Chapter 4: The Nervous System
False (Glial cells, or neuroglia, play both structural and supportive roles to neurons.)
True or False: Neurons are the only cell type in the nervous system.
False (Mature RBCs do not have a nucleus. The lack of a nucleus enables the RBC to have more room to contain hemoglobin which increases its efficiency to carrying oxygen.)
True or False: Red blood cells have nuclei.
knee-jerk
A classic example of a monosynaptic reflex arc is the ______-______ reflex, shown in the figure.
A
A disequilibrium exists in the concentration of ions across a membrane. A larger concentration of Ca2+ is typically found in the: A.) Extracellular fluid B.) Intracellular fluid
A (This explains why sodium passively diffuses INTO the cell because there is a higher concentration outside of the cell.)
A disequilibrium exists in the concentration of ions across a membrane. A larger concentration of Na+ is typically found in the: A.) Extracellular fluid B.) Intracellular fluid
resting membrane potential
All neurons exhibit a(n) ______ ______ ______ of approximately -70 mV, which means that there is an electrical potential difference (voltage) between the inside of the neuron that is negative relative to the extracellular space.
withdrawal
An example of a polysynaptic reflex arc is the reaction to stepping on a nail which involves the ______ reflex.
repolarization, hyperpolarization
As positively charged potassium cations are driven out of the cell, there will be a restoration of the negative membrane potential called ______. Potassium channels stay open long enough to overshoot the action potential, resulting in a ______ phase (red in figure); then, the potassium channels close.
K+
At the peak of the action potential (approximately +35 mV), sodium channels are inactivated and ______ channels open.
absolute
During a(n) _____ refractory period, no stimulus of any frequency/intensity can trigger another action potential.
impulse propagation
For a signal to be conveyed to another neuron, the action potential must travel down the axon and initiate neurotransmitter release. This movement is called ______ ______ and is shown in the figure. The influx of sodium in one segment of the axon brings the subsequent segment of the axon to threshold. The fact that the preceding segment of the axon is in its refractory period means that the action potential can only travel in one direction.
increase, decrease, increase
Ideally, you want to increase lambda as much as possible so that the depolarizing current will spread a great distance. How can each of the following variables maximize lambda? (INCREASE / DECREASE) membrane resistance (INCREASE / DECREASE) internal resistance (INCREASE / DECREASE) diameter
effector
If a neuron signals to a gland or muscle, rather than another neuron, the postsynaptic cell is termed a(n) ______.
threshold
If the axon hillock receives enough excitatory input to be depolarized to the ______ value (usually in the range of -55 to -40 mV), an action potential will be triggered.
monosynaptic
In a(n) ______ reflex arc, the sensory (afferent, presynaptic) neuron fires directly onto the (efferent, postsynaptic) neuron.
polysynaptic
In a(n) ______ reflex arc, there is at least one interneuron between the sensory and motor neurons.
white
In the CNS, ______ matter consists of myelinated axons.
grey
In the CNS, ______ matter consists of unmyelinated cell bodies and dendrites.
autonomic, preganglionic, postganglionic
In the _______ nervous system, two neurons work in series to transmit messages from the spinal cord. The first neuron is known as the ______ neuron (soma is in CNS; axon travels to PNS), whereas the second is the ______ neuron (soma is in PNS; affects target tissue).
tracts
In the central nervous system, axons may be bundled together to form ______.
nerves
In the peripheral nervous system, axons may be bundled together to form ______.
acetylcholine, norepinephrine
In the sympathetic nervous system, preganglionic neurons release ______, while most postganglionic neurons release ______.
Brain
In what part of the nervous system is white matter deeper than grey matter?
myelin sheath
Just like insulation prevents wires next to each other from accidentally discharging each other, the ______ ______ maintains the electrical signal within one neurons. In addition, it increases the speed of conduction within one neuron.
reuptake carriers
Many common drugs (either in clinical use or street drugs) modify processes that occur in the synapse. For instance, cocaine acts by blocking presynaptic ______ ______, thus prolonging the action of neurotransmitters in the synapse.
myelin
Most mammalian nerve fibers are coated in ______, an insulating substance that prevents signal loss or crossing of signals.
Excitatory, depolarization
Neurons can receive both excitatory and inhibitory input. ______ input causes ______ by raising the membrane potential, Vm, from its resting potential (becoming less negative inside the cell).
Na+/K+ ATPase
Resting potential (-70 mV) is maintained using selective permeability of ions as well as the ______, as shown in the figure.
autoreceptor
Serotonin (5-HT) can be taken back up by the presynaptic cell; a(n) ______ will signal the presynaptic cell to stop releasing serotonin and start the reuptake process.
closed, open, inactive
Sodium channels can exist in three states: ______ (before the cell reaches threshold and after inactivation has been reversed), ______ (from threshold to approximately +35 mV), and ______ (from approximately +35 mV to the resting potential).
synapse, synaptic cleft
The ______ consists of the nerve terminal of the presynaptic neuron, the membrane of the postsynaptic cell, and the space between the two, called the ______ ______.
length
The ______ constant, λ, corresponds to the distance where a graded potential has decreased to 37% of its original amplitude (distance at which there is a 63% decrease in potential).
presynaptic, postsynaptic
The neuron preceding the synaptic cleft is called the ______ neuron; the neuron after the synaptic cleft is called the ______ neuron.
faster, decreased
The speed at which action potentials move depends on the length and cross-section area of the axon. Greater cross-sectional areas allow for (SLOWER / FASTER) propagation due to (DECREASED / INCREASED) resistance.
higher, slower
The speed at which action potentials move depends on the length and cross-section area of the axon. Increased length of the axon results in (LOWER / HIGHER) resistance and (SLOWER / FASTER) conduction.
cervical, thoracic, lumbar, sacral
The spinal cord extends downward from the brainstem and can be divided into what four divisions?
vertebral column
The spinal cord is protected by the ______ ______, which transmits nerves at the space between adjacent vertebrae.
False (Unlike nerves, tracts only carry one type of information.)
True or False: Individual axons are bundled into nerves or tracts that carry sensory, motor, or mixed information.
True (Like any other cell, the neuronal plasma membrane is fairly impermeable to charged species. Because the plasma membrane contains a thick nonpolar barrier (fatty acid tails), it is not energetically favorable for ions to cross this barrier.)
True or False: It is not energetically favorable for ions to cross the neuronal plasma membrane.
True
True or False: Na+ has a relatively small membrane permeability.
sensory, motor, mixed (carry both sensory and motor information)
What are the three types of nerves in the PNS, which refers to the type(s) of information they carry?
sensory (afferent) neurons, motor (efferent) neurons, interneurons
What are the three types of neurons in the nervous system?
inactivated, deinactivated
When Vm approaches +35 mV, the sodium channels are ______ and will have to be brought back near the resting potential to be ______.
Motor neurons, ventral root
______ _____ run from the brain along the opposite side of the spinal cord and in the ______ ______ to control movements of skeletal muscle and glandular secretions.
Sensory neurons, dorsal root ganglia
______ ______ (red) transmit information about pain, temperature, and vibration up to the brain and have cell bodies in the ______ ______ ______ (blue) toward the back of the spinal cord.
Nodes of Ranvier
______ ______ ______ are exposed areas of myelinated axons that permit saltatory conduction.
Temporal summation (few synapses firing a lot)
______ ______ refers to the addition of multiple signals near each other in time; only a few active synapses fire, but if each generate EPSPs at a high enough frequency, threshold can be reached over a period of time.
Microglia, phagocytic
______ are ______ glial cells that ingest and break down waste products and pathogens in the CNS.
Astrocytes, blood-brain barrier
______ are a type of glial cell that nourish neurons and form the ______-______ ______, which controls the transmission of solutes from the bloodstream into nervous tissue.
Myelination
______ is the body's natural form of increasing membrane resistance.
Schwann cells
What type of glial cell produces myelin in the peripheral nervous system?
Ca2+
When an action potential arrives at the nerve terminal, voltage-gated ______ channels open.
Na+
When enough excitatory stimulation occurs, the cell is depolarized to the threshold voltage and voltage-gated ______ channels open.
Glial cells (also accept: neuroglia)
______ ______ are supportive cells in the nervous system that play four main functions: 1.) Surround neurons and hold them in place. 2.) Supply nutrients and oxygen to neurons. 3.) Insulate one neuron from another. 4.) Destroy pathogens and remove dead neurons.
refractory period
A _____ _____ is the period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation due to the temporary inactivation of Na+ channels and hyperpolarization of the axon.
A (Anionic proteins on the inside of the cell repel the negatively charged choride ions.)
A disequilibrium exists in the concentration of ions across a membrane. A larger concentration of Cl- is typically found in the: A.) Extracellular fluid B.) Intracellular fluid
B (The hip and hamstring muscles pull the foot away from the nail by a monosynaptic reflex, similar to the knee-jerk reflex. In order to plant the other foot on the ground, the motor neuron that controls the quadriceps muscles in the opposite limb must be stimulated, extending it. Interneurons in the spinal cord provide the connections from the incoming sensory information to the motor neurons in the supporting limb making this polysynaptic.)
A woman steps on a nail. Which of the following responses is an example of a polysynaptic reflex? A.) The extremity with which she stepped on the nail flexes to pull the foot way from the nail. B.) The muscles in the opposite limb extend to maintain balance.
B (First, consider the function of voltage-gated calcium channels. When the nerve terminal depolarizes, voltage-gated calcium channels open, allowing for influx of calcium. This influx of calcium triggers fusion of the synaptic vesicles containing neurotransmitters with the membrane of the neuron at the nerve terminal. This allows for exocytosis of the neurotransmitters into the synapse. If a disease blocked the influx of calcium, there would be no release of neurotransmitters. A lack of neurotransmitters means that the neuron cannot send signals. Thus, any symptoms resulting from this disease would be due to an inability of neurons to communicate. If neurons cannot communicate, flaccid paralysis may be one of the results.)
An autoimmune disease attacks the voltage-gated calcium channels in the nerve terminal. What is a likely symptom of this condition? A.) Spastic paralysis (inability to relax the muscles) B.) Flaccid paralysis (inability to contract the muscles) C.) Inability to reuptake neurotransmitters once released D.) Retrograde flow of action potentials
relative
During a(n) ______ refractory period, only a greater than normal stimulus can initiate an action potential because the membrane is starting from a potential that is more negative than its resting value.
Nerve gases, relaxation
Many common drugs (either in clinical use or street drugs) modify processes that occur in the synapse. ______ ______, which have been used in warfare and terrorism, are extremely potent acetylcholinesterase inhibitors; they cause rapid death by preventing (RELAXATION / CONTRACTION) of skeletal muscle, most importantly the diaphragm, leading to respiratory arrest.
Inhibitory, hyperpolarization
Neurons can receive both excitatory and inhibitory input. ______ input causes _______ by lowering the membrane potential from its resting potential (becoming more negative inside the cell).
C (The polarization of the neuron at rest is the result of an uneven distribution of ions between the inside and outside of the cell. This difference is achieved through the active pumping of ions into and out of the neuron (using the Na+/K+ ATPase). Voltage-gated calcium channels are important in the nerve terminal, where the influx of calcium triggers the fusion of vesicles containing neurotransmitter with the membrane, but not in maintaining resting membrane potential.)
Resting membrane potential depends on: I. differential distribution of ions across the axon membrane. II. the opening of voltage-gated calcium channels. III. active transport of ions across the membrane. A.) I only B.) I and II only C.) I and III only D.) II and III only
axon hillock, action potential
Signals arriving from the dendrites and transmitted through the cell body can be either excitatory or inhibitory; the ______ ______ sums these signals, and if the result is excitatory enough (reaches threshold), it will initiate a(n) ______ ______.
proteins, K+
The negative resting potential is generated by both negatively charged ______ within the cell and the relatively greater permeability of the membrane to ______.
electrochemical, negative, higher
Sodium flows into the neuron due to its strong ______ gradient. From an electric standpoint, the interior of the cell is more (NEGATIVE / POSITIVE) than the exterior of the cell, which favors the movement of positively charged sodium cations into the cell. From a chemical standpoint, there is a (LOWER / HIGHER) concentration of sodium outside the cell than inside, which also favors the movement of sodium into the cell.
larger
The (larger / smaller) the diameter, the less internal resistance and therefore less voltage is lost across that resistance as the current travels down the membrane.
Oligodendrocytes
What type of glial cell produces myelin in the central nervous system?
C (When a sensory neuron receives a signal that is strong enough to bring it to threshold, one can assume that the receptor becomes depolarized, allowing it to transduce the stimulus to an action potential. The action potential will then be carried by sensory neurons to the CNS, where the cell will release neurotransmitters. Therefore, among the given choices, the only incorrect statement is found in choice C. If a receptor is stimulated, it will promote the spread of the action potential to postsynaptic sensory neurons in the spinal cord, which can send the signal toward the brain.)
When a sensory neuron receives a stimulus that brings it to threshold, it will do all of the following EXCEPT: A.) become depolarized. B.) transduce the stimulus to an action potential. C.) inhibit the spread of the action potential to other sensory neurons. D.) cause the release of neurotransmitters onto cells in the CNS.
C (Nerves are collections of neurons in the PNS and may contain multiple types of information - sensory, motor, or mixed; they contain cell bodies in ganglia. Tracts are collections of neurons in the CNS and contain only one type of information; they contain cell bodies in nuclei.)
Which of the following correctly describes a difference between nerves and tracts? A.) Nerves are seen in the CNS; tracts are seen in the PNS. B.) Nerves have cell bodies in nuclei; tracts have cell bodies in ganglia. C.) Nerves may carry more than one type of information; tracts can only carry one type of information. D.) Nerves contain only one neuron; tracts contain many neurons.
D (The action potential is often described as an all-or-nothing response. This means that, whenever the threshold membrane potential is reached, an action potential with a consistent size and duration is produced. Neuronal information is coded by the frequency and number of action potentials, not the size of the action potential, eliminating B and C and making D the correct answer. Hyperpolarizing signals are not transmitted to the nerve terminal, eliminating A.)
Which of the following is true with regard to the action potential? A.) All hyperpolarized stimuli will be carried to the axon terminal without a decrease in size. B.) The size of the action potential is proportional to the size of the stimulus that produced it. C.) Increasing the intensity of the depolarization increases the size of the impulse. D.) Once an action potential is triggered, an impulse of a given magnitude and speed is produced.
Ependymal cells, cerebrospinal fluid
______ ______ are a type of glial cell that line the ventricles of the brain and produce ______ ______, which physically supports the brain and serves as a shock absorber.
Spatial summation (many synapses work together)
______ ______ refers to the addition of multiple signals near each other in space; a minimum of 10-30 synchronous EPSPs in the dendritic tree each generate at a different synapse.
B (This explains why potassium passively diffuses OUT of the cell because there is a higher concentration inside the cell.)
A disequilibrium exists in the concentration of ions across a membrane. A larger concentration of K+ is typically found in the: A.) Extracellular fluid B.) Intracellular fluid
B (These polyanionic substances are trapped inside by the cell membrane.)
A disequilibrium exists in the concentration of ions across a membrane. A larger concentration of anions (usually polyanionic substances like DNA and protein) are typically found in the: A.) Extracellular fluid B.) Intracellular fluid
tetrodotoxin (TTX), Na+
A toxin called ______ is found in the pufferfish, a delicacy in Japan. It blocks neuronal transmission by blocking the voltage-gated ______ channels. This can rapidly cause death because the phrenic nerves innervating the diaphragm can no longer depolarize, leading to paralysis of the muscle and a cessation of breathing. For this reason, chefs who prepare pufferfish must be specially trained and licensed.
saltatory
In myelinated axons, only the membrane exposed at the nodes is excitable. Because action potentials are only generated at these nodes, it means that the action potential will 'jump' from one place to the next and in between, you're not generating any action potential. This 'jumping' mode of conduction is known as ______ conduction.
nuclei
In the central nervous system, cell bodies of the individual neurons within a tract cluster in ______.
patellar, quadricep
In the knee-jerk reflex, when the ______ tendon is stretched, information travels up the afferent neuron to the spinal cord where it interfaces the efferent neuron that contracts the ______muscles. The net result is extension of the leg, which lessens the tension on the muscle to prevent potential injury (e.g. tearing).
ganglia
In the peripheral nervous system, cell bodies of neurons of the same type within a nerve cluster in ______.
Spinal Cord (The white matter lies on the outside of the cord and the gray matter is deep within it.)
In what part of the nervous system is gray matter deeper than white matter?
acetylcholinesterase (AchE)
Many common drugs (either in clinical use or street drugs) modify processes that occur in the synapse. There are clinically useful drugs (some of which are used to treat Alzheimer's disease, glaucoma, and myasthenia gravis) that inhibit ______, thereby elevating synaptic levels of acetylcholine.
reflex arcs
Neural circuits called ______ ______ use the ability of interneurons in the spinal cord to relay information to the source of a stimulus while simultaneously routing it to the brain. For example, when someone steps on a nail, receptors in the foot detect pain and the signal is transmitted up the spinal cord. At that point the sensory neurons connect with interneurons, which can then relay pain impulses to the brain. Rather than wait for the brain to send out a signal, interneurons in the spinal cord can also send signals to the muscles of both legs, causing the individual to withdraw the foot with pain while supporting with the other foot. The original sensory information still makes its way up to the brain; however, by the time it arrives there, the muscles have already responded to the pain.
ion, membrane potentials, neurotransmitter
Neurons communicate using both electrical and chemical forms of communication. 1.) Electrical communication occurs via ______ exchange and the generation of ______ ______ down the length of the axon. 2.) Chemical communication occurs via ______ release from the presynaptic cell and the binding of these to the postsynaptic cell.
B
Neurons may be either excitatory or inhibitory; this distinction truly comes at the level of the neurotransmitter receptors. If the receptor is a ______, it will cause either changes in the levels of cyclic AMP or an influx of calcium. A.) Ligand-gated ion channel B.) G protein-couple receptor
A
Neurons may be either excitatory or inhibitory; this distinction truly comes at the level of the neurotransmitter receptors. If the receptor is a ______, the postsynaptic cell will either be depolarized or hyperpolarized. A.) Ligand-gated ion channel B.) G protein-couple receptor
C
Neurotransmitters must be cleared from the postsynaptic receptors to stop the propagation of the signal. What mechanism is employed by nitric oxide, a gaseous signaling molecule? A.) Enzymatic breakdown B.) Reuptake by the presynaptic cell C.) Diffusion out of the synaptic cleft D.) None of the above
A (Acetylcholine is broken down by the enzyme acetylcholinesterase, AchE.)
Neurotransmitters must be cleared from the postsynaptic receptors to stop the propagation of the signal. What mechanism is employed to accomplish this goal in the figure? A.) Enzymatic breakdown B.) Reuptake by the presynaptic cell C.) Diffusion out of the synaptic cleft D.) None of the above
B (Serotonin, 5-HT, is brought back into the presynaptic neuron using a reuptake carrier. Dopamine and norepinephrine also utilize this mechanism.)
Neurotransmitters must be cleared from the postsynaptic receptors to stop the propagation of the signal. What mechanism is employed to accomplish this goal in the figure? A.) Enzymatic breakdown B.) Reuptake by the presynaptic cell C.) Diffusion out of the synaptic cleft D.) None of the above
primary active
The Na+/K+ ATPase is important for restoring ion gradients after action potentials have been fired. ATP is necessary because both Na+ and K+ are moved against their gradients by this process; thus, this qualifies as ______ ______ transport.
C
The Na+/K+-ATPase maintains a resting membrane potential of -70 mV by moving ______ for every ______ of the cell. A.) 3 Na+ In, 2 K+ Out B.) 2 Na + In, 3 K+ Out C.) 3 Na+ Out, 2 K+ In D.) 2 Na+ Out, 3 K+ In
axon hillock
The ______ ______ is where the cell body transitions to the axon and where action potentials are initiated.
nerve terminal
The ______ ______ or synaptic bouton is the end of the axon from which neurotransmitters are released. This structure is enlarged and flattened to maximize neurotransmission to the next neuron and ensure proper release of neurotransmitters.
axon
The ______ is a long appendage down which an action potential travels that terminates in close proximity to a target structure (a muscle, gland, or another neuron).
vagus (cranial nerve X)
The ______ nerve is responsible for much of the parasympathetic innervation of the thoracic and abdominal cavity (e.g. constricts bronchi, slows heartbeat, stimulates peristalsis and secretion, stimulates bile release).
summation
The additive effect of multiple signals (both excitatory and inhibitory) is known as ______ and there are two types: temporal and spatial.
soma
The cell body or ______ is the location of the nucleus as well as organelles such as the endoplasmic reticulum and ribosomes.
exocytosis
The influx of calcium causes fusion of vesicles filled with neurotransmitter with the presynaptic membrane, resulting in ______ of neurotransmitter into the synaptic cleft.
ligand-gated ion, G protein-coupled
The neurotransmitters bind to receptors on the postsynaptic cells, which can be either ______-______ ______ channels or ______ ______-______ receptors
False (Action potentials are propagated down the axon when proximal sodium channels open and depolarize the membrane, inducing neighboring sodium channels to open as well; because of the refractory character of these channels, the action potential can only move in one direction.)
True or False: Action potentials can travel bidirectionally.
True (Thus, increased intensity of a stimulus does not lead to an increased potential difference of the action potential, but rather an increased frequency of firing.)
True or False: All action potentials within the same type of neuron have the same potential difference during depolarization.
False (The resting membrane potential is largely determine by potassium concentrations because the cell membrane is more permeable to K+ than to other ions.)
True or False: K+ has a relatively small membrane permeability.
False (The effect of cross-sectional area is more significant than the effect of length on conduction.)
True or False: The effect of length is more significant than the effect of cross-sectional area on conduction.
False (One primary difference between the somatic and autonomic nervous systems is that the peripheral component of the autonomic nervous system contains two neurons. A motor neuron in the somatic nervous system goes directly from the spinal cord to the muscle without synapsing..)
True or False: The peripheral component of the somatic nervous system contains two neurons.
True (The insulation by myelin is extremely effective. A human spinal cord is about the thickness of a finger with myelination.)
True or False: Without myelination, the spinal cord would have to be almost as wide as a telephone pole to prevent signal loss.
Local anesthetics, small, small
______ ______ work by blocking voltage-gated Na+ channels. These drugs work particularly well on sensory neurons and therefore block the transmission of pain. They favor pain neurons because these neurons have (SMALL / LARGE) axonal diameters and a (SMALL / LARGE) amount of myelin, allowing easy access to sodium channels. Drug concentrations are kept sufficiently low to block pain neurons without significant effects on other sensory modalities or motor function.
Dendrites
______ are appendages that receive signals from other cells.
Neurons
______ are specialized cells capable of transmitting electrical impulses and then translating those electrical impulses to chemical signals.
Acetylcholine
______ is the neurotransmitter responsible for parasympathetic responses in the body and is released by both preganglionic and postganglionic neurons.
