ch 14 nervous tissue
DESCRIPTION
cal poly pomonaTRANSCRIPT
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Nervous Tissue
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Functions of the Nervous System
• Sensory input
– Sensory receptors detect stimuli
• Processing and integration
– The brain interprets stimuli and determines
how to respond
• Motor output
– Effector organs (muscles and glands) are
activated
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Organization of
the Nervous
System
• Structural organization
– Central nervous system (CNS)
• Brain
• Spinal cord
– Peripheral nervous system (PNS)
• Cranial nerves
• Spinal nerves
• Ganglia
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Organization of the Nervous System
• Functional organization
– Sensory nervous system
• Responsible for sensory input
• Sensory receptors (PNS organs) receive stimuli and nerves
transmit this information to the CNS for interpretation
– Motor nervous system
• Responsible for motor output
• The CNS sends information by way of nerves to effector
organs
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Organization of
the Sensory
Nervous
System
• The sensory nervous system consists of somatic
sensory and visceral sensory components
– The somatic sensory component receives stimuli from the skin,
joints, skeletal muscles, and special sense organs
• Voluntary (some control & are aware of the input)
– The visceral sensory component receives stimuli from the
viscera
• Involuntary (no control and generally not aware)
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Organization of the
Motor
Nervous System
• The motor nervous system consists of somatic motor
and autonomic motor components
– The somatic motor component sends information to skeletal
muscle
• Voluntary
– The autonomic motor component sends information to cardiac
muscle, smooth muscle, and glands
• Involuntary
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Nervous
Tissue
• Two types of cells make up nervous tissue
– Neurons
• The functional (excitable) cells of the nervous system
• Neurons receive and transmit nerve impulses (aka action
potentials)
– Glial cells
• Nonexcitable cells
• Glial cells support neurons
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Neurons – Special
Characteristics:
• Larger but less numerous than glial cells
• High metabolic rate
– Neurons require continuous supplies of glucose and oxygen
• Extreme longevity
– Neurons persist for the lifetime of an individual
• Amitotic
– Neurons do not divide to replace themselves
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Neuron
Structure • Cell body
– The neuron’s
control center
– Contains the
neuron’s nucleus,
nucleolus, and
other organelles
– Chromatophilic
substances = Nissl
bodies (ribosomes)
– “Interprets” the
input from dendrites
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Neuron
Structure • Dendrites
– Multiple short,
branching
processes
projecting off of
the cell body
– Receive nerve
impulses from
other neurons (or
sensory stimuli)
and pass the
signal to the cell
body
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Axon
Structure • A single long process projecting off of
the cell body
• Transmits nerve impulses from the
cell body to other neurons (or
effectors)
• Axon structures
– Axon hillock—the connection of
the axon to the cell body
– Axon collateral – side branch of
axon
– Telodendria—branches at the end
of the axon
– Synaptic knobs—expansions at
the ends of the telodendria
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Figure 14.3 dendrites
cell body
axon
nucleus
axon hillock
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Structural Classification of Neurons
Classified according to the number of processes emanating directly from the cell body of the neuron:
1. Unipolar
2. Bipolar
3. Multipolar
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Multipolar—many dendrites and a single axon, most common of all neurons
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1. Unipolar—single, short process that branches like a T 2. Bipolar—two processes, one dendrite and one axon
(Note: some neuro-anatomists prefer the term “pseudounipolar”
because of the ‘peripheral process’ of the axon.)
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Axon
or
Dendrite:
what is the
difference?
• Dendrites and the Soma can
generate “Graded Potentials”
– Can be either positive or
negative
– Different sized
– Become smaller as they
spread
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Axon
or
Dendrite:
what is the
difference?
• Axons & Axon Hillock, generate
“Action Potentials”
– “All or None” = always the
same size & polarity –
regardless of stimulus
– Always the same magnitude
– do NOT become smaller
as they spread.
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Correction to text
• The McLaughlin text is imprecise in its use of the
term ‘nerve impulse’ - sometimes using it when
the proper term is graded potential and
sometimes when the precise term is action
potential
• On page page 425 (section 14.3) it states that ‘A
nerve impulse is also known as an action
potential….” but nerve impulse is not a rigorous
scientific term.
• Dendrites & the soma do NOT generate action
potentials.
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Functional
Classification
of Neurons
Functionally, neurons are classified according to the direction that the nerve impulse is traveling relative to the CNS:
1. Sensory (afferent)
2. Motor (efferent)
3. Interneurons
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Sensory (afferent)—transmit impulses from sensory receptors to the CNS
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Motor (efferent)—transmit impulses from CNS to muscles or glands
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Interneurons—facilitate communication between sensory and motor neurons
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Structural and Functional class of each of these three neurons
Identify their dendrites and axons
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Glial Cells
• Smaller but more numerous than neurons
• Actively mitotic
– the reason they are one of the most common
cells involved in brain cancer
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Glial Cells of
the CNS
• Astrocytes – Attach to neurons and to capillaries
– Connect neurons to their nutrient supply
– Form the blood-brain barrier
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Glial Cells of
the CNS
• Ependymal cells – Line the internal cavities of the CNS
• The ventricles of the brain and the central canal of
the spinal cord
– Produce cerebrospinal fluid (CSF) and
secrete it into the cavities
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Glial Cells of
the CNS
• Microglial cells – Immune cells of the CNS
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Glial Cells of
the CNS
• Oligodendrocytes – Wrap around the axons of CNS neurons
– Form the myelin sheath in the CNS
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Astrocytes
Oligodendrocytes
Microglial cells
Ependymal cells
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Glial Cells of
the PNS
• Satellite cells
– Surround the cell bodies of PNS neurons
– Regulate exchange of nutrients & waste
products with surrounding fluids
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Glial Cells of
the PNS
• Neurolemmocytes (aka Schwann cells)
– Wrap around the axons of PNS neurons
– Form the myelin sheath in the PNS
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Myelin
Sheath
• Oligodendrocytes (CNS) and
neurolemmocytes (PNS) form
myelin sheath around a
neuron’s axon
– Oligodendrocytes and
neurolemmocytes are full of lipids
– They wrap around the axons like
gauze
• Multiple layers of plasma membrane
lipids
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Myelin Sheath
• Gaps exist between
neighboring
oligodendrocytes or
neurolemmocytes
– Termed neurofibril nodes
(aka nodes of Ranvier)
• Nerve impulses “jump”
from node to node
– Myelin sheath significantly
speeds up the
transmission of a nerve
impulse along an axon
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Synapse
• A synapse is the junction between the axon of one neuron
and the dendrite of another neuron (or an effector organ)
– Where the nerve impulse is transmitted to the neighboring neuron
(or effector)
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Synapse
• A synapse consists
of:
– presynaptic neuron
with its
– synaptic knobs;
– A synaptic cleft (small
space) between it and
the
– postsynaptic neuron
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Synapse
• The action potential travels
down the axon of the
presynaptic neuron to its
synaptic knob
• It causes voltage-gated calcium
channels to open, allowing Ca++
to enter
• The Ca++ causes synaptic
vesicles to release the
neurotransmitter (e.g.
acetylcholine – red balls) into
the synaptic cleft
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Synapse • Neurotransmitters bind
to receptors (ligand-
gated ion channels) on
the postsynaptic
membrane
• Sodium ions enter the
cell through the channel
• An action potential is
triggered on the
postsynaptic neuron
• Nerve transmission
converts from electrical
to chemical back to
electrical
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Figure 14.14b
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Identify:
1. Presynaptic neuron
2. Postsynaptic neuron
3. Synaptic knob
4. Synaptic cleft
5. Voltage-gated Ca++ channels
6. Synaptic vesicles
7. Receptor protein
6. Sodium ions
(do they enter the cell?)
8. Acetylcholine molecules
(do they enter the cell?)
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Nerves
• Nerves are bundles of axons running
parallel to each other
– Sensory nerves carry impulses only toward
the CNS
– Motor nerves carry impulses only away from
the CNS
– Mixed nerves carry impulses in both
directions
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Nerves
An individual nerve
is an organ
– Nerve axons and
blood vessels run
throughout
– Surrounded by
epineurium
• Dense irregular
connective tissue
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Nerves
Within the nerve,
axons are grouped
into bundles called
fascicles
– Fascicles are
separated from
other fascicles by
perineurium
• Dense irregular
connective tissue
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Nerves
Individual axons
within fascicles are
surrounded by
endoneurium
– Areolar
connective tissue
– Myelin sheath is
found within the
endoneurium
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What is the name of the
CT covering?
What kind of CT is it?
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What is the name of this
Structure?
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What is the name of the
CT covering?
What kind of CT is it?
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What is the name of the
CT covering?
What kind of CT is it?
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Identify:
1. Dendrites
2. Soma
3. Axon Hillock
4. Axon
5. Nucleus
6. Nucleolus
7. Chromatophilic substance
8. Axon collateral
9. Neurolemma
10.Neurofibril Node
11.Myelin Sheath
12.Telodendria
13.Synaptic knob
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