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Chapter 48
Gaby Gonzalez
Joyce Kim
Stephanie Kim
S
Introduction to Information
Processing
S Sensory neurons transmit information from eyes and other
sensors.
S Neurons in the brain are interneurons
S Motor neurons transmit signals to muscle
S The nervous system is divided into central nervous system
(CNS) and peripheral nervous system (PNS).
Neuron Structure and Function
- A neuron has numerous dendrites , which
receives signals from other neurons.
- A neuron has an axon, which transmits signals to
other cells.
- The axon hillock is where the signals that travel
down the axon are generated.
Neuron Structure and Function
S Neurotransmitters pass info from the transmitting
neuron to the receiving cell.
S Interneurons have highly branched dendrites that
take part in about 100,000 synapses.
Formation of the Resting Potential
-Ion pumps use the energy of ATP to actively transport NA+ out of the
cell and K+ into the cell.
- The concentration gradients of K+ and Na+ across the plasma
membrane represent a chemical form of potential energy.
-The diffusion of K+ through open potassium channels is important for
the resting potential.
-The negative charge within the neuron is the source of the membrane
potential.
Modeling of the Resting Potential
-A concentration gradient of K+ needs a solution of
140 mM potassium chloride in the inner
chamber and 5mM KCI in the outer.
-
The magnitude of the membrane voltage at
equilibrium for a ion is called equilibrium
potential.
-
The resting potential of an actual
neuron is -60 to -80 mV.
Action potentials are
the signals conducted by
axons
48.3
S
Basics of Electrical signaling
S Gated Ion potentials: ion channels that open/close in
response to stimuli
S Alters membrane’s permeability/potential
S Hyperpolarization: increase of magnitude of membrane
potential
S Depolarization: decrease
S Graded potentials
Action Potentials: Production
S VOLTAGE-gated ion channels: open/close in response to a
change in membrane potential
S Action potential(nerve impulse) : all or nothing response to
depolarization of the membrane of the nerve cell
Action Potentials: Production
S Threshold: the level of depolarization needed to activate
action potential
S The membrane potential is restored to its normal resting
value by the inactivation of NA+ channels and by opening
voltage gated K+ channels, which increases K+ leaving the
cell
Generation of Action Potential
Conduction
S Refractory period: follows the
action potential, a period in
which another another action
potential can’t be activated
S Action potentials are
propagated along the axon
S Zone of
depolarization/repolarization
S Currents only move ahead
Conduction Speed
S Myelin Sheath: a layer of electrical insulation
S Produced by 2 types of glia (oligodendrocytes and Schwann
cells)
S Saltadory conduction: the jumping of the nerve impulse
between “nodes of Ranvier” (area on the axon not covered by
the myelin sheath), speeds up the conduction of the nerve
impulse.
Neuron communicate
with other cells at
synapses
48.4
S
S The signal is conducted from the axon of a presynaptic cell
to the dendrite of a postsynaptic cell by an electrical or
chemical synapses.
Electrical Synapses
S Electrical synapses: allow electrical current to flow directly
from one neuron to another
- both vertebrates and invertebrates, this synapses synchronize
the activity of neurons responsible for certain rapid, unvarying
behaviors.
Chemical Synapses
S Involve the release of chemical neurotransmitter by the
presynaptic neuron.
S At each terminal, the presynaptic neuron synthesizes the
neurotransmitter and packages it in multiple membranebounded compartments called synaptic vesicles
Chemical Synapses
1)An action potential depolarized the plasma membrane of the
synaptic terminal
2)It opens voltage-gated calcium channels in the membrane, triggering
an influx of Ca^2+
3)The elevated Ca^2+ concentration in the terminal causes synaptic
vesicles to fuse with the presynaptic membrane
Chemical Synapses
4) The vesicles release neurotransmitter into the synaptic cleft
5)The neurotransmitter binds to the receptor portion of ligand-gated
ion channels in the postsynaptic membrane, opening the channels. In
the synapse illustrated here, both Na+ and K+ can diffuse through the
channels
6) The neurotransmitter is released from the receptors, and the
channels close. Synaptic transmission ends when the neurotransmitter
diffuses out of the synaptic cleft, is taken up by the synaptic terminal
or by another cells, or is degraded by an enzyme.
Two postsynaptic potentials
S Excitatory postsynaptic potential
: an electrical change, or depolarization, in the membrane of a
postsynaptic cell caused by the binding of an excitatory
neurotransmitter from a presynaptic cell to a postsynaptic
receptor; makes it more likely for a postsynaptic cell to
generate an action potential
S Inhibitory postsynaptic potentials
: an electrical change ,or hyperpolarization, in the membrane
of a postsynaptic neuron caused by the binding of an
inhibitory neurotransmitter from a presynaptic cell to a
postsynaptic receptor; makes it more difficult for a for a
postsynaptic neuron to generate an action potential.
Neurotransmitters
S
Acetylcholine
: most common neurotransmitter
-Binds to receptors on ligand-gated channels in the muscle cell, producing an EPSP.
-excitatory to vertebrate skeletal muscles
-excitatory or inhibitory at other sites. ex)heart muscles-> inhibitory
-certain bacteria produce a toxin that specifically inhibits presynaptic release of acetylcholine;
toxin caused of food poisoning called botulism
-secretion cites: CNS; PNS; vertebrate neuromuscular junction
Other Neurotransmitters
Neurotransmitter
Functional class
Section sites
Biogenic Amines
Norepinephrine
Dopamine
Serotonin
Excitatory/inhibitory
Generally excitatory
Generally inhibitory
CNS;PNS
CNS;PNS
CNS
Amino Acids
GABA
Glutamate
Glycine
Inhibitory
Excitatory
Inhibitory
CNS; invertebrate
neuromuscular junction
CNS; invertebrate
neuromuscular
CNS
Neuropeptides
Substance P
Met-enkephalin
Excitatoty
Generally inhibitory
CNS;PNS
CNS
Gas
Nitric Acid
Excitatory/ inhibitory
PNS