Tissues

1
Tissues

• Chapter 5

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Tissues

• Tissues are groups of cells with a specialized
  structure and function
• The cells of different tissues vary in size,
  shape, arrangement and function
• Within each tissue type there is a lot of
  similarity

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Tissues

• The cells within a given tissue are held together
  by an intercellular matrix which varies for each
  tissue type

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Tissues

• There are four major types of tissues
• Epithelial Tissues
• Connective Tissues
• Muscle Tissues
• Nervous Tissues

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Epithelial Tissues

• All epithelial tissues are found on a surface
• They cover organs, line body cavities and hollow
  organs
• They always have one exposed surface and it is
  connected to connective tissue by a basement
  membrane
• They are distinguished from each other by their
  differences in cell shape and cell orientation

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Epithelial Tissues

• Characteristics of epithelial tissues
• They lack blood vessels
• Their nutrients diffuse in from underlying
  tissues
• They divide readily to replace damaged or dead
  cells
• The cells are typically very tightly packed (very
  little intercellular matrix)

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Epithelial Tissues

• Functions of epithelial tissues
• Protection
• Secretion
• Absorption and excretion

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Epithelial Tissues

• Simple epithelial tissues have a single layer of
  cells
• Stratified epithelial tissues have multiple
  layers of cells

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Epithelial Tissues

• Many cuboidal and columnar tissues include cells
  that are specialized to produce and secrete
  substances
• One or more of these cells are called glands
• Tissues that contain glands are called glandular
  epithelia

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Simple Squamous Epithelium

• Characteristics
• Single layer of thin, irregularly shaped and
  flattened cells
• Easily damaged
• Divide rapidly

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Simple Squamous Epithelium

• Function
• Diffusion and filtration

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Simple Squamous Epithelium

• Location
• Alveoli of lungs, capillaries, blood and lymph
  vessels, covering visceral organs and lining body
  cavities

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Simple Squamous Epithelium
These cells come off the stratified squamous
epithelial tissue on the inner surface of the
cheek. These cells show the irregular, flat
shape characteristic of typical "squamous cells."
The nucleus (A) is centrally located, the cell
membrane (C) is very thin, and the cell is filled
with cytoplasm (B).
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Simple Squamous Epithelium
This piece of frog skin allows us to observe the
irregular shape of and close knit nature of the
cells that make up simple squamous epithelial
tissue. A - cell membrane B - nucleus, C -
cytoplasm.
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Simple Squamous Epithelium
At the left, simple squamous tissue (A) line the
walls of blood vessels at the right it makes up
the lung alveoli (A) wall. In both cases the
cells are very thin.
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Simple Cuboidal Epithelium

• Characteristics
• Single layer of cube shaped cells that are as
  wide and tall as they are deep

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Simple Cuboidal Epithelium

• Function
• Secretion, excretion, and absorption

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Simple Cuboidal Epithelium

• Location
• Lining kidney tubules, salivary ducts, pancreatic
  ducts, ovaries, thyroid gland and liver

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Simple Cuboidal Epithelium
In kidney tissue we find the kidney's tubules cut
such that they appear as rings of cells around
empty spaces. These cuboidal cells (A) that line
these tubules are as wide as they are tall as
they are deep - cuboidal. The nuclei (B) are
easily observed.
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Simple Columnar Epithelium

• Characteristics
• Single layer of elongated cells that are taller
  than they are wide
• Nuclei are all at the same level, usually at the
  base
• Often contain microvilli to increase absorptive
  surface area
• Often have very thin cell membranes

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Simple Columnar Epithelium

• Function
• Protection, secretion and absorption

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Simple Columnar Epithelium

• Location
• Lining most of the digestive tract and the uterus
  

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Simple Columnar Epithelium
The villi of the small intestine are lined by a
single layer of columnar cells (A) - thus the
name simple columnar epithelium. Note these
cells are not as wide as they are tall with the
darkly stained nuclei (B) located at the base of
the cells. The cell membranes (C) are very thin
but easily identified.
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Pseudostratified Columnar Epithelium

• Characteristics
• Cells start on the basement membrane but most do
  not reach the top
• Cells are columnar in shape but appear to be
  layered because nuclei are on multiple levels
• They have cilia which move constantly to move
  mucus

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Pseudostratified Columnar Epithelium

• Function
• Trap and move "pollutants" to the mouth where
  they are swallowed

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Pseudostratified Columnar Epithelium

• Location
• This is a respiratory epithelium being found in
  such places as the nasal septum, trachea, and
  bronchi

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Pseudostratified Columnar Epithelium
Line A cuts through this epithelium. The columnar
cells of this tissue all begin at the basement
membrane only a few reach the surface. The
nuclei (C) appear at various levels giving the
tissue a stratified appearance. The cilia (B) are
easily seen.
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Stratified Squamous Epithelium

• Characteristics
• Multiple layers of cells (relatively thick)
• Inner cells are living and actively dividing and
  pushing older cells up
• Outer cells are usually flattened and squamous in
  shape

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Stratified Squamous Epithelium

• Function
• Protection

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Stratified Squamous Epithelium

• Location
• Outer layer of the skin, mouth, throat, vagina,
  esophagus, anal canal

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Stratified Squamous Epithelium
The bracket labeled A marks the stratified
squamous epithelium. The many layers of cells
that make up this tissue are easily seen with
higher magnification (right). Observe that the
surface cells (at B) are flattened (are
squamous).
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Stratified Cuboidal Epithelium

• Characteristics
• Two or three layers of cuboidal cells

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Stratified Cuboidal Epithelium

• Function
• Gives more protection than simple cuboidal cells
  

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Stratified Cuboidal Epithelium

• Location
• Line the large ducts of the mammary glands, sweat
  glands, salivary glands, and the pancreas

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Stratified Cuboidal Epithelium
Cross-sectional view through a duct of a sweat
gland illustrating stratified cuboidal
epithelium.
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Stratified Columnar Epithelium

• Characteristics
• Multiple layers of cells
• Superficial cells are elongated (like columnar)
  and the basal layers are cuboidal

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Stratified Columnar Epithelium

• Function
• Protection and secretion

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Stratified Columnar Epithelium

• Location
• Stratified columnar epithelium is rare
• Found in the male urethra, the vas deferens,
  large salivary glands and parts of the pharynx

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Stratified Columnar Epithelium
Stratified Columnar epithelium is rare.  One
place you can find it is in the largest ducts of
salivary glands (parotid, submandibular, etc). 
The basal layer of cells are cuboidal cells and
the layer nearest the apical surface includes
columnar cells.  The large droplets are mucus, in
Goblet cells.
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Transitional Epithelium

• Characteristics
• Looks similar to stratified cuboidal or
  stratified squamous when relaxed, but is able to
  stretch into irregular shapes

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Transitional Epithelium

• Function
• Distension (able to change in response to
  tension)

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Transitional Epithelium

• Location
• Bladder, urethra and the ureters

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Transitional Epithelium
At the left observe the ureter is lined by
transitional epithelium (A). At the left the
epithelium is more highly magnified. Note that
the cells at the exposed surface (A) are large
and rounded. They are also larger than the cells
at the attached surface (B).
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Connective Tissues

1. Connective tissues are a very diverse group of
   tissues

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Connective Tissues

• Characteristics of connective tissues
• Typically, the cells are farther apart which
  requires an intercellular matrix
• Usually consists of fibers and a fluid or solid
  ground substance
• Typically have very good blood supply
• Range from very rigid (bone) to flexible (loose
  and adipose)

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Connective Tissues

• Because connective tissues are so varied, the
  have a wide variety of functions
• Bind structures and serve as a framework, provide
  support and protection, fill spaces, store fat,
  produce blood cells, fight infections, repair
  damaged tissues

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Connective Tissues

• There are two groups of connective tissues
• Connective tissue proper consists of the
  following types of tissues
• Areolar or loose connective tissue
• Dense regular connective tissue
• Elastic connective tissue
• Reticular connective tissue
• Adipose tissue

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Connective Tissues

• There are two groups of connective tissues
• b. Cartilage, bone and blood

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Connective Tissues

• The most abundant type of cells in connective
  tissue proper are fibroblasts which produce the
  fibers in the matrix

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Connective Tissues

• Fibers are composed of protein and there are
  three major types
• Collagenous fibers
• Thick threads of collagen protein
• Very strong
• Called white fibers

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Connective Tissues

• Fibers are composed of protein and there are
  three major types
• Elastic fibers
• Threads of the protein elastin
• Very branched
• Not as strong as collagenous but are able to
  stretch and return to their original shape
• Called yellow fibers

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Connective Tissues

• Fibers are composed of protein and there are
  three major types
• Reticular fibers
• Very thin collagenous fibers
• Very highly branched

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Areolar or Loose Connective Tissue

• Characteristics
• Has many blood vessels
• Forms many body membranes

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Areolar or Loose Connective Tissue

• Matrix
• Gel-like matrix with many fibroblasts
• Collagenous and elastic fibers

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Areolar or Loose Connective Tissue

• Function
• Binds one tissue to another (as skin connects to
  muscle)
• Protection and nourishment to the organs and
  structures it binds
• Stores body fluids

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Areolar or Loose Connective Tissue

• Location
• Beneath the skin and around blood vessels,
  muscles and nerves

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Areolar or Loose Connective Tissue
In the gel-like matrix (ground substance) observe
the nuclei of fibroblasts (A), collagen fibers
(B) and elastic fibers (C).
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Dense Regular Connective Tissue

• Characteristics
• Fibers are parallel
• Have poor blood flow which causes very slow
  healing
• Very strong tissue

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Dense Regular Connective Tissue

• Matrix
• Very few cells, but most are fibroblasts
• Closely packed collagenous fibers and many small
  elastic fibers

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Dense Regular Connective Tissue

• Function
• Strong flexible support

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Dense Regular Connective Tissue

• Location
• Tendons and Ligaments

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Dense Regular Connective Tissue
The fibroblasts (A) are clearly observed between
the parallel collagenous fibers (B).
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Elastic Connective Tissue

• Characteristics
• Fibers can stretch l 1/2 times their length and
  then recoil
• Fibers are parallel

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Elastic Connective Tissue

• Matrix
• Fibroblasts and elastic fibers

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Elastic Connective Tissue

• Function
• Elasticity to tissues

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Elastic Connective Tissue

• Location
• Large arteries and bronchial tubes

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Elastic Connective Tissue
This section of aorta shows a tremendous number
of elastic fibers (A). The fibroblasts are not
visible. The light pink in this tissue is smooth
muscle.
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Reticular Connective Tissue

• Characteristics
• Fibers are not parallel

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Reticular Connective Tissue

• Matrix
• Fibroblasts and reticular fibers

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Reticular Connective Tissue

• Function
• Provide support to soft organs

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Reticular Connective Tissue

• Location
• Spleen, lymph nodes and liver

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Reticular Connective Tissue
Observe that the reticular fibers (A) form a
network or lattice in this spleen tissue. Do not
confuse this tissue with elastic connective
tissue which has fibers that are parallel.
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Adipose (or fat) Tissue

• Characteristics
• The nucleus is pushed to the side
• Stores fat in droplets

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Adipose (or fat) Tissue

• Function
• Insulating the body
• Cushioning joints and organs
• Storing energy

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Adipose (or fat) Tissue

• Location
• Found anywhere in the body where there is excess
  space and fat can be stored
• Common below the skin, in spaces between muscles,
  in the abdomen, and around the heart

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Adipose (or fat) Tissue
Observe that the nucleus (A) is pushed to the
side of the cell giving the cell the appearance
of a signet ring. Cells are filled with fat
globules (B).
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Cartilage

1. Cartilage is a rigid connective tissue
2. Provides support and a framework for attachment
3. Matrix consists of collagenous fibers in a
   gel-like ground substance

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Cartilage

1. Cells are called chondrocytes and are found in
   spaces called lacunae
2. Surrounded by a covering called the perichondrium
   which contains the bloods vessels
3. Heals very slowly if damaged

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Types of Cartilage

• Hyaline cartilage
• Very fine collagenous fiber matrix (fibers are
  usually not visible
• Is a precursor to bone in the skeletal system
• Found in the trachea, nose, articular ends of
  bones and the fetal skeleton

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Hyaline Cartilage
At the left the bracket indicates the hyaline
cartilage. At the right this tissue is more
highly magnified. The chondrocytes (A) are
located in lacunae (C). The matrix (B) contain
collagen fibers that are so fine they are not
visible in tissue preparations.
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Types of Cartilage

• Elastic cartilage
• Dense elastic fiber matrix
• Provides flexible support
• Found in the external ears and the larynx

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Elastic Cartilage
Elastic cartilage is contained within the bracket
at the left. This tissue is more highly magnified
at the right. The chondrocytes (A) are contained
in lacunae (C). The matrix (B) contains abundant
elastic fibers.These fibers give great
flexibility to this tissue.
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Types of Cartilage

• Fibrocartilage
• Very tough tissue
• Chondrocytes are usually in rows
• Made of collagenous fibers
• Acts as a shock absorber in the vertebral column,
  the knees, and the pelvic girdle

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Fibrocartilage
This cartilage type is recognized by chondrocytes
(A) oriented in rows. The lacunae, which hold
the chondrocytes, are not visible. The matrix
(B) contains numerous fine collagen fibers. These
fibers give the tissue durability.
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Bone

1. Most rigid connective tissue
2. Functions for support, protection, salt storage,
   blood cell production, and muscle attachment
3. Cells are called osteocytes and they are found in
   lacunae

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Bone

1. Osteocytes are connected by channels called
   canaliculi
2. Calcium salts are stored between cells

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Bone
In the compact bone micrograph at the left,
several complete osteons are visible. In the
center of the osteon is the central canal (A)
which hold the blood vessels and a nerve. These
canals are surrounded by concentric rings of
inorganic matrix, the lamellae (B). Between the
lamellae are bone cells, the osteocytes (C)
located in lacunae. Nutrients diffuse from cell
to cell through the canaliculi (D).
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Blood

1. Functions to transport materials within the body
   (O2, CO2, nutrients)
2. Cells are red blood cells, white blood cells, and
   platelets
3. Matrix is a fluid called the plasma

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Blood
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Skeletal Muscle Tissue

• Characteristics
• Can be controlled consciously
• Have striations (light and dark banding)
• Have multiple nuclei
• Stimulated to contract by nerve impulses
• Extend the length of the muscle

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Skeletal Muscle Tissue

• Function
• Responsible for voluntary movement

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Skeletal Muscle Tissue

• Location
• Found in the muscles that attach to bones

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Skeletal Muscle Tissue
Skeletal muscle cells run the full length of a
muscle. Line A shows the width of one cell
(fiber). Note the striations characteristics of
this muscle type. These cells are multicellular,
B marks one nucleus.
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Smooth Muscle Tissue

• Characteristics
• Lacks striations
• Smaller cells that skeletal muscle
• Spindle shaped cells
• Single nucleus

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Smooth Muscle Tissue

• Function
• Involuntary movement
• Churning and moving food
• Moving urine

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Smooth Muscle Tissue

• Location
• Found lining the organs of the digestive track,
  urinary track and blood vessels

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Smooth Muscle Tissue
Smooth muscle cells are spindle shaped and
uninucleate
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Cardiac Muscle Tissue

• Characteristics
• Cells join end to end
• Produces branched fibers
• Junctions are called intercalated disks
• Each cell has a single nucleus
• Controlled involuntarily

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Cardiac Muscle Tissue

• Function
• Involuntary, rhythmic contraction

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Cardiac Muscle Tissue

• Location
• Only found in the heart

101
Cardiac Muscle Tissue
Cardiac muscle cells branch, are striated, are
uninucleate (B) and have intercalated discs (A).
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Nervous Tissue

1. Found in the brain and spinal cord
2. Composed of two types of cells, neurons and
   neuroglial cells

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Nervous Tissue

• Neurons (nerve cells)
• Transmit impulses as a form of communication
• Neuroglial cells
• Support and bind nervous tissue
• Connect neurons to blood vessels

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Nervous Tissue
The cell body is labeled A. The cell's axon can
not be distinguished from its dendrites in this
micrograph. B marks the axon and dendrite
threads. C marks the neuroglial cells (dark
spots).