BIO 405 Medical Histology
Compiled Notes | Second Semester
Epithelial Tissue
 High cellularity; avascular
 Minimal intervening intercellular substance
 Exhibit polarity
 Origin: ectoderm, endoderm, mesoderm
o Ectoderm: covers external surfaces of the body
(e.g., skin and cornea); mouth and liver
o Endoderm: digestive tract, liver, gallbladder,
pancreas, respiratory tract, urinary bladder, urethra
o Mesoderm: heart, blood, lymphatic vessels, serous
cavities, urinary system, male and female
reproductive systems
Basal Lamina
 Thin sheet of amorphous extracellular material
 >50 kinds of glycoproteins, several types of collagens, and
variety of proteoglycans)
 Provides structural support to the overlying epithelium
 impermeable barrier (exemption: water, small molecules)
 Limits contact between epithelial cells and other cell types in
the tissue
Lamina Fibroreticularis
 layer of extracellular material containing collagen and
reticular fibers and fibronectin
 between basal lamina and underlying tissue
 thicker than basal lamina
 absent in glomeruli (kidney) and lens of eye
 product of connective tissue cells (fibroblasts)
 Basement membrane = basal lamina + lamina
fibroreticularis
General Classification of Epithelial Tissue
A. Surface Epithelium
o Covering epithelium (skin)
o Lining epithelium (luminal surfaces of visceral
organs and ducts of glands)
B. Glandular Epithelium
o synthesis and secretion of macromolecules
Surface Epithelium
 Skin: protection
 G.I. tract: absorption
 Neuroepithelial cells (e.g., taste buds) and Olfactory
epithelium (e.g., olfactory cells): sensory
 Kidneys: waste product excretion; maintaining fluid and
electrolyte balance
 Testes  germ cells source
Epithelium
Characteristics
Location
Lung alveoli
Parietal layer of
Bowman’s Capsule
(kidneys)
Simple
Squamous
Epithelium
Simple Cuboidal
Epithelium
Nucleus at the
thickest part of the
cell
Irregular polygonal
outlines
Specialized
secretion and
absorption
Serous cavities
(e.g., pericardium,
peritoneum,
pleura) a.k.a.
mesothelium
Collecting tubules
of kidneys
Follicles of the
thyroid gland
Simple Columnar
Epithelium
Pseudostratified
Columnar
Epithelium
Stratified
Squamous
Epithelium
One layer (all cells
rest on the basal
lamina)
Keratinized
Stratified
Squamous
Epithelium (“dry”):
impervious to
water
Non-keratinized
Stratified
Squamous
Epithelium (“wet”):
kept moist by
glandular
secretions
Stratified
Columnar
Epithelium
Transitional
Epithelium
LTPR
Variant of simple
columnar
epithelium
Lining of uterus
and oviducts
(ciliated simple
columnar
epithelium)
Membranous and
spongy parts of
male urethra
Ciliated
Pseudostratified
Columnar
Epithelium/
Respiratory
Epithelium: Lining
of the larger
passageways of
the respiratory
system (e.g.,
trachea and main
bronchi)
New cells are
formed in the deep
layers
Stratified
Cuboidal
Epithelium
Lining of luminal
surface of the
heart, blood,
lymphatic vessels
(a.k.a.
endothelium)
Certain segments
of the ducts of
major salivary
glands and
pancreas
Absorption
Lubrication
Protection
Secretion
Surface of ovary
Lining of stomach,
intestines, and
large ducts of
some exocrine
glands
Usually 2-3 layers
At least 2 layers
(deeper layers are
cuboidal)
Designed to
withstand
stretching
Stratified
squamous and
Cuboidal Epithelia
Epidermis (skin,
“dry”)
Lining of oral
cavity, esophagus,
vagina, part of
urethra, most
superficial layer of
cornea (“wet”)
Lining of larger
ducts of some
glands (e.g., major
salivary glands)
Large ducts of
some glands
Urinary passages
(renal calyces,
renal pelvis,
ureter)
Urinary bladder
1
Micrographs
area of the
epithelium
Core: actin
filaments
Apical surfaces of
cells (for transport
of fluid or mucus
over the surfaces
of the epithelium)
Simple Squamous Epithelium
Kindey
Simple Cuboidal Epithelium
Parotid Gland
Cilia (Kinocilia)
Trachea
Propulsion and
motility
Bronchus
Longer and thicker
than microvilli
Simple Columnar Epithelium
Gallbladder
Flagella
Nonkeratinized Stratified
Squamous Epithelium
Lip
Stereocilia
Keratinized Stratified
Squamous Epithelium
Skin
Non-motile with
actin filaments in
the core
Spermatozoan
Epididymis and
ductus deferens
Hair cells of the
inner ear (auditory
and vestibular
perception)
Cilia
Lining of Bronchus
Transitional Epithelium
Urinary Bladder
Stereocilia
Ductus Epididymis
Modifications on the Lateral Surfaces
Modification
Function
Zonula occludens
Keep adjacent cells
of the surface
Zonula adherens
epithelium glued
Desmosome
together
Pseudostratified Columnar Epithelium
Lining of bronchus
Surface Modifications of Epithelial Cells
Function/
Modification
Location
Characteristic
Short and fine
finger-like
extensions of the
plasma membrane
Microvilli
Propulsion
Stratified Cuboidal Epithelium
Parotid Gland
Microvilli
Jejunum
Stratified Columnar Epithelium
Parotid Gland
Core: axoneme/
microtubules
Long cilia
Protrude from the
apical surface of
the cells
Gap Junction
Enable adjacent
cells to
communicate with
each other
Skin (only
desmosome is
present)
adherens: juxtaluminal
 Zonula occludens and Zonula
junctional complex/ terminal bar
Modifications on the Basal Surfaces
Modification
Function
Help anchor
epithelial cells to
Hemidesmosome
the underlying
basal lamina
Small intestine
Increase surface
LTPR
Location
Simple cuboidal
and simple
columnar epithelia
(e.g., lining of G.I.
tract)
Location
Stratum basale of
epidermis
2
Basal infoldings
cells lining some
Increase absorbing
of the
segments of the
capacity
plasmalemma
renal tubule
Glandular Epithelium
A. Exocrine Glands
o deliver secretions into the surface epithelium
o far from epithelial surface
o Unicellular Gland
 Goblet cell (both surface and glandular
epithelium)
o Multicellular Gland
 Secretory Epithelial Sheet: Ependyma
 Intraepithelial Gland: small orifice (ducts)
 Glands with ducts
B. Endocrine Glands
o Deliver secretions into blood/ lymph
o Ductless
o Invagination or evagination of covering epithelium
of body cavities
Classification of Exocrine Glands with Ducts According to
Morphology
Classification
Sub-classification
Description
According to
Single,
Simple Gland
Complexity of
unbranched
Duct
Compound Gland
branched
Tubular Gland
Tubules
Alveolar/ Acinous
Morphology of
Alveoli/ Acinous
Gland
Secretory Units
Tubuloalveolar/
Some tubular,
Tubuloacinous Gland
some globular
Exocrine Gland Classification
Gland
Location
Crypts of Lieberkühn
Simple Tubular Gland
(intestinal glands)
Simple Branched Tubular
Cardia glands in stomach
Gland
Simple Coiled Tubular Gland
Sweat Glands
Simple Branched Alveolar
Sebaceous Glands
Gland
Compound Coiled Tubular
Brunner’s Gland (Duodenum)
Gland
Compound Tubuloalveolar
Major salivary glands
Glands
Illustrations
Simple Coiled Tubular
Simple Branched Tubular
Simple Acinar
Simple Branched Acinar
Compound Branched Acinar
Simple Tubular
Compound Acinar
LTPR
3
 Glycosaminoglycans
(GAGs):
makes
the
ground
substance acidic due to the presence of sulfate and carboxyl
groups in their sugar components
o Hyaluronic acid: most abundant GAG; serves as
the backbone to which proteoglycan molecules are
attached by “link-proteins” to form proteoglycan
complexes
Extracellular Fibers
A. Collagen Fibers (Collagenous Fibers)
o present in all connective tissues; most commonly
occurring types of connective tissue (main
extracellular fiber)
o H&E stain: pink (collagen fibers are acidophilic)
o Masson’s Trichome: blue
o made up of collagen (most abundant protein in the
body, accounting for about 25% of the body’s dry
weight)
o 28 known distinct types (I
to XXVIII)
 each type differs
from each other in
their amino acid
composition
and
sequence
of
polypeptide chains
o Collagen types I, II, and
III: make up practically all
the collagen in connective
tissue
 Collagen fibers:
made up of collagen type I
o Collagen fibers have tensile strength and are
slightly flexible but inelastic
o Formation of collagen fibers:
 Procollagen:
molecular
precursor,
synthesized
by
fibroblasts
and
mesenchymal cells
 (1) Fibroblast and mesenchymal cells:
secrete procollagen into the ECM
 (2)
Procollagen
molecules
assemble
spontaneously to form tropocollagen by
twisting around each other
 (3) Tropocollagen molecules aggregate to
form microfibrils
 (4) Microfibrils group together to form
bigger
fibrillar
structures
called
macrofibrils (collagen fibrils)
 (5) Collagen fibrils group together in
parallel fashion to form collagen fibers
B. Elastic Fibers
o Able to branch and anastomose
o When abundant, elastic fibers impart a yellow color
to fresh tissue
o H&E stain: remained
unstained,
usually
appear as refractile,
pinkish-yellow lines
o Orcein stain: fibers
appear blue to black
o Selective stain used:
resorcin-fuchsin
and
aldehyde-fuchsin dyes
o Elastin: amorphous core making up an elastic fiber
Compound Tubulo-acinar
Classification of Secretory Cells (based on Nature of
Secretion)
A. Mucous-secreting: mucin  mucous (for lubrication)
B. Serous-secreting: thin watery secretion with enzymes
Classification of Exocrine Glands (based on Mode of
Secretion)
Classification
Mode of Secretion
Location
Major salivary glands
Merocrine
Exocytosis
Exocrine portion of
pancreas
Destruction of
Sebaceous glands
secretory cells
Apical part of
secretory cells is
Apocrine
Ceruminous glands
released with the
secretory product
Myoepithelial Cells (Basket Cells)
 Flattened, stellate cells present between epithelial cells and
basal lamina
 Contractile  eject the secretions of the acini into the ducts
and propel towards the main ducts
 Location: sweat glands, mammary glands, lacrimal glands,
major salivary glands
Connective Tissue
 Derived from mesoderm
 Two major groups: connective tissue proper and special
types of connective tissue
o Special types of connective tissue: cartilage, bone,
blood, hemopoietic tissue
Connective Tissue Proper
 Found all over the body; “glue” that binds body parts
together while allowing for some degree of movement
 Function:
o envelopes muscles
o forms the stroma and supporting framework of
various organs
o acts as a venue for the passage of blood vessels
and nerves into and from the interior organs and
other parts of the body
o serves as a venue for the exchange of gases and
substances between blood and other basic tissues
o provides the arena as week as the cells that are
needed to defend the body against invading
organisms and other harmful substances
Composition of Connective Tissue Proper
 composed of cells and extracellular substance/ matrix
 Cells are scattered individually in the extracellular substance
Extracellular Substance of Connective Tissue
Ground Substance
 amorphous, homogenous, transparent, and hydrated gel
 consists mainly of water that is stabilized by proteoglycans,
hyaluronic acid, mineral salts, and glycoproteins
 abundant water makes it easy for oxygen, nutrients, and
other needed materials to diffuse from blood to the
connective tissue cells (same for waste products from the
cells to the blood)
 Proteoglycans: main structural constituents and are
responsible got the gelatinous character of ground substance
Holocrine
LTPR
4
 surrounded by longitudinal bundles of
microfibrils, consisting mostly of fibrillin
 highly insoluble protein responsible for the
elasticity of elastic fibers
o Occurrence of elastin:
 (1) elastic fibers
 (2) elastic sheets or lamellae (e.g., walls of
large and medium-sized arteries)
o Elastic fibers: not as widely distributed as collagen
fibers
 particularly
abundant
in
structures
subjected to frequent stretching (e.g.,
ligamental flava between vertebrae, elastic
cartilage that form the framework of the
auricle and external acoustic meatus of the
ear,
external
nose,
auditory
tube,
epiglottis, and some parts of the larynx)
 able to recoil back to their original length
when stretching force is released
o Formation of elastic fibers:
 Fibroblasts and mesenchymal cells:
cells that have the capacity to secrete
substances that are needed in the
formation of elastic fibers
 (1)
Elastogenesis:
fibroblasts
and
mesenchymal cells secrete microfibrils
(mostly fibrillin) into the extracellular space
 (2) Microfibrils aggregate to form bundles
 Tropoelastin: precursor protein of elastin
is secreted by the same cells into the
extracellular space where it polymerizes
into elastin and then incorporated into the
outer aspect of the microfibril bundles
 (3)
More
and
more
elastin
gets
incorporated into the developing elastic
fiber
 (4) Elastin and microfibrils are re-arranged
where elastin gets to occupy the core of
the fiber while microfibrils fill the perimeter
C. Reticular Fibers (Reticulin Fibers)
o Also made up of
collagen
(collagen
type III)
o Very fine and tend to
branch
and
anastomose; can form
extensive networks
o Stain
black
when
impregnated with silver salts (argyrophilic fibers)
o React positively to PAS reagent
o Relatively sparce in most connective tissues
o Main extracellular fibers of reticular tissue
o Comprise the fibrillar component of the lamina
fibroreticularis of the basement membrane of
epithelial and other tissues
o Formation of reticular fibers:
 similar manner in collagen fibers
 Precursors
of
reticular
fibers
are
synthesized
and
excreted
into
the
intercellular
matrix
by
specialized
fibroblasts called reticular cells
Cells in Connective Tissue
Resident Cells
Visiting Cells
Mesenchymal cells
Fibroblasts and Fibrocytes
Inflammatory macrophages
Reticular Cells
Plasma cells
Adipose Cells
WBCs
Mast Cells
Resident Macrophages
A. Mesenchymal Cells: multipotential stem cells that have
differentiated from pluripotential cells; stem cells of most
connective tissue cells (i.e., fibroblasts, fibrocytes, reticular
cells, adipose cells)
o capable of differentiating into several types of cells
o Abundant in the embryo and in the umbilical cord
 rare in adults but could exist in the bone
marrow and connective tissues near
capillaries
o Stellate cells having a delicate cytoplasmic process
and an oval nucleus that contains fine chromatin
and a distinct nucleolus
B. Fibroblasts and Fibrocytes
o Fibroblasts: most abundant cells in most
connective tissues
 synthesize organic components of the
ground substance of connective tissue
matrix
 synthesize precursors of collagen and
elastic fibers
 in histology preparations, fibroblasts are
often seen lying close to or adhering to
collagen fibers
o Fibrocytes: fibroblasts that are idle or resting
 under proper conditions (e.g., woundhealing) can assume its active fibroblast
form
 smaller than fibrocytes, having fewer
processes than fibroblasts
C. Reticular Cells: fibroblasts specialized to synthesize the
precursors of type III collagen fibers
o slightly larger than typical fibroblasts
o H&E preparations: large and lightly-staining nucleus
and long cytoplasmic processes that embrace
reticular fibers
D. Adipose Cells: a.k.a. fat cells or adipocytes
o store lipids or fats (mainly triglycerides)
o synthesized by the cells from glucose that is
brought to the cells from the liver or obtained by
the cell from ingested food via the bloodstream
(chylomicron)
o Lipoblast: fat cells only starting to accumulate fat
(few small fat droplets)
 Droplets coalesce to form larger fat
droplets  single large droplet
 Fat droplet pushes and flattens the nucleus
and cytoplasmic organelles to one side of
the cell
o Adipose cells are also called signet ring cells
o Osmium tetroxide stain: black
o Fat cells are sourced from mesenchymal cells or
from pre-fat cells (preadipocytes)
 an intermediate step between stem cells
and fat cells
E. Mast Cells: a.k.a. mastocytes or histaminocytes
LTPR
5
o large, ovoid cells with centrally located spherical
nuclei and numerous cytoplasmic granules
o Toluidine blue stain: cytoplasmic granules are
stained dark purple
o Cytoplasmic granules: membrane-bound pouches
containing a variety of chemical mediators of
inflammation
 heparin: anticoagulant
 histamine: dilates and makes blood
capillaries more permeable; stimulates the
smooth muscle cells (esp., bronchioles)
o During an inflammation and immediate-type
hypersensitivity reaction (allergic reaction)
 activated mast cells degranulate, releasing
the content of their granules
 cells synthesize and release substances
that mediate inflammatory response
o Mast cells also play a role in wound healing and
defense against pathogens
o Colony-Forming Unit-Mast Cell (CFU-Mast):
cells in the bone marrow where mast cells are
derived from
o Sparse in most connective tissues; abundant in the
lamina propria of G.I. and respiratory tracts,
underneath the skin, and along the course of small
blood vessels
F. Macrophages:
phagocytes
that
differentiate
from
monocytes; a.k.a. histocytes (in connective tissue)
o effector cells of the mononuclear phagocyte
system (MPS)
o widely distributed all over the body, present in all
tissues
o in connective tissues, morphologically similar to
fibroblasts
o Macrophages: ingest and destroy bacteria,
exogenous particulate materials, dead or dying
cells, and senescent tissue elements
 also play a major role in the body’s nonimmune or inflammatory response (by
engulfing and digesting)
 help the body’s immune response by
serving as antigen-presenting cells
(APCs)
o Fixed or free
 Fixed macrophages: attached to collagen
fibers
 Free macrophages: wander about in the
ECM
o Resident or inflammatory
 Resident macrophages: inhabit a given
site
 Inflammatory macrophages:
differentiate from monocytes and migrate
to a site in response to a stimulus
G. Plasma Cells: a.k.a. plasmocytes
o slightly bigger than RBC; has a strongly basophilic
cytoplasm and eccentric nucleus
o Nucelus has a “clock-face”/ “cartwheel” appearance
o B lymphocytes (B Cells): play a major role in the
body’s immune response because they produce
immunoglobulins (antibodies)
o Plasma cell: terminally differentiated cell incapable
of cell division or reverting back to a B lymphocyte
H. Leukocytes (WBCs)
o Types: neutrophils, basophils, eosinophils,
monocytes, and lymphocytes
o Exclusively produced in the bone marrow (except
for lymphocytes which are also generated from
various lymphoid tissue and organs)
o Mature leukocytes enter the blood capillaries of the
bone marrow and join the circulating blood
o Gather in inflamed areas of the body
Types Connective Tissues
 Collagenous connective tissue/ ordinary connective tissue:
most abundant type of connective tissue in the body
 Predominant extracellular fiber: collagen fiber (collagen type
I)
 Predominant cell type: fibroblasts
Dermis of skin
Capsule of
Dense
some organs
Collagenous
(lymph nodes,
Connective
liver, spleen,
Tissue
Dense
Collagen fibers
testes)
Scanty
Irregular
run in various
Sheath of large
intercellular
Connective
directions
nerves
ground
Tissue
Periosteum
substance,
that envelops
abundant
bones
number of
closely
Dura mater
packed
collagen
Tendons
fibers and
Dense
Collagen fibers
relatively
Regular
are arranged
Ligaments
embedded
Connective
in a definite
cells
Tissue
pattern
Fibrous
membranes
Hypodermis of
Support and
skin
protection of
(subcutaneous
organs,
tissue)
muscles, and
tissues
Tunica
adventitia of
Areolar
Helps bind
blood vessels
Connective
skin together
Loose
Tissue
Lamina propria
Collagenous
Protective
Connective
framework
Submucosa of
Tissue
keeping major
digestive,
High
structures in
respiratory,
vascularity
place
and urogenital
and
tracts
abundant
extracellular
Predominant
substance
cellular
where
element is fat
relatively few
or adipose cell
collagenous
fibers are
Represents
arranged
the largest
haphazardly;
energy
more cellular
storage site of
than dense
Adipose
the body
Subcutaneous
connective
Tissue
area
tissue
Thermal
insulator and
shock
absorber
Yellow (white)
adipose
tissue: store
lipid in a
LTPR
6
o elongated cells (often referred to as muscle fibers)
o Cell membrane: sarcolemma
o Cytoplasm: sarcoplasm
o Smooth ER: sarcoplasmic reticulum
o Mitochondria: sarcosomes
Skeletal Muscle
 Skeletal muscle tissue is organized to form mouse-shaped
organs
 Muscle is attached at either end by dense regular connective
tissue (tendon) to a part of the skeletal system (bone or
cartilage)  origin and insertion
 Also referred to as voluntary muscle
 Contraction: quick and forceful
Organization of Skeletal Muscle
 Fascicles (bundles): collection of numerous skeletal
muscle fibers bunched in groups
 Epimysium: tough, dense, irregular connective tissue that
envelopes the fascicles
 Perimysium: encases each of the fascicles; keeps the
muscle fibers within the fascicle together
o also serves as a venue for the blood vessels and
nerve fibers that supply the muscle fibers
 Endomysium: delicate connective tissue layer that
individually wraps and supports each of the muscle fibers
o external to the basal lamina
o extracellular fibers are mainly reticular fibers
single fat
vacuole
Brown adipose
tissue: richly
supplied with
mitochondria;
numerous
droplets
Predominant
cell: reticular
cell
Reticular
Tissue
Elastic Tissue
Predominant
extracellular
fiber: reticular
fiber
Reticular cells
are usually
seen attached
to reticular
fibers, forming
complicated
networks
Predominant
fibrillar
component:
elastic fiber
Elastic fibers
often form
bundles
arranged
parallel to
each other
Predominant
cells:
fibroblasts
Abundance of
amorphous
and jelly-like
ground
substance
Mucous Tissue
Scarce
number of
collagen,
elastic, and
reticular fibers
Stroma
(supporting
framework) of
liver
Myeloid tissue
Lymphoid
tissues and
organs (nodes
and spleen)
Ligamenta
flava of
vertebral
column
Suspensory
ligament of the
penis
Skeletal Muscle Cells
 long, tapering, cylindrical, and multinucleated
 arise in the embryo from the fusion of mononuclear muscle
cell precursors (myoblasts) that evidently differentiate from
mesenchymal cells
 oval nuclei longitudinally oriented and located in the
peripheral portion of the cells, near the sarcolemma
 Sarcoplasm is acidophilic
o also contains myoglobin (oxygen-binding protein
responsible for the brownish color of the muscle)
Common in the
embryo but
rare in adults
Wharton’s jelly
(at the
umbilical cord)
Mainly
composed of
hyaluronic
acid
Muscle Tissue
 Contractility: ability to shorten; exhibited by a high degree
including
o Pericytes: associated with very small blood vessels
o Myoepithelial cells: embrace the acini and small
ducts of some exocrine glands
o Muscle cells: a.k.a. myocytes/ myoid cells;
exhibit the greatest degree of contractility
 Muscle tissue: highly cellular tissue composed of muscle
cells that are supported and bound together by intercellular
material consisting of connective tissue
o basic tissue responsible for locomotion and
movement of various parts of the body
 Muscle cells: derived from the mesoderm
 Myofibrils: numerous long but thin filamentous elements
o arranged parallel to the long axis of the cell and
exhibit transverse striations of altering light and
dark bands
 Light bands: isotropic bands (Ibands); do not alter polarized light
 Dark bands: anisotropic bands (Abands); display birefringence in polarize
light
 Z-line: dark transverse line; bisects the Iband
LTPR
7
 H-band: found within the A-band, lighter
mid-portion that is further bisected by a
thin dark stripe (M-line)
 myosin molecule is much bigger and
heavier than an actin molecule; composed
of six polypeptide chains, two heavy
chains, and four light chains, which are so
arranged as to form a structure that has
two heads and a tail
o F-actin: principal protein component of the thin
filaments
 it is the filament form of actin that consists
of two strands of globular and soluble actin
(G-actin) molecules coiled around each
other
 to keep the actin filaments aligned, Factins are anchored to the Z-line by
proteins, notably α-actinin and desmin
 each of the two G-actin molecules that
makes up a thin filament possesses binding
sites for myosin
o tropomyosin and troponin: form what are called
the troponin-tropomyosin complexes that are
arranged along both sides of each actin filament
 troponin-tropomyosin complexes play a
role in the regulation of contraction
 Mechanism of skeletal muscle contraction: sliding filament
theory (contraction  muscle shortens because the
interaction of the actin and myosin molecules causes the thin
and thick filaments to slide past each other, resulting in the
shortening of the sarcomeres)
o During muscle contraction: thick filaments remain
stationary while the thin filaments get pulled by the
thick filaments towards the center of the sarcomere
 overlap between the thin and thick
filaments increases, causing a progressive
diminution in width of the I- and H-bands
 Z-lines move towards the center of the
sarcomere because they get dragged by
the thin filaments attached to them
 Insertion moves towards the origin
 Events in the sliding filament theory:
o (1) in a resting muscle, binding sites of actin are
covered by troponin-tropomyosin complexes
o (2) Calcium ions bind with the troponin-tropomyosin
complexes, exposing actin binding sites (initiation of
muscle contraction)
o (3) heads of myosin molecules promptly and
spontaneously bind with actin molecules
o (4) binding triggers the hydrolysis of ATPs by the
ATPases present in the myosin heads (resulting to
the release of energy)
o (5) the energy that has been generated enables the
heads of the myosin molecules to bend or flex,
pulling the thin filament (i.e., actin molecule)
towards the center of the sarcomere
o (6) myosin heads remain in flexed position until
new ATP molecules bind to them and get hydrolyzed
o (7) myosin heads are able to disengage, recoil back
to their former positions, reattach themselves to
other binding sites in the actin molecules, and
repeat the bending action they performed earlier
o (8) movements of the myosin heads are repeated in
a rapid fashion until the thick (myosin) and thin
(actin) filaments have completely overlapped
 Transverse tubules (T-tubules) and sarcoplasmic reticulum
 Sarcomeres: small contractile units making up a myofibril
(laid end to end)
o refers to the region that spans two Z-lines
o consists of a collection of thread-like structures
(myofilaments)
 Muscle Filaments: thick and thin
o Thick filaments: occupy the middle zone of a
sarcomere
 span the region of the A-band
 kept aligned by the attachment of their
midpoints at the M-line
o Thin filaments: occupy the peripheral zones of a
sarcomere
 more numerous, but are only about half as
thick and are shorter than the thick
filaments
 one end of each thin filament is attached to
a Z-line while the other end is free
o Resting muscle cell, the thick and thin filaments
partially overlap each other at the A-band
 cross section of this overlap reveals that
each thick filament is surrounded, in
hexagonal pattern, by six thin filaments
 in the central region of the A-band, the
thick filaments are not overlapped by the
thin filaments
 Proteins in muscle filaments: made up mainly of four
proteins: actin, tropomyosin, troponin, and myosin
o actin and myosin are the most abundant,
accounting for about 60% of total muscle protein
o thin filaments consist of actin, tropomyosin,
and troponin
o thick filaments consist of myosin
LTPR
8
o Sarcolemma: forms tubular invaginations that
penetrate the muscle fiber and create anastomosing
systems of tubes that surround the sarcomeres of
the myofibrils at the junction of the A- and I-bands
 lumen:
are
continuous
with
the
extracellular space, are called transverse
tubules (T-tubules)
o Sarcoplasmic reticulum: creates an intricate and
complex system of membrane-bound channels
whose function is to capture and store calcium ions
needed for muscle contraction
 At the junction of the A- and I-bands, the
membrane-bound channels form a pair of
large, flattened cisternae that are closely
applied to either side of a T-tubule
(terminal cisternae)
 Triad: T-tubule and the pair of terminal
cisternae associated with it
o Depolarization of SER  releases its store of
calcium ions into the area of the overlapping A-and
I-bands
 signal for the sarcoplasmic reticulum to
depolarize comes from the motor endplate
on the surface of the muscle cell
 Motor endplate: point of contact of an axon terminal and
the sarcolemma of a skeletal muscle fiber (each muscle fiber
has only one motor endplate)
o command for a skeletal muscle to contract is a
neural one
o originates from the central nervous system and is
carried to the surface of the muscle cells by the
myelinated nerve fibers (i.e., axons) of somatic
motor (efferent) neurons
o axon of a somatic motor neuron arborizes and
forms numerous bulb-like terminations (axon
terminals)
 terminals
make
contact
with
the
sarcolemma of up to 160 muscle fibers
o Motor unit = somatic motor neuron + muscle
fibers
 Events occurring in the motor endplate
o an axon terminal sheds its myelin and settles into a
depression on the surface of the muscle fiber
(synaptic trough/ primary synaptic cleft)
o sarcolemma in the primary synaptic cleft further
forms numerous deep folds called junctional folds
(secondary synaptic clefts) perpendicular to the
primary synaptic cleft
o In the expanded axon terminal, a very large
number
of
vesicles
that
contain
the
neurotransmitter acetylcholine are found
o Upon the arrival of the nerve impulse for muscle
contraction
at
the
axon
terminal,
the
neurotransmitter-containing vesicles release their
acetylcholine content into the synaptic cleft
o Acetylcholine then diffuses across the synaptic cleft
and triggers local depolarization that rapidly spreads
across the surface of the muscle fiber, the Ttubules, and sarcoplasmic reticulum, which then
releases calcium ions to start muscle contraction
Types of Skeletal Muscle Fibers
 Smaller with richer blood supply
Red muscle
 Sarcoplasm has more mitochondria,
fibers
glycogen granules, and myoglobin
 Slow twitch muscle fibers (contracting at a
slower rate)
White
 Contact faster
muscle
 More forceful contraction, fatigue faster
fibers
Intermediate  Morphological and physiological
muscle
characteristics in-between of red and white
fibers
muscle fibers
Proprioceptive Organs
 Sensory receptors: simple nerve endings (free nerve
endings), Vater-Pacinian corpuscles, and Ruffini’s corpuscles
 Proprioceptors: simple nerve endings (free nerve endings),
neuromuscular spindles (muscle spindles), and Golgi tendon
organs
o Function of proprioceptors: monitoring of the
position of the limbs and state of contraction of the
muscles
 Neuromuscular spindle: present in all skeletal muscles
(particularly numerous in muscles involved in fine motor
movements such as the extra-ocular muscles)
o stretch receptor that detects the degree and
velocity of stretch applied to a muscle
o encapsulated fusiform structure consisting of
connective tissue encloses a fluid-filled space that
contains several modified striated muscle fibers
(intrafusal fibers) which are smaller and shorter
than the surrounding skeletal muscle fibers
(extrafusal fibers)
o Intrafusal fibers: nuclear bag and nuclear chain
 Nuclear bag fibers possess a dilated central
area that contains a bunch of nuclei
 Nuclear chain fibers do not manifest any
dilatation; nuclei are set in a single row
o Intrafusal fibers are provided with two types of
sensory nerve endings: annulospiral ending and
flower-spray ending
 Annulospiral ending: consists of the
unmyelinated terminations of sensory
neurons that are spirally wrapped around
the central portion of the intrafusal fiber
 Flower-spray ending: consists of smaller
nerve endings that innervate the peripheral
portions of the intrafusal fiber
 Golgi tendon organ: small structures located in the
tendons that attach skeletal muscles to their insertions and
origins
o consists of collagen fibers enclosed by a thin, coneshaped connective tissue capsule
o supplied by a single afferent nerve fiber that
discards its myelin and breaks into branches as it
enters the capsule
o slender nerve endings are in between the collagen
fibers
o sensitive to muscle contraction; measure the
tension that is generated by muscle contraction
Cardiac Muscle
 occurs only in the heart and sometimes in small areas in the
wall of some of the big blood vessels attached to the heart
 striated with forceful contractions
 Organization: cardiac muscle fibers form bundles or fascicles
(similar to skeletal muscle)
Cardiac Muscle Cells
 cylindrical cells that typically split longitudinally at their ends
to give off a few branches
LTPR
9
 contain only one or two nuclei and are centrally located
 Sarcoplasm is more abundant than in skeletal muscle (along
with mitochondria)
Smooth Muscle
 a.k.a.
visceral muscles;
comprises
the
muscular
component of the wall of visceral organs
 also present in the parenchyma of most internal organs and
even the skin
 sometimes referred to as involuntary muscle because it is
not under conscious control
 contractions are slow and not as forceful as striated muscles
 Organization: Smooth muscle cells sometimes occur singly or
in disorganized clusters, but more often, those in an area or
organ are organized to form bundles (fascicles) enveloped by
perimysium
o cell membranes of adjacent cells in smooth muscle
fascicles are attached to each other by desmosomes
and gap junctions that are similar to those seen
between epithelial cells
o arrangement of smooth muscle fascicles varies
depending on their location
 walls of the gastro-intestinal tract: has two
layers
–
longitudinally-oriented
fascicles
and
circumferentiallyarranged muscle fascicles
 urinary bladder: three ill-defined layers –
two
layers
of
longitudinally-arranged
muscle that sandwich a layer of circularlyarranged muscle fibers
Smooth Muscle Cells
 fusiform cells that are broad in the middle and tapering at
both ends
 contain a single, oval nucleus located in the thick part of the
cell
 Myofibrils: similar to skeletal muscle fibers; cross striations
of their myofibrils are not as prominent as those of skeletal
muscle cells
 T-tubules: surrounds the Z-lines with bigger lumens
o only one expanded terminal cisterna is associated
with a T-tubule (dyads)
 Intercalated discs: specialized junctional complexes that
attach end-to-end terminal branches of neighboring terminal
branches
o appear as dark, transverse lines that occur at
irregular intervals
o Two regions: transverse portion and lateral portion
 Transverse portion: fascia adherens and
desmosome (thin filaments of the terminal
sarcomeres of a cardiac muscle cell attach
into the fasciae adherens)
 Lateral portion: runs parallel to the
myofilaments;
characterized
by
gap
junctions that are likewise identical to
those between epithelial cells
o transverse portion of the intercalated discs serves
to anchor the myofibrils and to keep the cells
together
o lateral portion allows for instantaneous spread of
contractile stimuli from one cell to another
 Mechanism of cardiac muscle contraction: similar to that of
skeletal muscle cells
o source of Calcium ions: sarcoplasmic reticulum and
outside the cell
o cardiac muscle cells contract without neural
stimulation
o Sinoatrial node or SA node: generates the
impulse that initiates their contaction
 small structure in the heart that consists of
Purkinje fibers
o Purkinje fibers: modified cardiac muscle cells
 non-contractile cells that are specialized to
comprise the impulse conducting system of
the heart which generates and propagates
the electrical impulse that initiates cardiac
contraction
o cardiac muscle cells are supplied with efferent
fibers by the motor neurons of the autonomic
nervous system
 efferent fibers serve to regulate the rate
and strength of cardiac muscle contraction
 axon terminals of these efferent fibers end
a short distance from the muscle cells they
supply
 on arrival of an efferent stimulus, the axon
terminals release their neurotransmitters
into the intercellular space
 sarcoplasm is acidophilic
 smooth muscle cells are arranged parallel to each other with
the thick part of one cell lying on the thin parts of
neighboring cells
 Myofilaments: thick filaments of smooth muscle cells consist
of myosin while the thin filaments are made up mostly of
actin
o the thick filaments contain much less myosin and
the thin filaments do not contain troponin
o smooth muscle cells do not form sarcomeres
o thick filaments are scattered all over the sarcoplasm
while the thin filaments which surround the thick
filaments are anchored on dense bodies that contain
the protein a-actinin
o poorly developed sarcoplasmic reticulum
o sarcolemma does not form T-tubules
 Mechanism of contraction:
o dense bodies where the thin filaments are attached
do not form a straight line, shortening occurs in all
directions
LTPR
10
o calcium ions also regulate smooth muscle
contraction (source of calcium: extracellular
substance)
 they enter the cell when the cell surface
depolarizes
 Once inside the cell, calcium ions interact
with
 an enzyme complex on the myosin
molecule, calmodulin-myosin light chain
kinase
 this interaction activates the enzyme
myosin light chain kinase which breaks
down ATP
o the breakdown of ATP releases energy that enables
the myosin molecule to interact with actin molecules
o Smooth muscle cells do not need neural stimulation
to contract; they are inherently contractile
 Pacesetter cells of small and large intestine
trigger contraction of the muscle cells
o smooth muscle cells are supplied with efferent fibers
by the autonomic nervous system whose axon
terminals end a short distance from the cells they
supply
Repair and Regeneration of Muscle Tissue
 Skeletal and smooth muscle: limited regenerative
capacity
o for smooth muscle: regenerative capacity depends
on its location in the body
 Cardiac muscle: does not have regenerative capacity
 Satellite cells: source of new muscle cells; myoblast-like
stem cells
 Dead tissue cells are replaced by connective tissue elements
that form a scar
Nervous Tissue
 made up of closely packed cells that are separated by very
little amount of intercellular substance; highly cellular
 Arose from embryonic ectoderm
 Two divisions:
o (1) Central Nervous System (CNS): brain and
spinal cord
 devoid of connective tissue, except those
associated with blood vessels
 consists of a mass of cells that neighbor
each other
o (2) Peripheral Nervous System (PNS): all other
nervous tissue in the body
 there is some amount of intercellular
material (mainly connective tissue)
Cells of Nervous Tissue
Neurons (nerve cells)
 functional units of nervous tissue
 highly specialized cells exhibiting irritability and conductivity
o Irritability: ability to react to stimulus
o Conductivity: ability to transmit and react
 vary in shapes
o stellate neurons: characterize the ventral grey
matter of the spinal cord and motor nuclei of the
brain stem
o pyramidal neurons: present in the cerebral cortex
o flask-shaped neurons (Purkinje cells): give off
a dendrite which arborizes like a tree (seen in the
middle layer of the cerebellar cortex)
 Parts of a neuron
o Perikaryon: cell body consisting of a nucleus
surrounded by basophilic cytoplasm (neuroplasm)
and enclosed by a cell membrane (neurolemma)
that envelops the processes of the cell
o Nucleus: large, spherical or ovoid, and centrally
located
o Organelles:
 rER: deeply basophilic, with granular
masses (Nissl bodies) that are abundant
through the perikaryon and are also found
in dendrites (but are absent in the axon
and axon hillock)
 Golgi complex: present in all neurons, but
confined to the perikaryon
 rER and Golgi complex: synthesis of
proteins essential for the maintenance of
the structural and metabolic integrity of
the cell; also synthesize neurotransmitters
 Mitochondria: abundant in neurons;
profuse in axon terminals
 Lysosomes:
also
abundant,
recycle
proteins from senescent cellular structures
and in dealing with abnormal and foreign
proteins
 Peroxisomes: help in preventing the
degeneration of the neuron by not allowing
the accumulation of strong oxidizing
agents; detoxifies noxious substances
 Centrosome (MTOC): source of the
microtubules that the cells need
LTPR
11
 axon terminals or boutons are where
axon synapses
 Capable of axonal transport: substances
can move along the axon
 Anterograde
axonal
transport:
movement
of
substances
from
the
perikaryon to the axon terminals
 Retrograde axonal transport: transport
of substances from the axon terminals to
the perikaryon
 Covering of axons: all axons are enveloped by a sheath of
cells, the neurilemmal sheath
o many axons are further encased by a myelin
sheath (in the PNS, also by basal lamina)
 Covering of axons in PNS: neurilemmal sheath is called
Schwann sheath; formed by flattened cells with flattened
nuclei called Schwann cells
o Nodes of Ranvier: points of discontinuity between
successive Schwann cells
o Myelin: material that envelops the axons
o Myelin sheath: structure that myelin forms around
the axon, lying internal to the Schwann sheath
o myelin is actually made up of Schwann cell plasma
membranes that have been spirally wrapped, many
times over, around the axon
o Kinds of axon depending on the presence or
absence
of
myelin
–
myelinated
and
unmyelinated
 conduction of a nerve impulse is faster in
myelinated than unmyelinated axons
o Incisures or clefts of Schmidt-Lantermann:
layers of myelin in a myelin sheath yhat separated
in some areas
o Inclusions:
 Fat droplets: lipochrome and lipofuschin
granules
 Pigment granules: melanin and iron
 Melanin granules: present in the nerve
cells of the substantia nigra of the
midbrain, locus coeruleus near the fourth
ventricle, and the spinal and sympathetic
ganglia
 Iron granules: present in the neurons in
the globus pallidus
o Cytoskeleton of neurons:
 Three fibrillar elements (neurofibrils):
microfilaments,
intermediate
filaments, and microtubules
 Microfilaments: finest of the fibrillar
elements; made up of the fibrillar type of
actin (F-actin) that consists of two strands
of helically-arranged, polymerized G-actin
filaments
 Intermediate
filaments
(neurofilaments): present in the cell
body and the cell processes, particularly
abundant in the axon; provide internal
support for the cell and fix the diameter of
dendrites and axons
 Microtubules (neurotubules): provide
internal
support
for
the
neurons;
strengthen synapses and play a role in the
intracellular transport of organelles and
secretory vesicles
 Processes of a neuron
o axon: conducts impulses away from the cell body
 arises from a conical elevation on the
perikaryon called axon hillock
 usually more slender and is typically longer
 Longest axons in the body: those that form
the sciatic nerve
 only one axon is present in a neuron, but
gives off collateral branches
o dendrite: carry impulses towards the cell body
 more than one dendrite is usually present
 provide most of the receptive surface of
the neuron
 branch more extensively (but are shorter
than axons
 forms small, rounded swellings called
boutons
(terminals)
at
the
ends
(terminal boutons) or along the course
(bouton en passant) of its branches
 Covering of axons in CNS: functions of the Schwann cells
are performed by cells called oligodendrocytes
o forms segments of myelin sheaths of numerous
neurons
o oligodendrocytes: not surrounded by basal lamina
 Classification of neurons (according to morphology)
o Unipolar: only one process (axon) is present;
exists in early embryonic life but rarely present in
adults
o Bipolar: single dendrite and an axon arise at
opposite poles of the cell body (e.g., olfactory
epithelium of the nose and in vestibular and
cochlear ganglia)
o Pseudounipolar: single process, morphologically
an axon, leaves the body, but soon bifurcates (e.g.,
sensory neurons present in the craniospinal ganglia)
LTPR
12
o Multipolar: numerous dendrites are present (e.g.,
most neurons)
 Classification of neurons (according to function)
o Sensory neurons (afferent neurons): receive
and transmit stimuli to the CNS
o Motor neurons (efferent neurons): transmit
impulses from the CNS to effector cells
o Interneurons (association neurons): convey
impulse from one neuron to another
 Synaptic
vesicles:
contain
neurotransmitters
 Presynaptic membrane: axolemma of
the presynaptic neuron in a synapse that is
thickened (postsynaptic membrane for
postsynaptic cell)
 Synaptic cleft: small gap separating the
two membranes
o Synapse: presynaptic membrane + synaptic
cleft + postsynaptic membrane
Nerve Fibers
 Nerve fibers = axon + coverings (neurilemmal sheath)
o (when present) also includes myelin sheath and
basal lamina
 Endoneurium: envelopes every nerve fiber in the PNS; a
type of connective tissue
 in CNS, nerve fibers are not invested by connective tissue
Synapse
 Synapse: point of contact between a neuron and another
neuron or another cell
 site of transmission of a nerve impulse which can either be
excitatory or inhibitory in nature
 allows neurons to communicate with each other or with
effector (muscle and gland) cells and accomplish their
integration and control functions
 Types of synapses
o Electrical Synapse: occur rarely; exist between
some neurons in the brain stem, retina, and
cerebral cortex
 consists
of
gap
junctions,
enabling
neighboring neurons to communicate with
each other by allowing adjacent cells to
exchange molecules and small ions
o Chemical Synapses: more common; nerve
impulse is transmitted from one neuron to another
cell by means of chemical substances called
neurotransmitters
 Presynaptic
neuron:
neuron
that
communicates the impulse
 Postsynaptic cell: cell or neuron that
receives the impulse (could be a neuron,
muscle cell, or a cell of a gland)
 Axon terminal (bouton): part of the
presynaptic neuron that participates in the
synapse
 Impulse transmission at the synapse
o When an impulse reaches the axon terminal of a
presynaptic neuron, neurotransmitters in its
synaptic vesicles are released by exocytosis at the
presynaptic membrane into the synaptic cleft
o Neurotransmitter diffuse across the synaptic cleft
and are taken up by receptors (proteins) at the
postsynaptic membrane
 Synapses between neurons:
o Axodendritic Synapse: axon of a neuron synapses
with a dendrite of another neuron
o Axosomatic Synapse: axon of a neuron synapses
with a perikaryon of another neuron
o Axoaxonic Synapse: axon of a neuron synapses
with the axon of another neuron
o Other
types of
contacts:
dendrodendritic,
somatodendritic,
somatosomatic,
somatoaxonic,
dendroaxonic,
and
axoaxodendritic (serial)
Neuroglial Cells
 Neuroglial cells: supporting cells interspersed among the
neurons in nervous tissue
o protect neurons
o aid them in performing their functions by creating
and maintaining an appropriate environment where
neurons can carry out their function
o play a role in neural nutrition
 outnumber neurons; but they are smaller than most neurons
CNS
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
LTPR
PNS
Schwann cells
Satellite cells
13
 neuroglial cells, except for the microglia, arise from
embryonic ectoderm
o microglia
evidently
arise
from
embryonic
mesoderm
 Unlike neurons, neuroglial cells have the capacity to divide
by mitosis
 Astrocytes: largest and most abundant of the neuroglial
cells
o shaped and have numerous, branching processes
o involved in many metabolic processes that occur in
nervous tissue
o they form scar tissue in damaged areas
 Two types of astrocytes based on their processes:
o Protoplasmic astrocytes: abundant cytoplasm;
found mainly within the gray matter of the brain
and spinal cord
o Fibrous astrocytes: have longer, more slender
processes; located chiefly in the white matter
Types of
Characteristics
astrocytes
smaller, and have fewer and shorter
processes than astrocytes
Oligodendrocytes
Nervous System
 Integration and control functions of the nervous system are
performed by:
o collecting stimuli from the environment by means of
receptors
o transmitting these stimuli, called nerve impulses, to
highly organized reception and correlation areas for
interpretation
o issuing orders to effector organs for appropriate
responses to the stimuli
Anatomic Divisions of the Nervous System
A. Central Nervous System: large mass of nervous tissue in
the cranial cavity and vertebral canal (brain and spinal cord)
o no connective tissue stroma
o nervous tissue: soft and jelly-like (making it fragile)
o protected by bony structures (skull and vertebral
column)
o Internal to the bony structures that protect them,
the brain and the spinal cord are further protected
by enveloping membranes called meninges made up
of connective tissue
Meninges
Characteristics
o Outermost; made up of
dense
collagenous
Dura
connective tissue
Pachymeninx
mater
o Outer surface of the dura
mater adheres to the inner
aspect of the cranium
o Middle layer; flat, sheeto like
membrane that is
thinner than the dura mater
o smooth on its outer surface,
Arachnoid
but projecting from its inner
membrane
surface
is
cobweb-like
connective tissue
o strands
(arachnoid
trabeculae) that connect it
to the underlying pia mater
o Innermost layer; thin but
highly
vascular
loose
connective tissue layer that
Leptomeninx
closely adheres to the
(piasubstance of the brain and
arachnoid)
spinal cord
o spans the entire surface of
the brain and is continuous
with the ependyma that
Pia mater
lines the ventricles of the
brain
o separated
from
nervous
tissue by neuroglial cells
o mainly
made
up
of
interlacing
bundles
of
collagen fibers surrounded
by networks of fine elastic
fibers
scanty cytoplasm with ovoid/ spherical
nucleus
located mainly in the white matter of the
CNS where they form the neurilemmal
and myelin sheaths of the axons
Smaller than astrocytes and
oligodendrocytes
distributed throughout the CNS
Microglial
small and elongated nuclei; scanty
cytoplasm with many lysosomes
phagocytes that remove cellular debris
from sites of injury or normal cell
turnover
cuboidal cells that possess short cilia and
microvilli
Ependymal Cells
also have cytoplasmic processes on their
basal surface that are relatively short
except for those present in some
ependymal cells in the floor of the third
ventricle (called tanycytes), which are
very long and extend into the
hypothalamus
comprise the simple cuboidal epithelium
that lines the cavities of the central
nervous system
form the secretory epithelial lining of the
choroid plexuses that secrete
cerebrospinal fluid (CSF); their ciliary
movement also helps circulate CSF
 Schwann Cells: form the neurilemmal and myelin sheaths
of peripheral nerves
 Satellite Cells: small, flattened cells that surround the cell
bodies of neurons that are in ganglia
o PNS counterparts of astrocytes
o provide structural support for, and are involved in
numerous metabolic processes of neurons
LTPR
14
o In the brain, the outer surface of the dura mater
adheres to the inner aspect of the cranium 
synonymous with periosteum of the cranial bones,
and is called periosteal dura
o In the spinal cord, the outer surface of the dura
mater is lined by a simple squamous epithelium and
does not adhere to the vertebrae
 The vertebrae have a distinct periosteum
connected
to
the
dura
mater
by
ligamentous strands  a space exists
between the periosteum and dura mater

Epidural
space:
space
occupied by fat and venous
plexuses
o The inner surface of the dura mater in the brain and
the spinal cord is also lined by a simple squamous
epithelium, is referred to as the meningeal dura
o Subdural space: between meningeal dura and the
arachnoid membrane
 contains minimal amount of serous fluid
and is more of a potential space
o Subarachnoid space: space separating arachnoid
membrane and the pia mater
 contains cerebrospinal fluid (CSF)




o Cerebrospinal Fluid (CSF): clear, slightly viscous
fluid that circulates within the ventricles of the
brain, the subarachnoid space, and the central canal
of the spinal cord
 contains sugar, inorganic salts, and traces
of protein; only cells that are normally
present in CSF are lymphocytes
 protects the central nervous system by
acting as a water cushion
 plays an important role in the metabolism
of nervous tissue
 constantly being renewed; comes primarily
from the choroid plexuses, but some
LTPR
amount is also produced by the pia mater
and the brain substance
 maintenance of CSF volume: some CSF is
regularly drained into the venous side of
the circulation via specialized areas of the
arachnoid membrane called arachnoid
villi
 Arachnoid villus: granular structure from
the arachnoid membrane that penetrates
the dura mater and then projects into an
intracranial venous sinus (vein); acts like a
tube with a one-way valve that allows
passage of CSF from subarachnoid space
into the vein, but not of blood from the
vein into the subarachnoid space
o Choroid plexuses: chief sources of CSF; located
on the roof of the third and fourth ventricles of the
brain and in parts of the wall of the two lateral
ventricles
 consist of small blood vessels (i.e.,
arterioles and capillaries) of the pia mater
that form clumps that protrude into the
ventricles
o Arrangement of neurons in the CNS
Gray Matter
White Matter
contains the cell bodies,
 does not contain nerve cell
dendrites, and proximal
bodies, but it includes
portions of the axons of the
those of neuroglial cells in
neurons that populate the
the region
CNS and neuroglial cells
 also contains the axons of
nuclei of the neurons
neurons whose cell bodies
account for the color of the
are in the gray matter or in
gray matter
a ganglion (i.e., collection
cell bodies of neurons with
of cell bodies outside the
common functions often
CNS)
cluster together to form
 myelin sheath of the axons
what is called a nucleus
accounts for the
(e.g., caudate nucleus
characteristic white color of
located in the basal ganglia
white matter
of the brain whose neurons
 nerve fibers having a
are partly responsible for
common origin,
body movement and
termination, and function
coordination)
often bundle together to
regions of the gray matter
form what is known as
where there are numerous
tract (e.g., lateral
cell bodies not forming
spinothalamic tract in the
distinct nuclei are called
spinal cord that carries
nuclear areas
pain, touch and
temperature sensory
stimuli to the thalamus in
the brain)
 Tracts that are flattened
are otherwise called
lemnisci (singular,
lemniscus)
 while those that are
rounded or thick are called
funiculi (singular,
funiculus)
 Brain: gray matter at the peripheral area;
white matter at the central area
 Spinal cord: gray matter is centrally
located; white matter is in the periphery
 Golgi type I neurons: (in CNS) neurons
that have long axons that leave either CNS
or gray matter and terminate at some
distance in another part of the gray matter
15
 Golgi type II neurons: neurons with
relatively short axons that do not leave the
region of the gray matter where their cell
bodies lie
 within the fascicle, each of the nerve fibers
is individually wrapped and supported by
delicate,
loose
connective
tissue
(endoneurium)
 Cranial nerves: nerves whose cell bodies
are in the brain (12 pairs)
 Spinal nerves: nerves whose cell bodies
are in the spinal cord (31 pairs)
o Mixed nerves: most nerves; contain both afferent
(sensory) and efferent (motor and secretory) fibers
o Afferent nerve fibers: contain axons of sensory
(afferent) neurons
 transmit impulses from the skin, muscles,
bones, internal organs, and special senses
to the CNS
o Efferent nerve fibers: contain axons of the
efferent (motor) neurons
 order muscles to contract and glands to
secret
o Nerve endings: terminations of nerves in
epithelial, connective, and muscle tissues
 Sensory (afferent) nerve endings:
terminations of afferent nerves
 Motor
(efferent)
nerve
endings:
termination of efferent nerves
o Sensory nerve endings: collect stimuli and are
dispersed all over the body
Type of Sensory
Characteristics
Nerve Ending
 merely the naked terminations of axons
Simple Nerve
of afferent nerves; found in all tissues
Endings
 can discern pressure; most sensitive to
touch, pain, and temperature
 exemplified by Merkel discs found in
the skin and mucosal surfaces
 Merkel discs: consists of the naked
Expanded-tip
leaf-like terminal of an axon that is in
Nerve Endings
contact with a Merkel cell
 Merkel discs are sensitive to touch and
pressure
 made up of naked axon terminals
enclosed by a lamellated connective
tissue capsule
 Examples: Ruffini’s corpuscle, end bulb
of Krause, Vater-Pacinian corpuscle,
Meissner’s corpuscle, neuromuscular
spindles, and Golgi tendon organs
 Ruffini’s corpuscle: small spindleshaped structure seen in the dermis of
the skin, tendon, and ligaments;
consisting of bulb-like expansions of the
terminal branches of a naked axon that
are enclosed by a very thin connective
Encapsulated
tissue capsule
Nerve Endings
o sensitive to deep pressure and
stretch
 End bulbs of Krause: found in the
conjunctiva and mucous membrane of
the lips, dermis, glans penis, and
clitoris; consist of an axon enclosed by
a thin, lamellated capsule consisting of
connective tissue
o tactile and pressure receptors
 Vater-Pacinian corpuscle: largest of
the sensory nerve endings; white, oval
structures consisting of 30 or more
layers of circularly arranged flattened
cells
Cerebellum
Spinal Cord
B. Peripheral Nervous System
o nerve cell bodies are bound together by some
amount of connective tissue in the form of ganglia
o nerve fibers are likewise bound together by
connective tissue to form nerves (peripheral
nerves)
o receives and relays all nerve impulses originating
from stimuli from both within and external to the
body to the CNS
 CNS then integrates these stimuli and
formulates appropriate responses that are
then relayed to the effector cells, tissues,
and organs by the PNS
o Ganglia/ ganglion: collection of cell bodies of
neurons that have a common function in the PNS
 counterpart of a CNS nucleus
 ganglion is delineated from surrounding
structures by a connective tissue capsule
 each neuron is surrounded by supporting
cells called satellite cells
 a neuron and its satellite cells are
separated from their neighboring neurons
and their respective satellite cells by
connective tissue elements
o Peripheral
nerves:
nerves
are
the
PNS
counterparts of tracts in the CNS
 nerve: collection of fibers that are
bunched in groups called bundles/ fascicles
 the nerve is enveloped by dense irregular
connective tissue (epineurium) that keeps
fascicles together
 within the nerve, each fascicle is likewise
encased by perineurium
LTPR
16
 axon (postganglionic fiber) of the
postganglionic neuron, on the other hand,
leaves the autonomic ganglion to terminate
in an effector organ
o Preganglionic fibers leave the central nervous
system at several levels, via the
 (1) III, VII, IX, and X cranial nerves
 (2) thoracic spinal nerves
 (3) upper lumbar spinal nerves
 (4) sacral spinal nerves
 Divisions of the ANS
Division
Location
Function
Preganglionic
neurons whose
fibers exit the CNS
via the thoracic
Responds to
and lumbar spinal
impending danger
nerves
or stress
o usually supplied with a single
axon; axon gives off numerous
bulbous terminal branches
o widely distributed in the body
(dermis,
subcutaneous
connective tissue, pancreas,
mammary
glands,
mesenteries,
and
external
genitalia)
o sensitive to vibration, stretch,
and pressure (course touch)
 Meissner’s corpuscle: seen in the
dermis of the skin of the fingers, toes,
palms, and soles
o has a capsule that encloses a
mass of ovoid cells that are
arranged perpendicular to the
long axis of the corpuscle
o axon
that
supplies
the
corpuscle enters the capsule at
its inferior pole
o tactile (touch) receptor
o Motor nerve endings: responsible for transmitting
the stimulus that commands muscle fibers to
contract and glandular cells to secrete
 Motor endplates: specialized junctions
formed from axon terminals of the efferent
nerve fibers of the somatic motor neurons
(those that supply the skeletal muscle) and
skeletal muscle fibers they innervate
 axon terminals of the efferent nerve fibers
of visceral motor neurons (those that
supply cardiac and smooth muscle fibers
and glandular cells) do not form specialized
junctional complexes with the cells that
they innervate
Function Divisions of the Nervous System
Somatic Nervous System
Autonomic Nervous System
(SNS)
(ANS)
Composed of all neurons in
All neurons in the CNS and
the CNS and PNS concerned
PNS associated with muscles,
with the regulation of visceral
skin, and sense organs
organs
Somatic Nervous System
 Somatic afferent (sensory) neurons: responsible for the
reception of sensory stimuli from the external environment
and proprioceptive stimuli from skeletal muscle, tendons,
and joints
 Somatic efferent (motor) neurons: innervate the skeletal
muscles responsible for voluntary movements
Autonomic Nervous System
 Visceral efferent neurons: control the activity of cardiac
and smooth muscles and glands
o two visceral efferent neurons are involved in the
transmission of an impulse from the CNS to the
effector cells
 cell body of the first visceral efferent
neuron (preganglionic neuron) is in the
CNS
 cell body of the second visceral efferent
neuron (postganglionic neuron) is in an
autonomic ganglion
 axon (preganglionic fiber) of the
preganglionic neuron leaves the CNS and
enters an autonomic ganglion to synapse
with the postganglionic neuron
Sympathetic
Division
Postganglionic
neurons in the
vertebral and
prevertebral
ganglia
with which the
fibers of
preganglionic
neurons synapse
Sympathetic trunk:
collective term for
vertebral ganglia
Preganglionic
neurons whose
fibers leave the
CNS via the cranial
and sacral spinal
nerves
Parasympathetic
Division
Enteric Division
postganglionic
neurons in ganglia
(which are near or
within the walls of
the structures they
innervate) with
which the fibers of
preganglionic
neurons connect
Made up of the
visceral efferent
neurons whose cell
bodies and fibers
form ganglionated
plexuses in the
walls of the
digestive tract as
well as in the
pancreas and the
gallbladder
responsible for the
increase of one’s
heartbeat and
blood pressure,
sense of
excitement, and
other physiological
changes that occur
in “fight or flight”
situations
Called upon during
resting and
relaxing situations
Responsible for
things such as
constriction of the
pupil, slowing of
heart rate, and
dilation of the
blood vessels
responsible for
regulating the
activities of the
digestive tract
has connections
with the
sympathetic and
parasympathetic
nervous systems,
but it functions
autonomously
LTPR
17