CHAPTER 48 NEURONS, SYNAPSES, & SIGNALING

48.1 Neuron organization & StructureI. Intro to information processing

A. Processing1. Sensory input

a. Sensory neurons1. Transmits information into the processing centers of brain and ganglia

2. Integrationa. Analyze & interpret b. Interneurons

1. localized communication2. Neuronneuron

3. Motor outputa. Motor neurons

1. Transmits info from processing centers to body

B. Organization1. Central nervous system (CNS)2. Peripheral nervous system (PNS)

II. Neuron structure & function

48.2 Ion pumps, ion channels & resting potentialI. Resting potential

A. The cell is more negative inside than outsideII. Formation of resting potential

A. Na+/K+ pump, K+ ion channels, Na+ ion channels1. Na+/K+ pump actively pumps K+ in and Na+ out

a. More Na+ pumped out than K+ inb. More open K+ channels than Na+ channels keeping levels of Na+ high

outside & low insidec. 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 axonsI. Gated ion channels

A. Ion channels that open or close in response to stimuli1. Opening and closing of channels alters membrane permeability to ions

a. Alters [ ] of ions across membraneb. Alters membrane potential

B. Opening K+ gated ion channels1. Hyperpolarization2. Net diffusion of K+ out of the cell

a. Inside of cell becomes more negative than resting potential

C. Opening Na+ gated ion channels1. Deplorization2. Net diffusion of Na+ into the cell

a. Inside of cell becomes less negative than the resting potential

II. Production of action potentialsA. 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 look1. Resting state

a. Most voltage-gated channels are closedb. Na+/K+ pump is maintaining resting potential

2. Depolarizationa. Stimulus receivedb. Na+ voltage-gated channels open allowing inflow of Na+ causing

depolarization1. positive feedback system

3. Rising phasea. Threshold reached increasing positive feedbackb. K+ voltage gated channels still closedc. Inside of cell becomes positive, outside becomes negative

4. Falling phasea. Na+ voltage-gated channels become inactivated (not closed)

1. Unable to respond to 2nd depolarization stimulusa. Refractory period

b. K+ voltage-gated channels openc. Inside of cell becomes negative again and outside becomes negative

5. Undershoota. Na+ voltage-gated channels close but some K+ voltage-gated channels

remain open causing hyperpolarizationb. Membrane potential returns to resting

1. depolarization can now occur again if stimulus received

III. Conduction of Action Potential

A. Conduction speed1. Axon Diameter2. Myelin sheath

a. Lipid insulation

1. Saltatory conduction

48.4 Neurons communicate w/ other cells at synapsesI. Transmission of impulse from cell to cell

II. Generation of postsynaptic potentialsA. Excitatory postsynaptic potentials (EPSPs)

1. Neurotransmitters that cause depolarization of postsynaptic cells2. increase permeability to K+ & Na+

B. Inhibitory postsynaptic potentials (IPSPs)1. Neurotransmitters that cause hyperpolarization of postsynaptic cell2. increase permeability to K+ & Cl-

III. Summation of postsynaptic potentialsA. Temporal summation

1. 2nd EPSP received before resting potential reached after 1st EPSPa. 2 EPSPs added together

B. Spatial1. Multiple EPSPs received simultaneously from different synapses

a. EPSPs added together

IV. Modulated synaptic transmissionA. Signal transduction pathways

1. Slower but longer lasting response

V. NeurotransmittersA. Acetylcholine

1. One of the most common2. Main target = Skeletal muscles3. Main affect = excitation muscle contraction

a. Inhibitory to cardiac muscle4. Nicotine/botulism

B. Biogenic Amines1. Norepinephrine

a. Neurotransmitter & hormoneb. Main target = Autonomic nervous system

1. Control of internal env.a. Smooth & cardiac, digestive, cardiovascular, excretion, & endocrine

c. Main affect = excitationd. Acts through a G protein-coupled receptor

2. Dopamine & Serotonina. Released in brainb. Main affect = Sleep, mood, attention, learning

1. Ritalin increases levels of dopamine

C. Neuropeptides1. Work through signal transduction pathways2. Endorphins

a. Decrease pain perception