General Histology and Histotechnique Student-made handout. Credits to the original owner of the reference in this handout,

1. General Histology and Histotechnique (1st semester; 2012-2013)
NERVOUS TISSUE - respond and integrates decision
Motor or efferent neurons
Nervous system - Carry information out of the brain and spinal cord
- Complex, highly organized network of billions of going to the effectors
neurons and even more neuroglia Effectors
Components: - Cells and organs innervated by motor neurons
 Brain – contain 100 billion of neurons - Simply the muscle and glands.
 Cranial nerves and their branches
- 12 pairs of left and right, emerge from the base of Nervous Tissue
brain. - Responsible for communication and sending
 Spinal cord impulses.
- It connects to the brain through the foramen Consists of Two principal kinds of cells:
magnum
- Spinal nerves – 31 pairs emerging from the spinal 1. Neurons/ nerve cells
cord. 2. Neuroglia/ glial cells
 Spinal nerves and their branches
 Ganglia – small mass of nervous tissue and contains I. Neurons
cell bodies of neurons - Responsible for most special functions attributes to
Location: outside of central nervous tissue, outside of the nervous system:
the brain & spinal cord o Sensing
- Closely associated with the cranial nerve and spinal o Thinking
cord. o Remembering
 Enteric plexus – located on the walls of digestive o Controlling muscle activity
tracts – G.I.T. o Regulating glandular secretions
Function: Regulate the functions of Digestive system - Have the property of electrical excitability
 Sensory receptors  Capacity to produce
- Either dendrites of sensory neurons action potential or
- Specialized cells that monitor change in the internal responses to stimuli
wall as well as the external environment. - Many neurons also contain Lipofuscin
Ex. Pacinian corpuscles, ductile corpuscles  Pigments
 Occur as clumps of
Major structures of Nervous system yellowish brown
granules in the
Three Basic functions of Nervous System cytoplasm of neurons.
 Product of neuronal
1. Sensory function lysosomes that
- Internal: increase in blood acidity accumulate as neuron
- External: raindrop landing on arm ages.
Sensory or afferent neurons Parts:
- Neurons that carry information into the brain and
spinal cord. 1. Cell body
- Star shaped
2. Integrative function Components:
- Integrates (process) sensory information o Cytoplasm = Neuroplasm
- Analyze, store, made decisions regarding o Plasma membrane = Neurolemma
appropriate responses Organelles:
Interneurons: neurons for integration o Mitochondria
- Makes up vast majority of neurons in the body o Lysosomes
o Golgi complex
3. Motor function o Nissl bodies

2. General Histology and Histotechnique (1st semester; 2012-2013)
- prominent clusters of rough endoplasmic reticulum Synapse
Function: - the site of communication between two neurons or
- Produces proteins that are used by the cell body between a neuron and an effectors cell
- Replaced cellular components Synaptic end bulb: bulb-shaped structure of axon
- Used as a material for growth of neurons terminals.
- Regenerate damage axons in PNS Varicosities: String of swollen bumps of axon terminals
- Contains synaptic vesicles
2. Processes  Stores chemical neurotransmitter
 Triggers acetylcholine
a. Dendrites (little trees) - Neurotransmitter - acetylcholine
- receiving input portion of the neuron  Influenced the activity of other
neurons, muscle fibers and gland cells.
b. Axon (axis)
- Propagates nerve impulses toward another neuron, Types of transport systems:
a muscle fiber, or a gland cell.
- A long, thin, cylindrical projection 1. Slow axonal transport
- Slower system
Parts: - Moves materials about 1-5mm per day
1. Axon Hillock - Conveys axoplasm in one direction only
- Resemble a small hill - From cell body to axon terminals
- Cone- shaped elongation that joins the cell body - Supplies new axoplasm for developing or
and the axon. regenerating axons
- Replenishes axoplasm in growing and mature axon
2. Initial segment - Carry materials from body to axon then back again
- First part of axon
*** 1 &2 Function: 2. Fast axonal transport
- Responsible for the occurrence of impulses in an - Faster system
axon known as trigger zone. - Capable of moving materials a distance of 200-400
mm per day
3. Axoplasm – cytoplasm of axon - Uses proteins that function as motors to move
materials in both directions – away from and
4. Axolemma – plasma membrane that covers the toward the cell body – along the surface of
axon. microtubules
- Moves various organelles and materials that form
5. Axon Collateral the membranes of the axolemma, synaptic and
- Side branches of axons at right angle of the axon bulbs and synaptic vesicles
Function: Provides modulation of axon/cell firing
Clinical application
6. Node of Ranvier
- Neurofibril node Tetanus
- Indentation between the axon connecting one from - Fast axonal transport is the route by which some
the other. toxins and disease – causing viruses make their way
Importance: To speed-up the process of transmitting from axon terminals near the skin cuts to cell bodies
signals from the CNS to effectors cells (Muscle cell of neurons, where they can cause damage.
glands). - Toxin produced by Clostridium tetanus is carried by
fast axonal transport to the CNS disrupting the
7. Axon terminal actions of motor neurons, causing prolong painful
- Fine processes at end of the axon muscle spasms – condition called Tetanus.
- Swell into bulb shaped structures
- Synaptic end bulb Structural Diversity of Neurons

3. General Histology and Histotechnique (1st semester; 2012-2013)
Neurons display great diversity in size and shape - Multiply and divide in the mature nervous system
- Supporting tissues of the brain and spinal cord
A. According to function
Types:
1. Motor neuron
- Transmit impulses to the motor cells 1. Astrocytes
- Largest neuroglia
2. Sensory neuron - Star shape with long processes
- Transmit impulses from neurons to the senses Functions:
- Help maintain appropriate chemical environment
3. Associative neuron for the generation of action potential
- Neurons connecting motor from sensory neuron - Provides nutrients to neurons
- It takes up excess neurotransmitters and participate
B. According to number of nerve process in the metabolism of neurotransmitters
1. Multipolar neurons Two types of Astrocytes:
- Have a several dendrites and one axon a. Protoplasmic astrocyte
- Abundance of cyplasmic granules
2. Bipolar neurons - Found in gray matter
- One dendrites and One Axon
Location: Retina of the eye, inner ear, olfactory area of b. Fibrous astrocyte
the brain. - Long-slender
- Found in white matter
3. Unipolar neurons
- Sensory neurons that originate from the embryo as 2. Oligodendrocyte
bipolar - Round/oval body
- One dendrite and One axon - Few processes
- Smaller than astrocyte
C. According to size and shape Functions:
- It forms the supporting network around the CNS
1. Interneurons neuron
- Occupy 90% of the total neurons of the body - Produce myelin sheath around axon of CNS neurons
Function: Carry impulses from one neuron to another
3. Microglia
a. Pyramidal cells - Small cells
- Pyramid like shape - Fewer than oligodendrocyte
- Center of cerebral cortex - Derived in mesodermal cells
 Largest part of brain - It gives rise to monocyte and macrophages
Functions:
b. Purkinje cells - It protects CNS cells from diseases
- Found in the cerebellum - Engulfed microorganisms
- Clear away debris/dead cells
c. Renshaw cells/ Inhibitory interneuron
- Stellate cells 4. Ependymal cells
- Found in the spinal cord - Epithelial cells and arranged in single layer with
microvilli and cilia
II. Neuroglia - Shape: Columnar  cuboidal
- Constitute about half the volume of CNS - Ciliated
- 5-50 time more numerous than neurons Functions:
- Do not generate action potential

4. General Histology and Histotechnique (1st semester; 2012-2013)
- It lines the ventricles of brain and central canal of 3. Gives color to the white matter in the CNS
spinal cord
- It forms the CSF (cerebrospinal fluid); assist in 2. Unmyelinated nerve fiber
circulation - No myelin sheath
- Surrounded by coat of neuroglial plasma membrane
5. Schwann cells - Fiber is enclosed by the Schwann cell only in PNS
- Flattened cell - Fiber is not unsheathed in CNS
- Encircles the PNS axon - Impulse is conducted as a continuous wave of
- Produces myelin sheath around the single axon of voltage reversal to the end of the axon.
PNS neuron
Function: Neuroglial cells that produces Myelin sheath:
- Participate in the regeneration of PNS axon.
1. Schwann cells in PNS
6. Satellite cell - Begin to form myelin sheath around axon during
- Surrounds neurons cell body fetal development neurolemma: sheath of Schwann
Function: enclosing myelin sheath.
- Support neurons in ganglia - Aids in regeneration that forms regeneration tube
that guides and stimulates regrowth of axon.
Nodes of Ranvier: gaps in myelin sheath
Nerve fibers
- General term for any process (axon of dendrite) 2. Oligodendrocytes in CNS
projecting from the cell body of a neuron - Myelinated parts of many axons in the same
- It is also a connective tissue manner that a Schwann cell myelinates part of a
single PNS axon
Connective tissue sheaths: - Neurolemma is not present
- Nodes of Ranvier present but few in number
1. Epineurium - Axon in CNS display little regrowth after injury due
- Encircles the entire nerve to absence of neurolemma
- Certain diseases such as multiple sclerosis and Tay-
2. Perineurium sachs diseases destroy myelin sheath
- Wrapped around individual fascicles
*** 1&2 – composed of dense connective tissue Gray and White Matter
3. Endoneurium White matter
- Surrounds the individual axon - Aggregations of Myelinated processes from many
- Loose Areolar connective tissue neurons
- In spinal cord, white matter surrounds an inner core
Types of Nerve fibers: of gray matter shaped like a butterfly or the letter
H.
1. Myelinated nerve fiber
- With myelin Gray Matter
Nodes of Ranvier – gaps in the myelin sheath - Contains neuronal bodies, dendrites, unmyelinated
Internodes axons, axon terminals, and neuroglia
- Looks grayish rather that white because there is
Significance of myelin sheath: little or no myelin in these areas.
1. Increase speed of nerve impulse transmission - In the brain, a shell gray matter covers the surface
due to node of ranvier by salutatory conduction: of the largest portions of the brain, the cerebrum
electrical alteration jumps as current flow from and cerebellum.
one node of ranvier to another
2. Electrically insulates the axon of neuron