Cells of the Nervous System

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Cells of the Nervous System
neurons communicating cells in nervous
system form networks between brain
regions different kinds with very different
properties oligodendrocytes myelinating
cells cover axons in an insulating
sheath astrocytes support cells produce
survival factors and support neurons microglia
scavenger/ defense cells of the brain produced
by the immune system
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Neurons- Principle Cells of the Nervous System
or soma
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Neurons- Principle Cells of the Nervous System
neurons generally have only 1 axon that goes out
and connects to multiple cells action
potentials (outgoing signals from neurons) start
at the axon hillock and travel outward to the
axon arbor axonal arbors will end at synaptic
boutons on dendrites or somas
axon hillock
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Neurons- Principle Cells of the Nervous System
synapses range from the neuromuscular junction at
50-100 microns to central nervous synapses,
which are usually smaller than 1 micron
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Neurons- Principle Cells of the Nervous System
dendrites are usually numerous and may have
several per neuron dendritic spine specialized
area of the dendrite next to an axon changes
in response to activity postsynaptic density
(psd) area next to released neurotransmitters
usually shows up as dark, protein rich in
electron micrographs
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Neurons- Principle Cells of the Nervous System
dendritic spines receive synaptic signals and can
change over time several neurological diseases
and behavioral deficits also have changes
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Neurons- Principle Cells of the Nervous System
neurons form both microcircuits within a tissue
(ie. retina) or macrocircuits connecting one
region with another (retina to tectum)
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Neurons- Principle Cells of the Nervous System
neurons can be further subdivided by type--
inhibitory or excitatory excitatory neurons
encourage other neurons to activate
(depolarize) inhibitory neurons make it harder
for other neurons to activate neuronal subtypes
are found intermixed in various areas but are
usually found in very defined locations
performing specific functions whether a neuron
is excitatory or inhibitory depends on 2
characteristics 1) type of neurotransmitter
that is released 2) type of neurotransmitter
receptor found on the target cell
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Neurons- Principle Cells of the Nervous System
the human cortex is divided into 6 layers, each
with defined patterns of cells, axons, and
dendrites running through it
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Neurons- Principle Cells of the Nervous System
the mouse superior colliculus has 5 cell types
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Neurons- Principle Cells of the Nervous System
using the right conditions, each one can be
individually labeled
the structure of the neurons determine their
function ie. wide-field vertical cells detect
movement narrow field vertical cells are more
detail oriented
stellate
wide-field vertical
narrow vertical
piriform
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Glial Cells- Support Cells of the Nervous System
oligodendrocytes insulating cells around many
axons in the CNS Schwann cells
oligodendrocytes in the peripheral nervous
system myelin lipid/protein membrane
surrounding axons nodes of Ranvier areas of
unmyelinated axon where action potentials can
be regenerated-- full of ion channels to
strengthen the signal
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Glial Cells- Support Cells of the Nervous System
oligodendrocytes in the CNS are optimized for
minimum space Schwann cells are optimized for
protection/regeneration a) secrete growth
factors to support cells b) secrete a basal
lamina (extracellular matrix) for strength and
support
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Glial Cells- Support Cells of the Nervous System
P0 major protein of PNS myelin sheaths-- 80 of
membrane protein PLP- proteolipid protein,
same job, different protein in CNS these
proteins are NOT interchangeable switching
either causes axon degeneration (ie. multiple
sclerosis type diseases) other myelin proteins
act to prevent axon regeneration in the CNS,
preventing our nerves from regrowing several
lower vertebrates (ie. goldfish or frogs or
newts) do not show this
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Glial Cells- Support Cells of the Nervous System
astrocytes 'star shaped' cells that make up much
of the brain volume form the glial limitans, a
covering around the surface of the brain, both
externally (pia mater) and internally (ependyma)
lining the ventricles radial glia specialized
type of astrocyte using during the growth of the
nervous system, where cells migrate out from
the ependymal surface
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Glial Cells- Support Cells of the Nervous System
astrocytes produce growth factors and
extracellular matrix that support the
survival of neurons- most neurons require
astrocytes to survive astrocytes also import and
neutralize neurotransmitters from
synapses astrocytes also proliferate in response
to diseases such as strokes and
neurodegenerative diseases can help form glial
'scars' in the CNS
control section
glial scar
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Glial Cells- Support Cells of the Nervous System
microglia constitute the immune cells of the
nervous system phagocytic ingests cell debris
and dying cells similar to macrophages mostly
derived from the bone marrow microglia become
activated in response to disease or injury
resting
activated
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Blood Vessels Deliver Oxygen to Active Brain
Regions
patterns of blood vessels are consistent
depending upon the brain region some areas have
a higher density than others oxygenated blood
flow is used to follow brain activity using MRIs
more oxygen consumed more active brain area
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Blood Vessels Deliver Oxygen to Active Brain
Regions
blood-brain barrier layer formed around
capillaries composed of an endothelial cell
and pericytes (specialized supporting
astrocytes) forms tight junctions between
endothelial cells to prevent leakage blood brain
barrier also is often damaged in diseases