Transcript Chapter 8b
Chapter 8b Neurons: Cellular and Network Properties Cell-to-Cell: A Chemical Synapse • Chemical synapses use neurotransmitters; electrical synapses pass electrical signals. Axon of presynaptic neuron Mitochondrion Axon terminal Postsynaptic neuron Synaptic vesicles Synaptic cleft Neurotransmitter Receptors Postsynaptic membrane Figure 8-20 Cell-to-Cell: Events at the Synapse and Exocytosis 1 An action potential depolarizes the axon terminal. 2 The depolarization opens voltage-gated Ca2+ channels and Ca2+ enters the cell. 3 Calcium entry triggers exocytosis of synaptic vesicle contents. Axon terminal Synaptic vesicle Neurotransmitter molecules Action potential 4 Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell. 5 Neurotransmitter binding initiates a response in the postsynaptic cell. 1 3 Ca2+ Synaptic cleft Docking protein 2 4 Receptor Postsynaptic cell Voltage-gated Ca2+ channel Cell response 5 Figure 8-21 Cell-to-Cell: Neurocrines • Seven classes by structure • • • • • • • Acetylcholine Amines Amino acids Purines Gases Peptides Lipids Cell-to-Cell: Synthesis and Recycling of Acetylcholine at a Synapse Mitochondrion Axon terminal CoA Acetyl CoA Enzyme Myasthenia gravis Acetylcholine 1 Synaptic vesicle 2 In the synaptic cleft ACh is rapidly broken down by the enzyme acetylcholinesterase. 3 Choline Acetate 1 Acetylcholine (ACh) is made from choline and acetyl CoA. 2 Cholinergic receptor Acetylcholinesterase (AChE) Postsynaptic cell 3 Choline is transported back into the axon terminal and is used to make more ACh. Figure 8-22 Amines • Derived from single amino acid • Tyrosine • Dopamine • Norepinephrine is secreted by noradrenergic neurons • Epinephrine • Others • Serotonin is made from tryptophan • Histamine is made from histadine Amino Acids • • • • Glutamate: Excitatory CNS Aspartate: Excitatory brain GABA: Inhibitory brain Glycine • Inhibitory spinal cord • May also be excitatory Other Neurotransmitters • Purines • AMP and ATP • Gases • NO and CO • Peptides • Substance P and opioid peptides • Lipids • Eicosanoids Receptors • Cholinergic receptors • Nicotinic on skeletal muscle, in PNS and CNS • Monovalent cation channels Na+ and K+ • Muscarinic in CNS and Parsympathetic NS • Linked to G proteins to 2nd messengers • Adrenergic Receptors • and • Linked to G proteins and 2nd messengers • Glutaminergic • Excitatory in CNS • Metabotropic and Ionotropic Cell-to-Cell: Postsynaptic Response • Fast and slow responses in postsynaptic cells Presynaptic axon terminal Rapid, short-acting fast synaptic potential Slow synaptic potentials and long-term effects Neurocrine G protein–coupled receptor Chemically gated ion channel Postsynaptic cell Alters open state of ion channels Ion channels open More Na+ in EPSP = excitatory depolarization Inactive pathway Activated second messenger pathway Ion channels close More K+ out or Cl– in Less Na+ in IPSP = inhibitory hyperpolarization Modifies existing proteins or regulates synthesis of new proteins Less K+ out EPSP = excitatory depolarization Coordinated intracellular response Figure 8-23 Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Rapid, short-acting fast synaptic potential Neurocrine G protein–coupled receptor Chemically gated ion channel Postsynaptic cell Ion channels open More Na+ in EPSP = excitatory depolarization More K+ out or Cl– in IPSP = inhibitory hyperpolarization Figure 8-23, step 1 Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Rapid, short-acting fast synaptic potential Neurocrine Slow synaptic potentials and long-term effects G protein–coupled receptor Chemically gated ion channel Postsynaptic cell Ion channels open More Na+ in EPSP = excitatory depolarization More K+ out or Cl– in IPSP = inhibitory hyperpolarization Figure 8-23, steps 1–2 Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Rapid, short-acting fast synaptic potential Slow synaptic potentials and long-term effects Neurocrine G protein–coupled receptor Chemically gated ion channel Postsynaptic cell Alters open state of ion channels Inactive pathway Activated second messenger pathway Ion channels open More Na+ in EPSP = excitatory depolarization More K+ out or Cl– in IPSP = inhibitory hyperpolarization Figure 8-23, steps 1–3 Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Rapid, short-acting fast synaptic potential Slow synaptic potentials and long-term effects Neurocrine G protein–coupled receptor Chemically gated ion channel Postsynaptic cell Alters open state of ion channels Ion channels open More Na+ in EPSP = excitatory depolarization Inactive pathway Activated second messenger pathway Ion channels close More K+ out or Cl– in Less Na+ in Less K+ out IPSP = inhibitory hyperpolarization Figure 8-23, steps 1–4 Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Rapid, short-acting fast synaptic potential Slow synaptic potentials and long-term effects Neurocrine G protein–coupled receptor Chemically gated ion channel Postsynaptic cell Alters open state of ion channels Ion channels open More Na+ in EPSP = excitatory depolarization Inactive pathway Activated second messenger pathway Ion channels close More K+ out or Cl– in Less Na+ in IPSP = inhibitory hyperpolarization Less K+ out EPSP = excitatory depolarization Figure 8-23, steps 1–5 Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Rapid, short-acting fast synaptic potential Slow synaptic potentials and long-term effects Neurocrine G protein–coupled receptor Chemically gated ion channel Postsynaptic cell Alters open state of ion channels Ion channels open More Na+ in EPSP = excitatory depolarization Inactive pathway Activated second messenger pathway Ion channels close More K+ out or Cl– in Less Na+ in IPSP = inhibitory hyperpolarization Modifies existing proteins or regulates synthesis of new proteins Less K+ out EPSP = excitatory depolarization Coordinated intracellular response Figure 8-23, steps 1–6 Cell-to-Cell: Inactivation of Neurotransmitters 1 Neurotransmitters can be returned to axon terminals for reuse or transported into glial cells. Rapid termination of NTs 2 Enzymes inactivate neurotransmitters. 3 Neurotransmitters can diffuse out of the synaptic cleft. Blood vessel Axon terminal of presynaptic cell Synaptic vesicle 3 Glial cell 1 Enzyme Postsynaptic cell 2 Figure 8-24