Nervous Tissue (2)

Nervous Tissue 1 Olibrian P. Mallari, RMT, IMT, MLS(ASCPi), CPT(IMET)

Nervous Tissue

Introduction

It is widely distributed in the body Consists of tissue which receives stimuli from both internal and external environment

o Receptors Receiver of various forms of energy

Contains intercommunicating cells known as neurons

Functions

1. It plays an important role in irritability and conductivity 2. Regulation of behavior and personality 3. Some are capable of transporting and secreting hormones

Division

1. Somatic portion Derived from the embryo Responsible for voluntary functions

2. Autonomic portion Has an independent function Controls involuntary actions

Neurons

Functional unit of the tissue Usually large and complex in shape Surrounded by a thin plasma membrane called as nerve cell body or cyton Found in the gray matter of the CNS

o Nuclei Cluster or aggregates of neurons in the gray matter

Contains a cell body (perikaryon) and extensions (dendrons and axons) o Synapses

2 Nervous Tissue Olibrian P. Mallari, RMT, IMT, MLS(ASCPi), CPT(IMET)

Point of contact where they are functionally inter-related o Function of Perikaryon

It is the portion of the cell surrounding the nucleus and is vital for the survival of the cell

Can receive stimuli generated by other nerve cells Supplies nourishment to the nerve cell

a. Reception of various stimuli Performed by the dendritic zones, of the neuron including the

cell body or axon of another cell b. Conduction

Performed by the axon c. Synaptic transmission of signal to subsequent neuron

Occurs in the nerve terminals

Can occur inside or outside in the peripheral nervous system where they are termed as ganglion cells

Shapes of neurons is determined by the number and arrangement of the dendrites They can either have long (Golgi type I neuron) or short (Golgi type II neurons)

Types of Neurons

1. Unipolar neurons

Nerve cells having only 1 process Rare type except during early embryonic stages

2. Bipolar neurons

Contains processes projecting from each end of the fusiform cell body Found in the retina, olfactory epithelia, and cochlear ganglia

3. Multipolar neurons Have more than two processes but only one axon

4. Stellate or star shape Includes the motor nerve cells of the ventral gray matter, and motor nuclei of the

brain stem 5. Pyrimidal neurons Present in the cerebral cortex

6. Anaxonic neurons Small cells in the CNS that does not possess an axon Contains both receptor and effector regions on their dendrites

Cytoplasmic Organelles

1. Neurofibril and Microfibril Slender, interlacing threads It courses through the cytoplasm of the perikaryon from one dendrite to another Formed by bundles of neuro-filaments

2. Nissl bodies

Chromophilic substances which appears in the cytoplasm when stained with aniline dyes (toluidine blue, thionin, or cresyl violet)

Contains rich amounts of ribo-nucleoprotein, and RNA in the ribosome Found in the perikaryon and in the proximal parts of the dendrites


Composed of clusters of endoplasmic reticulum o Chromatolysis

Term given to the dissolution of Nissl bodies

3. Golgi bodies

Present in al nerve cells and appears as network of irregular, wavy strands that are coarser than the network of neurofibrils; responsible for protein synthesis

4. Mitochondria Numerous, and elongated The number varies from cell to cell and in different parts of the cell Numerous in axon endings or terminal areas and in the region of the nodes of

Ranvier 5. Centrosome

Paired with centrioles, present only in young neurons It does not have a function (adult)

6. Lysosome Located near the Golgi apparatus Associated with hydrolysis of end products of cellular metabolism, and

degradation of lipids 7. Nucleus

Large, round and centrally located Has a single prominent nucleolus Appears pale and vesicular (owls eye or fish eye)

o Barr bodies Found in the female

Cytoplasmic Inclusions

Melanin, lipid droplet, and iron in the substancia nigra of the midbrain, globus pallidus of the nucleus lentiformis

Lipofuschin golden brown pigment which increases with advancing age Glycogen granules seen only in embryonal neurons and neuroglia Vasopressin, oxytocin, and neurophysior are found in the neurosecretory

neurons

Nerve cell processes

These are cytoplasmic extension, developed to provide conduction pathways and provide greater surface area for contact

Two Kinds of Processes 1. Dendrites (dendrons)

Broad base, tapering gradually along its length towards the end Relatively short and are confined immediate vicinity of the body Covered with gemmules (dendritic spines) Contains Nissl bodies, microtubules, and neurofilaments

2. Axon (Axis cylinder) Only one axon per cell or none at all (amacrine cells of the retina) The plasma membrane is called Axolemma Arises from the elevation of the Nissl bodies called the Axon

hillock or Implantation cone attached by an initial segment

Ganglia


Refers to the collection of nerve cells outside the gray matter (if not outside the gray matter the aggregate is called Nucleus)

Composed of nerve cells, nerve fibers and supporting areolar connective tissue Each ganglia is covered by a capsule with a single layer of small flattened cells termed as

satellite cells Classifications of Ganglia

1. Cerebrospinal Ganglia (Cranio-spinal Ganglia)

Fusiform or globular swelling located in the dorsal roots of the spines True neurons which are unipolar type Contains small sized Nissl Bodies that are uniformly distributed Commonly referred as dendraxon These are often called as pseudo-unipolar Characterized nucleus as owls eye or fish eye Supported by areolar connective tissue

2. Visceral motor ganglia

Cell bodies are small and multipolar Capsule is less distinct than those of the cerebrospinal ganglia and are

absent when located at certain organs Nissl bodies are intermediate in size Presence of fish eye nucleus No definite grouping of cells Do not show regular arrangement of large bundles of myelinated fibers

transversing the ganglion

Nerve Fibers

Applied term to a long axon but includes all nerve cell processes Contains one or more cellular sheath (glia or myelin = CNS and sheath of Schwann =

PNS) Myelin Sheath

It is a white, lipid glistening substance that imparts a whitish color of the white matter

Stained by osmium tetroxide It is a series of concentric layers of Schwann cell plasma membrane Formed by surrounding the developing axon Part of the Schwann cell

Ectodermal in origin and is essential in the vitality of the peripheral nerve fibers

Necessary for the regeneration of axons Not present in the CNS making the oligodendrocytes to

replace their function in the CNS Sheath of Schwannn or neurilemma

Sheath of flattened cells called as neurolemmal Forms a thin sheet around the myelin which in turn surrounds the axon Most superficial lamella containing the nucleus


Classification of Nerve Fibers

1. Medullated nerve fiber with Neurolemma Both covering of myelin sheath and neurilemma Biggest among the different nerve fibers Made up of a central core of neurofibril which originated from the

cell body (embedded in the axoplasm) Covered by a thin membrane known as the Axolemma of Kuhne Nodes of Ranvier (will branch the collateral a right angle)

o Internodal Segment Portion in between two successive nodes of

Ranvier Appears shorter towards the end of a nerve due to

the diminution of the neurofibril o Schmidt Lantermans Lines or incisures of Schmidt

Black staining (Osmic oxide) Oblique radial lines in the myelin sheath within

each intermodal segments Neuro-keratin framework supporting the myelin

Myelin segment Between two Schmidts Covered by nucleated sheath of

Schwann o Sheath of Key and Retzius or the Sheath of Henle

Delicate fibrous connective tissue sheath outside the neurolemma

Carries blood vessels to the individual nerve fibers 2. Medullated nerve fibers without Neurolemma

Found only in the white matter Composed of the axis cylinder surrounded by the axolemma and

which is covered by the myelin sheath Does not have a node of Ranvier

3. Non-medullated nerve fiber Neurolemma Contains sympathetic nerves termed as Remak fibers Composed of the axis cylinder surrounded by the axolemma and

which is covered by the myelin sheath Does not have a node of Ranvier The Schwann cell membrane envelopes the fibers

4. Non-medullated nerve fiber without neurolemma Contains only an axis cylinder without any covering Found in the cyto-proximal and cyto-distal portions of all nerve

fibers

Classification of Nerve fibers according to Diameter 1. Group A fibers

Large fibers (1-22um in diameter) Can conduct 15-100 meters per second Includes motor and sensory fibers

2. Group B fibers Fibers (1-3um in diameter) can conduct 3-14 meters per second


Includes visceral sensory fibers 3. Group C fibers

Small unmyelinated fibers (0.3-1.3 um in diameter) conducting 0.5-2 m/s

Carries autonomic and some sensory impulse

Cerebrospinal Nerve

Constitute the cranial and spinal nerve which are composed of medullated or myelinated fibers with neurilemma

Continuations of the processes outside the brain and the spinal cord

Autonomic Nerves

Sympathetic nerves Composed of preganglionic myelinated fibers (spinal cord to the

peripheral ganglion) and post-ganglionic unmyelinated fibers (nerve cells from the ganglia to some organs of non-medullated nerve fibers with neurolemma)

Parasympathetic nerves Composed of long pre-ganglionic myelinated fibers coming from the

brain

Peripheral Nerve Endings

Telodendrion (end) o Dendrites (sensory receptor) o Axons (motor or secretory endings)

Found in almost all tissues except in cartilage, mucous tissue, enamel of teeth and in the calcareous matrix of bones

o Afferent fibers receptor portions are located throughout the body o Efferent fibers attached in tissue and responsible for releasing acetylcholine

Receptor endings Receiver of impression from the outside world

a. Mechanoreceptor respond to mechanical deformation

b. Thermoreceptor respond to changes in temperature

c. Nociceptors respond to any stimulus that bring about damage to the tissue

d. Electromagnetic receptor refers to the rods and cones of the eyes sensitive to light intensity

e. Chemoreceptor respond to chemical changes associated with taste and smell and oxygen and CO2

f. Free nerve ending widely distributed throughout the body

Found in between epithelial cells of the epidermis of the skin, cornea, alimentary tract, periosteum


Detection of pain g. Merkels Discs

Found in hairless skin and in hair follicles

An aggregate of Merkel discs is called tactile domes

h. Meissners Corpuscles Located in the dermal papillae of the

skin (sole and palm), and nipples of the breast

Very sensitive to touch i. Pacinian Corpuscle

Resembles a sliced onion Sensitive to deformation and

pressure j. Golgi Mazzoni Corpuscle

Resembles the Pacinian with a thin lamella capsule

k. Ruffinis Corpuscle

External Sources: You are required to watch the video clip, by simply clicking the link below.

https://www.youtube.com/watch?v=u1bDqMpKa_g

Note: The coverage of your exam will be cover to cover, however, the bulk of it will be on the following topics:

Blood and Hematopoiesis Bones and Ossification Muscle Tissue Connective Tissue

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Nervous Tissue (2)