Chapter 8 Neuronal Structure and Function

Equilibrium potential of K+

-90 mV

What is a polysynaptic reflex arc?

pathway in which signals travel over many synapses on their way back to the muscle

microglia function

phagocytosis

function of ependymal cells

produce CSF

Chemical synapses are

unidirectional

People who suffer from severe epilepsy are sometimes treated with "split brain" procedure that prevents most communication between the left and right hemispheres of the brain. The structure that is most likely cut in this operation is the: A. Corpus callosum B. Medulla C. Thalamus D. Pons

A;

Which of the following neurotransmitters stimulates autonomic postganglionic neurons? A. Acetylcholine B. Norepinephrine C. Epinephrine D. Serotonin

A;

Tetrodotoxin (TTX) is a potent neurotoxin that binds to and inhibits the action of voltage-gated sodium channels in neurons. Poisoning can be rapidly fatal, within 4-6 hours of ingestion. Which of the following is the most likely cause of death from TTX poisoning? A. Respiratory failure B. Cardiac arrest C. Dehydration from excessive vomiting D. Increased blood pH due to hypoventilation

A; Blocking the action of voltage-gated sodium channels in neurons would prevent the occurrence of action potentials, leading to skeletal muscle paralysis. Because the diaphragm is made of skeletal muscle, it too would become paralyzed, leading to respiratory failure and death. According to the question text, cardiac muscle is not affected, and since heart contraction is not dependent on neural stimulation, TTX would not have a direct effect on the heart ("cardiac arrest" is wrong). Vomiting may occur, but death due to dehydration would take a few days, not a few hours ("dehydration from excessive vomiting" is wrong), and while hypoventilation probably occurs (remember diaphragm contraction depends on neural stimulation), hypoventilation would lead to decreased blood pH, not increased ("increased blood pH due to hypoventilation" is wrong).

Action potentials can involve voltage-gated calcium channels. Intracellular Ca2+ concentration is typically several fold below extracellular Ca2+concentration. In which of the following processes might calcium play a role? A. Depolarization B. Repolarization C. Polarization D. Hyperpolarization

A; From the stem of the question, voltage-gated calcium channels are similar to voltage-gated sodium channels. When membrane potential reaches the threshold for a voltage-gated channel, the channel opens. In this case, calcium would flow into the cell (down its concentration gradient) causing membrane potential to move in the positive direction, i.e., depolarization (choice A is correct). Repolarization is a return to rest potential (choice B is wrong) and hyperpolarization is a movement from rest potential to more negative values (choice D is wrong). Polarization simply describes the cell at rest potential, i.e., negative inside with respect to the outside (choice C is wrong).

Which of the following would have the greatest impact on the resting membrane potential? A. Increasing membrane permeability to sodium B. Increasing membrane permeability to potassium C. Increasing extracellular calcium concentration D. Decreasing extracellular calcium concentration

A; Resting membrane potential is dictated by the relative ion concentrations inside and outside of the cell as well as by their relative permeabilities. At rest, the resting membrane potential of a typical neuron is -70 mV which arises primarily from the potassium leak channels present in the membrane (the equilibrium potential of potassium is -90 mV). There is relatively little sodium permeability across the membrane under resting conditions and an increase would significantly depolarize the membrane (bringing it closer to sodium's equilibrium potential of +40 mV, choice A is correct). An increase in potassium permeability may hyperpolarize the membrane, but this would have a less significant effect than an increase in sodium permeability (choice B is wrong). Calcium cannot cross the plasma membrane; simply altering its concentration without changing membrane permeability to calcium would not affect resting membrane potential (choices C and D are wrong).

Which of the following is true concerning myelinated and unmyelinated axons? A. The amount of energy consumed by the Na+/K+ ATPase is much less in myelinated axons than in unmyelinated axons B. Myelinated axons can conduct many more action potentials per second than can unmyelinated axons C. The size of action potential depolarization is much greater in myelinated axons than in unmyelinated axons D. Voltage-gated potassium channels do not play a role in repolarization in myelinated axons.

A; Since the area of membrane that is conducting is much less in myelinated axons, Na+/K+ ATPase only works to maintain the resting membrane potential in the nodes of Ranvier, whereas in unmyelinated axons the Na+/K+ ATPase hydrolyzes ATP to maintain the resting potential across the entire membrane (choice A is correct) B is wrong: length of refractory period is based on the characteristics of the voltage gated and potassium channels, which do not change Choice C wrong: The size of depolarization in the action potential does not vary greatly. Choice D is wrong: Voltage-gated potassium channels are the same in both neurons.

When the channels open in depolarization, sodium flows into the cell, down its concentration gradient, depolarizing that section of a membrane until is reaches _______ mV before inactivating

+35

Equilibrium potential of sodium

+60mV; (+) means that the (+) Na+ ions are moving into cell; at this voltage, sodium is equally entering and leaving the neuron

Action potentials are triggered at which voltage?

-50 mV

What happens in repolarization?

1. Voltage-gated sodium channels inactivate very quickly 2. Voltage-gated potassium channels open more slowly and stay open longer. This causes an overshoot by about 20mV to -90 mV. 3. Potassium leak channels and the Na+/K+ ATPase continue to function to bring it back to -70mV.

What are the three ways in which neurotransmitters are removed from the synaptic cleft

1. enzymatic degradation 2. reuptake carriers 3. diffusion

[Na+] concentration inside and outside the cell

12 mM inside and 145 mM outside

[K+] concentration inside and outside a neuron

140 mM inside and 4 mM outside

The PNS consists of _______ spinal nerves and _______ cranial nerves

31; 12

A decrease in blood pH can lead to a decrease in CSF pH, which can trigger an increase in ventilation rate. Which region of the brain contains the respiratory center that can alter the rate of ventilation? A. Medulla oblongata B. Hypothalamus C. Cerebellum D. Corpus callosum

A

A disease results in the death of Schwann cells. Which portion of the nervous system is NOT likely to be affected? A. Central nervous system B. Somatic nervous system C. Autonomic nervous system D. Parasympathetic nervous system

A

Which of the following accurately describes sensory neurons? A. Sensory neurons are afferent and enter the spinal cord on the dorsal side. B. Sensory neurons are efferent and enter the spinal cord on the dorsal side. C. Sensory neurons are afferent and enter the spinal cord on the ventral side. D. Sensory neurons are efferent and enter the spinal cord on the ventral side.

A

Which of the following neurotransmitters is used in the ganglia of both the sympathetic and parasympathetic nervous systems? A. Acetylcholine B. Dopamine C. Norepinephrine D. Serotonin

A

What is the difference between a neuron and a nerve?

A neuron is a single cell while a nerve is a large bundle of many different axons from different neurons

When the bladder is full, neurons in the sacral spinal cord notify the brainstem of the need to urinate. Inhibitory signals from the brain prevent urination until the time is judged appropriate; then the inhibition is removed and urination is allowed to proceed under the control of neurons in the sacral spinal cord. Cutting the thoracic spinal cord would most likely cause: A. automatic bladder, in which the entire bladder empties when it becomes full, whether the time is appropriate or not. B. inability to urinate. C. return of normal bladder function. D. stress incontinence, in which urine leaks from the bladder upon physical stress, as in climbing stairs.

A; When the bladder is full, neurons in the sacral spinal cord notify the brainstem of the need to urinate. Inhibitory signals from the brain prevent urination until the time is judged appropriate; then the inhibition is removed and urination is allowed to proceed under the control of neurons in the sacral spinal cord. Cutting the thoracic spinal cord would most likely cause automatic bladder, in which the entire bladder empties when it becomes full, whether the time is appropriate or not. The brain is required for the inhibition of urination, not the actual urination itself, which is controlled by the sacral neurons. If the brain is removed from the picture by severing the spinal cord between the sacral neurons and the brain (the thoracic region), then urination would simply become automatic. There is no reason to assume stress incontinence, and in any case, severing the spinal cord in the thoracic region would prevent lower body motor function, so climbing stairs would not be possible.

If a fruit fly mutant I sound that has voltage-gated potassium channels that shut more quickly after repolarization, how would this affect the refractory period in the fly?

Absolute would not be affected Relative would be reduced

What are action potentials?

An area of depolarization of a plasma membrane that travels in a wave-like manner along an axon.

How does cross sectional area affect action potentials?

As area increases, there is faster propagation

How does length affect action potential?

As length increases, there is slower conduction

A neuron only fires an action potential if multiple presynaptic cells release neurotransmitter onto the dendrites of the neuron. This is an example of: A. saltatory conduction. B. summation. C. a feedback loop. D. inhibitory transmission.

B

A surgeon accidentally clips a dorsal root ganglion during a spinal surgery. What is a likely consequence of this error? I. Loss of motor function at that level II. Loss of sensation at that level III. Loss of cognitive function A. I only B. II only C. I and II only D. I, II, and III

B

In which neural structure are ribosomes primarily located? A. Dendrites B. Soma C. Axon hillock D. Axon

B

Myelination facilitates in which of the following? I. Increasing action potential rate of travel II. Increasing action potential strength III. Restricting ion flow across the membrane A. I only B. I and III only C. II and III only D. I, II, and III

B

Nerve cells that control thermoregulation are concentrated in which portion of the brain? A. Cerebrum B. Hypothalamus C. Medulla D. Cerebellum

B

The cell bodies of a somatic sensory nerve are located in the: A. ventral horn. B. dorsal root ganglion. C. brain. D. spinal cord.

B

The myelin sheath of many axons is produced by the: A. nerve cell body. B. Schwann cells. C. nodes of Ranvier. D. axon hillock.

B

Which of the following senses relies on chemoreceptors? I. Touch II. Taste III. Olfaction A. III only B. II and III only C. I only D. I and II only

B

In which of the following ways can a presynaptic neuron increase the intensity of signal it transmits? A. Increase the size of presynaptic action potentials B. Increase the frequency of action potentials C. Change the type of neurotransmitter it releases D. Change the speed of action potential propagation

B;

Both the sympathetic and parasympathetic divisions of the ANS can affect the cardiovascular system. Which of the following statements regarding sympathetic activation is/are true? I. Activation causes the heart to contract II. Activation relaxes smooth muscle in blood vessels serving skeletal muscle III. Activation relaxes smooth muscle in blood vessels serving skin and digestive organs A. I only B. II only C. I and II only D. I and III only

B; Both the sympathetic and parasympathetic divisions of the ANS can affect the cardiovascular system. Regarding sympathetic activation, Item II only is true. Activation of the sympathetic division of the ANS leads to the "fight or flight" stress response. Item I is false: The heart is autorhythmic and can generate its own contraction without input from the nervous system. However, activation of the sympathetic division can make the heart contract more frequently (i.e., increase the heart rate). Item II is true: It is helpful to have increased blood flow to skeletal muscles during times of stress to provide adequate oxygen and nutrients to the working muscles. Relaxing the smooth muscle in the blood vessels serving the skeletal muscle would cause dilation of the vessels and increased blood flow. Item III is false: during stress situations, blood is diverted from skin and digestive organs by constricting those vessels (i.e., contracting the smooth muscle).

A neuroscientist develops a chemical that increases the permeability of neuron membranes to potassium. After administering this drug, she attempts to elicit action potentials, but notes the rates of firing have changed dramatically. Which of the following best explains this observation? A. The resting membrane potential shifted in a more positive direction. B. The resting membrane potential shifted in a more negative direction. Correct Answer C. The Na+/K+ ATPase is unable to maintain concentration gradients. D. The rapid depolarization phase of the action potential was most significantly impacted.

B; By increasing the permeability of the neuron membrane to potassium, the researcher shifted the resting membrane potential in a more negative direction. This pushes the neuron further from threshold and it would require more stimulation in order to generate action potentials, resulting in a probable decrease in firing rate (choice B is correct and choice A is wrong). The Na+/K+ ATPase is an active transporter, using ATP to move Na+ ions out of the cell and K+ ions into the cell; its action would be unaffected by an increase in membrane potassium permeability (choice C is wrong). The rapid depolarization seen in an action potential is due to the opening of voltage-gated sodium channels. Assuming the cell could get to threshold, the opening of these channels should not be affected by an increase in potassium permeability (choice D is wrong).

If an inhibitor of acetylcholinesterase is added to a neuromuscular junction, then the postsynaptic membrane will: A. Be depolarized by action potentials more frequently B. Be depolarized longer with each action potential C. Be resistant to depolarization D. Spontaneously depolarize

B; Choice B is correct. If acetylcholinesterase is inhibited, acetylcholine will remain in the synaptic cleft longer, and acetylcholine gated sodium channels will remain open longer with each action potential that reaches the synapse. If the sodium channels are open longer, the depolarization of the postsynaptic membrane will last longer.

Voltage-gated sodium channels inactivate via a "ball-and-chain" mechanism, where a peptide "ball" tethered to the channel blocks the channel, preventing sodium influx. Increasing the length of the tether on the inactivation peptide increases the time required for inactivation. Which of the following would be observed? A. Decreased time required between action potentials B. Decreased maximal rate (frequency) of firing C. Increased maximal sodium conductance rate D. Increased maximal rate (frequency) of firing

B; Increased time required for inactivation would result in a lengthened absolute refractory period which could decrease the maximal rate, or frequency, of firing (choice B is correct and choices A and D are wrong). Increasing the time required for inactivation would not alter the maximal sodium conductance rate (choice C is wrong). Note that answer choices A and D are identical and both cannot be correct.

Signals can be sent in only one direction through the synapse such as the neuromuscular junction. Which of the following best explains unidirectional signaling at synapses between neurons? A. The neurotransmitter is always degraded by the postsynaptic cell or in the synaptic cleft B. Only the presynaptic cell has vesicles of neurotransmitter C. Axons can propagate action potential in only one direction D. Only the postsynaptic membrane cell has a resting membrane

B; Signaling is unidirectional because only the presynaptic cell has vesicles of neurotransmitter that are released in response to action potential, and only the postsynaptic neuron has receptors that bind neurotransmitter to either depolarize or hyperpolarize the cell. Choice B is correct. The degradation of neurotransmitters is irrelevant in the direction of signal propagation, making A wrong. Axons are capable of propagating action potentials one both directions, even though this is not what they normally do. Choice C is wrong. All cells have a resting membrane potential. Choice D is wrong

Which of the following neurons could directly stimulate the relaxation of bronchial smooth muscle? A. Parasympathetic postganglionic neurons B. Sympathetic postganglionic neurons C. Sympathetic preganglionic neurons D. Somatic motor neurons

B; Sympathetic postganglionic neurons could directly stimulate the relaxation of bronchial smooth muscle. Relaxation of bronchial smooth muscle is an involuntary process that is triggered by activation of the sympathetic nervous system. Postganglionic neurons directly stimulate target tissues; preganglionic neurons stimulate postganglionic neurons.

Depletion of extracellular calcium would have which of the following effects on synaptic transmission? A. Increased neurotransmitter release B. Decreased neurotransmitter release C. Increased EPSPs D. Increased IPSPs

B; Synaptic transmission depends on calcium influx through voltage-gated calcium channels at the axon terminal. Calcium influx triggers neurotransmitter release and subsequent changes in the postsynaptic membrane potential. A decrease in extracellular calcium would lead to a significant decrease in neurotransmitter release (choice B is correct and choice A is wrong). This decrease in neurotransmitter release would result in a decrease in either EPSPs (excitatory postsynaptic potentials) or IPSPs (inhibitory postsynaptic potentials), depending on the synapse in question (choices C and D are wrong).

Temporal summation relies upon which of the following? A. The rate of recovery must be more rapid than the excitation rate. B. The rate of excitation must be more rapid than the recovery rate. C. The synaptic inputs must be in close proximity to one another. D. The synaptic inputs may be distant, but must still be additive.

B; Temporal summation is the repeated activation of a given synapse resulting in a response of greater magnitude. In order to accomplish this, the rate of excitation must outpace the rate of recovery or else the postsynaptic neuron will have returned to its resting state before the second stimulation arrives (choice B is correct and choice A is wrong). As temporal summation results from the repeated stimulation of a single postsynaptic neuron, proximity is not an issue (choice C and D are wrong).

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

B; 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. 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.

Brain damage due to head trauma can be seen as lesions in different areas of the brain. A patient recently involved in a car accident presents with severely unsteady gait (difficulty walking), uncoordinated eye movements, and poor motor control in general . Which of the following regions of the brain is the likely location of the lesion afflicting this patient? A. Cerebrum B. Hypothalamus C. Cerebellum D. Corpus callosum

C

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

C

Which of the following physiological responses is LEAST likely to occur upon stimulation of the parasympathetic division of the ANS? A. Increased digestive secretion and motility B. Constricted bronchial tubes C. Enhanced distance vision D. Reduced heart rate

C

Which one of the following can cause the interior of the neuron to have a momentary positive charge? A. Opening of potassium leak channels B. Activity of the Na+/K+ ATPase C. Opening of voltage gated sodium channels D. Opening of voltage gated potassium channels

C

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 central nervous system.

C;

If a toxin prevents voltage-gated sodium channels from closing, which of the following will occur? I. Voltage-gated potassium channels will open but not close II. The membrane will not repolarize to the normal resting potential. III. The Na+/K+ ATPase will be inactivated. A. I only B. II only C. I and II only D. II and III only.

C; I is true: Voltage gated potassium channels are normally closed by the repolarization, so if the membrane is repolarized, they will not close. II is true: sodium will continue to flow into the cell.

All of the following are associated with the myelin sheath EXCEPT: A. faster conduction of nerve impulses. B. nodes of Ranvier forming gaps along the axon. C. increased magnitude of the potential difference during an action potential. D. saltatory conduction of action potentials.

C; Action potentials are often described as being "all-or-nothing"; the magnitude of the potential difference in an action potential is constant, regardless of the intensity of the stimulus. Thus, myelin does not affect the magnitude of the potential difference in an action potential, making choice (C) the correct answer.

A bipolar neuron could be composed of which of the following? A. A neuron with a soma and a single dendrite B. A neuron with a soma and a single axon C. A neuron with a soma, a single dendrite, and a single axon D. A neuron with a soma, multiple dendrites, and a single axon

C; Bipolar neurons possess two extensions from the cell body (or soma); one dendrite and one axon (choice C is correct). Unipolar neurons possess only a single extension from the cell body (choices A and B are wrong), while multipolar neurons have multiple dendrites (or a dendritic arbor) extending from the cell body, but only a single axon (choice D is wrong).

Which of the following correctly describes a difference between nerves and tracts? A. Nerves are seen in the central nervous system; tracts are seen in the peripheral nervous system. 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.

C; Nerves are collections of neurons in the peripheral nervous system and may contain multiple types of information (sensory or motor); they contain cell bodies in ganglia. Tracts are collections of neurons in the central nervous system and contain only one type of information; they contain cell bodies in nuclei.

Sodium plays the principle role in rapid depolarization during action potentials due to which of the following? A. The rapid inactivation of voltage-gated sodium channels B. The rapid efflux of sodium from the neuron Your Answer C. Sodium conductance results in a positive membrane potential D. Sodium conductance results in a negative membrane potential

C; Sodium conductance is responsible for the rapid depolarization observed during the action potential. This is due to the fast opening of voltage-gated sodium channels which allow the flow of sodium across the membrane. Sodium flows into the cell down its electrochemical gradient resulting in depolarization of the cell (choice C is correct and choices B and D are wrong). While inactivation of the voltage-gated sodium channels does occur, this occurs after the rapid depolarization observed and thus cannot be the cause of the depolarization (choice A is wrong).

Which description below correctly identifies the role of the myelin sheath in action potential transmission? A. Protein fibers assemble along the axon of neurons, preventing leakage of current across the membrane. B. Convolutions in the axons of neurons dissipate current through specialized leakage channels. C. Schwann cells insulate the axons of neurons, causing membrane depolarization to jump from node to node. D. Glial cells cover the nodes of Ranvier to prevent backflow of current along the axon of neurons.

C; The role of the myelin sheath in action potential transmission is correctly identified by the following description: Schwann cells insulate the axons of neurons, causing membrane depolarization to jump from node to node. The myelin sheath insulates the neuronal axon except for small gaps (nodes of Ranvier) through which ions can traverse the membrane, causing the action potential to leap from node to node (saltatory conduction).

Landmark studies establishing the quantal nature of synaptic transmission utilized curare to block postsynaptic receptors and prevent action potential transmission. Which of the following best explains the impact of curare on the synapse? A. Decreases neurotransmitter release B. Increases calcium influx into the presynaptic terminal C. Decreases cation flow into the postsynaptic neuron D. Blocks voltage-gated calcium channels

C; The stem of the question informs us that curare has an impact on postsynaptic receptors. This makes it unlikely to have any effect presynaptically, such as neurotransmitter release (choice A can be eliminated) or calcium influx into the presynaptic terminal (choice B can be eliminated). Voltage-gated calcium channels are present on the presynaptic neuron and are also not likely to be affected by a compound which blocks postsynaptic receptors (choice D can be eliminated). The only answer choice which clearly has a postsynaptic action is choice C; often neurotransmitter receptors on postsynaptic neurons are linked to ion channels. The opening of these ion channels impacts ion flow into the postsynaptic cell. If curare blocked the receptors from binding neurotransmitter, the ion channels could not be opened, leading to a decrease in cation flow into the postsynaptic neuron and ultimately, prevention of action potential transmission (choice C is correct). Curare is a competitive inhibitor of acetylcholine which is a neurotransmitter that acts, among other places, at the neuromuscular junction. Note that you did not have to know anything about curare specifically to answer this question.

Processing of sensory information is the integrative function. This is carried out by the

CNS

A motor protein called kinesin is one of several different proteins that drive movement of vesicles and organelles in axons. Kinesin specifically provides anterograde movement (movement from the soma toward the axon terminus). If a kinesin inhibitor is added to neurons in a culture, what is likely the result? A. Spontaneous action potential B. Cell division C. Accumulation of material in the synaptic knob D. Atrophy of axons

D

How does myelin increase the efficiency with which an action potential is conducted in a neuron? A. Decreasing the amount of Na+ allowed into the cell B. Increasing the amount of neurotransmitter released C. Increasing the number of K+ channels D. Decreasing the surface area to be depolarized

D

Seizures, which result from foci of abnormal excessive brain activity, can spread to surrounding areas of the brain. In select patients, this activity can spread beyond the originating hemisphere. Severing which of the following structures would aid in limiting the spread of excessive activity? A. Brainstem B. Cerebral cortex C. Thalamus D. Corpus callosum

D

When is a neuron in its relative refractory period? A. During depolarization B. During the transmission of an action potential C. During repolarization D. During hyperpolarization

D

Which of the following is a function of the parasympathetic nervous system? A. Increasing blood sugar during periods of stress B. Dilating the pupils to enhance vision C. Increasing oxygen delivery to muscles D. Decreasing heart rate and blood pressure

D

A researcher treats cultured neurons with an RNA polymerase II inhibitor.Which of the following areas of the neuron will be most directly impacted? A. Axon terminal B. Axon hillock C. Dendrites D. Soma

D;

Given the above description, which of the following best describes the response of voltage-gated sodium channels to a membrane depolarization from -70 to -60 mV. A. All of the channels open fully B. 50% of the channels open fully C. All of the channels open 50% D. None of the channels open

D;

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.

D;

Myasthenia gravis, an autoimmune disorder, results from the production of antibodies against acetylcholine receptors in the body. Which of the following statements is FALSE? A. A patient may have difficult opening his/her eyes B. Repeated injections of human acetylcholine receptor into an animal model will produce clinical symptoms in the animal. C. The disease does not directly affect the release of neurotransmitter D. This disease only impacts the neuromuscular junction

D; Acetylcholine is a neurotransmitter in several areas of the body including the neuromuscular junction, pre and postganglionic parasympathetic neurons, and preganglionic sympathetic neurons. Choice D is correct. As acetylcholine receptors become nonfunctional with the binding of antibody, patients have difficulty with muscle contraction, and opening of the eyes may be one possible symptom of this.

Continuous myelination of the axon would most likely result in which of the following? A. Increased ion flow across the plasma membrane B. Increased membrane depolarization required to fire an action potential C. Decreased membrane resistance D. Decreased reliable signal transduction to the axon terminus

D; Continuous myelination of the axon would decrease the ability of an action potential to reach the axon terminus (choice D is correct). Under normal conditions, myelin surrounds the plasma membrane and prevents ion flow, resulting in an increase in membrane resistance (choices A and C are wrong). Breaks in the myelin sheath along the axon, known as nodes of Ranvier, are where voltage-gated sodium channels exist at high concentrations. These nodes effectively boost the signal as the action potential travels along the axon. Without these nodes, the ability of that initial action potential to reach the axon terminus would be greatly impaired. The threshold of voltage-gated sodium channels is unlikely to change with myelination (choice B is wrong).

Which of the following is the correct order of events during synaptic transmission? A. Depolarization of presynaptic membrane —> voltage-gated calcium channels open —> neurotransmitter binds to ligand-gated ion channels —> membrane depolarization of postsynaptic cell —> neurotransmitters cross the synaptic cleft B. An action potential reaches the end of an axon at the synaptic bob -> depolarization of the presynaptic membrane —> voltage gated sodium channels open —> neurotransmitter binds to ligand-gated ion channels —> membrane depolarization of postsynaptic cell C. Depolarization of presynaptic membrane —> neurotransmitter binds to ligand-gated ion channels —> neurotransmitter in the synaptic cleft is degraded and/or removed —> An action potential reaches the end of an axon D. An action potential reaches the end of an axon —> voltage gated calcium channels open —> neurotransmitter binds to ligand-gated ion channels —> neurotransmitter in the synaptic cleft is degraded and/or removed

D; Correct order: 1. Action potential reaches the end of an axon 2. Depolarization of presynaptic membrane 3. Voltage-gated calcium channels open 4. Neurotransmitter is released from the presynaptic cell 5. Neurotransmitter crosses the synaptic cleft 6. Neurotransmitter binds to ligand gated ion channels on the postsynaptic membrane 7. Membrane depolarization of postsynaptic cell 8. Voltage gated sodium channels open 9. An action potential is initiated 10. Neurotransmitter is degraded/removed

A researcher isolates a squid giant axon and places it into an electrolyte bath that mimics its normal conditions. She stimulates the axon and normal action potentials occur. She then introduces a drug into the electrolyte bath that blocks voltage-gated potassium channels, and again attempts to elicit action potentials. Which of the following is most likely to occur? A. Since the voltage-gated channels are blocked, the action potential will not occur. B. The resting potential will become more positive since potassium is unable to exit the cell normally through leak channels. C. Since the cell remains depolarized for a longer period of time, subsequent action potentials will be easier to elicit and the frequency of action potentials will increase. D. The axon will depolarize normally when stimulated but the time to return to rest potential will be exceedingly long.

D; If a drug is introduced that blocks voltage-gated potassium channels, the most likely occurrence is that the axon will depolarize normally when stimulated but the time to return to rest potential will be exceedingly long. Since the voltage-gated sodium channels are not affected, the cell should still be able to depolarize normally. However, the voltage-gated potassium channels are critical for repolarizing the cell; if these are blocked, the cell will remain in a depolarized state for much, much longer than normal. This would prevent the firing of subsequent action potentials (decrease the action potential frequency) since when depolarized, the cell is in an absolute refractory period, unable to fire additional action potentials. The resting potential of the cell should not be affected since it does not depend on voltage-gated channels (only on the Na+/K+ ATPase and the potassium leak channels).

Which of the following best characterizes the difference between the soma and axon hillock? A. Increased ribosomal activity in the axon hillock B. Axon hillocks are denoted by demyelinated areas between myelin sheets along the axon C. Decreased myelination surrounding the soma D. Decreased voltage-gated sodium channel density in the soma

D; The difference between the soma and axon hillock is that there is decreased voltage-gated sodium channel density in the soma. The axon hillock, the area linking the soma to the axon, possesses an increased voltage-gated sodium channel density, allowing it to fire action potentials. In the soma, the decreased density allows for local depolarization which degrades exponentially over the distance of the soma. Neither the soma nor axon hillock are myelinated, and biosynthetic activity takes place in the soma, not the axon hillock. Nodes of Ranvier are the demyelinated areas between myelin sheets along the axon; the hillock is only at the area connecting the axon and soma.

A researcher records the membrane potential changes in a neuron in cell culture. Following excitation of a single nearby neuron, the membrane potential increases by 20 mV. If an additional nearby neuron is stimulated at the same time, an increase in membrane voltage of 32 mV is observed. Which of the following best explains this observation? A. Long-term depression B. Neural adaptation C. Temporal summation D. Spatial summation

D; The experiment describes two neurons synapsing with a third neuron from which membrane potential is recorded. When one neuron is excited, a depolarization is recorded, and when the second neuron is excited at the same time, a larger depolarization is recorded. This additive effect (two neurons synapsing on a single neuron and generating a larger response) is known as spatial summation (choice D is correct). Temporal summation involves the additive response due to repeated stimulation of a single neuron (choice C is wrong). Long-term depression is a decrease in neural excitability (choice A is wrong) and neural adaptation is a change in response over time (usually a decrease in firing) with a constant stimulus (choice B is wrong).

A man on a hunting trip sustains an accidental gunshot wound. The bullet penetrates the skull and travels a short way into the cerebral cortex. Shortly after the accident, the man finds that his sense of smell has been impaired.Which of the following brain regions was most likely damaged? A. Parietal lobe B. Occipital lobe C. Frontal lobe D. Temporal lobe

D; The region of the brain that processes olfactory sensation (smell) is the temporal lobe. The parietal lobe is for general sensations of pain, pressure, and touch (choice A is wrong), the occipital lobe processes visual sensation (choice B is wrong), and the frontal lobe controls voluntary movement and problem solving (choice C is wrong).

Which of the following statements concerning the somatic division of the peripheral nervous system is INCORRECT? A. Its pathways innervate skeletal muscle. B. Its pathways are usually voluntary. C. Some of its pathways are referred to as reflex arcs. D. Its pathways always involve more than two neurons.

D; The somatic division of the peripheral nervous system innervates skeletal muscles and is responsible for voluntary movement. Some of the pathways in this part of the nervous system are reflex arcs, which are reflexive responses to certain stimuli that involve only a sensory and a motor neuron.

How does myelin increase efficiency?

Decrease the surface area to be polarized and also increases speed of conduction

Nerst Equation

E(ion) = RT/zF ln [x] outside / [x] inside

What are excitatory postsynaptic potentials (or EPSPs)

Excitatory neurotransmitters cause postsynaptic depolarization

What is a cell's resting membrane potential?

For neurons, it is about -70 mV. It is the net electric potential difference that exists across the cell membrane.

What happens in depolarization of a neuron?

In repose to a change in membrane potential, these ion channels open to allow sodium ions to flow down their gradient into the cell and depolarize that section of the membrane. These channels are opened by depolarization of the membrane from the resting membrane potential of -70 mV to a threshold of -50mV.

If a neurotransmitter causes the entry of chloride into the postsynaptic cell, is the neurotransmitter excitatory or inhibitory?

Inhibitory

What are inhibitory postsynaptic potentials (IPSPs)?

Inhibitory neurotransmitters cause IPSPs

function of autonomic nervous system

Involuntary nervous system, innervates cardiac and smooth muscle.

How does myelin on the axon affect ions?

Ions cannot enter or exit where the axonal membrane is covered in myelin.

What is the axon?

Large appendage in which the action potential travels

What are the two primary proteins required to establish the resting membrane potential?

Na+/K+ ATPase and potassium leak channels.

Are electrical synapses regulated?

No

Do chemical synapses touch?

No

If an action potential starts at one end of the axon, can it run out of energy and not reach the other end?

No; Action potentials are continuously renewed at each point in the axon as they travel.

If an axon were completely covered in sheath, could it conduct action potentials?

No; action potentials require the movement of ions across the plasma membrane to create a wave of depolarization

The periodic gaps between myelin sheaths on a neuron are called ___________________.

Nodes of Ranvier

What is electrical communication?

Occurs via ion exchange

What is chemical communication?

Occurs via neurotransmitter release

Receiving information is the sensory function of the nervous system; this is carried out by the

PNS

Acetylcholine binds to the receptor on the _________ cell membrane. When acetylcholine binds, the receptor opens its associated _____ channel, allow the ions to flow down the gradient into the cell.

Postsynaptic; sodium

Myelin is produced by _______ in the PNS

Schwann cells

What would happen to a membrane potential if sodium ions were allowed to flow down their concentration gradient?

Sodium ions would flow into the cell and reduce the potential across the plasma membrane, making the interior less negative and even relatively positive if enough ions flow into the cell.

If the potassium leak channels are blocked, what will happen to the membrane potential?

The flow of K+ makes the cell more negatively charged. Blocking this would reduce the magnitude of the resting membrane potential, making the cell less negative.

The relative refractory period of an action potential could be extended by which of the following? A. Increasing the rate of voltage-gated Na+ channel inactivation B. Increasing the rate of voltage-gated K+ channel deactivation C. Decreasing the rate of voltage-gated Na+ channel inactivation D. Decreasing the rate of voltage-gated K+ channel deactivation

The relative refractory period results from the hyperpolarization of the membrane due to the slow deactivation of voltage-gated potassium channels. To extend the relative refractory period, we would need to decrease the rate of deactivation of these channels (i.e., make them deactivate even more slowly). This would result in an extended period of hyperpolarization where a greater stimulus would be required in order to fire an action potential (choice D is correct and choice B is wrong). Changing the rate of voltage-gated sodium channel inactivation would change the absolute refractory period, not the relative refractory period (choices A and C are wrong).

What is the axon hillock?

This is a part of the neuron, between the cell body and the axon, that controls traffic down the axon through summation of excitatory and inhibitory postsynaptic potentials. This is where the action potential is initiated

What is the relative refractory period?

When an AP can occur if a stimulus is strong enough. A grater stimulus is required to open the voltage-gated sodium channels. Cell is too negative.

What is the absolute refractory period?

When an AP cannot occur regardless of the stimulus strength. During this time, voltage-gated sodium channels have been inactivated and the cell is too positive, near the Na+ equilibrium potential.

What is synaptic transmission?

When an action potential reaches the terminal buttons, it causes the release of specialised chemicals (neurotransmitters) that travel across the synaptic cleft and are received by the dendrites of other neurons

What is reciprocal inhibition?

When antagonist relaxes due to contraction by agonist. This is seen in the knee stretch reflex. Quads contract, hamstring relaxes.

Function of synaptic bouton

Where neurotransmitter is released

Are chemical synapses regulated?

Yes

All somatic neurons use ________ as their neurotransmitter

acetylcholine

What neurotransmitter is commonly used at the neuromuscular junction?

acetylcholine

What is impulse propagation?

action potential moving in discrete jumps down a myelinated axon

Sensory neurons are known as

afferent neurons

What is a reflex?

an action that is performed as a response to a stimulus and without conscious thought.

Which two types of glial cells, if not properly functioning, will make an individual most susceptible to a CNS infection?

astrocytes and microglia

Electrical synapses are _______

bidirectional

CNS is composed of

brain and spinal cord

Where are electrical synapses found?

cardiac and smooth muscle

What is the soma of a neuron?

cell body

What are glial cells?

cells in the nervous system that support, nourish, and protect neurons

What are the regions of the spinal cord?

cervical, thoracic, lumbar, sacral

What are leak channels?

channels that are always open

The sympathetic ganglia is located ______ to the cord, and ________ from target

close; far

White matter in the spinal cord is called a

column (or tract)

Voltage-gated sodium and potassium channels are concentrated where on the axon?

concentrated in the nodes of ranvier

function of somatic nervous system

conscious control of skeletal muscles

How does the parasympathetic nervous system affect bronchial smooth muscle

constricts

How does the parasympathetic nervous system affect the eyes?

constricts

How does the parasympathetic nervous system affect the urinary system?

contraction of bladder (stimulates urination) relaxation of urethral sphincter

grey matter on surface of the brain

cortex

What is the location of the parasympathetic preganglionic soma?

craniosacral

In the brain, white matter lies ________ than grey matter

deeper

How does the sympathetic nervous system affect the eyes?

dilates

The cell bodies of the sensory neurons are found in the

dorsal root ganglia

All somatic neurons have a long dendrite extending from a sensory receptor toward the soma, which is located outside the CNS in a

dorsal root ganglion.

If a neuron signals to a gland or muscle, rather than another neuron, the postsynaptic cell is termed an _____

effector

Motor neurons are known as

efferent neurons

What are the two types of synapses?

electrical and chemical

Electrical synapses are always

excitatory

If a neurotransmitter opens a channel that depolarizes the postsynaptic membrane, the neurotransmitter is _________

excitatory

Chemical synapses can be

excitatory or inhibitory

The parasympathetic ganglia is ________ from the cord and _______ to the target

far; close

The magnitude of an action potential is ________, regardless of the intensity of the stimulus

fixed

function of astrocytes

form blood brain barrier

Function of Scwann Cells

form myelin in the PNS

grey matter in the PNS

ganglion

Electrical synapses occur when the cytoplasm of two cells are joined by

gap junctions (require physical touch!)

Unmyelinated neurons in both the CNS and PNS are referred to as

grey matter

grey matter in the spinal cord

horn

In temporal summation, the presynaptic neuron fires an action potential so rapidly that EPSPs and IPSPs pile up on top of each other. If additive, it might be enough for a postsynaptic action potential. If they are IPSPs, the postsynaptic cell will __________

hyperpolarize

Neurotransmitters that induce hyper polarization are termed

inhibitory

Neurons are more negative on the

inside

What is a synapse?

junction between two neurons

The speed at which action potentials move depends on what?

length and area

The parasympathetic preganglionic axon is

long

The postganglionic axon is _________ and uses _______- as its neurotransmitter

long; norepinephrine

Most mammalian nerve fibers are insulated by ________, a fatty membrane to prevent signal lose

myelin

White matter in the PNS is called

nerves

What are multipolar dendrites?

neurons with multiple dendrites

The presynaptic axon has vesicles filled with

neurotransmitter

Grey matter deep in the brain is called a

nuclei

Myelin is produced by _______ in the CNS

oligodendrocytes

What are bipolar neurons?

one axon and one dendrite

In the spinal cord, white matter lies on the ________ of the cord

outside

function of oligodendrocytes

produce myelin in CNS

Function of Na+/K+ pump

pumps 3 Na+ out of the cell and 2 K+ ions into the cell.

What are dendrites?

receives signals from other neurons, conducts impulses TOWARD the body of a neuron

On the postsynaptic cell, there are ________ for neurotransmitters

receptors

What is a monosynaptic reflex arc?

reflex involving only two neurons and one synapse

How does the sympathetic nervous system affect bronchial smooth muscle?

relaxation (opens airways)

How does the sympathetic nervous system affect the urinary system?

relaxation of bladder (inhibits urination) contraction of urethral sphincter

After depolarization, the membrane is _________, reestablishing the original resting membrane potential.

repolarized

How do reflexes work?

sensory neuron transmits an action potentials to synapse with a motor neuron in the spinal cord, which causes an action to occur.

What is temporal summation?

several impulses from one neuron over time; Multiple signals are integrated during a relatively short period of time.

The sympathetic preganglionic axon is

short

What is an inhibitory interneuron?

short neuron which forms an inhibitory synapse with a motor neuron

The parasympathetic postganglionic axon is _________ and uses __________ as its neurotransmitter

short; acetylcholine

All somatic motor neurons innervate

skeletal muscle cells

What is spatial summation?

summing from several different presynaptic neurons

What are the divisions of the autonomic nervous system?

sympathetic and parasympathetic

Vesicles are only released when an action potential occurs. They are bound to the cytoskeleton and _________ forms a bond between the cytoskeleton and vesicles. The bond is broken by ________

synapsin; calcium

What is the end of an axon called?

synaptic knob/nerve terminal

What is summation?

the process of adding up postsynaptic potentials and responding to their net effect

What is saltatory conduction?

the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.

What determines if a neurotransmitter is excitatory or inhibitory

the receptor for that neurotransmitter

Where is the sympathetic preganglionic soma located?

thoracolumbar

White matter in the brain is called a

tract

Motor neurons exit the spinal cord

ventrally

The spinal cord is protected by the

vertebrae

myelinated axons in both the CNS and PNS are referred to as

white matter