Functional Organization of Nervous Tissue

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Functional Organization of Nervous Tissue

• Chapter 11

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Nervous System Overview

• Functions
• mental activity
• monitors senses
• integration, processing and coordination

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Divisions of the Nervous system

• Central Nrevous System (CNS)
• Peripheral Nervous System (PNS)
• Sensory (afferent)
• Motor (efferent)
• Voluntary (somatic)
• Involuntary (autonomic)
• Synpathetic
• parasympathetic

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• The Nervous System
• CNS PNS
• motor sensory
• voluntary involuntary
• sympathetic parasympathetic enteric

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Cells of the Nervous System

• neurons (conducting cells)
• neuroglia (supporting cells)

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Cells of the Nervous system Neurons (nerve cells

• Transmit nerve impulses
• There are several different types of neurons
• that have a different appearance.
• - However, all neurons have some of the same
• basic parts.
• - each neuron has a cell body and two kinds of
• processes.
• - most neurons are not physically attached to
• each other

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Structure of Neurons 1) Cell body (soma) -
Contains the nucleus and organelles 2)
Dendrites (processes) - numerous, branch into
dendritic spines - input side of the neuron -
transmits impulse toward the cell body 3) Axon
(process) - usually only one per neuron but, may
branch - output side of the neuron - transmits
impulses away from the cell body - begins at the
axon hillock - many bundled together form nerves
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Types of Neurons Classification is based on
function and structure Functional
classification 1) motor, transmit away from the
CNS 2) sensory, transmit toward the CNS 3)
interneurons (association neurons), between
neurons within the CNS
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Structural Classification 1) multipolar - has
many dendrites and a single axon - motor neurons
and most CNS neurons 2) Bipolar - has one
dendrite and one axon - used in the eye and
sense of smell 3) Unipolar - has one short
process attached to one long axon - one end
has dendrite-like sensory receptors - most
sensory neurons
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• Cells of Nervous System
• glial cells or neuroglial cells (supporting
  cells)
• non-conduction cells
• assist neurons anatomically and physiologically
• - more numerous than neurons

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Types of glial cells, CNS 1) Astrocytes,
star-shaped - form a supporting framework for
blood vessels and neurons - regulate
extracellular composition of brain fluid -
help form the blood-brain barrier - active after
CNS damage - synthesis, recycling, and
absorption of neurotransmitters 2) Ependymal
cells - line cavities of brain and spinal
cord - work with blood vessels to form
cerebrospinal fluid from blood
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Types of glial cells, CNS 3) Microglia -
phagocytes - remove dead tissue, microbes,
foreign material 4) Oligodendrocytes - form
insulating coverings (myelin sheaths) on
axons - one oligodendrocyte can form myelin
sheaths on several axons
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Types of glial cells, PNS 1) Schwann cells
(neurolemmocytes) - wrap around axons of neurons
to form myelin sheaths - each Schwann cells
forms a myelin sheath on only a portion of
one axon 2) Satellite cells - surround neuron
cell bodies in sensory ganglia - provide
support and nutrition to neuron - protects
neurons from heavy metals (lead, mercury)
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Myelin sheaths - formed by Schwann cells (PNS)
or oligodendrocytes (CNS) - made of lipid -
insulates axon - speeds the rate of nerve
impulse - gaps between myelin called nodes of
Ranvier - some axons are myelinated and some are
not
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• Organization of nerve tissue
• - axons are bundled together and travel together
• to specific locations they are called nerves
  (PNS),
• tracts (CNS)
• cell bodies and their dendrites are clumped
• together to form ganglia (PNS), nucleii (CNS)
• - myelinated axons form white matter
• - unmyelinated axons, cell bodies, dendrites form
• grey matter
• - tied together with connective tissue

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Nerve impulses (action potentials) - nerves
function by sending electrical signals -
electrical signals are produced by the movement
of ions within an axon - axons at rest have a
charge (resting potential)
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• Depolarization
• - When a neuron loses the charge on its
• membrane
• caused by chemical, electrical, mechanical,
• temperature stimulation
• results when channels in the cell membrane
• open and allow ions to flow freely across
  causing
• the loss of the potential difference
• (separation of charges)
• positive charges move into the cell, negative
• charges move out of the cell
• begins in one spot and depolarization moves
• down the axon like a wave

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• Types of depolarization
• Graded potential
• - vary in strength
• (weak stimulusweak depolarization)
• - travel only a short distance then die out
• - generate action potentials

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2) Action potential - caused by graded
potentials - all or none, all the same
strength - occurs from a threshold stimulus
(stimulus strong enough) - self
propagating, travels until it reaches the end
of the axon
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• Action potentials in myelinated axons
• - only occurs between myelinated segments
• (nodes of Ranvier)
• myelin insulates axon and prevents
• depolarization underneath myelin
• action potential jumps over myelinated
• segments
• called saltatory conduction and is much
• faster

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The synapse the junction between neurons
and the cells they communicate with. Neurons
communicate with other neurons, Muscle cells,
glands, etc. Electrical synapses - not
common - cells are connected together -
action potential moves directly from on cell
to the next
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• Chemical synapses
• nerve cells do not actually touch each other.
• there is a miniscule gap (synaptic cleft)
• between the cells
• the neurons communicate with other cells by
  releasing
• neurotransmitters (chemicals) that cross the
• synaptic cleft and stimulate the next cell
• - allows precise control
• - the synapse is comprised of
• 1) presynaptic axon terminal
• 2) synaptic cleft
• 3) postsynaptic membrane

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Sequence of events at a chemical
synapse 1) an action potential reaches the axon
terminals of the presynaptic neuron 2) the action
potential stimulates the release of the
neurotransmitter by the presynaptic axon
terminal 3) the neurotransmitter crosses the
synaptic cleft and binds to the postsynaptic
membrane 4) binding of the neurotransmitter
depolarizes the postsynaptic membrane 5)
neurotransmitter is removed by a) reuptake b)
diffusion c) degraded
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Examples of neurotransmitters -
acetylcholine - serotonin - dopamine -
norepinephrine
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Circuit pathways - convergent circuits -
divergent circuits - oscillating circuits
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