Chapter 11

What type of current flows through the axolemma during the steep phase of repolarization?

chiefly a potassium current

Assume that an EPSP is being generated on the dendritic membrane. Which will occur?

specific sodium ion channels will open

The velocity of nerve impulse conduction is greatest in

myelinated, large-diameter

fibers

Chemical synapses are characterized by:

• the release of neurotransmitter by the presynaptic membranes

• postsynaptic membranes bearing receptors that bind neurotransmitter

• a fluid-filled gap separating neurons,

Biogenic amine neurotransmitters include:

• norepinephrine

• dopamine

• serotonin

Inhibition of acetylcholinesterase by poisoning blocks neurotransmission at the neuromuscular junction because

ACh is not degraded, hence prolonged depolarization is enforced on the postsynaptic cell

The anatomical region of a multipolar neuron that has the lowest threshold for generating an AP is the

axon hillock

An IPSP is inhibitory because

it hyperpolarizes the postsynaptic membrane

helps regulate the ionic composition of CNS extracellular fluid

Astrocyte

Lines brain cavities

Ependymal cell

CNS phagocyte

Microglial cell

Myelinates nerve fibers in the CNS

Oligodendrocyte

Myelinates nerve fibers in the PNS

Schwann cell

Many neurons influence a few neurons

Converging

May be involved in exacting types of mental activity

Parallel after-discharge

Impulses continue around and around the circuit until one neuron stops firing

Reverberating

One or a few inputs ultimately influence large numbers of neurons

Diverging

For an open ion channel, what factors determine in which direction ions will move through the channel?

The concentration gradient and the electrical gradient, which together form the electrochemical gradient.

Why is action potential considered an all-or-none phenomenon

a neuron either fires a full-strength signal if a stimulus reaches the threshold, or it does not fire at all

What events must occur to generate an action potential

• Depolarization

• Repolarization

• Hyperpolarization

• Resting state

How does Depolarization help generate action potential?

It triggers a positive feedback loop that rapidly changes a neuron’s membrane potential, casuing it to “fire” an electrical impulse 

How does Repolarization help action potential occur?

Returns the neurons membrane to its negative resting state after depolarization, making it ready to fire again.

How does Hyperpolarization help generate action potential?

Temporarily prevents action potential by making the neurons membrane potential more negative, increacing the threashold needed to trigger an action potential. 

How does the resting state help generate action potential?

establishes the necessary electronical gradients, which act as a stored form of potential energy

How does the CNS “know” whether a stimulus is strong or weak since all action potentials generated by a given nerve fiber have the same magnitude?

By the frequency of action potentials and the number of nerve fibers activated

What specifically determines whether an EPSP or IPSP will be generated at the postsynaptic membrane?

The type of neurotransmitter released by the vpresynaptic neuron and the specific ion channels that are opened on the postsynaptic membrane

What is EPSP?

a temporary depolarization of a postsynaptic neuron’s membrane potential caused by the influx of positively charged ions, typically Na+ into the cell.

What is ISPS?

A temporary hyperpolarization of a postsynaptic neuron’s membrance potential caused by an influx of negatively charged ions, such as Cl-, or the efflux of possitviely charged ions, such as K+

How is neuronal activity (to fire or not to fire) determined since at any moment a neuron is likely to have thousands of neurons releasing neurotransmitters at its surface?

The summation of exciatory and inhibitory postsynaptic potentials

Why are the effects of neurotransmitter binding very brief?

Neurotransmitters are rapidly removed from the synaptic cleft

What causes ACh to excite skeletal muscle and also inhibit heart muscle

The presence of different types of receptors on the muscle cells

Which is bigger, a graded potential or an action potential? 

an action potential

Which travels the farthest a graded potential or an action potential?

an action potential

Which initiates the other a graded potential or an action potential?

a graded potential

Which structural and functional type of neuron is activated first when you burn your finger?

Sensory Neuron

Which structural and functional type is activated last to move your finger away from the heat source?

Motor Neuron

___ neurons have many processes that extend from the cell body. All of these processes are dendrites except for a single axon.

Multipolar

A neuron that has as its primary function the job of connecting other neurons is called a ___.

interneuron

Complete the following analogy: Electrical wire is to electrical insulating tape as peripheral neurons are to ___

Schwann cells

Function of dendrites:

• Provide enormous surface area for receiving signals from other neurons

• Produce short-distance signals called graded potentials

• Convey incoming messages toward the cell body

Dopamine and serotonin are examples of which class of neurotransmitters?

Biogenic amines

An amino acid that functions as an inhibitory neurotransmitter in the brain is ____.

GABA

Central nervous system refers to the ____.

brain and spinal cord

An excitatory neurotransmitter secreted by motor neurons innervating skeletal muscle is ____.

acetylcholine

Events of synaptic transmission in the correct sequence:

• action potential occurs in sending cell

• neurotransmitter is released from vesicles in sending cell

• neurotransmitter binds to receptor on receiving cell

• local potential is generated in receiving cell

• excess neurotransmitter is reabsorbed into sending cell

In what way does the interior surface of a cell membrane of a resting (nonconducting) neuron differ from the external environment? The interior is ____.

negatively charged and contains less sodium

The sodium-potassium pump ____ the cell for every ____ the cell.

pumps three sodium ions outside ... two potassium ions inside

Immediately after an action potential has peaked (finished the depolarization phase), which cellular gates open to cause repolarization?

potassium

The sympathetic and parasympathetic are subdivisions of the ____.

autonomic nervous system

Interneurons are located in the ____. These neurons perform the ____ function of the nervous system.

CNS ... association

The part of a neuron that conducts impulses away from its cell body is called a(n) ____.

axon

The ___ of action potentials that travel through a sensory neuron codes for stimulus intensity.

frequency

The substance released at axon terminals (knobs) to propagate a nervous impulse is called a(n) ____.

neurotransmitter

Most neurons are ____ with one axon and many dendrites.

multipolar

An efferent neuron ____.

carries motor output from the CNS to an effector

Nodes of Ranvier are important for ____.

the rapid saltatory conduction of action potentials down an axon

An inhibitory postsynaptic potential (IPSP) is best associated with ____.

hyperpolarization

A neuron with which of the following features would transmit action potentials at the fastest speed?

 

large diameter axon with myelin

Ciliated CNS neuroglia that play an active role in moving the cerebrospinal fluid are called ____.

 

ependymal cells

Schwann cells are functionally similar to ____.

oligodendrocytes

To trigger an action potential in the membrane of a receiving cell (post-synaptic neuron), ____ must be generated to reach the threshold membrane potential of about ____.

many EPSPs ... -55 mV

The point at which an impulse from one nerve cell is communicated to another nerve cell is the ____.

synapse

During the depolarization phase of an action potential in a neuron, ____ gates open and these ions move ____ the cell.

Na+ ... into

Numerous nerve impulses from a single sending cell arrive at a synapse at closely timed intervals and exert a cumulative effect on the receiving cell.

temporal summation

"Change in local potential producing slight depolarization" best describes ____.

an excitatory postsynaptic potential

The interior of the cell becomes more negative due to the opening of potassium ion gates.

Repolarization

An exceptionally strong stimulus can trigger a response (action potential).

Relative refractory period

Period during which the neuron cannot respond to a second stimulus, no matter how strong.

Absolute refractory period