Neurons Flashcards
1
Q
What are the main components of a typical neuron?
A
The main components are the cell body (soma), dendrites, axon, axon terminals, and the myelin sheath.
2
Q
What is the function of the cell body (soma) in a neuron?
A
The cell body contains the nucleus, which stores genetic information, and organelles like mitochondria that provide energy. It integrates signals received by the dendrites.
3
Q
What is the function of dendrites in a neuron?
A
Dendrites are branched extensions that receive electrical signals (neurotransmitters) from other neurons and transmit them to the cell body.
4
Q
What is the function of the axon in a neuron?
A
The axon is a long projection that carries electrical impulses away from the cell body to the axon terminals or another neuron.
5
Q
What is the myelin sheath and its function?
A
The myelin sheath is a fatty covering surrounding the axon, which insulates the axon and increases the speed of electrical signal transmission.
6
Q
What are Nodes of Ranvier, and why are they important?
A
Nodes of Ranvier are gaps in the myelin sheath where the axon is exposed. They help in saltatory conduction, which allows the electrical signal to jump from node to node, speeding up transmission.
7
Q
What are axon terminals, and what is their function?
A
Axon terminals are the ends of the axon where neurotransmitters are released to transmit signals to the next neuron or muscle.
8
Q
What is the synapse, and how does it function?
A
The synapse is the junction between two neurons or a neuron and a target cell, where neurotransmitters are released from the axon terminal to carry the signal across the gap to the next cell.
9
Q
How are neurons classified based on their structure?
A
Neurons are classified as multipolar, bipolar, and unipolar, based on the number of processes extending from the cell body.
10
Q
What is a multipolar neuron, and where is it found?
A
A multipolar neuron has one axon and multiple dendrites. It is the most common type, found in the CNS (brain and spinal cord).
11
Q
What is a bipolar neuron, and where is it typically found?
A
A bipolar neuron has one axon and one dendrite. It is commonly found in the sensory organs, such as the retina of the eye and olfactory system.
12
Q
What is a unipolar neuron, and where is it found?
A
A unipolar neuron has one process extending from the cell body, which splits into two branches. It is found in sensory neurons of the peripheral nervous system.
13
Q
How are neurons classified based on their function?
A
Neurons are classified as sensory (afferent) neurons, motor (efferent) neurons, and interneurons (relay neurons) based on the direction they transmit signals.
14
Q
What is the function of sensory (afferent) neurons?
A
Sensory neurons carry signals from sensory receptors (like skin or organs) to the CNS for processing.
15
Q
What is the function of motor (efferent) neurons?
A
Motor neurons carry signals from the CNS to muscles or glands to produce movement or secretions.
16
Q
What is the function of interneurons (relay neurons)?
A
Interneurons are found within the CNS and connect sensory neurons to motor neurons, facilitating communication between different parts of the nervous system.
17
Q
What are neuroglia (glial cells), and what is their general function?
A
Neuroglia, or glial cells, are supporting cells of the nervous system that provide structural support, protection, insulation, and assist in the maintenance and repair of neurons.
18
Q
What are the four types of glial cells found in the Central Nervous System (CNS)?
A
The four types are astrocytes, oligodendrocytes, microglia, and ependymal cells.
19
Q
What is the function of astrocytes, and where are they located?
A
Astrocytes are found throughout the CNS. Their functions include maintaining the blood-brain barrier, regulating ion concentrations, providing nutrients to neurons, and aiding in repair after injury.
20
Q
What is the function of oligodendrocytes, and where are they located?
A
Oligodendrocytes are located in the CNS and are responsible for producing the myelin sheath that insulates axons, speeding up electrical signal transmission.
21
Q
What is the function of microglia, and where are they located?
A
Microglia are the immune cells of the CNS, located throughout the brain and spinal cord. They act as phagocytes, removing cellular debris, pathogens, and dead neurons.
22
Q
What is the function of ependymal cells, and where are they located?
A
Ependymal cells line the ventricles of the brain and the central canal of the spinal cord. They produce and circulate cerebrospinal fluid (CSF), which cushions the brain and spinal cord.
23
Q
What are the two types of glial cells found in the Peripheral Nervous System (PNS)?
A
The two types are Schwann cells and satellite cells.
24
Q
What is the function of Schwann cells, and where are they located?
A
Schwann cells are found in the PNS and form the myelin sheath around peripheral axons, similar to oligodendrocytes in the CNS, aiding in the rapid transmission of electrical signals.
24
What is the function of satellite cells, and where are they located?
Satellite cells are located in ganglia of the PNS. They provide support and regulate the exchange of nutrients and waste between neurons and the surrounding environment.
25
How do Schwann cells differ from oligodendrocytes in terms of myelination?
Schwann cells in the PNS myelinate a single axon, while oligodendrocytes in the CNS can myelinate multiple axons at once.
26
Why are neuroglia critical for neuronal function?
Neuroglia provide support, nourishment, and protection to neurons, maintain the homeostasis of the neural environment, and play key roles in repair and immune defense in the CNS and PNS.
27
How do glial cells contribute to the blood-brain barrier?
Astrocytes in the CNS help maintain the blood-brain barrier by regulating the passage of substances from the bloodstream to the brain, protecting neural tissue from harmful chemicals.
28
What role do glial cells play in neural repair?
Schwann cells assist in repairing peripheral nerves by guiding the regrowth of damaged axons, while astrocytes help form scar tissue and support CNS recovery after injury.
29
What is the resting membrane potential of a neuron?
The resting membrane potential is the electrical charge difference across the cell membrane when the neuron is not transmitting a signal. It is typically around -70 mV.
30
What causes the resting membrane potential to be negative inside the cell?
The inside of the cell is negative due to a higher concentration of negatively charged proteins and potassium ions (K⁺), along with a lower concentration of positively charged sodium ions (Na⁺) compared to the outside.
31
What are the key ions involved in establishing the resting membrane potential?
The key ions are potassium (K⁺), sodium (Na⁺), and chloride (Cl⁻). K⁺ is more concentrated inside the cell, while Na⁺ and Cl⁻ are more concentrated outside the cell.
32
What is the role of the sodium-potassium pump (Na⁺/K⁺ pump) in maintaining the resting membrane potential?
The Na⁺/K⁺ pump uses ATP to actively transport 3 Na⁺ ions out of the cell and 2 K⁺ ions in, helping to maintain the concentration gradients of sodium and potassium, which are crucial for the resting membrane potential.
33
Why is the sodium-potassium pump considered electrogenic?
The Na⁺/K⁺ pump is electrogenic because it moves 3 positively charged Na⁺ ions out of the cell for every 2 positively charged K⁺ ions it brings in, creating a net negative charge inside the cell.
34
What role do potassium ions (K⁺) play in establishing the resting membrane potential?
K⁺ ions tend to move out of the cell through leak channels due to their concentration gradient, but are pulled back inside by the negative charge inside the cell. This movement is crucial for maintaining the negative resting potential.
35
How does the permeability of the membrane to different ions affect the resting membrane potential?
The membrane is more permeable to K⁺ than Na⁺, allowing K⁺ to move out of the cell more easily, contributing to the negative charge inside. The low permeability to Na⁺ helps keep the inside of the cell negative.
36
What is the equilibrium potential of potassium (K⁺), and why is it important?
The equilibrium potential of K⁺ is around -90 mV. It represents the point at which the electrical force pulling K⁺ in and the concentration gradient pushing K⁺ out are balanced, helping to set the resting membrane potential.
37
What is the role of sodium ions (Na⁺) in the resting membrane potential?
Sodium ions have a low permeability at rest, but a small amount leaks into the cell, making the resting membrane potential slightly less negative than the K⁺ equilibrium potential.
38
How do chloride ions (Cl⁻) influence the resting membrane potential?
Chloride ions are negatively charged and tend to be more concentrated outside the cell. They passively distribute across the membrane, stabilizing the negative resting membrane potential.
39
How does the resting membrane potential prepare a neuron for action potential generation?
The resting membrane potential establishes a polarized state (inside negative, outside positive), allowing the neuron to respond quickly to stimuli and generate an action potential when depolarized.
40
What happens to the resting membrane potential if the Na⁺/K⁺ pump is inhibited?
If the Na⁺/K⁺ pump is inhibited, the concentration gradients of Na⁺ and K⁺ would gradually dissipate, leading to a loss of the resting membrane potential and impairing the neuron's ability to generate action potentials.
41
What is a graded potential in the nervous system?
A graded potential is a temporary change in the membrane potential of a neuron, usually occurring in the dendrites or cell body. It varies in size depending on the strength of the stimulus.
42
How does a graded potential differ from an action potential?
Graded potentials are small, local, and variable in magnitude, while action potentials are all-or-nothing and always of the same magnitude once the threshold is reached.
43
What causes graded potentials to occur?
Graded potentials are caused by opening of ion channels in response to a stimulus such as neurotransmitters binding to receptors, light, pressure, or changes in temperature.
44
What are the two types of graded potentials?
The two types of graded potentials are depolarizing potentials (making the inside of the cell less negative) and hyperpolarizing potentials (making the inside more negative).
45
What is a depolarizing graded potential?
A depolarizing graded potential occurs when the membrane potential becomes less negative (closer to zero) due to influx of Na⁺ ions or other positive ions, making the neuron more likely to fire an action potential.
46
What is a hyperpolarizing graded potential?
A hyperpolarizing graded potential makes the membrane potential more negative (further from zero) due to efflux of K⁺ ions or influx of Cl⁻ ions, making it less likely that an action potential will be generated.
47
How do graded potentials vary in magnitude?
Graded potentials vary in amplitude based on the strength of the stimulus. A stronger stimulus opens more ion channels, resulting in a larger potential change.
48
What is spatial summation in graded potentials?
Spatial summation occurs when multiple graded potentials from different locations on the neuron are added together, potentially leading to an action potential if the combined depolarization reaches the threshold.
49
What is temporal summation in graded potentials?
Temporal summation occurs when multiple graded potentials happen in rapid succession at the same location, adding together to create a larger potential that might reach the threshold for an action potential.
50
Why do graded potentials decrease in strength as they spread?
Graded potentials decrease in strength because they undergo passive decay due to the leakage of ions and the resistance of the neuron’s membrane. This is called decremental conduction.
51
Where do graded potentials typically occur in a neuron?
Graded potentials typically occur in the dendrites and cell body of the neuron, where synaptic input or sensory stimuli are received.
52
How can graded potentials lead to an action potential?
If the combined graded potentials depolarize the neuron's membrane enough to reach the threshold potential at the axon hillock, an action potential will be triggered.
53
What are excitatory postsynaptic potentials (EPSPs)?
EPSPs are depolarizing graded potentials that make the neuron more likely to reach the threshold for firing an action potential, usually by allowing Na⁺ or Ca²⁺ ions to enter the cell.
54
What are inhibitory postsynaptic potentials (IPSPs)?
IPSPs are hyperpolarizing graded potentials that make it less likely for an action potential to occur, typically by allowing K⁺ ions to exit or Cl⁻ ions to enter the cell.
55
Can graded potentials occur in sensory receptors?
Yes, graded potentials can occur in sensory receptors, where they are known as receptor potentials or generator potentials, which lead to the initiation of action potentials in sensory neurons.
56
What is an action potential?
An action potential is a rapid, large change in membrane potential that occurs when a neuron sends a signal along its axon, characterized by a depolarization followed by repolarization.
57
What triggers the generation of an action potential?
The generation of an action potential is triggered when the membrane potential reaches the threshold (typically around -55 mV) due to sufficient depolarization from graded potentials.
58
What occurs during the depolarization phase?
During depolarization, voltage-gated sodium channels open, allowing Na⁺ ions to rush into the cell, causing the membrane potential to become more positive (up to +30 mV).
59
What is the threshold potential?
The threshold potential is the critical level of depolarization (-55 mV) that must be reached to initiate an action potential, leading to the opening of more voltage-gated sodium channels.
60
What is the all-or-nothing principle?
The all-or-nothing principle states that an action potential either occurs fully (once the threshold is reached) or does not occur at all; there are no partial action potentials.
61
What happens during the repolarization phase?
During repolarization, voltage-gated sodium channels close and voltage-gated potassium channels open, allowing K⁺ ions to exit the cell, which restores the membrane potential back to negative.
62
What is the role of potassium (K⁺) during action potential repolarization?
K⁺ ions exit the cell during repolarization, causing the membrane potential to become more negative, moving towards the resting membrane potential.
63
What is the afterhyperpolarization phase?
The afterhyperpolarization phase occurs when the membrane potential temporarily becomes more negative than the resting potential due to the continued efflux of K⁺ ions before the channels close.
64
What is the refractory period?
The refractory period is the time following an action potential during which a neuron cannot generate another action potential. It includes the absolute refractory period (no action potential can occur) and the relative refractory period (a stronger stimulus is needed).
65
How does the action potential propagate along the axon?
The action potential propagates by a wave of depolarization, where the influx of Na⁺ in one segment of the axon causes the adjacent segment to depolarize, continuing the signal along the axon.
66
What is saltatory conduction?
Saltatory conduction is the rapid transmission of action potentials along myelinated axons, where the action potential jumps from one Node of Ranvier to the next, increasing conduction speed.
67
What are the Nodes of Ranvier?
Nodes of Ranvier are gaps in the myelin sheath where voltage-gated ion channels are concentrated, allowing for the rapid conduction of action potentials through saltatory conduction.
68
What role does the myelin sheath play in action potential propagation?
The myelin sheath acts as an insulator, preventing ion leakage and allowing action potentials to travel faster by facilitating saltatory conduction.
69
What is the significance of action potential propagation for neuronal communication?
Action potential propagation allows for rapid and efficient communication between neurons and other cells, facilitating responses to stimuli and the transmission of signals throughout the nervous system.
70
How do neurotransmitters relate to action potentials?
Neurotransmitters released at synapses can cause graded potentials in the postsynaptic neuron, and if these graded potentials reach the threshold, they can trigger an action potential, continuing the signal transmission.
71
What is the conduction velocity of an action potential?
Conduction velocity refers to the speed at which an action potential travels along an axon, typically measured in meters per second (m/s).
72
How does axon diameter affect action potential speed?
Larger axon diameters reduce internal resistance, allowing for faster action potential propagation. Thicker axons can conduct impulses more quickly than thinner ones.
73
What is the role of myelination in action potential speed?
Myelination increases conduction speed by insulating the axon and facilitating saltatory conduction, where action potentials jump from one Node of Ranvier to the next.
74
How does the presence of Nodes of Ranvier influence action potential propagation?
Nodes of Ranvier contain concentrated voltage-gated ion channels, allowing for rapid depolarization and quick jumping of the action potential between nodes, thus increasing conduction speed.
75
What effect does temperature have on action potential conduction?
Higher temperatures increase the speed of action potential propagation by enhancing the kinetic energy of ions and the rate of chemical reactions involved in depolarization and repolarization.
76
How do ion channel properties influence action potential speed?
The density and kinetics of voltage-gated ion channels affect how quickly ions can move in and out of the neuron, impacting the rate of depolarization and repolarization.
77
What is the impact of demyelination on action potential propagation?
Demyelination slows down action potential propagation by reducing the insulation of the axon, leading to increased leakage of ions and a higher likelihood of action potentials failing to reach the next node.
78
How do various neurotransmitters affect action potential speed?
Neurotransmitters can influence the excitability of neurons and the generation of graded potentials, which can affect whether the threshold for action potentials is reached, indirectly impacting speed.
79
What is the significance of the refractory period in action potential propagation?
The refractory period prevents immediate reactivation of action potentials in the same segment of the axon, ensuring one-way propagation but also limiting the frequency of action potentials.
80
How does extracellular ion concentration affect action potential speed?
The concentration of ions like Na⁺ and K⁺ in the extracellular space can affect the availability of these ions for generating action potentials, thereby influencing conduction speed.
81
How does the length of the axon affect conduction velocity?
Longer axons may experience greater resistance to ion flow, potentially slowing down action potential propagation compared to shorter axons, although diameter and myelination are more significant factors.
82
What is the effect of pathological conditions (e.g., multiple sclerosis) on conduction speed?
Pathological conditions can impair action potential propagation by damaging myelin sheaths or altering ion channel function, leading to slower conduction velocities and potential neurological deficits.
83
How are axons classified based on conduction velocity?
Axons are classified into three main types based on conduction velocity:
A fibers: Myelinated, large diameter, fast conduction (5-120 m/s).
B fibers: Myelinated, medium diameter, moderate conduction (3-15 m/s).
C fibers: Unmyelinated, small diameter, slow conduction (0.5-2 m/s)
84
What factors influence the classification of axons?
The classification of axons is influenced by factors such as myelination, diameter, and conduction velocity, determining their functional roles in the nervous system.
85
What is a synapse?
A synapse is a specialized junction between two neurons or between a neuron and a target cell (such as a muscle or gland), allowing for communication through the transmission of signals.
86
What are the main components of a chemical synapse?
The main components of a chemical synapse include:
Presynaptic terminal: Contains neurotransmitter vesicles and synaptic machinery.
Synaptic cleft: The small gap (20-40 nm) between the presynaptic and postsynaptic membranes.
Postsynaptic membrane: Contains receptors for neurotransmitters
87
What is the role of neurotransmitters in synaptic transmission?
Neurotransmitters are chemical messengers released from the presynaptic terminal that bind to receptors on the postsynaptic membrane, triggering a response in the target cell.
88
Describe the process of neurotransmitter release.
The process includes:
Action potential arrival: An action potential reaches the presynaptic terminal.
Calcium influx: Voltage-gated calcium channels open, allowing Ca²⁺ ions to enter.
Vesicle fusion: Increased Ca²⁺ concentration causes neurotransmitter-containing vesicles to fuse with the presynaptic membrane.
Neurotransmitter release: Neurotransmitters are released into the synaptic cleft via exocytosis.
89
What happens after neurotransmitters are released into the synaptic cleft?
Neurotransmitters diffuse across the synaptic cleft and bind to specific receptors on the postsynaptic membrane, leading to changes in the postsynaptic cell's membrane potential.
90
What are the two main types of receptors on the postsynaptic membrane?
The two main types are:
Ionotropic receptors: Ligand-gated ion channels that open upon neurotransmitter binding, causing immediate changes in ion flow and membrane potential.
Metabotropic receptors: G-protein-coupled receptors that activate intracellular signaling pathways, leading to slower but longer-lasting effects.
91
What is an excitatory postsynaptic potential (EPSP)?
An EPSP is a depolarization of the postsynaptic membrane caused by the influx of positively charged ions (like Na⁺) following neurotransmitter binding, increasing the likelihood of an action potential.
92
What is an inhibitory postsynaptic potential (IPSP)?
An IPSP is a hyperpolarization of the postsynaptic membrane caused by the influx of negatively charged ions (like Cl⁻) or efflux of positively charged ions (like K⁺), decreasing the likelihood of an action potential.
93
How is neurotransmitter signaling terminated?
Termination can occur through:
Reuptake: Transport proteins on the presynaptic terminal retrieve neurotransmitters from the synaptic cleft.
Enzymatic degradation: Enzymes break down neurotransmitters in the synaptic cleft (e.g., acetylcholinesterase breaks down acetylcholine).
Diffusion: Neurotransmitters diffuse away from the synaptic cleft.
94
What are the differences between electrical and chemical synapses?
Electrical synapses: Directly connect the cytoplasm of two neurons via gap junctions; faster transmission but less control.
Chemical synapses: Use neurotransmitters and involve synaptic clefts; allow for complex signaling and modulation.
95
What are neurotransmitters?
Neurotransmitters are chemical messengers released by neurons that transmit signals across a synapse to a target cell, influencing its activity.
96
What are neuromodulators?
Neuromodulators are substances that affect neurotransmission by modulating the effects of neurotransmitters, often influencing the strength and duration of their action.
97
What is acetylcholine (ACh)?
ACh is a neurotransmitter involved in muscle contraction and autonomic nervous system functions. It can cause depolarization (EPSP) in skeletal muscle and hyperpolarization (IPSP) in cardiac muscle.
98
What is the role of dopamine?
Dopamine is a neurotransmitter associated with reward, motivation, and motor control. Its effects depend on receptor types: D1 receptors cause EPSP, while D2 receptors can lead to IPSP.
99
What are the effects of norepinephrine (NE)?
NE is involved in the "fight or flight" response, increasing heart rate and blood flow. It generally causes EPSPs in postsynaptic neurons, enhancing alertness and arousal.
100
What is serotonin (5-HT)?
Serotonin is a neurotransmitter that regulates mood, appetite, and sleep. It typically causes IPSPs in certain brain regions, contributing to feelings of well-being and calmness.
101
What is gamma-aminobutyric acid (GABA)?
GABA is the primary inhibitory neurotransmitter in the brain. It binds to receptors that allow Cl⁻ ions to enter the postsynaptic neuron, causing hyperpolarization (IPSP) and reducing neuronal excitability.
102
What is glutamate?
Glutamate is the main excitatory neurotransmitter in the brain. It binds to receptors like NMDA and AMPA, causing depolarization (EPSP) and playing a crucial role in learning and memory.
103
What are endorphins?
Endorphins are neuromodulators that act as natural painkillers and mood enhancers. They bind to opioid receptors, inhibiting pain signals and producing feelings of euphoria.
104
What is substance P?
Substance P is a neuropeptide involved in pain transmission. It enhances the perception of pain by causing EPSPs in pain pathways, transmitting signals to the brain.
105
How do neuromodulators differ from neurotransmitters?
Neuromodulators have broader effects, influencing groups of neurons over longer periods, whereas neurotransmitters act more locally and quickly to transmit specific signals.
106
What is the significance of receptor types in neurotransmitter action?
Different receptor types determine the effect of neurotransmitters: excitatory receptors lead to depolarization (EPSP), while inhibitory receptors lead to hyperpolarization (IPSP), influencing overall neuronal activity.
107
What is information processing in neural tissue?
Information processing in neural tissue involves the reception, integration, and transmission of signals through networks of neurons, enabling responses to stimuli and coordination of bodily functions.
108
How do sensory neurons contribute to information processing?
Sensory neurons detect environmental stimuli (e.g., light, sound, touch) and convert them into electrical signals that are transmitted to the central nervous system (CNS) for processing.
109
What is the role of interneurons in neural processing?
Interneurons act as connectors between sensory and motor neurons within the CNS, integrating sensory input and coordinating responses, thus playing a key role in reflexes and complex behaviors.
110
How do motor neurons facilitate information processing?
Motor neurons transmit signals from the CNS to effectors (muscles and glands), enabling responses to processed information, such as muscle contraction and gland secretion.
111
What is synaptic transmission, and why is it important?
Synaptic transmission is the process by which neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron. It is crucial for communication between neurons and allows for the integration of information.
112
What is neural plasticity?
Neural plasticity is the ability of neural networks to change and adapt over time in response to experience, learning, and injury, facilitating improved information processing and memory formation.
113
How do graded potentials contribute to information processing?
Graded potentials are small, localized changes in membrane potential that occur in response to stimuli. They can summate to generate action potentials if they reach the threshold, allowing for signal transmission.
114
What role do action potentials play in information processing?
Action potentials are rapid, large changes in membrane potential that propagate along axons, allowing for long-distance transmission of electrical signals and enabling coordinated responses throughout the nervous system.
115
What is the significance of neurotransmitter receptors in processing?
Neurotransmitter receptors on the postsynaptic membrane determine the type of response (excitatory or inhibitory) based on the binding of neurotransmitters, influencing how signals are integrated and processed.
116
How do modulatory neurotransmitters affect information processing?
Modulatory neurotransmitters (e.g., serotonin, dopamine) can influence the overall activity of neural circuits by enhancing or inhibiting the effects of primary neurotransmitters, affecting mood, attention, and learning.
117
What is the role of feedback loops in neural processing?
Feedback loops involve the interaction between different neural circuits, allowing for self-regulation and adaptation in response to ongoing information processing, enhancing the precision of neural responses.
118
How do networks of neurons enable complex processing?
Networks of interconnected neurons can process information through parallel pathways, integration of multiple inputs, and generation of complex outputs, allowing for sophisticated functions like decision-making and problem-solving.
