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88 terms

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.