Lecture 3 Flashcards
The nervous system is divided into two main branches name them and the branches under those branches
The CNS and PNS
CNS is divided into brain and spinal cord
PNS is divided into somatic and autonomic.
Somatic is divided into sensory and motor
Autonomic is divided into sympathetic and parasympathetic and enteric
Enteric Nervous System:
• A distinct branch of the autonomic nervous system that operates mostly independently, sometimes called the “second brain” or “gut brain.”
The parasympathetic system is under direct control of the brain and spinal cord, whereas the enteric system can operate independently of the brain but can be influenced by sympathetic and parasympathetic signals
• Functions: The parasympathetic system broadly regulates the body’s energy conservation and homeostasis, while the enteric system specifically manages digestive functions.
• Areas of influence: Parasympathetic activity affects many organs throughout the body, while the enteric system is localized to the gastrointestinal tract.
How many neurons are in the brain
100 billion neurons
~ 104 synapses/ neuron
~ Trillions of synapses
Apart from neurons, the brain is made up of glial cells.
State the 4 types of glial cells and their functions
Which of these types is the most abundant glial cells
What is the blood brain barrier
- Astrocytes: most abundant glial cells and make contact with all surfaces
• Functions: Provide structural support, responsible for metabolic activities in the brain such as glucose metabolism, maintain the blood-brain barrier(managing the kind of things that enter the blood brain barrier and what goes out) , regulate blood flow, influence synaptic activity, and manage ion balance and neurotransmitter recycling.
• Location: Found throughout the brain and spinal cord.- Oligodendrocytes:
• Functions: Produce myelin in the central nervous system, which insulates axons or neurons and enhances the speed of electrical signal transmission.
• Location: Predominantly in the white matter of the brain and spinal cord. - Microglia: they police the brain
• Functions: Act as the primary immune cells of the central nervous system, engaging in phagocytosis to remove debris, damaged neurons, and pathogens. They also play a role in inflammation and repair processes.
• Location: Scattered throughout the brain and spinal cord. - Ependymal Cells:
• Functions: Line the ventricles of the brain and the central canal of the spinal cord. They produce and circulate cerebrospinal fluid (CSF) through their cilia.ependymal cells form a blood CSF barrier
• Location: Within the ventricles of the brain and the central canal of the spinal cord.
- Oligodendrocytes:
Neurones need metabolic support
Blood vessels lined with endothelial cells with tight junctions ensure an adequate energy supply to the brain as well as a protective barrier (blood-brain barrier)
State six functions of the brain
Cognition: learning, memory, decision-making etc
Movement, posture and balance
Regulation of heart rate, blood pressure etc
Hunger and satisfaction
Hormonal regulation
Sleep and circadian rhythms
Reproduction (sex etc.)
Sensations like pain, touch etc
Vision, hearing, olfaction, taste
Emotions: happiness, reward and punishment
The brain is, perhaps,… MTN
State three basic functions of the nervous system(not just the brain)
.Sensory Function
- Detection of both internal and external stimuli
• Interpretive Function
- Analyzes, stores, and makes decisions based on sensory information
• Motor Function (Response)
— Response to interpretive data
What is the morphology of a nerve cell or state the six main parts of the nerve cell
Which part of the nerve cell doesn’t have nissl granules. Which part has a lot of it?
What are nissl granules?
Look at picture of the nerve cell in the slide after trying to answer
What is a synapse? A synapse contains what three things?
Where are action potentials generated from at the start?
What is the function of the axon terminal or terminal bouton
Generally the nerve cell is divided into the soma part and the axonal part.
-Axon hillock: The axon hillock is a specialized region of the neuron where the cell body transitions into the axon. Action potentials is propagated from or initiated at. - It is located at the junction between the cell body (soma) and the axon.
- The axon hillock is characterized by a lack of Nissl bodies, making it appear clear when stained and viewed under a microscope.
-Nucleus
-Nissi granules in the cytoplasm : Nissl Granules
Nissl granules, also known as Nissl bodies, are structures found within the cell body (soma) and dendrites of neurons.
- Nissl granules are composed of rough endoplasmic reticulum (RER) and ribosomes. The abundance of Nissl granules reflects the high metabolic activity of neurons
-. Cell Body (Soma):
- Contains the nucleus and organelles (such as the endoplasmic reticulum, Golgi apparatus, and mitochondria).
- Responsible for maintaining the cell’s health and metabolic activities.
- Acts as the main site for protein synthesis and other cellular processes.
-Dendrites**:
- Branched, tree-like extensions from the cell body. It connects to other nerve cells
- Receive incoming signals from other neurons and transmit them toward the cell body.
- Contain receptors for neurotransmitters released by other neurons( so they can receive the information from the neurotransmitters or signals from the neurotransmitters released by other neurons)
-Axon**:
- A long, thin projection that transmits signals away from the cell body to other neurons, muscles, or glands.
- Can vary in length from less than a millimeter to over a meter in some cases (e.g., the sciatic nerve).
- The axon hillock is the area where the axon joins the cell body and is typically the site where action potentials are initiated.
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Myelin Sheath:
- A fatty layer that insulates the axon and speeds up the transmission of electrical signals.
- Formed by glial cells: oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system.
- The myelin sheath is segmented, with gaps called nodes of Ranvier.
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Nodes of Ranvier:
- Gaps in the myelin sheath where the axon membrane is exposed.
- Allow for saltatory conduction, where the action potential jumps from node to node, greatly increasing the speed of signal transmission.
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Axon Terminals (Synaptic Boutons):
- The ends of the axon that make synaptic contacts with other neurons or effector cells.
- Contain synaptic vesicles filled with neurotransmitters, which are released into the synaptic cleft to transmit signals to the next cell. Yes, axon terminals and terminal boutons refer to the same structure in a neuron.
- Axon Terminals: These are the distal endings of an axon, where the neuron makes synaptic connections with other neurons, muscle cells, or glands.
- Terminal Boutons: This term specifically describes the small, bulb-like structures at the very end of the axon terminals. These boutons contain neurotransmitters that are released into the synaptic cleft to communicate with the next cell.
In essence, “terminal boutons” is a more detailed term referring to the small structures found at the axon terminals.
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Synapse:
- synapse is a specialized junction where a neuron communicates with another cell, which can be another neuron, a muscle cell, or a gland cell
- Includes the presynaptic membrane, synaptic cleft, and postsynaptic membrane.
What are the two main types of synapses
Which is more common and why
Which is faster
Why does the action potential only travel in one direction along a neuron?
• a) Because sodium channels behind the action potential are inactivated
• b) Because potassium channels are only present at the axon terminal
• c) Because neurotransmitters prevent backward movement
• d) Because the myelin sheath blocks backward conduction
Which factor does not significantly contribute to the resting membrane potential?
• a) Sodium-potassium pump
• b) Leak channels
• c) Intracellular anions
• d) Voltage-gated calcium channels
Which of the following conditions will lead to hyperpolarization of a neuron?
• a) Increased extracellular sodium concentration
• b) Increased permeability to chloride ions
• c) Increased intracellular potassium concentration
• d) Increased permeability to sodium ions
Why does the action potential have an all-or-none characteristic?
• a) Because it depends on the strength of the stimulus
• b) Because it only occurs if the membrane potential reaches the threshold
• c) Because it varies with the duration of the stimulus
• d) Because it can be partially activated
How does the sodium-potassium pump contribute to the maintenance of the resting membrane potential?
• a) By passively allowing ions to move according to their gradients
• b) By actively transporting sodium out of the cell and potassium into the cell
• c) By blocking all ion movement across the membrane
• d) By generating action potentials
Which protein complex is directly involved in the fusion of synaptic vesicles with the presynaptic membrane?
• a) SNARE complex
• b) GABA receptor
• c) Na+/K+ ATPase
• d) Voltage-gated sodium channel
Which of the following processes is directly involved in the recycling of synaptic vesicles?
• a) Exocytosis
• b) Endocytosis
• c) Transcytosis
• d) Phagocytosis
What is the primary function of synaptotagmin in synaptic vesicle fusion?
• a) Sensing calcium levels
• b) Binding to neurotransmitters
• c) Transporting sodium ions
• d) Forming the vesicle membrane
During synaptic transmission, which process follows the fusion of synaptic vesicles with the presynaptic membrane?
• a) Binding of neurotransmitters to postsynaptic receptors
• b) Depolarization of the presynaptic terminal
• c) Influx of potassium ions into the presynaptic terminal
• d) Breakdown of the synaptic vesicle membrane
36. What would happen to the resting membrane potential if the cell membrane became equally permeable to sodium and potassium ions? • a) It would become more negative • b) It would become more positive • c) It would remain unchanged • d) It would oscillate
There are two main types of synapses: chemical synapses and electrical synapses. Here, we’ll focus on the more common chemical synapses:
Electrical synapses are faster. This is because electrical synapses involve direct current flow between cells through gap junctions, allowing for almost instantaneous transmission of signals.
Direct Current Flow: Electrical synapses transmit signals via gap junctions that allow ions to pass directly between adjacent cells. This means the signal is passed with minimal delay and without the need for neurotransmitters. However, this also means there is less opportunity for modulation
But chemical synapses are more common because they allow more complex signaling . Neurotransmitters can activate different different types of receptors on the postsynaptic cell leading to different responses. They also allow for modulation of the signaling. The amount of neurotransmitters being released can be controlled while in electrical synapses, it’s less easy to control the signaling.
Structure of a Chemical Synapse
1. Presynaptic Neuron: • Axon Terminal: The end of the axon of the presynaptic neuron. • Synaptic Vesicles: Membrane-bound sacs in the axon terminal that contain neurotransmitters. • Presynaptic Membrane: The membrane of the axon terminal that faces the synaptic cleft. 2. Synaptic Cleft: • A small gap (about 20-40 nanometers wide) between the presynaptic and postsynaptic membranes. • Neurotransmitters are released into this space. 3. Postsynaptic Cell: • Postsynaptic Membrane: The membrane of the postsynaptic cell (which can be a neuron, muscle cell, or gland cell). • Receptors: Proteins on the postsynaptic membrane that bind neurotransmitters.
Function of a Chemical Synapse
1. Neurotransmitter Release: • When an action potential reaches the axon terminal of the presynaptic neuron, it triggers the opening of voltage-gated calcium channels. • Calcium ions enter the axon terminal, prompting synaptic vesicles to fuse with the presynaptic membrane and release their neurotransmitter content into the synaptic cleft through exocytosis. 2. Neurotransmitter Binding: • Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane. • This binding causes ion channels to open or close, leading to changes in the postsynaptic cell’s membrane potential. 3. Signal Transmission: • Depending on the type of neurotransmitter and receptor, the postsynaptic cell may become depolarized (excited) or hyperpolarized (inhibited). • If the postsynaptic cell is a neuron and the signal is strong enough, it can generate an action potential that propagates along its axon. 4. Neurotransmitter Clearance: • To terminate the signal, neurotransmitters are removed from the synaptic cleft through reuptake into the presynaptic neuron, enzymatic degradation, or diffusion away from the synapse.
Types of Synapses
1. Chemical Synapses: • Most common type. • Utilize neurotransmitters to relay signals across the synaptic cleft. 2. Electrical Synapses: • Less common. • Use gap junctions to allow direct electrical communication between neurons. • Allow ions and small molecules to pass directly from one cell to another, enabling rapid and synchronous transmission of signals.
Why does the action potential only travel in one direction along a neuron?
• a) Because sodium channels behind the action potential are inactivated
• b) Because potassium channels are only present at the axon terminal
• c) Because neurotransmitters prevent backward movement
• d) Because the myelin sheath blocks backward conduction
Answer: a) Because sodium channels behind the action potential are inactivated
Which factor does not significantly contribute to the resting membrane potential?
• a) Sodium-potassium pump
• b) Leak channels
• c) Intracellular anions
• d) Voltage-gated calcium channels
Answer: d) Voltage-gated calcium channels
Leak channels are a type of ion channel found in cell membranes that allow ions to pass through continuously, without the need for external signals like voltage changes or ligand binding. These channels are always open, permitting ions to “leak” across the membrane down their electrochemical gradient, which contributes to the maintenance of the resting membrane potential in cells.
Which of the following conditions will lead to hyperpolarization of a neuron?
• a) Increased extracellular sodium concentration
• b) Increased permeability to chloride ions
• c) Increased intracellular potassium concentration
• d) Increased permeability to sodium ions
Answer: b) Increased permeability to chloride ions
In this case, the correct answer is (b) Increased permeability to chloride ions because chloride ions (Cl⁻) are negatively charged. When a neuron becomes more permeable to chloride ions, more Cl⁻ will enter the neuron, making the inside more negative and leading to hyperpolarization (moving the membrane potential further away from zero, typically below the resting potential of around -70 mV).
While potassium ions (K⁺) also contribute to hyperpolarization, this is only true when potassium exits the cell. However, the option given is increased intracellular potassium concentration (which implies K⁺ staying inside or even entering the cell), which would make the inside of the cell less negative, not more negative.
For hyperpolarization to occur via potassium, it would have to involve increased permeability to potassium, allowing K⁺ to flow out of the cell, further driving the cell’s interior to a more negative state.
Thus, chloride influx is the best explanation in this context, as increased Cl⁻ permeability directly leads to hyperpolarization by increasing the negative charge inside the neuron.
Why does the action potential have an all-or-none characteristic?
• a) Because it depends on the strength of the stimulus
• b) Because it only occurs if the membrane potential reaches the threshold
• c) Because it varies with the duration of the stimulus
• d) Because it can be partially activated
Answer: b) Because it only occurs if the membrane potential reaches the threshold
How does the sodium-potassium pump contribute to the maintenance of the resting membrane potential?
• a) By passively allowing ions to move according to their gradients
• b) By actively transporting sodium out of the cell and potassium into the cell
• c) By blocking all ion movement across the membrane
• d) By generating action potentials
Answer: b) By actively transporting sodium out of the cell and potassium into the cell
36. What would happen to the resting membrane potential if the cell membrane became equally permeable to sodium and potassium ions?
• a) It would become more negative
• b) It would become more positive
• c) It would remain unchanged
• d) It would oscillate
Answer: b) It would become more positive
The correct answer is (b) It would become more positive because if the cell membrane became equally permeable to sodium (Na⁺) and potassium (K⁺) ions, the resting membrane potential would shift toward a more positive value.
- Resting Membrane Potential is typically around -70 mV in neurons, largely due to the high permeability of the membrane to potassium ions (K⁺) compared to sodium ions (Na⁺). This is because K⁺ leak channels allow more K⁺ to exit the cell, keeping the inside of the cell more negative.
- Sodium ions (Na⁺), however, have a much more positive equilibrium potential (about +60 mV), meaning if the membrane became highly permeable to Na⁺, sodium would rush into the cell, making the inside more positive.
- In a typical resting neuron, K⁺ permeability is much higher than Na⁺, so the resting membrane potential is close to the equilibrium potential of K⁺ (around -90 mV). However, if the membrane became equally permeable to Na⁺ and K⁺, the membrane potential would be influenced by both ions equally.
Since the equilibrium potential of Na⁺ is much more positive than K⁺, the membrane potential would shift closer to 0 mV or even become slightly positive. This shift would be toward the positive side because sodium influx (positive charge) would dominate over potassium efflux (removal of positive charge).
The resting membrane potential would become more positive because Na⁺, which has a higher positive equilibrium potential, would significantly contribute to the membrane potential if its permeability increased to be equal to that of K⁺.
Which of the following processes is directly involved in the recycling of synaptic vesicles?
• a) Exocytosis
• b) Endocytosis
• c) Transcytosis
• d) Phagocytosis
Answer: b) Endocytosis
What is the primary function of synaptotagmin in synaptic vesicle fusion?
• a) Sensing calcium levels
• b) Binding to neurotransmitters
• c) Transporting sodium ions
• d) Forming the vesicle membrane
Answer: a) Sensing calcium levels
During synaptic transmission, which process follows the fusion of synaptic vesicles with the presynaptic membrane?
• a) Binding of neurotransmitters to postsynaptic receptors
• b) Depolarization of the presynaptic terminal
• c) Influx of potassium ions into the presynaptic terminal
• d) Breakdown of the synaptic vesicle membrane
Answer: a) Binding of neurotransmitters to postsynaptic receptors
Which protein complex is directly involved in the fusion of synaptic vesicles with the presynaptic membrane?
• a) SNARE complex
• b) GABA receptor
• c) Na+/K+ ATPase
• d) Voltage-gated sodium channel
Answer: a) SNARE complex
What is an action potential
Explain the process of action potential in a muscle cell or a nerve cell
What is the normal resting membrane potential?
What causes depolarization of the cel?
What causes repolarization of the cell
What is the falling phase of an action potential?
The sudden fast change in electrical potential or charge that is associated or that occurs with the passage of an impulse along the membrane of a muscle cell or nerve cell.
- It is a sudden, fast, transitory(temporary or short lived), and propagating(moves through the entire cell) change of the resting membrane potential. After the change, the cell returns to it regular resting state.
Depolarisation and opening of Na channels
Membrane potential is driven towards ENa
Na channels are gradually inactivated, while more K channels open
The membrane is now repolarized.
At the end of the AP, there is a period of hyperpolarisation
Action Potential Phases
1. Resting Membrane Potential: • The resting membrane potential is the voltage difference across the cell membrane when the cell is not transmitting an impulse. It is typically around -70 mV in neurons. Associate the number 70 with the idea of resting or calm: • Think of the retirement age being around 70, a time of rest. • Or imagine a person calmly resting at 70 years old, reinforcing the idea that the cell’s resting state is at -70 mV. Also because more potassium which is -ve is in the cell( on a regular). The voltage difference across the cell membrane, also known as the membrane potential, refers to the difference in electrical charge between the inside and the outside of a cell. In neurons, this voltage difference is typically around -70 millivolts (mV), meaning the inside of the cell is 70 mV more negative than the outside when the cell is at rest (not transmitting an impulse).
Explanation:
1. Separation of Charges: • The cell membrane separates ions (charged particles) inside and outside the cell. This separation of charges creates an electrical gradient. • The inside of the cell contains more negatively charged ions, mainly due to large proteins and the higher concentration of potassium ions (K⁺) compared to the outside. Leak channels, especially potassium leak channels, allow K⁺ ions to diffuse out of the cell more freely than Na⁺ can diffuse in, further contributing to the negative charge inside. 3. Electrochemical Gradient: • This voltage difference represents the balance between the concentration gradients (the difference in ion concentrations inside vs. outside the cell) and the electrical gradients (the tendency of opposite charges to attract and like charges to repel). • At rest, the neuron maintains a relatively stable voltage difference, with more negative charge inside compared to the outside.
How dispersed the ions are in and outside of the cell. Net charge between extra cellular fluid and intracellular fluid. A change in the resting memerbane potential is what will cause an action potential to be propagated along the membrane of the nerve cell.
• This potential is maintained by the sodium-potassium pump (Na+/K+ ATPase), which pumps three sodium ions out of the cell and two potassium ions into the cell, and by the relative permeability of the membrane to potassium ions.
2. Depolarization:
• When a stimulus reaches a threshold level, voltage-gated sodium (Na+) channels open rapidly.
• Sodium ions rush into the cell due to the electrochemical gradient, causing the membrane potential to become more positive (toward the equilibrium potential of sodium, , which is around +60 mV).
• This rapid influx of sodium ions depolarizes the membrane, leading to the rising phase of the action potential.
3. Peak of Action Potential:
• The membrane potential approaches but does not reach because the Na+ channels begin to inactivate shortly after opening.
• At this peak, the inside of the cell is positively charged relative to the outside.
4. Repolarization:
• As the Na+ channels inactivate, voltage-gated potassium (K+) channels open.
• Potassium ions flow out of the cell, driven by their electrochemical gradient, causing the membrane potential to become more negative and return toward the resting potential. Ion Distribution and Permeability:
• Inside the cell, there is a high concentration of potassium ions (K+) and negatively charged proteins and other anions.
• Outside the cell, there is a high concentration of sodium ions (Na+) and chloride ions (Cl-). As potassium ions move out of the cell down their concentration gradient, they leave behind negatively charged proteins and other anions that cannot cross the membrane.
• This movement of positive K+ ions out of the cell makes the inside of the cell more negative relative to the outside.
• This phase is the falling phase of the action potential.
5. Hyperpolarization (Afterhyperpolarization):
• The K+ channels remain open longer than necessary, causing an overshoot and making the membrane potential more negative than the resting potential.
• This period is known as hyperpolarization or the afterhyperpolarization phase.
• Eventually, the K+ channels close, and the membrane potential returns to the resting level, reestablishing the resting membrane potential.
Yes, the action potential in neurons and muscle cells is primarily based on the movement of sodium (Na⁺) and potassium (K⁺) ions across the cell membrane. Here’s a step-by-step overview of how an action potential occurs:
- The neuron is at its resting membrane potential, typically around -70 mV.
- The inside of the cell is negatively charged relative to the outside.
- Sodium and potassium channels are closed.
- The Na⁺/K⁺ pump helps maintain this resting potential by pumping 3 Na⁺ out of the cell and 2 K⁺ into the cell.
- A stimulus causes the membrane potential to become less negative (depolarizes) and reaches a threshold, typically around -55 mV.
- Voltage-gated sodium channels open rapidly.
- Na⁺ rushes into the cell due to its electrochemical gradient.
- The influx of Na⁺ causes the membrane potential to become positive, peaking around +30 to +40 mV.
- At the peak of the action potential, voltage-gated sodium channels inactivate.
- Voltage-gated potassium channels open.
- K⁺ rushes out of the cell, driven by its electrochemical gradient.
- The efflux of K⁺ causes the membrane potential to become negative again.
- The membrane potential temporarily becomes more negative than the resting potential due to the continued efflux of K⁺ (hyperpolarization).
- This is because K⁺ channels are slow to close.
- Voltage-gated potassium channels close.
- The Na⁺/K⁺ pump and other ion channels restore the resting membrane potential.
- The neuron is now ready for another action potential.
- Depolarization is caused by the influx of Na⁺.
- Repolarization is caused by the efflux of K⁺.
- The action potential is a rapid, temporary change in the membrane potential that propagates along the axon, allowing neurons to transmit electrical signals over long distances.
What is a refractory period?
What are the types of refractory periods in action potentials
The refractory period is a crucial aspect of action potentials in neurons and muscle cells. It refers to the period of time following an action potential during which a neuron or muscle cell is less excitable and less likely to generate another action potential. There are two types of refractory periods: the absolute refractory period and the relative refractory period.
- Definition: During the absolute refractory period, it is impossible for another action potential to be initiated, regardless of the strength of the incoming stimulus.
- Cause: This occurs because the voltage-gated sodium (Na+) channels, which opened to initiate the action potential, become inactivated. They cannot reopen until the membrane potential returns to near the resting state and the Na+ channels have reset.
- Duration: The absolute refractory period typically lasts about 1-2 milliseconds following the initiation of the action potential.
- Importance: This period ensures that each action potential is a discrete, all-or-nothing event and helps to enforce the unidirectional one way propagation of the action potential along an axon.
So in absolute, it occurs right at the peak of the action potential where sodium channels are inactivated and ends in the early stages of repolarization. This period end when a significant number of sodium channels have recovered from the inactivation and have closed completely.
### 2. Relative Refractory Period
- Definition: During the relative refractory period, another action potential can be initiated, but it requires a stronger-than-normal stimulus to do so.
- Cause: This period corresponds to the time when voltage-gated potassium (K+) channels are still open, and the membrane is hyperpolarized (more negative than the resting potential). Additionally, some Na+ channels may still be in the process of resetting.
- Duration: The relative refractory period follows the absolute refractory period and lasts for several milliseconds.
- Importance: This period allows the neuron to limit the frequency of action potentials and contributes to the precise timing of signal transmission.
Relative Refractory period starts in the latter stages of the repolarization after the absolute own. It needs a stronger than normal stimulus to occur cuz the membrane potential is far away from threshold potential.
Slow Closing of Potassium Channels:
• The slow closing of K⁺ channels means that they remain open for a longer period than Na⁺ channels. As a result, K⁺ continues to exit the cell even after the membrane potential begins to drop.this leads to hyperpolarization
- Absolute Refractory Period: No new action potential can be initiated, regardless of stimulus strength. Ensures unidirectional propagation of the action potential and maintains the integrity of the signal.
- Relative Refractory Period: A stronger-than-normal stimulus is required to initiate a new action potential. Helps control the frequency of action potentials and fine-tunes signal timing.
These refractory periods are essential for the proper functioning of neurons and muscle cells, allowing them to reset and prepare for subsequent action potentials while maintaining the fidelity and directionality of signal transmission. Refractory Period: Ensures unidirectional propagation of the action potential and prevents immediate reactivation of the Na⁺ channels.
Return to Resting Potential
• Na⁺/K⁺ Pump: Restores and maintains the resting membrane potential by pumping Na⁺ out and K⁺ in.
Explain what happens at the synapse at the nerve terminal
At the nerve terminal, there is supposed to be exchange of Sodium potassium and other things as well as stimulus but it doesn’t have a membrane that continues to the other nerve membrane or the other cell. The stimulus could be excitatory (it will propagate action potential to the next cell) or inhibitory (it wouldn’t propagate action potential to the next nerve cell)
Certainly! Here’s a more detailed explanation incorporating the excitatory and inhibitory aspects at the synapse:
- Neurotransmitter Release: When an action potential reaches the presynaptic terminal, it triggers the release of neurotransmitter molecules from synaptic vesicles into the synaptic cleft.
- Neurotransmitter Binding: Neurotransmitters diffuse across the synaptic cleft and bind to specific receptor molecules on the postsynaptic membrane.
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Postsynaptic Response:
- Excitatory Synapses: Neurotransmitters like glutamate bind to excitatory receptors (e.g., AMPA receptors) on the postsynaptic membrane, causing depolarization (reduction in the membrane potential towards zero). This depolarization increases the likelihood that the postsynaptic neuron will fire an action potential.
- Inhibitory Synapses: Neurotransmitters such as GABA (gamma-aminobutyric acid) or glycine bind to inhibitory receptors (e.g., GABA receptors) on the postsynaptic membrane, causing hyperpolarization (increase in the membrane potential away from zero). This hyperpolarization decreases the likelihood that the postsynaptic neuron will fire an action potential.
- Termination of Neurotransmission: To ensure precise signaling, neurotransmission is terminated through mechanisms such as reuptake into the presynaptic terminal, enzymatic degradation in the synaptic cleft, or diffusion away from the synapse.
- Integration of Signals: The postsynaptic neuron integrates excitatory and inhibitory signals from multiple synapses. The balance between excitatory and inhibitory inputs determines whether the neuron will reach its threshold for firing an action potential.
These processes are crucial for neural communication, allowing for the transmission of information across synapses in the nervous system while maintaining the delicate balance between excitation and inhibition necessary for proper brain function.
What is the role of calcium and sodium in Neuro transmission
At the synapse, the exchange of ions like sodium (Na+) and calcium (Ca2+) plays a crucial role in neurotransmission. Here’s how these ions are involved:
-
Sodium (Na+):
- Action Potential Propagation: When an action potential reaches the presynaptic terminal, voltage-gated calcium channels open, allowing calcium ions to enter the terminal.
- Neurotransmitter Release: The influx of calcium ions triggers the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane, leading to neurotransmitter release into the synaptic cleft.
- Postsynaptic Response: After neurotransmitter release, sodium channels on the postsynaptic membrane may open in response to neurotransmitter binding, allowing sodium ions to enter the postsynaptic neuron. This influx of sodium ions can depolarize the postsynaptic membrane if the synapse is excitatory.
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Calcium (Ca2+):
- Neurotransmitter Release: Calcium ions are critical for triggering the fusion of synaptic vesicles with the presynaptic membrane. This process is essential for the release of neurotransmitters into the synaptic cleft.
- Postsynaptic Response: In some cases, calcium ions can directly influence postsynaptic responses. For example, in certain types of synapses, calcium influx into the postsynaptic neuron can activate signaling pathways that contribute to synaptic plasticity or long-term changes in synaptic strength.
Overall, the exchange of sodium and calcium ions at the synapse is essential for both the transmission of signals from the presynaptic neuron to the postsynaptic neuron and for regulating synaptic function and plasticity. These ion movements are tightly regulated and coordinated to ensure precise and efficient neural communication in the nervous system.
What is the role of calcium at the nerve terminal
Exchange of sodium and calcium sends the action potential along the membrane of the nerve all the way to the nerve terminal when it gets there,it causes calcium gates to open and these calcium gates attach themselves to the membrane of the terminal and that is where the synaptic vesicles are exocytosed to the synaptic cleft. Exchange of sodium and calcium sends the action potential along the membrane of the nerve all the way to the nerve terminal when it gets there,it causes calcium gates to open and these calcium gates attach themselves to the membrane of the terminal and that is where the synaptic vesicles are exocytosed to the synaptic cleft. The neurotransmitters in the synaptic vesicles will decide whether they are going to propagate the action potential or they aren’t going to propagate the action potential.
Calcium is responsible for the synaptic vesicles that contain the neurotransmitters to be released to wherever it has to
Calcium is responsible for the synaptic vesicles that contain the neurotransmitters to be released to wherever it has to.
When does repolarization occur?
At what mV does it occur?
Repolarization occurs immediately after the peak of the action potential. Typically, the peak of the action potential is around +30 to +40 mV. Repolarization begins when the membrane potential reaches this peak and the voltage-gated sodium (Na⁺) channels inactivate while the voltage-gated potassium (K⁺) channels open.
- Peak of the Action Potential: Around +30 to +40 mV.
- Repolarization Starts: Immediately after the peak when the membrane potential is at +30 to +40 mV.
During repolarization, the membrane potential moves from the positive peak back towards the negative resting membrane potential (around -70 mV).
Explain the sodium equilibrium potential
Sodium is higher in which part of the cell? Extracellular or intracellular
What is the equilibrium potential for Na?
Sodium is higher in the Extracellular space and lower in intracellular space.
The concentration gradient for Na tends to move this ion into the cell because Na is higher outside and lower inside.
2 The inside of the cell becomes more positive as Na+ ions move to the inside down their concentration gradient.
3 The outside becomes more negative as Na ions move in, leaving behind in the ECF unbalanced negatively charged ions, mostly C. So they leave the ECf and move into the ICF
4 The resulting electrical gradient tends to move Na out of the cell.
5 No further net movement of Nat occurs when the outward electrical gradient exactly counterbalances the inward concentration gradient. The membrane potential at this equilibrium point is the equilibrium potential for Nat (ENa+) at +60 mV.
At the equilibrium potential, the movement of sodium ions into the cell (driven by both the concentration gradient and electrical gradient) is equal to the movement of sodium ions out of the cell.
What is equilibrium potential?
Action potential generation is based on the electrochemical gradient as well as movement of what two ions?
The equilibrium potential for an ion is the membrane potential at which there is no net flow of that particular ion in or out of the cell. It’s determined by the concentration gradient of the ion across the membrane and the ion’s charge. The most common ions of interest are sodium (Na⁺) and potassium (K⁺).
Action potential is based on movement of sodium and potassium across the cell membrane.
During depolarization, Na⁺ rushes into the cell due to its electrochemical gradient (high concentration outside and electrical attraction to the negative interior), causing the membrane potential to become positive.
During repolarization, K⁺ flows out of the cell due to its electrochemical gradient (high concentration inside and electrical repulsion from the now-positive interior), driving the membrane potential back towards a negative value.
