Mastering Biology for test 2

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The fundamental excitable cell in the nervous system is the _____.


The knee-jerk reflex has sensory neurons arising in the _____, interneurons in the _____, and efferent neurons that stimulate contraction in the _____.

Quadriceps muscle, spine, Hamstrings

The cerebrospinal fluid is _____.

A filtrate of the blood

A neuron’s nucleus is located in its _____.

Cell Body

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


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

The axon

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

node of Ranvier … node of Ranvier

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

Synaptic Terminal

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

Schwann Cells

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

Myelin Sheath

The "information receiving" section of a neuron is its _____.


Most of the neurons in the human brain are _____.


In a simple synapse, neurotransmitter chemicals are released by _____.

The presynaptic membrane

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

Potassium ion K+

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

Membrane Potential

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

False-The potential energy of a membrane potential comes both from the difference in electrical charge and from the concentration gradient of ions across a membrane.

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

Potassium Leak Channel

Which term describes an electrical signal generated by neurons?

Action Potential

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

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

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. Sodium ions flow into the cell when the membrane potential is between -20 mV and 30 mV.

The operation of the sodium-potassium "pump" moves _____.

Sodium Ions out of the cell and Potassium ions into the cell.

The membrane potential in which there is no net movement of the ion across the membrane is called the _____.

Equilibrium Potential

Two fundamental concepts about the ion channels of a "resting" neuron are that the channels _____.

open and close depending on stimuli, and are specific as to which ion can traverse them

Which event triggers the creation of an action potential?

The membrane depolarizes above a certain threshold potential.-Influx of Na+ ions into the neuron can lead to membrane depolarization above the threshold potential; this event triggers the creation of an action potential.

Which of the following terms describes how a neuronal membrane’s potential is altered in the presence of inhibitory signals?


Where in the neuron do action potentials begin?

Axon Hillock

How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron’s membrane?

Sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon. -The entry of sodium ions into the neuron and their diffusion to adjacent areas of the membrane causes those portions of the membrane to become depolarized and results in the opening of voltage-gated sodium channels farther down the axon, which release potassium ions to the outside, returning the charge to its previous state.

A neuron has a resting potential of about _____ millivolts.

-70 millivolts

An action potential moves along a(n) _____.


The transmission of a nerve impulse first triggers the _____.

opening of voltage-gated sodium channels and the diffusion of sodium 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

A graded hyperpolarization of a membrane can be induced by _____.

increasing its membrane’s permeability to K+

After the depolarization phase of an action potential, the resting potential is restored by _____.

the opening of voltage-gated potassium channels and the closing of sodium channels

The "undershoot" phase of after-hyperpolarization is due to _____.

sustained opening of voltage-gated potassium channels

Why are action potentials usually conducted in one direction?

The brief refractory period prevents reopening of voltage-gated Na+ channels.

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

Which of the following will increase the speed of an action potential moving down an axon?
I) Action potentials move faster in larger diameter axons.
II) Action potentials move faster in axons lacking potassium ion channels.
III) Action potentials move faster in myelinated axons.

I and III

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

Synaptic cleft

Which of these causes the release of neurotransmitter molecules?

An action potential reach the end of the axon

Neurons store neurotransmitter molecules in vesicles located within _____.

Synaptic Terminals

A nerve poison that blocks acetylcholine receptors on dendrites would _____.

reduce the binding of acetylcholine to its receptors on the postsynpatic membrane

Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal?

Voltage-gated calcium channels in the membrane open.

Suppose a particular neurotransmitter causes an IPSP in postsynaptic cell X and an EPSP in postsynaptic cell Y. A likely explanation is that __________.

cells X and Y express different receptor molecules for this particular neurotransmitter

The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels?

Membrane depolarization first opens sodium channels and then opens potassium channels.

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