, glycogen granules and various purple granules.
142

143. Smear of Human Blood Cells
143

144. Membranes that combine epithelial sheets plus
underlying connective tissue proper
• Cutaneous membranes
– Skin: epidermis and dermis
• Mucous membranes, or mucosa
– Lines every hollow internal organ that opens to the outside
of the body
• Serous membranes, or serosa
– Slippery membranes lining the pleural, pericardial and
peritoneal cavities
– The fluid formed on the surfaces is called a transudate
• Synovial membranes
– Line joints 144

145. (a) Cutaneous membrane
(b) Mucous membrane
(c) Serous membrane
145

146. • Four basic types of tissue
–Epithelium
–Connective tissue
–Muscle tissue
• Skeletal
• Cardiac
• Smooth
–Nervous tissue
146

147. Skeletal Muscles
• Skeletal muscle arises from mesenchyme of mesodermal
origin.
• The mesenchymal cells retract their cytoplasmic processes
and assume a shortened spindle shape to be come myoblasts;
these fuse to form multinucleated myotubes.
• SKELETAL MUSCLE CELLS:
• 1) Myofilaments in skeletal muscle fibers are of two major
types.
• Thin Filaments : have several components.
 Filamentous actin (F-Actin) : is a polymeric chain of globular
actin(G Actin) monomers.
147

148. • Each thin filament contains two F-actin strands wound in a
double helix.
• 2) Tropomyosin is a long , thin, double helicle polypeptide
that wraps around the actin double helix, lies in the grooves
on its surface, and spans seven G-actin monomers.
• 3) Troponin is a complex of three globular proteins. TnT
(troponin T) attches each complex to a specific site on each
tropomyosin molecule, TnC ( troponin C) binds calcium ions,
and TnI ( troponin I ) inhibits interaction between thin and
thick filaments.
 Thick Filaments : A myosin molecule is a long, golf club-
shaped polypetide.
• A thick myosin filament is a bundle of myosin molecules
whose shaft points towards and overlap in the bundle’s
middle and whose heads project from the bundle’s ends.
148

149. 149
Structure of Actin and Myosin

150. • This arrangement leaves a headless region in the center of
each filament corresponding to the H band.
• Myofilament Organization : Skeletal muscle banding reflects
the grouping of thick and thin myofilaments into parellel
bundles called MYOFIBRILS.
• Each muscle fiber may contain several myofibrils, depending
on its size.
• 1) Myofibrils in cross-section : Images of myofibrils reveal
large and small dots corresponding to thick and thin
filaments, respectively.
• 2) Myofibrils in longitudinal section : At both light and
electron microscopic level, each myofibrils exhibit repeating,
linearly arranged, functional subunits called SARCOMERES,
whose bands runs perpendicular to the myofibril’s long axis.
150

151. • BANDS : Under the light microscope, skeletal muscle fiber
exhibit alternating light-dark staining bands that run
perpendicular to the cells’ long axes.
• The light staining bands contain only thin filaments and are
known as I BANDS (isotropic) because they do not rotate
polarized light.
• Each I bands bisect by Z line. Thus, each sarcomere has two
half I bands, one at each end. One dark staining band lies in
the middle of each sarcomere and shows the position of thick
filament bundles; this is known as A BAND(anisotropic)
because it rotates polarized light.
• At the EM level, each A band has a lighter central region, or H
band, which is bisected by M line. 151

152. 152

153. 153

154. Sarcoplasmic reticulum :
• Sarcoplasmic reticulum is the SER of striated muscle cells and
is specialized to sequester calcium ions.
• In skeletal muscle, this anastomosing complex of membrane-
limited tubules and cisternae unsheathes each myofibrils.
• At each A-I band junction, a tubular invagination of the
sarcolemma, termed a transverse tubule (or T tubule),
penetrates the muscle fiber and overlies the surface of the
myofibrils.
• On each side of the T tubule lies an expansion of the
sarcoplasmic reticulum termed a terminal cisterna.
• Two terminal cisternae and an intervening T tubule comprise
a triad. Which are important in muscle contraction.
154

155. 155

156. 156

157. MOTOR END- PLATES:
• A motor end plate, or myoneural junction, is a collection of
specialized synapses of a motor neuron’s terminal buttons
with a skeletal muscle fibere’s sarcolemma.
• It transmits nerve impulses to muscle cells, initiating
contraction,
157

158. • Each myoneural junction has three major components:
• 1) The presynaptic (neural) component is the terminal
button.
• Although extensions of Schwann cell cytoplasm cover the
button, the myelin sheath ends before reaching it.
• The button contains mitochondria and acetylcholine-filled
synaptic vesicles.
• The part of the button’s plasma membrane directly facing the
muscle fiber is the presynaptic membrane.
158

159. • 2) The synaptic cleft lies between the presynaptic membrane
and the opposing postsynaptic membrane and contains a
continuation of the muscle fiber’s basal lamina.
• It also contains acetylcholinesterase, which degrades the
neurotransmitter so that when neural stimulation ends,
contraction ends.
• The primary Synaptic cleft lies directly beneath the
presynaptic membrane and communicates directly with a
series of secondary synaptic clefts created by infoldings of the
postsynaptic membrane.
• 3) The post synaptic(muscular) component includes the
sarcolemma(post synaptic membrane) and the sarcoplasm
directly under the synapse.
159

160. • The postsynaptic membrane contains acetylcholine receptors
and is thrown into numerous Junctional folds.
• The sarcoplasm beneath the folds contains nuclei,
mitochondria, ribosomes, and glycogen, but lacks synaptic
vesicles.
160

161. Sliding Filament Model of Contraction
• Thin filaments slide past the thick ones so that the
actin and myosin filaments overlap to a greater
degree
• In the relaxed state, thin and thick filaments overlap
only slightly
• Upon stimulation, myosin heads bind to actin and
sliding begins
• How striated muscle works: The Sliding
Filament Model
161

162. 162
• The lever movement drives displacement of the actin
filament relative to the myosin
• head (~5 nm), and by deforming internal elastic structures,
produces force (~5 pN).
• Thick and thin filaments interdigitate and “slide” relative to
each other.

163. 163

164. 164
Now, putting it all together to perform the function of muscle:
Contraction

165. Skeletal Muscle
165

166. Organization of Connective Tissues
• Muscles have 3 layers of connective tissues:
1. Epimysium-Exterior collagen layer
• Connected to deep fascia
• Separates muscle from surrounding tissue
2. Perimysium- Surrounds muscle fiber bundles (fascicles)
• Contains blood vessel and nerve supply to fascicles
3. Endomysium-Surrounds individual muscle cells (muscle
fibers)
• Contains capillaries and nerve fibers contacting muscle cells
• Contains satellite cells (stem cells) that repair damage
166

167. Structure of Cardiac Tissue
• Characteristics of Cardiocytes
– are small
– have a single nucleus
– have short, wide T
tubules
– are aerobic (high in
myoglobin,
mitochondria)
– have intercalated discs
• Cardiac muscle is striated, found only in the heart.
167

168. • Histogenesis: Cardiac muscle arises as parellel chains of
elongated splenchnic mesenchymal cells in the walls of the
embryonic heart tube.
• Cells in each chain develop specialized junctions between
them and often branch and blind to cells accumulate
myofilaments in their sarcoplasm.
• The branched network of myoblasts forms interwoven
bundles of muscle fibers, but cardiac myoblasts do not fuse.
• MECHENISM OF CONTRACTION :
• Although the arrangement of the sarcoplasmic reticulum and
T tubule complex of cardicac muscle fibers different from that
of skeletal muscle, the composition and arrangement of
myofilaments are almost identical . Thus, at the cellular level,
cardicac and skeletal muscle contractions are essentially
same.
168

169. Intercalated Discs
• These unique histologic features of cardiac muscle appear as
dark transverse lines between the muscle fibers and
represents specialized junctional complexes.
• In Ems, intercalated disks exhibit 3 major components
arranged in a stepwise fashion.
• a) The Fascia adherens, similar to zonula adherens, is found in
the vertical (transverse) portion of the step.
• Its Alpha-actinin anchors the thin filaments of the terminal
sarcomeres.
• b) The macula adheres (desmosome) is the second component
of the junction’s transverse portion.
• It prevents detachment of the cardiac muscle fibers from one
another during contraction.
169

170. 170
Functions of Intercalated
Discs
•Maintain structure
•Enhance molecular and
electrical connections
•Conduct action potentials
• The gap junction of intercalated disc from the horizontal
(lateral) portion of the step.
• They provide electronic coupling between adjacent cardiac
muscle fibers and pass the stimulus for contraction from cell
to cell.

171. Cardiac Muscle
171

172. Functions of Cardiac Tissue
1. Automaticity:
– contraction without neural stimulation
– controlled by pacemaker cells
2. Variable contraction tension:
– controlled by nervous system
3. Extended contraction time
4. Prevention of wave summation and tetanic contractions by
cell membranes
172

173. Smooth Muscle
• Forms around other tissues
• In blood vessels:
– regulates blood pressure and flow
• In reproductive and glandular systems:
– produces movements
• In digestive and urinary systems:
– forms sphincters
– produces contractions
• In integumentary system:
– arrector pili muscles cause goose bumps
173

174. Characteristics of Smooth Muscle Cells
1. Long, slender, and spindle shaped
2. Have a single, central nucleus
3. Have no T tubules, myofibrils, or sarcomeres
4. Have no tendons or aponeuroses
5. Have scattered myosin fibers
6. Myosin fibers have more heads per thick filament
7. Have thin filaments attached to dense bodies
8. Dense bodies transmit contractions from cell to cell
174

175. Smooth Muscle
175

176. Smooth Muscle cells:
• Mature smooth muscle fibers are spindle-shaped cells with a
single central ovoid nucleus.
• The sarcoplasm at the nuclear poles contains many
mitochondria, and large gogi complex.
• Each fiber produces its own basal lamina, which consist of
proteoglycan-rich material and type 3 collagen fibers.
1) Myofilaments :
a) Thin filaments. Smooth muscle actin filaments are less stable
than those of skeletal and cardiac muscle.
• They are stable and are anchored by alpha-actinin to dense
bodies associated with plasma membrane.
176

177. b) Thick filament : Smooth muscle myosin filaments are less
stable than those in striated muscle; they form in response to
contractile stimuli.
•Unlike the thick filaments in striated muscle cells, those in
smooth muscle have heads along most of their length and bare
areas at the ends of the filaments.
C) Organization of myofilaments. The thick and thin filaments
run mostly parallel to the cell’s long axis, but they overlap much
more than those of striated muscle, accounting for the absence
of cross-striations.
•The greater overlap results from the unique organization of
thick filaments and permits greater contraction.
•The ratio of thic and thin filaments in smooth muscle is of 12:1,
and arrangement of the filaments is less regular and crystalline
than in striated muscle.
177

178. 178

179. 179

180. Smooth Muscle Relaxation: Mechanism
180

181. 181
Comparisons Among Skeletal, Smooth, and Cardiac Muscle

182. • Four basic types of tissue
–Epithelium
–Connective tissue
–Muscle tissue
–Nervous tissue
• Neurons
• Supporting cells
182

183. The Nervous system has three major functions:
• Sensory – monitors internal & external environment through
presence of receptors
 Integration – interpretation of sensory information
(information processing); complex (higher order) functions
 Motor – response to information processed through
stimulation of effectors
 muscle contraction
 glandular secretion
183

184. General Organization of the nervous system
• Two Anatomical Divisions
– Central nervous system (CNS)
• Brain
• Spinal cord
– Peripheral nervous system (PNS)
• All the neural tissue outside CNS
• Afferent division (sensory input)
• Efferent division (motor output)
– Somatic nervous system
– Autonomic nervous system
184

185. Histology of neural tissue
• Two types of neural cells in the nervous system:
• Neurons - For processing, transfer, and storage of
information
• Neuroglia – For support, regulation & protection of neurons
185

186. Neuroglia (glial cells)
• CNS neuroglia:
• astrocytes
• oligodendrocytes
• microglia
• ependymal cells
• PNS neuroglia:
• Schwann cells (neurolemmocytes)
• satellite cells
186

187. • Astrocytes
• Create supportive
framework for neurons
• create “blood-brain
barrier”
• monitor & regulate
interstitial fluid
surrounding neurons
• secrete chemicals for
embryological neuron
formation
• stimulate the formation
of scar tissue secondary
to CNS injury
187

188. • Oligodendrocytes
• create myelin sheath around axons of neurons in the CNS.
Myelinated axons transmit impulses faster than unmyelinated
axons
• Microglia
• “brain macrophages”
• phagocytize cellular wastes & pathogens
• Ependymal cells
• line ventricles of brain & central canal of spinal cord
• produce, monitor & help circulate CSF (cerebrospinal fluid)
188

189. • Schwann cells
• surround all axons of
neurons in the PNS
creating a neurilemma
around them.
Neurilemma allows for
potential regeneration of
damaged axons
• creates myelin sheath
around most axons of
PNS
• Satellite cells
• support groups of cell
bodies of neurons within
ganglia of the PNS
189

190. Neuron structure
190

191. Neurons
191

192. • Most axons of the nervous system
are surrounded by a myelin sheath
(myelinated axons)
• The presence of myelin speeds up
the transmission of action
potentials along the axon
• Myelin will get laid down in
segments (internodes) along the
axon, leaving unmyelinated gaps
known as “nodes of Ranvier”
• Regions of the nervous system
containing groupings of myelinated
axons make up the “white matter”
• “gray matter” is mainly comprised
of groups of neuron cell bodies,
dendrites & synapses (connections
between neurons) 192

193. Structural classification based on number of processes
coming off of the cell body:
193

194. • Anaxonic neurons
• no anatomical clues to
determine axons from
dendrites
• functions unknown
194

195. • Multipolar neuron
• multiple dendrites &
single axon
• most common type
195

196. Bipolar neuron
two processes
coming off cell
body – one
dendrite & one
axon
only found in
eye, ear & nose
196

197. • Unipolar
(pseudounipolar)
neuron
• single process coming
off cell body, giving rise
to dendrites (at one
end) & axon (making
up rest of process)
197

198. Functional classification based on type of information &
direction of information transmission:
• Sensory (afferent) neurons –
• transmit sensory information from receptors of PNS
towards the CNS
• most sensory neurons are unipolar, a few are bipolar
• Motor (efferent) neurons –
• transmit motor information from the CNS to effectors
(muscles/glands/adipose tissue) in the periphery of the
body
• all are multipolar
198

199. • Association (interneurons) –
• Transmit information between neurons within the
CNS; analyze inputs, coordinate outputs.
• Are the most common type of neuron. (20 billion)
• All are multipolar.
199

200. Anatomical organization of neurons
• Neurons of the nervous system tend to group together into
organized bundles
• The axons of neurons are bundled together to form nerves in
the PNS & tracts/pathways in the CNS. Most axons are
myelinated so these structures will be part of “white matter”
• The cell bodies of neurons are clustered together into ganglia
in the PNS & nuclei/centers in the CNS. These are
unmyelinated structures and will be part of “gray matter”
200

201. Synapses (chemical)
• Synapses are specialized junctions by means of which stimuli
are transmitted from a neuron to its target cell.
• Artificially stimulated axons can propagate a wave
depolarization in either direction, but the signal can travel in
only one direction across a synapse, which functions as a
unidirectional signal valve.
• Synapses are named according to the structures they connect
(eg. Axodendritic, axosomatic, axoaxonic, and
dendrodendritic).
• The three major structural components of each synapse are
the presynaptic membranes and the synaptic cleft between
them.
201

202. 202

203. • Presynaptic Membrane: This is the part of the terminal
button membrane closest to the target cell.
• It includes an electron-dense thickening into which many
short intermediated filaments insert, as in
hemidesmosome.
• In response to stimulation, neurosecretory vesicles in the
button fuse with presynaptic membrane and exocytose their
neurotransmitters into the synaptic cleft.
• Neuroscretory vesicles occur only in the presynaptic
component of the junction.
• Vesicle membrane added to the presynaptic membrane is
recycled by endocytosis of the membrane lateral to the
synaptic cleft.
• Intact vesicles do not cross the cleft.
203

204. • Synaptic cleft (Synaptic Gap) : This is a fluid-filled space,
generally 20-nm wide, between the presynaptic and post
synaptic membranes.
• It is shielded from the rest of the extracellular space by
supporting cell processes and basal lamina material that binds
the presynaptic and postsynaptic membranes together.
• Some clefts are traversed by dense filaments that link the
membranes and perhaps guide neurotransmitters across the
gap.
• Postsynaptic membrane: This thickening of the plasma
membrane of the target cell (eg, neuron or muscle) resembles
the presynaptic membrane but also contain receptors for
neurotransmitters.
• When enough receptors are occupied, hydrophilic channels
open, depolarizing the postsynaptic membrane.
204

205. • Neurotransmitter (eg, acetylcholine) remaining in the cleft
after stimulating the postsynaptic neuron (or other target
cells) is degraded by enzyme (eg, acetylcholinesterase) in the
cleft.
• Degradation products undergo endocytosis by coated pits in
the button membrane, lateral to the presynaptic thickening.
• Removal of excess transmitter allows the postsynaptic
membrane to reestablish its resting potential and prevents
continuous activation of the target cell in response to a single
stimulus.
205

206. Anatomical structure of Nerves
206

207. Signal Generation and Transmission
• The basic function of nerve tissue is to generate and transmit
signals in the form of nerve impulses, or action potentials,
from one part of the body to another.
• The arrangement of neurons in chains and circuits allows the
integration of simple on-off signals into complex information.
• The microscopic structure of nerve tissue (eg, axon
diamaeter, presence or absence of myelin) exploits
phyicochemical phenomena to regulate the rate and
sequence of signal transmission.
1. Resting membrane potential.
• The k+ concentration is 20-fold higher inside neurons than
outside, whereas the Na+ concentration is 10-fold higher
outside than inside.
207

208. • Because the plasma membrane is more permeable to k+ than
to other ions, k+ ions tend to leak out until the accumulated
positive charge outside the cell inhibits further k+ movement.
• In this state of equilibrium, the inside of the cell is negatively
charged (-40 to -100 mV) relative to outside; this potential
difference (voltage) across the membrane help maintain the
resting potential, keeping the neuron ready to receive and
transmit the signals.
• The best known pump is na+/K+-ATPase, which exchange
internal Na+ for escaped K+ when ATP is availabe.
2 ) Firing and propagating action potentials.
• The binding of excitatory neurotransmitter (eg, acetylcholine)
to receptors in the postsynaptic membrane allows positive
ions to enter the cell, reducing the potential difference across
the membrane.
208

209. • When this membrane depolarization reaches a critical level,
or threshold, integral membrane proteins acting as voltage
sensitive Na+ channels (voltage-gated channels) open,
allowing Na+ ions to rush in and reverse the membrane
potential in one region of the membrane.
• This is the firing of the action potential.
3) Refractory period.
• Reversal of the membrane potential at threshold opens
voltage gated K+ channels and allow K+ ions to exit the cell,
returning the membrane to its resting potential
(repolarization).
• An even greater potential difference (hyperpolarization) may
be achieved before stabilizing at normal resting levels.
209

210. 4) Direction of signal transmission.
•For action potentials fired by neurotransmitters crossing a
synapse, the sequence of depolarization is usually dendrites
soma axon synapse next neuron (or end-organ).
•This is termed orthodontic spread.
5)Saltatory conduction.
•Depolarization of myelinated axons occurs only at nodes of
Ranvier, where insulation is reduced and Na+ and K+ channels
are concentrated.
•The action potential must therefore jump from node to node
along the axons, a phenomenon called saltatory conduction.
•The result is faster impulse conduction, less change in ion
concentration, and thus a lower energy requirenment for
recovery of resting potential.
210

211. 6) Blocking signal transmission:
•Cold, heat and pressure on a nerve can block impulse
conduction.
•Local anesthetic allow more complete and reversible impulse
blocking by disturbing the resting potential.
•Some poisons block ion channels and prevent propagation of
the action potential.
211

212. References
• Gray’s Anatomy: Textbook on “Anatomical basis of Medicine & Surgery”.
38th
Edition, Churchill Livingstone Pub.
• Luiz Carlos Junquiera & Jose Carneiro Basic Histology-Text & atlas, 11th
edition, McGraw Hill Pub.
• David H. Cormack Textbook on “Ham’s Histology”, 9th
edition, J.B.
Lippincott Pub.
• B. Young & Heath – Text & color atlas on Wheater’s functional histology,
4th
edition, Churchill Livingstone Pub.
• Tencate - Oral Histology, 5th
edition.
212