Neurons and Supporting Cells
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Nervous System Neurons Classification of
Neurons and Nerves Supporting Cells
Neurilemma and Myelin
Sheath Myelin Sheath in PNS Myelin Sheath in CNS Regeneration of a cut
axon Neurotrophins Functions of
Astrocytes Blood-Brain Barrier Ion Gating in Axons/
Action Potentials
All or None Law Stimulus intensity Refractory periods Cable properties of
Neurons Conduction of Nerve
Impulses Unmyelinated Myelinated The synapse Electrical synapses:
Gap Junction Chemical Synapses Acetylcholine Monoamines Serotonin Dopamine Nigrostriatal Dopamine Mesolimbic Dopamine Norepinephrine Other
neurotransmitters Amino Acids Excitatory Inhibitory Poly peptides Synaptic
Plasticity Endogenous
Opioids Neuropeptide
Y Endocannabinioids Nitric Oxide and
Carbon Monoxide Long-term potentiation
Synaptic Inhibition |
Central Nervous System
(CNS): ·
brain and spinal cord. Peripheral Nervous
System (PNS): ·
cranial nerves and spinal
nerves Cell Types:
Composed of: ·
Dendrite ·
Axon ·
Cell body Cell body ·
Nucleus ·
Macromolecule production ·
Endoplasmic reticulum called
Nissil bodies (chapter3) ·
Clusters of cell bodies
called nuclei in CNS ·
Clusters of cell bodies
called ganglia in PNS Dendrite ·
Processes ·
Transmit electrical impulse
to cell body Axon ·
Conducts impulses away from
cell body ·
Length 1mm to 1 meter (in
whale can be very long) ·
Axon hillock is site of
impulse origin ·
Axon collaterals are side
branches off axon ·
Axoplasmic flow is
cytoplasmic movement from contractions ·
Axonal transport uses
microtubules to transport materials Sensory or Afferent:
into CNS Motor or efferent: out
of CNS Somatic:
reflex and voluntary control Autonomic:
involuntary muscles, smooth and cardiac, glands Sympathetic
Parasympathetic Association
or interneurons in CNS Cell shapes: Pseudounipolar-
letter T, sensory neuron, acts like axon Bipolar-
2 processes, retina of eye Multipolar-1
process, motor neuron Nerve: bundle of axons
outside CNS. Derived from ectoderm
like neurons. PNS: Schwann
cells, myelin sheath on axon Satellite
cell or ganglionic gliocytes support neuron cell bodies in ganglia CNS: ·
Oligodendrocytes, myelin
sheath in CNS ·
Microglia, eat invaders and
waste ·
Astrocytes, reglulate
external environment ·
Ependymal cell, line cavities
of brain and spinal cord Act
as neural stem cells! MS
destroys myelin sheath. Caused by autoimmune attack on oligodendrocytes
and myelin, triggered by viruses. Genetic component too. In PNS: Sheath of
Schwann or neurilemma ·
Both PNS and CNS have myelin
sheath ·
Short axons are unmyelinated ·
Myelin increases nerve
impulse speed. Formed
by Schwann cells, wrapped like electrician tape, cytoplasm squeezed to
outside like toothpaste. Leaves
gaps called Nodes of Ranvier
Axon of peripheral
nerve cut
Nerve Growth Factor (NGF) NGF
maintains sympathetic ganglia, sensory neuron regeneration G(lial)DNF: Maintains
spinal motor neuron and dopamine neurons. Interact
with synapse area and capillaries Influence
neuron/neuron and neuron/blood interactions Astrocytes may:
Capillaries in brain
have tight junctions between cells. Astrocytes
involved. Some drugs can't cross
the blood brain barrier Dopamine
or some antibiotics Use
L-dopa or antibiotics that can cross. Action
potential or Nerve impulse
Membrane proteins
Anesthetics reversibly
block action potential in sensory neuron by binding voltage-gated Na+
channel. Examples: cocaine,
procaine, lidocaine, tetracaine Once threshold value
is achieved action potential occurs to +30 mv. Always the same change
in voltage. Increased stimulus increases frequency of action potentials.
Called recruitment. Time during which
action potential can not occur. Due to ball and chain blocking channel or
other molecular configuration Does not take the
movement of many ions to generate an action potential. Transmission of
properties through the cytoplasm of cell. Very weak in neurons. + charges conducted by
cable properties to adjacent region and starts
next depolarization. Each action potential
follows along neuron. Slowed by each channel,
and moves in one direction (refractory period) 1 m/second Much faster, less
action potentials needed, channels at nodes of Ranvier, salutatory
conduction. 225 mph Diameter of neuron
also influences speed. Thicker is faster. Axons stimulate or
inhibit the next neuron (gland or muscle) by releasing
neurotransmitters(chemicals) across a synapse. Can be between: Axon
axon Axon
dendrite (most common) Axon
cell body Adjacent cells
electrically coupled have gap junctions. ·
Smooth muscle and cardiac
muscle ·
Excitation and contraction of
muscle masses ·
Gap junctions in brain tissue ·
Gap junctions in glial tissue ·
Gap junctions in embryonic
tissue, disappear during specialization One way from terminal
boutons across synaptic cleft. ·
Neurotransmitters in synaptic
vesicles fuse with membrane. ·
# of vesicles depends on
frequency of action potential. ·
Vesicles at docking sites
forming a fusion complex with presynaptic membrane. ·
Ca 2+channels
at axon terminal near
docking sites. ·
AP arrives open Ca channel. ·
Ca 2+ comes in. ·
Triggers fusion. ·
Ca2+ activates calmodulin,
which activates protein kinase. Protein kinase adds phosphate to synapsins. ·
Tetanus toxin(inhibit) and
botulinum toxin(Ach) are
proteases that destroy parts of fusion complex and inhibit exocytosis. ·
Neurotransmitters bind
receptor proteins. ·
Gates in postsynaptic
membrane open. ·
Chemically regulated
channels. ·
Excitatory postsynaptic
potential (EPSP) ·
Inhibitory
postsynaptic potential(IPSP) Can
cause EPSP or IPSP CNS
and somatic motor neurons Different
Ach receptors Nicotinic
Ach: skeletal muscles Muscarinic
Ach: smooth muscle, cardiac muscle And
glands Ligand-operated
channels: Channel in receptor Nicotinic
receptor has 5 subunits. 2 subunits bind Ach, channel opens when both subunits
bound by ligand. Na and K both flow causing EPSP. EPSP can sum and
exhibit graded response. Myasthenia gravis: Ach
receptors blocked by antibodies. Tetrodotoxin blocks Na
channels. Muscarinic Ach: one
subunit
Examples of G protein
action:
Acetylcholinesterase
(AChE) --inactivates Ach Nerve gas inhibits
AChE. Dursban In PNS Ach produces
"end-plate potentials" at muscle fibers. Curare (South American
Indians) competes with Ach for nicotinic receptors and reduces end plate
potentials. Produces EPSP and IPSP
in autonomic nervous system controlling heart, blood vessels, visceral
organs and glands. Ach used in CNS also. Alzheimers associated
with loss of cholinergic neurons. (hippocampus and cerebral cortex)
Treated with AChE. In CNS Examples: Tyrosine Catecholamines Dopamine,
Norepinephrine:
both hormone and neurotransmitter Epinephrine (adrenaline)
hormone from adrenal gland Tyrptophan Serotonin-
Inhibition of
Monoamines after release:
MAO inhibitors stop
degradation of monoamines and serotonin.
Treatment for Parkinson's (dopamine) and depression. Work via second
messenger cAMP
5-HT
used in raphe nuclei in midline of brain stem. Regulates
mood, behavior, appetite, and cerebral circulation. LSD
mimics 5-HT SSRI-
Serotonin specific reuptake inhibitors include Prozac,
Paxil, Zoloft and Luvox Many
different serotonin receptors. Cell bodies of
dopaminergic neurons concentrated in midbrain. Axons involved in
Motor control Axons involved in
emotional reward Cell bodies in
substantial nigra which sends fibers to corpus striatum. Regions part of
basal nuclei, deep in cerebrum involved in movement. Parkinsons disease is
caused by degeneration of dopaminergic neurons in substantia nigra. Treat with MAO
inhibitors and L-Dopa to increase dopamine transmission. Neurons originate in
midbrain and send axons to forebrain (limbic system) Involved
in behavior Twin
studies show D2 subtype of dopamine receptors implicated in alcoholism Cocaine,
morphine, amphetamines activate dopaminergic pathways. Cocaine
binds reuptake transporters for dopamine, norepinephrine, and serotonin.
Overstimulation.
Used in CNS(behavior
arousal) and PNS(cardiac, smooth, glands) Amphetamines stimulate
norepinephrine pathways. In CNS Glutamate Aspartic
acid Cause
EPSP Glutamate receptor
encloses ion channel 3 types
NMDA receptors
involved in memory storage, are complex and permit the entry of Ca and NA
into postsynaptic neuron Glycine-IPSP Used to inhibit
muscles of opposing muscle groups. Strychnine blocks
glycine receptors, die due to asphyxiation, diaphragm won't relax GABA (glutamic
acid)-IPSP Valium
(benzodiaxepines) increase GABA to activate receptors. Involved in motor
control. Treats anxiety and sleeplessness. CCK (also
hormone)-makes you feel full? Substance P-mediates
pain Synapses can change at
the molecular level. Can occur in hours.
May have role in learning. Made by brain and
pituitary gland B-endorphin Enkephalins Dynorphin Block
pain Naloxone
blocks receptors. Inhibits
glutamate in hippocampus Stimulates
appetite Leptin
suppresses appetite by inhibiting release of neuropeptide Y. Binds
the same as THC receptors Reverse
neurotransmitter Lipid Inhibit
GABA Relaxes
smooth muscle Kills
bacteria Stimulates
cGMP Involved
in erection Viagra
increases action of NO Knowledge
of NO used to treat a variety of conditions. Synaptic
potentials can sum. Spatial: #
of presynaptic axons sum on one postsynaptic membrane. Temporal-
# of waves of release. LPT-priming
increases potenitation or excitability. Learning. Mice
with enhanced NMDA receptors were smarter Too
much glutamate causes cell death. PCP
blocks NMDA receptors. EPSP
+ IPSP Opiates
are analgesic because they block neurons that have substance P. |
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