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Questions and Answers
What is the resting potential of a neuron?
What is the resting potential of a neuron?
Which type of neuron is most abundant in the CNS?
Which type of neuron is most abundant in the CNS?
What mechanism is used to maintain the resting potential by exchanging ions?
What mechanism is used to maintain the resting potential by exchanging ions?
Which ions are primarily concentrated outside the neuron at resting potential?
Which ions are primarily concentrated outside the neuron at resting potential?
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What are the nodes of Ranvier associated with?
What are the nodes of Ranvier associated with?
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Which type of receptor detects sensory input?
Which type of receptor detects sensory input?
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What type of neuron is primarily involved in inter-neuronal communication?
What type of neuron is primarily involved in inter-neuronal communication?
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Which cells produce the myelin sheath in the peripheral nervous system?
Which cells produce the myelin sheath in the peripheral nervous system?
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What cells are responsible for providing the myelin sheath in mammalian axons?
What cells are responsible for providing the myelin sheath in mammalian axons?
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What is the primary role of the myelin sheath in axons?
What is the primary role of the myelin sheath in axons?
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Where do action potentials occur in a myelinated axon?
Where do action potentials occur in a myelinated axon?
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What initiates the release of neurotransmitters from the presynaptic neuron?
What initiates the release of neurotransmitters from the presynaptic neuron?
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What is the primary effect of excitatory postsynaptic potentials (EPSPs) on a postsynaptic neuron?
What is the primary effect of excitatory postsynaptic potentials (EPSPs) on a postsynaptic neuron?
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What neurotransmitter is known to act on ionotropic receptors, such as nicotinic receptors?
What neurotransmitter is known to act on ionotropic receptors, such as nicotinic receptors?
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What consequence does hyperpolarization have on a postsynaptic cell?
What consequence does hyperpolarization have on a postsynaptic cell?
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What action does the binding of neurotransmitters trigger at ionotropic receptors?
What action does the binding of neurotransmitters trigger at ionotropic receptors?
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What initiates the action potential in a neuron?
What initiates the action potential in a neuron?
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What characterizes the action potential as 'all-or-none'?
What characterizes the action potential as 'all-or-none'?
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After depolarization, what follows in the action potential process?
After depolarization, what follows in the action potential process?
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During which phase does the neuron experience hyperpolarization?
During which phase does the neuron experience hyperpolarization?
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Which accurately describes the role of myelination in neuron conduction?
Which accurately describes the role of myelination in neuron conduction?
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What occurs during the refractory period following an action potential?
What occurs during the refractory period following an action potential?
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What causes the membrane potential to change from -70mV to +40mV?
What causes the membrane potential to change from -70mV to +40mV?
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What mechanism reduces energy consumption during nerve impulse transmission?
What mechanism reduces energy consumption during nerve impulse transmission?
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Study Notes
Function of the Nervous System
- The nervous system is responsible for receiving sensory input and coordinating motor output
- Sensory receptors detect changes in the environment
- Effectors carry out responses to stimuli
Neuron Interaction & Integration
- Sensory neurons carry information from sensory receptors to the central nervous system
- Interneurons process and integrate incoming sensory information
- Motor neurons carry information from the CNS to effectors
Neuroglia
- Neuroglia are cells that support and protect neurons
- Neuroglia include Schwann cells, oligodendrocytes, astrocytes, microglia, and ependymal cells
Typical Neuron
- A typical neuron has a cell body, dendrites, and an axon
- Dendrites receive information from other neurons and transmit it towards the cell body
- The cell body contains the nucleus and other cellular organelles
- The axon transmits information away from the cell body towards other cells
- The myelin sheath, a fatty covering, insulates the axon and increases the speed of signal transmission
- The synapse is the junction between an axon and another cell, where communication occurs
Myelin Sheath and Schwann Cells
- The myelin sheath is made up of Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system
- Myelin sheaths wrap around axons, creating an insulator that allows for faster signal transmission
- The gaps between the myelin sheath are called nodes of Ranvier, where the action potential jumps from one node to the next, allowing for faster transmission
Types of Neurons
- Unipolar neurons have a single process extending from the cell body and are found in the dorsal root ganglia
- Bipolar neurons have two processes extending from the cell body and are found in the eye, ear, and olfactory epithelium
- Multipolar neurons have multiple processes extending from the cell body and are the most abundant type of neuron in the central nervous system
Information Transmission
- Information must be transmitted both within each neuron and between neurons
- The membrane surrounding the neuron is composed of lipids and proteins and has an electrical charge across it
Membrane Potential
- The difference in electrical charge across the membrane is called the membrane potential
- The resting potential, when the cell is not firing, is -70mV, with the inside of the cell being more negatively charged than the outside
Maintaining the Resting Potential
- The resting potential is maintained by the concentration of ions on different sides of the membrane
- Sodium (Na+) and chloride (Cl-) ions are more concentrated outside the cell
- Potassium (K+) ions and organic anions are more concentrated inside the cell
- The sodium-potassium pump actively transports 3 Na+ ions out of the cell for every 2 K+ ions pumped into the cell, using energy to maintain the concentration gradient
The Action Potential
- The action potential is a rapid depolarization of the membrane that travels down the axon
- When the membrane becomes partially depolarized and reaches the activation threshold, voltage-gated sodium ion channels open, allowing Na+ ions to rush into the cell rapidly, causing the membrane potential to change from -70mV to +40mV
Repolarization and Hyperpolarization
- The sodium channels close and become refractory, preventing further depolarization for a short time
- Voltage-gated potassium channels open and K+ ions rush out of the cell, repolarizing the membrane and then hyperpolarizing it briefly
- The action potential is “all-or-none”, meaning it is always the same size, and can either be triggered completely or not at all
Conduction of the Action Potential
- The action potential travels down the axon through passive conduction and saltatory conduction
- Passive conduction allows the depolarization to spread to adjacent regions of the membrane
- Saltatory conduction, which is much faster and more efficient, is achieved through myelination
Myelination and Saltatory Conduction
- Myelin sheaths, formed by Schwann cells and oligodendrocytes, insulate the axon, preventing the passage of ions across the membrane
- Action potentials only occur at the nodes of Ranvier, where there is no myelin, allowing the signal to jump from one node to the next, making transmission much faster
Synapse
- Information is transmitted from the presynaptic neuron to the postsynaptic cell via neurotransmitters, which cross the synapse
- The synapse is a very narrow gap between the axon terminal of the presynaptic neuron and the dendrite or soma of the postsynaptic cell
Neurotransmitter Release
- The arrival of an action potential at the axon terminal causes the release of neurotransmitters from the presynaptic membrane through exocytosis
- Vesicles containing neurotransmitters fuse with the presynaptic membrane and release their contents into the synaptic cleft, where they diffuse across the gap
Postsynaptic Effects
- Neurotransmitters bind to receptors on the postsynaptic membrane, altering the membrane potential of the receiving neuron
- This binding triggers either excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs) depending on the neurotransmitter and receptor involved
Excitatory and Inhibitory Effects
- Excitatory neurotransmitters depolarize the postsynaptic cell, making it more likely to fire an action potential
- Inhibitory neurotransmitters hyperpolarize the postsynaptic cell, making it less likely to fire an action potential
Ionotropic Receptors
- Ionotropic receptors are fast-acting receptors that directly open ion channels when neurotransmitters bind to them
- An example is acetylcholine (ACh) acting on nicotinic receptors at the neuromuscular junction
Postsynaptic Membrane Potential
- The opening of Na+ and Ca2+ channels in the postsynaptic membrane leads to depolarization, contributing to an EPSP and making an action potential more likely
- The opening of Cl- channels results in hyperpolarization contributing to an IPSP and making the postsynaptic cell less likely to fire an action potential
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