Lecture 3 Flashcards
(53 cards)
The nervous system is divided into two main branches name them and the branches under those branches
- What does the “separation of powers” across a membrane refer to in cell physiology?
A. Division of the nucleus and cytoplasm
B. The presence of gap junctions in the membrane
C. Unequal distribution of electrical charges across the membrane
D. The separation of organelles by membranes
- What creates the “potential” for the membrane to do electrical work?
A. Movement of water molecules
B. Uniform ion distribution
C. Separation of opposite charges across the plasma membrane
D. Fusion of vesicles with the membrane
- When does a cell have no membrane potential?
A. When there is a strong electrical gradient
B. When charges are evenly distributed on both sides
C. When Na⁺ and K⁺ are separated
D. When the membrane is impermeable
- Why is the membrane potential considered “potential energy”?
A. It makes the membrane more rigid
B. It can be used to drive electrical signals or transport
C. It stores energy in ATP
D. It only functions during cell division
- Which condition would result in the greatest membrane potential?
A. No difference in ion concentration
B. Equal permeability to all ions
C. Large difference in ion concentration and selective permeability
D. Closed ion channels
Why is the resting membrane more permeable to potassium (K⁺) than to sodium (Na⁺)?
A. Sodium ions are smaller and move faster
B. There are more open potassium channels than sodium channels
C. Potassium ions are actively pumped out of the cell
D. Sodium channels are always open at rest
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.
Here are the correct answers and explanations for each MCQ:
- What does the “separation of powers” across a membrane refer to in cell physiology?
Correct answer: C. Unequal distribution of electrical charges across the membrane
Explanation:
This “separation of powers” is not political but physiological—it refers to separating positive and negative charges across the plasma membrane, creating an electrical gradient (membrane potential).
- What creates the “potential” for the membrane to do electrical work?
Correct answer: C. Separation of opposite charges across the plasma membrane
Explanation:
When charges are separated, they can be allowed to move (like opening a channel), releasing energy that can be used for work like nerve impulse transmission or muscle contraction.
- When does a cell have no membrane potential?
Correct answer: B. When charges are evenly distributed on both sides
Explanation:
If the charge on the inside and outside of the cell is the same, there is no electrical gradient—no stored energy to drive movement, so the membrane potential is zero.
- Why is the membrane potential considered “potential energy”?
Correct answer: B. It can be used to drive electrical signals or transport
Explanation:
It’s called “potential” because it’s stored energy that can be used for action potentials, secondary active transport, etc., once channels open and ions flow down their gradient.
- Which condition would result in the greatest membrane potential?
Correct answer: C. Large difference in ion concentration and selective permeability
Explanation:
A steep concentration gradient plus selective permeability (e.g., K⁺ leaks out but negative proteins stay in) creates a strong charge difference = strong membrane potential.
Why is the resting membrane more permeable to potassium (K⁺) than to sodium (Na⁺)?
A. Sodium ions are smaller and move faster
B. There are more open potassium channels than sodium channels
C. Potassium ions are actively pumped out of the cell
D. Sodium channels are always open at rest
Correct answer: B. There are more open potassium channels than sodium channels
Explanation:
At rest, more K⁺ leak channels are open compared to Na⁺ channels, so K⁺ diffuses out more easily, making the membrane more permeable to K⁺. This contributes to the negative resting membrane potential.
Distribution of lons Across the Plasma Membrane due to lon channels
• Nat and K+ can passively diffuse across the membrane through specific protein channels
At resting membrane potential, the membrane is much more permeable to K+ than to Nat because the cell has many more channels open for passive K+ traffic than for passive Na+ traffic
Sodium (Na⁺) and potassium (K⁺) passively diffuse across the membrane through leak channels:
Specific channels:
1. Potassium leak channels (K⁺ leak channels)
• Always open
• Allow K⁺ to leak out of the cell
• Responsible for the high K⁺ permeability at rest
2. Sodium leak channels (Na⁺ leak channels)
• Fewer in number
• Allow limited Na⁺ to leak in
• Contribute slightly to the resting membrane potential
These are non-gated (always open) channels that allow passive diffusion based on the electrochemical gradient.
How many neurons are in the brain
Explain separation of powers and how it affects membrane potential ( when will we say there is a potential?)
100 billion neurons
~ 104 synapses/ neuron
~ Trillions of synapses
All living cells have a plasma membrane potential (electrical polarization), which is measured in millivolts (mV).
Separation of opposite charges across plasma membrane allows a “potential” to do work.
When oppositely changed particles have been separated, the electrical force of attraction between them can be harvested to perform work once they are permitted to come together again (“potential” to do work).
The membrane potential is due to differences in concentration and permeability of key ions.
Inside cell: negative; Outside cell: positive
Membrane Potential = Electrical Potential Energy
• It exists when there is a separation of opposite charges across the plasma membrane.
• Ions like Na⁺, K⁺, and Cl⁻ are unequally distributed inside and outside the cell.
• This unequal distribution + selective membrane permeability (via ion channels/pumps) creates a voltage (potential) across the membrane.
When the Cell Has Membrane Potential:
• There is a separation of charge across the membrane:
• More positive charges outside, more negative charges inside.
• This creates an electrical gradient, usually around –70 mV in neurons (resting membrane potential).
• The cell is said to have “potential” energy, which can be used for nerve signals, muscle contraction, etc.
When the Cell Has No Membrane Potential:
• There is no charge difference across the membrane:
• Ions are evenly distributed on both sides.
• No electrical force exists to drive ion movement.
• This is called depolarization to zero or electrical neutrality.
• In this state, the cell has no potential to do electrical work.
So for a membrane to have potential, for the outside, it’s supposed to be more positive than the inside and for the inside, it’s supposed to be more negative than the outside. Example is outside (15+,10-) and inside being (15-,10+)
Your example works:
• Outside: 15 positive, 10 negative → Net: +5
• Inside: 15 negative, 10 positive → Net: –5
This separation of charges creates a voltage difference (membrane potential). The cell now has potential to do electrical work, like sending nerve impulses.
If both sides had equal net charges (e.g., +5 inside and +5 outside), then no membrane potential would exist
Exactly — that’s a perfect example.
In this case:
• Outside: 10 positive, 10 negative → Net charge = 0
• Inside: 10 positive, 10 negative → Net charge = 0
There is no difference in charge across the membrane, so the membrane potential = 0 mV.
This means no electrical gradient, and the cell has no stored electrical energy for work.
That’s what we mean when we say the cell has no membrane potential.
Would you like a quick table summarizing different scenarios for clarity?
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)
Which of the following best describes the electrochemical gradient that drives ion diffusion through open channels?
A. It is created only by the electrical charge difference across the membrane
B. It is the combination of concentration and electrical gradients across the membrane
C. It requires ATP to move ions through the channel
D. It only applies to neutral molecules, not ions
What is the role of the electrical driving force in ion movement through an open channel?
A. It pumps ions against their concentration gradient
B. It only affects uncharged molecules
C. It causes opposite charges to repel each other
D. It attracts opposite charges and repels like charges
When do the chemical and electrical driving forces act in the same direction?
A. When the ion is neutral
B. When the ion is pumped using energy
C. When both the concentration gradient and electrical gradient favor the same direction of movement
D. When the membrane potential is zero
The potential difference generated across a membrane results from what?
State the two criteria needed to achieve diffusion potential
State the four main types of diffusion potential (the explanations are at the end)
.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
Diffusion Potential of Electrolytes
• Potential difference generated across a membrane resulting from:
• Unequal diffusion of positive and negative ions
• Two criteria to achieve diffusion potential:
• Concentration gradient across the membrane
• Selective permeability of membrane
• Diffusion potential is created by movement of few ions which end up creating large changes in membrane potential.
Which of the following best describes the electrochemical gradient that drives ion diffusion through open channels?
A. It is created only by the electrical charge difference across the membrane
B. It is the combination of concentration and electrical gradients across the membrane
C. It requires ATP to move ions through the channel
D. It only applies to neutral molecules, not ions
Correct answer: B. It is the combination of concentration and electrical gradients across the membrane
Explanation:
• The electrochemical gradient combines:
• Chemical gradient (difference in ion concentration)
• Electrical gradient (difference in charge)
• Ions move passively through open channels according to this combined force.
What is the role of the electrical driving force in ion movement through an open channel?
A. It pumps ions against their concentration gradient
B. It only affects uncharged molecules
C. It causes opposite charges to repel each other
D. It attracts opposite charges and repels like charges
Correct answer: D. It attracts opposite charges and repels like charges
Explanation:
Negative areas attract positive ions and repel negative ions, and vice versa. This electrical force influences how ions move across the membrane.
- When do the chemical and electrical driving forces act in the same direction?
A. When the ion is neutral
B. When the ion is pumped using energy
C. When both the concentration gradient and electrical gradient favor the same direction of movement
D. When the membrane potential is zero
Correct answer: C. When both the concentration gradient and electrical gradient favor the same direction of movement
Explanation:
The chemical and electrical forces can work together (same direction) or oppose each other. When they work together, ion movement is faster and easier.
Note: Driving forces for Diffusion of lons through an Open Channel
Chemical driving force = the concentration gradient across the membrane
Electrical driving force = separation of charges causes an electrical gradient across the membrane
negative areas tend to attract positive ions and repel negative ions, and vice versa
Combined these forces lead to an electrochemical gradient.
Note that chemical and electrical forces can act in the same or opposite directions.
Diffusion of an ion through an open shannel is passive and requires no energy expenditure.
Types of Diffusion Potential
• Equilibrium Potential
• Resting membrane potential
• Graded Potential
• Action Potential
Of course! Here’s a much simpler version:
- Equilibrium Potential
The point where an ion stops moving in or out. Balance between charge and concentration.
- Resting Membrane Potential
The normal state of the cell when it’s not active. Inside is more negative than outside.
- Graded Potential
A small change in charge that happens near where a signal starts. It can grow or fade.
- Action Potential
A big, fast change in charge that travels down the cell. It happens when the signal is strong enough.
Let me know if you’d like even shorter one-line versions!
Or:
Sure! Here are two short sentences for each type of diffusion potential:
- Equilibrium Potential
It is the membrane potential at which there is no net movement of a specific ion. It reflects the balance between that ion’s concentration gradient and electrical gradient.
- Resting Membrane Potential
This is the steady voltage difference across the membrane of a resting (non-excited) cell, typically around -70 mV. It is mainly due to K⁺ leak channels and Na⁺/K⁺ pump activity.
- Graded Potential
These are small, localized changes in membrane potential that vary with stimulus strength. They can either depolarize or hyperpolarize the membrane and fade with distance.
- Action Potential
A rapid, large, and brief change in membrane potential that travels along excitable cells like neurons. It occurs when a threshold is reached, causing voltage-gated Na⁺ and K⁺ channels to open in sequence.
Would you like these summarized further into flashcard form?
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.
-
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.
-
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.
-
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.
-
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.
-
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.
-
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.
Explain the potassium equilibrium potential
Potassium is higher in which part of the cell? Extracellular or intracellular
What is the equilibrium potential for K or at what mV is K at equilibrium ?(it’s in mV)
Development of the equilibrium potential for K+.
The membrane is permeable to K+ but not Cl. Explain how this is useful in creating equilibrium potential for K+
1
The concentration gradient for K+ tends to move this ion out of the cell.
The outside of the cell becomes more positive as K* ions move to the outside down their concentration gradient.
The membrane is impermeable to the large intracellular protein anion (A). The inside of the cell becomes more negative as K+ ions move out, leaving behind A-.
4
The resulting electrical gradient tends to move K+ into the cell.
5
No further net movement of K+ occurs when the inward electrical gradient exactly counterbalances the outward concentration gradient. The membrane potential at this equilibrium point is the equilibrium potential for K+ (Ek+) at
-90 mV.
When a membrane is permeable to K⁺ but not permeable to Cl⁻, and there is a concentration gradient of K⁺ across the membrane, the following process occurs, leading to the development of the equilibrium potential for K⁺:
- Initial Condition:
• Inside the cell: High K⁺, High Cl⁻ (to balance charge)
• Outside the cell: Low K⁺, Low Cl⁻
There is no net charge difference initially because positive and negative ions are balanced on both sides.
- Diffusion of K⁺:
Since the membrane is permeable only to K⁺, these ions begin to move down their concentration gradient, from inside to outside.
- Development of Charge Separation:
As K⁺ moves out:
• The inside becomes more negative because positive charges (K⁺) are leaving.
• The outside becomes more positive.
But Cl⁻ cannot follow to balance the charge because the membrane is not permeable to it.
- Opposing Electrical Gradient Builds Up:
The growing negative charge inside the membrane begins to attract K⁺ back and oppose further K⁺ efflux.
- Equilibrium Potential is Reached:
Eventually, the chemical driving force (concentration gradient) pushing K⁺ out is exactly balanced by the electrical force pulling K⁺ back in.
At this point, there is no net movement of K⁺, and the equilibrium potential for K⁺ (also called Eₖ) is established.
- Calculated by the Nernst Equation:

This gives the voltage across the membrane that balances the concentration gradient of K⁺.
Yes, Cl⁻ not being permeable actually helps the K⁺ equilibrium potential to develop and remain stable.
Here’s why:
- Fixed Negative Charges Inside:
When K⁺ leaves the cell, the inside becomes negatively charged.
If Cl⁻ could also leave, it would follow K⁺ (because opposite charges attract), and reduce the buildup of negative charge inside.
This would weaken the electrical force pulling K⁺ back in, so Eₖ would not develop properly.
- Membrane Selectivity Is Key:
The membrane’s impermeability to Cl⁻ means the negative charges remain inside as K⁺ leaves.
This amplifies the electrical gradient, helping the inside become more negative quickly, which opposes further K⁺ loss.
- Stable Equilibrium Potential:
With Cl⁻ unable to move, only K⁺ contributes to the charge separation.
This makes the equilibrium potential for K⁺ well-defined and predictable using the Nernst equation.
In summary:
Cl⁻ not being permeable supports and stabilizes the formation of the K⁺ equilibrium potential by allowing a strong, unopposed electrical gradient to build up.
Would you like a simple analogy to make this clearer?
Define the Nernst equation and what it determines
Used to calculate the equilibrium potential for an ion at a given concentration difference across the membrane (assuming membrane is permeable to ion). The Nernst equation is indeed used to calculate the equilibrium potential for a specific ion based on its concentration difference across the cell membrane. It helps determine the voltage at which there is no net flow of that ion across the membrane
Determines the electrical force required to just balance a given diffusion force ([ion]in - [ion]out).
cell
What is the calculation for the Nernst equation
Note: equilibrium potential for sodium is +65mV, for potassium is -90mV, for chloride is -70mV
Here’s the Nernst equation in detail:
Original equation is Eion =(RT/zF)In([ion]out/[ion]in)
Where R is universal gas constant,T is temperature in Kelvin,F is faraday constant
However, at body temperature (approximately 37°C or 310 K), the equation can be simplified and converted to a more convenient form for practical use in biological system. This simplified Nernst equation at body temperature is the equation below:
Eion = (60/z) log ( [ion]out/ [ion]in)
E ion = equilibrium potential for ion (mV)
z = ionic valence of ion (charge of the ion +/-) For example, for Na⁺, ( z = +1 ); for K⁺, ( z = +1 ); for Ca²⁺, ( z = +2 ); and for Cl⁻, ( z = -1 ).
[ion]out = extracellular concentration for ion (mmol/L)
[ion]in = intracellular concentration for ion (mmo/L)
Calculate electrochemical potential difference required to achieve electrochemical equilibrium for K+
• Eion = (60/z) log([ion]out / [ion]in)
E ion = equilibrium potential for ion
Z = ionic valence of ion
[ion]out= 5mM
[ion]in= 150 mM
What does your answer mean?
Ek+ = (60/+1) log(5 / 150)= -88.6 rounded to -89 mV
This means that when [K]in = 150 mM and [K]out = 5 mM, potassium flux is at
equilibrium when the cell is -89 mV inside.
Remember that equilibrium implies
that concentration force = electrical force; so that influx = efflux.
The chemical aspect of this equation is where the concentration gradient plays a role and the electrical aspect falls about the charges
The separation of charges across the cell membrane creates the membrane potential. Explain how this occurs
Which ions are concentrated more outside the cell than inside?
Which are more concentrated inside the cell than outside?
Why is the cell membrane selectively permeable to different ions?
Which ion mainly determines the resting membrane potential and why?
What is the Goldman-Hodgkin-katz equation and how is it different from the Nernst equation?
How is action potential generated ?
Separation of Charges
• Ion Distribution: Cells maintain different concentrations of ions inside and outside the cell. Key ions include sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), and various other anions (A⁻). • Na⁺: High outside, low inside • K⁺: High inside, low outside • Cl⁻: High outside, low inside • A⁻ (other anions, e.g., proteins): High inside, low outside • Selective Permeability: The cell membrane is selectively permeable to different ions, primarily due to specific ion channels that open and close in response to various signals. • Na⁺/K⁺ Pump: This pump actively transports 3 Na⁺ ions out of the cell and 2 K⁺ ions into the cell, using ATP. (So the pump sends the ions back to where they’re supposed to be. Which is sodium outside and potassium inside but the concentration gradient moves the ions to make things equal. )This creates and maintains the concentration gradients for Na⁺ and K⁺, contributing to the charge separation.
- Creation of Membrane Potential• Resting Membrane Potential: The membrane potential at rest, typically around -70 mV in neurons, is mainly determined by the K⁺ gradient. The cell membrane is more permeable to K⁺ than to Na⁺ or other ions at rest.
• K⁺ tends to move out of the cell due to its concentration gradient(So because potassium on a regular is more inside, it wants to make things equal so it pumps
Potassium out and sodium in. ), but this movement is balanced by the electrical gradient pulling K⁺ back in.
• The equilibrium potential for K⁺ (Eₖ) is about -90 mV, which significantly influences the resting membrane potential.
• Goldman-Hodgkin-Katz Equation: While the Nernst equation calculates the equilibrium potential for a single ion, the Goldman-Hodgkin-Katz equation considers multiple ions to determine the resting membrane potential:• ( V_m ) = membrane potential
• ( P_{ion} ) = permeability of the ion
• = concentration of the ion inside/outside the cell - Action Potential Generation• Depolarization: A stimulus opens voltage-gated Na⁺ channels, allowing Na⁺ to rush into the cell. This influx of positive charge depolarizes the membrane, making the inside more positive.
• Peak: The membrane potential can reach around +30 to +40 mV, where Na⁺ channels inactivate, and K⁺ channels open.
• Repolarization: K⁺ ions flow out of the cell, restoring the negative membrane potential.
• Hyperpolarization: The membrane potential briefly becomes more negative than the resting potential due to continued K⁺ efflux.
• Return to Resting Potential: Na⁺/K⁺ pumps and leak channels restore the resting membrane potential.
Summary
• Separation of Charges: Due to different ion concentrations inside and outside the cell and selective permeability of the membrane. • Membrane Potential: The electrical potential difference across the cell membrane due to this separation. • Resting Membrane Potential: Primarily determined by K⁺ gradients and membrane permeability. • Action Potential: A rapid change in membrane potential due to the sequential opening and closing of Na⁺ and K⁺ channels.
For action potential, There’s been a stimuli and the stimuli is great enough to destabilize the resting membrane potential to an extent that it reaches the threshold potential. What is the threshold potential?
How does it initiate action potential?
This is when the action potential fires. This causes depolarization. When the action potential is fired and it reaches the maximum,it goes back down or stabilizes. This is when repolarization starts(trying to send membrane back to its resting potential).
he threshold potential is the critical level to which the membrane potential must be depolarized in order to initiate an action potential. It is the point at which the influx of sodium ions (Na⁺) through voltage-gated sodium channels becomes self-sustaining, leading to a rapid and large depolarization of the membrane.
Key Points about Threshold Potential:
1. Value: The threshold potential is typically around -55 mV in neurons, but this value can vary depending on the type of cell and its specific conditions. 2. All-or-None Principle: If the membrane potential reaches the threshold, an action potential will be triggered. If the depolarization does not reach this threshold, an action potential will not occur. This is known as the “all-or-none” principle.
Initiation of Action Potential: The threshold potential marks the point where the membrane’s depolarization is sufficient to trigger the opening of enough voltage-gated Na⁺ channels to produce a rapid and irreversible depolarization. This leads to the peak of the action potential. If the depolarization is strong enough, it will bring the membrane potential to the threshold level (around -55 mV).
Action Potential Initiation: At threshold, voltage-gated Na⁺ channels open rapidly, causing a large influx of Na⁺. This depolarizes the membrane even further, triggering a full action potential.
5. Role in Excitability: The threshold potential is crucial in determining the excitability of a neuron. Factors that affect the threshold potential include:
• The density and distribution of voltage-gated Na⁺ channels.
• The presence of other ion channels and their conductance.
• The overall membrane properties, such as capacitance and resistance.
What is a neurotransmitter
State five properties of the neurotransmitter
Who discovered neuro transmitters
Neurotransmitters are classified by their chemical nature and functional nature. State them.
neurotransmitter is a chemical messenger that transmits signals across a synapse from one neuron (the presynaptic neuron) to another neuron, muscle cell, or gland cell (the postsynaptic cell).
A substance is generally considered a neurotransmitter if it is/has:
-synthesized in the neuron (typically in the cell body or in the synaptic terminals and stored in synaptic vesicles within the presynaptic neuron.
-found in the presynaptic terminal (must be present in the presynaptic terminal, where it is stored in synaptic vesicles ready for release.)
-released to have an effect in the postsynaptic cell (Upon arrival of an action potential at the presynaptic terminal, the neurotransmitter must be released into the synaptic cleft through a process called exocytosis and bind to specific receptors on the postsynaptic cell, eliciting a physiological response(effect could be excitatory or inhibitory))
-mimicked by exogenous application to the postsynaptic cell(When the neurotransmitter is applied externally (exogenously) to the postsynaptic cell, it should produce the same effect as when it is released endogenously from the presynaptic neuron. Example is Exogenous application of acetylcholine to the postsynaptic cell mimics the natural effects, such as muscle contraction when applied to a neuromuscular junction.)
-a specific mechanism for termination of its action.(This can include reuptake into the presynaptic neuron, enzymatic degradation, or diffusion away from the synaptic cleft.)
Neurotransmitters
• History-discovery by Loewi
• Inclusion criteria:
• Synthesized and released by neuron,
• Present in neuron,
• Neurotransmitters
• Classification: Chemical nature
• Amino acids: Involved in fast synaptic transmission. Excitatory or inhibitory eg:
GABA, glycine, glutamate, aspartate.
• Amines: Involved in slow synaptic transmission. Can be excitatory or inhibitory eg: adrenaline, noradrenaline, dopamine, serotonin, histamine.
• Others: Acetylcholine, NO…
Classification: functional
• Excitatory: opening of Na+ channels causing EPSP
• Inhibitory: opening of K+ channels causing IPSP
Here are examples of functionally classified synapses:
Excitatory Synapse (EPSP):
• Mechanism: Opening of Na⁺ channels, allowing Na⁺ to enter the postsynaptic neuron and make the membrane potential more positive (toward threshold).
• Example:
• Glutamate acting at AMPA receptors in the hippocampus or cortex.
• Acetylcholine at nicotinic receptors in the neuromuscular junction.
Excitatory neuro-
transmitters
1. Acetycholine
2. Nitric oxie
3. Histamine
4, Clutamale
5, Aspartae
Inhibitory Synapse (IPSP):
• Mechanism: Opening of K⁺ or Cl⁻ channels, causing the membrane potential to become more negative (hyperpolarized).
• Examples:
• GABA acting at GABA-A receptors (Cl⁻ channels) in the brain.
• Glycine acting in the spinal cord to open Cl⁻ channels.
• Some GABA-B receptors open K⁺ channels (inhibitory via K⁺ efflux).
Inhibitory neuro* transmitters
1. GABA
2. Glycine
3. Dopamine
4, Serotonin
Neurotransmitters with excitatory and inhibitory actions
1. Noradrenaline
2. Adrenaline
. The neurotransmitters types are acetylcholine, biogenic amines, amino acids and neuropeptides.
Catecholamines are derived from what amino acid?
Indoleamines are derived from what amino acid?
State two excitatory amino acids
State two inhibitory amino acids
Endorphin is what type of neurotransmitter?
Oxytocin and Vasoactive Intestinal Peptide (VIP) are what types of neurotransmitters?
Histamine is what type of neurotransmitter
Neurotransmitters in the Body
1.• Acetylcholine (ACh)
2.• Biogenic Amines:
• Catecholamines; these are Derived from tyrosine.(• Dopamine,• Norepinephrine, • Epinephrine) Remember TyroCat
•Indoleamines: Derived from tryptophan(•Serotonin: Regulates mood, appetite, and sleep,Melatonin)
remember TryptoIndo
•Histamine: Involved in arousal, attention, and allergic responses.
3• Amino Acids:
• Excitatory Amino Acids(• Aspartate,Glutamate)
• Inhibitory Amino Acids:
(• Gamma-amino-butyric Acid (GABA), • Glycine)
4.• Neuropeptides:
• Endogenous opioids (for example, endorphin for pain regulation)
• Vasoactive Intestinal Peptide (VIP) which plays a role in vasodilation and relaxes smooth muscles in the GIT
• Oxytocin
At the synaptic cleft, the action potential causes release of calcium through voltage gated calcium channels. These channels open to allow calcium to enter. This causes binding of the vesicles that hold neurotransmitters and the membrane of the neuron. When they bind, the neurotransmitters are synapsed into the synaptic cleft then they go and bind to the receptors they are to go and bind to(the post synaptic receptors). Whether it produces an inhibitory or excitatory effect depends on the type of neurotransmitter. After doing its effect. It is either broken down to be recycled to produce more of it later or diffused out of the cleft or undergoes active neurotransmitter reuptake by presynaptic cell
Or The presynaptic neuron at rest. Calcium hannels are closed, and no neurotransmitter is being released. (b) An active presynaptic neuron. ommunication occurs as follows: The membrane is depolarized by the arrival of an action otential. 2 Calcium channels open. 3 Calcium enters the cell and triggers the release of eurotransmitter by exocytosis. Neurotransmitter diffuses across the synaptic cleft; some of it inds to receptors on the postsynaptic cell membrane. A response is produced in the ostsynaptic cell. 6 Some neurotransmitter is degraded by enzymes. Some neurotransmitter s taken up by the presynaptic cell.
® Some neurotransmitter (or products of its degradation)
