Figure 48.1a

Figure 48.1b

CONCEPT 48.1: Neuron structure and organization reflect function in information transfer

Neuron Structure and Function

A synapse is a junction between an axon and another cellThe part of each axon branch that forms this junction is a synaptic terminalAt most synapses, chemical messengers called neurotransmitters pass information from the transmitting neuron to the receivi

Figure 48.2

Lines of Communication

Introduction to Information Processing

Sensory neurons transmit information about external stimuli such as light, touch, or smellInterneurons integrate (analyze and interpret) the informationMotor neurons transmit signals to muscle cells, causing them to contract

Figure 48.3

Interpreting signals in the nervous system involves sorting a complex set of paths and connectionsThe shape of a neuron can vary from simple to quite complex, depending on its role in information processingWhen grouped together, the axons of neurons form

Figure 48.3

Sensory neurons transmit information about external stimuli such as light, touch, or smellInterneurons integrate (analyze and interpret) the informationMotor neurons transmit signals to muscle cells, causing them to contract

Introduction to Information Processing

Lines of Communication

Figure 48.2

Lines of Communication

Introduction to Information Processing

Sensory neurons transmit information about external stimuli such as light, touch, or smellInterneurons integrate (analyze and interpret) the informationMotor neurons transmit signals to muscle cells, causing them to contract

Figure 48.3

Interpreting signals in the nervous system involves sorting a complex set of paths and connectionsThe shape of a neuron can vary from simple to quite complex, depending on its role in information processingWhen grouped together, the axons of neurons form

Figure 48.4

Many animals have a complex nervous system that consists ofA central nervous system (CNS), where integration takes place; this includes the brain or simpler clusters called gangliaA peripheral nervous system (PNS), which carries information into and out o

Figure 48.5

Video: Dendrites of a Neuron

CONCEPT 48.2: Ion pumps and ion channels establish the resting potential of a neuron

Formation of the Resting Potential

Table 48.1

Figure 48.6

Ion channels are pores that span the plasma membrane, and allow ions to diffuse back and forth across the membraneConcentration gradients of ions across a membrane represent a form of potential energy that can be harnessed for cellular processesIon channe

A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cellThe resulting build up of negative charge within the neuron is the major source of membrane potential

Figure 48.7

BioFlix® Animation: Resting Potential

** after 神經.pptx

BioFlix® Animation: Resting Potential

Animation: Membrane Potentials

** after 神經.pptx

Animation: Membrane Potentials

Modeling the Resting Potential

Animation: Membrane Potentials

Modeling the Resting Potential

Figure 48.8a

The equilibrium potential (Eion) is the membrane voltage for a particular ion at equilibrium and can be calculated using the Nernst equation:

Figure 48.8b

In a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steady

CONCEPT 48.3: Action potentials are the signals conducted by axons

Figure 48.9

Figure 48.10

Hyperpolarization and Depolarization

Figure 48.11a

Opening other types of ion channels triggers a depolarization, a reduction in the magnitude of the membrane potentialFor example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the cell

Figure 48.11b

Graded Potentials and Action Potentials

Action potentials have a constant magnitude, are all-or-none, and transmit signals over long distancesThey arise because some ion channels are voltage-gated, opening or closing when the membrane potential passes a certain level called threshold

Figure 48.11

Generation of Action Potentials: A Closer Look

Figure 48.12_1

Generation of Action Potentials: A Closer Look

Figure 48.12_1

When an action potential is generated,Voltage-gated Na+ channels open first, and Na+ flows into the cellDuring the rising phase, the threshold is crossed, the membrane potential increases close to ENa During the falling phase, voltage-gated Na+ channels b

Figure 48.12_2

Figure 48.12_3

Figure 48.12_2

Figure 48.12_3

Figure 48.12_4

During the undershoot, membrane permeability to K+ is at first higher than at rest, then voltage-gated K+ channels close and resting potential is restored

Figure 48.12_5

BioFlix® Animation: Action Potential

** after 神經.pptx

BioFlix® Animation: Action Potential

index 2

Conduction of Action Potentials

Figure 48.13

The rate at which action potentials are produced in a neuron is proportional to input signal strengthGated ion channels and action potentials play a central role in nervous system activityMutations in genes that encode ion channels lead to disorders affe

BioFlix® Animation: Conduction of an Action Potential

Evolutionary Adaptations of Axon Structure

Figure 48.14

Voltage-gated sodium channels are restricted to nodes of Ranvier, gaps in the myelin sheath Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction

Figure 48.15

CONCEPT 48.4: Neurons communicate with other cells at synapses

The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminalThe action potential causes the release of the neurotransmitter The neurotransmitter diffuses across the synaptic cleft and is receiv

Figure 48.16

BioFlix® Animation: How Synapses Work

** after 神經.pptx

BioFlix® Animation: How Synapses Work

Generation of Postsynaptic Potentials

Postsynaptic potentials fall into two categoriesExcitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward thresholdInhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane poten

Summation of Postsynaptic Potentials

Individual postsynaptic potentials can combine to produce a larger potential in a process called summationIf two P S P s are produced in rapid succession, an effect called temporal summation occurs

In spatial summation, E P S P s produced nearly simultaneously by different synapses on the same postsynaptic neuron add together The combination of E P S P s through spatial and temporal summation can trigger an action potential

Through summation, an I P S P can counter the effect of an E P S PThe summed effect of E P S P s and I P S P s determines whether an axon hillock will reach threshold and generate an action potential

Figure 48.17

Animation: Action Potentials

Termination of Neurotransmitter Signaling

Clearing neurotransmitter from the synaptic cleft is an essential step in nervous system transmissionBlocking this process can have severe effectsThe nerve gas sarin triggers paralysis and death due to inhibition of the enzyme that breaks down the neurotr

Figure 48.18

Modulated Signaling at Synapses

Binding of a neurotransmitter to a metabotropic receptor activates a signal transduction pathway in the postsynaptic cell involving a second messengerThe signal transduction pathway leads to amplification such that many channels can be opened or closed in

Neurotransmitters

Acetylcholine

A number of toxins disrupt acetylcholine neurotransmissionThese include nicotine, the nerve gas sarin, and the botulinium toxin produced by certain bacteriaAcetylcholine is just one of more than 100 known neurotransmittersThe remainder fall into four clas

index 103

Amino Acids

Biogenic Amines

Neuropeptides

Gases

Although inhaling C O can be deadly, the vertebrate body synthesizes small amounts of it, some of which is used as a neurotransmitter

Gases

Although inhaling C O can be deadly, the vertebrate body synthesizes small amounts of it, some of which is used as a neurotransmitter

Figure 48.UN01

Figure 48.UN01

Figure 48.UN02

Figure 48.UN01

Figure 48.UN02

Figure 48.UN01

Figure 48.UN01

Although inhaling C O can be deadly, the vertebrate body synthesizes small amounts of it, some of which is used as a neurotransmitter

Gases

Neuropeptides

Biogenic Amines

Amino Acids

Table 48.2

A number of toxins disrupt acetylcholine neurotransmissionThese include nicotine, the nerve gas sarin, and the botulinium toxin produced by certain bacteriaAcetylcholine is just one of more than 100 known neurotransmittersThe remainder fall into four clas

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