Nervous System 2

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Synapses

Neurons communicate with other cells at junctions called ______.

muscles, glands, and other neurons

Neurons form synapses with _______, ________, and ________ ________.

neuromuscular junction

A synapse between a somatic motor neuron and a skeletal muscle fiber is called a ________ ________.

contract

When an action potential arrives at a neuromuscular junction, it initiates a series of events which excite the underlying muscle fiber, causing it to ______.

two neuron chain

Signals in the autonomic nervous system travel over a ____ _____ _____ to their effector organ. The second neuron, or autonomic motor neuron, contacts the organ.

secrete

Signals from the central nervous system can cause glands to _______.

effector organs

In addition to sending signals to _______ _______, neurons send signals to each other.

dendrites, soma, or axon

In the brain, a variety of synapses have evolved to serve complex transmission needs between neurons. Synapses located between axon terminals of one neuron and ______, ______, or ______ of another are most common.

electrical & chemical

There are two major types of synapses, ________ and ________.

electrical synapse

Electrical synapses depolarize and generate action potentials simultaneously. When one neuron forms a gap junction with another neuron, an _________ _________ is made.

gap junction

Electrical current, in the form of ions, flows directly from one neuron to the other through the ______ _______.

excitatory

Electrical synapses are always __________.

2 advantages of electrical synapse

1. fast signal transmission between neurons. 2. signal transmission to a gruop of electricaly cupled neurons can synchronize their activity.

synaptic cleft

At a chemical synapse, neuronal membranes are separated by a gap called the ______

neurotransmitter

Electrical current cannot flow directly from one neuron to the other. A chemical, called a ____________, is released from the sending axon and carries the signal to the next neuron.

electrical synapse, excitatory, inhibitory

Chemical synapses transmit signals more slowly than __________ ________ but the signal may be either ________ or __________, and the signal can be modified as it passes from one neuron to the next.

synapse,learning and memory

Chemical synapses are the most common type of ________, and they are associated with the most complex human behaviors, including __________ and ____________.

presynaptic neuron

The neuron conducting an action potential toward the synapse is called the ________ _______ .

synaptic vesicles, neurotransmitter

The axon terminal of the presynaptic neuron contains membranous sacs called _________ ________ which are filled with ______________.

synaptic cleft

The gap separating the cells is called the ________ _______.

neurotransmitter, synaptic cleft

An action potential that reaches the axon terminal causes synaptic vesicles, to fuse with it, releasing ____________ into the _________ _________.

ion channels

The neuron receiving the signal is called the postsynaptic neuron. When activated, receptors on the postsynaptic neuron open ____ _________.

synaptic potential, synaptic potential

The movement of ions across the neuronal membrane creates an electrical signal called a ________ __________. ___________ _________ vary in amplitude and travel only a short distance. Thus they are very different from action potentials.

neurotransmitters

At synapses, ions move across cell membranes through chemically-gated channels. The gates are opened or closed by __________.

dendrites, the cell body and the axon

Nongated channels are located in the cell membrane on the ______, _______, and the ______.

resting membrane potential

Nongated channels are responsible for establishing the ______ _________ ________.

dendrites and cell body

Most chemically-gated channels are located on the _________, and the _____ ______.

synaptic potentials

Chemically-gated channels are responsible for producing _______ _______.

axon hillock, unmyelinated axons, nodes of ranvier

Most voltage-gated channels are found on the _______ ________, all along __________ _____, and at the in _____ ___ ________ in myelinated axons.

action potentials

Voltage-gated channels are responsible for generation and propagation of the _______ _______.

open, close

Binding neurotransmitter to a receptor on the postsynaptic cell causes a change in the shape of the receptor. This can ______, or in some cases ______, the ion channel.

postsynaptic cell

Neurotransmitters that bind to ion channels are said to act directly. They cause a brief, rapid change in the membrane potential of the _____________ ______.

excitatory postsynaptic potential, ESPS

An __________ __________ __________, or ______, is produced when the movement of ions makes the inside of the cell more positive.

into the cell & out of the cell

Ion channels at a typical excitatory synapse are specific for cations, having a watery pore large enough to pass both sodium and potassium. In a resting neuron, the electrochemical gradient for sodium is very large and causes sodium to move ______ _____ _____. The electrochemical gradient for potassium causes it to move ____ ____ ____, but the gradient is very small.

depolarize

Excitatory postsynaptic potentials ___________ neurons

threshold

If the neuron is depolarized to ___________, an action potential is generated

inhibitory postsynaptic potential, IPSP

An ___________ __________ __________, or ________, is produced when the movement of ions makes the inside of the cell more negative.

hyperpolarize, negative

Ion channels at a typical inhibitory synapse are specific for chloride and the electrochemical gradient for chloride causes it to move into the cell. Inhibitory postsynaptic potentials _________ neurons making the membrane potential more _________.

pending

Some neurotransmitters bind to receptors that are separate from ion channels. This process most often leads to production of ______________ __________ _________, which ultimately alter ion channels. Such neurotransmitters are said to act indirectly.

g protein

The receptor is coupled to the ion channel by a ___ __________.

enzyme

Part of the activated G protein travels in the membrane and activates an ________, which induces production of a second messenger.

neurotransmitter

The _______________ is the first messenger.

phosphorylates

The second messenger activates an intracellular enzyme, which __________ a potassium ion channel and closes it.

potassium

In the resting neuron, movement of _________ out of the cell acts to hyperpolarize the cell.

less negative and depolarizing

Closing these channels results in the membrane potential becoming ____ ______ and _________ the cell.

depolarization & synaptic potential

__________ of the cell by the indirect method is time consuming. The resulting __________ __________ is slow in onset, and long in duration.

acetylcholine,glutamate,gaba,and serotoinin

Besides excitation, indirectly-acting neurotransmitters can also produce slow inhibition. The neurotransmitters __________, _________, ______, and ______ can act indirectly as well as directly, depending on the receptor to which they bind.

norepinephrine, epinephrine&dopamine

The catecholamines (____________, _________, and __________) and peptide neurotransmitters only act indirectly.

1

An action potential in the axon terminal causes voltage-gated calcium channels to open and calcium to enter the terminal.

2

The presence of calcium inside the cell causes the synaptic vesicles to fuse with the membrane.

3

Each vesicle releases a fixed amount of neurotransmitter into the synaptic cleft.

4

Neurotransmitter diffuses across the synaptic cleft.

5&6

Neurotransmitter binds to a receptor on the postsynaptic neuron where it can act. Most often, the neurotransmitter is pumped back into the presynaptic terminal and into nearby glial cells.

postsynaptic neuron

Neurotransmitter binds to a receptor on the ___________ __________ where it can act directly or indirectly.

neurotransmitter

Chemically-gated ion channels remain open as long as the ___________ is bound to the receptor, and are not sensitive to changes in the membrane potential.

depolarize, hyperpolarize

Synaptic current, or ion movement through chemically-gated channels, may _____________ or ___________ the neuron.

neurotransmitter

Synaptic transmission ends when the _____________ dissociates from the receptor and is removed from the synaptic cleft.

presynaptic neuron

Most often, the neurotransmitter is pumped back into the __________ __________and into nearby glial cells.

acetyl choline

In some cases, the neurotransmitter is broken down by enzymes, and the breakdown products are taken up by the presynaptic cell. The neurotransmitter __________ ___________ is an example of this process.

presynaptic terminal

When breakdown products are transported into the ____________ __________, they are used to resynthesize neurotransmitter.

postsynaptic neuron

We have examined the mechanism of synaptic transmission. Now let's look at the consequences of synaptic activity on the postsynaptic cell. The action of the ______________ _______ depends on which neurotransmitter is involved, and the specific receptor found on that cell.

pending

Each such ______________ activates a different ion channel, causing a different effect in the postsynaptic cell.

nicotine,muscarine

There are two families of cholinergic receptors, which bind acetylcholine. One family is also activated by the chemical ________; the other family is also activated by the chemical __________.

nicotinic

The __________ cholinergic receptor, or nACh receptor, is the ion channel found at the neuromuscular junction.

nicotinic

At this receptor, acetylcholine acts directly to open these channels, producing a fast excitatory postsynaptic potential. Acetylcholine is excitatory at ________ receptors. It causes skeletal muscle to contract.

muscarinic

Some subtypes of __________ acetylcholine receptor, or mACh receptors, are found in the central nervous system and on most effector organs of the parasympathetic branch of the nervous system.

nAcCh

Acetylcholine acts indirectly at these _____ receptors producing a slow excitatory postsynaptic potential.

pending

Acetylcholine is excitatory at these ____________ receptors, causing neurons to fire action potentials, and smooth muscle to contract.

heart

Other subtypes of mACh receptor are found in the central nervous system and in the

slow inhibition, decreases

Acetylcholine acts indirectly at these receptors, producing a _______ ___________of the postsynaptic cells. In the heart, this effect _________ the heart rate.

hyperpolarize

Acetylcholine is inhibitory at these muscarinic receptors, causing postsynaptic cells to _________ and the heart to slow down.

postsynaptic neuron

The action of acetylcholine may be excitatory or inhibitory. The effect depends on which receptor is present on the _________ _______.

alpha, beta

There are two families of receptors for the neurotransmitter norepinephrine, _______ receptors and ______ receptors.

adrenergic

These are called _________ receptors, and norepinephrine acts indirectly when binding to them.

SNS

Both alpha and beta adrenergic receptors are found in the central nervous system, and more importantly, on effector organs of the _____________ ___________ ___________.

blood vessels

Norepinephrine acts indirectly at alpha-one receptors to produce slow excitation. This causes smooth muscle to contract. Alpha-one receptors are located on ______ ______, which supply the skin, mucosae, and abdominal viscera. Norepinephrine is excitatory at alpha one receptors.

Heart rate

Norepinephrine also acts indirectly at beta-one receptors in the heart to produce slow excitation. ________ ______ and strength of contraction increase. Norepinephrine is excitatory at beta one receptors.

skeletal

Beta two receptors located on the respiratory airways, and blood vessels that supply _________ muscle and heart cause dilation. Epinephrine from the adrenal medulla is more potent than norepinephrine, and both are inhibitory at beta two receptors.

acetyl choline, norepinephrine

We have learned that ________ ________ and _______________ are found in the central nervous system and at effector organs of the nervous system.

acetylcholine, cholinergic, nACh

Motor neurons of the somatic nervous system release __________. They are __________. Skeletal muscles bear ____ receptors.

excitatory

Thus the action of acetylcholine on skeletal muscle is direct, fast, and _________.

cholinergic

The first of two neurons in the sympathetic chain, the preganglionic neuron, is

cholinergic

The first of two neurons in the parasympathetic chain, the preganglionic neuron, is also ________.

nACh

The second neuron, or ganglionic neuron, in both the sympathetic and parasympathetic chains, has ______ receptors.

norepinephrine, adrenergic

Sympathetic ganglionic neurons release ___________. They are _________. a. norepinephrine, adrenergic b. acetyl choline, cholinergic

acetyl choline, cholinergic

Parasympathetic ganglionic neurons release ___________. They are __________.

sodium, potassium

Glutamate is the most common and most potent excitatory neurotransmitter in the central nervous system. Glutamate acts directly on ion channels that permit passage of both _______ and _______, producing fast excitatory postsynaptic potentials.

chloride

The major inhibitory neurotransmitters in the central nervous system are GABA and glycine. Like GABA, glycine binds to receptors which directly open ___________ channels, producing fast inhibitory postsynaptic potentials.

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