Lecture 20- Synapses & Sensory Receptors Flashcards
What is a synapse?
A junction between a synaptic terminal and another cell
An action potential is a signal that travels _____ the synapse _______ the neuron.
An action potential is a signal that travels to the synapse in the neuron.
What are the types of synapses?
Electrical synapses and chemical synapses
What are electrical synapses?
Current flows directly from cell to cell. Less common.
True or False: The presynaptic cell synthesizes and stores neurotransmitters.
True
How are action potentials passed from presynaptic cells to postsynaptic cells?
Presynaptic action potential triggers voltage-gated calcium ion channels to open which allows neurotransmitters to cross the synaptic cleft.
True or False: Neurotransmitters bind to voltage-gated ion channels on the postsynaptic membrane.
False, neurotransmitters bind to ligand-gated ion channels (proteins) on the postsynaptic membrane.
Explain the process of chemical synapses.
The presynaptic neuron is the neuron sending the signal. It has an axon terminal that ends near the receiving neuron. The synaptic cleft refers to the tiny space between the presynaptic and postsynaptic neurons.
the presynaptic neuron makes neurotransmitters which are stored in synaptic vesicles.
Action Potential Arrival: When an action potential travels down the axon of the presynaptic neuron, it reaches the axon terminal.
Calcium Influx: This triggers the opening of voltage-gated calcium (Ca2+) channels in the membrane of the axon terminal. Now that these channels are open, the Ca2+ enters the presynaptic neuron.
This influx of calcium causes some of the synaptic vesicles to fuse with the presynaptic membrane.
As a result, the neurotransmitters inside the synaptic vesicle are released into the synaptic cleft.
The neurotransmitters diffuse across the synaptic cleft. They then bind and activate specific postsynaptic receptors.
How do postsynaptic potentials work and how are they triggered?
Postsynaptic potentials refer to the change in membrane potential of postsynaptic cells. They are triggered by ligand-gated ion channels.
The neurotransmitters released from the presynaptic neuron bind to the specific receptors and bind to the ligand-gated ion channel, serving as a key that can open and close the gate to allow ions to enter the cell and cause a cellular response (either depolarization or hyperpolarization).
What are the two types of postsynaptic potentials and what do they do?
- Excitatory Postsynaptic Potential (EPSP): Depolarizes (Makes more positive inside)
- Inhibitory Postsynaptic Potential (IPSP): Hyperpolarizes (Makes more negative inside)
What is summation of postsynaptic potentials?
There are often 100s of terminals to dendrite and cell body, some excitatory and some inhibitory. Postsynaptic potential is due to interactions, distance, and neurotransmitters.
What is temporal summation?
2+ EPSPs at 1 synapse. The 2nd arrives before the MP resets, causing stronger depolarization and resulting in AP.
(If an excitatory neurotransmitter is released and binds to the receptor, causing EPSP but doesn’t depolarize to reach the threshold for an action potential, in this scenario a rapid 2nd EPSP is released at the same synapse, triggering a second EPSP and increasing the likelihood of AP due to combined stronger depolarization).
What is spatial summation?
2+ EPSPs nearly simultaneously. Different synapses. Same postsynaptic neuron. Causes stronger depolarization.
What is the distinction between temporal summation and spatial summation?
Temporal summation has to do with time- Leverages timing for a stronger overall effect for a SINGLE synapse.
Spatial summation considers the location of DIFFERENT synapses on the same postsynaptic neuron.
Both cause stronger depolarization and increase the chances of an AP.
Where is the neuron’s integration system?
Axon hillock
How do EPSP and IPSP interactions work?
The membrane potential at the axon hillock is the summed effects of all EPSPs and IPSPs. The AP results if the sum of these effects reaches the threshold (-55mV).
Nervous System Development
NS macro organization is established during development and regulated by gene expression, signal transduction. After birth, the brain develops and continues to remodel.
Neuronal Plasticity
Response to activity- neurons that are frequently used become stronger.
Remodeling via competition among neurons for growth supporting factors- molecules that promote the growth and survival of neurons. Neurons that are more active are more likely to attract these factors, allowing them to strengthen their connections and survive. Competition ensures that the most frequently used neural pathways have the resources they need to function effectively.
Synapse elimination- keeps only required- Eliminates weak synapses to ensure remaining connections are strong and reliable.
How can synapses be strengthened?
When two neurons are active together frequently, their connection (synapse) between them becomes stronger.
What does “use it or lose it” mean?
Synapses that are not used frequently may weaken or even be eliminated.
Where is short-term memory held? What links different pieces of information in STM?
Held in the cerebral cortex (outermost layer of brain). The hippocampus links different pieces of information in the STM.
Short-Term Memory
Information is held briefly: temporary holding area for information. Located in the cerebral cortex, the hippocampus links different pieces of information in STM. Intermediate step for forming LTM, but is not responsible for long-term storage. Can remember things for seconds to minutes, number of items ~ 7
Long-Term Memory
Info stored in cerebral cortex. Temporary links replaced by connections within cerebral cortex.
-> Permanent, theoretically unlimited capacity
Long-Term Potentiation
Lasting increase in strength of synaptic transmission. Fundamental process of memory storage and learning.
