Synapse Lecture Outline
Synapse Lecture Outline BIOL 221
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This 5 page Class Notes was uploaded by Chantay Harris on Sunday April 3, 2016. The Class Notes belongs to BIOL 221 at Towson University taught by Professor Colleen Winters in Spring 2016. Since its upload, it has received 20 views.
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Date Created: 04/03/16
Nervous System Lecture – Synapses and Information Processing OUTLINE Spring 2015 Reading: pages 413425 Vocabulary Exocytosis Effector Modulate Integration Suppress Transmission Neurotransmitter Ligand Receptor Stimulus Facilitate Enhance Synapse – a specialized site of contact between two neurons or a neuron and an effector (gland or muscle) that allows oneway flow of neural impulses • Neuromuscular junction • Neuroglandular junction • Synaptic bulb – tips of the presynaptic neuron that contain synaptic vesicles containing a neurotransmitter that will aid in signal transmission across the synaptic cleft (2030nm in length) Neurotransmitters (Table 12.4) • can have an excitatory (Na+) or inhibitory effect (Cl or K+) on the postsynaptic cell • Examples include: o acetylcholine (ACh) • CNS and PNS • cholinergic synapses (ACh is neurotransmitter) • neuromuscular junctions • excitatory & inhibitory o norepinephrine (NE) • CNS and PNS • Symathethetic Nervous system (fight or flight) • adrenergic synapses (adrenaline is neurotransmitter) • excitatory & inhibitory o dopamine • CNS (brain) • inhibitory (movement control) • excitatory (mood) • Loss = Parkinson’s disease o serotonin • CNS • Effects attention span, emotions • Loss = chronic depression Synapse transmission – excitatory cholinergic synapse (old figure, 12.16) 2+ • Action potential arrives at the synaptic knob; voltageregulated Ca channe in the synaptic membrane open • Ca enters synaptic knob and triggers exocytosis of ACh • ACh diffuses across the cleft and binds chemically (ligand)regulated Na channels ; + channels open allowing Na in = depolarize postsynaptic membrane 20ms • influx of Na produces a local potential that carries to the axon hillock and if strong enough will generate an action potential Synapse transmission – inhibitory GABAergic synapse Cessation of the synaptic signal (Fig 12.16) While it is important to stimulate or inhibit the postsynaptic cell with a neurotransmitter, the stimulus must be turned off otherwise the effector will continue responding to the signal when it is inappropriate and this can be life threatening • the presynaptic cell stops releasing the neurotransmitter • the neurotransmitter is released from the membrane channel on the postsynaptic membrane and diffuses into the extracellular fluid o astrocytes may absorb it and return it to the neurons o synaptic knob may reabsorb the neurotransmitter by endocytosis then break it down with an enzyme called monoamine oxidase (MAO) o some neurotransmitters, like ACh, are degraded in the synaptic cleft Neuromodulators • chemicals (small peptides) released by the synaptic bulb along with neurotransmitters that modify the effect of the neurotransmitter How neurotransmitters and neuromodulators work (Fig 12.17) • compounds that have a direct effect on membrane potential (Fig 12.17A) • compounds that have an indirect effect on membrane potential (Fig 12.17B) • lipidsoluble gases that exert their effects inside the cell (Fig 12.17C) Drugs and their effect on synapse activity Synapses are the decisionmaking devices of the nervous system. Memory Postsynaptic potentials (Fig 12.19) • graded potentials that develop in the postsynaptic membrane (local potentials) o excitatory postsynaptic potential (EPSP) o inhibitory postsynaptic potential (IPSP) Summation One neuron may receive input from thousands of other neurons. Some incoming signals may produce EPSPs and some may produce IPSPs. The neuron’s response depends on the additive effects of the EPSPs and IPSPs. o Temporal summation (Fig 12.18A) – addition of stimuli in a short period of time at a single synapse o Spatial summation (Fig 12.18B) – addition of EPSPs from multiple synapses Summation of EPSPs and IPSPs (Fig 12.6 Hill and Wyse) Presynaptic Facilitation (Fig 12.20B) • Facilitation is the process in which one neuron enhances the effect of another. • Axoaxonal synapse Presynaptic Inhibition (Fig 12.20A) • Inhibition is the process in which one neuron blocks the effect of another. • axoaxonal synapse Neural coding Neural coding is the process the nervous system uses to convert this information into meaningful patterns of action potentials. The qualitative information is carried by specific neurons The quantitative information – the intensity of the stimulus – is encoded two ways: neuron thresholds and frequency of stimulation. Videos to help you with the material! https://www.youtube.com/watch?v=ZuclwAOJFh8 How synapses work – good video! These are from the Khan Academy – sometimes they can get a bit busy but you might try them! https://www.youtube.com/watch?v=C_HONQFjpQ Sodium Potassium ATPase pump https://www.youtube.com/watch?v=TbqKZaXiL4 Neuronal synapses https://www.youtube.com/watch?v=Sa1wM750Rvs Action potential propagation https://www.youtube.com/watch?v=7wgb7ggzFNs Saltatory propagation Review questions from the book 1. Describe the five steps that occur between the arrival of an action potential at the synaptic knob and the beginning of a new action potential in the postsynaptic neuron. 2. Contrast the actions of acetylcholine, GABA, and norepinephrine at their respective synapses. 3. Describe three mechanisms to stop synaptic transmission. • astrocytes may absorb it and return it to the neurons • synaptic knob may reabsorb the neurotransmitter by endocytosis then break it down with an enzyme called monoamine oxidase (MAO) • some neurotransmitters, like ACh, are degraded in the synaptic cleft 4. What is the function of neuromodulators? Compare and contrast neuromodulators and neurotransmitters. • A neurotransmitter is one of several substances released by the nerve ending of a neuron that is used to communicate with the adjacent neuron. Chemicals like Serotonin, Acetylcholine, Dopamine, GABA, Glycine, and Norepinephrine are considered neurotransmitters. They are released by the presynaptic neuron and either excite or inhibit the post synaptic neuron. They are quickly degraded in the synaptic cleft or taken up by the presynaptic neuron to limit the amount of time they are in the synaptic cleft. • Neuromodulators are not the same. They are released by the nerve endings and have their effect sometimes quite far from the neuron from which they were released. They are not rapidly degraded or taken up, so the amount of time for their activity is not limited as in neurotransmitters. They can either dampen or enhance the excitability of their effector neurons. Examples of neuromodulators are opioid peptides such as enkephalins, endorphins, dynorphins. • Some neurotransmitters also act as neuromodulators: substance P, octopamine, serotonin, an acetylcholine are such examples. 5. Why is a single EPSP insufficient to make a neuron fire? • A single EPSP will not have enough strength to reach threshold 6. Contrast the two types of summation at a synapse. • Temporal summation more than one stimuli at a single snaps • Spatial summation more than one ESPS synapse 7. Describe how the nervous system communicates quantitative and qualitative information about stimuli. 8. List the four types of neural circuits and describe their similarities and differences. • DIVERGENCE AMPLIFYING CIRCUITS one incoming fiver triggers responses in EVER INCREASING amount of neurons further and further along curcuit, so that one neuron from brain can activate hundreds of motor neurons and thereby thousands of motor units in skeletal muscle fibres • CONVERGING CIRCUIT where postsynaptic neuron receives input from several of its dendrites (can be InH or ExC), usuallly this is from multople different presynaptic neurons, or it can be from a single presynaptic neurons channeling signals to multiple dendrites has concentrating/funneling effect convergence from different areas explain how different types of sensory stimuli can have same ultimate effect or even a summation effect i .e. linking different senses like sight and sound and smell to associate it with a concept • REVERTEBRATING OSCILLATING CIRCUITS incoming signals travel through chain of neurons, each of which makes collateral synapses with neurons in PREVIOUS part of pathway POSITIVE FEEDBACK, impulses are sent though circuit again and again giving continous output until a neuron in the chain does not fire involved in control of RHYTHMIC ACTIVITY i.e. sleep, breathing, arm swinging when walking can occur in single pathway (same pathway) or along several (multiple pathway) + 9. The local anesthetics lidocaine (Xylocaine) and procaine (Novocaine) prevent voltagegated Na channels from opening. Explain why this would block the conduction of pain signals in a sensory nerve. The production of action potentials involves Na+ inflow into a neuron through these voltage regulated gates. If the gates were inhibited, then no action potentials and no nerve signals could be generated, so tissue damage would not trigger the transmission of pain signals in a nerve.