CH 11 MAP

Which component has a role in the postsynaptic cell during synaptic activity?

chemically gated channels (Neurotransmitter binds to receptors on the postsynaptic cell. These chemically gated channels open, allowing the transfer of the "signal" from a presynaptic neuron to the postsynaptic cell.)

Saltatory propagation occurs in _________ axons, in which action potentials _________.

myelinated; move from one node of Ranvier to another (Saltatory propagation is much faster than continuous propagation. The speed of propagation along an axon varies in two ways: 1) myelin sheaths limit the movement of ions across the axon membrane, thereby requiring the action potentials to "leap" from node to node during propagation, thus traveling at a greater speed; and 2) the diameter of the axon directly relates to the speed of propagation (i.e., the larger the diameter of the axon, the faster the speed of propagation).)

Which of the following is NOT a type of circuit? -diverging circuits -reverberating circuits -converging circuits -pre-synaptic circuits

pre-synaptic circuits (do not exist)

What most accurately describes the effects caused by binding of the neurotransmitter (green dots) to the structure labeled C?

The membrane potential of the postsynaptic membrane changes (Binding of the neurotransmitter to the receptor at C causes the opening of receptor-associated ion channels. Depending on the particular types of channels that open, diffusion of certain ions (typically Na+, K+, or Clâˆ') will cause a depolarizing or hyperpolarizing effect on the postsynaptic membrane.)

Which of the following is not characteristic of neurons? -They are mitotic. -They conduct impulses. -They have an exceptionally high metabolic rate. -They have extreme longevity.

They are mitotic

Which of the following membrane regions would have significant numbers of voltage-gated ion channels?

Voltage-gated Na+ and K+ channels allow for the triggering of an action potential at the axon hillock (C) and its propagation down the axon (D).

A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell?

a neuron (A neuron is the only type of presynaptic cell. Neurons release neurotransmitters, effectively changing an electrical signal or action potential into a chemical signal that can communicate across the synaptic cleft to the postsynaptic cell.)

What is a factor that determines the rate of impulse propagation, or conduction velocity, along an axon?

degree of myelination of the axon (the rate of impulse propagation depends largely on two factors, degree of myelination and axon diameter. The presence of a myelin sheath dramatically increases the rate of impulse (action potential) propagation. Heavily myelinated axons propagate impulses faster than lightly myelinated axons. Also, larger (thicker) axons conduct impulses faster than smaller (thinner) axons.)

Which membrane potential occurs because of the influx of Na+ through chemically gated channels in the receptive region of a neuron?

excitatory postsynaptic potential (An excitatory postsynaptic potential, a type of graded potential, occurs because of the influx of Na+ through chemically gated channels in the receptive region, or postsynaptic membrane, of a neuron. Graded potentials are generated by chemically gated channels, whereas action potentials are produced by voltage-gated channels.)

Neurotransmitter is released from presynaptic neurons through what mechanism?

exocytosis (Neurotransmitter molecules are released from vesicles that fuse with the plasma membrane through exocytosis. Note that "exo-" means "outside" and "cytosis" means "cell." Once released, neurotransmitter diffuses across the synaptic cleft.)

What does the central nervous system use to determine the strength of a stimulus?

frequency of action potentials

Collections of nerve cell bodies in the peripheral nervous system are called ________.

ganglia

What describes the excitatory postsynaptic potential?

short distance depolarization

The generation of an action potential in a neuron requires the presence what type of membrane channels?

voltage gated channels

Synaptic response to an action potential Drag the labels to identify the sequence of events that occurs at a synapse.

1. An action potential arrives at the synaptic terminal. 2. Calcium channels open, and calcium ions enter the synaptic terminal. 3. Vesicles containing neurotransmitter fuse with the plasma membrane of the sending neuron. 4. Neurotransmitter molecules diffuse across the synaptic cleft. 5. The neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, causing ion channels there to open.

In which area of the neuron is an action potential initially generated?

C Graded potentials originating in the dendrites and cell body are integrated (summated) at the axon hillock (C). Membrane potentials above threshold at the hillock will open voltage-gated Na+ channels found in the "trigger zone," producing an action potential that proceeds down the axon.

What is the role of calcium in synaptic activity?

Calcium influx into the synaptic terminal causes vesicle fusion. (When an action potential reaches the synaptic terminal, voltage-gated channels open and calcium enters the cell. Calcium causes vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft.)

True or False? Strong stimuli cause the amplitude of action potentials generated to increase.

False

True or False? The all-or-none phenomenon as applied to nerve conduction states that the whole nerve cell must be stimulated for conduction to take place.

False

The concentration of ___ is higher inside than outside the cell

K+

The membrane is more permeable to ___

K+

The resting membrane potential is maintained by Na+-K+ pumps that actively transport ___ into the cell and ___ out of the cell

K+, Na+

The concentration of ___ is higher outside the cell than inside the cell

Na+

What is the direct role of neurotransmitter at a chemical synapse?

Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane. (Neurotransmitter leaves the presynaptic neuron by exocytosis and binds receptors on the postsynaptic cell membrane, opening the channels. When ions enter the postsynaptic cell, a graded potential takes place.)

What charges are at the correct side of the membrane to represent the resting membrane potential of a typical neuron.

Outside is +, Inside is - (The separation of charges creates a voltage (electrical potential difference), which can be measured using a voltmeter. The resting membrane potential of a neuron averages -70mV (millivolts). All neural activities begin with a change in the resting membrane potential of a neuron.)

Synapse Structure

See Diagram

Events that occur during synaptic activity are listed here, but they are arranged in an incorrect order. Choose the correct order of these events below. (a) Voltage-gated calcium channels open (b) Neurotransmitter binds to receptors (c) Action potential arrives at axon terminal (d) Neurotransmitter is removed from the synaptic cleft (e) Neurotransmitter released into synaptic cleft (f) Graded potential generated in postsynaptic cell

( (c) Action potential arrives at axon terminal (a) Voltage-gated calcium channels open (e) Neurotransmitter released into synaptic cleft (b) Neurotransmitter binds to receptors (f) Graded potential generated in postsynaptic cell (d) Neurotransmitter is removed from the synaptic cleft

The propagation of an action potential (AP) in an unmyelinated axon is called continuous propagation. This activity will test your understanding of the sequence of events that occur during continuous propagation.

1. Local current flows to axon segment 2. Axon segment depolarized to threshold 3. Voltage-gated Na+ channels open 4. Influx of Na+ 5. AP regenerated in adjacent axon segment

Action potentials (nerve impulses) are changes in the membrane potential that, once started, will affect the entire excitable membrane. The first action potential is usually generated at the initial segment of the neuron's axon.

1. Threshold stimulus Na+ channels open 2. Na+ influx Depolarization 3. Na+ channels close K+ channels open 4. K+ efflux Repolarization 5. Hyperpolarization K+ channels close

Which of the following statements is true of both membrane potential responses shown in the graphs?

Both responses are examples of graded potentials. (Both responses are short-lived, relatively small changes in the membrane potential.)

Local anesthetics block voltage-gated Na+ channels, but they do not block mechanically gated ion channels. Sensory receptors for touch (and pressure) respond to physical deformation of the receptors, resulting in the opening of specific mechanically gated ion channels. Why does injection of a local anesthetic into a finger still cause a loss of the sensation of touch from the finger?

Touch stimulation of this sensory receptor will open the mechanically gated ion channels, but action potentials are still not initiated because propagation of an action potential requires the opening of voltage-gated Na+ channels. (Propagation (spreading) of an action potential from the cell body to the axon hillock and eventually the axon terminals (synaptic knobs) requires the sequential opening of mechanically and voltage-gated ion channels. When the sequence is interrupted, the message cannot spread to the sensory regions of the central nervous system, causing numbness.)

True or False? A postsynaptic potential is a graded potential that is the result of a neurotransmitter released into the synapse between two neurons.

True

True or False? During depolarization, the inside of the neuron's membrane becomes less negative.

True

What mechanism is most significant in returning Na+ and K+ concentrations to resting ionic conditions (from point D to point E)?

active transport by the Na+-K+ pump (Maintenance (and restoration) of the resting ion concentrations depends on the Na+-K+ pump. Once gated ion channels are closed, the combined action of the pump and ion leakage (particularly that of K+) establishes a resting membrane potential in a typical neuron of around âˆ'70 mV.)

Which of the following is not a function of the autonomic nervous system? -innervation of skeletal muscle -innervation of cardiac muscle -innervation of glands -innervation of smooth muscle of the digestive tract

innervation of skeletal muscle

Which of the following stimuli caused the reaction in the graph on the left?

opening of gated Na+ channels (Opening of gated Na+ channels allows Na+ to diffuse into the neuron, causing an increase in the local membrane potential.)

What is expected to occur first if the membrane potential decrease shown in the graph on the left were to reach the threshold value indicated at ~ -55 mV?

opening of voltage-gated Na+ channels (The threshold value is the point at which voltage-sensitive Na+ channels open. This leads to the characteristic rapid depolarization phase of the action potential.)

In addition to diffusion, what are two other mechanisms that terminate neurotransmitter activity?

reuptake and degradation (To terminate neurotransmitter effects, neurotransmitter molecules must be removed from the synaptic cleft. Reuptake does this by moving neurotransmitter back into the presynaptic neuron. Diffusion causes neurotransmitter to drift away from the synaptic cleft. Degradation occurs when enzymes break down neurotransmitter. As long as neurotransmitter molecules remain in the synaptic cleft, the chemically gated channels on the postsynaptic cell will continue to bind them and cause graded potentials.)

Saltatory conduction is made possible by ________.

the myelin sheath

As you start working out, you notice that your heart rate and breathing rate start to increase. Which division of your nervous system is generating this response? Be as specific as possible.

the sympathetic division of the autonomic nervous system (The sympathetic division of the autonomic, or involuntary, nervous system consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands. This division is responsible for generating actions required during activity)