1

LABORATORY ACTIVITY HISTOLOGY

FOR STUDENT

Module author : Dr. Wida Purbaningsih, dr., M.Kes

Resource Person : Dr. Wida Purbaningsih, dr., M.Kes

Subject : Nerve tissue

Department : Histology

A. Sequence

I. Introduction : 40 min

II. Pre Test : 5 min

III. Activity Lab : 70 min

- Discussion 20 min

- Identify 50 min

IV. Post Test : 5 min

B. Topic

1. General microstructure of the neuron, neuroglia, and nerve tissue

2. General microstructure of the central nerve tissue (CNS)

Cerebrum

Cerebellum

Medulla spinalis

3. Genral microstructure of the peripheral nerve tissue (PNS)

C. Venue

Biomedical Laboratory Faculty of Medicine, Bandung Islamic Universtity

D. Equipment

1. Light microscopy

2. Stained tissue section :

Neuron and neuroglia 1. Motor Neuron

2. Cerebrum/Cerebellum/Medulla spinalis

Nerve tissue

Meningens

3. Cerebrum

4. Cerebellum

5. Medulla spinalis

Peripheral Nerve

Tissue

6. Ganglion otonom

7. Ganglion Snesorik

8. Nervus ischiadicus

3. Colouring pencils

E Pre-requisite

- Before following the laboratory activity, the students must prepare :

1. Draw the schematic picture of neuron and give explanation

2. Mention four type of neuroglia and their functional (astrocyte, microglia,

oligodendrosit, sel schwan, and ependymal cell), then draw the schematic

neuroglia and give explanation

3. Draw the schematic picture of nerve tissue microsructure and give explanation

2

4. Draw the schematic picture of cerebrum microsructure and give explanation

5. Draw the schematic picture of cerebellum microstructure and give explanation

6. Draw the schematic picture medulla spinalis microstrusture and give explanation

7. Draw the schematic picture of meningens microstructure and give explanation

about tissue type

8. Draw the schematic ganglion sensorik microstrusture and give explanation

9. Draw the schematic ganglion otonom microstrusture and give explanation.

10. Draw the schematic nervus (nerve fiber) microstrusture and give explanation

- Content lab in manual book ( pre and post test will be taken from the manual, if

scorring pre test less than 50, can not allowed thelab activity )

- Bring your text book, reference book e.q atlas of Histology, e-book etc. (minimal 1

group 1 atlas ).

- Bring colouring pencils for drawing

NERVE TISSUE

The human nervous system, by far the most complex system in the body, is formed by a

network of many billion nerve cells (neurons), all assisted by many more supporting cells

called glial cells. Each neuron has hundreds of interconnections with other neurons,

forming a very complex system for processing information and generating responses. Nerve

tissue is distributed throughout the body as an integrated communications network.(Gartner

2017)

Nervous tissue, comprising perhaps as many as a trillion neurons with multitudes of

interconnections, forms the complex system of neuronal communication within the body.

Certain neurons have receptors, elaborated on their terminals, that are specialized for

receiving different types of stimuli (e.g., mechanical, chemical, thermal) and transducing

them into nerve impulses that may eventually be conducted to nerve centers. These impulses

are then transferred to other neurons for processing.(Mescher 2018)

The nervous system develops from the ectoderm of the embryo in response to signaling

molecules from the notochord (Gartner 2017). Cells of the nervous system are classified into

two categories: neurons and neuroglia. Neurons are responsible for the receptive,

integrative, and motor functions of the nervous system. Neuroglial cells are responsible for

supporting, protecting, and assisting neurons in neural transmission.

I. NEURONS

The cells responsible for the reception and transmission of nerve impulses to and from

the CNS are the neurons. Ranging in diameter from 5 to 150 μm, neurons are among both

the smallest and the largest cells in the body. Most neurons are composed of three distinct

parts:

o A cell body (perikaryon or soma): the central portion of the cell where the nucleus and

perinuclear cytoplasm are contained.

o multiple dendrites, which are the numerous elongated processes extending from the

perikaryon and specialized to receive stimuli from other neurons at unique sites called

3

synapses. Dendrites processes specialized for receiving stimuli from sensory cells, axons,

and other neurons

o a single axon. which is a single long process ending at synapses specialized to generate

and conduct nerve impulses to other cells (eg, nerve, muscle, and gland cells). Axons

may also receive information from other neurons, information that mainly modifies the

transmission of action potentials to those neurons. Axon have varying diameter and up to

100 cm in length (Gartner 2017).

o Nerve Impulses

o Synaptic Communication

Generally, neurons in the CNS are polygonal (Fig. 1.a), with concave surfaces between

the many cell processes, whereas neurons in the dorsal root ganglion (a sensory ganglion of

the PNS) have a round cell body from which only one process exits (Fig. 1.c). Cell bodies

exhibit different sizes and shapes that are characteristic for their type and location.

Figure 1. Shown are the four main types of neurons, with short descriptions. (a) Most neurons, including all motor neurons and CNS interneurons, are multipolar. (b) Bipolar neurons include sensory neurons of the retina, olfactory mucosa, and inner ear. (c) All other sensory neurons are unipolar or pseudounipolar. (d) Anaxonic neurons of the CNS lack true axons and do not produce action potentials, but regulate local electrical changes of adjacent neurons.

I.1 Cell Body (Perikaryon or Soma)

The neuronal cell body contains the nucleus and surrounding cytoplasm, exclusive of the

cell processes (Figure 4–a and b). It acts as a trophic center, producing most cytoplasm for

the processes. Most cell bodies are in contact with a great number of nerve endings

conveying excitatory or inhibitory stimuli generated in other neurons. A typical neuron has

an unusually large, euchromatic nucleus with a prominent nucleolus, indicating intense

synthetic activity.

Cytoplasm of perikarya often contains numerous free polyribosomes and highly

developed RER, indicating active production of both cytoskeletal proteins and proteins for

transport and secretion. Histologically these regions with concentrated RER and other

4

polysomes are basophilic and are distinguished as chromatophilic substance (or Nissl

substance, Nissl bodies) (Figure 4-a and b). The amount of this material varies with the

type and functional state of the neuron and is particularly abundant in large nerve cells such

as motor neurons (Figure 4–a and b). The Golgi apparatus is located only in the cell body,

but mitochondria can be found throughout the cell and are usually abundant in the axon

terminals.

In both perikarya and processes microtubules, actin filaments and intermediate filaments

are abundant, with the latter formed by unique protein subunits and called neurofilaments

in this cell type. Cross-linked with certain fixatives and impregnated with silver stains,

neurofilaments are also referred to as neurofibrils by light microscopists. Some nerve cell

bodies also contain inclusions of pigmented material, such as lipofuscin, consisting of

residual bodies left from lysosomal digestion.

I.2 Dendrites

Dendrites (Gr. dendron, tree) are typically short, small processes emerging and branching

off the soma (Figure 2). Usually covered with many synapses, dendrites are the principal

signal reception and processing sites on neurons. The large number and extensive

arborization of dendrites allow a single neuron to receive and integrate signals from many

other nerve cells. For example, up to 200,000 axonal endings can make functional contact

with the dendrites of a single large Purkinje cell of the cerebellum. Dendrites become

much thinner as they branch, with cytoskeletal elements predominating in these distal

regions. In the CNS most synapses on dendrites occur on dendritic spines, which are

dynamic membrane protrusions along the small dendritic branches, visualized with silver

staining (Figure 2) and studied by confocal or electron microscopy. Dendritic spines serve

as the initial processing sites for synaptic signals and occur in vast numbers, estimated to be

on the order of 1014 for cells of the human cerebral cortex. Dendritic spine morphology

depends on actin filaments and changes continuously as synaptic connections on neurons are

modified. Changes in dendritic spines are of key importance in the constant changes of the

neural plasticity that occurs during embryonic brain development and underlies adaptation,

learning, and memory postnatally.

5

Figure 2. The large Purkinje neuron in this silver-impregnated section of cerebellum has

many dendrites (D) emerging from its cell body (CB) and forming branches. The small

dendritic branches each have many tiny projecting dendritic spines (DS) spaced closely

along their length, each of which is a site of a synapse with another neuron. Dendritic

spines are highly dynamic, the number of synapses changing constantly. (X650; Silver stain)

I.3 Axon

Most neurons have only one axon, typically longer than its dendrites. Axonal processes

vary in length and diameter according to the type of neuron. Axons of the motor neurons

that innervate the foot muscles have lengths of nearly a meter; large cell bodies are required

to maintain these axons, which contain most of such neurons’ cytoplasm. The plasma

membrane of the axon is often called the axolemma and its contents are known as

axoplasm (contains mitochondria, microtubules, neurofilaments, and transport vesicles, but

very few polyribosomes or cisternae of RER, features that emphasize the dependence of

axoplasm on the perikaryon). Axons originate from a pyramid-shaped region of the

perikaryon called the axon hillock (Figure 4), just beyond which the axolemma has

concentrated ion channels that generate the action potential. At this initial segment of the

axon, the various excitatory and inhibitory stimuli impinging on the neuron are algebraically

summed, resulting in the decision to propagate—or not to propagate—a nerve impulse.

Axons generally branch less profusely than dendrites, but do undergo terminal

arborization (Figure 4). Axons of interneurons and some motor neurons also have major

branches called collaterals that end at smaller branches with synapses influencing the

activity of many other neurons. Each small axonal branch ends with a dilation called a

terminal bouton (Fr. bouton, button) that contacts another neuron or non-nerve cell at a

synapse to initiate an impulse in that cell. If an axon is severed from its cell body, its distal

part quickly degenerates and undergoes phagocytosis.

DS

CB

D

D

D

6

Figure 4. (a) A “typical” neuron has three major parts: (1) The cell body (also called the perikaryon

or soma) is often large, with a large, euchromatic nucleus and well-developed nucleolus. The cyto-plasmic contains basophilic Nissl substance or Nissl bodies, which are large masses of free polysomes

and RER indicating the cell’s high rate of protein synthesis. (2) Numerous short dendrites extend from the perikaryon, receiving input from other neurons. (3) A long axon carries impulses from the cell body

and is covered by a myelin sheath composed of other cells. The ends of axons usually have many small

branches (telodendria), each of which ends in a knob-like structure that forms part of a functional connection (synapse) with another neuron or other cell.

(b) Micrograph of a large motor neuron showing the large cell body and nucleus (N), a long axon (A) emerging from an axon hillock (AH), and several dendrites (D). Nissl substance (NS) can be seen

throughout the cell body and cytoskeletal elements can be detected in the processes. Nuclei of

scattered glial

II. GLIAL CELLS

Glial cells support neuronal survival and activities, and are 10 times more abundant

than neurons in the mammalian brain. Like neurons most glial cells develop from progenitor

cells of the embryonic neural plate. In the CNS glial cells surround both the neuronal cell

bodies, which are often larger than the glial cells, and the processes of axons and dendrites

occupying the spaces between neurons. Except around the larger blood vessels, the CNS has

only a very small amount of connective tissue and collagen. Glial cells substitute for

cells of connective tissue in some respects, supporting neurons and creating immediately

around those cells microenvironments that are optimal for neuronal activity. The fibrous

a b a a b a

7

intercellular network of CNS tissue superficially resembles collagen by light microscopy,

but is actually the network of fine cellular processes emerging from neurons and glial cells.

Such processes are collectively called the neuropil (Figure 5).

Figure 5. (a) Most neuronal cell bodies (N) in the CNS are larger than the much more numerous glial cells (G)

that surround them. The various types of glial cells and their relationships with neurons are difficult to distinguish by most routine light microscopic methods. However, oligodendrocytes have condensed, rounded nuclei and unstained cytoplasm due to very abundant Golgi complexes, which stain poorly and are very likely represented by the cells with those properties seen here. The other glial cells seen here similar in overall size, but with very little cytoplasm and more elongated or oval nuclei, are mostly astrocytes. Routine H&E staining does not allow neuropil to stand out well. (X200; H&E) (b) With the use of gold staining for neurofibrils, neuropil (Np) is more apparent. (X200; Gold chloride and

hematoxylin)

There are six major kinds of glial cells, as shown schematically in Figure 9–9, four in the

CNS and two in the PNS. Their main functions, locations, and origins are summarized in

Table 9–2.

2.1 Oligodendrocytes

Oligodendrocytes (Gr. oligos, small, few + dendron, tree + kytos, cell) extend many

processes, each of which becomes sheetlike and wraps repeatedly around a portion of a

nearby CNS axon (Figure 9–9a). During this wrapping most cytoplasm gradually moves out

of the growing extension, leaving multiple compacted layers of cell membrane collectively

termed myelin. An axon’s full length is covered by the action of many oligodendrocytes.

The resulting myelin sheath electrically insulates the axon and facilitates rapid transmission

of nerve impulses. Found only in the CNS oligodendrocytes are the predominant glial cells

in white matter, which is white because of the lipid concentrated in the wrapped membrane

sheaths. The processes and sheaths are not visible by routine light microscope staining, in

which oligodendrocytes usually appear as small cells with rounded, condensed nuclei and

unstained cytoplasm (Figure 5.a).(Mescher 2018)

2.2 Astrocytes

Also unique to the CNS astrocytes (Gr. astro-, star + kytos) have a large number of long

radiating, branching processes (Figures 9–6 and 9–9a). Proximal regions of the astrocytic

processes are reinforced with bundles of intermediate filaments made of glial fibrillary acid

protein (GFAP), which serves as a unique marker for this glial cell. Distally the processes

lack GFAP, are not readily seen by microscopy, and form a vast network of delicate

terminals contacting synapses and other structures. Terminal processes of a single astrocyte

typically occupy a large volume and associate with over a million synaptic sites.

Astrocytes originate from progenitor cells in the embryonic neural tube and are by far the

most numerous glial cells of the brain, as well as the most diverse structurally and func-

8

tionally. Fibrous astrocytes, with long delicate processes, are abundant in white matter;

those with many shorter processes are called protoplasmic astrocytes and predominate in

the gray matter. The highly variable and dynamic processes mediate most of these cells

many functions.

Figure 6. (a) Astrocytes are the most abundant glial cells of the CNS and are characterized by numerous cytoplasmic

processes (P) radiating from the glial cell body or soma (S). Astrocytic processes are not seen with routine light microscope staining but are easily seen after gold staining. Morphology of the processes allows astrocytes to be classified as fibrous (relatively few and straight processes) or protoplasmic (numerous branching processes), but functional dif-ferences between these types are not clear. (X500; Gold chloride) (b) All astrocytic processes contain intermediate filaments of GFAP, and antibodies against this protein provide a simple method to stain these cells, as seen here in a fibrous astrocyte (A) and its processes. The small pieces of other GFAP-positive processes in the neuropil around this cell give an idea of the density of this glial cell and its processes in the CNS. Astrocytes form part of the blood-brain barrier (BBB) and help regulate entry of molecules and ions from blood into CNS tissue. Capillaries at the extreme upper right and lower left corners are enclosed by GFAP-positive perivascular feet (PF) at the ends of numerous astrocytic processes. (X500; Anti-GFAP immunoperoxidase and hematoxylin counterstain) (c) A length of capillary (C) is shown here completely covered by silver-stained terminal processes extending from astrocytes (A). (X400; Rio Hortega silver)

(Mescher 2018)

Functions attributed to astrocytes of various CNS regions include the following:

1. Extending processes that associate with or cover synapses, affecting the formation,

function, and plasticity of these structures.

2. Regulating the extracellular ionic concentrations around neurons, with particular

importance in buffering extracellular K+ levels.

3. Guiding and physically supporting movements and locations of differentiating neurons

during CNS development.

4. Extending fibrous processes with expanded perivascular feet that cover capillary

endothelial cells and modulate blood flow and help move nutrients, wastes, and other

metabolites between neurons and capillaries (Figure 9–9a).

5. Forming a barrier layer of expanded protoplasmic processes, called the glial limiting

membrane, which lines the meninges at the external CNS surface.

6. Filling tissue defects after CNS injury by proliferation to form an astrocytic scar.

MEDICAL APPLICATION Most brain tumors are astrocytomas derived from fibrous astrocytes. These are distinguished pathologically by their expression of GFAP.

a b c

9

Finally, astrocytes communicate directly with one another via gap junctions, forming a

very large cellular network for the coordinated regulation of their various activities in

different brain regions.

(Mescher 2018)

2.3 Ependymal Cells

Ependymal cells are columnar or cuboidal cells that line the fluid-filled ventricles of the

brain and the central canal of the spinal cord (Figures 9–9a and 9–7). In some CNS

locations, the apical ends of ependymal cells have cilia, which facilitate the movement of

cerebrospinal fluid (CSF), and long microvilli, which are likely involved in absorption.

Ependymal cells are joined apically by apical junctional complexes similar to those of

epithelial cells. However, unlike a true epithelium there is no basal lamina. Instead, the basal

ends of ependymal cells are elongated and extend branching processes into the adjacent

neuropil.

MEDICAL APLICATION

Alzheimer disease, a common type of dementia in the elderly, affects both neuronal perikarya

and synapses within the cerebrum. Functional defects are due to neurofibrillary tangles, which

are accumulations of tau protein associated with microtubules of the neuronal perikaryon and

axon hillock regions, and neuritic plaques, which are dense aggregates of β-amyloid protein that

form around the outside of these neuronal regions.

Figure 7 Ependymal cells are epithelial-like cells that form a single layer lining the fluid-filled ventricles and central canal of the CNS.

(a) Lining the ventricles of the cerebrum, columnar ependymal cells (E) extend cilia and microvilli from the apical surfaces into the ventricle (V). These modifications help circulate the CSF and monitor its contents. Ependymal cells have junctional complexes at their apical ends like those of epithelial cells but lack a basal lamina. The cells’ basal ends are tapered, extending processes that branch and penetrate some distance into the adjacent neuropil (N). Other areas of ependyma are responsible for production of CSF. (X100; H&E) (b) Ependymal cells (E) lining the central canal (C) of the spinal cord help move CSF in that CNS region. (X200; H&E)

10

2.4 Microglia

Less numerous than oligodendrocytes or astrocytes but nearly as common as neurons in

some CNS regions, microglia are small cells with actively mobile processes evenly

distributed throughout gray and white matter (Figures 9–9a and 9–12). Unlike other glial

cells microglia migrate, with their processes scanning the neuropil and removing

damaged or effete synapses or other fibrous components. Microglial cells also constitute

the major mechanism of immune defense in the CNS, removing any microbial invaders

and secreting a number of immunoregulatory cytokines. Microglia do not originate from

neural progenitor cells like other glia, but from circulating blood monocytes, belonging to

the same family as macrophages and other antigen-presenting cells.

Nuclei of microglial cells can often be recognized in routine hematoxylin and eosin

(H&E) preparations by their small, dense, slightly elongated structure, which contrasts with

the larger, spherical, more lightly stained nuclei of other glial cells. Immunohistochemistry

using antibodies against cell surface antigens of immune cells demonstrates microglial

processes. When activated by damage or microorganisms microglia retract their processes,

proliferate, and assume the morphologic characteristics and functions of antigen-presenting

cells.

2.5 Schwann Cells

Schwann cells (named for 19th century German histologist Theodor Schwann), sometimes

called neurolemmocytes, are found only in the PNS and differentiate from precursors in the

neural crest. Schwann cells are the counterparts to oligodendrocytes of the CNS, having

trophic interactions with axons and most importantly forming their myelin sheathes.

However unlike an oligodendrocyte, a Schwann cell forms myelin around a portion of only

one axon. Figure 9–9b shows a series of Schwann cells sheathing the full length of an axon,

a process described more fully with peripheral nerves.

2.6 Satellite Cells of Ganglia

Also derived from the embryonic neural crest, small satellite cells form a thin, intimate

glial layer around each large neuronal cell body in the ganglia of the PNS (Figures 9–9b and

9–13). Satellite cells exert a trophic or supportive effect on these neurons, insulating,

nourishing, and regulating their microenvironments.

Figure 8. Microglia are monocyte-derived, antigen-

presenting cells of the CNS, less numerous than astrocytes but nearly as common as neurons and evenly distributed in both gray and white matter. By immunohistochemistry, here using a monoclonal antibody against human leukocyte antigens (HLA) of immune-related cells, the short branching processes of microglia can be seen. Routine staining demonstrates only the small dark nuclei of the cells. Unlike other glia of the CNS, microglia are not interconnected; they are motile cells, constantly used in immune surveillance of CNS tissues. When activated by products of cell damage or by invading microorganisms, the cells retract their processes, begin phagocytosing the damage- or danger-related material, and behave as antigen-presenting cells. (X500; Antibody against HLA-DR and peroxidase) (Used with permission from Wolfgang Streit, Department of Neuroscience, University of Florida College of Medicine, Gainesville.)

11

Dikutip dari: (Mescher 2018)

12

B. CENTRAL NERVOUS SYSTEM (CNS)

The CNS is completely covered by connective tissue layers, the meninges, but CNS

tissue contains very little collagen or similar material, making it relatively soft and easily

damaged by injuries affecting the protective skull or vertebral bones.

I. White matter

The main components of white matter are myelinated axons (Figure 9–14), often grouped

together as tracts, and the myelin-producing oligodendrocytes. Astrocytes and microglia are

also present, but very few neuronal cell bodies. Most white matter is found in deeper region

of both the cerebrum and the cerebellum

II. Gray matter Gray matter contains abundant neuronal cell bodies, dendrites, astrocytes, and microglial

cells, and is where most synapses occur. Gray matter makes up the thick cortex or surface

layer of both the cerebrum and the cerebellum.

Many regions show organized areas of white matter and gray matter, differences

caused by the differential distribution of lipid-rich myelin. Deep within the brain are

localized, variously shaped darker areas called the cerebral nuclei, each containing large

numbers of aggregated neuronal cell bodies.

In the folded cerebral cortex, neuroscientists recognize six layers of neurons with

different sizes and shapes. The most conspicuous of these cells are the efferent pyramidal

neurons (Figure 9–15). Neurons of the cerebral cortex function in the integration of sensory

information and the initiation of voluntary motor responses.

The sharply folded cerebellar cortex coordinates muscular activity throughout the body

and is organized with three layers (Figure 9–16):

1. A thick outer molecular layer has much neuropil and scattered neuronal cell bodies.

2. A thin middle layer consists only of very large neurons called Purkinje cells (named for

the 19th century Czech histologist Jan Purkinje). These are conspicuous even in H&E-

stained sections, and their dendrites extend throughout the molecular layer as a branching

basket of nerve fibers (Figures 9–16c and d).

3. A thick inner granular layer contains various very small, densely packed neurons

(including granule cells, with diameters of only 4-5 μm) and little neuropil.

13

In cross sections of the spinal cord, the white matter is peripheral and the gray matter

forms a deeper, H-shaped mass (Figure 9–17). The two anterior projections of this gray

matter, the anterior horns, contain cell bodies of very large motor neurons whose axons

make up the ventral roots of spinal nerves. The two posterior horns contain interneurons

which receive sensory fibers from neurons in the spinal (dorsal root) ganglia. Near the

middle of the cord the gray matter surrounds a small central canal, which develops from

the lumen of the neural tube, is continuous with the ventricles of the brain, is lined by

ependymal cells, and contains CSF.

III. Meninges

The skull and the vertebral column protect the CNS, but between the bone and nervous

tissue are membranes of connective tissue called the meninges. Three meningeal layers are

distinguished: the dura, arachnoid, and pia maters (Figures 9–18 and 9–19).

3.1 Dura Mater

The thick external dura mater (L. dura mater, tough mother) consists of dense

irregular connective tissue organized as an outer periosteal layer continuous with the

periosteum of the skull and an inner meningeal layer. These two layers are usually fused,

but along the superior sagittal surface and other specific areas around the brain they separate

to form the blood-filled dural venous sinuses (Figure 9–19). Around the spinal cord the

dura mater is separated from the periosteum of the vertebrae by the epidural space, which

contains a plexus of thin-walled veins and loose connective tissue (Figure 9–18). The dura

mater may be separated from the arachnoid by formation of a thin subdural space.

3.2 Arachnoid

The arachnoid (Gr. arachnoeides, spider web-like) has two components: (1) a sheet of

connective tissue in contact with the dura mater and (2) a system of loosely arranged

trabeculae composed of collagen and fibroblasts, continuous with the underlying pia

mater layer. Surrounding these trabeculae is a large, sponge-like cavity, the subarachnoid

space, filled with CSF. This fluid-filled space helps cushion and protect the CNS from

minor trauma. The subarachnoid space communicates with the ventricles of the brain where

the CSF is produced.

The connective tissue of the arachnoid is said to be avascular because it lacks nutritive

capillaries, but larger blood vessels run through it (Figures 9–18 and 9–19). Because the

arachnoid has fewer trabeculae in the spinal cord, it can be more clearly distinguished from

the pia mater in that area. The arachnoid and the pia mater are intimately associated and are

often considered a single membrane called the pia-arachnoid.

In some areas, the arachnoid penetrates the dura mater and protrudes into blood-filled

dural venous sinuses located there (Figure 9–19). These CSF-filled protrusions, which are

covered by the vascular endothelial cells lining the sinuses, are called arachnoid villi and

function as sites for absorption of CSF into the blood of the venous sinuses.

3.3 Pia Mater

The innermost pia mater (L. pia mater, tender mother) consists of flattened,

mesenchymally derived cells closely applied to the entire surface of the CNS tissue. The pia

does not directly contact nerve cells or fibers, being separated from the neural elements by

14

the very thin superficial layer of astrocytic processes (the glial limiting membrane, or glia

limitans), which adheres firmly to the pia mater. Together, the pia mater and the layer of

astrocytic end feet form a physical barrier separating CNS tissue from CSF in the

subarachnoid space (Figure 9–19).

Blood vessels penetrate CNS tissue through long perivascular spaces covered by pia mater,

although the pia disappears when the blood vessels branch to form the small capillaries.

However, these capillaries remain completely covered by the perivascular layer of astrocytic

processes (Figures 9–9a and 9–10c).

IV. Blood-Brain Barrier

The blood-brain barrier (BBB) is a functional barrier that allows much tighter control

than that in most tissues over the passage of substances moving from blood into the CNS

tissue. The main structural component of the BBB is the capillary endothelium, in which

the cells are tightly sealed together with well-developed occluding junctions, with little or

no transcytosis activity, and surrounded by the basement membrane. The limiting layer of

perivascular astrocytic feet that envelops the basement membrane of capillaries in most

CNS regions (Figure 9–10c) contributes to the BBB and further regulates passage of

molecules and ions from blood to brain.

The BBB protects neurons and glia from bacterial toxins, infectious agents, and other

exogenous substances, and helps maintain the stable composition and constant balance of

ions in the interstitial fluid required for normal neuronal function. The BBB is not present in

regions of the hypothalamus where plasma components are monitored, in the posterior

pituitary which releases hormones, or in the choroid plexus where CSF is produced.

V. Choroid Plexus

The choroid plexus consists of highly vascular tissue, elaborately folded and projecting into

the large ventricles of the brain (Figure 9–20a). It is found in the roofs of the third and

fourth ventricles and in parts of the two lateral ventricular walls, all regions in which the

ependymal lining directly contacts the pia mater.

Each villus of the choroid plexus contains a thin layer of well-vascularized pia mater

covered by cuboidal ependymal cells (Figure 9–20b). The function of the choroid plexus is

to remove water from blood and release it as the CSF. CSF is clear, contains Na+, K+, and

Cl– ions but very little protein, and its only cells are normally very sparse lymphocytes. It is

produced continuously and it completely fills the ventricles, the central canal of the spinal

cord, the subarachnoid and perivascular spaces. It provides the ions required for CNS

neuronal activity and in the arachnoid serves to help absorb mechanical shocks. Arachnoid

villi (Figure 9–19) provide the main pathway for absorption of CSF back into the venous

circulation. There are very few lymphatic vessels in CNS tissue.

PERIPHERAL NERVOUS SYSTEM The main components of the peripheral nervous system (PNS) are the nerves, ganglia,

and nerve endings. Peripheral nerves are bundles of nerve fibers (axons) individually sur-

rounded by Schwann cells and connective tissue.

1. Nerve Fibers

Nerves are analogous to tracts in the CNS, containing axons enclosed within sheaths of glial

cells specialized to facilitate axonal function. In peripheral nerves, axons are sheathed by

15

Schwann cells or neurolemmocytes (Figure 9–9b). The sheath may or may not form myelin

around the axons, depending on their diameter.

1.a Myelinated Fibers

As axons of large diameter grow in the PNS, they are engulfed along their length by a

series of differentiating neurolemmocytes and become myelinated nerve fibers. The

plasma membrane of each covering Schwann cell fuses with itself at an area termed the

mesaxon and a wide, flattened process of the cell continues to extend itself, moving

circumferentially around the axon many times (Figure 9–21). The multiple layers of

Schwann cell membrane unite as a thick myelin sheath. Composed mainly of lipid bilayers

and membrane proteins, myelin is a large lipoprotein complex that, like cell membranes, is

partly removed by standard histologic procedures (Figures 9–14 and 9–17d). Unlike

oligodendrocytes of the CNS, a Schwann cell forms myelin around only a portion of one

axon.

With high-magnification TEM, the myelin sheath appears as a thick electron-dense

axonal covering in which the concentric membrane layers may be visible (Figure 9–22). The

prominent electron-dense layers visible ultrastructurally in the sheath, the major dense

lines, represent the fused, protein-rich cytoplasmic surfaces of the Schwann cell membrane.

Along the myelin sheath, these surfaces periodically separate slightly to allow transient

movement of cytoplasm for membrane maintenance; at these myelin clefts (or Schmidt-

Lanterman clefts) the major dense lines temporarily disappear (Figure 9–23). Faintly seen

ultrastructurally in the light staining layers are the intraperiod lines that represent the

apposed outer bilayers of the Schwann cell membrane.

Membranes of Schwann cells have a higher proportion of lipids than do other cell

membranes, and the myelin sheath serves to insulate axons and maintain a constant ionic

microenvironment most suitable for action potentials. Between adjacent Schwann cells on

an axon the myelin sheath shows small nodes of Ranvier (or nodal gaps, Figures 9–9b, 9–

23, and 9–24), where the axon is only partially covered by interdigitating Schwann cell

processes. At these nodes the axolemma is exposed to ions in the interstitial fluid and has a

much higher concentration of voltage-gated Na+ channels, which renew the action potential

and produce saltatory conduction (L. saltare, to jump) of nerve impulses, their rapid

movement from node to node. The length of axon ensheathed by one Schwann cell, the

internodal segment, varies directly with axonal diameter and ranges from 300 to 1500 μm.

1.b. Unmyelinated Fibers

Unlike the CNS where many short axons are not myelinated at all but course among other

neuronal and astrocytic processes, the smallest diameter axons of peripheral nerves are still

enveloped within simple folds of Schwann cells (Figure 9–25). These very small

unmyelinated fibers do not however undergo multiple wrapping to form a myelin sheath

(Figure 9–21). In unmyelinated nerves each Schwann cell can enclose portions of many

axons with small diameters. Without the thick myelin sheath, nodes of Ranvier are not seen

along unmyelinated nerve fibers. Moreover, these small-diameter axons have evenly

distributed voltage-gated ion channels; their impulse conduction is not saltatory and is much

slower than that of myelinated axons.

Nerve Organization

In the PNS, nerve fibers are grouped into bundles to form nerves. Except for very thin

nerves containing only unmyelinated fibers, nerves have a whitish, glistening appearance

because of their myelin and collagen content.

16

Axons and Schwann cells are enclosed within layers of connective tissue (Figures 9–24,

9–26, and 9–27). Immediately around the external lamina of the Schwann cells is a thin

layer called the endoneurium, consisting of reticular fibers, scattered fibroblasts, and

capillaries. Groups of axons with Schwann cells and endoneurium are bundled together as

fascicles by a sleeve of perineurium, containing flat fibrocytes with their edges sealed

together by tight junctions. From two to six layers of these unique connective tissue cells

regulate diffusion into the fascicle and make up the blood-nerve barrier which helps

maintain the fibers’ microenvironment. Externally, peripheral nerves have a dense, irregular

fibrous coat called the epineurium, which extends deeply to fill the space between

fascicles.

Very small nerves consist of one fascicle (Figure 9–28). Small nerves can be found in

sections of many organs and often show a winding disposition in connective tissue.

Peripheral nerves establish communication between centers in the CNS and the sense organs

and effectors (muscles, glands, etc). They generally contain both afferent and efferent fibers.

Afferent fibers carry information from internal body regions and the environment to the

CNS. Efferent fibers carry impulses from the CNS to effector organs commanded by these

centers. Nerves possessing only sensory fibers are called sensory nerves; those composed

only of fibers carrying impulses to the effectors are called motor nerves. Most nerves have

both sensory and motor fibers and are called mixed nerves, usually also with both

myelinated and unmyelinated axons.

2. Ganglia

Ganglia are typically ovoid structures containing neuronal cell bodies and their surrounding

glial satellite cells supported by delicate connective tissue and surrounded by a denser

capsule. Because they serve as relay stations to transmit nerve impulses, at least one nerve

enters and another exits from each ganglion. The direction of the nerve impulse determines

whether the ganglion will be a sensory or an autonomic ganglion.

2.a Sensory Ganglia

Sensory ganglia receive afferent impulses that go to the CNS. Sensory ganglia are

associated with both cranial nerves (cranial ganglia) and the dorsal roots of the spinal nerves

(spinal ganglia). The large neuronal cell bodies of ganglia (Figure 9–29) are associated with

thin, sheetlike extensions of small glial satellite cells (Figures 9–9b and 9–13). Sensory

ganglia are supported by a distinct connective tissue capsule and an internal framework

continuous with the connective tissue layers of the nerves. The neurons of these ganglia are

pseudounipolar and relay information from the ganglion’s nerve endings to the gray matter

of the spinal cord via synapses with local neurons.

2.b Autonomic Ganglia

Autonomic (Gr. autos, self + nomos, law) nerves effect the activity of smooth muscle, the

secretion of some glands, heart rate, and many other involuntary activities by which the

body maintains a constant internal environment (homeostasis). Autonomic ganglia are

small bulbous dilations in autonomic nerves, usually with multipolar neurons. Some are

located within certain organs, especially in the walls of the digestive tract, where they

constitute the intramural ganglia. The capsules of these ganglia may be poorly defined

among the local connective tissue. A layer of satellite cells also envelops the neurons of

autonomic ganglia (Figure 9–29), although these may also be inconspicuous in intramural

ganglia.

Autonomic nerves use two neuron circuits. The first neuron of the chain, with the

preganglionic fiber, is located in the CNS. Its axon forms a synapse with postganglionic

17

fibers of the second multipolar neuron in the chain located in a peripheral ganglion system.

The chemical mediator present in the synaptic vesicles of all preganglionic axons is

acetylcholine.

As indicated earlier autonomic nerves make up the autonomic nervous system. This has

two parts: the sympathetic and the parasympathetic divisions. Neuronal cell bodies of

preganglionic sympathetic nerves are located in the thoracic and lumbar segments of the

spinal cord and those of the parasympathetic division are in the medulla and midbrain and in

the sacral portion of the spinal cord. Sympathetic second neurons are located in small

ganglia along the vertebral column, while second neurons of the parasympathetic series are

found in very small ganglia always located near or within the effector organs, for example in

the walls of the stomach and intestines. Parasympathetic ganglia may lack distinct capsules

altogether, perikarya and associated satellite cells simply forming a loosely organized plexus

within the surrounding connective tissue.

NEURAL PLASTICITY & REGENERATION Despite its general stability, the nervous system exhibits neuronal differentiation and

formation of new synapses even in adults. Embryonic development of the nervous system

produces an excess of differentiating neurons, and the cells which do not establish correct

synapses with other neurons are eliminated by apoptosis. In adult mammals after an injury,

the neuronal circuits may be reorganized by the growth of neuronal processes, forming new

synapses to replace ones lost by injury. Thus, new communications are established with

some degree of functional recovery. This neural plasticity and reformation of processes are

controlled by several growth factors produced by both neurons and glial cells in a family of

proteins called neurotrophins.

Neuronal stem cells are present in the adult CNS, located in part among the cells of the

ependyma, which can supply new neurons, astrocytes, and oligodendrocytes. Fully

differentiated, interconnected CNS neurons cannot temporarily disengage these connections

and divide to replace cells lost by injury or disease; the potential of neural stem cells to

allow tissue regeneration and functional recovery within the CNS components is a subject of

intense investigation. Astrocytes do proliferate at injured sites and these growing cells can

interfere with successful axonal regeneration in structures such as spinal cord tracts.

In the histologically much simpler peripheral nerves, injured axons have a much greater

potential for regeneration and return of function. If the cell bodies are intact, damaged, or

severed PNS axons can regenerate as shown in the sequence of diagrams in Figure 9–30.

Distal portions of axons, isolated from their source of new proteins and organelles,

degenerate; the surrounding Schwann cells dedifferentiate, shed the myelin sheaths, and

proliferate within the surrounding layers of connective tissue. Cellular debris including shed

myelin is removed by blood-derived macrophages, which also secrete neurotrophins to

promote anabolic events of axon regeneration.

The onset of regeneration is signaled by changes in the perikaryon that characterize the

process of chromatolysis: the cell body swells slightly, Nissl substance is initially dimin-

ished, and the nucleus migrates to a peripheral position within the perikaryon. The proximal

segment of the axon close to the wound degenerates for a short distance, but begins to grow

again distally as new Nissl substance appears and debris is removed. The new Schwann

cells align to serve as guides for the regrowing axons and produce polypeptide factors which

promote axonal outgrowth. Motor axons reestablish synaptic connections with muscles and

function is restored.

18

F Activity Lab

1. Students will be divided into 17 groups

2. Discussion in 20 minute:

3. Identify tissue section using light microscopy and draw it , in 50 minute

4. LIST MICROSTRUCTURE IDENTIFY REVIEW ( give the checklist √ if you

have already known)

I. Neuron and neuroglia Check

list

1. Neuron (Preparat: Motor neuron)

- Identify part of the neuron cell (cell body, axon and dendrit).

Draw !

100 x

1000X

19

Identify the structure below, then fill in the box below with the appropriate structure

!

20

2. Neuroglia ( Preparat : Medulla spinalis/cerebrum cortex/)

Identify type cell of neuroglia : astrocyte, microglia, oligodendrosit.)

Draw !

21

Ada halo Bening di sekitar sel

22

II. Nerve tissue (Grey matter of cerebrum)

1. Cerebrum

- Indentify part of cerebrum (grey matter/cortex) and medulla (white matter) 40X

- Identify of neuron, Neuroglia , meningens (piamater, arachnoid space and

arachnoid) 400x/1000x

Mention layer of cerebrum

23

Grey matter 1000X White matter 1000X

Meningens: Piamater and Arachnoid 1000x

Indentify meningens of cerebrum and fill in the box below with the appropriate

structure name.

2. Cerebellum

24

- Identify three layer of cerebellum -- 100X

- Indentify of purkinje cell in middle layer 400x

malphigian layer

Draw ( 100x)

Draw (400x/1000X)

Identify the structure below

25

Cerebellum

Layers of the skin

]

Neuron cell

2. Medulla spinalis

…………. layer

………….. layer

26

- Indentify part of medulla spinalis (grey matter/central) and medulla (white

matter/perifer) -> 40X

- Identify of neuron, meningens, canalis centralis, duramater 400x/1000x

Draw !

Medulla spinalis 40 X

III. Peripheral Nerve Tissue

Canalis ……….

27

3.1 Ganglion

1. Sensorik Ganglion (somatik)

- Identify distribution of ganglion cell and ganglion organ microstructure

- Indentify morfology of the ganglion cells bellow

Draw

2. Autonom genglion

- Identify distribution of ganglion cell and ganglion organ microstructure

- Indentify morfology of the ganglion cells bellow

Draw

Identify the structure bellow and fill in the box below with the appropriate structure

28

Sensorik Ganglion 100X

Ganglion Cells 1000X

Give an arrow to the appropriate structure !

Satelit cells

Ganglion cells

29

Ganglion Autonom 40X

Ganglion Autonom 1000X

3.2 Nerve fiber

30

1. Cross section

- Identify epineurium, perineurium and endoneurium

Draw !

2. Longitudinal section

Draw !

Identify teh structure bellow, fill

31

IV. Motor end plate (sceletal muscle, Ag Nitrat)

32

1. Motor end plate

Identify motor end plate at scleletal muscle preparat

Draw 400X

Identify the structure below, and fill in the box below with the appropriate structure

G Reference

Gartner, L.P., 2017. Text Book of Histology Fourth.,

Mescher, A.L., 2018. The text book of Histology Edisi 15.,