Assignment 13

Which term describes an electrical signal generated by neurons?

Action potential

At location ___, the membrane potential changes sign (from a positive value to a negative value) and the voltage-gated K+ channels are open.

C

At location ____, the axon membrane is at resting potential.

G

Resting neurons are most permeable to which of the following ions?

K+

Which of the following is most likely to result in an action potential at a postsynaptic neuron?

many EPSPs and few IPSPs

An impulse relayed along a myelinated axon "jumps" from _____ to _____.

node of Ranvier ... node of Ranvier

Rank the axons from slowest to fastest conduction speed. If two axons have the same conduction speed, place one on top of the other.

non-myelinated 20 non-myelinated 30 non-myelinated 40 myelinated 30

The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____.

synaptic cleft

What part of a neuron relays signals from one neuron to another neuron or to an effector?

synaptic terminal

Neurons store neurotransmitter molecules in vesicles located within _____.

synaptic terminals

At location ___, the voltage-gated Na+ channels reactivate.

A

A neuron has a resting potential of about _____ millivolts.

-70

What would happen when an artificial K+ channel is inserted into an axon membrane at resting potential? Answer questions 1-4 by selecting only from the three answer choices to the left of each question. Drag the correct answer to the right of each question.

1. out of the cell 2. promote 3. impede 4. causes hyperpolarization

Which statement correctly describes what causes the second voltage-gated Na+ channel to open?

After the first channel opens, the movement of many types of ions (both inside and outside the cell) alters the distribution of charges near the second channel, causing it to open.

At resting potential, the inside and outside of a neuron differ in _____. charge sodium ion concentration potassium ion concentration All of the listed responses are correct.

All of the listed responses are correct.

At location ____, the voltage-gated K+ channels are closing.

B

Drag each word or phrase to the appropriate bin. If the word or phrase applies to both the central nervous system and peripheral nervous system, drag it to the "both CNS and PNS" bin.

CNS: processes information received from sense organs brain and spinal cord initates signals to muscles and organs PNS: cranial nerves and spinal nerves afferent and efferent neurons carries signals to muscles and organs carries sensory information toward the spinal cord Both: reflexes enables voluntary locomotion

Neurotransmitters are released from neurons in response to the increase in intracellular concentration of what ion?

Calcium

At location ____, the voltage-gated Na+ channels are inactivating and the voltage-gated K+ channels are opening.

D

At location ____, the membrane potential changes sign (from a negative value to a positive value) and the voltage-gated Na+ channels are open.

E

Sort the phrases into the appropriate bins depending on which type of postsynaptic potential they describe. If a phrase describes both types of potentials, drag it to the "both" bin.

Excitatory Postsynaptic Potential (EPSP): depolarizes the postsynaptic membrane, results from the movement of Na+ ions into the postsynaptic cell, brings the postsynaptic membrane potential closer to threshold Inhibitory Postsynaptic Potential (IPSP): hyper polarizes the postsynaptic membrane, results from the movement of K+ ions out of the postsynaptic cell, moves the postsynaptic membrane potential farther away from the threshold Both: is a graded potential

At location ___ , the axon membrane reaches threshold and the voltage-gated Na+ channels open.

F

True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.

False

Drag the labels onto the flowchart to show the sequence of events that occurs once the membrane potential reaches threshold. You may use a label once or not at all.

Membrane potential reaches threshold many voltage-gated Na+ channels open Na+ ions rush into the cell membrane potential rises (depolarizes) rapidly

Which of the following statements about action potentials is false?

Movement of ions during the action potential occurs mostly through the sodium pump.

The peripheral nervous system (PNS) transmits information to and from the central nervous system (CNS) and plays a role in regulating an animal's movements and internal environment. Determine which of the following statements about the PNS are true. Select the four statements that are true.

Neurons in the parasympathetic division release neurotransmitters that act on receptors that slow heart rate. Parasympathetic nerves are associated with the cranial and sacral regions of the spinal cord, whereas sympathetic nerves are associated with the thoracic and lumbar regions. The sympathetic division of the PNS prepares the body for physical exertion in stressful situations. Stimulating the organs of digestion is a parasympathetic response.

Will net flow of K+ move out of the cell indefinitely?

No, it will stop once the membrane reaches the equilibrium potential for K+

Which channel is mainly responsible for the resting potential of a neuron?

Potassium leak channel.

What type of cell makes up the myelin sheath of a motor neuron?

Schwann cells

What would probably happen if a long neuron had one continuous myelin sheath down the length of the axon with no nodes of Ranvier?

The signal would fade because it is not renewed by the opening of more sodium channels.

What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?

The sodium channel opens, and Na+ ions flow in.

Which channel maintains the concentration gradients of ions across a neuronal membrane?

The sodium-potassium pump moving Na+ ions out and K+ ions in.

How do myelin sheaths increase the speed with which action potentials are propagated along an axon?

They cause action potentials to "jump" down the axon rather than travel in a continuous path along every site on the axon.

Drag the labels onto the graph to indicate which presynaptic neuron produced each change in the axon hillock's membrane potential. Assume that the same number of ligand-gated ion channels opens at each synapse. (To review the effect of distance between the synapse and the axon hillock, see Hint 2.) Labels can be used once, more than once, or not at all.

a. I2 b. E2 c. E1 d. I1 e. E2 f. E1

Drag the appropriate labels onto the graph to indicate the status (open or closed) of the voltage-gated Na+ and K+ channels during each phase of an action potential. Labels may be used once, more than once, or not at all.

a. Na+ closed, K+ closed b. open, closed c. closed, open d. closed, open e. closed, closed

Drag the labels to their appropriate locations on the diagram of the neurons below. Use only the pink labels for the pink targets (which indicate the locations of gated ion channels).

a. cell body b. myelin sheath c. synaptic terminal d. axon hillock e. nucleus f. location of voltage-gated channels g. location of ligand-gated channels h. axon i. dendrite

The central nervous system consists of the spinal cord and the brain, which is one of the most complex organs in animals. On the diagram below, label the parts of the human brain and identify one function of each part of the brain.

a. cerebrum b. diencephalon c. working a crossword puzzle d. sending signals from the senses to the appropriate brain region e. communicating between left and right cerebral hemispheres f. brainstem g.cerebellum h.regulating a person's resting heart rate i. maintaining balance while walking

Drag the arrows onto the diagram to show the direction of Na+ (gray arrows) and K+ (red arrows) movement through each transport protein at resting potential. If no ions move through a transport protein at resting potential, leave that target blank.

a. none b. none c. na+ out, k+ in d. K+ out e. na+ in

Which of these causes the release of neurotransmitter molecules?

an action potential reaching the end of the axon

A nerve impulse moves away from a neuron's cell body along _____.

axon

A neuron sends a signal toward another neuron along its _____.

axon

An action potential moves along a(n) _____.

axon

Enter the sequence in which the action potential would pass through the points. Enter the letters in the correct order separated by commas. For example if the order is point (c), then (b), then (a), enter c, b, a. If the action potential would not pass though a point, do not include that point in your answer.

b,a,c

Why do Na+ ions enter the cell when voltage-gated Na+ channels are opened in neurons?

because the Na+ concentration is much higher outside the cell than it is inside, and the Na+ ions are attracted to the negatively charged interior

A neuron's nucleus is located in its _____.

cell body

Which of the following parts of the brain is involved in coordination of motor patterns?

cerebellum

A nerve impulse moves toward a neuron's cell body along _____

dendrites

Which of the following characteristics determines when the refractory period ends?

how long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential

Which term describes the difference in electrical charge across a membrane?

membrane potential

Axons insulated by a(n) _____ are able to conduct impulses faster than those not so insulated.

myelin sheath

The transmission first triggers the _____.

opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron

At rest, which of these plays a role in establishing the charge differential across a neuron's plasma membrane?

pump moving sodium ions out of the neuron and potassium ions into the neuron

A stimulus has opened the voltage-gated sodium channels in an area of a neuron's plasma membrane. As a result, _____ rushes into the neuron and diffuses to adjacent areas; this in turn results in the _____ in the adjacent areas.

sodium ... opening of voltage-gated sodium channels

Action potentials are only propagated "downstream" (away from the cell body) because _____.

sodium channels upstream are refractory to action potentials

In terms of signaling, what is most significant about action potentials?

the frequency