Chapter 48 Neurons Synapses and Signaling Power Point

Chapter 48 Neurons, Synapses, and Signaling Power. Point® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Overview: Lines of Communication • Neurons are nerve cells that transfer information within the body • Neurons use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance) • The transmission of information depends on the path of neurons along which a signal travels • Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brain Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 48 -3 Sensory input Integration Sensor Motor output Effector Peripheral nervous system (PNS) Central nervous system (CNS)

Fig. 48 -4 Dendrites Stimulus Nucleus Cell body Axon hillock Presynaptic cell Axon Synapse Synaptic terminals Postsynaptic cell Neurotransmitter

Fig. 48 -5 Dendrites Axon Cell body Portion of axon Sensory neuron Interneurons Cell bodies of overlapping neurons 80 µm Motor neuron

Concept 48. 2: Membrane & Resting Potential • Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential – Messages are transmitted as changes in membrane potential • The resting potential is the membrane potential of a neuron not sending signals – Ion pumps and ion channels maintain the resting potential of a neuron Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

The Resting Potential • The resting potential is the membrane potential of a neuron that is not transmitting signals • In all neurons, the resting potential depends on the ionic gradients that exist across the plasma membrane EXTRACELLULAR FLUID CYTOSOL [Na+] 15 m. M – + [Na+] 150 m. M [K+] 150 m. M – + [K+] 5 m. M – + 10 m. M – [Cl–] + 120 m. M [A–] 100 m. M – + [Cl–] Plasma membrane Figure 48. 10 Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 48 -6 Key Na+ K+ OUTSIDE CELL OUTSIDE [K+] CELL 5 m. M INSIDE [K+] CELL 140 m. M [Na+] [Cl–] 150 m. M 120 m. M [Na+] 15 m. M [Cl–] 10 m. M [A–] 100 m. M INSIDE CELL (a) (b) Sodiumpotassium pump Potassium channel Sodium channel

Concept 48. 3: Action Potentials • Action potentials are the signals conducted by axons • Neurons contain gated ion channels that open or close in response to stimuli – Membrane potential changes in response to opening or closing of these channels Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 48 -9 http: //bcs. whfreeman. com/thelifewire/content/chp 44/4402 s. swf Stimuli +50 0 Threshold +50 0 – 50 Resting potential Threshold Resting potential 0 1 2 3 4 5 Time (msec) (a) Graded hyperpolarizations – 100 Action potential 0 – 50 Threshold Resting potential Depolarizations Hyperpolarizations – 100 Membrane potential (m. V) +50 – 50 Strong depolarizing stimulus – 100 0 1 2 3 4 Time (msec) (b) Graded depolarizations 5 0 (c) Action potential 1 2 3 4 5 Time (msec) 6

Generation of Action Potentials: A Closer Look • A neuron can produce hundreds of action potentials per second • The frequency of action potentials can reflect the strength of a stimulus • An action potential can be broken down into a series of stages Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 48 -10 -5 Key Na+ K+ 3 4 Rising phase of the action potential Falling phase of the action potential Membrane potential (m. V) +50 Action potential – 50 2 2 4 Threshold 1 1 5 Resting potential Depolarization Extracellular fluid 3 0 – 100 Sodium channel Time Potassium channel Plasma membrane Cytosol Inactivation loop 5 1 Resting state Undershoot

Fig. 48 -11 -3 - http: //highered. mcgraw-hill. com/sites/0072495855/student_view 0/chapter 14/animation__the_nerve_impulse. html Axon Plasma membrane Action potential Cytosol Na+ K+ Action potential Na+ K+

Fig. 48 -12 Node of Ranvier Layers of myelin Axon Schwann cell Axon Nodes of Myelin sheath Ranvier Schwann cell Nucleus of Schwann cell 0. 1 µm

Fig. 48 -13 Schwann cell Depolarized region (node of Ranvier) Cell body Myelin sheath Axon

Synapses – Communication Between Neurons • Neurons communicate with other cells at synapses • The vast majority of synapses – Are chemical synapses • In a chemical synapse, a presynaptic neuron releases chemical neurotransmitters, which are stored in the synaptic terminal Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Fig. 48 -15 http: //bcs. whfreeman. com/thelifewire/content/chp 44/4402003. html 5 Synaptic vesicles containing neurotransmitter Voltage-gated Ca 2+ channel 1 Ca 2+ Synaptic cleft Presynaptic membrane Postsynaptic membrane 4 2 3 Ligand-gated ion channels 6 K+ Na+

Synapses – Communication Between Neurons • After release, the neurotransmitter – May diffuse out of the synaptic cleft – May be taken up by surrounding cells – May be degraded by enzymes Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Neurotransmitters • The same neurotransmitter can produce different effects in different types of cells • There are five major classes of neurotransmitters: – acetylcholine, – biogenic amines, – amino acids, – neuropeptides, – and gases Copyright © 2008 Pearson Education, Inc. , publishing as Pearson Benjamin Cummings

Table 48 -1