This document provides an overview of general histology, covering topics like cytology, embryology, tissues, blood, and more. It begins with definitions of noncellular structures like symplasts and syncytium. It then discusses cells in detail, including their membranes, organelles, and inclusions. The document covers embryology, describing the stages of fertilization, cleavage, gastrulation, and histogenesis. It provides information on the four basic tissues - epithelial, connective, muscular and nervous. Specific cell and tissue types are defined such as erythrocytes, stratified squamous epithelium, and exocrine glands.

1. 1
GENERAL HISTOLOGY

2. 2
CONTENTS:
Cytology................................................................................ 3
Embryology.......................................................................... 33
Tissues.................................................................................. 47
Epithelium............................................................................ 48
Blood..................................................................................... 68
Connective tissue................................................................... 85
Muscular tissue..................................................................... 107
Nervous tissue....................................................................... 112
Sense organs.......................................................................... 123

3. 3
CYTOLOGY
The branch of biology concerned with the
study of cells, including their anatomy,
chemistry, pathology, and physiology.

4. 4
NONCELLULAR STRUCTURES
● SYMPLAST
● SYNCYTIUM
● INTERCELLULARSUBSTANCE

5. 5
SYMPLAST
Multinucleate mass of protoplasm which is not
subdivided into individual cellular compartments.
1- nuclei; 2- sarcoplasm.

6. 6
SYNCYTIUM
The structure composed of cells having long
cytoplasmic extensions which appear to join with
those of other cells.

7. 7
INTERCELLULAR SUBSTANCE
Тhe matrix in which cells live. There are two main
types of intercellular substance:
● amorphous (ground substance), it is
nonformed
● fibrous, it is formed.

8. 8
CELL
Cell is the fundamental unit of which all
organisms are composed.

9. 9
CELL
● CELL MEMBRANE (PLASMA
MEMBRANE)
● PROTOPLASM

10. 10
CELL MEMBRANE (PLASMA
MEMBRANE)
The trilaminar membrane separating the
cytoplasm of the cell from surrounding
structutres. Plasmolemma is 8 to 11 nm thick.

11. 11
CELL MEMBRANE (PLASMA
MEMBRANE):
● LIPIDS
● PROTEINS
● CARBOHYDRATES

12. 12
LIPIDS OF PLASMA MEMBRANE
Lipid molecules (predominantly phospholipids)
constitute the basic framework of the plasma
membrane.
Their arrangement produce the trilaminar
structure of cell membrane.
Each phospholipid molecule consists of an
enlarged head in which the phosphate portion is
located; and two thin tails consisting of fatty acids.

13. 13
PROTEINS OF PLASMA MEMBRANE
The proteins are present in the form of irregularly
rounded masses.
___________________________________
____________________________________
PERIPHERAL PROTEINS
They adhere to the membrane surface.
TRANSMEMBRANE PROTEINS
They occupy the entire thickness of the membrane and
may project out of both its surfaces.
INTEGRAL MONOTOPIC PROTEINS
They are embedded within the thickness of the
membrane and partly project on one of its surfaces:
either outer (outer membrane proteins) or inner (inner
membrane proteins).

14. 14

15. 15
CARBOHYDRATES
(Carbohydrates are present at the surface of the
membrane.)
● GLYCOPROTEINS (they are attached to the
proteins)
● GLYCOLIPIDS (they are attached to the lipids)

16. 16
PROTOPLASM
● NUCLEUS
● CYTOPLASM

17. 17
NUCLEUS
Central more dense part of protoplasm.
● NUCLEOLUS
● NUCLEOPLASM
● NUCLEAR MEMBRANE
● CHROMATIN

18. 18
NUCLEOLUS
A dense spherical accumulation of fibres and
granules found in the nucleus.
***
NUCLEOPLASM
Nuclear sap which contains dispersed
chromatin, some small granules, and protein.

19. 19
NUCLEAR MEMBRANE
A boundary between the nucleus and the
cytoplasm, composed of two unit membranes
separated by the perinuclear space.
At several points the inner and outer layers of the
nuclear membrane fuse leaving gaps (nuclear
pores).

20. 20
CHROMATIN
Nuclear material that contains DNA and proteins.

21. 21
СYTOPLASM
Outer less dense part of protoplasm.
● CYTOSOL (HYALOPLASM)
A fluid base or matrix of cytoplasm.
● ORGANELLES
Intracellular structures having a specialized
function.

22. 22
CELL ORGANELLES
● MEMBRANOUS ORGANELLES
* ENDOPLASMIC RETICULUM
* GOLGI COMPLEX
* MITOCHONDRIA
* LYSOSOMES
● NONMEMBRANOUS ORGANELLES
* CYTOSKELETON
* CENTRIOLES
* RIBOSOMES

23. 23
ENDOPLASMIC RETICULUM
A cytoplasmic system of membranes that may be
arranged in the form of flattened sacs (or cisternae) or
of tubules.
● GRANULAR ENDOPLASMIC RETICULUM
A system of membranes studded with ribosomes. It
represents the site at which proteins are synthesized.
● AGRANULAR ENDOPLASMIC RETICULUM
Cell organelle that is composed of smooth-surfaced
membranes unassociated with ribosomes. It represents
the site at which lipids and carbohydrates are
synthesized.

24. 24
GOLGI COMPLEX
A number of flattened sacs (cisternae) that form
an independent system.
* * *
It has two 'faces' - the cis (receiving) face, and
the trans (exit) face

25. 25
Cis face receives vesicles from smooth
endoplasmic reticulum.
Trans face releases vesicles that transport the
products to other parts of the cell or to the cellular
environment.

26. 26
MITOCHONDRIA
Cytoplasmic organelles enclosed by a double
membrane. Mitochondria are the main source of
energy in the cell.
● OUTER MEMBRANE (it is smooth)
● INNER MEMBRANE (it forms cristae)
● INTERMEMBRANOUS SPACE (it
separates the inner and outer membranes)
● MATRIX (it is granular material that fills
the space bounded by the inner membrane; it
contains numerous enzymes, RNA, and DNA)

27. 27
LYSOSOMES
Мembrane-limited cytoplasmic organelles
containing hydrolytic enzymes.
The enzymes can destroy unwanted material
present within a cell.
Lysosomes arise in Golgi complex.

28. 28
CYTOSKELETON
A number of fibrillar elements (permeating the
cytoplasm) that collectively form a supporting
network.

29. 29
CENTRIOLES
Short cylinders that lie at right angles to each
other. They play an essential role in mitosis.

30. 30
RIBOSOMES
Cytoplasmic organelles that consist of proteins and
ribonucleic acid (RNA). Each ribosome is made up of
two subunits one of which is larger than the other.
They play an essential role in protein synthesis.
Ribosomes may be present in relation to granular
endoplasmic reticulum, or may also lie free in the
cytoplasm.
● MONOSOMES
Ribosomes that are present singly.
● POLYRIBOSOMES (POLYSOMES)
Ribosomes that are present in groups.

31. 31
CELLULAR INCLUSIONS
Cellular inclusions are not obligatory
components of cytoplasm. They appear and
disappear depending on metabolic condition of
the cell.

32. 32
___________________________________________________________
Intercellular Adhesion & Other Junctions

33. 33
EMBRYOLOGY
The study of the development of human
organism from an egg to the establishment of
form and shape.

34. 34
EMBRYOGENESIS
(the development of an embryo from the initial
fertilization of an egg)
● PRIMARY PERIOD
(The first week of development.)
● EМBRYONIC PERIOD
(Second to eighth weeks of development.)
● FETAL PERIOD
(Continues from ninth week of intranatal
development till the birth of child.)

35. 35
PRINCIPAL STAGES OF THE
HUMAN EMBRYOGENESIS
● FERTILIZATION
● CLEAVAGE (FRAGMENTATION)
● GASTRULATION
● HISTOGENESIS, ORGANOGENESIS,
SYSTEMOGENESIS

36. 36
FERTILIZATION
Fusion of male and female sexual cells with
formation of unicellular embryo (zygote) with
diploid number of chromosomes. It occurs in
ampullar part of uterine tube.

37. 37
CLEAVAGE (FRAGMENTATION)
A series of rapid division which occurs after
fertilization.
Human cleavage is:
complete (cleavage is characterized by complete
division of the mass of the fertilized egg to form the
blasomeres);
unequal (cleavage in which the dark and light
blastomeres are unequal in size);
asynchronous (light blastomeres divide faster than
dark blastomeres)

38. 38
BLASTOCYST
The germinal vesicle that consists of a hollow sphere
of cells which results from the process of cleavage.
● TROPHOBLAST (it forms as a result of light
blastomere division)
● EMBRYOBLAST (it forms as a result of dark
blastomere division)
● BLASTOCOELE (fluid-filled cavity)

39. 39
GASTRULATION
Differentiation of primary germ layers:
● ECTODERM
● ENDODERM
● MESODERM

40. 40
HISTOGENESIS
The creation and development of tissues arising
from undifferentiated embryonic cells.
ORGANOGENESIS
Formation and development of inner organs.
SYSTEMOGENESIS
Formation of functional systems of inner
organs.

41. 41
EXTRAEMBRYONIC ORGANS
Temporary organs that develop outside the
body of germ in the process of embryogenesis.
Extraembryonic organs create necessary
condition for growth and development of the
embryo.
These organs include:
● UMBILICAL CORD
● AMNION
● ALLANTOIS
● VITELLINE SAC
● CHORION
● PLACENTA

42. 42
UMBILICAL CORD
Vascular cable that connects the embryo to
placenta.
The umbilical cord of the fetus is covered by the
amniotic epithelium and contains two umbilical
arteries and one umbilical vein embedded into
the Wharton’s jelly.
It also contains remains of allantois and vitelline
sac. It is first formed during the fifth week of
embryonic life.
1- amniotic epithelium
2- Wharton’s jelly
3- umbilical vein
4- umbilical artery
5- remain of allantois
6- remain of vitelline sac

43. 43
AMNION
The thin, transparent, tough membrane lining the
fluid-filled cavity which contains the embryo.
* * *
ALLANTOIS
One of the extraembryonic membranes, providing
respiratory exchange. It is covered by a conjoined
vascular layer.
* * *
VITELLINE SAC
Vitelline sac is a site of hematopoiesis.
* * *

44. 44
CHORION
It is the outermost of the fetal membranes.
The chorion develops villi, engaged in fetal-
maternal exchange.
CHORIONIC VILLI:
● PRIMARY VILLI
● SECONDARY VILLI
● TERTIARY VILLI

45. 45
PRIMARY CHORIONICVILLUS
(it is small non-vascularchorionic villus
containing only trophoblast)
SECONDARY CHORIONICVILLUS
(it is ramifying chorionic villuscontaining
trophoblast and mesoderm)
TERTIARY CHORIONIC VILLUS
(it is vascularized ramifying chorionic villus
containing trophoblast, mesoderm, and
blood vessels)

46. 46
PLACENTA
An organ with many physiologic functions
destined to assure the development of the fetus.
The human placenta is hemochorial in type:
the maternal blood is in direct contact with the
chorion.

47. 47
TISSUES
● EPITHELIAL TISSUE
● CONNECTIVE TISSUE
● MUSCULAR TISSUE
● NERVE TISSUE

48. 48
EPITHELIUM
● Epithelial tissues are formed by closely apposed
polygonal cells with little or no intercellular
material.
● The epithelium is normally separated from the
underlying connective tissue by a basement
membrane.
● There are no blood vessels within the
epithelium. As a result, oxygen, nutrients, and
metabolites must diffuse from the blood vessels
that supply the underlying connective tissue.

49. 49
EPITHELIUM
● SURFACE EPITHELIUM
● GLANDULAR EPITHELIUM
● SENSORY EPITHELIUM

50. 50
SURFACE EPITHELIUM
It lines the outer surface of the body and the
luminal surfaces of cavities within the body.
_________
SURFACE EPITHELIUM
● UNILAYERED
● MULTILAYERED(STRATIFIED)

51. 51
UNILAYERED EPITHELIUM
(It consists of only one layer of cells.)
● SIMPLE (All the cells are adjacent to the
basal membrane and have equal height.)
1. SQUAMOUS
2. CUBOIDAL
3. COLUMNAR
● PSEUDOSTRATIFIED (All the cells are
adjacent to the basal membrane. However, because the
cells are of different shapes and heights, not all reach
the surface. The cell nuclei lie at different levels.)
* * *
MULTILAYERED (STRATIFIED)
EPITHELIUM
(It consists of several layers of cells.)
● SQUAMOUS(Superficial cells are
squamous in shape.)
● TRANSITIONAL (Superficial cells are
able to change their form depending upon the degree of
distension.)

52. 52
SIMPLE SQUAMOUS EPITHELIUM

53. 53
SIMPLE CUBOIDAL EPITHELIUM

54. 54
SIMPLE COLUMNAR EPITHELIUM

55. 55
PSEUDOSTRATIFIED EPITHELIUM

56. 56
STRATIFIED SQUAMOUS NONKERATINIZED EPITHELIUM
STRATIFIED SQUAMOUS NON-
KERATINIZED EPITHELIUM
(its superficial cells are living and contain
nuclei)

57. 57
TRANSITIONAL EPITHELIUM

58. 58
GLANDS
They consist of epithelial cells that are specialized
to perform secretory function.
● UNICELLULAR GLAND
(Gland that consists of one cell).
● MULTICELLULAR GLAND
(Gland that consists of a lot of cells.)
- ENDOCRINE GLAND (Gland
that pours its secretion into blood.)
- EXOCRINE GLAND (Gland that
pours its secretion on to an epithelial surface.)

59. 59

60. 60
EXOCRINE GLANDS CONSIST OF:
● EXCRETORY DUCTS
● ACINI
- Tubular
- Alveolar

61. 61
EXOCRINE GLANDS
(TYPES)
● SIMPLE GLANDS
(They contain one excretory duct.)
- UNBRANCHED (They contain one
acinus.)
- BRANCHED (They contain several
acini.)
● COMPOUND GLANDS
(They contain several ducts. These ducts unite to
form a larger duct which ultimately drains on to
an epithelial surface.)

62. 62

63. 63
TYPES OF SECRETION OF
EXOCRINE GLANDS
● MEROCRINE TYPE OF SECRETION
● APOCRINE TYPE OF SECRETION
● HOLOCRINE TYPE OF SECRETION
________________________________
MEROCRINE TYPE OF SECRETION
(Secretions are thrown out of the cells by a
process of exocytosis the cell remaining intact.)

64. 64
APOCRINE TYPE OF SECRETION
(The apical parts of the cells are shed off to
discharge the secretion.)
HOLOCRINE TYPE OF SECRETION
(The entire cell disintergates while discharging
its secretion.)

65. 65
SIMPLE UNBRANCHED ALVEOLAR GLAND
(it contains one excretory duct and one
alveole-shaped acinus)

66. 66
SIMPLE BRANCHED TUBULAR GLAND
(it contains one excretory duct and several
tubule-shaped acini)

67. 67
SENSORY EPITHELIUM
SENSORY EPITHELIUM IS FOUND IN THE
INDIRECTLY SENSING ORGANS (ORGAN OF
HEARING AND EQUILIBRIUM, ORGAN OF
TASTE)

68. 68
BLOOD
● PLASMA
● CELLULAR (FORMED)
ELEMENTS

69. 69
CELLULAR (FORMED) ELEMENTS
OF BLOOD
● ERYTHROCYTES
● LEUCOCYTES
● BLOOD PLATELETS
(THROMBOCYTES)

70. 70
ERYTHROCYTES
(Red blood corpuscles that have lost their nuclei
and their cytoplasmic organelles. They contain a
red coloured protein called haemoglobin.)
Erythrocytes in surface view and in profile

71. 71
LEUCOCYTES
(They are true cells, each leucocyte having a
nucleus and organelles.)
● GRANULOCYTES
(They have granules in their cytoplasm. They contain
many-lobed nucleus.)
● AGRANULOCYTES
(They have homogeneous cytoplasm and spherical or
reniform nuclei.)

72. 72
GRANULOCYTES
● BASOPHILS (Their large cytoplasmic
granules stain intensely with basic dyes.)
● EOSINOPHILS (Their large
cytoplasmic granules stain brightly with acid dyes.)
● NEURTOPHILS (Their very fine
cytoplasmic granules stain lightly with both acidic and
basic dyes.)
AGRANULOCYTES
● LYMPHOCYTES (They have a
relatively large nucleus surrounded by a narrow rim of
cytoplasm.)
● MONOCYTES (Large cells containing
eccentrically placed nucleus and relatively abundant
cytoplasm.)

73. 73
Blood platelets
(thrombocytes)
Small protoplasmic discs devoid of nuclei. They
contain two regions:
● the granulomere - a centrally located
granular zone;
● the hyalomere - homogenous peripheral
zone.)

74. 74
Basophils
● Basophilscontain large cytoplasmic
granulesthat stain intenselywith basic
dyes.
● Granulesoverlie the nucleusand
obscure its outline.
________________________________

75. 75
Eosinophils (acidophils)
● Eosionophilscontain large cytoplasmic
granulesthat stain intenselywith acid dyes.
________________________________

76. 76
Neutrophils
They contain fine cytoplasmic granulesthat
stain lightly with both acidic and basic dyes.
________________________________

77. 77
Lymphocytes
Lymphocytes contain a relativelylarge
nucleus surroundedby a narrow rim of
cytoplasm.
________________________________

78. 78
Monocytes
Monocytes are large cells containing
eccentrically placed nucleusand relatively
abundantcytoplasm.

79. 79
Blood platelets (thrombocytes)
● Thrombocytes are small protoplasmic
discs devoid of nuclei.
● A thrombocyte contains two regions, a
centrally located granular zone (the
granulomere), and pale, homogenous
peripheral zone (the hyalomere).

80. 80
DIFFERENCES BETWEEN ERYTHROCYTES AND
LEUCOCYTES
Leucocytes are different from erythrocytes in several
ways.
ERYTHROCYTES LEUCOCYTES
1. Erythrocytesare cells that
have lost their nuclei and other
organelles.
1. Leucocytes are true cells,
each leucocyte having a
nucleus,mitochondria, Golgi
complex, and other organelles.
2. They contain a red
coloured protein called
haemoglobin.
2. They do not contain
haemoglobin and, therefore,
appear colourless in unstained
preparations.
3. Erythrocytes do not have
any mobility of their own.
3. Leucocytes can move
actively.
4. Erythrocytesdo not
normally leave the vascular
system.
4. Leucocytes can move out
of vascular system to enter
surrounding tissues.

81. 81
HEMOPOIESIS

82. 82
ERYTHRОPOIESIS
● Proerythroblast
● Basophilic erythroblast
● Polychromatic erythroblast
● Acidophilic erythroblast (at this stage the
nucleus is thrown out of the cell)
● Reticulocyte
● Erythrocyte
_______________________________________

83. 83
GRANULOPOIESIS
● Myeloblast
● Promyelocyte
● Myelocyte
● Band cell
● Granulocyte
____________________________________
MONOCYTOPOIESIS
● Monoblast
● Promonocyte
● Monocyte
_______________________________________
THROMBOCYTOPOIESIS
● Megakaryoblast
● Promegakaryocyte
● Megakaryocyte
● Thrombocyte

84. 84

85. 85
CONNECTIVE TISSUE
The term connective tissue is applied to a tissue
which fills the interstices between more
specialized elements; and serves to hold them
together and support them.
______________________________________________
CONNECTIVE TISSUE
● GENERAL CONNECTIVE TISSUE
● SKELETAL CONNECTIVE TISSUE

86. 86
GENERAL CONNECTIVE TISSUE
● CONNECTIVE TISSUE POSSESSING
SPECIAL PROPERTIES
- MUCOID (MUCOUS) TISSUE
- ADIPOSE TISSUE
- PIGMENT TISSUE
- RETICULAR TISSUE
● FIBROUS CONNECTIVE TISSUE
- DENSE CONNECTIVE TISSUE
1. REGULAR
2. IRREGULAR
- LOOSE CONNECTIVE TISSUE

87. 87
CONNECTIVE TISSUE POSSESSING
SPECIAL PROPERTIES
● MUCOID (MUCOUS)TISSUE
(This kind of tissue is found in Wharton’s jelly of
the umbilical cord. Its most conspicuous
component is a jelly like ground substance rich in
hyaluronic acid.)
● ADIPOSE TISSUE
(An aggregation of fat cells or adipocytes. Each fat
cell contains a large droplet of fat that almost fills
it.)
● PIGMENT TISSUE
(Pigment cells that contain brown pigment
melanin in their cytoplasm.)
● RETICULAR TISSUE
(It consists of: a. stellate cells that have long
cytoplasmic extensions which join with those of
other cells; b. reticular fibres; c.intercellular
substance.)

88. 88
MUCOUS TISSUE
ADIPOSE TISSUE

89. 89
PIGMENT TISSUE
RETICULAR TISSUE

90. 90
FIBROUS CONNECTIVE TISSUE
● DENSE CONNECTIVE TISSUE
(It contains many fibres and few cells.)
1. REGULAR (Bundles of fibres
are arrаnged parallel to one another in a very orderly
manner.)
2. IRREGULAR (Bundles of
fibres interlace in various directions.)
● LOOSE CONNECTIVE TISSUE
(It contains many cells and few fibres.)

91. 91
STRUCTURAL COMPONENTS OF
FIBROUS CONNECTIVE TISSUE
● CELLS
- HISTIOCYTES (MACROPHAGES)
- FIBROBLASTS
- PIGMENT CELLS
- FAT CELL (ADIPOCYTES)
- MAST CELLS
- LYMPHOCYTES
- PLASMA CELL (PLASMOCYTES)
● INTERCELLULAR SUBSTANCE
- GROUND SUBSTANCE
- FIBRES
1. COLLAGEN
2. ELASTIC
3. RETICULAR

92. 92
HISTIOCYTES (MACROPHAGES)
(Small mobile cells with prominent outlines.
They have the ability to phagocytose unwanted
material.)
HISTIOCYTES (MACROPHAGES)

93. 93
FIBROBLASTS
(Large motionless cells with indistinct outlines.
They produce intercellular substance.)

94. 94
COLLAGEN FIBRES
(Thick strong fibres that form bundles.)

95. 95
ELASTIC FIBRES
(Thin flexible fibres that run singly, not in
bundles.)

96. 96
LOOSE CONNECTIVE TISSUE

97. 97
DENSE IRREGULAR CONNECTIVE TISSUE
DENSE REGULAR CONNECTIVE TISSUE

98. 98
SKELETAL CONNECTIVE TISSUE
● CARTILAGE
- HYALINE CARTILAGE
- ELASTIC CARTILAGE
- FIBROCARTILAGE
● BONE
- WOVEN BONE
- LAMELLAR BONE
* cancellous bone
* compact bone

99. 99
CARTILAGE
● CELLS
- CHONDROCYTES
● INTERCELLULAR SUBSTANCE
(MATRIX)
- GROUND SUBSTANCE
- COLLAGEN FIBRES

100. 100
HYALINE CARTILAGE
● CELLS (CHONDROCYTES)
In the zone of the young cartilage (just under the
perichondrium) chondrocytes are flattened and
are present singly. Toward the centre of a mass of
hyaline cartilage the chondrocytes are large and
are usually present in groups (isogenous groups).
● INTERCELLULAR SUBSTANCE
Homogenous interecellular substance is
transparent.
- GROUND SUBSTANCE
- COLLAGEN FIBRES

101. 101
ELASTIC CARTILAGE
It is similar in many ways to hyaline cartilage.
The main differences are:
● intercellular substance is less transparent
than that in hyaline cartilage
● intercellular substance contains both collagen
and elastic fibres.

102. 102
FIBROCARTILAGE
The cells are arranged in short rows.
Intercellular substance is not transparent, it
consists of ground substance and collagen fibres.

103. 103
BONE
● CELLS
- OSTEOCYTES (These are mature
bone cells.)
- OSTEOBLASTS (These are bone
producing cells.)
- OSTEOCLASTS (These are bone
removing cells.)
- OSTEOPROGENITOR CELLS
(These cells give rise to osteoblasts and
osteocytes.)
● INTERCELLULAR SUBSTANCE
(MATRIX)
- GROUND SUBSTANCE
- COLLAGEN FIBRES
* * *

104. 104
COMPACT BONE
● EXTERNAL CIRCUMFERENTIAL
LAMELLAE
● OSTEON LAYER
- OSTEONS
- INTERSTITIAL LAMELLAE
● INTERNAL CIRCUMFERENTIAL
LAMELLAE

105. 105

106. 106
OSTEON
The basic unit of compact tubular bone.
Each osteon is composed of a central core (the
Haversian canal) containing blood vessels and
nerve endings, surrounded by a variable number of
concentric osseous lamellae,

107. 107
MUSCULAR TISSUE
● STRIATED MUSCLE
TISSUE
- SKELETAL MUSCLE TISSUE
- CARDIAC MUSCLE TISSUE
● SMOOTH MUSCLE
TISSUE

108. 108
SKELETAL MUSCULAR TISSUE
(It consists of separate muscle fibres each of
which is symplast.)
The most striking feature of skeletal muscle fibres
is the transverse striations that are seen as
alternate dark and light bands that stretch across
the muscle fibre.
The dark bands are called A-bands.
The light bands are called I-bands.

109. 109
Running across the middle of each I-band there is
a thin dark line called Z-band.
The part of a myofibril situated between two
consecutive Z-bands is called a sarcomere.
Sarcomere represents the structural unit of the
myofibril.

110. 110
CARDIAC MUSCULAR TISSUE
(It consists of fibres that branch and anastomose
with one another.
Each muscle represents a chain of cardiac muscle
cells or cardiac myocytes.
A cardiac myocyte is rectangular in shape and
contains a centrally located nucleus.
Cardiac muscle cells are joined end to end at
special junctional zones called intercalated discs.)

111. 111
SMOOTH MUSCLE TISSUE
(It consists of spindle-shaped smooth muscle
cells. The cells are so arranged that the thick
central part of one cell is opposite the thin
tapering ends of adjoining cells.)

112. 112
NERVOUS TISSUE
● NEURONS
● NEUROGLIA

113. 113
NEURON
● CELL BODY (soma, perikaryon)
(It contains:
- a large central nucleus
- Nissl substance (that consists of rough
surfaced endoplasmic reticlum).
● NEURITES (processes)
- DENDRITE(It transmits the
nerve impulse towards the cell body.)
- AXON (It transmits the nerve
impulse from the cell body.)

114. 114
Nissl substance extends into the dendrites
but not into the axon.

115. 115
Another distinctive feature of neurons is the
presence of fibrils permeating the
cytoplasm. These neurofibrils consist of
microfilaments and microtubules. They
extend into both axons and dendrites.

116. 116
NEURON (TYPES)
● MULTIPOLAR NEURON
(It has one axon and several dendrites.)
● BIPOLAR NEURON
(It has one axon and one dendrite.)
● UNIPOLAR NEURON
(It has one axon.)
● PSEUDOUNIPOLARNEURON
(It has a single process which after a very short
course divides into two.)

117. 117

118. 118
NERVE FIBRES
● MYELINATED NERVE FIBRES
● UNMYELINATED NERVE
FIBRES

119. 119
MYELINATED NERVE FIBRE
FORMATION OF МYELINATED NERVE
FIBRE
1. A neurogliacyte envelopsan axis
cylinder.
An axis cylinder (neuronal process)
invaginatesinto the neurogliacyte. The
plasma membraneof the neurogliacyte
remains intact.

120. 120
2. The axis cylinder comes to be suspended
by a fold of the cell membraneof the
neurogliacyte: this fold is called mesaxon.
3. The neurogliacytethen rotates around
the axis cylinder, wrapping its plasma
membrane loosely around it in successive
layers.
The mesaxon becomes greatly elongated
and comes to be spirallywound around the
axis cylinder, which is thus surroundedby
several layers of cell membrane.
4. Lipids are deposited between adjacent
layers of the membrane.
These layers of the mesaxon, along with
lipids, form the myelin sheath.
__________________________

121. 121
An axis cylinder is related to a large number
of neurogliacytes over its length.
Each neurogliacyte forms a short segment of
the myelin sheath.
At the junction of any two such segments
there is a short gap in the myelin sheath.
These gaps are called the nodes of Ranvier.

122. 122
UNMYELINATED NERVE FIBRE
FORMATION OF UNMYELINATED NERVE
FIBRE
Several axis cylinders invaginate into a
single neurogliacyte.
The plasma membrane of the neurogliacyte
remains intact.
But the mesaxon does not spiral around axis
cylinders.

123. 123
SENSE ORGANS
● DIRECTLY SENSING ORGANS
- ORGAN OF SIGHT
- ORGAN OF SMELL
● INDIRECTLY SENSING ORGANS
- ORGAN OF HEARING AND
EQUILIBRIUM
- ORGAN OF TASTE

124. 124
ORGAN OF SIGHT

125. 125
EYEBALL
● SCLERA
● CHOROID
● RETINA

126. 126

127. 127
CORNEA
● STRATIFIED SQUAMOUS NON-KERATINIZED
EPITHELIUM (OUTERMOST LAYER)
● ANTERIOR LIMITING LAMINA
● SUBSTANTIA PROPRIA (CORNEAL STROMA)
(it is made up of dense regular connective tissue)
● POSTERIOR LIMITING LAMINA
● SIMPLE CUBOIDAL EPITHELIUM

128. 128
CORNEA
1- stratified squamous non-keratrinized epithelium;
2- anterior limiting lamina;
3- substantia propria;
4- posterior limiting lamina;
5- simple cuboidal epithelium.

129. 129
RETINA

130. 130
ROD AND CONE CELLS

131. 131
ORGAN OF SMELL

132. 132
OLFACTORY EPITHELIUM
The olfactory epithelium is pseudostratified.
It contains three types of cells.
● OLFACTORY CELLS (bipolar neurons)
● SUPPORTING (SUSTENTACULAR)
CELLS
● BASAL CELLS

133. 133
ORGAN OF HEARING AND
EQUILIBRIUM

134. 134
COCHLEA
● SCALA VESTIBULI
● SCALA TYMPANI
● DUCT OF COCHLEA

135. 135
SPIRAL ORGAN (OF CORTI)

136. 136
ORGAN OF TASTE

137. 137
STRUCTURE OF TASTE BUD
● SUPPORTING (SUSTENTACULAR)
CELLS
● NEUROEPITHELIAL TASTE CELLS
(RECEPTOR CELLS, GUSTATORY CELLS)
● BASAL CELLS

138. 138