MA&P Chapter 12
What is the magnitude (amplitude) of an action potential?
100 mV
What is the typical duration of a nerve action potential?
2 ms
The ________ division of the peripheral nervous system brings sensory information to the central nervous system.
afferent
The part of the peripheral nervous system that carries sensory information to the CNS is the
afferent division
The ________ principle states that the size and speed of the action potential are independent of the stimulus strength
all or none
The all-or-none principle states that
all stimuli great enough to bring the membrane to threshold will produce identical action potentials.
Neurons that are rare, small, and lack features that distinguish dendrites from axons are called
anaxonic
The buildup of depolarization when EPSPs arrive in rapid succession is called ________ summation.
temporal
The simplest level of information processing takes place at the __________.
axon hillock
The site in the neuron where EPSPs and IPSPs are integrated is the
axon hillock
Which type of synapse is most common in the nervous system?
chemical
________ open or close in response to binding specific molecules.
chemically gated channels
Branches that may occur along an axon are called
collaterals
The ________ division of the nervous system carries motor commands to muscles and glands.
efferent
________ carry motor information to peripheral effectors.
efferent neurons
Binding of the neurotransmitter to its receptor causes the membrane to __________.
either depolarize or hyperpolarize
In a(n) ________ synapse, current flows directly between cells.
electrical
The sum of the electrical and chemical forces acting on an ion is known as its
electrochemical gradient
________ monitor the digestive, respiratory, cardiovascular, urinary, and reproductive systems.
internoceptors
A molecule that carries information across a synaptic cleft is a
neurotransmitter
Clusters of RER and free ribosomes in neurons are called
nissl bodies
The tiny gaps between adjacent Schwann cells are called
nodes of Ranvier
Adrenergic synapses release the neurotransmitter
norepinephrine
Which of these neurotransmitters is released at CNS adrenergic synapses?
norepinephrine
The myelin sheath that covers many CNS axons is formed by
oligodendrocytes
Hyperpolarization results from __________.
slow closing of voltage gated potassium channels
The velocity of the action potential is fastest in which of the following axons?
small myelinated axon
What ion is responsible for the depolarization of the neuron during an action potential?
sodium
When cholinergic receptors are stimulated,
sodium ions enter the postsynaptic neuron
The ________ nervous system controls the skeletal muscles.
somatic
Summation that results from the cumulative effect of multiple synapses at multiple places on the neuron is designated
spatial summation
What is the electrochemical gradient of an ion?
the sum of the electrical and chemical gradients for that ion
The minimum stimulus required to trigger an action potential is known as the
threshold stimulus
Which of the following types of nerve fiber possesses the fastest speed of impulse propagation?
type A
Sensory information from skeletal muscles travels over
type A fibers
Neurons in which dendritic and axonal processes are continuous and the soma lies off to one side are called
unipolar
Sensory neurons of the PNS are
unipolar
Neurotransmitters ready for release are stored in synaptic
vesicles
The generation of an action potential in a neuron requires the presence what type of membrane channels?
voltage gated channels
The depolarization phase of an action potential results from the opening of which channels?
voltage gated sodium channels
Deteriorating changes in the distal segment of an axon as a result of a break between it and the soma is called ________ degeneration.
wallerian
Regions of the CNS with an abundance of myelinated axons constitute the
white matter
Where do most action potentials originate?
initial segment
What is an example of a presynaptic cell?
neuron
The resting membrane potential of the cell is
-70 mV
The sodium-potassium exchange pump stabilizes resting potential of the neuron membrane at about __________.
-70 mV
In a typical neuron, what is the equilibrium potential for potassium?
-90 mV
The point at which there is no net movement of K+ into or out of the cell is
-90 mV
In a typical neuron, what is the equilibrium potential for sodium?
66 mV
The concentrations of which two ions are highest outside the cell?
Na+ and Cl−
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
What type of channel in the postsynaptic membrane binds neurotransmitter?
a chemically gated channel
If the axolemma becomes more permeable to potassium ion,
a stronger stimulus will be required to cause an action potential.
The period during which an excitable membrane cannot respond to further stimulation is the ________ period.
absolute refractory
Cholinergic synapses release the neurotransmitter
acetylcholine.
The largest and most numerous of the glial cells in the central nervous system are the
astrocytes
The neuroglial cells that participate in maintaining the blood-brain barrier are the
astrocytes
When a person has a stroke, blood leaks into the brain tissue. Which type of neuroglia cells would repair the damage?
astrocytes
Where are action potentials regenerated as they propagate along a myelinated axon?
at the nodes
The ________ nervous system provides involuntary regulation of smooth muscle, cardiac muscle, and glandular activity.
autonomic
The plasma membrane of an axon is called the
axolemma
The axon is connected to the soma at the
axon hillock
What is the role of neurotransmitter at a chemical synapse?
binds to receptors on the postsynaptic cell membrane.
________ neurons are short, with a cell body between dendrite and axon, and occur in special sense organs
bipolar
Raising the potassium ion concentration in the extracellular fluid surrounding a nerve cell will have what effect?
both hyperpolarize it and decrease the magnitude of the potassium equilibrium potential
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
Which ion triggers synaptic vesicles to discharge neurotransmitter into the synaptic cleft?
calcium
The afferent division of the PNS __________.
carries sensory information
The ________ nervous system is composed of the brain and spinal cord.
central
Most neurons lack ________ and so are permanently blocked from undergoing cell division.
centrioles
Leak channels allow the movement of potassium and sodium ions by what type of membrane transport?
channel mediated diffusion
Functions of astrocytes include all of the following except
conducting action potentials
Integral membrane proteins that connect electrical synapses are called
connexons
What type of conduction takes place in unmyelinated axons?
continuous conduction
A movement of charges in response to a potential difference is called
current
The sensory loss and muscle weakness associated with multiple sclerosis are a consequence of
demyelination
A shift of the resting transmembrane potential toward 0 mV is called
depolarization
Opening of sodium channels in the axon membrane causes
depolarization
A threshold stimulus is the
depolarization necessary to cause an action potential
What triggers the release of acetylcholine from a synaptic terminal?
diffusion of calcium ions into the synaptic terminal
Which of the following is a recognized class of opioid neuromodulators?
endomorphins, dynorphins, enkephalins and endorphins
Which of these substances is considered a neuromodulator?
endorphins
________ line the brain ventricles and spinal canal.
ependymal cells
What mechanism releases neurotransmitter from presynaptic neurons?
exocytosis
________ provide information about the external environment.
exteroceptors
What type of membrane transport causes the depolarization phase of the action potential in neurons?
facilitated diffusion
Compared to nerve action potentials, muscle action potentials do NOT have __________.
faster propagation
Damage to ependymal cells would most likely affect the
formation of cerebrospinal fluid
The efferent division of the peripheral nervous system innervates ________ cells.
glandular, heart muscle, skeletal muscle and smooth muscle
Regions of the CNS where neuron cell bodies dominate constitute the
gray matter
Voltage-gated channels are present
in the membrane that covers axons
Voltage-gated sodium channels have both an activation gate and a(n) ________ gate.
inactivation
What is the function of the myelin sheath?
increases the speed of action potential conduction from the initial segment to the axon terminals
Which of the following is true about threshold for an action potential?
it is more positive than the resting potential
If a nerve cell receives many IPSPs in different locations at the same time, __________.
it will show spatial summation
Ion channels that are always open are called
leak channels
________ open or close in response to physical distortion of the membrane surface.
mechanically gated channels
Which of the following is not a function of the neuroglia?
memory
Small, wandering cells that engulf cell debris and pathogens in the CNS are called
microglia
The sodium-potassium ion exchange pump
moves sodium and potassium to the direction opposite of their gradients
Neurons that have several dendrites and a single axon are called
multipolar
The most abundant class of neuron in the central nervous system is
multipolar
In which type of axon will velocity of action potential conduction be the fastest?
myelinated axons with the largest diameter
Saltatory propagation occurs in _________ axons, in which action potentials _________.
myelinated; move from one node of Ranvier to another
________ account for roughly half of the volume of the nervous system.
neuroglia
Compounds that alter the rate of neurotransmitter release by the presynaptic neuron or change the postsynaptic cell's response to neurotransmitters are called
neuromodulators
The basic functional unit of the nervous system is the
neuron
The repolarization phase of an action potential results from __________.
opening of voltage gated potassium channels
Which type of ion channel is always open?
passive channel
The cytoplasm that surrounds the nucleus of a neuron is called the
perikaryon
The nervous tissue outside of the central nervous system composes the ________ nervous system.
peripheral
A neuron that receives neurotransmitter from another neuron is called
postsynaptic neuron
What ion causes repolarization of the neuron during an action potential?
potassium
During repolarization of a neuron
potassium ions move out of the cell
The most abundant intracellular cation is __________ while the most abundant extracellular anion is __________.
potassium; chloride
The separation of positive and negative charges across the membrane creates a ________ difference, or voltage.
potential
GABA produces what?
presynaptic inhibition
In a synapse, neurotransmitters are stored in vesicles located in the __________.
presynaptic neuron
________ monitor the position of skeletal muscles and joints.
proprioceptors
The period during which an excitable membrane can respond again, but only if the stimulus is greater than the threshold stimulus, is the ________ period.
relative refractory
A change in the conditions in the synaptic terminal can influence the soma as a result of ________ transport.
retrograde
Rapid impulse conduction from "node" to "node" is called
saltatory propagation
Glial cells that surround the neurons in ganglia are
satellite cells
Which of the following is a type of glial cell found in the peripheral nervous system?
satellite cells
________ neurons form the afferent division of the PNS.
sensory
Opioids relieve pain by blocking the release of
substance P
The __________ nervous system controls glandular secretion.
sympathetic and parasympathetic
The site of intercellular communication between a neuron and another cell is the
synapse
Axons terminate in a series of fine extensions known as
telodendria