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Questions and Answers
What characterizes an electrical synapse?
What characterizes an electrical synapse?
Which neurotransmitter is NOT commonly associated with chemical synapses?
Which neurotransmitter is NOT commonly associated with chemical synapses?
How do chemical synapses differ from electrical synapses in signal transmission?
How do chemical synapses differ from electrical synapses in signal transmission?
What is the resting membrane potential in a typical nerve cell?
What is the resting membrane potential in a typical nerve cell?
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What primarily causes the more negative charge inside a resting nerve cell?
What primarily causes the more negative charge inside a resting nerve cell?
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What is the threshold voltage that must be reached for the action potential to occur?
What is the threshold voltage that must be reached for the action potential to occur?
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What occurs during depolarization of the membrane potential?
What occurs during depolarization of the membrane potential?
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How does an excitatory postsynaptic potential (EPSP) affect the membrane potential?
How does an excitatory postsynaptic potential (EPSP) affect the membrane potential?
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What is the main ion that contributes to the repolarization of the membrane potential?
What is the main ion that contributes to the repolarization of the membrane potential?
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What happens during hyperpolarization?
What happens during hyperpolarization?
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What is the primary outcome of signal convergence on a neuron?
What is the primary outcome of signal convergence on a neuron?
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What mechanism prolongs the excitation of a neuron after the initial stimulus has ceased?
What mechanism prolongs the excitation of a neuron after the initial stimulus has ceased?
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What characterizes a reverberatory (oscillatory) circuit?
What characterizes a reverberatory (oscillatory) circuit?
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In synaptic after-discharge circuits, what allows excitatory signals to reach the output neuron at staggered times?
In synaptic after-discharge circuits, what allows excitatory signals to reach the output neuron at staggered times?
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What is an example of prolonged excitation as a result of after discharge?
What is an example of prolonged excitation as a result of after discharge?
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What type of transport does kinesin facilitate in neurons?
What type of transport does kinesin facilitate in neurons?
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Which type of neuron carries information from target organs to the CNS?
Which type of neuron carries information from target organs to the CNS?
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What is the primary function of dynein in axonal transport?
What is the primary function of dynein in axonal transport?
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What defines the peripheral nervous system?
What defines the peripheral nervous system?
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How are nerves classified according to their structure?
How are nerves classified according to their structure?
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What impact can a synapse have on nerve impulses?
What impact can a synapse have on nerve impulses?
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Which of the following neurons is located within the CNS?
Which of the following neurons is located within the CNS?
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Which type of nerve fibers are typically unmyelinated?
Which type of nerve fibers are typically unmyelinated?
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What is the role of transport proteins in axonal transport?
What is the role of transport proteins in axonal transport?
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What occurs at the axon hillock when the graded potential reaches the threshold level?
What occurs at the axon hillock when the graded potential reaches the threshold level?
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Which classification describes nerves based on the transmitters they secrete?
Which classification describes nerves based on the transmitters they secrete?
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What is the result of inhibitory postsynaptic potential (IPSP)?
What is the result of inhibitory postsynaptic potential (IPSP)?
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Which best describes divergence in neuronal pools?
Which best describes divergence in neuronal pools?
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What can lead to hyperpolarization in a neuron?
What can lead to hyperpolarization in a neuron?
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Which process allows a signal to be transmitted to different areas from the same neuronal pool?
Which process allows a signal to be transmitted to different areas from the same neuronal pool?
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What happens when the graded potential is not strong enough to reach the axon hillock?
What happens when the graded potential is not strong enough to reach the axon hillock?
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Which of the following statements about action potentials is true?
Which of the following statements about action potentials is true?
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In impulse processing, what characterizes impulse convergence?
In impulse processing, what characterizes impulse convergence?
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Study Notes
Axonal Transport
- Proteins are transported within neurons via vesicles along the cytoskeleton, which consists of three types of fibers: microtubules, neurofilaments, and microfilaments
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Anterograde transport carries material from the soma (cell body) to the axon terminal and dendrites; this is done by the protein kinesin
- Fast axonal transport is for vesicles and organelles
- Slow axonal transport is for regenerative materials used to repair the axon
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Retrograde transport carries materials from the axon towards the soma; this is done by the protein dynein
- Functions: carries trophic substances (like nerve growth factors) and waste products
Functional Classification of Neurons
- Sensory (afferent) neurons: carry information from target organs to the central nervous system (CNS)
- Motor (efferent) neurons: carry information from the CNS to the target organs
- Interneurons: process information within the CNS (brain and spinal cord)
Nerves
- Nerves connect the neurons of the CNS to target organs
- Form the peripheral nervous system
- Composed of bundles called fasciculi, which are made up of neuronal axons
Classification of Nerves
- Structure: Myelinated vs. Non-myelinated (myelinated nerves conduct faster due to saltatory conduction)
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Distribution:
- Somatic: To skeletal muscles
- Autonomic: To smooth muscles and glands
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Origin:
- Cranial nerves: Originate from the brain
- Spinal nerves: Originate from the spinal cord
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Neurotransmitter:
- Cholinergic: Release acetylcholine
- Adrenergic: Release norepinephrine
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Function:
- Sensory: Receive information
- Motor: Send motor commands
- Mixed: Contain both sensory and motor fibers
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Fiber Diameter:
- Thickest fibers: Myelinated and conduct with the highest velocity
- Type C fibers: Non-myelinated and conduct with the lowest velocity
Central Nervous System Synapse and Synaptic Transmission
- Information is transmitted in the CNS via nerve action potentials (nerve impulses)
- Impulses pass from one neuron to another through a functional contact called a synapse
- A neuron can have 1,000-10,000 synaptic interactions with other cells
- Synapses can:
- Block impulse transmission
- Convert a single impulse into multiple impulses
- Integrate impulses from multiple neurons into a complex pattern
Types of Synapses
- Chemical synapses: The most common type, involves neurotransmitter release and receptor activation
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Electrical synapses: Fast transmission due to direct electrical connections (gap junctions) between cells
- Allow signals to pass in both directions
- Rare in the adult CNS, more common during embryonic development
Chemical Synapse
- Components: Presynaptic axon terminal, synaptic cleft, postsynaptic receptors
- Process: Neurotransmitters are released from the presynaptic neuron, diffuse across the synaptic cleft, and bind to receptors on the postsynaptic neuron
- One-way transmission: From presynaptic to postsynaptic neuron
- Major neurotransmitters: Acetylcholine, norepinephrine, epinephrine, histamine, GABA, glycine, serotonin, glutamate
Resting Membrane Potential and Action Potential
- Resting membrane potential: Difference in electrical charge across the cell membrane; inside is more negative than outside
- Nerve cell resting potential: -70 mV
- Resting potential is caused by: Unequal ion concentration and permeability across the membrane, with K+ efflux exceeding Na+ influx
- Action potential: A temporary reversal of the membrane potential, where the inside becomes positive
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Action potential initiation:
- Must be a stimulus to open Na+ channels
- Influx of Na+ depolarizes the membrane until the threshold potential (-55 mV) is reached, triggering the opening of voltage-gated Na+ channels
- Na+ influx drives membrane potential to +35 mV (depolarization)
- Na+ channels close, K+ channels open, and K+ efflux repolarizes the membrane
- Hyperpolarization: Membrane potential may become more negative than the resting potential
Generation of Nerve Action Potential
- Neurotransmitter release from presynaptic neuron
- Neurotransmitters bind to receptors on postsynaptic neuron, which can be excitatory or inhibitory
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Excitatory Postsynaptic Potential (EPSP):
- Neurotransmitters bind to excitatory receptors (ligand-gated Na+ channels)
- Increase Na+ permeability
- Influx of Na+ depolarizes the membrane
- Graded potential: Amplitude varies with stimulus strength
- Local depolarization: Conducts passively along the soma membrane - If the EPSP is strong enough to reach the axon hillock and the threshold (-55 mv) is reached, it triggers an action potential - Action potentials are "all-or-none": Either occur or don't occur - Soma does not generate action potential because it has limited voltage-gated Na+ channels
Inhibitory Postsynaptic Potential (IPSP)
- Neurotransmitters bind to inhibitory receptors (ligand-gated Cl- channels and/or K+ channels)
- Increase Cl- permeability or K+ permeability
- Chloride influx and potassium efflux: hyperpolarize the membrane, making it more negative
- Inhibitory effect: Hyperpolarization counteracts excitatory graded potentials, preventing the neuron from reaching threshold and firing an action potential
Impulse Processing: Neuronal Circuits
- The CNS is composed of neuronal pools, containing mostly interneurons
- Pools can be small or large, receive input from sensory neurons, process information, and generate output signals
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Key processes:
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Impulse Divergence: One neuron sends signals to multiple neurons – amplifies the signal
- Amplifying divergence: Spread of a signal to increasing numbers of neurons in successive orders
- Divergence into multiple tracts: Signal transmitted in different directions to different areas
- Impulse Convergence: Multiple inputs excite a single neuron – allows for summation of signals
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Impulse Prolongation and Repetitive Discharge: Signals continue after the stimulus has stopped, prolonging the excitation
- Reverberatory (Oscillatory) circuit: Positive feedback within the circuit re-excites the outputs, resulting in rhythmic activity
- Synaptic after-discharge circuit: Divergence followed by convergence, with signals arriving at different times to sustain excitation
- Excitatory and inhibitory output signals: An input signal can result in excitatory outputs to some neurons and inhibitory outputs to others
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Impulse Divergence: One neuron sends signals to multiple neurons – amplifies the signal
- Amplifying divergence: Spread of a signal to increasing numbers of neurons in successive orders
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Description
Explore the fascinating processes of axonal transport in neurons, including anterograde and retrograde transport mechanisms. Learn about the different types of neurons and their functional classifications, such as sensory, motor, and interneurons. Test your understanding of these crucial concepts in neuroscience.