Download Learning Objectives

Learning Objectives
At the end, a student should be able to define
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Nervous Tissue (NT)
Types of NT: Neurons & Neuroglia
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Definition
Structure & Function
Comparison
Classification
Myelin Structure
Nerve Structure
Lecture outline:
Nervous Tissue (NT) Definitions
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NT Comprises of Neurons, Neuroglia, and blood vessels
Neuron is the basic structural and functional unit of nervous tissue
Neuroglia is the supporting or glial tissue that is 10-times more
abundant in mammalian brain than neurons
Neuron: Structure & Function
Parts of Neuron
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Body: Soma/Perikaryon
Processes: Axon and Dendrites
Neuron: Structure & Function
Body Contains
 Nucleus:
 Cytoplasmic organelles:
 Inclusions
 Cytoskeletal components
Neuron: Structure & Function
Nucleus:
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Centrally located
Large
Pale-staining
Spherical (Owl-eye appearance, large nucleolus)
Euchromatin (shows intense activity of cells)
Bi-nuclear neurons in sensory and symp-ganglia
Neuron: Structure & Function
Cytoplasmic Organelles
 Nissel bodies
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Polysomes and RER
More abundant in motor neurons
Golgi complex (located near nucleus)
Mitochondria (scattered diffusely cytoplasm)
No centriole (non-capable of division)
Neuron: Structure & Function
Inclusions
 Melanin containing granule in CNS neuron and dorsal root sympathetic
ganglia
 Lipofuscin granules in some neurons increase with age
 Lipid droplet present occasionally
Neuron: Structure & Function
Cytoskeletal Components
 Neurofilaments
 Microtubules
 Microfilaments
Neuron: Structure & function
Processes: Dendrites
 Input receiving process
 Conveys afferents signals to Soma
 Usually multiple and small in length
 Thickness decreases near terminals
 Arborized terminals
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Cytoplasmic organelles similar with Soma
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except bi-polar neuron
only lack golgi complex
Organelles reduces near terminals
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except mitochondria
Neuron: Structure & Function
Processes: Axons
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Output receiving process
Conduct impulse away from soma
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… to axon terminals – efferent signals
Different lengths, golgi type-I & type-II
Single and usually long
Diameter remains uniform through length
Originates from axon hillock
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Specialized region of soma
lacks RER, ribosomes
shows many microtubules & neurofilaments
Neuron: Structure & Function
Processes: Axons …
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Axolemma surrounds the axons
Terminates at many small branches
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May have collateral branching
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… called Axon terminals
at right angle from main trunk axon
Axon terminal passes impulses to another neuron
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or other type of cell, ie, muscle or gland
Neuron: Classification
Morphological Classification
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Unipolar
Bipolar
Multipolar
Pseudounipolar
Neuron: Classification
Morphological Classification
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Unipolar
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Bipolar
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single process, eg …
neurons of mesencephleic nucleus of 5th CN
single axon & single dendrite, eg …
Special sensory organs, retina, taste, …
Multipolar …
Pseudounipolar …
Neuron: Classification
Morphological Classification
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… Unipolar
… Bipolar
Multipolar
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Single axon & multiple dendrites
Most common type in men, eg
Motor cortex, interneuron, …
Pseudounipolar
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Single process arises from body
Branches into an axon and dendrite, eg
Present in spinal and cranial ganglia
Neuron: Classification
Functional Classification
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Sensory or Afferent
Motor or Efferent
Interneurons
Neuron: Classification
Functional Classification
 Sensory/Afferent: 3-types of receptions
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Exteroceptors (external: touch, temp)
Proprioceptors (position: muscle & joints)
Interoceptors (internal: GIT, UGT, RT)
Motor/Efferent: 2-types of commands
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Somatic motor (PNS-skeletal muscles)
Visceral motor (ANS-gut)
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Pre-ganglionic fiber & Post-ganglionic fiber
Interneurons
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Runs b/n sensory & motor neurons
Most numerous type – only in CNS
Coordinates b/n sensory inputs & motor outputs
Neuron: Supporting Tissue
… or Glial Tissue or Neuroglia
 In CNS (dividing tissues)
 Astrocytes (macroglia)
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protoplasmic & fibrous
Helps establish & maintain blood-brain barrier
Oligodendrocytes (macroglia)
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Produce myelin
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Microglia (phagocytic cells)
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a sheath that wraps axons of several cells
Several cells with multiple branching processes
Ependyma (epithelial cells with cilia)
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Contributes for choroids plexus formation
Neuron: Supporting Tissue
… or Glial Tissue or Neuroglia
 In PNS (dividing tissues)
 Satellite Cells
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Found in ganglia, around nerve cell body
Functions as exchange of nutrients and waste
Schwann Cells (neurolemmocytes)
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Flattened cell produce myelin sheath in PNS
 … that surround axons
 … only associated with a single axon
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Forms myelinated or unmyelinated coverings over neurons
Myelin: the sheath
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Produced by oligodendrocytes in CNS and Schwann cells in PNS
Several spiral layers of plasma membrane
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Not continues along the length of axon
Interrupted by gaps (nodes of ranvier)
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of oligodendrocytes or …
Schwann cells wrapping around axons
Nodes of ranvier lack myelin
Internodes: segments of nerve fiber b/n adjacent nodes of ranvier
Nerves: cord like bundles
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Cord like bundles of nerve fibers
Surrounded by connective tissue sheath
Appears whitish due to myelin
Connective tissue coverings include
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Epineurium
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Perineurium
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Fibrous DCT forms external coats of nerve trunks
Surrounds each bundle of nerve fibers (fasicle)
Endoneurium
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Thin layer of reticular fibers surrounds individual nerve fibers
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… produced mainly by Schwann cells