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Nervous System: Part III What Happens at a Synapse?

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Presentation on theme: "Nervous System: Part III What Happens at a Synapse?"— Presentation transcript:

1 Nervous System: Part III What Happens at a Synapse?

2 3.E.2 Continued Animals have nervous systems that detect external and internal signals, transmit and integrate information, and produce responses. This is the essential knowledge statement from the curriculum framework. Detect---process---response We begin with a bit of review… (You may want to have the teacher notes for Part II handy as you start this.)

3 Falling phase of the action potential 3
Key Na K 4 Falling phase of the action potential 3 Rising phase of the action potential 50 Action potential 3 Membrane potential (mV) Threshold 4 2 50 1 1 5 2 Depolarization Resting potential 100 The role of voltage-gated ion channels in the generation of an action potential. Ask students to explain what is happening at each of these 5 positions on the graph. Ask for details! Time OUTSIDE OF CELL Sodium channel Potassium channel INSIDE OF CELL Inactivation loop 1 Resting state 5 Undershoot 3

4 Membrane potential (mV)
? Time Membrane potential (mV) 50 100 50 1 2 3 4 5 Resting state Depolarization Hyperpolarization Repolarization What is represented by each question mark? Describe what is occurring at 1,2,3,4,5 using the words: Resting state, depolarization, repolarization, and hyperpolarization

5 What happens when the impulse reaches the end of the axon?

6 Synapses Transmission of information between neurons occurs across synapses. A chemical synapse is a junction between two nerve cells consisting of a minute gap across which impulses pass by means of a neurotransmitter. 3.E.2.c begins here. Emphasize that there is much more to the story!

7 Neurotransmitters: Chemical Messengers
3.E.2.c. In most animals, transmission across synapses involves chemical messengers called neurotransmitter such as: Acetylcholine Epinephrine Norepinephrine Dopamine Serotonin GABA These neurotransmitters are illustrative examples of the chemical messengers. Students should be familiar with all of these and become an expert on at least one of them.

8 Calcium gated channels in the synaptic knob
Note the structural features that allow the cell to cell communication to occur in the synaptic region: Calcium gated channels in the synaptic knob Sodium channels in the post-synaptic membrane Fluidity of the lipid bi-layer allows for exocytosis of the neurotransmitter The transfer of information that occurs at the synapse is a classic example of cell to cell communication. The membrane is specifically adapted for this task. The synaptic knob membrane contains voltage gated Ca2+ channels, the post synaptic membrane contains receptor-bearing sodium, Na+ channels, and the fluidity of the membrane allows for the fusion of vesicles.

9 Action potential depolarized the membrane of synaptic terminal, this triggers an influx of Ca2+.
That causes synaptic vesicles to fuse with the membrane of the presynaptic neuron. Vesicles release neurotransmitter molecules into the synaptic cleft. Neurotransmitters bind to the receptors of ion channels embedded in the postsynaptic membrane.

10 Cell To Cell Communication Events
Action potential depolarized the membrane of synaptic terminal, this triggers an influx of Ca2+. That causes synaptic vesicles to fuse with the membrane of the pre-synaptic neuron. Vesicles release neurotransmitter molecules into the synaptic cleft. Neurotransmitters bind to the receptors of ion channels embedded in the postsynaptic membrane.

11 Calcium enters Calcium stimulates the fusion of the neurotransmitter -bearing vesicles to fuse with the presynaptic membrane to release the neurotransmitter into the synaptic cleft.

12 Neurotransmitters will then be released into the cleft.
At synaptic cleft

13 Neuron Transmitter Binds With A Receptor On The Postsynaptic Membrane
The released neurotransmitter binds with the receptor on the postsynaptic membrane causing the channel to open allowing sodium ions to rush in. This influx of sodium can contribute to the development of an action potential in the receiving cell.

14 Exocytosis Neurotransmitter release is a form of exocytosis.
In exocytosis, internal vesicles fuse with the plasma membrane to secrete macromolecules out of the cell.

15 The neurotransmitter will then be released from the postsynaptic membrane and degraded.

16 Neurotransmitters There are more than 100 neurotransmitters, belonging to five groups: acetylcholine, biogenic amines, amino acids, neuropeptides, and gases A single neurotransmitter may have more than a dozen different receptors

17 There are a variety of neurotransmitters
There are a variety of neurotransmitters. Some neurotransmitters inhibit impulse generation while others increase the likelihood an impulse will be generated.

18 Acetylcholine Acetylcholine is a common neurotransmitter in vertebrates and invertebrates. It is involved in muscle stimulation, memory formation, and learning. Vertebrates have two major classes of acetylcholine receptor, one that is ligand gated and one that is metabotropic, requiring a second messenger. Neurotransmitters are important in cell to cell communication. One cell (presynaptic) communicates with the second cell (postsynaptic) through the release and actions of the neurotransmitter. Acetylcholine stimulates the contraction of skeletal muscles. Interestingly, it acts as an inhibitor to cardiac muscle cell contraction. A metabotropic receptor is type of membrane receptor of eukaryotic cells that acts through a second messenger. It may be located at the surface of the cell or in vesicles.

19 Here you see an image of the post synaptic cleft as sodium enters.
Point out that some synapses are electrical and some are chemical. Electrical- Fast, cells are connected by gap junctions, intercellular channels that allow the local ion currents of an action potential to flow b/n neurons. Chemical- narrow gap or synaptic cleft, separates the neurons. Series of events converts the electrical signal of the action potential into a chemical signal that travels across the synapse, where it is converted back to a electrical signal in the postsynaptic cell. Post synaptic

20 Response Transmission of information along neurons and synapses results in a response. The response can be stimulatory or inhibitory. 3.E.2.c.2

21 Ask students to practice talking through the events occurring at the chemical synapse with their partner. (Provide students with a copy of the diagram to label)

22 Injecting ethylene glycol tetraacetic acid (EGTA), a chelating agent that prevents calcium ions from moving across membranes, to a synaptic region would likely a. increase the release of neurotransmitters by the presynaptic neuron. b. decrease the release of neurotransmitters by the presynaptic neuron. c. result in neurotransmitters being released, but could not bind to its receptors on the post synaptic neuron. d. result in the lack of calcium ions keeping the ligand-gated ion channels open on the post synaptic neurons. Answer: b

23 Some synapses are excitatory others inhibitory
Some synapses are excitatory others inhibitory. Think of them as “on” and “off” switches.

24 Created by: Debra Richards Coordinator of Secondary Science Programs Bryan ISD Bryan, TX


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