Nervous system
Nervous tissue is highly specialized to
employ modifications in membrane
electrical potentials to relay signals
throughout the body.
Neurons form intricate circuits that (1)
relay sensory information from the
internal and external environments; (2)
integrate information among millions of
neurons; and (3) transmit effector signals
to muscles and glands.
Anatomical subdivisions of nervous
tissue
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Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
Nerves
Ganglia (singular, ganglion)
Cells of Nervous Tissue
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➢ Neurons
_ Functional units of the nervous system; receive,
process, store, and transmit information to and
from other neurons, muscle cells, or glands
Nervous Tissue
_ Composed of a cell body, dendrites, axon and its
terminal arborization,
and synapses
_ Form complex and highly integrated circuits
➢ Supportive cells
_ Provide metabolic and structural support for
neurons, insulation(myelin sheath), homeostasis,
and phagocytic functions
_ Comprised of astrocytes, oligodendrocytes,
microglia, and ependymal cells in the CNS;
comprised of Schwann cells in the PNS
Structure of a “Typical” Neuron
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➢ Cell body (soma, perikaryon)
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_ Nucleus
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_ Large, spherical, usually centrally located in the soma
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_ Highly euchromatic with a large, prominent nucleolus
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_ Cytoplasm
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_ Well-developed cytoskeleton
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_ Intermediate filaments (neurofilaments). 8–10 nm in diameter
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_ Microtubules. 18–20 nm in diameter
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_ Abundant rough endoplasmic reticulum and polysomes (Nissl
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substance)
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_ Well-developed Golgi apparatus
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_ Numerous mitochondria
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➢ Dendrite(s)
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_ Usually multiple and highly branched at acute angles
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_ May possess spines to increase surface area for synaptic contact
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_ Collectively, form the majority of the receptive field of a neuron;
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conduct impulses toward the cell body
Structure of a “Typical” Neuron
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_ Organelles
_ Microtubules and neurofilaments
_ Rough endoplasmic reticulum and polysomes
_ Smooth endoplasmic reticulum
_ Mitochondria
➢ Axon
_ Usually only one per neuron
_ Generally of smaller caliber and longer than dendrites
_ Branches at right angles, fewer branches than dendrites
_ Organelles
_ Microtubules and neurofilaments
_ Lacks rough endoplasmic reticulum and polysomes
_ Smooth endoplasmic reticulum
_ Mitochondria
_ Axon hillock. Region of the cell body where axon originates
_ Devoid of rough endoplasmic reticulum
_ Continuous with initial segment of the axon that is a highly electrically
excitable zone for initiation of nervous impulse
_ Usually ensheathed by supporting cells
_ Transmits impulses away from the cell body to
_ Neurons
_ Effector structures. Muscle and glands
_ Terminates in a swelling, the terminal bouton, which is the presynaptic
element of a synapse
Type of Neurons by Shape and
Function
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➢ Multipolar neuron. Most numerous and
structurally diverse type
_ Efferent. Motor or integrative function
_ Found throughout the CNS and in autonomic
ganglia in the PNS
➢ Pseudounipolar neuron
_ Afferent. Sensory function
_ Found in selected areas of the CNS and in
sensory ganglia of cranial nerves and spinal nerves
(dorsal root ganglia)
➢ Bipolar neuron
_ Afferent. Sensory function
_ Found associated with organs of special sense
(retina of the eye,olfactory epithelium, vestibular
and cochlear ganglia of the innerear)
Supporting cells of the CNS
(neuroglial cells); outnumber neurons
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_ Astrocytes
_ Stellate morphology
_ Types
_ Fibrous astrocytes in white matter
_ Protoplasmic astrocytes in gray matter
_ Functions
_ Physical support
_ Transport nutrients
_ Maintain ionic homeostasis
_ Take up neurotransmitters
_ Form glial scars (gliosis)
_ Oligodendrocytes
_ Present in white and gray matter
_ Interfascicular oligodendrocytes are located in the white matter ofthe CNS,
where they produce the myelin sheath.
_ Ependymal cells. Line ventricles
_ Microglia
_ Not a true neuroglial cell; derived from mesoderm whereas neuroglial
cells, as well as neurons, are derived from ectoderm
_ Highly phagocytic cells
Supporting cells of the PNS
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. Schwann cells
_ Satellite Schwann cells surround cell bodies in
ganglia
_ Ensheathing Schwann cells
_ Surround unmyelinated axons. Numerous axons
indent the Schwann cell cytoplasm and are
ensheathed only by a singlewrapping of plasma
membrane.
_ Produce the myelin sheath around axons
Myelin Sheath
➢ The myelin sheath is formed by the plasma
membrane of supporting cells wrapping around the
axon. The sheath consists of multilamellar, lipid-rich
segments produced by Schwann cells in the PNS
and oligodendrocytes in the CNS.
Functions
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_ Increases speed of conduction (saltatory conduction)
_ Insulates the axon
➢ Similar structure in CNS and PNS with some differences in
protein
composition
➢ Organization
_ Internode. Single myelin segment
_ Paranode. Ends of each internode where they attach to the
axon
_ Node of Ranvier. Specialized region of the axon between
myelin
internodes where depolarization occurs
➢ In the PNS, each Schwann cell associates with only one axon
and
forms a single internode of myelin.
➢ In the CNS, each oligodendrocyte associates with many (40–
50) axons
(i.e. each oligodendrocyte forms multiple internodes on
differentaxons).
Connective Tissue Investments of Nervous Tissue
➢ Peripheral nervous system
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_ Endoneurium. Delicate connective tissue
surrounding Schwann
cells; includes the basal lamina secreted by Schwann
cells as well as reticular fibers
_ Perineurium. Dense tissue surrounding groups of
axons and their surrounding Schwann cells, forming
fascicles; forms the bloodnerve barrier
_ Epineurium. Dense connective tissue surrounding
fascicles and the entire nerve
Glial cells
Astrocyte, protoplasmic ,Astrocyte, fibrous ,Astrocyte
nuclei ,Astrocytic end feet,Microglial cell nuclei, Myelin
sheath,Oligodendrocyte nuclei ,Oligodendrocyte,
satellite,Oligodendrocyte, interfascicular,Grey matter,
Meninges,Arachnoid,Dura mater,Pia
mater,Subarachnoid space,Subdural space
Neuron Types
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Bipolar neurons,Central
axons,Peripheral axons,Cochlear branch
of cranial nerve
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Multipolar neurons,Axon,Axon
hillock,Cell body,Dendrite,Nissl
substance
Nucleolus,Nucleus
Central nervous system
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_ Meninges
_ Pia mater
_ Thin membrane lying directly on the surface of
the brain andspinal cord
_ Accompanies larger blood vessels into the brain
and spinalcord
_ Arachnoid membrane
_ Separated from pia mater by connective tissue
trabeculae
_ Encloses the subarachnoid space, which contains
blood vessels and the cerebrospinal fluid (CSF)
produced by the cells of thechoroid plexus
_ Together with pia mater, constitute the
leptomeninges; inflammation
of these membranes produces meningitis
_ Dura mater
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_ Outermost of the meninges
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_ Dense connective tissue that includes the periosteum of theskullStructures Identified
in This SectionAutonomic ganglionPurkinje cell (neuron),Purkinje cell body,Purkinje cell
dendrites,Dendritic spines,Pyramidal neuron,Apical endrites,Pseudounipolar
neuronsAxons,Dorsal root ganglion,Myelin,Satellite Schwann cells,Peripheral nerveAdipose
tissue,Axon,Basal lamina,Blood vessels,Connective tissue,Duct of sweat
glands,Endoneurium,Epineurium,Microtubules,Muscle tissue,Myelin lamella,Myelin
sheath,Nerve fascicle,Neurofilaments,Node of RanvierParanodal loops,Paranodal
region,Perineurium,Schwann cell nucleusSchwann cell process ,Unmyelinated
axons,Receptors,Axon,Meissner’s corpuscle,Muscle spindle,Skeletal muscle fibers,Modified
skeletal muscle fibers,Capsule,Sensory axon,Pacinian corpuscle,Perineurial cells,Spinal
cord,Spinal nerve roots,Synapses,Motor end plate,Skeletal muscle,AxonsCNS
synapse,Terminal bouton,Synaptic vesicles (Neurotransmitter,vesicles) ,Mitochondria,
Synaptic cleft,Postsynaptic cell,Postsynaptic density,Dendrite Dendritic spine.
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