Topic 4: chpt 8 and chpt 11 Flashcards
What are the two parts of the nervous system?
-Central Nervous System (CNS): Consists of the brain and the spinal cord.
-Peripheral Nervous System (PNS): Comprises sensory (afferent) neurons and efferent neurons.
Describe the flow of information through the nervous system.
1.) Sensory Input: Sensory receptors monitor internal and external environments and send information along sensory neurons to the CNS.
2.) Integration: The CNS integrates sensory information and determines if a response is necessary.
3.) Motor Output: If a response is needed, the CNS sends output signals through efferent neurons to target muscles and glands.
How are efferent neurons subdivided in the nervous system?
-Somatic Motor Division: Controls skeletal muscles.
-Autonomic Division: Regulates smooth and cardiac muscles, exocrine glands, some endocrine glands, and some types of adipose tissue.
How are autonomic neurons further divided, and what distinguishes them?
Sympathetic and Parasympathetic Branches: Distinguished by their anatomical organization and the chemicals they use to communicate with target cells.
What is the enteric nervous system, and how does it function?
The enteric nervous system is a network of neurons in the walls of the digestive tract. It is controlled by the autonomic division but can also function autonomously as its own integrating center.
How are neurons classified structurally?
Neurons are classified structurally based on the number of processes originating from the cell body. Common structural classifications include multipolar, pseudounipolar, bipolar, and anaxonic neurons
Describe the structure of sensory neurons.
Peripheral sensory neurons are pseudounipolar, with cell bodies located close to the CNS and very long processes extending out to receptors in the limbs and internal organs. Sensory neurons in the nose and eye are smaller bipolar neurons.
What are interneurons, and where are they located?
Interneurons, also known as interconnecting neurons, lie entirely within the CNS. They have complex branching processes that allow communication with many other neurons.
What are the characteristics of efferent neurons?
Efferent neurons, both somatic motor and autonomic, typically have axons that divide into branches called collaterals and have enlarged endings called axon terminals. Many autonomic neurons also have enlarged regions along the axon called varicosities, which store and release neurotransmitters.
What are nerves, and how are they formed?
Nerves are cordlike fibers formed by the bundling together of the long axons of both afferent and efferent peripheral neurons with connective tissue. Nerves extend from the CNS to the targets of the component neurons
What are the types of nerves based on the signals they carry?
Nerves that carry only afferent signals are called sensory nerves, those that carry only efferent signals are called motor nerves, and those that carry signals in both directions are called mixed nerves.
What is the primary function of the cell body (cell soma) of a neuron?
The cell body contains DNA that serves as the template for protein synthesis, essential for the well-being of the cell.
Describe the structure and function of dendrites in neurons.
Dendrites are thin, branched processes that receive incoming information from neighboring cells. They increase the surface area of a neuron, allowing it to receive communication from multiple other neurons. Dendritic spines on dendrites can function as independent compartments and change their size and shape in response to input from neighboring cells.
What is the function of axons in neurons?
The primary function of an axon is to transmit outgoing electrical signals from the integrating center of the neuron to target cells at the end of the axon.
What is axonal transport, and how does it occur?
Axonal transport is the process by which proteins synthesized in the cell body are moved in vesicles down the axon to the axon terminal. It occurs through the action of motor proteins (kinesin-1 and dynein) that “walk” along stationary microtubules as tracks, powered by ATP.
How is axonal transport classified based on the speed of material movement?
Axonal transport is classified into fast and slow transport. Fast axonal transport moves material in both directions at rates of up to 400 mm per day, while slow axonal transport moves soluble proteins and cytoskeleton proteins at rates of 0.2–8 mm/day.
What are the implications of mutations or alterations in proteins associated with axonal transport?
Mutations or alterations in proteins associated with axonal transport have been linked to various inherited and acquired disorders, including microcephaly, fragile X syndrome, Alzheimer’s disease, and other neurodegenerative diseases.
What is a synapse, and what are its components?
A synapse is the region where an axon terminal meets its target cell. The presynaptic cell delivers a signal to the synapse, while the postsynaptic cell receives the signal. The narrow space between the two cells is called the synaptic cleft, filled with extracellular matrix fibers holding the cells in position.
Describe the difference between chemical and electrical synapses.
Chemical synapses involve the release of a chemical signal from the presynaptic cell, which diffuses across the synaptic cleft and binds to a receptor on the postsynaptic cell. Electrical synapses allow electrical current and chemical signals to pass directly between cells through gap junction channels, enabling bidirectional communication and faster signaling.
How do embryonic nerve cells find their correct targets and form synapses during development?
Embryonic nerve cells send out growth cones, special tips of axons that extend through the extracellular compartment until they find their target cell. Growth cones depend on various signals, including growth factors, molecules in the extracellular matrix, and membrane proteins, to guide them to their targets.
What is the significance of neurotrophic factors in the formation and maintenance of synapses?
Neurotrophic factors, secreted by neurons and glial cells, play a crucial role in the survival of neuronal pathways. Without electrical and chemical activity following synapse formation, the synapse may disappear. Neurotrophic factors ensure the survival of synapses and promote brain growth and development.
How does synaptic rearrangement occur throughout life, and why is it important?
Variations in electrical activity can cause rearrangement of synaptic connections, a process that continues throughout life. This synaptic plasticity allows for adaptation to changing environments and experiences. Maintaining synapses through learning new skills and information is essential for cognitive function and brain health throughout life.
What are glial cells, and what is their role in the nervous system?
Glial cells, also known as glia or neuroglia, outnumber neurons by 10–50 to 1 and provide important biochemical and structural support in the nervous system. They wrap around neurons to create structural stability, support, and insulation. Glial cells also communicate with neurons and with each other, influencing information processing and neural function.
Describe the function of Schwann cells and oligodendrocytes in the nervous system.
Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS) support and insulate axons by forming myelin, a substance composed of multiple concentric layers of phospholipid membrane. Myelin acts as insulation around axons and speeds up signal transmission. Schwann cells associate with one axon in the PNS, while oligodendrocytes branch and form myelin around portions of several axons in the CNS.
What are the nodes of Ranvier, and what role do they play in signal transmission along axons?
The nodes of Ranvier are tiny gaps between myelin-insulated segments of axons in the peripheral nervous system (PNS). At the nodes, a small section of axon membrane remains in direct contact with the extracellular fluid. These nodes play an important role in the transmission of electrical signals along the axon by allowing the signal to “jump” from node to node, a process known as saltatory conduction.
What are satellite cells, and where are they found in the nervous system?
Satellite cells are a type of nonmyelinating Schwann cell found in the peripheral nervous system (PNS). They form supportive capsules around nerve cell bodies located in ganglia, which are collections of nerve cell bodies found outside the central nervous system (CNS).
Describe the functions of astrocytes, microglia, and ependymal cells in the nervous system.
- Astrocytes are highly branched CNS glial cells that provide structural support and form a functional network. They are closely associated with synapses, provide metabolic substrates for ATP production, help maintain homeostasis in the CNS extracellular fluid, and contribute to the blood-brain barrier.
-Microglia are specialized immune cells that reside permanently in the CNS. They remove damaged cells and foreign invaders but can also release damaging reactive oxygen species when activated, contributing to neurodegenerative diseases.
-Ependymal cells create a selectively permeable epithelial layer, the ependyma, that separates the fluid compartments of the CNS. They are a source of neural stem cells and contribute to the maintenance and repair of the nervous system.
What happens when adult neurons are injured, and how do mature neurons respond to injury?
When adult neurons are injured, the responses are similar to the growth of neurons during development. If the cell body dies, the entire neuron dies, but if only the axon is severed, the cell body and attached segment of axon survive. Cellular events following neuron damage include leakage of axon cytoplasm, swelling of the attached axon segment, signaling from Schwann cells to the cell body, cessation of synaptic transmission, and eventual clearance of debris by scavenger cells.
Describe the process of axon regeneration in the peripheral nervous system (PNS).
In the PNS, axons can regenerate under certain conditions. Schwann cells secrete neurotrophic factors that keep the cell body alive and stimulate axon regrowth. The regenerating axon tip behaves like a growth cone, following chemical signals in the extracellular matrix until it forms a new synapse with its target cell. However, regeneration is not always successful, and permanent loss of the axon and its pathway may occur.
Why is axon regeneration less likely to occur naturally in the central nervous system (CNS)?
In the CNS, glial cells tend to seal off and scar the damaged region, and damaged CNS cells secrete factors that inhibit axon regrowth. This inhibitory environment makes axon regeneration less likely to occur naturally in the CNS compared to the PNS.
How do neural stem cells contribute to neuron replacement and repair in the nervous system?
Neural stem cells, located in specific areas of the brain such as the hippocampus and lateral ventricle walls, remain unspecialized until they receive signals to replace damaged cells. When activated, neural stem cells transform into neurons and glial cells, contributing to neuron replacement and repair. Researchers are studying ways to control this transformation to develop treatments for injuries and degenerative neurological diseases.
What distinguishes nerve and muscle cells as excitable tissues?
They propagate electrical signals rapidly in response to stimuli, generating electrical signals for intracellular processes and communication over long distances.
What is the purpose of the Nernst Equation in the context of membrane potential?
It predicts the membrane potential for an individual ion (E_ion), based on the ion’s concentration gradient across the cell membrane, using the equation E_ion = (61/z) * log([ion]_out/[ion]_in).
What two factors influence the resting membrane potential according to the Nernst Equation?
- The uneven distribution of ions, particularly Na+, K+, Cl-, and Ca2+ across the cell membrane.
- The membrane’s permeability, with K+ having the most significant effect because the membrane is more permeable to K+ than Na+ or Ca2+.
How does the GHK (Goldman-Hodgkin-Katz) equation provide a more comprehensive prediction of membrane potential than the Nernst equation?
The GHK equation considers the contribution of all ions that can cross the membrane, incorporating their relative permeabilities, not just a single ion like the Nernst equation.
What is the full formula of the GHK equation? (for NA, K and CL)
The formula is V_m = 61 * log((P_K[K+]_out + P_Na[Na+]_out + P_Cl[Cl-]_in) / (P_K[K+]_in + P_Na[Na+]_in + P_Cl[Cl-]_out)),
-where V_m represents the membrane potential and P_ion symbolizes the relative permeability of the membrane to the ion.
-it can be simplified into words to say: Resting membrane potential (V m ) is determined by the combined contributions of the (concentration gradient * membrane permeability) for each ion.
-The GHK equation explains how the cell’s slight permeability to Na + makes the resting membrane potential more positive than the Ek determined with the Nernst equation.
-The GHK equation can also be used to predict what happens to membrane potential when ion concentrations or membrane permeabilities change.
What primarily determines the resting membrane potential of living cells?
The resting membrane potential is determined primarily by the permeability to potassium (K+), the concentration gradient of K+, and the resting permeabilities to sodium (Na+) and chloride (Cl-).
How do changes in K+ concentration gradient or ion permeabilities affect membrane potential?
Any change in the K+ concentration gradient or the permeabilities of ions like Na+ and Cl- can alter the membrane potential.
How is the GHK equation used to calculate changes in membrane potential?
The Goldman-Hodgkin-Katz (GHK) equation calculates the membrane potential by using numerical values for ion concentrations and permeabilities, allowing prediction of changes in membrane potential.
What happens when the membrane’s permeability to Na+ increases suddenly?
An increase in Na+ permeability allows Na+ to enter the cell, moving down its electrochemical gradient and depolarizing the membrane, thereby creating an electrical signal.
What causes a cell to hyperpolarize or depolarize?
Hyperpolarization occurs when the cell becomes more negative than the resting potential, and depolarization occurs when it becomes less negative (more positive).
Does a change in membrane potential from -70 mV to +30 mV indicate a reversal of ion concentration gradients?
No, a significant change in membrane potential does not imply that ion concentration gradients have reversed. Even a large change in membrane potential involves the movement of very few ions relative to total ion concentration.
How many ions need to move to change the membrane potential significantly?
To change the membrane potential by 100 mV, only about 1 out of every 100,000 K+ ions needs to move, which is a tiny fraction that does not significantly alter the overall ion concentration within the cell.
What are the primary ways a cell can change its ion permeability?
Cells can alter ion permeability by opening or closing existing channels or by adjusting the number of channels in the membrane, either by inserting new channels or removing existing ones.
What are the four major types of selective ion channels found in neurons?
Neurons contain selective ion channels specifically for Na+ (sodium), K+ (potassium), Ca2+ (calcium), and Cl- (chloride). Each type is named for the primary ion it transports.
What are monovalent cation channels, and how are they different from selective ion channels?
Monovalent cation channels are less selective and can allow both Na+ and K+ to pass through, unlike the selective channels that are specific to one type of ion.
What does channel conductance refer to, and how does it vary?
Channel conductance (G) refers to the ease with which ions flow through a channel. It varies with the gating state of the channel and the specific isoform of the channel protein.
What are the three main categories of gated channels found in neurons?
- Mechanically gated ion channels: Open in response to physical forces like pressure or stretch.
- Chemically gated ion channels: Respond to extracellular neurotransmitters and neuromodulators, or intracellular signal molecules.
- Voltage-gated ion channels: Open and close in response to changes in membrane potential.
How do voltage-gated Na+ and K+ channels contribute to neural signaling?
Voltage-gated Na+ channels open very rapidly upon depolarization, allowing Na+ to flow into the neuron, while K+ channels, which open more slowly, allow K+ to flow out during repolarization. This sequence supports the initiation and propagation of electrical signals along the axon.
What is channel inactivation, and how is it different from regular gating?
Channel inactivation occurs when a channel “times out” and closes automatically, despite the presence of the activating stimulus. This mechanism is different from regular gating, which depends directly on changes in membrane potential. An inactivated channel returns to its normal closed state shortly after the membrane repolarizes. The specific mechanisms underlying channel inactivation vary with different channel types
Discuss the diversity and modulation mechanisms of ion channels
Ion channels have multiple subtypes and isoforms that differ in their opening and closing kinetics and are often associated with proteins that modify their properties. Channel activity can also be modulated by chemical factors such as phosphate groups, altering how they respond to stimuli.
State Ohm’s law and its relevance to current flow in biological systems
Ohm’s law states that current flow (I) is directly proportional to the electrical potential difference (V) between two points and inversely proportional to the resistance (R) of the system to current flow, expressed as: 𝐼 = 𝑉/𝑅
Describe the typical movement patterns of K+, Na+, Cl-, and Ca2+ ions and their effects on the cell.
K+ ions usually exit the cell, leading to hyperpolarization. In contrast, Na+, Cl-, and Ca2+ usually enter the cell, often resulting in depolarization. These movements affect the cell’s membrane potential, either exciting or inhibiting cellular activity depending on the direction and magnitude of ion flow.
What is the impact of Na+ and K+ movement on membrane potential?
Influx of Na+ depolarizes the cell membrane, while K+ efflux hyperpolarizes it. The differential permeability to these ions influences the resting membrane potential.
What role does the Na+/K+ pump play in membrane potential?
The Na+/K+ pump helps maintain the resting membrane potential by moving 3 Na+ out of the cell and 2 K+ into the cell against their concentration gradients, using ATP for energy.
What are the three phases of an action potential?
The three phases of an action potential are the rising phase (depolarization), the peak (overshoot), and the falling phase (repolarization), followed by after-hyperpolarization.
How do graded potentials differ in the way they change membrane potential?
Graded potentials can be either depolarizations or hyperpolarizations and their amplitude depends on the strength of the stimulus. They decrease in strength as they spread through the cell
What is the initial segment in the context of action potential generation?
The initial segment, often found at the axon hillock, is where the action potential is typically initiated due to a high concentration of voltage-gated Na+ channels.
Explain the difference between conductance and conduction in neurons.
Conductance refers to the ability of ions to flow through channels, while conduction refers to the transmission of electrical signals along the axon.
Describe the term “current leak.”
Current leak refers to the flow of ions through the neuron cell body’s open leak channels, allowing some ions to leak out into the extracellular fluid.
Explain the term ‘multiplicity of form’ in the context of channel proteins.
Channel proteins have multiple subtypes and variants, which can express different gating and conductance behaviors known as ‘multiplicity of form.’
How do graded potentials reflect stimulus strength?
Graded potentials vary in amplitude according to the strength of the stimulus, with larger stimuli producing stronger depolarizations or hyperpolarisations.
Differentiate between graded potentials and action potentials.
Graded potentials have variable amplitude and occur mainly in dendrites and cell bodies, while action potentials have a consistent amplitude and propagate along axons.
What initiates the signal for graded potentials and action potentials?
Graded potentials are initiated by the entry of ions through gated channels, whereas action potentials are initiated by graded potentials that reach a threshold at the trigger zone.
Unique characteristics of graded potentials vs. action potentials.
Graded potentials have no minimum level required to initiate and can summate, while action potentials follow an all-or-none principle and cannot summate during the refractory period.
Describe the role of the absolute refractory period in action potential propagation.
The absolute refractory period occurs when the voltage-gated Na+ channels are either open or inactivated, making it impossible to initiate another action potential. This period ensures the unidirectional flow of the action potential along the axon and sets a limit on the frequency of action potentials.
What are the main sources of resistance to current flow in biological electricity?
The main sources of resistance to current flow in biological electricity are the resistance of the cell membrane (Rm) and the internal resistance of the cytoplasm (Ri). The resistance from the extracellular fluid (Ro) is usually negligible compared to Rm and Ri.
How does the opening of ion channels affect membrane resistance?
The opening of ion channels decreases membrane resistance. When ion channels open, ions (current) flow across the membrane if there is an electrochemical gradient for them, leading to a decrease in membrane resistance.
What determines the internal resistance of most neurons?
The internal resistance of most neurons is determined by the composition of the cytoplasm and the diameter of the cell. While cytoplasmic composition is relatively constant, internal resistance decreases as cell diameter increases. Therefore, larger diameter neurons have lower resistance.
What is the length constant in biological electricity, and how is it determined?
The length constant, sometimes called the space constant, is a measure of how far current will flow through a neuron before the energy is dissipated and the current dies. It is determined by the combination of resistances (Rm, Ri, and Ro) and can be calculated mathematically. The length constant is influenced by membrane resistance, internal resistance, and extracellular resistance.
What determines the strength of the initial depolarization in a graded potential?
The strength of the initial depolarization in a graded potential is determined by the amount of charge that enters the cell, similar to how the size of waves from a thrown stone depends on the stone’s size.
Why do graded potentials lose strength as they move through the cytoplasm?
Graded potentials lose strength due to two factors: current leak (where positive charge leaks out into the extracellular fluid) and cytoplasmic resistance (which resists the flow of electricity).
What is the trigger zone in a neuron?
The trigger zone is the integrating center of the neuron, located at the axon hillock or the initial segment of the axon in efferent neurons and interneurons, and next to the receptor in sensory neurons. It contains a high concentration of voltage-gated Na+ channels.
What happens when a graded potential reaches the trigger zone?
If a graded potential reaching the trigger zone depolarizes the membrane to the threshold voltage, voltage-gated Na+ channels open, starting an action potential. If it doesn’t reach the threshold, the potential dies out.
What are excitatory and inhibitory graded potentials?
Excitatory graded potentials make a neuron more likely to fire an action potential by depolarizing it, while inhibitory potentials make it less likely by hyperpolarizing it.
What is the difference between subthreshold and suprathreshold graded potentials?
Subthreshold graded potentials are below the threshold at the trigger zone and do not initiate an action potential, while suprathreshold graded potentials are strong enough to exceed the threshold and initiate an action potential.
What is neuronal excitability?
Neuronal excitability is the ability of a neuron to respond to a stimulus and potentially fire an action potential.
What are action potentials?
Action potentials, also known as spikes, are uniform-strength electrical signals that travel from a neuron’s trigger zone to the end of its axon without losing strength.
How do action potentials maintain their strength along the axon?
In action potentials, voltage-gated ion channels open sequentially along the axon, allowing additional Na+ to enter and reinforce the depolarization, ensuring the action potential does not lose strength over distance.
What is the amplitude of depolarization in an action potential?
The depolarization in an action potential is about 100 mV in amplitude, remaining constant along the axon from start to end.
What is meant by the “conduction” of an action potential?
The conduction of an action potential refers to the high-speed movement of this electrical signal along the axon.
How are action potentials described in terms of occurrence?
Action potentials are described as “all-or-none” phenomena—they either occur fully as a maximal depolarization if the stimulus reaches threshold or not at all if it’s below threshold.
Does the strength of the initiating graded potential affect the amplitude of the action potential?
No, the strength of the graded potential that initiates an action potential does not influence the amplitude of the action potential.
How does an action potential propagate along the axon?
Action potentials propagate along the axon like a series of falling dominos, where each segment of the axon sequentially depolarizes and repolarizes, maintaining the energy state along the axon.
What would recording electrodes show if placed along the axon during an action potential?
Recording electrodes would show overlapping action potentials at different stages along the axon, similar to dominos captured in different positions of falling.
What initiates an action potential in a neuron’s axon?
An action potential is initiated when a suprathreshold stimulus at the trigger zone depolarizes the membrane to the threshold (around -55 mV), causing voltage-gated Na+ channels to open.
What changes occur in the axon membrane during an action potential?
During an action potential, voltage-gated Na+ channels open increasing Na+ permeability, followed by the opening of K+ channels which increase K+ permeability. This sequence supports the phases of depolarization and repolarization.
What are the three phases of an action potential?
The three phases of an action potential are: 1) Rising phase (depolarization due to Na+ influx), 2) Falling phase (repolarization due to K+ efflux), 3) After-hyperpolarization phase (undershoot due to continued K+ outflow).
Describe the rising phase of the action potential.
In the rising phase, the permeability of Na+ dramatically increases due to voltage-gated Na+ channels opening. Na+ flows into the cell, driven by both concentration and electrical gradients, causing the membrane potential to rise rapidly and even reverse polarity momentarily.
What happens during the falling phase of an action potential?
During the falling phase, voltage-gated K+ channels open (slower than Na+ channels) as Na+ channels close. K+ moves out of the cell, driven by its concentration and electrical gradients, rapidly bringing the membrane potential back towards the resting level.
What is the after-hyperpolarization phase?
After-hyperpolarization, or undershoot, occurs when the membrane potential dips below the normal resting potential due to continued K+ efflux, even as K+ permeability begins to decrease and the cell approaches the K+ equilibrium potential.
How does the neuron return to resting membrane potential after an action potential?
After the action potential, slow voltage-gated K+ channels close, and the leak of ions through channels slowly returns the membrane potential to -70 mV, the resting state determined by permeability to K+, Cl-, and Na+.
What contributions did A.L. Hodgkin and A.F. Huxley make regarding action potentials?
A.L. Hodgkin and A.F. Huxley described the mechanism of action potentials in neurons and won the Nobel Prize in 1963 for their work detailing how voltage-gated ion channels contribute to neuronal signaling.
How many action potentials could a neuron fire before its ion gradients are significantly altered if the Na+ K+ pump were non-functional?
A neuron without a functional Na+ K+ pump could fire a thousand or more action potentials before a significant change in the ion gradients occurred.
What are the two gates of a voltage-gated Na+ channel and their roles?
Voltage-gated Na+ channels have two gates: the activation gate and the inactivation gate. The activation gate opens in response to depolarization allowing Na+ to enter the cell, while the inactivation gate, which delays closing, eventually stops Na+ influx to end the action potential.
How do the activation and inactivation gates of Na+ channels function during an action potential?
Upon depolarization, the activation gate quickly opens allowing Na+ in, further depolarizing the cell. The inactivation gate then closes after a delay of 0.5 msec, stopping Na+ entry and leading to the peak of the action potential.
What happens to Na+ channels after the action potential peaks?
After the action potential peaks, as the cell repolarizes due to K+ efflux, the Na+ channel gates reset to their original positions, with the activation gate closing and the inactivation gate opening, preparing for the next potential depolarization.
How does the double-gating mechanism of Na+ channels influence the directionality of electrical signals in neurons?
The double-gating mechanism ensures that electrical signals in neurons are conducted in only one direction, a feature further explored in subsequent sections of the neuron study.
What is the refractory period in the context of neuron action potentials?
The refractory period is the time during which a neuron cannot trigger a second action potential, no matter how strong the incoming stimulus is. This period ensures that action potentials are unidirectional and do not overlap.
What is the absolute refractory period?
The absolute refractory period is the time after an action potential begins during which no second action potential can be triggered, typically lasting about 1–2 msec. This is the time required for the Na+ channel gates to reset to their resting positions.
How does the absolute refractory period affect the directionality of action potentials?
Due to the absolute refractory period, action potentials cannot overlap and cannot travel backward, ensuring they move from the trigger zone to the axon terminal in a controlled manner.
What is the relative refractory period?
Following the absolute refractory period, the relative refractory period is when some Na+ channels have reset, but not all. A stronger-than-normal stimulus is required to trigger another action potential during this period.
How does the relative refractory period affect action potential amplitude?
During the relative refractory period, action potentials that do occur may have a smaller amplitude than normal. This is due to some Na+ channels still being inactive and simultaneous K+ efflux, which opposes depolarization.
How do refractory periods differ between action potentials and graded potentials?
Unlike action potentials, graded potentials can summate if they occur close in time. During the absolute refractory period, even suprathreshold graded potentials have no effect on triggering an action potential, as the Na+ channels are inactivated.
How do refractory periods affect signal transmission in neurons and ensure the directionality of action potentials?
Refractory periods limit the rate at which neurons can transmit signals by preventing a new action potential from starting too soon after the previous one. The absolute refractory period ensures that action potentials travel in only one direction—from the cell body to the axon terminal—by preventing backward travel of the action potential. This is crucial for the proper functioning of neural circuits and signal propagation
How does the conduction of an action potential occur at the cellular level?
Conduction occurs when depolarization of a section of axon causes local current flow in the cytoplasm and back toward the depolarized section from the outside of the axon. Voltage-gated Na+ channels open in response to depolarization, allowing Na+ to enter, reinforcing the depolarization and maintaining the strength of the action potential.
What role do voltage-gated Na+ channels play in action potential conduction?
Voltage-gated Na+ channels play a crucial role in action potential conduction by opening in response to depolarization, allowing more Na+ to enter the cell. This positive feedback loop ensures continuous depolarization along the axon, preventing the signal from diminishing.
How does the action potential prevent signal loss as it travels down the axon?
As the action potential propagates, each axonal segment depolarizes sequentially due to local current flow and the opening of Na+ channels. This results in a continuous entry of Na+ that keeps the action potential’s strength constant.
