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234 Cards in this Set

  • Front
  • Back
Basic functional units of nervous system, which perform all communication, info processing and control functions of the nervous system
neurons
supporting cells (supporting neural tissue)
neuroglia (a.k.a. glial cells), which outnumber neurons
how neuroglia (glial cells) support neural tissue:
separate and protect neurons, provide supportive framework for neural tissue, act as phagocytes, help regulate composition of interstitial fluid
neural tissue forms body parts:
brain, spinal cord, receptors in complex sense organs (in eye and ear), nerves that link nervous system with other systems
central nervous system (components)
spinal cord and brain (including both neural tissue and blood vessels and connective tissues
central nervous system (CNS function)
integrating, processing, coordinating sensory data and motor commands

aka

seat of higher functions
sensory data
info about conditions inside and outside the body
motor commands
actions to control activities of peripheral organs (such as skeletal muscles)
peripheral nervous system components
includes all neural tissue outside CNS, bundles of axons (nerves) and their supporting tissue
peripheral nervous system subtypes
peripheral nerves/nerves, cranial nerves, spinal nerves
Peripheral nervous system (PNS) is divided into two divisions
Afferent (afferens to bring to)

and

Efferent (effero to bring out)
Afferent division of PNS
brings sensory information to CNS from receptors in peripheral tissues and organs
receptors, which may be neurons or specialized cells, are:
sensory structures that:

detect changes in environment (internal body or external)

OR

respond to specific stimuli
function of the Efferent division (PNS), which has both somatic and autonomic components,
carries motor commands from CNS to three types of effectors: muscles, glands and adipose tissue
effectors
target organs which respond by doing something
Somatic section (SNS) of the Efferent division of CNS:
controls skeletal muscle contractions, which mostly means voluntary movements along with a few involuntary limb reflexes
Autonomic section (ANS) of the Efferent division of CNS:
regulates smooth muscle

cardiac muscle contractions and

glandular secretions

adipose tissue

(this is all subconscious)
Most common type of neuron shape
multipolar neuron (large cell body, several short branched dendrites, long single axon which ends in several telodendria)
cell body is called
soma
soma/cell body contains
perikaryon (cytoplasm around nucleus) and its cytoskeleton,

a large round nucleus...
neurofibrils in a neuron
bundles of neurofilaments extend into dendrites and axon, providing internal support
perikaryon
includes cytoplasm around nucleus which contains neurofilaments and neurotubules

contains organelles that provide energy and synthesize organic materials
organelles inside the perikaryon of the neuron
regions withRough endoplasmic reticulum and free ribosomes

= nissl bodies (gray) (cause brain etc to be gray)
organelles not inside the perikaryon of the neuron
centrioles are not present
CNS neurons cannot
divide
dendrites
-variable in number
-extend from cell body
-highly branched
-each branch has studded dendritic spines
axon
a long cytoplasmic process capable of propagating an electrical impulse aka action potential
dendrites' roles
involved in intercellular communication
a process in anatomy is a
a projection or outgrowth of tissue from a larger body
electrical impulse
action potential
axoplasm is:
cytoplasm of the axon containing neurofibrils, neurotubules, small vesicles, lysosomes, mitochondria and enzymes
-next to the slender axon
-specialized portion of plasma membrane which surrounds the axoplasm
axolemma
type of fluid that an axolemma MAY be exposed to in CNS, OR type of cells that the axolemma MAY be covered by
interstitial fluid, neuroglia
thick base of an axon
initial segment
thickest part of initial segment base
axon HILLOCK
axon may branch out along its length in side branches called
collaterals
collaterals (function)
enable a single neuron to communicate with several other cells
collaterals end in fine extensions (with circular tips)

Those extensions/endings are called:
telodendria
telodendria also known as
terminal branches
circular endings of telondria are called
synaptic terminals
synapse includes the
synaptic terminal (tips)
synapse
specialized site where the neuron communicates with another cell
every synapse involves two cells, the:
presynaptic cell (sends message) and post synaptic cell (receives message)
synaptic cleft
area between two cells
chemicals released into synaptic cleft space after the arrival of the action potential
neurotransmitters
presynaptic cell is usually
a neuron
structures that house neurotransmitters within the synaptic cleft
synaptic vesicles
post synaptic cell can be
either a neuron or another type of cell
synapse between neuron and muscle
a neuromuscular junction
a neuroglandular junction
where a neuron controls or regulates the activity of a secretory (gland) cell
to innervate
to be distributed to
neurons innervates several cell types including
adipocytes
structure of synaptic terminal depends on
the type of postsynaptic cell
structure of synaptic terminal is simple and round
post-synaptic cell is another neuron
neurotransmitters are released from
the presynaptic membrane
where receptors for neurotransmitters are
postsynaptic membrane
when the postsynaptic cell is a muscle and it is a neuromuscular junction, the synaptic terminal is
more complex
mitochondria, endoplasmic reticulum, vesicles filled with neurotransmitter molecules
are located at the synaptic terminal
synaptic terminal reabsorbs and reassembles the
breakdown products of neurotransmitters formed at the synapse
neurotransmitters, enzymes and lysosomes
are received by synaptic terminal, after being hauled by molecular motors KINESIN and DYNEIN
AXOPLASMIC TRANSPORT
the movement of materials between the cell body and synaptic terminals
types of axoplasmic transport
slow stream and fast stream
neurotransmitters move in axoplasmic transport using
fast stream
types of axoplasmic flow of materials: if from cell body to the synaptic terminals then it is
anterograde flow
types of axoplasmic flow of materials: if from synaptic terminals to cell body then it is
retrograde flow
anaxonic neurons
have more than two processes
anaxonic neurons' axons
cannot be distinguished from dendrites
bipolar neurons
have 2 processes separated from the cell body
bipolar neurons
have dendritic branches
unipolar neurons
have a single elongate process, with the cell body situated off to the side
multipolar neuron
have more than two processes
multipolar processes
have a single axon and multiple dendrites
bipolar neurons
have one dendrite that branches extensively into the dendritic branches at its distal tip,

and one axon with the cell body between the two
bipolar neuron
are actually small and rare and occur in special sense organs
unipolar neurons are aka
pseudounipolar neurons
unipolar neurons' dendrites and axons are
continuous
initial segment of a unipolar neuron is located
where the dendrites converge
most sensory neurons of the peripheral nervous system are
unipolar neurons
unipolar neurons' axons may extend
a meter or more. the longest carry sensations from the tips to the toes to the spinal cord
multipolar neurons have
2 or more dendrites and a single axon
the most common neurons in the CNS are
multipolar neurons
true or false: the axons of multipolar neurons can be as long as those of unipolar neurons
true, the longest axons of multipolar neurons carry motor commands from the spinal cord to small muscles that move the toes
The graded potential is a stimulus that
temporarily causes a localized change in the resting potential.
The oligodendrocyte functions to
sheath certain axons of the central nervous system (CNS).
Astrocytes have many functions, including
the maintenance of the blood - brain barrier (BBB).
Microglial cells are
the phagocytes of the central nervous system (CNS).
An action potential is an electrical impulse, which
propagates along the surface of the axon.
The graded potential is a stimulus that
temporarily causes a localized change in the resting potential.
The resting membrane potential is the
moment-to-moment variation of the transmembrane potential in all living cells.
Synaptic activity results in the production of graded potentials in
the plasma membrane of the postsynaptic cell.
The resting membrane potential is the
moment-to-moment variation of the transmembrane potential in all living cells.
An action potential is the brief but striking reversal of
the membrane potential in excitable cells.
A threshold potential is the
minimum depolarization required to elicit an action potential.
Synaptic activity results in the production of
graded potentials in the plasma membrane of the postsynaptic cell.
The resting membrane potential is the
baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.
Sodium-potassium ATPases are present in all cells, but they actively transport Na+ and K+ across the
plasma membrane.
Some ligand-gated channels do permit Na+ and K+ to
passively move across plasma membranes, but they are not present in all cells.
Leak channels for Na+ and K+ are ubiquitous, and they allow for the
diffusion of these ions across plasma membranes.
The inside surface of the plasma membrane accumulates more negative charge because
of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+.
There are many more K+ leak channels than
than Na+ leak channels in the plasma membrane.
More leak channels translates into more
leakiness. Thus the outward flux of K+ is greater than the inward flux of Na+.
The Na+-K+ pumps maintain the resting membrane potential by
maintaining the Na+ and K+ gradients across the plasma membrane.
True or False: Pump activity is not a major determinant of the RMP.
True
Due to the time involved in calcium influx and neurotransmitter release, the transmission of an action potential is delayed at
the synaptic cleft.
The events that occur at a functioning cholinergic synapse cause
synaptic delay
Where do most action potentials originate?
initial segment
Voltage-gated K+ channels are comparatively slow to open in response to
a threshold stimulus.
Ligand-gated Cl- channels are located in the
plasma membrane of postsynaptic cell bodies and dendrites.
The opening of Ligand-gated Cl- channels allows
Cl- to diffuse into the cell.
This Cl- diffusion results in a hyperpolarization, which can lead to
inhibition.
Ligand-gated cation channels are located in the
plasma membrane of postsynaptic cell bodies and dendrites.
Na+ and K+ diffusion results in a depolarization, which can lead to
excitation.
The opening of Ligand-gated cation channels allows
Na+ to enter and K+ to exit the cell.
Synaptic transmission refers to the transfer of neural information between a neuron and
another cell
A synapse between two neurons influences the generation and propagation of
an action potential in the postsynaptic axon.
An action potential is conducted in a saltatory (Latin, saltare; to leap) fashion along
myelinated axons
An action potential is conducted continuously along
an unmyelinated axon from its initial segment to the axon terminals.
The term continuous in continuous conduction refers to the fact that the action potential is regenerated when voltage-gated Na+ channels open in
every consecutive segment of the axon, NOT at nodes of Ranvier.
An action potential is self-regenerating because
flow down the axon and trigger an action potential at the next segment
Regeneration of the action potential occurs in one direction BECAUSE
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
The myelin sheath increases the speed of action potential conduction from the
initial segment to the axon terminals.
What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?
Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
Closing of voltage-gated channels is
time dependent. Typically, the inactivation gates of voltage-gated Na+ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+ channels open.
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
Where in the neuron is an action potential initially generated?
axon hillock
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels (when the voltage-gated Na+ channels open, Na+ rushes into the cell causing depolarization.)
The repolarization phase of an action potential results from
the opening of voltage-gated K+ channels
as the voltage-gated K+ channels open, K+ rushes out of the cell, causing
the membrane potential to become more negative on the inside, thus repolarizing the cell.
Hyperpolarization results from
slow closing of voltage-gated K+ channels
the slow closing of the voltage-gated K+ channels means that more K+ is leaving the cell, making it more _____ inside.
negative
the membrane goes from –70 mV to
+30 mV.
Thus, during the action potential, the inside of the cell becomes more ______ than the outside of the cell.
positive
What is the magnitude (amplitude) of an action potential?
100 mV
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent area.
the influx of sodium ions depolarizes adjacent areas, causing the membrane to
reach threshold and cause an action potential. Thus, the action potential is regenerated at each new area.
Why does the action potential only move away from the cell body?
The areas that have had the action potential are refractory to a new action potential. (sodium channels are inactivated in the area that just had the action potential.)
The velocity of the action potential is fastest in which of the following axons?
a small myelinated axon
the myelination acts as insulation and the action potential is generated only at
the nodes of Ranvier.
Propagation along myelinated axons is known as
saltatory conduction.
slower propagating
smaller diameter
unmyelinated
characteristics of TYPE C AXONS, compared to to the faster, larger more myelinated type A axons are
Compared to nerve action potentials, muscle action potentials do not have __________.
faster propagation
Which of these axons will conduct an action potential most quickly?
Type A fiber
The activation gates of voltage-gated Na+ channels open very
rapidly in response to threshold stimuli.
relative to the activation gates of voltage-gated Na+ channels, the activation gates of voltage-gated K+ channels are comparatively
slow to open.
The synaptic cleft is the small space between
the sending neuron and the receiving neuron.
Neurotransmitter molecules carry information across
a synaptic cleft.
Resting voltage of -70 mV to a threshold value of -55 mV, this is the minimum value required to
open enough voltage-gated Na+ channels so that depolarization is irreversible.
When calcium ions enter the synaptic terminal, they cause
vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to
a positive value.
The activation gates of voltage-gated Na+ channels open, and ____ diffuses into the cytoplasm.
Na+
When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,
ion channels in the plasma membrane of the receiving neuron open.
If a signal from a sending neuron makes the receiving neuron more negative inside,
the receiving neuron is less likely to generate an action potential.
acetylcholine is broken down by acetylcholinesterase AND THEN IS
returned to the presynaptic neuron’s axon terminal.
Which of the neurotransmitter is broken down by an enzyme before being returned?
acetylcholine
the neurotransmitter can cause the postsynaptic membrane to either
depolarize or hyperpolarize, depending on which ion channels are opened.
the neurotransmitter is a chemical released from the presynaptic membrane, so it would open
chemically gated channels on the postsynaptic membrane.
Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.
Binding of a neurotransmitter to its receptors opens _____CHEMICALLY GATED_____ channels on the ______POSTSYNAPTIC____ membrane.
An action potential releases neurotransmitter from a neuron by opening which channels?
voltage-gated Ca2+ channels
opening of voltage-gated Ca2+ channels causes calcium to move into
the axon terminal.
Calcium inside the neuron causes the vesicles to merge with the _____ and release the ______ via exocytosis into the synaptic cleft
Calcium inside the neuron causes the vesicles to merge with the membrane and release the neurotransmitter via exocytosis into the synaptic cleft.
neurotransmitters are stored in the axon terminals of the presynaptic neuron.
neurotransmitters are stored in the axon terminals of the presynaptic neuron.
Which of these neurotransmitters does not bind to a plasma membrane receptor?
nitric oxide
The sodium-potassium exchange pump stabilizes resting potential at about __________.
-70 mV
The most abundant intracellular cation is __________ while the most abundant extracellular anion is __________.
The most abundant intracellular cation is potassium while the most abundant extracellular anion is chloride
Which type of ion channel is always open?
passive
Action potential propagation begins (is first generated at) what region of a neuron?
initial segment
Graded potentials created in the dendrites and soma will, if sufficiently depolarizing, generate an action potential in the initial segment of the axon.
an action potential in the initial segment of the axon.
Where are action potentials regenerated as they propagate along an unmyelinated axon?
at every segment of the axon
The action potential will then propagate away from
the initial segment, down the axon.
In unmyelinated axons, the action potential is regenerated continuously along every segment of the axon

and that is called
continuous propagation
The movement of what ion is responsible for the local currents that depolarize other regions of the axon to threshold?
sodium (Na+)
Sodium ions enter the cell during the
beginning of an action potential.
In an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?
The previous axonal segment is refractory.
Approximately how fast do action potentials propagate in unmyelinated axons in humans?
1 meter per second
In contrast to the internodes of a myelinated axon, the nodes
have lower membrane resistance to ion movement
Where are action potentials regenerated as they propagate along a myelinated axon?
at the nodes
In myelinated axons, voltage-gated sodium channels are largely restricted to the nodes between
myelinated internodes.
action potentials only regenerate at
the nodes.
The high membrane resistance of the internodes ensures that local currents generated at one node will quickly
bring the next node to threshold, even though it is 1-2 mm away.
The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.
Saltatory propagation, which is derived from the Latin word saltare, which means leaping.
How do action potential propagation speeds in myelinated and unmyelinated axons compare?
Propagation is faster in myelinated axons.
Multiple sclerosis (MS) is a disease that stops action potential propagation by destroying the myelin around (normally) myelinated axons. Which of the following best describes how MS stops action potential propagation?
Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes.
Myelin increases the membrane resistance of the axon section it surrounds, allowing local currents to
travel between nodes, even though they are 1-2 mm apart.
The initial segment has the lowest threshold and, therefore, is the place where
most action potentials are initiated.
During an action potential of a neuron, what directly causes the different channels to open and close?
the transmembrane potential (voltage)
Changes in transmembrane potential directly cause voltage-gated channel proteins to
change shape and allow the flow of ions across the cell membrane.
What is the typical duration of a nerve action potential?
2 ms (although they can be longer in the heart)
Around what transmembrane potential does threshold commonly occur?
At approximately -60 mV, an action potential is initiated. A transmembrane potential -60 mV corresponds to a depolarization of 10-15 mV away from the resting membrane potential.
A transmembrane potential of ______ is near the resting potential of the cell.
-70 mV
What ion is responsible for the depolarization of the neuron during an action potential?
Na+ (sodium)
What type of membrane transport causes the depolarization phase of the action potential in neurons?
diffusion
Ions move through channels according to
their electrochemical gradient from one side of the membrane to the other.
Ions move through channels according to their electrochemical gradient from one side of the membrane to the other AND THIS
movement is known as channel-mediated diffusion.
During an action potential, after the membrane potential reaches +30 mV, which event(s) primarily affect(s) the membrane potential?
Voltage-gated sodium channels begin to inactivate (close) and voltage-gated potassium channels begin to open.
The repolarization phase of the action potential involves decreasing sodium influx via inactivation of sodium channels and increasing potassium efflux (exit) via opening
potassium channels. Both of these processes begin near the peak of the action potential.
What ion causes repolarization of the neuron during an action potential?
K+ (potassium)
What causes repolarization of the membrane potential during the action potential of a neuron?
potassium efflux (leaving the cell)
Positively charged potassium ions flowing out of the cell makes the transmembrane potential more
negative, repolarizing the membrane towards the resting potential.
What is primarily responsible for the brief hyperpolarization near the end of the action potential?
voltage-gated potassium channels taking some time to close in response to the negative membrane potential
Which of these is the earliest step in the generation of an action potential?
Sodium channels open.
What happens just after an axon is depolarized to threshold?
Some sodium channels open.
During propagation of the action potential, WHAT 3 THINGS HAPPEN?
1-the axon hillock depolarizes the initial segment

2-Local currents depolarize a spot adjacent to the active zone

3-after threshold is reached, sodium channels open rapidly
What causes calcium channels in the synaptic knob to open?
depolarization of the presynaptic membrane due to an arriving action potential
Which of the following best describes the role of calcium in synaptic activity?
Calcium enters the presynaptic cell and causes the release of ACh.
As a presynaptic action potential reaches the synaptic terminal, _____ channels open.
voltage-gated calcium channels open.
The open calcium channels allow calcium to
diffuse into the synaptic terminal.
This calcium influx causes synaptic vesicles to
fuse with the presynaptic membrane.
Neurotransmitters exit the presynaptic cell via __________.
Neurotransmitters exit the presynaptic cell via exocytosis
When ACh receptors open, what ion causes depolarization of the postsynaptic membrane?
sodium
Positively charged sodium ions cross the postsynaptic membrane
open ACh receptors.
Which of the following best describes how ACh causes depolarization of the postsynaptic membrane?
ACh opens ACh receptors.
ACh receptors on the postsynaptic membrane are
chemically gated ion channels. These channels open when they bind ACh.
Once open, chemically gated channels allow sodium to enter, depolarizing the cell. Chemically gated channels are often called
"receptors" because they must "receive" (or bind) a particular chemical before they can open.
Which of the following best describes the order of events in synaptic activity?
An action potential arrives and depolarizes the synaptic knob. Extracellular calcium enters the synaptic knob, triggering exocytosis of ACh. ACh binds to receptors and depolarizes postsynaptic membrane. ACh is removed by AChE.
Where is acetylcholinesterase (AChE) primarily located?
in the synaptic cleft
What is the primary role of acetylcholinesterase (AChE) at a cholinergic synapse?
AChE degrades acetylcholine in the synaptic cleft.
Curare is a drug that prevents ACh from binding to ACh receptors. How would you expect curare to affect events at a cholinergic synapse?
The postsynaptic cell would not depolarize.
Which ion triggers synaptic vesicles to discharge neurotransmitter into the synaptic cleft?
calcium
The effect of a nerve impulse on a postsynaptic neuron depends on the __________.

what 3 things?
1) characteristics of the receptor on the postsynaptic neuron

2) kind of neurotransmitter released by the presynaptic neuron

3) quantity of neurotransmitter released
EPSPs and IPSPs summate at the __________.
axon hillock
EPSPs are ___________.
excitatory, postsynaptic, graded
If a nerve cell receives many IPSPs at the same time, __________.
it will show spatial summation
If EPSPs summate to a sustained value above threshold, then the initial segment will __________.
generate a string of action potentials
At rest, why is the transmembrane potential of a neuron (-70 mV) closer to the potassium equilibrium potential (-90 mV) than it is to the sodium equilibrium potential (+66 mV)?
The membrane is much more permeable to potassium ions than to sodium ions.
In a typical neuron, what is the equilibrium potential for sodium?
+66 mV
true or false: the equilibrium potential for sodium must be positive.
positive, because it must oppose the entry of sodium ions.
In a typical neuron, what is the equilibrium potential for sodium?
+66 mV
Compared to the electrical gradient for sodium at rest, the electrical gradient for potassium at rest is __________.
in the same direction and of the same magnitude.
The electrochemical gradient for sodium ions in a neuron when the transmembrane potential is at the resting potential is caused by what?
chemical and electrical gradients both going into the cell
In a typical neuron, what is the equilibrium potential for potassium?
-90 mV
What is the electrochemical gradient of an ion?
the sum of the electrical and chemical gradients for that ion
The electrochemical gradient for potassium ions when the transmembrane potential is at the resting potential (-70 mV) is caused by what?
a chemical gradient going out of the cell and an electrical gradient going into the cell
Leak channels allow the movement of potassium and sodium ions by what type of membrane transport?
channel-mediated diffusion
In a neuron, sodium and potassium concentrations are maintained by the sodium-potassium exchange pump such that __________.
the sodium concentration is higher outside the cell than inside the cell and the potassium concentration is higher inside the cell than outside the cell.