Chapter 48
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62 terms
Terms | Definitions |
|---|---|
 cone snail | The ____ kills prey with venom that disables neurons. |
| neurons | ___ are nerve cells that transfer information within the body. |
| electrical, chemical | ____ and ____ are the two types of signals neurons use to communicate. |
| path | The transmission of information depends on the ___ of neurons along which a signal travels. |
| ganglia, brain | Processing of information is done in ____ (simple clusters of neurons) and the ____ (complex organization of neurons) |
| organization, structure | Neuron ___ and ___ reflect function in information transfer. |
| squid | The ___ possesses extremely large nerve cells and is a good model for studying neuron function. |
| sensory input, integration, motor output | Nervous systems process information in three stages: ___, ___, and ___. |
| sensory neurons | Sensors detect external stimuli and internal conditions and transmit information along ____. |
| interneurons | Sensory information is sent to the brain or ganglia, where ____ integrate the information. |
| motor neurons | Motor output leaves the brain or ganglia via ____, which trigger muscle or gland activity. |
| central, peripheral | Many animals have a complex nervous system: A ___ nervous system (CNS) where integration takes place; this includes the brain and a nerve cord. A ___ nervous system (PNS), which brings information into and out of the CNS. |
| cell body, dendrites, axon | Most of a neuron's organelles are in the ____. Most neurons have ___, highly branched extensions that receive signals from other neurons. The ___ is typically a much longer extension that transmits signals to other cells at synapses. |
| axon hillock, synapse | An axon joins the cell body at the ___. A ____ is a junction between an axon and another cell. |
| synaptic terminal, neurotransmitters | The ___ of one axon passes information across the synapse in the form of chemical messengers called ____. |
| presynaptic, postsynaptic, glia | Information is transmitted from a ____ cell (a neuron) to a ____ cell (a neuron, muscle, or gland cell). Most neurons are nourished or insulated by cells called ___. |
| resting potential | Ion pumps and ion channels maintain the ___ of a neuron, which is the membrane potential of a neuron not sending signals. |
| membrane potential | Every cell has a voltage (difference in electrical charge) across its plasma membrane called a ____. Messages are transmitted as changes in this. |
| K, Na | In a mammalian neuron at resting potential: the concentration of ___+ is greater inside the cell while the concentration of __+ is greater outside the cell. |
| chemical potential energy | concentration gradients = ___ ____ ____ |
| ion channels | The opening of ____ in the plasma membrane converts chemical potential to electrical potential. |
| Na, K, anions | A neuron at resting potential contains many open K+ channels and fewer open __+ channels; __+ diffuses out of the cell. ___ trapped inside the cell contribute to the negative charge within the neuron. |
| action potentials | ___ are the signals conducted by axons. |
| gated ion channels | Neurons contain ____ that open or close in response to stimuli. |
| membrane potential | ____ changes in response to opening or closing of these channels. |
| negative, hyperpolarization | When gated K+ channels open, K+ diffuses out, making the inside of the cell more ___. This is ___, an increase in magnitude of the membrane potential. |
| depolarization | Other stimuli trigger a ____, a reduction in the magnitude of the membrane potential. For example, this occurs if gated Na+ channels open and Na+ diffuses into the cell. |
| graded potentials | ___ are changes in polarization where the magnitude of the change varies with the strength of the stimulus. |
| depolarizes, action potential | When a stimulus ____ the membrane, Na+ channels open, allowing Na+ to diffuse into the cell. The movement of Na+ into the cell increases the depolarization and causes even more Na+ channels to open. A strong stimulus results in a massive change in membrane voltage called an ____. |
| action potential | An ___ occurs if a stimulus causes the membrane voltage to cross a particular threshold. It is a brief all-or-none depolarization of a neuron's plasma membrane. They are also signals that carry information along axons. |
| neuron | A ___ can produce hundreds of action potentials per second, which can be broken down into a series of stages. |
| stimulus | The frequency of action potentials can reflect the strength of a ____. |
| resting potential | At ___, most voltage-gated Na+ and K+ channels are closed, but some K+ channels (not voltage-gated) are open. |
| rising, increases, falling | An action potential is generated: During the ___ phase, the threshold is crossed, and the membrane potential ___. During the ___ phase, voltage-gated Na+ channels become inactivated; voltage-gated K+ channels open, and K+ flows out of the cell. |
| undershoot | An action potential is generated: During the ___, membrane permeability to K+ is at first higher than at rest, then voltage-gated K+ channels close; resting potential is restored. |
| refractory period | During the ____ after an action potential, a second action potential cannot be initiated. This is a result of a temporary inactivation of the Na+ channels. |
| axon hillock | An action potential can travel long distances by regenerating itself along the axon. At the site where the action potential is generated, usually the ___, an electrical current depolarizes the neighboring region of the axon membrane. |
| inactivated Na+, synaptic terminals | ____ channels behind the zone of depolarization prevent the action potential from traveling backwards Action potentials travel in only one direction: toward the ___. |
| increases | The speed of an action potential ____ with the axon's diameter. |
| myelin sheath, increase | In vertebrates, axons are insulated by a ___, which causes an action potential's speed to ___. |
| glia | Myelin sheaths are made by ___— oligodendrocytes in the CNS and Schwann cells in the PNS. |
| nodes of ranvier | Action potentials are formed only at ___, gaps in the myelin sheath where voltage-gated Na+ channels are found. |
| saltatory conduction | Action potentials in myelinated axons jump between the nodes of Ranvier in a process called ____. |
| electrical synapses | At ___, the electrical current flows from one neuron to another. |
| chemical synapses | At ___, a chemical neurotransmitter carries information across the gap junction. These are the most common synapses. |
| presynaptic neuron, neurotransmitters, postsynaptic cell | The ___ synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal. The action potential causes the release of the ____, which diffuse across the synaptic cleft and are received by the ____. |
| direct synaptic transmission | ____ ___ ___ involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell. |
| neurotransmitter, postsynaptic potential | ___ binding causes ion channels to open, generating a ____. |
| excitatory postsynaptic potentials, inhibitory postsynaptic potentials | Postsynaptic potentials fall into two categories: ____ are depolarizations that bring the membrane potential toward threshold. ____ are hyperpolarizations that move the membrane potential farther from threshold. |
| postsynaptic potentials | Unlike action potentials, ____ are graded and do not regenerate. |
| dendrites, cell body | Most neurons have many synapses on their ___ and ___. |
| temporal summation | A single excitatory postsynaptic potential is usually too small to trigger an action potential in a postsynaptic neuron. If two EPSPs are produced in rapid succession, an effect called ___ occurs. |
| spatial summation | In ___, EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together. Through this, an IPSP can counter the effect of an EPSP. |
| action potential | The summed effect of EPSPs and IPSPs determines whether an axon hillock will reach threshold and generate a(n) ___. |
| indirect synaptic transmission | In ____, a neurotransmitter binds to a receptor that is not part of an ion channel. This binding activates a signal transduction pathway involving a second messenger in the postsynaptic cell. Effects of this have a slower onset but last longer. |
| neurotransmitters | ___ can produce different effects in different types of cells. |
| acetylcholine | _____ is a common neurotransmitter in vertebrates and invertebrates (for vertebrates it is usually an excitatory transmitter) |
| biogenic amines | ____ are epinephrine, norepinephrine, dopamine, and serotonin. They are active in the CNS and PNS. |
| amino acids | ___: two are known to function as major neurotransmitters in the CNS: gamma-aminobutyric acid (GABA) and glutamate. |
| neuropeptides, neurotransmitters, opiates | ____ are (several) relatively short chains of amino acids, which also function as ____. They include substance P and endorphins, which both affect our perception of pain. ___ bind to the same receptors as endorphins and can be used as painkillers. |
| gases | ___: e.g. nitric oxide and carbon monoxide: are local regulators in the PNS. |
| synaptic cleft, cells, enzymes | After release, the neurotransmitter may diffuse out of the ____, be taken up by surrounding ___, or be degraded by ___. |
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