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CHAPTER VIII: NERVOUS TISSUE

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Riz Raquel

on 7 October 2013

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Transcript of CHAPTER VIII: NERVOUS TISSUE

CHAPTER VIII: NERVOUS TISSUE
PRESENTATION OF GROUP 5:
Flores, Mark
Altarez, Dane
de Guzman, Trisha
Lazona, Lianne
Ramos, Marisse

Classification of Nerve Fibers
1)Medullated Nerve Fiber w/ Neurolemma
this type constitute nearly all the cerebro-spinal nerves. They have the biggest size among the other types because they contain both coverings.
Nervous tissues have a wide distribution throughout the body, innervating most visceral and peripheral tissues. It is found within the most highly specialized system of the body, the nervous system w/c is composed of an intercommunicating network of specialized cells (neurons) and supporting cells (glia).

FUNCTIONS
Reception of stimulus

Transformation into nervous impulses (excitations)

Transmission to nervous centers

Reorganization to give a response

NERVOUS TISSUE
COMPOSITION
*nerve cells(neuron)-basic unit of the nervous sytem
nerve fibers;
*supporting neuroglia- supporting tissue of CNS


ORIGIN:
The nervous tissue is a derivative of the ectoderm w/c in the beginning forms an invagination or groove along the dorsal surface of the embryo.

NERVE PROCESSES
a nerve cell has two varieties of processes, a dendron or dendrites and an axon. If it has more than one process, only one is the axon and all the rest are dendrons.
DENDRITES
-shorter process w/c arises from the cell body w/c contains both the stainable and fine unstainable substance of Nissl.
-the numerous, shorter and highly branched cytoplasmic extensions that transmit impulses towards the cell body

*synapse- terminal arborization of a dendron in relation w/ other cell bodies or w/ the terminations of axons of other cells.

AXON
- is the longer process and it arises from the nerve cell body.
- the long unbranched cytoplasmic extension that transmits impulses away from the cell body.

*hillock or implantation cone- a clear conical area devoid of chromophilic substance
*axoplasm- a neuroplasm w/c contains only the granular unstainable substance of Nissl.
*telodendrion- terminal arborization of the remaining constituent neurofibrils
*neuropod- a knb-like or plate-like expansion
TYPES OF NERVE CELLS ACCDG. TO LENGTH OF AXON
GOLGI CELLS TYPE 1 OR DEITER'S CELLS OR PROJECTION NEURONS
-neurons w/ long axon w/c leaves the origin to become peripheral nerves.
GOLGI CELLS TYPE II OR ASSOCIATION NEURONS
- numerous w/ short axon w/c do not leave the origin where the cell body is found
* Purkinje Cells- are small bipolar granular cells found in the cerebellum.
NEUROGLIA
is the supporting tissue of the CNS including the olfactory nerves, optic chiasm, and the retina
COMPOSITION OF NEUROGLIA
*GLIA CELLS
*GLIA FIBERS
1)
Ependymal Cells
- regarded as undifferentiated spongioblasts from w/c
the neurons and the glia cells originated.
- found lining the venricles of the brain and central canal of the spinal cord.
- they are tall columnar cells w/c are ciliated in fetal life but w/c cilia are lost in adult life.
3)Oligodendroglia or Olioglia
- are small cells w/ dark staining nucleus and a scanty cytoplasm but w/ vwery few short processes that have also few branches. Accdg to their location these cells are subdivided into the ff:

a)
Perineura satellites
- are the ones found surounding the nerve cells in the gray matter of the CNS.
b)
Perivascular satellites
- their cell bodies and processes are clasping in the walls of blood vessels instead of the ends of the processes as in the perivascular feet.
c)
Interfascicular or sheath cells
- form an incomplete sheath or covering membrane for the myelinated nerve fibers in the white matter of CNS.
4)Microglia or Mesoglia
- are small cells w/ a dark staining nucleus, scanty cytoplasm and few short processes. These cells are capable of emeboid movement and phagocytosis.
- considered as the macrophages of CNS.
- they have no fixed location because they move to places where infection or destruction set in.
GLIA CELLS
may be classified into the ff:
2)
Astroglia, Astocytes or Macroglia
- small cells w/ dark staining nucleus, several processes and a scanty cytoplasm. They are subdivided into:
a)
Protoplasmic astrocyte, short rayed astrocyte or mossy cell
- they are astrocytes whose numerous processes are short and wavy or tortuous; the cytoplasm w/in these processes is granular.

b)
Fibrous astrocyte, long-rayed astrocyte or spider cell
- these are astrocytes whose processes are fewer but longer and more or less straight w/ fewer branches; the cytoplasm is more fibrous in appearance.
*Neuroglia does not provide a firm support, hence, the central nervous tissue is soft.
1) Myelinated nerve fibers w/ a few non-myelinated ones.
2) Neuroglia together w/ a few fine strands of delicate areolar tissue containing small blood vessels.
General Structure of White Matter
In contrast to the gray matter, the white white matter does not contain any nerve cell body but only fibers w/c may be myelinated or non-myelinated w/out neurolemma. The white matter is practically composed only of:
Pia Matter
- is a thin delicate areolar tissue cover w/c is very vesicular. Pia means tender. Its closely adherent to the substance of the brain and spinal cord dipping in all the tissues and sulci. It carries the blood supply into the substance of the brain and spinal cord.
Arachnoid
- It is an avascular membrane of fibrous connective w/c is intimately associated w/ the pia matter, hence others call them as the pia-arachnoid membrane. It is composed of collagenous and elastic fibers that form a delicate network of lacelike appearance.
Dura Matter
It is the outermost covering w/c is thick and of a tough or harder consistency. Dura means hard. It is made up of a dense fibrous connective tissue. It is very vascular especially the brain where it outlayers serves as the inner periosteum of the vault.
NERVOUS TISSUE OF THE PERIPHERAL NERVOUS SYTEM
GANGLIA
- a ganglion is a collection of a nerve cells covering along the course of a peripheral nerve trunk. Only sensory nerves are provided w/ ganglia. The supporting tissue of ganglia is areolar connective tissue.

*GANGLION CELL- a nerve cell or a neuron located w/in a ganglion; that is, a nerve cell outside of the CNS.
Classification of Ganglia.
Sympathetic Ganglia
- they are collections of nerve cells occuring along the course of autonomic nerves, both symoathetic and parasympathetic ganglia or plexus of Meissner and Aubach. These ganglia are in relation w/ many unmyelinated nerve fibers.
Cerebro-spinal Ganglia
- they are collections of of nerve cells along the course of cerebro-spinal nerve trunks. These ganglia are associated mostly w/ myelinated nerves.
Cerebro-Spinal Ganglion Cells
- are true neurons mostly of the unipolar type. Their neuroplasm is also divisible into the stainable substance of Nissl w/ their chromophilic flakes very small in size.
- w/ the presence of epitheliod capsule w/c surrounds the cell body.
Types of Cerebro-Spinal Ganglion Cells
1) Big unipolar cells w/ a thick dendraxon w/c is convulated in its proximal portion.
2) Small unipolar cells w/ a slender dendraxon not convulated and w/c breaks up into numerous fine branches w/in the gonglion to form a pericapsular plexus. Also called association ganglion cells.
3) Small pyriform unipolar cells w/ a thin unmyelinated dendraxon w/c is rarely convulated, one of the branches remains w/in the ganglion.
AXON AND DENDRITES
Sympathetic Ganglia
The symathetic division of the nervous system w/c includes both the sympathetic and parasympathetic has three sets of ganglia namely:
1) Vertebral Ganglia. They form a chain along each side of the vertebral column.
2) Prevertebral or Collateral Ganglia. They are found midway between the CNS and the organs supplied by the nerves, as the coeliac plexus.
3) Terminal Ganglia. They are found on the surface or w/in the organs they supply like the cardiac, Meissner's and Auerbach's plexuses w/c are located w/in the organs supplied.
Sympathetic or Autonomic Ganglion Cells
They are generally multipolar neurons occuring along the course of mostly unmyelinated nerve fibers. They are also true neurons like the most of the nerve cells.
Types of Sympathetic Ganglion Cells.
1) Small and multipolar spheroidal nerve cells w/ many but short dendrons (6 to 20) w/c do not leave the ganglion and one unmyelinated axon w/c joins a nerve trunk. These are motor neurons.
2) Bigger cells w/ fewer but longer and slender dendrons (1 to 16) w/c leave the ganglion and together w/ one unmyelinated axon and may also join a nerve trunk. These are sensory neurons.
NERVE FIBERS
- are those portions of axons or dendrons that have come out of the gray matter or ganglia of the nervous system
Coverings of a Nerve Fiber
1)
Myelin or medullary Sheath
- a layer of mixed lipids and protein/ arranged to form a system of controlling lamellar membrane w/c to wrap around the axon in concentric fashion.

2)
Neurolemma or Nucleated Sheath of Schwann
- made up of flattened cells of Schwann w/c surround the axon from beginning to near its peripheral termination.
Medullated Nerve Fibers w/out Neurolemma
This type of nerve fiber is found only in the white matter and corresponds to the portions of the axons or dendrons that transverse the white substance. Its composed of the axis cylinder w/c is surrounds by the axolemma of the Kuhne and outside of this is myelin substance.
Non- Medullated Nerve Fibers w/ Neurolemma
This type of nerve fiber constitutes a great majority of the sympathetic nerves w/c are sometimes called Remak fibers. A nerve fiber of this type is composed of axis cylinder w/ its axolemma of Kuhne covered externally by thin neurolemma.
Non- Medullated Nerve fiber w/out Neurolemma
These nerve fibers are naked. They have not acquired any covering at all and therefore are merely axis cylinders. This type is found in the cytoproximal and cytodistal portions of all nerve fibers.
Nerve Degeneration and Regeneration
The nerve cell is the trophic center for all its processes. Since each nerve fiber is dependent upon the nerve cell from w/c it arises for its nutrition, separation from it causes the degeneration of the distal cut end of the fiber.
>NERVE INJURY
>NERVE WILL BE DEGRADE
>AXON AND SURROUNDING MYELIN BREAK DOWN
>PHAGOCYTIC MACROPHAGES INTERACT W/ SCHWANN
CELLS TO REMOVE THE INJURED TISSUE DEBRIS
>CONNECTION W/ THE TISSUE TARGET IS LOST,
LEADING TO MUSCLE ATROPHY AND FIBROSIS
>AXON SPROUTS W/ A FINGER-LIKE GROWTH
CONE ADVANCE USING THE SCHWANN CELLS AS GUIDE
>NEWLY CONNECTED AXON MATURES AND THE PRE-INJURY
CYTOARCHITECTURE AND FUNCTION ARE RESTORED
NERVE TRUNK
A nerve trunk is made up of several bundles or fasciculi of nerve fibers covered externally by dense areolar tissue called epineurum. This covering gives off several septa w/c surround the bigger bundles of nerve fibers and w/c constitute the perineurum.
Chracteristics Properties:
The properties of irritability and conductivity are predominantly developed in the nervous tissue.
Distribution
The Central Nervous System
comprises the:
*Brain
*Spinal Cord
The Pripheral Nervous System
comprises the:
*Cerebral
*Spinal
*Sympathetic nerves including
their corresponding ganglia

Glia Fibers
-are fine fibrils w/c are independent of the glia cells just as the connective tissue fibers are independent from the connective tissue cells.
- the delicate network formed by these fibrils together w/ other unmyelinated fibrils and the processes of the glia cells constitute the neuropil.
Nervous Tissue of the Central
Nervous System
The CNS is composed of:
*neurons or nerve cells
*supporting neuroglia
*small amount of delicate aleolar tissue
NEURONS
- the unit structure of the nervous tissue.
3) Terminal Ganglia. They are found on the surface or w/in the organs they supply like the cardiac, Meissner's and Auerbach's plexuses w/c are located w/in the organs supplied.
Nerve Cell
- are found in the gray matter in the CNS including the different small areas of gray matter emmbedded in white matter of the brain and in the different ganglia of the peripheral nerves both cerebro-spinal and sympathetic.
Size & Shape
Size- size of a nerve cell varies from 4 micra to 400 micra in diamter.
Shape- the shape depends more or less on the number of processes.
>
Unipolar cells
- flask or pyriform in shape w/ only a single process.
>
Bipolar
- spindle or fusiform in shape w/ two processes.
>
Multipolar cells
- irregularly stellate in shape w/ more than two processes.

Nerve Cell Body(CYTON)
- believe to without a cell membrane. The Neuroplasm is divisible into two parts namely:

1) Stainable substance of Nissl or chromophilic substance
2) Unstainable substance of Nissl
Stainable substance of Nissl
On staining w/ aniline dyes, like toluidine and methylene blue, the Nissl's substance appear in the form of flake-like structures of varying size and shapes in different nerve cells
Nerve cells w/ an abundance of Nissl's substance are said to be pyknomorphous and those in w/c it is scanty are said to be apyknomorphous.
Unstainable substance
This constitute the remaining portion of the neuroplasm w/c contains theorganoids and inclusions of the cell. Centrosomes are present only in very young nerve cells but are absent in the adult highly . specialized cells. Hence, adult nerve cells are incapable of mitosis.

*Neurons when destroyed are dead forever.
NUCLEUS
a.k.a. "Fish Eye Nucleus"
The nucleus of a nerve cell is relatively big and usually accentrically located. It contains very little chromatin material and is therefore vesicular in appearance. It has small darkly staining nucleus the chracteristic fish eye look.
CEREBRUM
- The cerebrum or hemispheres of the brain, consists of an inner central portion of white matter composed of neuroglia and medullated nerve fibers, covered by a layer of gray matter w/c is termed the cerebral cortex, in w/c the nerve cells are found together w/ a supporting neuroglia.
MENINGES
- Meninges are the connective tissue covering of the CNS, brain and spinal cord. They originate from mesoderm. There are three connective tissue coverings w/ fluid filled spaces between them. They are the ff:
1) Pia Matter
2) Arachnoid
3) Dura Matter
QUESTIONS CLARIFICATIONS
THAT'S ALL FOLKS!
GODBLESS <3

CARPE DIEM!
NEUROGLIA
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