1. © 2017 Pearson Education, Inc.

2. Concept 48.1: Neuron structure and organization reflect function in information transfer
Neurons are nerve cells that transfer information within the body
Neurons use two types of signals to communicate:
Electrical signals (long-distance)
Chemical signals (short-distance)
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3. Neuron Structure and Function
Most of a neuron’s organelles are in the cell body
Most neurons have dendrites, highly branched extensions that receive signals from other neurons
The axon is typically a much longer extension that transmits signals to other cells at synapses\
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4. Neuron Structure and Function
A synapse is a junction between an axon and another cell
The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters
Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell)
Most neurons are nourished or insulated by cells called glia, or glial cells
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5. Dendrites Axon hillock Nucleus Cell body Axon Presynaptic cell Synapse
terminals
Synaptic
terminal
Figure 48.2 Neuron structure
Synaptic
terminals
Postsynaptic
cell
Postsynaptic cell
Neurotransmitter

6. Introduction to Information Processing
Nervous systems process information in three stages:
Sensory neurons transmit information about external stimuli such as light, touch, or smell
Interneurons integrate (analyze and interpret) the information
Motor neurons transmit signals to muscle cells, causing them to contract
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7. Introduction to Information Processing
Many animals have a complex nervous system that consists of:
A central nervous system (CNS), where integration takes place; this includes the brain and a nerve cord
A peripheral nervous system (PNS), which carries information into and out of the CNS
The neurons of the PNS, when bundled together, form nerves
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8. Cell body Dendrites Axon Sensory neuron Interneuron Motor neuron
Figure 48.5 Structural diversity of neurons
Motor neuron

9. Concept 48.2: Ion pumps and ion channels establish the resting potential of a neuron
Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential
The resting potential is the membrane potential of a neuron not sending signals
Changes in membrane potential are called action potentials
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10. Formation of the Resting Potential
In most neurons, the concentration of K+ is higher inside the cell, while the concentration of Na+ is higher outside the cell
Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane
These concentration gradients represent chemical potential energy
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11. Formation of the Resting Potential
The opening of ion channels in the plasma membrane converts chemical potential to electrical potential
A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell
The resulting buildup of negative charge within the neuron is the major source of membrane potential
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12. OUTSIDE OF CELL INSIDE OF CELL Na+ Sodium- potassium pump Potassium
Figure 48.6 The basis of the membrane potential
INSIDE OF CELL
Na+
Sodium-
potassium
pump
Potassium
channel
Sodium
channel K+

13. Generation of Action Potentials: A Closer Look
An action potential results from changes in membrane potential as ions move through voltage- gated channels
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14. Axon Plasma Action membrane potential Cytosol Action potential Action
Na+
Cytosol
Action
potential K+
Na+
Figure 48.12_3 Conduction of an action potential (step 3) K+
Action
potential K+
Na+ K+

15. Evolutionary Adaptations of Axon Structure
The speed of an action potential increases with the axon’s diameter
In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase
Voltage-gated sodium channels are restricted to nodes of Ranvier, gaps in the myelin sheath
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16. Node of Ranvier Layers of myelin Axon Schwann cell Schwann cell Axon
Nucleus of
Schwann cell
Nodes of
Ranvier
Myelin sheath
0.1 µm
Figure Schwann cells and the myelin sheath

17. Schwann cell Depolarized region (node of Ranvier) Cell body Myelin
sheath
Axon
Figure Propagation of action potentials in myelinated axons

18. Concept 48.4: Neurons communicate with other cells at synapses
At chemical synapses (which most are), a chemical neurotransmitter carries information between neurons
The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal
The action potential causes the release of the neurotransmitter
The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell
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19. Presynaptic cell Postsynaptic cell Axon Synaptic vesicle containing
neurotransmitter
Synaptic
cleft
Postsynaptic
membrane
Presynaptic
membrane
Figure A chemical synapse K+
Ca2+
Voltage-gated
Ca2+ channel
Ligand-gated
ion channels
Na+

20. Termination of Neurotransmitter Signaling
After a response is triggered, the chemical synapse returns to its resting state
The neurotransmitter molecules are cleared from the synaptic cleft
Blocking this process can have severe effects
The nerve gas sarin triggers paralysis and death due to inhibition of the enzyme that breaks down the neurotransmitter controlling skeletal muscles
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21. Enzymatic breakdown of neurotransmitter in the synaptic cleft
PRESYNAPTIC NEURON
Neurotransmitter
Fragments
of inactivated
neurotransmitter
Neurotransmitter
receptor
POSTSYNAPTIC NEURON
Inactivating enzyme
Enzymatic breakdown of neurotransmitter in the synaptic cleft
Figure Two mechanisms of terminating neurotransmission
Neurotransmitter
Neurotransmitter
transport channel
Neurotransmitter
receptor
Reuptake of neurotransmitter by presynaptic neuron

22. Neurotransmitters
A single neurotransmitter may bind specifically to more than a dozen different receptors
Following is a sample of common neurotransmitters
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23. 1. Acetylcholine
Acetylcholine is a common neurotransmitter in vertebrates and invertebrates
involved in muscle stimulation, memory formation, and learning
A number of toxins disrupt acetylcholine neurotransmission
These include the nerve gas sarin and the botulism toxin produced by certain bacteria
Insecticide poisoning
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24. 2. Amino Acids
Glutamate is one of several amino acids that can act as a neurotransmitter, in vertebrates and invertebrates
Gamma-aminobutyric acid (GABA) is the neurotransmitter at most inhibitory(releases) synapses in the brain
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25. 3. Biogenic Amines
Have a central role in a number of nervous system disorders
Parkinson’s disease is associated with a lack of dopamine in the brain
Examples include:
Serotonin: “Happy Molecule”
Dopamine: Reward, motivation and attention
Epinephrine: Stimulant
Norepinephrine: Alertness in the brain
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26. 4. Neuropeptides Relatively short chains of amino acids, including:
Substance P: perception of pain and inflammation response
Endorphins: perception of pain and euphoria
Opiates bind to the same receptors as endorphins and can be used as painkillers and are highly addictive
Morphine
Fentanyl
Oxycodone
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27. 5. Gases
Gases such as nitric oxide (NO) are local regulators in the PNS
Unlike most neurotransmitters, NO is not stored in cytoplasmic vesicles, but is synthesized on demand
Important in vasodilation of blood vessels
It is broken down within a few seconds of production
Although inhaling CO can be deadly, the vertebrate body synthesizes small amounts of it, some of which is used as a neurotransmitter
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