Chapter 8 - B

The specificity of neural communication depends on what?
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The specificity of neural communication depends on what?
The signal molecules secreted, the target cell receptors for these chemicals, the anatomical connections b/w neurons and their targets
Synapse is made of what 2 parts
1. axon terminal of presynaptic neuron 2. membrane of postsynaptic neuron - may be neurons or non-neural cells
Neuron-to-neuron synapses occur where
the presynaptic axon terminals are next to either the dendrites or the cell body of the post synaptic neuron
- Can also occur on the axon or axon terminal
Number of synapses
moderate number = 10,000
Electrical Synapses
-pass an electrical signal directly from the cytoplasm of one cell to another through the pores of gap junction proteins
- info can flow in both directions
- Mainly in CNS or in glial cells in cardiac and smooth muscle and pancreatic beta cell
- rapid conduction of signals
- also allow chemical signal molecules to diffuse b/w adjacent cells
Chemical synapses
-Majority
-use neurocrine molecules to carry information from one cell to the next
- The electrical signal of the presynaptic cell is converted into a neurocrine signal (neurotransmitters) that crosses the synaptic cleft then binds to a receptor on its target cell
What Secretes chemical signals
Neurons
Neurotransmitter vs neuromodulator
transmitter - fast
modulator - act as synaptic and non-synaptic sites - therefore slower
Different types of neurocrine receptors
1. receptor-channels which are ligand-gated channels, and G protein-coupled receptors
Ionotropic receptors
receptor-channels that mediate rapid responses across the membrane
- Specificity depends on the ion
Metabotropic receptorsG protein-coupled receptors - mediate slow response b/c the signal must be transduced through a second message - open/close ion channelsWhat do neurotransmitters bind toone or more receptors - each receptor will have multiple subtypes - allowing one transmitter to have different effects - Letter and number subscripts7 Classes of NeurotransmittersAcetylcholine, amines, amino acids, peptides, purines, gases and lipidsWhat neurocrines do CNS neurons releasemany different ones including hormone activityPNS neurons releaseOnly 3: acetylcholine, norepinephrine and epinephrine (neurohormone) and co secrete ATPAcetylcholine- made from acetyl CoA and choline - acetyl CoA links glycolysis to the citric acid cycle - in its own chemical class - small molecule found in membrane phospholipids - Have Cholinergic receptorsCholinergic ReceptorsNicotinic - receptor-channels found on skeletal muscle in Autonomic division of the PNS and CNS - Monovalent cation channels through Na+ and K+ - Na+ enters, K+ leaves - Na+ entry depolarizes the cell Muscarinic - G protein-coupled receptors linked to second messenger systems - in PNS and CNSAmines- In CNS - derived from single amino acidsCholinergic -Neurons that secrete ACh and receptors that bind AChSerotoninmade from tryptophanHistaminemade from histadine - plays a role in allergic responsesTyrosineconverted to dopamine, norepinephrine and epinephrine - norepinephrine - PNS autonomic sympathetic division - all 3 function as neurohormonesAdrenergic Neuronssecrete norepinephrineAdrenergic receptorsdivided into: Beta and Alpha - G coupled proteins - B - epinephrine - A - norepinephrineAmino AcidsGlutamate - excitory in CNS (excitory - depolarize their target cells) Aspartate - excitory in brain GABA - inhibitory in the brain (inhibitory - hyper polarize) Glycine - inhibitory of spinal cord - may also be excitoryPeptidesSubstance P - pain pathway Opioid - mediate pain reliefPurinesAMP and ATP - bind to purinergic receptors in the CNS in the heart - bind to G protein-coupled receptorsGasesNitric Oxide (NO) - unstable gas synthesized from oxygen and arginine Carbon monoxide and H2S - both toxic gases produced in tiny amountsLipidsEicosanoidsNeurotransmitters are released from whatVesiclesNeurotransmitter Synthesistakes place in the nerve cell body and the axon terminal - polypeptides are made in the cell body -Neurotransmitter Release1. Action potential depolarizes the axon terminal 2. Opens gated Ca2+ channels and Ca2+ enters the cell 3. Calcium entry triggers exocytosis of synaptic vesicle contents 4. Neurotransmitter diffuses across the synaptic cleft and binds with the receptors 5. Initiates a responseKiss and run Pathwaysynaptic vesicles fuse to the presynaptic membrane at the fusion pore - Neurotransmitters pass through the channel - Vesicles pull back from the fusion poreTermination of Neurotransmitter Activity1. Acetylecholine (ACh) is made from choline and acetyl CoA 2. The synaptic cleft ACh is rapidly broken down by the enzyme acetylecholinesterase 3. Choline is transported back into the axon terminal by cotransport with Na+ 4. Recycled choline is used to make more AChDivergentOne presynaptic neuron branches to affect a larger number of postsynaptic neurons ex. purkinje cellConvergentmany presynaptic neurons provide input to influence a smaller number of postsynaptic neurons