CHAPTER 48  NEURONS, SYNAPSES, & SIGNALING 48.1  Neuron organization & Structure I. Intro to information processing A. Processing 1. Sensory input a. Sensory neurons 1. Transmits information into the processing centers of brain and ganglia 2. Integration a. Analyze & interpret b. Interneurons 1. localized communication 2. Neuron  neuron 3. Motor output a. Motor neurons 1. Transmits info from processing centers to body B. Organization 1. Central nervous system (CNS) 2. Peripheral nervous system (PNS)

II. Neuron structure & function 48.2  Ion pumps, ion channels & resting potential I. Resting potential A. The cell is more negative inside than outside II. Formation of resting potential A. Na + /K + pump, K + ion channels, Na + ion channels 1. Na + /K + pump actively pumps K + in and Na + out a. More Na + pumped out than K + in b. More open K + channels than Na + channels keeping levels of Na + high outside & low inside c. Cl - and other anions cannot cross membrane 2. A slightly negative charge inside and positive charge outside

48.3  Action potentials are the signals conducted by axons I. Gated ion channels A. Ion channels that open or close in response to stimuli 1. Opening and closing of channels alters membrane permeability to ions a. Alters [ ] of ions across membrane b. Alters membrane potential

B. Opening K + gated ion channels 1. Hyperpolarization 2. Net diffusion of K + out of the cell a. Inside of cell becomes more negative than resting potential C. Opening Na + gated ion channels 1. Deplorization 2. Net diffusion of Na + into the cell a. Inside of cell becomes less negative than the resting potential

II. Production of action potentials A. Action potential 1. The rapid change in the membrane potential by a stimulus causing voltage- gated ion channels to open or close 2. “Nerve impulses/signals” B. A closer look 1. Resting state a. Most voltage-gated channels are closed b. Na + /K + pump is maintaining resting potential

2. Depolarization a. Stimulus received b. Na + voltage-gated channels open allowing inflow of Na + causing depolarization 1. positive feedback system 3. Rising phase a. Threshold reached increasing positive feedback b. K + voltage gated channels still closed c. Inside of cell becomes positive, outside becomes negative

4. Falling phase a. Na + voltage-gated channels become inactivated (not closed) 1. Unable to respond to 2 nd depolarization stimulus a. Refractory period b. K + voltage-gated channels open c. Inside of cell becomes negative again and outside becomes negative

5. Undershoot a. Na + voltage-gated channels close but some K + voltage-gated channels remain open causing hyperpolarization b. Membrane potential returns to resting 1. depolarization can now occur again if stimulus received

III. Conduction of Action Potential A. Conduction speed 1. Axon Diameter 2. Myelin sheath a. Lipid insulation

1. Saltatory conduction 48.4  Neurons communicate w/ other cells at synapses I. Transmission of impulse from cell to cell

II. Generation of postsynaptic potentials A. Excitatory postsynaptic potentials (EPSPs) 1. Neurotransmitters that cause depolarization of postsynaptic cells 2. increase permeability to K + & Na + B. Inhibitory postsynaptic potentials (IPSPs) 1. Neurotransmitters that cause hyperpolarization of postsynaptic cell 2. increase permeability to K + & Cl - III. Summation of postsynaptic potentials A. Temporal summation 1. 2 nd EPSP received before resting potential reached after 1 st EPSP a. 2 EPSPs added together

B. Spatial 1. Multiple EPSPs received simultaneously from different synapses a. EPSPs added together IV. Modulated synaptic transmission A. Signal transduction pathways 1. Slower but longer lasting response

V. Neurotransmitters A. Acetylcholine 1. One of the most common 2. Main target = Skeletal muscles 3. Main affect = excitation  muscle contraction a. Inhibitory to cardiac muscle 4. Nicotine/botulism B. Biogenic Amines 1. Norepinephrine a. Neurotransmitter & hormone b. Main target = Autonomic nervous system 1. Control of internal env. a. Smooth & cardiac, digestive, cardiovascular, excretion, & endocrine c. Main affect = excitation d. Acts through a G protein-coupled receptor 2. Dopamine & Serotonin a. Released in brain b. Main affect = Sleep, mood, attention, learning 1. Ritalin  increases levels of dopamine

C. Neuropeptides 1. Work through signal transduction pathways 2. Endorphins a. Decrease pain perception