Week 2—2 Peer Response 800w. due9-16-23

Instructions:

Please read and respond to the two peers’ initial postings for week 2 below. Consider the following questions in your responses.

Compare and contrast your initial posting with those of your peers.  

1. How are they similar or how are they different?

2. What information can you add that would help support the responses of your peers?

3. Ask your peers a question for clarification about their post.

4. What most interests you about their responses? 

5. Summaries at least 1 evidence based article that supports there point.

Please be sure to validate your opinions and ideas with citations and references in APA format.

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Response 1 400 words

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Week 2 Discussion: Neurotransmitters

Describe the chemical and electrical processes used in neurotransmission.

        The central and peripheral nervous system both have a very complex and precise structure. The brain has trillions of specialized nerve cells called neurons. Neurons are connected to each other via synapses. Each neuron is connected to thousands of other neurons. Synapses serve as specialized centers that direct communication between neurons via a mechanism known as neurotransmission (Masoli et al., 2022). In other words, neurotransmission means how an impulse moves through one neuron to another neuron. Pulses can move through neurons electrically or chemically.

        Electrical process involves cell membranes. Each neuron has a cell membrane that separates intracellular space from extracellular space and has electrical charge (ions). When a signal arrives to the cell membrane, the ion channels both voltage-sensitive sodium channels (VSSCs) and voltage-sensitive calcium channels (VSCCs ) open and NA+  ions can transfer through these channels and create electrical signals (action potential). This electrical signal will move through axons to reach to the axon terminal (presynaptic nerve terminal) and opens calcium channels.

        According to Huang et al. (2022), in the nervous system, the functioning of brain circuits depends on the accurate integration of synaptic vesicles filled with neurotransmitters at a region known as the presynaptic active zone. When an action potential reaches these vesicles and calcium ions are transferred, the neurotransmitters are released from these vesicles. In other words, electrical impulses within the neuron are then transformed into chemical messengers, a process known as Excitation–Secretion Coupling. When these messengers (neurotransmitters) are released, they activate the receptors on a postsynaptic neuron. Communication within a neuron is electrical, while communication between neurons is chemical (Stahl, 2021). A single synapse can have many communication lines, each using its own neurotransmitter, and each neurotransmitter can be understood by a different set of receptors. This complex setup allows for rich and diverse communication between nerve cells (Agnati et al., 2023).

Why are depolarizations referred to as excitatory postsynaptic potentials and hyperpolarization as inhibitory postsynaptic potentials?

        The neurotransmitter can affect the postsynaptic neuron’s cell membrane in two different ways. If the neurotransmitter binds to the receptors on the postsynaptic neuron and reduces the negative charge of the cell membrane, causing slight depolarization, the postsynaptic neuron will reach the threshold to initiate an action potential and transmit signals further along the neural pathway. This process is called Excitatory Postsynaptic Potentials (EPSP). In other words, when the neurotransmitter depolarizes the postsynaptic cell membrane, it is termed excitatory because it initiates an action potential (Stahl, 2021).

        On the other hand, if the neurotransmitter binds to the postsynaptic cell membrane and creates a more negative charge, hyperpolarization occurs. In this case, the postsynaptic neuron receives an inhibitory signal, which means the neuron moves further away from the threshold for initiating an action potential. This pathway is referred to as Inhibitory Postsynaptic Potentials (IPSP). The balance between EPSP and IPSP regulates the activity of neurons (Stahl, 2021).

What are the differences between absolute and relative refractory periods?

        When a neuron has been depolarized and an action potential has been created, this neuron is not anymore able to start another action potential for a limited amount of time. The duration, lasting approximately 1-2 milliseconds, beginning with the initiation of the action potential and extending just beyond the spike potential. This period is referred to as the Absolute Refractory Period (ARP). It’s important to note that, even in response to stronger or supra threshold stimuli, no additional action potentials can be generated during the ARP. During this period, sodium channels are closed and sodium ions are not able to flow and create another action plan (Kartik et al., 2023). This is because the system prefers to create one-directional manner and prevent backward transmission of signals along the neuron’s axon.

        Relative refractory period usually follows absolute refractory period. Some neurons acquire their abilities to create another action potential little by little, however, the signal should be stronger to depolarize the neurons. Following the inactivation of the sodium (Na) channels, the opening of potassium (K) channels leads to the efflux of K ions. Subsequent recovery of the Na channels from their inactivated state permits the generation of a second action potential. However, due to the sustained efflux of K ions, there is a natural resistance to further depolarization. As a result, a stimulus stronger than the norm is required to start a second action potential (Kartik et al., 2023). This period, lasting approximately 3-4 milliseconds after the absolute refractory period, during which a second action potential can be fired with stronger stimuli due to the recovery of Na channels. The reason of this period is that some ion channels have been recovered and now are able to open their channels and let the sodium ions to flow and create action plan. The relative refractory period is usually longer that absolute refractory period. These refractory periods help to ensure proper timing in neural circuits (Stahl, 2021). 

References

Agnati, L. F., Guidolin, D., Cervetto, C., Guido, M., & Marcoli, M. (2023). Brain structure and function: Insights from chemical neuroanatomy.
 Life, 13(4), 940. 
https://doi.org/10.3390/life13040940Links to an external site.

Huang, S., Piao, C., Beuschel, C. B., & Zhao, Z. (2022). A brain-wide form of presynaptic active zone plasticity orchestrates resilience to brain aging in Drosophila.
 PLoS Biology, 20(12) 
https://doi.org/10.1371/journal.pbio.3001730Links to an external site.

Kartik, S., Hrudini, D., Aparna, J., Navya, T., & Chelliah, S. (2023). “Knowing it before blocking It,” the ABCD of the peripheral nerves: Part A (Nerve anatomy and physiology).
 Cureus, 15(7) https://doi.org/10.7759/cureus.41771

Masoli, S., Rizza, M. F., Tognolina, M., Prestori, F., & D’Angelo, E. (2022). Computational models of neurotransmission at cerebellar synapses unveil the impact on network computation.
 Frontiers in Computational Neuroscience,

 
https://doi.org/10.3389/fncom.2022.1006989Links to an external site.

Stahl, S. M. (2021). 
Stahl’s essential psychopharmacology: Neuroscientific basis and practical application (5th ed.). 

Response 2. 400 words

Describe the chemical and electrical processes used in neurotransmission.

Neurons which are nerve cells can communicate with each other through electrical and chemical signals. Communication occurs at the synapses; this is the site where chemical transmission occurs (Lovinger, 2008). Presynaptic neurons release neurotransmitters which are then received by the postsynaptic neuron also referred to as the neurotransmitter receptor protein (Lovinger, 2008). Neurotransmitter molecules bind to the receptor protein thus changing its function. Electrical signals also called action potential on the other hand are a result of charged particles that create rapid conduction from one end of the cell through the axon and to the next, its speed is dependent on the myelin sheath (Lall, 2023)

Why are depolarizations referred to as excitatory postsynaptic potentials and hyperpolarization as inhibitory postsynaptic potentials?

Depolarizations are referred to as excitatory postsynaptic potentials and hyperpolarization as inhibitory postsynaptic potentials due to the synaptic response that is facilitated by the Ligand-gated ion channels. In other words, the response of the postsynaptic neurons determines if it is excitatory (fires an action potential) or inhibitory (doesn’t fire an action potential) (Lovinger, 2008). Depolarization refers to the opening of sodium ion channels allowing an influx of sodium to enter the cell membrane increasing the likelihood of an action potential. This is followed by resting potential and rapid repolarization (Grider, 2023).

What are the differences between absolute and relative refractory periods?

An absolute refractory period is a period that follows an action potential in which a second action potential cannot occur due to the inactivation of the voltage-gated sodium channel (Grider, 2023). Whereas the relative refractory period is the duration of time in which a second action potential can occur. During this time sodium channels move from an inactive state to a closed state, however, in order for an action potential to happen a larger amount of stimulation is needed (Grider, 2023).

References

Grider, M. H. (2023, May 8). 
Physiology, action potential. StatPearls – NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK538143/#:~:text=In%20neurons%2C%20the%20rapid%20rise,opening%20of%20potassium%20ion%20channels.

Lall, S. (2023, May 24). 
How do neurons communicate (so quickly)? – MIT McGovern Institute. MIT McGovern Institute. https://mcgovern.mit.edu/2019/02/28/ask-the-brain-how-do-neurons-communicate/

Lovinger, D. M. (2008). 
Communication Networks in the Brain: Neurons, Receptors, Neurotransmitters, and Alcohol. PubMed Central (PMC). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3860493/#:~:text=Nerve%20cells%20(i.e.%2C%20neurons),the%20cell%20to%20the%20other.

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