Chapter 48: Neurons, Synapses, and Signaling Flashcards
Most of a neuron’s organelles, including its nucleus,
are located in the ____ _____. In a typical neuron, the cell body
is studded with numerous highly branched extensions called
_____. Together they receive signals from other neurons.
Most of a neuron’s organelles, including its nucleus,
are located in the cell body. In a typical neuron, the cell body
is studded with numerous highly branched extensions called
dendrites (from the Greek dendron, tree). Together with the
cell body, the dendrites receive signals from other neurons.
A typical neuron has a single ____, the extension that
transmits signals to other cells.
A typical neuron has a single axon, the extension that
transmits signals to other cells.
Each branched end of an axon transmits information to
another cell at a junction called a _____. The
part of each axon branch that forms this specialized junction
is a ____ _____
Each branched end of an axon transmits information to
another cell at a junction called a synapse. The
part of each axon branch that forms this specialized junction
is a synaptic terminal
Sensory neurons transmit information about
external stimuli and internal conditions
Interneurons connect neurons in the …. They are responsible for
form the circuits connecting neurons in the brain/ganglia
Responsible for the analysis and interpretation of sensory input
Motor neurons transmit signals to
muscle cells
If the way a neuron transmits electrical signals within the cell is always identical, what distinguishes the type of information being transmitted?
The particular connections made by the active neuron are what distinguish the type
of information being transmitted
When grouped together, the axons of
neurons form the bundles we call ____
When grouped together, the axons of
neurons form the bundles we call nerves
Neurons of both the CNS and PNS require
supporting cells called ____
Neurons of both the CNS and PNS require
supporting cells called glial cells, or glia
Compare and contrast the structure and function of axons
and dendrites
A typical neuron has multiple dendrites and one axon. Dendrites transfer
information to the cell body, whereas axons transmit information from the cell
body. Both axons and dendrites extend from the cell body and function in infor-
mation flow
The charge difference, o r volatage, across the plasma membrane is called
membrane potential
The membrane potential for a resting neuron is referred to as
resting potential
In most neurons, the concentration
of K + is higher ____ the cell, while the concentration of Na +
is higher ____.
In most neurons, the concentration
of K + is higher inside the cell, while the concentration of Na +
is higher outside.
The sodium-potassium pump transports ___ Na + out of
the cell for every ___K + that it transports in
The sodium-potassium pump transports three Na + out of
the cell for every two K + that it transports in
The resulting change in the
membrane potential from the sodium potassium pump is quite small. Why, then, is there a membrane potential of -60 to
-80 mV in a resting neuron?
ion movement through ion channels
In neurons, ion channels that convert chemical potential energy to electrical potential energy can do so because of
selective permeability
Why is diffusion of K+ through potassium channels (which are always open) critical for establishing resting potential?
The K+ concentration is higher outside the cell than within
the gradient favors an outflow of K+
Most abundant channel, so outflow leads to a net negative charge inside the cell
Under what circumstances could ions flow through an
ion channel from a region of lower ion concentration to a
region of higher ion concentration?
. Ions can flow against a chemical concentration gradient if there is an oppos-
ing electrical gradient of greater magnitude
Suppose a cell’s membrane potential shifts from
-70 mV to -50 mV. What changes in the cell’s permeability
to K + or Na+ could cause such a shift?
A decrease in permeability to
K +, an increase in permeability to Na +, or both
How does a stimulus alter the membrane potential?
gated ion channels, open
or close in response to stimuli. When a gated ion channel
opens or closes, it alters the membrane’s permeability to par-
ticular ions
rapid flow of ions across the membrane alters potential
What is hyperpolarization?
Stimulus causes voltage-gated ion channels to open
membranes permability to K+ increases
Diffusion of K+ out of neuron increases, shifting membrane potential toward EK(-90mV)
overall increase in magnitude of membrane potential
inside of membrane is more negative
What is depolarization
reduction in magnitude of membrane potential
often involves gated sodium channels
Permability to Na+, membrane potential shifts toward ENa (+62mV)
What is graded potential?
The response to hyperpolarization or depolarization is a shift in membrane potential
Induce a small electrical current that dissipates as it flows down membrane
decay with time
If a depolarization shifts the membrane potential sufficiently,
the result is a massive change in membrane voltage called an
____ ____.
If a depolarization shifts the membrane potential sufficiently,
the result is a massive change in membrane voltage called an
action potential.
Why are action potentials well suited for transmitting a signal over long distances?
Unlike graded potentials, they have a constant magnitude and can regenerate
can spread along axons
How do action potentials come about?
If a depolarization increases the membrane potential to a threshold, voltage-gated sodium channels open
Flow of Na+ into neuron causes further depolarization
Chain reaction/positive feedback, marked change in membrane potential
Why is inactivation of channels required during an
action potential?
Because they are voltage gated, the sodium
channels open when the membrane potential reaches
the threshold of -55 mV and don’t close until the resting
potential is restored. They are therefore open throughout
the action potential. However, the resting potential cannot
be restored unless the flow of Na + into the cell stops. This is
accomplished by inactivation. The sodium channels remain
in the “open” state, but sodium ions cease flowing once inac-
tivation occurs. The end of Na + inflow allows K + outflow to
repolarize the membrane
The “downtime”
when a second action potential cannot be initiated due to the inactivation of ___ _____, is called
the _____
The “downtime”
when a second action potential cannot be initiated due to the inactivation of sodium channels is called
the refractory period
Myelin sheaths
are produced by glia: _____ in the CNS and
____ ____ in the PNS.
Myelin sheaths
are produced by glia: oligodendrocytes in the CNS and
Schwann cells in the PNS.
In myelinated axons, voltage-gated sodium channels
are restricted to gaps in the myelin sheath called ____ ___ ____
In myelinated axons, voltage-gated sodium channels
are restricted to gaps in the myelin sheath called nodes of
Ranvier
This mechanism for propagating
action potentials is called ____ ____ because the action potential appears to
jump from node to node along the axon.
This mechanism for propagating
action potentials is called saltatory conduction because the action potential appears to
jump from node to node along the axon.
How do action potentials and graded potentials differ?
. A graded potential has a magnitude that varies with stimulus strength,
whereas an action potential has an all-or-none magnitude that is independent
of stimulus strength
Compare electrical synapses to chemical synapses
electrical: contain gap junction. Often play a role in synhcronizing the activity of neurons that direct rapid, unvarying behaviors. Found in heart and brain.
Chemical: Rely on release of an NT. When an action potential arrives at a chemical synapse, it depolarizes plasma membrane at synaptic terminal
At many chemical synapses, the receptor protein that binds
and responds to neurotransmitters is a…
At many chemical synapses, the receptor protein that binds
and responds to neurotransmitters is a ligand-gated
ion channel
compare the ligand-gated ion channels for excitatory postsynaptic potential and inhibitory postsynaptic potential
EPSP: channels are permeable to both K+ and Na+, potential is between Ek and ENa when these channels open
IPSP: channels are permeable for only K+ and Cl-, membrane hyperpolarizes
On some occasions, individual postsynaptic potentials
combine to produce a larger postsynaptic potential, a process called _____
On some occasions, individual postsynaptic potentials
combine to produce a larger postsynaptic potential, a process called summation
What happens when a resting neuron’s membrane depolarizes?
(A) There is a net diffusion of Na + out of the cell.
(B) The equilibrium potential for K + (E K) becomes more positive.
(C) The neuron’s membrane voltage becomes more positive.
(D) The cell’s inside becomes more negative than the outside
The neuron’s membrane voltage becomes more positive.
A common feature of action potentials is that they
(A) cause the membrane to hyperpolarize and then depolarize.
(B) can undergo temporal and spatial summation.
(C) are triggered by a depolarization that reaches threshold.
(D) move at the same speed along all axons.
are triggered by a depolarization that reaches threshold.
Where are neurotransmitter receptors located?
(A) the nuclear membrane
(B) the nodes of Ranvier
(C) the postsynaptic membrane
(D) synaptic vesicle membrane
the postsynaptic membrane
Why are action potentials usually conducted in one direction?
(A) Ions can flow along the axon in only one direction.
(B) The brief refractory period prevents reopening of voltage-
gated Na + channels.
(C) The axon hillock has a higher membrane potential than the
terminals of the axon.
(D) Voltage-gated channels for both Na + and K + open in only
one direction.
The brief refractory period prevents reopening of voltage-
gated Na + channels.
Which of the following is the most direct result of depolarizing
the presynaptic membrane of an axon terminal?
(A) Voltage-gated calcium channels in the membrane open.
(B) Synaptic vesicles fuse with the membrane.
(C) Ligand-gated channels open, allowing neurotransmitters to
enter the synaptic cleft.
(D) An EPSP or IPSP is generated in the postsynaptic cell.
Voltage-gated calcium channels in the membrane open.
Suppose a particular neurotransmitter causes an IPSP in
postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely
explanation is that
(A) the threshold value in the postsynaptic membrane for cell
X is different from that for cell Y.
(B) the axon of cell X is myelinated, but that of cell Y is not.
(C) only cell Y produces an enzyme that terminates the activity
of the neurotransmitter.
(D) cells X and Y express different receptor molecules for this
particular neurotransmitter
cells X and Y express different receptor molecules for this
particular neurotransmitter
