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Chapter 2
Structure and Functions of Cells of the
Nervous System
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 The Nervous System
 Central Nervous System (CNS)
• Comprised of the brain and spinal cord
• Encased within the skull and spinal column
 Peripheral Nervous System (PNS)
• Comprised of nerve tissue located outside of the
brain and spinal cord.
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 Cells of the Nervous System
Neuron Basic Structure
 Soma or “cell body”:
• The cell body of a neuron, which contains the
nucleus.
 Dendrite:
• A branched treelike structure attached to the
soma of a neuron; receives information from the
terminal button of other neurons.
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 Cells of the Nervous System
Neuron Basic Structure
 Terminal button:
• The bud at the end of a branch of an axon; forms
synapses with another neuron; sends information
to that neuron.
 Neurotransmitter:
• A chemical that is released by a terminal button;
has an excitatory or inhibitory effect on another
neuron.
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Neuron
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 Cells of the Nervous System
Neuron Basic Structure
 Synapse:
• A junction between the terminal button of an axon
and the membrane of another neuron.
 Axon:
• The long, thin cylindrical structure that conveys
information from the soma of a neuron to its
terminal button.
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 Cells of the Nervous System
 There are three general types of neurons:
 Sensory neuron:
• A neuron that detects changes in the external or
internal environment and sends information
about these changes to the central nervous
system.
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 Cells of the Nervous System
 There are three general types of neurons:
 Motor neuron:
• A neuron located within the central nervous
system that controls the contraction of a muscle
or the secretion of a gland.
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 Cells of the Nervous System
 There are three general types of neurons:
 Interneuron:
• A neuron located entirely within the central
nervous system.
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 Cells of the Nervous System
Neuron Basic Structure
 Multipolar neurons:
• A neuron with one axon and many dendrites.
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 Cells of the Nervous System
Neuron Basic Structure
 Bipolar neurons:
• A neuron with one axon and one dendrite
attached to its soma.
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 Basic Structures of Neurons
 Three classifications of
neurons
 Unipolar neurons:
• A neuron with one axon
attached to its soma; the
axon divides, with one
branch receiving sensory
information and the other
sending the information
into the central nervous
system.
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 Cells of the Nervous System
Internal structure
 Membrane:
• A structure consisting principally of lipid
molecules that defines the outer boundaries of a
cell and also constitutes many of the cell
organelles, such as the Golgi apparatus.
 Nucleus:
• A structure in the central region of a cell,
containing the nucleolus and chromosomes.
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 Cells of the Nervous System
Internal structure
 Nucleolus:
• A structure within the nucleus of a cell that
produces the ribosomes.
 Ribosomes:
• A cytoplasmic structure, made of protein, that
serves as the site of production of proteins
translated from mRNA.
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Nucleus
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 Cells of the Nervous System
Internal structure
 Chromosome:
• A strand of DNA, with associated proteins, found
in the nucleus; carries genetic information.
 Deoxyribonucleic acid (DNA):
• A long complex macromolecule consisting of two
interconnected helical strands; along with
associated proteins, strands of DNA constitute
the chromosomes.
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 Cells of the Nervous System
Internal structure
 Gene:
• The functional unit of the chromosome, which
directs synthesis of one or more proteins.
 Messenger ribonucleic acid (mRNA):
• A macromolecule that delivers genetic
information concerning the synthesis of protein
from a portion of a chromosome.
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 Cells of the Nervous System
Internal structure
 Enzyme:
• A molecule that controls a chemical reaction,
combining two substances or breaking a
substance into two parts.
 Cytoplasm:
• The viscous, semi-liquid substance contained in
the interior of a cell.
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 Cells of the Nervous System
Internal structure
 Mitochondria:
• An organelle that is responsible for extracting
energy from nutrients.
 Adenosine triphosphate (ATP):
• A molecule of prime importance to cellular energy
metabolism; its breakdown liberates energy.
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 Cells of the Nervous System
Internal structure
 Endoplasmic reticulum:
• Parallel layers of membrane found within the
cytoplasm of a cell. Rough endoplasmic
reticulum contains ribosomes and is involved in
production of proteins that are secreted from the
cell. Smooth endoplasmic reticulum is the site of
synthesis of lipids and provides channels for the
segregation of molecules involved in various
cellular processes.
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 Cells of the Nervous System
Internal structure
 Golgi apparatus:
• A complex of parallel membranes in the
cytoplasm that wraps the products of a secretory
cell.
 Exocytosis:
• The secretion of a substance by a cell through
means of vesicles; the process by which
neurotransmitters are secreted.
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 Cells of the Nervous System
Internal structure
 Lysosome:
• An organelle surrounded by membrane; contains
enzymes that break down waste products.
 Cytoskeleton:
• Formed of microtubules and other protein fibers,
lined to each other and forming cohesive mass
that gives a cell its shape.
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 Cells of the Nervous System
Internal structure
 Microtubule:
• A long strand of bundles of protein filaments
arranged around a hollow core; part of the
cytoskeleton and involved in transporting
substances from place to place within the cell.
 Axoplasmic transport:
• An active process by which substances are
propelled along microtubules that run the length
of the axon.
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 Cells of the Nervous System
Internal structure
 Anterograde:
• In a direction along an axon from the cell body to
the terminal buttons.
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 Cells of the Nervous System
Internal structure
 Retrograde:
• In a direction along an axon from the terminal
buttons toward the cell body.
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 Cells of the Nervous System
 Glia
 Glial cell:
• The supporting cells of the central nervous
system.
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 Cells of the Nervous System
 Glia
 Astrocyte:
• A glial cell that
provides support for
neurons of the
central nervous
system, provides
nutrients and other
substances, and
regulates the
chemical composition
of the extracellular
fluid.
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 Cells of the Nervous System
 Phagocytosis:
• The process by which cells engulf and digest
other cells or debris caused by cellular
degeneration.
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 Cells of the Nervous System
 Oligodendrocyte:
• A type of glial cell in the central nervous system
that forms myelin sheaths.
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 Cells of the Nervous System
 Myelin sheath:
• A sheath that surrounds axons and insulates
them, preventing messages from spreading
between adjacent axons.
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 Cells of the Nervous System
 Node of Ranvier:
• A naked portion of a myelinated axon, between
adjacent oligodendroglia or Schwann cells.
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 Cells of the Nervous System
 Microglia:
• The smallest glial cells; act as phagocytes and
protect the brain from invading microorganisms.
 Schwann cell:
• A cell in the peripheral nervous system that is
wrapped around a myelinated axon, providing
one segment of its myelin sheath..
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 The Blood-Brain Barrier (BBB)
 Features of the Blood-Brain Barrier
• Regulates the chemicals that can enter the CNS
from the blood.
• Helps the CNS maintain the proper composition
of fluids inside and outside the neurons.
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 The Blood-Brain Barrier (BBB)
 Features of the Blood-Brain Barrier
 Blood-brain barrier:
• A semipermeable barrier between the blood and
the brain produced by cells in the walls of the
brain’s capillaries.
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 The Blood-Brain Barrier (BBB)
 Features of the Blood-Brain Barrier
 Area postrema:
• A region of the medulla where the blood-brain
barrier is weak; poisons can be detected there
and can initiate vomiting.
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 Communication Within a Neuron
 Measuring Electrical Potentials of Axons
 Axons have two basic electrical potentials:
• Resting Membrane Potential
• Action Potential
 The membrane potential can change:
• Depolarization
• Hyperpolarization
• Threshold of excitation
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Communication Within a Neuron
 Measuring Electrical Potentials of Axons
 Membrane potential:
• The electrical charge across a cell membrane;
the difference in electrical potential inside and
outside the cell.
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Communication Within a Neuron
 Measuring Electrical Potentials of Axons
 Resting membrane potential:
• The membrane potential of a neuron when it is
not being altered by excitatory or inhibitory
postsynaptic potentials; approximately -70 mV in
the giant squid axon.
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Communication Within a Neuron
 Measuring Electrical Potentials of Axons
 Depolarization:
• Reduction (toward zero) of the membrane
potential of a cell from its normal resting
potential.
 Hyperpolarization:
• An increase in the membrane potential of a cell,
relative to the normal resting potential.
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Communication Within a Neuron
 Measuring Electrical Potentials of Axons
 Action potential:
• The brief electrical impulse that provides the
basis for conduction of information along an
axon.
 Threshold of excitation:
• The value of the membrane potential that must
be reached to produce an action potential.
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 Communication Within a Neuron
 The Membrane Potential is the result of a balance between
two forces.
 Diffusion:
• Movement of molecules from a region of high
concentration to regions of low concentration.
 Electrostatic pressure :
• The force exerted by the attraction or repulsion of ions,
• Particles the same charge repel each other.
• Particles with different charges attract each other.
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 Communication Within a Neuron
 The Membrane Potential is the result of a balance
between two forces.
 Diffusion:
• Movement of molecules from a region of high
concentration to regions of low concentration,
i.e. when you put sugar in your coffee the sugar
goes to the bottom and over time would diffuse
throughout the coffee.
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 Communication Within a Neuron
 The Membrane Potential is the result of a balance
between two forces.
 Electrostatic Pressure
• The force exerted by the attraction or repulsion
of ions.
• Particles with the same charge repel each other.
• Particles with opposite charges attract each other.
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 Communication Within a Neuron
 The Membrane Potential
 Ion:
• A charged molecule. Cations are positively
charged , and anions are negatively charged.
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 Communication Within a Neuron
 The Membrane Potential
 Intracellular fluid:
• The fluid contained within cells.
 Extracellular fluid:
• Body fluids located outside cells.
 Sodium-potassium transporter:
• A protein found in the membrane of all cells that
extrudes sodium ions.
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 Communication Within a Neuron
 The Membrane Potential
 Extracellular fluid:
• Body fluids located outside cells.
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 Communication Within a Neuron
 The Membrane Potential
 Intracellular fluid:
• The fluid contained within cells.
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 Communication Within a Neuron
 The Membrane Potential
 Sodium-potassium transporter:
• A protein found in the membrane of all cells that
extrudes sodium ions.
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 Communication Within a Neuron
 The Action Potential
 Ion channel:
• A specialized protein molecule that permits
specific ions to enter or leave the cell.
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 Communication Within a Neuron
 The Action Potential
 Voltage-dependent ion channel:
• An ion channel that opens or closes according
to the value of the membrane potential.
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Communication Within A Neuron
 Conduction of the Action Potential:
 All-or-none law:
• The principle that once an action potential is
triggered in an axon, it is propagated without
decrement to the end of the fiber.
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Communication Within A Neuron
 Conduction of the Action Potential:
 Cable properties:
• The passive conduction of electrical current, in a
decremental fashion, down the length of an axon.
 Saltatory conduction:
• Conduction of action potentials by myelinated
axons. The action potential appears to jump from
one node of Ranvier to the next..
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Communication Between Neurons
 The Concept of Chemical Transmission
 Postsynaptic potential:
• Alterations in the membrane potential of a
postsynaptic neuron, produced by the liberation
of neurotransmitter at the synapse.
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 Communication Between
Neurons
 The Concept of
Chemical Transmission
 Neuromodulator:
• A naturally secreted
substance that acts
like a
neurotransmitter
except that it is not
restricted to the
synaptic cleft but
diffuses through the
extracellular fluid.
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Communication Between Neurons
 Structures of Synapses
 Presynaptic membrane:
• The membrane of a terminal button that lies
adjacent to the postsynaptic membrane and
through which the neurotransmitter is released.
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Communication Between Neurons
 Structures of Synapses
 Synaptic cleft:
• The space between the presynaptic membrane
and the postsynaptic membrane.
 Synaptic vesicle:
• A small, hollow, beadlike structure found in the
terminal buttons; contains molecules of a
neurotransmitter.
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Communication Between Neurons
 Structures of Synapses
 Release zone:
• A region of the interior of the presynaptic
membrane of a synapse to which synaptic
vesicles attach and release their neurotransmitter
into the synaptic cleft.
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Communication Between Neurons
 Activation of Receptors
 Postsynaptic receptor:
• A receptor molecule in the postsynaptic
membrane of a synapse that contains a binding
site for a neurotransmitter.
 Neurotransmitter-dependent ion channel:
• An ion channel that opens when a molecule of a
neurotransmitter binds with a postsynaptic
receptor.
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Communication Between Neurons
 Activation of Receptors
 Ionotropic receptor:
• A receptor that contains a binding site for a
neurotransmitter and an ion channel that opens
when a molecule of the neurotransmitter attaches
to the binding site.
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Communication Between Neurons
 Activation of Receptors
 Metabotropic receptor:
• A receptor that contains a binding site for a
neurotransmitter; activates an enzyme that
begins a series of events that opens an ion
channel elsewhere in the membrane of the cell
when a molecule of the neurotransmitter attaches
to the binding site.
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Communication Between Neurons
 Activation of Receptors
 G protein:
• A protein coupled to a metabotropic receptor;
conveys messages to other molecules when a
ligand binds with and activates the receptor.
 Second messenger:
• A chemical produced when a g protein activates
an enzyme; carries a signal that results in the
opening of the ion channel or causes other
events to occur in the cell.
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Communication Between Neurons
 Postsynaptic Potentials
 Excitatory postsynaptic potential (EPSP):
• An excitatory depolarization of the postsynaptic
membrane of a synapse caused by the liberation
of a neurotransmitter by the terminal button.
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Communication Between Neurons
 Postsynaptic Potentials
 Inhibitory postsynaptic potential (IPSP):
• An inhibitory hyperpolarization of the
postsynaptic membrane of a synapse caused by
the liberation of a neurotransmitter by the
terminal button.
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Communication Between Neurons
 Termination of Postsynaptic Potentials
 Reuptake:
• The reentry of a neurotransmitter just liberated by
a terminal button back through its membrane,
thus terminating the postsynaptic potential.
 Enzymatic deactivation:
• The destruction of a neurotransmitter by an
enzyme after its release, for example, the
destruction of acetylcholine by
acetylcholinesterase.
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Communication Between Neurons
 Effects of Postsynaptic Potentials: Neural
Integration
 Neural integration:
• The process by which inhibitory and excitatory
postsynaptic potentials summate and control the
rate of firing of a neuron.
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Communication Between Neurons
 Autoreceptors
 Autoreceptor:
• A receptor molecule located on a neuron that
responds to the neurotransmitter released by that
neuron.
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Communication Between Neurons
 Autoreceptors have a variety of functions:
• A receptor molecule located on the presynaptic
neuron that responds to the neurotransmitter
released by the presynaptic neuron.
• Regulate internal processes of the cell
• Regulate synthesis of the neurotransmitter
• Regulate the release of a neurotransmitter
• Generally serve to inhibit the activity of a
transmitter
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