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7/26/2019 7.Nervous Tissue
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The most complex system in the body histologicallyand physiologically
Network of billion neurons and many more supporting
glial cells Process information and generate various responses
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Derived from the ectoderm
In the embryo, it arises from Neural tube: where brain and spinal cord are
derived (glial cells, ependymal cells, andepithelial cells of the choroid plexus)
Neural crest: nervous tissue outside of CNS likethe ganglia, capsular cells, Schwann cells
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Irritability Capacity to react in a gradual manner to physical
or chemical stimuli
Conductivity Transmit excitation rapidly from one place to
another
Integrates and coordinates functions ofthe organs
Synthesize chemical compound Neurotransmitters and neuromodulators
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Neurons or Nerve Cells Structural and functional unit of the nervous
tissue
Non-neural or Supporting Cells
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Parts of a Neuron
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Cell body (perikaryon) trophic or synthetic center
Covered by cell membrane
Vary in size and shape and themode of branching of its processesWell developed RER and free
ribosomesNissl bodies Neurofilaments
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Cell body Generally in the PNS, the body is rounded In the CNSthe cell body is typically
angular or polygonal with slightlyconcave surfaces between the processes
Axon hillockis the conical extension inthe cell body where the axon arises
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Nucleus Large, spherical or ovoid with conspicuous
nucleolus, pale staining or vesicular
Cell processesDendrites
Principal signal reception and processing sites
Dendritic spines: first locale for synaptic signalsneuronal plasticity
Axons
Long processes extending from axon hillock Covered by axolemma
Initial segment :site for excitatory and inhibitorystimuli summation
Collateral branches : axon branches
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AxonsAnterograde transport : kinesinRetrograde transport : dynein
Membrane potential
Potential difference (-65mV)
Action potential or impulse
-65mV+30mV
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Basis Axon Dendrites
Number of Processes 1 to a neuron Several or none
Length Generally longer Shorter, terminate inthe vicinity of neuron
Size and shape Small, cylindrical &
uniform in diameter
Broad-based & taper
off as it branches
Nissl bodies Absent Present
Contour or outline Smooth Rough due to
presence of fine
spines which are
sites of synapticcontact
Presence of myelin
sheath
Present Absent
Direction of impulses Away from neurons Toward neurons
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Types of Neurons: (Based on the
size and shape of their processes)
Most neurons
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Retina, olfactorymucosa, cochlear and
vestibular ganglia
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Spinal and cranial
ganglia
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Motor (efferent) Neurons
Control effector organs
Sensory (afferent) Neurons
Reception of sensory stimuli
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Sites of functional contact betweenneurons or between neurons and othereffector cells (muscle and gland cells)
Responsible for the unidirectionaltransmission of nerve impulses
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Converts an electrical signal (impulse)from the pre-synaptic cell into a chemicalsignal that acts on the post-synaptic cell
Transmits information by releasingneurotransmitters during signaling
process
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Types of Synapse
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Glial cells Astrocytes
Oligodendrocytes
Microglial cells Ependymal cells
Neuroloemmocyte
Neuropil: dense network of fibers fromprocesses of both neurons and glial cells thatfills the interneuronal space of the CNS
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Cell body is small and nucleus smaller thanastrocytes
Fewer cell processes and seldom branch
Responsible for synthesis of myelin in theCNS
Predominant glial cell in the CNS white
matter
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Star-shaped; largest of the glial cells Most numerous of glial cells
Have bundles of intermediate filaments madeof glial fibrillary acid protein (GFAP)
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Fibrous astrocytes Located in the white matter
With few long processes
Protoplasmic astrocytes Found in the gray matter
With many short-branched processes
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Maintain homeostasis in the extracellularfluid
Bind neurons to capillaries and to the piamater
Structural support
Repair processes
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Small elongated cells with short irregularprocesses
Phagocytic cells of the Mononuclear-phagocytic system
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A layer of cuboidal or low columnar cells liningthe ventricles of the brain and the central canal ofthe spinal cord
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Central Nervous System (CNS)
Brain
Spinal cord
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Cerebrum Cerebellum
Spinal cord
White matter
Gray matter
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Six layers with most neurons arrangedvertically
Efferent pyramidal neurons mostabundant
Integration of sensory info andinitiation of voluntary motor
responses
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Coordinates muscular activity
3 layers: Outer molecular layer
Central layer Purkinje cells Inner granular layer
Formed by smallest neurons
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Surfaces of cerebrum and cerebellum(forming cerebral cortex)
Contain neuronal bodies, dendrites andthe initial unmyelinated portions of axonsand glial cells This is the region at which synapses occur
Nuclei are aggregates of neuronal bodiesforming islands of gray matter embeddedin the white matter
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Central portion
Main component is myelinated axons and themyelin-producing oligodendrocytes
Does not contain neuronal cell bodies
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White matter is peripheral while graymatter is central
Assuming the shape of an H Where central canal (lined by ependymal
cells) is located
Anterior horn (motor)
Posterior horn (sensory)
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Gray matter Contains abundant astrocytes and large
neuronal bodies
White matter Surrounds gray matter
Contains oligodendrocytes and tracts of myelinatedaxons
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Main components are Nerves
Ganglia
Nerve endings
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Consist of axons enveloped by a specialmyelin sheath
Groups of nerve fibers constitute the tracts of
the brain, spinal cord and peripheral nerves Myelin sheath form gaps along the path called
the nodes of Ranvier Represent the spaces between adjacent
Schwann cells (neurolemmocytes) alongthe length of the axon
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Cranial Nerves
Spinal nerves
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I Olfactory VII Facial
II Optic VIII Auditory
III Oculomotor IX Glossopharyngeal
IV Trochlear X Vagus
V Trigeminal XI Spinal Accessory
VI Abducens XII Hypoglossal
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31 pairs of spinal nerves
Ganglia Sensory ganglia
Autonomic ganglia
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Afferent pathways (ascending pathways) Carry sensory impulses toward the CNS
Efferent pathways (descending pathways) Innervate skeletal muscle or effector organs by
transmitting motor impulses away from theCNS
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Relay information from the CNS to musclesand effector organs through Cranial and spinal nerve tracts that are
arranged in fascicles Multiple fascicles bound together to form the
peripheral nerve
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Somatic Nervous System Consists of pathways that regulate voluntary
motor control Ex. Skeletal muscles
Autonomic Nervous System Involuntary control of organ system (viscera)
Sympathetic Nervous System: mobilize energy intimes of need (fight or flight)
Parasympathetic Nervous System: conserve andrestore energy
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Cranium
Meninges
CSF Vertebral Column
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Composed of 8 bones that fuse early inchildhood
Cranial vault encloses and protects the brainand its associated structures
Floor of the cranial vault is irregular andcontains many foramina for cranial nerves,blood vessels and the spinal cord to exit
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Dura mater
Arachnoid membrane
Pia mater
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Thick external dense, fibroelatic CTcontinous w/ the periosteum
Composed of 2 layers with venous sinuses
between them
Epidural space Space between the cranium and dura mater
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Characterized by its spongy web-likestructure
Arachnoid villi protrudes into venous
sinuses Space between the dura and arachnoid is
the subdural space which contain many
veins disruption of veins may cause subdural
hematoma
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Follows the contour of the brain and spinalcord very closely
Provides support for the blood vesselssupplying the brain tissue
Subarachnoid space lies between thearachnoid and pia mater Contains cerebrospinal f luid Disruption of the intracranial vessels can lead
to subarachnoid hemorrhage
The choroid plexus arise from pial membrane
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Clear, colorless fluid which cushions theCNS by protecting soft tissue from joltsand blows
Produced by choroid plexuses made up ofependymal cells
Approximately 600 ml is produced daily
Circulate within ventricles of brain,
subarachnoid space and spinal cord
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Choroid plexuses of the lateral, third, andfourth ventricles produce the major portionof the CSF
Normal CSF pressure is 120
180 mm ofH 2O or approximately 9 14 mm Hgpressure
CSF from lateral ventricles
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CSF from lateral ventricles
Interventricular foramen(foramen of Monro)
Third ventricle
Cerebral aqueduct
(aqueduct of Sylvius)
Fourth ventricle
Pass either foramen of Luschka or
foramen of Magendie
Subarachnoid space ofthe brain and spinal cord
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33 vertebrae 7 cervical
12 thoracic
5 lumbar 5 fused sacral
4-5 fused coccygeal
Intervertebral disks
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Highly selective interface between the bloodand the CNS
Depends on special properties of the capillary
endothelium(main structural component) Have tight junctions that are highly resistant to
passage of ions or small molecules
Perivascular feet of astrocytes
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Protects the CNS from abrupt changes in theconcentration of ions in the extra-cellularfluid and from molecules that may interfere
with normal neural function Disadvantage
It excludes some drugs particularly antibiotics
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Epineurium Dense ,irregular fibrous coat
Perineurium Sleeves of specialized CT formed by layers of
flattened epithelial-like cells
Surrounds each fascicle
Endoneurium Sparse layer of loose CT that merges w/ type IV
collagen, laminin and proteins produced by theSchwann cells
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Contain both afferent and efferent fibers Nerves possessing sensory fibers are called sensory
nerves; those with motor fibers are motor nerves
Most nerves have mixed nerves
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Ovoid structures containing neuronal cellbodies and glial cells supported by connectivetissues
Serve as relay stations to transmit nerveimpulses Sensory gangliareceive afferent impulses that
go to the CNS
Autonomic gangliaare especially found in thewalls of the digestive tract
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Satellite cells Flattened cells which form a continuous
capsule around nerve cell bodies in the
ganglion
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Schwann cells or Neurolemmocytes Elongated cells arranged end to end along
the course of the nerve fibers in the PNS
Form a long thin tube which surround thenerve fiber called the sheath of Schwannor neurilemma
Responsible for the formation of myelinsheath in the PNS
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Myelination of PNS axons
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Neuronal Plasticity and Regeneration
Neuronal stem cells are present in adult CNS
the potential of neural stem cells to allow
regeneration of CNS components is a subject
of intense investigation
peripheral nerves have a good capacity forregeneration and return of function
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Thank you!
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