Neurons that have one axon and one dendrite, with the soma in between, are called
Which of the following activities or sensations is not monitored by interoceptors?
cardiovascular activities activities of the digestive system taste sight (NOT) urinary activities
1. interoceptors 2. exteroceptors 3. proprioceptors A) monitor the position and movement of skeletal muscles and joints B) provide sensations of taste, deep pressure, and pain C) provide information about the external environment
Neurotransmitter for release is stored in synaptic
Neurons that have several dendrites and a single axon are called
The axon is connected to the soma at the
The most abundant class of neuron in the central nervous system is
The site of intercellular communication between neurons is the
Neurons in which dendritic and axonal processes are continuous and the soma lies off to one side are called
Active neurons need ATP to support which of the following?
the synthesis of neurotransmitter molecules the recovery from action potentials the movement of materials from the soma by axoplasmic transport the movement of materials to the soma by axoplasmic transport all of the above
The rabies virus travels to the CNS via
retrograde axoplasmic transport.
Neurons that are rare, small, and lack features that distinguish dendrites from axons are called
The axoplasm of the axon contains which of the following?
mitochondria vesicles neurofibrils neurotubules all of the above
________ neurons are small and have no anatomical features that distinguish dendrites from axons.
How does blocking retrograde axoplasmic transport in an axon affect the activity of a neuron?
The soma becomes unable to respond to changes in the distal end of the axon.
________ neurons form the afferent division of the PNS.
________ neurons are the most common class in the CNS.
In a(n) ________ neuron, the dendrites and axon are continuous or fused.
________ neurons are short, with a cell body between dendrite and axon, and occur in special sense organs.
________ carry sensory information to the CNS.
The basic functional unit of the nervous system is the ________.
________ carry motor information to peripheral effectors.
________ are nerves that connect to the brain.
________ monitor the digestive, respiratory, cardiovascular, urinary, and reproductive systems.
________ monitor the position of skeletal muscles and joints.
________ monitor the internal environment.
Most neurons lack ________ and so are permanently blocked from undergoing cell division.
The tiny gaps between adjacent Schwann cells are called ________.
nodes of Ranvier
In the peripheral nervous system, Schwann cells participate in the repair of damaged nerves by
forming a cellular cord that directs axonal regrowth.
Extensive damage to oligodendrocytes in the CNS could result in
loss of sensation and motor control.
After a stroke, what type of glial cell accumulates within the affected brain region?
Which of the following is not a function of the neuroglia?
maintenance of blood-brain barrier support memory(NOT) secretion of cerebrospinal fluid phagocytosis
Glial cells that surround the neurons in ganglia are
Which of the following are a type of glial cell found in the peripheral nervous system?
The neurilemma of axons in the peripheral nervous system is formed by
________ account for roughly half of the volume of the nervous system.
________ line the brain ventricles and spinal canal.
The largest and most numerous of the glial cells in the central nervous system are the
Small, wandering cells that engulf cell debris and pathogens in the CNS are called
Functions of astrocytes include all of the following, except
maintaining the blood-brain barrier. guiding neuron development. responding to neural tissue damage. conducting action potentials. (NOT) forming a three-dimensional framework for the CNS
The myelin sheath that covers many CNS axons is formed by
The largest and most numerous neuroglia in the CNS are the
Which of the following are types of neuroglia?
ependymal cells microglia astrocytes oligodendrocytes all of the above
Which of the following are properties of cerebrospinal fluid?
fills the brain ventricles transports nutrients surrounds the brain and spinal cord circulates continuously all of the above
Deteriorating changes in the distal segment of an axon as a result of a break between it and the soma is called ________ degeneration.
Which of the following is a function of neuroglia?
act as phagocytes provide a supportive framework produce cerebrospinal fluid regulate the composition of interstitial fluid all of the above
Many medications introduced into the bloodstream cannot directly affect the neurons of the CNS because
the endothelium of CNS capillaries forms a blood-brain barrier.
When pressure is applied to neural tissue, all these effects are possible, except
the axon becomes inexcitable. neurons are triggered to divide.(NOT) glial cells degenerate. a decrease in blood flow. action potentials are generated spontaneously
The smallest neuroglia of the CNS are the
The function of the astrocytes in the CNS includes which of the following?
repairing damaged neural tissue maintaining the blood-brain barrier adjusting the composition of the interstitial fluid guiding neuron development all of the above
The sensory loss and muscle weakness associated with multiple sclerosis are a consequence of ________.
If the sodium-potassium pumps in the plasma membrane fail to function, all of the following occur, except
the intracellular concentration of potassium ions will increase(NOT). the intracellular concentration of sodium ions will increase. the neuron will slowly depolarize. the inside of the membrane will have a resting potential that is more positive than normal. the membrane will slowly lose its capacity to generate action potentials
When cholinergic receptors are stimulated,
sodium ions enter the postsynaptic neuron.
The sodium-potassium ion exchange pump
moves sodium and potassium opposite to the direction of their electrochemical gradients.
Puffer fish poison blocks voltage-gated sodium channels like a cork. What effect would this neurotoxin have on the function of neurons?
The axon would be unable to generate action potentials.
Ion channels that are always open are called ________ channels.
Ions can move across the plasma membrane in which of the following ways?
by ATP-dependent ion pumps like the sodium-potassium exchange pump through chemically-gated channels as in neuromuscular transmission through voltage-gated channels as in the action potential through passive or leak channels all of the above
Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference?
Resting membrane potential (RMP)
Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?
On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?
The inside surface of the plasma is much more negatively charged than the outside surface.
The plasma membrane is much more permeable to K+ than to Na+. Why?
There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.
The presence of concentration gradients and leak channels
What prevents the Na+ and K+ gradients from dissipating?
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
During depolarization, which gradient(s) move(s) Na+ into the cell?
both the electrical and chemical gradients
What is the value for the resting membrane potential for most neurons?
The Na+-K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped?
Na+ is pumped out of the cell and K+ is pumped into the cell.
The concentrations of which two ions are highest outside the cell.
Na+ and Cl-
What type of conduction takes place in unmyelinated axons?
An action potential is self-regenerating because __________.
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
Why does regeneration of the action potential occur in one direction, rather than in two directions?
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
What is the function of the myelin sheath?
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.
In which type of axon will velocity of action potential conduction be the fastest?
Myelinated axons with the largest diameter
Where do most action potentials originate?
What opens first in response to a threshold stimulus?
Voltage-gated Na+ channels
What characterizes depolarization, the first phase of the action potential?
The membrane potential changes from a negative value to a positive value.
What characterizes repolarization, the second phase of the action potential?
Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
What event triggers the generation of an action potential?
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
What is the first change to occur in response to a threshold stimulus?
Voltage-gated Na+ channels change shape, and their activation gates open.
Where in the neuron is an action potential initially generated?
The depolarization phase of an action potential results from the opening of which channels?
voltage-gated Na+ channels
The repolarization phase of an action potential results from __________.
the opening of voltage-gated K+ channels
Hyperpolarization results from __________.
slow closing of voltage-gated K+ channels
What is the magnitude (amplitude) of an action potential?
How is an action potential propagated along an axon?
An influx of sodium ions from the current action potential depolarizes the adjacent 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.
The velocity of the action potential is fastest in which of the following axons?
a small myelinated axon
The minimum stimulus required to trigger an action potential is known as the ________.
Which of the following does not influence the time necessary for a nerve impulse to be transmitted?
whether or not the impulse begins in the CNS(NOT) presence or absence of a myelin sheath diameter of the axon length of the axon presence or absence of nodes
Which of the following types of nerve fiber possesses the fastest speed of impulse propagation?
Which of the following comparisons between neurons and muscle tissue is false?
Action potentials last longer in muscle fibers. Resting potentials are greater in muscle fibers. Muscle fibers conduct action potentials at slow speeds. Muscle fibers conduct action potentials only by continuous propagation. Action potentials are briefer in muscle fibers.(FALSE)
Type ________ fibers have the largest diameter axons.
Which type of synapse is most common in the nervous system?
The ion that triggers the release of acetylcholine into the synaptic cleft is
Cholinergic synapses release the neurotransmitter
An action potential traveling along an axon is also called a(n) ________.
At a(n) ________ synapse, a neurotransmitter is released to stimulate the postsynaptic membrane.
Presynaptic facilitation by serotonin is caused by
calcium channels in the presynaptic membrane remaining open longer.
The effect that a neurotransmitter has on the postsynaptic membrane depends on
the quantity of neurotransmitters released. the frequency of neurotransmitter release. the characteristics of the receptors. the nature of the neurotransmitter. all of the above
Adrenergic synapses release the neurotransmitter
Opioids relieve pain by blocking the release of
Which of the following is a recognized class of opioid neuromodulators?
endomorphins endorphins enkephalins dynorphins all of the above
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.
Neurotransmitters exit the presynaptic cell via __________.
The acetylcholine receptor is an example of what type of channel?
a chemically gated channel
When ACh receptors open, what ion causes depolarization of the postsynaptic membrane?
Which of the following best describes how ACh causes depolarization of the postsynaptic membrane?
ACh opens ACh receptors.
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.
What is the primary role of acetylcholinesterase (AChE) at a cholinergic synapse?
AChE degrades acetylcholine in the synaptic cleft.
Where is acetylcholinesterase (AChE) primarily located?
in the synaptic cleft
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.