Neurons: Cellular and Network Properties Chapter 8b Neurons: Cellular and Network Properties

Cell-to-Cell: A Chemical Synapse Axon of presynaptic neuron Postsynaptic neuron Axon terminal Mitochondrion Synaptic vesicles Synaptic cleft Receptors Neurotransmitter Postsynaptic membrane Chemical synapses use neurotransmitters; electrical synapses pass electrical signals. 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. Axon terminal Synaptic vesicle Neurotransmitter molecules 3 Calcium entry triggers exocytosis of synaptic vesicle contents. Action potential 4 Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell. 1 3 5 Neurotransmitter binding initiates a response in the postsynaptic cell. 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 Myasthenia gravis Axon terminal Acetyl CoA CoA Enzyme Acetylcholine 1 1 Acetylcholine (ACh) is made from choline and acetyl CoA. Synaptic vesicle 2 In the synaptic cleft ACh is rapidly broken down by the enzyme acetylcholinesterase. 3 Choline Cholinergic receptor 2 3 Choline is transported back into the axon terminal and is used to make more ACh. Acetate Acetylcholinesterase (AChE) Postsynaptic cell Figure 8-22

Derived from single amino acid Tyrosine 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

Glutamate: Excitatory  CNS Aspartate: Excitatory  brain 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

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 Postsynaptic cell Presynaptic axon terminal Ion channels open More Na+ in More K+ out or Cl– in EPSP = excitatory depolarization IPSP = inhibitory hyperpolarization Ion channels close Less Less K+ out Alters open state of ion channels Activated second messenger pathway Inactive pathway Modifies existing proteins or regulates synthesis of new proteins Coordinated intracellular response Rapid, short-acting fast synaptic potential Neurocrine Slow synaptic potentials and long-term effects Chemically gated ion channel G protein–coupled receptor Figure 8-23

Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Rapid, short-acting fast synaptic potential Neurocrine Chemically gated ion channel G protein–coupled receptor Postsynaptic cell Ion channels open More Na+ in More K+ out or Cl– in EPSP = excitatory depolarization IPSP = inhibitory hyperpolarization Figure 8-23, step 1

Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Slow synaptic potentials and long-term effects Rapid, short-acting fast synaptic potential Neurocrine Chemically gated ion channel G protein–coupled receptor Postsynaptic cell Ion channels open More Na+ in More K+ out or Cl– in EPSP = excitatory depolarization IPSP = inhibitory hyperpolarization Figure 8-23, steps 1–2

Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Slow synaptic potentials and long-term effects Rapid, short-acting fast synaptic potential Neurocrine Chemically gated ion channel G protein–coupled receptor Inactive pathway Postsynaptic cell Alters open state of ion channels Activated second messenger pathway Ion channels open More Na+ in More K+ out or Cl– in EPSP = excitatory depolarization IPSP = inhibitory hyperpolarization Figure 8-23, steps 1–3

Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Slow synaptic potentials and long-term effects Rapid, short-acting fast synaptic potential Neurocrine Chemically gated ion channel G protein–coupled receptor Inactive pathway Postsynaptic cell Alters open state of ion channels Activated second messenger pathway Ion channels open Ion channels close More Na+ in More K+ out or Cl– in Less Na+ in Less K+ out EPSP = excitatory depolarization IPSP = inhibitory hyperpolarization Figure 8-23, steps 1–4

Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Slow synaptic potentials and long-term effects Rapid, short-acting fast synaptic potential Neurocrine Chemically gated ion channel G protein–coupled receptor Inactive pathway Postsynaptic cell Alters open state of ion channels Activated second messenger pathway Ion channels open Ion channels close More Na+ in More K+ out or Cl– in Less Na+ in Less K+ out EPSP = excitatory depolarization IPSP = inhibitory hyperpolarization EPSP = excitatory depolarization Figure 8-23, steps 1–5

Cell-to-Cell: Postsynaptic Response Presynaptic axon terminal Slow synaptic potentials and long-term effects Rapid, short-acting fast synaptic potential Neurocrine Chemically gated ion channel G protein–coupled receptor Inactive pathway Postsynaptic cell Alters open state of ion channels Activated second messenger pathway Ion channels open Ion channels close Modifies existing proteins or regulates synthesis of new proteins More Na+ in More K+ out or Cl– in Less Na+ in Less K+ out EPSP = excitatory depolarization IPSP = inhibitory hyperpolarization 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. Blood vessel 3 Neurotransmitters can diffuse out of the synaptic cleft. Axon terminal of presynaptic cell Synaptic vesicle 3 Glial cell 1 Enzyme Postsynaptic cell 2 Figure 8-24