Chapter 8 Neurons: Cellular and Network Properties

Is Na + -dependent neurotransmitter reuptake facilitated diffusion,primary active transport, or secondary active transport? Explain your reasoning.

Neurotransmitter uptake is secondary active transport because it uses energy stored in the Na+ concentration gradient to concentrate neurotransmitter inside the axon terminal.

Action potentials are:

Rapid electrical signals that travel undiminished in amplitude (strength) down the axon from the cell body to the axon terminals

(a) axon (b) dendrite (c) afferent (d) efferent (e) trigger zone 1. process of a neuron that receives incoming signals 2. sensory neuron, transmits information to CNS 3. long process that transmits signals to the target cell 4. region of neuron where action potential begins 5. neuron that transmits information from CNS to the rest of the body

(a) 3, (b) 1, (c) 2, (d) 5, (e) 4

Match the glial cell(s) on the right to the functions on the left. Theremay be more than one correct answer for each function. (a) modified immune cells (b) help form the blood-brain barrier (c) form myelin (d) separate CNS fluid compartments (e) found in peripheral nervous system (f) found in ganglia 6. Schwann cells 1. astrocytes 2. ependymal cells 3. microglia 4. oligodendrocytes 5. satellite cells

(a) 3, (b) 1, (c) 4, 6; (d) 2, (e) 5, 6; (f) 5

List the four major types of ion channels found in neurons. Are they chemically gated, mechanically gated, or voltage-gated?

-Na+ channels (voltage-gated along axon; any type of gating on dendrites); -voltage-gated K+ channels along axon; -voltage-gated Ca2+ channels in axon terminal; -chemically gated Cl- channels

Nervous System

A complex network of neurons that form the rapid control system of the body.

How does the axon terminal make acetyl CoA for acetylcholine synthesis?

Acetyl CoA is made from pyruvate, the end product of glycolysis, and CoA.

Neurotransmitters come in a variety of forms. They include:

Acetylcholine, norepinephrine, Glutamate, GABA, serotonin, adenosine, and nitric oxide are other major neurotransmitters.

If human babies' muscles and neurons are fully developed and functional at birth, why can't they focus their eyes, sit up, or learn to crawl within hours of being born? (Hint: Muscle strength is not the problem.)

All the necessary synapses have not yet been made between neurons or between neurons and effectors.

What is the primary function of each of the following: myelin, microglia, ependymal cells?

Myelin insulates axon membranes. Microglia are scavenger cells in the CNS. Ependymal cells form epithelial barriers between fluid compartments of the CNS.

Very few ions cross the membrane during:

an action potential.

Would the cell membrane depolarize or hyperpolarize if a small amount of Na + leaked into the cell?

depolarize

Match the numbers of the appropriate characteristics with the two types of potentials. Characteristics may apply to one or both types. (a) action potential (b) graded potential 1. all-or-none 2. can be summed 3. amplitude decreases with distance 4. exhibits a refractory period 5. amplitude depends on strength of stimulus 6. has no threshold

(a) 1, 4; (b) 2, 3, 5, 6

Chemical synapses use:

neurotransmitters to carry information from one cell to the next

Somatic motor neurons control:

skeletal muscles

Which cells are modified immune cells that act as scavengers?

Microglia

What is the function of mitochondria in a cell?

Mitochondria are the primary sites of ATP synthesis.

10. Match each ion's movement with the type of graded potential it creates. (a) Na + entry (b) Cl - entry (c) K + exit (d) Ca2+ entry 1. depolarizing 2. hyperpolarizing

(a) 1 (b) 2 (c) 2 (d) 1

Choose from the following ions to fill in the blanks correctly: Na+ , K + , Ca2 + , Cl - . (a) The resting cell membrane is more permeable to ... than to ... . Although ... contribute little to the resting membrane potential, they play a key role in generating electrical signals in excitable tissues. (b) The concentration of ... is 12 times greater outside the cell than inside. (c) The concentration of ... is 30 times greater inside the cell than outside. (d) An action potential occurs when ... enter the cell. (e) The resting membrane potential is due to the high ... permeability of the cell.

(a) K+, Na+, Na+, (b) Na+, (c) K+, (d) Na+, (e) K+

Define, compare, and contrast the following concepts: (a) threshold, subthreshold, suprathreshold, all-or-none, overshoot, undershoot (b) graded potential, EPSP, IPSP (c) absolute refractory period, relative refractory period (d) afferent neuron, efferent neuron, interneuron (e) sensory neuron, somatic motor neuron, sympathetic neuron, autonomic neuron, parasympathetic neuron (f) fast synaptic potential, slow synaptic potential (g) temporal summation, spatial summation (h) convergence, divergence

(a) Threshold signals trigger action potentials. Suprathreshold also trigger action potentials, but subthreshold do not unless summed. Action potentials are all-or-none events. Overshoot—portion of the action potential above 0 mV. Undershoot—after-hyperpolarization portion of the action potential. (b) Graded potentials may be depolarizing or hyperpolarizing. Graded potential in a postsynaptic cell is an EPSP if depolarizing and an IPSP if hyperpolarizing. (c) No stimulus can trigger another action potential during the absolute refractory period, but a suprathreshold stimulus can trigger an action potential during the relative refractory period. (d) See answer to question 1. (e) Sensory are afferents; all others are efferents. (f) Fast synaptic potentials result from neurotransmitters altering ion channel gating, occur rapidly, and are short-lived. Slow synaptic potentials are mediated through second messengers, may involve protein modification, and last longer. (g) Temporal Answers to Review Questions A-5 18. Associative and nonassociative. Habituation—a person responds less and less to a repeated stimulus; sensitization—an enhanced response to a dangerous or unpleasant stimulus. 19. Broca's area and Wernicke's area Level Two Reviewing Concepts 20. Include information from Table 9.1 and Figures 9.3, 9.4, and 9.6. 21. Secreted into the ventricles and flows into the subarachnoid space around the brain and spinal cord before being reabsorbed by the cerebral arachnoid membrane. 22. sensory system, behavioral state system, and cognitive system 23. Wernicke's area—understand language; Broca's area— produce language. 24. (a) Diffuse modulatory—attention, motivation, wakefulness, memory, motor control, mood, and metabolism. Reticular formation—arousal and sleep, muscle tone, breathing, blood pressure, and pain. Reticular activating system— helps maintain consciousness. Limbic system—links higher cognitive functions with more primitive emotions such as fear. (b) Short-term memory—disappears unless consolidated; long-term memory—stored for recall. Long-term includes reflexive, or unconscious, memory, and declarative, or conscious, memory. (c) Nuclei—clusters of nerve cell bodies in the CNS; ganglia—clusters of nerve cell bodies outside the CNS. (d) Tracts—bundles of axons within the CNS. Nerves— bundles of axons outside the CNS. Horns—extensions of spinal cord gray matter that connect to peripheral nerves. Nerve fibers—bundles of axons. Roots—branches of peripheral nerves that enter or exit the spinal cord. 25. Primary somatic sensory cortex—parietal lobe. Visual cortex—processes information from eyes. Auditory cortex—processes information from ears. Olfactory cortex— processes information from nose. Frontal lobe motor cortices—control skeletal muscle movements. Association areas— integrate sensory information into perception. 26. (a) Lower frequency: wave peaks farther apart. (b) Larger amplitude: taller peaks. (c) Higher frequency: peaks closer together. 27. Drives increase arousal, initiate goal-oriented behavior, and coordinate disparate behaviors to achieve goals. 28. new synapses and changes in effectiveness of synaptic transmission Level Three Problem Solving 29. Expressive aphasia—could understand people but unable to communicate in any way that made sense. Speech centers are in the left brain. If music centers are in the right brain, then perhaps information from Wernicke's area can be integrated by the right brain so that Mr. Anderson can musically string together words so that they make sense. 30. Learning probably occurred, but need not be translated into behavioral responses. The participants who didn't buckle their seat belts learned that wearing seat belts was important but did not consider this knowledge important enough to act on. 31. Sleep-deprived dogs are producing a substance that induces sleep. Controls: putting CSF from normal dogs into sleep-deprived dogs, CSF from normal dogs into normal dogs, and CSF from sleep-deprived dogs into other sleepdeprived dogs. 32. (a) No, other information that should be taken into consideration include genetics, age, and general health. (b) The application of this study would be limited to women of similar age, background, and health. Other factors you might be interested in would include the ethnicity of the participants, factors as listed in (a), and geographical location. 33. Decreasing ECF osmolality by drinking a lot of water causes water to move into cells. The brain is enclosed in the bony cranium and has limited room in which to expand. If pressure inside the skull rises because of brain swelling, seizures will result. Chapter 10 Level One Reviewing Facts and Terms 1. Carry information from sensory receptors to the CNS. 2. The ability to tell where our body is in space and to sense the relative locations of different body parts. summation—multiple stimuli arrive at the trigger zone close together in time. Spatial summation—multiple stimuli from different locations arrive simultaneously at the trigger zone. (h) Divergence—a single neuron branches and its collaterals synapse on multiple targets. Convergence—many presynaptic neurons provide input to a smaller number of postsynaptic neurons.

A neuron has a resting membrane potential of -70 mV. Will the neuron hyperpolarize or depolarize when each of the following events occurs? (More than one answer may apply; list all those that are correct.) (a) Na+ enters the cell (b) K + leaves the cell (c) Cl - enters the cell (d) Ca2 + enters the cell

(a) depolarize, (b) hyperpolarize, (c) hyperpolarize, (d) depolarize

Match the best term (hyperpolarize, depolarize, repolarize) to the following events. The cell in question has a resting membrane potential of - 70 mV. (a) membrane potential changes from -70 mV to -50 mV (b) membrane potential changes from -70 mV to -90 mV (c) membrane potential changes from +20 mV to -60 mV (d) membrane potential changes from -80 mV to -70 mV

(a) depolarize, (b) hyperpolarize, (c) repolarize, (d) depolarize

Characterize each of the following stimuli as being mechanical, chemical, or thermal: (a) bath water at 106 °F (b) acetylcholine (c) a hint of perfume (d) epinephrine (e) lemon juice (f) a punch on the arm

(a) thermal, (b) chemical, (c) chemical, (d) chemical, (e) chemical, (f)mechanical

Place the following neurons in order of their speed of conduction, from fastest to slowest: (a) myelinated axon, diameter 20@mm (b) unmyelinated axon, diameter 20@mm (c) unmyelinated axon, diameter 200@mm

(a), (c), (b)

If you put ouabain, an inhibitor of the Na + -K + pump, on a neuron and then stimulate the neuron repeatedly, what do you expect to happen to action potentials generated by that neuron? (a) They cease immediately. (b) There is no immediate effect, but they diminish with repeated stimulation and eventually disappear. (c) They get smaller immediately, then stabilize with smaller amplitude. (d) Ouabain has no effect on action potentials.

(b)

The presence of myelin allows an axon to (a) produce more frequent action potentials. (b) conduct impulses more rapidly. (c) produce action potentials of larger amplitude. (d) produce action potentials of longer duration

(b)

An action potential is (circle all correct answers) (a) a reversal of the Na+ and K + concentrations inside and outside the neuron. (b) the same size and shape at the beginning and end of the axon. (c) initiated by inhibitory postsynaptic graded potentials. (d) transmitted to the distal end of a neuron and causes release of neurotransmitter.

(b) and (d)

One of the pills that Jim takes for high blood pressure caused his blood K + level to decrease from 4.5 mM to 2.5 mM. What happens to the resting membrane potential of his liver cells? (Circle all that are correct.) (a) decreases (b) increases (c) does not change (d) becomes more negative (e) becomes less negative (f) fires an action potential (g) depolarizes (h) hyperpolarizes (i) repolarizes

(b), (d), and (h)

Axonal transport refers to the: (a) release of neurotransmitters into the synaptic cleft. (b) use of microtubules to send secretions from the cell body to the axon terminal. (c) movement of organelles and cytoplasm up and down the axon. (d) movement of the axon terminal to synapse with a new postsynaptic cell. (e) none of these

(c). Answer (b) is only partly correct because not all axonal transport uses microtubules and not all substances moved will be secreted.

What causes the depolarization phase of an action potential? (Circle all that apply.) (a) K + leaving the cell through voltage-gated channels (b) K + being pumped into the cell by the Na+-K +-ATPase (c) Na+ being pumped into the cell by the Na+-K +-ATPase (d) Na+ entering the cell through voltage-gated channels (e) opening of the Na+ channel inactivation gate

(d)

Arrange the following events in the proper sequence: (a) Efferent neuron reaches threshold and fires an action potential. (b) Afferent neuron reaches threshold and fires an action potential. (c) Effector organ responds by performing output. (d) Integrating center reaches decision about response. (e) Sensory organ detects change in the environment.

(e) - (b) - (d) - (a) - (c)

Arrange the following terms to describe the sequence of events after a neurotransmitter binds to a receptor on a postsynaptic neuron. Terms may be used more than once or not at all. (a) action potential fires at axon hillock (b) trigger zone reaches threshold (c) cell depolarizes (d) exocytosis (e) graded potential occurs (f) ligand-gated ion channel opens (g) local current flow occurs (h) saltatory conduction occurs (i) voltage-gated Ca2 + channels open (j) voltage-gated K + channels open (k) voltage-gated Na+ channels open

(f) - (c) - (g) - (e) - (b) - (k) - (c) - (a) - (h) - (j) - (i) - (d)

How do mitochondria get to the axon terminals?

Mitochondria reach the axon terminal by fast axonal transport along microtubules

What is the difference between a nerve and a neuron?

A neuron is a single nerve cell. A nerve is a bundle of axons from many neurons

In electrical synapses, an electrical signal passes directly from the cytoplasm of one cell to another through:

gap junctions

Why are axon terminals sometimes called "biological transducers"?

Axon terminals convert (transduce) the electrical action potential signal into a chemical neurotransmitter signal.

When pharmaceutical companies design drugs, they try to make a given drug as specific as possible for the particular receptor subtype they are targeting. For example, a drug might target adrenergic b1- receptors rather than all adrenergic a- and b-receptors. What is the advantage of this specificity?

Because different receptor subtypes work through different signal transduction pathways, targeting drugs to specific receptor subtypes decreases the likelihood of unwanted side effects.

efferent neurons

Carry information away from the CNS back to various parts of the body

Gated ion channels in neurons open or close in response to:

Chemical or mechanical signals or in response to depolarization of the cell membrane.

Where do neurons that secrete neurohormones terminate?

Close to blood vessels so that the neurohormones can enter the circulation.

What is the difference between conductance and conduction in neurons?

Conductance refers to the movement of ions across a cell membrane. Conduction is the rapid, undiminished movement of an electrical signal down the axon of a neuron.

Emergent properties of the nervous system include:

Consciousness, intelligence, and emotion.

Graded potentials are:

Depolarizations or hyperpolarizations whose strength is directly proportional to the strength of the triggering event.

When Na + channel gates are resetting, is the activation gate opening or closing? Is the inactivation gate opening or closing?

During resetting, the activation gate is closing, and the inactivation gate is opening.

Classify the H +-neurotransmitter exchange as facilitated diffusion, primary active transport, or secondary active transport. Explain your reasoning

The exchange is secondary active transport because it uses energy stored in the H + concentration gradient to concentrate neurotransmitter inside the vesicles

Conductance (G) is the reciprocal of resistance:

G = 1/R

For Ca2 + , the electrical charge z is +2; the ratio of ion concentrations is 1/0.0001 = 10,000 or 104. Log of 104 is 4 (see Appendix B). Thus Eion (in mV) = (61 * 4)/(+2) = 122 mV.

Given the values in Table 8.2, use the Nernst equation to calculate the equilibrium potential for Ca2 + . Express the concentrations as powers of 10 and use your knowledge of logarithms [Appendix B] to try the calculations without a calculator.

What are the sections of uninsulated membrane occurring at intervals along the length of an axon?

The nodes of Ranvier

Current flow (I) obeys Ohm's Law:

I = voltage/resistance.

The trigger zone for the sensory neurons is close to where the dendrites converge. You cannot tell where the trigger zone is for the anaxonic neuron. For multipolar neurons, the trigger zone is at the junction of the cell body and the axon

Identify the trigger zones of the neurons llustrated in Figure 8.2, if possible.

The postsynaptic neuron will fire an action potential, because the net effect would be a 17 mV depolarization to -70 - (-17) = -53 mV, which is just above the threshold of -55 mV.

In Figure 8.24b, assume the postsynaptic neuron has a resting membrane potential of -70mV and a threshold of -55 mV. If the inhibitory presynaptic neuron creates an IPSP of -55 mV, and the two excitatory presynaptic neurons have EPSPs of 10 and 12 mV, will the postsynaptic neuron fire an action potential?

The membrane potential does not change at the same time as the stimulus because the depolarization must travel from the point of the stimulus to the recording point.

In the graphs of Figure 8.24c and 8.24d, why doesn't the membrane potential change at the same time as the stimulus?

The voltage-gated Na+ channels of a neuron open when the neuron depolarizes. If depolarization opens the channels, what makes them close when the neuron is maximally depolarized?

Inactivation gates also respond to depolarization, but they close more slowly than the activation gates open, allowing ions to flow for a short period of time.

What is the myelin sheath?

Insulating membranes around neurons that prevent current leak

The permeability of a cell to ions changes when:

Ion channels in the membrane open and close.

The Goldman-Hodgkin-Katz (GHK) equation predicts membrane potential based on:

Ion concentration gradients and membrane permeability for multiple ions.

What is the Nernst equation?

It describes the membrane potential of a cell that is permeable to only one ion.

What are the mechanisms by which neurons change the strength of their synaptic connections?

Long-term potentiation and long-term depression

Why would depolarization of the membrane drive Mg2+ from the channel into the extracellular fluid?

Membrane depolarization makes the inside of the membrane more positive than the outside. Like charges repel one another, so the more positive membrane potential tends to repel Mg2 +.

TheNa+ -K + -ATPase eventually restores:

Na+ and K + to their original compartments.

Which cells can develop into new neurons and glia, and are found in the ependymal layer as well as in other parts of the nervous system?

Neural stem cells

Which glial cells are found in the CNS?

Oligodendrocytes, astrocytes, microglia, and ependymal cells.

Which organelles are needed to synthesize proteins and package them into vesicles?

Proteins are synthesized on the ribosomes of the rough endoplasmic reticulum; then the proteins are directed into the Golgi apparatus to be packaged into vesicles.

Changes in blood K + concentration affect:

Resting membrane potential and the conduction of action potentials

One class of antidepressant drugs is called selective serotonin reuptake inhibitors (SSRIs). What do these drugs do to serotonin activity at the synapse?

SSRIs decrease reuptake of serotonin into the axon terminal, thereby increasing the time serotonin is active in the synapse

The apparent jumping of action potentials from node to node is called:

Saltatory conduction

Which glial cells form insulating myelin sheaths around neurons?

Schwann cells and oligodendrocytes

Which glial cells are associated with the peripheral nervous system?

Schwann cells and satellite cells

Name the two glial cell types that form myelin. How do they differ from each other?

Schwann cells are in the PNS, and each Schwann cell forms myelin around a small portion of one axon. Oligodendrocytes are in the CNS, and one oligodendrocyte forms myelin around axons of several neurons.

List the three functional classes of neurons, and explain how they differ structurally and functionally.

Sensory afferents carry messages from sensory receptors to CNS. Their cell bodies are located close to the CNS. Interneurons are completely contained within the CNS and are often extensively branched. Efferents carry signals from the CNS to effectors. They have short, branched dendrites and long axons.

If all action potentials within a given neuron are identical, how does the neuron transmit information about the strength and duration of the stimulus?

Strength is coded by the frequency of action potentials; duration is coded by the duration of a train of repeated action potentials.

Autonomic neurons are subdivided into:

Sympathetic and parasympathetic branches.

Autonomic neurons control:

Smooth and cardiac muscles, glands, and some adipose tissue.

The efferent neurons include:

Somatic motor neurons, which control skeletal muscles, and autonomic neurons, which control smooth and cardiac muscles, glands, and some adipose tissue.

If you place an electrode in the middle of an axon and artificially depolarize the cell above threshold, in which direction will an action potential travel: to the axon terminal, to the cell body, or to both? Explain your answer.

The action potential will go in both directions because the Na+ channels around the stimulation site have not been inactivated by a previous depolarization. See discussion of refractory periods.

The nervous system is divided into:

The central nervous system (CNS), composed of the brain and spinal cord, and the peripheral nervous system (PNS).

Membrane potential is influenced by:

The concentration gradients of ions across the membrane and by the permeability of the membrane to those ions.

The pyrethrin insecticides, derived from chrysanthemums, disable inactivation gates of Na + channels so that the channels remain open. In neurons poisoned with pyrethrins, what happens to the membrane potential? Explain your answer.

The membrane potential depolarizes and remains depolarized.

In an experiment on synaptic transmission, a synapse was bathed in a Ca2 + -free medium that was otherwise equivalent to extracellular fluid. An action potential was triggered in the presynaptic neuron. Although the action potential reached the axon terminal at the synapse, the usual response of the postsynaptic cell did not occur. What conclusion did the researchers draw from these results?

The researchers concluded that some event between arrival of the action potential at the axon terminal and depolarization of the postsynaptic cell is dependent on extracellular Ca2 + . We now know that this event is neurotransmitter release

Neurons have an axon to:

Transmit electrical signals from the cell body to the axon terminal.

An unmyelinated axon has a much greater requirement for ATP than a myelinated axon of the same diameter and length. Can you explain why?

Unmyelinated axons have many ion channels, so more ions cross during an action potential and must be returned to their original compartments by the Na+-K+-ATPase, using energy from ATP.

Postsynaptic modulation occurs when:

a modulatory neuron synapses on a postsynaptic cell body or dendrites.

Action potentials begin in the trigger zone if:

a single graded potential or the sum of multiple graded potentials exceeds the threshold voltage.

Would a cell with a resting membrane potential of - 70 mV depolarize or hyperpolarize in the following cases? (You must consider both the concentration gradient and the electrical gradient of the ion to determine net ion movement.) (a) Cell becomes more permeable to Ca2+ . (b) Cell becomes less permeable to K +

a) depolarize b) depolarize

Cholinergic neurons secrete:

acetylcholine

Material is transported between the cell body and axon terminal by:

axonal transport

sensory (afferent) neurons

bring information into the CNS

Neurons have a ... with a nucleus and organelles to direct cellular activity.

cell body

Developing neurons find their way to their targets by using:

chemical signals

When several presynaptic neurons provide input to a smaller number of postsynaptic neurons, the pattern is known as:

convergence

G protein-coupled receptors either:

create slow synaptic potentials or modify cell metabolism.

When a presynaptic neuron synapses on a larger number of postsynaptic neurons, the pattern is known as:

divergence

List three ways neurotransmitters are removed from the synapse.

enzymatic degradation, reabsorption, and diffusion

Neurotransmitters are released by:

exocytosis

The voltage-gated Na+ channels of the axon have a:

fast activation gate and a slower inactivation gate

Ion channels create:

fast synaptic potentials

Larger- diameter axons conduct action potentials:

faster

Channels also close through:

inactivation

The falling phase of the action potential is due to:

increased K + permeability.

The rising phase of the action potential is due to:

increased Na+ permeability.

The myelin sheath around an axon speeds up conduction by:

increasing membrane resistance and decreasing current leakage.

List two factors that enhance conduction speed

larger axon diameter and the presence of myelin

Hyperpolarizing graded potentials make a neuron:

less likely to fire an action potential.

Neurotransmitter receptors are either:

ligand-gated ion channels (ionotropic receptors) or G protein-coupled receptors (metabotropic receptors)

A higher-than-normal graded potential is required to trigger an action potential during the:

relative refractory period

The wave of depolarization that moves through a cell is known as:

local current flow

Movement of only a few ions significantly changes the:

membrane potential

Depolarizing graded potentials make a neuron:

more likely to fire an action potential.

Graded potentials lose strength as they:

move through the cell

Name the two primary cell types found in the nervous system.

neurons and glial cells

Interneurons are:

neurons that lie entirely within the CNS

Adrenergic neurons secrete:

norepinephrine

Glial cells provide:

physical support and communicate with neurons.

The target cell where an axon terminal meets its target is called the:

postsynaptic cell

the neuron that releases the chemical signal is known as the:

presynaptic cell.

Neurons have dendrites to:

receive incoming signals

Neurotransmitters diffusing across the synaptic cleft to bind with:

receptors on target cells.

Increased frequency of action potentials:

releases more neurotransmitter

Neurotransmitter action is rapidly terminated by:

reuptake into cells, diffusion away from the synapse, or enzymatic breakdown

Presynaptic modulation of an axon terminal allows:

selective modulation of collaterals and their targets.

The peripheral nervous system has which types of neurons?

sensory (afferent) neurons and efferent neurons

Somatic motor neurons control ... , and ... neurons control smooth and cardiac muscles, glands, and some adipose tissue.

skeletal muscles; autonomic

Smaller-diameter axons conduct action potentials:

slower

The summation of simultaneous graded potentials from different neurons is known as:

spatial summation

Autonomic neurons are classified as either ... or ... neurons.

sympathetic or parasympathetic

The region where an axon terminal meets its target cell is called a:

synapse

The region between two neurons cells is the:

synaptic cleft

Synaptic transmission can be modified in response to activity at the synapse, a process known as :

synaptic plasticity

Neurotransmitters are stored in:

synaptic vesicles

The summation of graded potentials that closely follow each other sequentially is called:

temporal summation.

Once an action potential has begun, there is a brief period of time known as:

the absolute refractory period during which a second action potential cannot be triggered, no matter how large the stimulus. Because of this, action potentials cannot be summed.

Information about the strength and duration of a stimulus is conveyed by:

the amount of neurotransmitter released.

Neurotransmitters are synthesized in:

the cell body or in the axon terminal

Resistance to current flow comes from:

the cell membrane, which is a good insulator, and from the cytoplasm.

Action potentials are uniform, all-or-none depolarizations that can:

travel undiminished over long distances.

Exocytosis occurs when:

when an action potential reaches the axon terminal.