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• Neurons in brain
and spinal cord=
Central Nervous
System (CNS)
• Nerves that
connect CNS to
rest of body=
Peripheral
Nervous System
(PNS)
• Neuronstransmit
electrochemical
“information”
as nerve
impulses along
nerve fibers
• Nerve impulses
are carried to
Effectors
(muscles and
glands)
Neuron Structure
• Cell body- main
structure
• Dendrites- receive
impulses, one or
many
• Axon- sends
impulses, branched,
usually only one
• Large axons of
peripheral neurons
are enclosed in
sheaths of neuroglia
called Schwann cells
– Myelin sheathcontains lipidprotein
– Surrounded by
membrane called
Neurilemma
• Nodes of Ranvier- gaps between Schwann
cells of myelin sheath
• Myelinated cell
fibers appear
white (white
matter)
• Unmyelinated
fibers and cell
bodies appear
gray (gray
matter)
Path of travel
Sensory Neurons---Interneurons---Motor Neurons
Figure 12.10
Types of Neuroglia
• Microglial cells- support and
phagocytosis in CNS
• Oligodendrocytes- form myelin sheaths in
brain and spinal cord (CNS)
• Astrocytes- between neurons and blood
vessels; support, nutrient regulation, form
scar tissue (CNS)
• Ependymal cells- form epithelial-like
membrane that covers parts of brain
and forms inner lining that encloses
spaces within brain and spinal cord
(CNS)
Schwann cells- myelinate PNS
Satellite cells: surround cell bodies of PNS ganglia
• All resting neurons are polarized (different
charge outside than inside),
– determined by ions, channel pores in
membrane
• K+ crosses easily; Na+ and Ca++ with more
difficulty
Greater Na+ concentration outside
Greater K+ concentration inside
• Due to diffusionresting nerve cell
always has a slight
surplus of positive
charge outside and
slight surplus of
negative charge
inside
– This is called
resting potential
• A threshold potential must be reached to
achieve an action potential
– Na+ permeability suddenly increases, resulting
in an inward rush (action potential)
• Nerve impulse- when
one action potential
stimulates adjacent
portions of nerve fiber
to reach threshold
potential and thus
action potential
– Results in a wave
of action potentials
moving down a
nerve fiber
• The firing of a
nerve is an “All or
None” response
(due to threshold
potential)
• Certain local anesthetics decrease
membrane permeability to sodium ions
• Synaptic transmission
occurs between axon
of one neuron
(sending signal) and
dendrite or cell body
of another neuron
(receiving signal)
• At this gap,
Neurotransmitters are
released from
synaptic vesicles
• Certain
neurotransmitters
increase ion
permeability
(excitatory)
• Others decrease
permeability
(inhibitory)
Small Molecule Neurotransmitter Substances
Acetylcholine (ACh)
Dopamine (DA)
Norepinephrine (NE)
Serotonin (5-HT)
Histamine
Epinephrine
Amino Acids
Gamma-aminobutyric acid (GABA)
Glycine
Glutamate
Soluble Gases
Aspartate
Nitric Oxide
Neuroactive Peptides - partial list!!</FONT<
(NO) td>
Carbon
Monoxide
bradykinin
beta-endorphin
bombesin
calcitonin
cholecystokinin
enkephalin
dynorphin
insulin
gastrin
substance P
neurotensin
glucagon
secretin
somatostatin
motilin
vasopressin
oxytocin
prolactin
thyrotropin
angiotensin II
sleep peptides
galanin
neuropeptid
eY
thyrotropinreleasing hormone
gonadotropninreleasing hormone
growth hormonereleasing hormone
luteinizing
hormone
vasoactive intestinal
peptide