This document summarizes the structure and function of nervous tissue. It describes the key components of neurons including the soma, dendrites, axon, and inclusions. It discusses the classifications of neurons based on morphology and function. The roles of neuroglial cells like astrocytes, oligodendrocytes, microglia, ependymal cells, and Schwann cells are outlined. The generation and conduction of nerve impulses, synaptic transmission, and the layers of connective tissue surrounding peripheral nerves are also summarized.

1. NERVOUS TISSUE
Prof. Redem C. Deligero, MATMRS, MSES

2. SOMA OF A NEURONS

For the reception and transmission
of nerve impulses to and from the
CNS.
Component of the Soma/Perikaryon:
1. Nucleus

Large, spherical to ovoid &
centrally located.
2. Cytoplasm

Abundant RER with many
cisternae in parallel arrays.

With scattered polyribsomes.

Prominent Golgi Complex &
numerous mitochondria

There is only one centriole
present.

3. SOMA OF NEURONS
3. Inclusions

Nonliving substance that encompass the neuronal
cell bodies.
A. Melanin Granules

Found in regions of CNS mostly in the substancia
nigra, locus ceruleus & symphathetic ganglia of PNS.
B. Lipofuscin

Irregularly shaped, yellowish brown pigment
granules.

Prevalent in neuronal cytoplasm of older adult.
C. Lipid Droplets

Maybe observed as a result of faulty metabolism or
energy reserves.

4. DENDRITES OF NEURONS

A ramification of a single short trunk into
smaller and smaller branches tapering at the
end like branches of trees.

Dendritic base contain the usual complement
organelle except Golgi Complexes.

Spines are found on the surface of some
dendrites.

5. AXON OF NEURONS

Transmit impulses to other neurons or
effector cells. (e.g. muscles or glands)

Arises from axon hillock of the cell body
extending in long distance.

Its thickness is related to conduction velocity.

On the axolemma of of the initial segment
lacks RER & ribosomes but with abundant
microtubules and neurofilaments.

Spike trigger zone is also present in the initial
segment.

6. AXON OF NEURONS

The axoplasm has short profiles of SER, long thin
mitochondria & numerous microtubules.

RER and polyribosomes are absent.

Somes axons of the CNS and PNS are myelinated.

Axonal Transport of materials between soma and axon
terminals is crucial to trophic relationship.(e.g. neurons
and muscle or glands)

Organelles, vesicles, actin, myosine, clathrin and
enzymes for neurotransmitter synthesis at axon
terminals.

Protien building blocks of neurofilament, sub units of
microtubules, soluble ezymes and materials taken by
endocytosis.

7. MORPHOLOGICALCLASSIFICATION OF NEURONS
1. BIPOLAR

Has 2 processes from the soma, a single denrite and single
axon.
 Located at vestibular and cochlear ganglia, & in olfactory
epithelium of nasal cavity.
2. UNIPOLAR

Only one process that branch in peripheral and central
branches.
 Develop from embryonic bipolar neurons.

Present in dorsal root ganglia and some cranial nerve ganglia.
3. MULTIPOLAR

Most common with various arrangement of multiple
dendrites from soma and single axon.

Present throughout the nervous system and most are motor
neurons.

9. FUNCTIONAL CLASSIFICATION OF NEURONS
1. SENSORY (Afferent)

Receive sensory input at dendritic terminals and
conduct impulse to CNS for processing.
2. MOTOR (Efferent)

Conduct impulse from CNS to muscles, glands and
other neurons.
3. INTERNEURON

Neuronal circuits between sensory and motor
neurons and other neurons.

10. NEUROGLIAL CELLS (Astrocytes)

Largest of the neuroglial cells.

For physical and metabolic support of neurons.
Astrocyte Types:
1. Protoplasmic Astrocyte

In the Gray Matter of CNS.

Stellate cells with abundant cytoplasm and large nucleus.

Tip of some processes end as pedicels (vascular feet)
2. Fibrous Astrocyte

In the white matter of CNS.

With euchromatic cytoplasm with few organelles, free
ribosomes and glycogen.

11. NEUROGLIAL CELLs (Oligodendrocytes)

Resembles astrocytes but
are smaller and has fewer
processes.

Darkly stained in the Gray
& White Matter of CNS.
Types of Oligodendrocytes:
1. Iterfasicular
Oligodendrocytes

For manufacturing and
maintaining myelin.
2. Satellite
Oligodendrocytes

Closely applied to cell
bodies of large
neurons whose
function is not clear.

12. NEUROGLIAL CELLS (Microglia)

Member of mononuclear phagocyte system &
scattered throughout CNS.

It resembles oligodendrocyte with oval to
triagular nucleus.

Spines adorn the body.

When activated will act as antigen-presenting
cells and secrete cytokines.

13. NEUROGLIAL CELLS (Ependymal Cells)

Low columnar to cuboidal cells lining brain
ventricles and central canal of spinal cord.

Derived from embryonic epithelium of
developing nervous system.

It facilates the movement of cerebrospinal
fluid.

14. NEUROGLIAL (Schwann Cells)

Serves as axon envelop at the PNS.

Cells and nucleus are flattened, small golgi apparatus and few
mitochondria.

Schwann cells plasmalemma (myelin) wrapped axons several
times.

Basal lamina (outer portion of schwann cells) dips into the
nodes of Ranvier.

Schwann cells cytoplasm trapped within the lamellae of
myelin.

Cytoplasmic surface of schwann cell plasmalemma fused
producing series of alternating wide dense line and less dense
line.

Gaps are formed to provide access for small molecules to
reach axons.

16. GENERATION AND CONDUCTION OF NERVE IMPULSE
1. Stimulation of a neuron causes opening of
voltage gated Na+
channels in small region of
membrane leading to an influx of sodium into
the cell at the site.
2. Sodium channels becomes inactivated for 1-2
msec.
3. Influx of K+
into the extracellular fluid that
restores resting membrane potential.
4. Voltage-gated K+
channel close and refractory
period ended.

17. TRANSMISSION OF NERVE IMPULSE

Nerve impulse are tranmitted from presynaptic
cell to postsynaptic cell.
2 Ways of Synapse Transmission:
1. Electrical Synapses

At brain stem, retina & cerebral cortex.

This synapse is represented by gap junction
which permits free movement of ions.
2. Chemical Synapses

The most common mode of communication
between two nerve cells.

Impulse is carried in the form of
neurotransmitter released into synaptic cleft.

18. SYNAPTIC CONTACTS
1. AXODENDRITIC SYNAPSE - Axon & Dendrite
2. AXOSOMATIC SYNAPSE - Axon and Soma
3. AXOAXONIC SYNAPSE - 2 axons
4. DENDRODENDRITIC SYNAPSE - 2 dendrites

19. SYNAPTIC MORPHOLOGY

Synapse may form bulbous expansion at the
terminal end.

Some synapse form from swelling along the
axons.

Presynaptic membrane has mitochondria, few
elements of SER and abundance of synaptic
vessels.

Cell adhesion molecules are presents both at
presynaptic and postsynaptic aspects of
synapse.

20. DIFFERENT CELL ADHESION MOLECULES
1. SYNAPSIN I

Small proteins that assists in the clustering of
synaptic vesicle.
2. SYNAPSIN II

Also known as (rab3a) controls association of the
vesicles with actin microfilaments.

Synaptotagamin and Synaptophysin are additional
synaptovesicle proteins.

SNARE (SNAP receptor) influence fusion of
synaptic vesicle with presynaptic membrane.

21. PERIPHERAL NERVES

Bundles of nerve fibers surrounded by several investments of connective
tissue sheaths.
Connective Tissue Investments:
1. EPINEURIUM

Dense collagenous connective tissue

Has thick elastic fibers that ensheath the nerve.

Collagen fibers are also present.

Thick at dura covering CNS at spinal cord or brain.
2. PERINEURIUM

Dense connective tissue.

Inner surface is lined with epitheloid cells joined by zonolae occuledentes
surrounded by basal lamina.
3. ENDONEURIUM

A loose connective tissue surrounding an axon.

Composed of reticular fibers, scattered fibroblast, fix macrophages,
capillaries and perivascular mast cells.