32 Questions
What is the primary function of electrical and chemical signals in neurons?
To communicate information within and between neurons
What determines the distance over which communication can occur between neurons?
The type of potential, action or graded
What is the direction of ion movement through open ion channels?
Down their electrochemical gradient
What is the net charge on the outside of a neuron's membrane at rest?
Positive
What is the relationship between the quantity of charge and the electric force of attraction?
The electric force of attraction increases with the quantity of charge
What is the primary difference between action potentials and graded potentials?
The distance over which the potential can communicate
What is the primary function of Voltage-gated channels in the nervous system?
To give the membrane its ability to undergo an action potential propagation
What is the main difference between myelinated and unmyelinated neurons?
Presence or absence of saltatory conduction
How does temperature affect the speed of action potential propagation?
It decreases the speed by decreasing the rate of channel opening
What is the purpose of gap junctions in electrical synapses?
To allow local ionic currents to flow from one cell to the next
What determines the resting membrane potential?
All of the above
What is the function of metabotropic receptors?
To activate second messengers in the cytosol
What is the role of the Na+/K+ pump?
To generate concentration gradients
What is the term for the ability of a single neuron to synapse with many other post-synaptic cells?
Divergence
What is the name of the structure that joins the plasma membranes of two cells in an electrical synapse?
Gap junction
What type of ion channel is gated by a mechanical stimulus?
Mechanically gated channel
What is the primary mechanism by which ionotropic receptors contribute to the generation of an action potential?
Influx of positively charged ions into the postsynaptic neuron
What is the direction of the net flux of K+ and Na+ ions?
From high to low concentration
What is the term for the delay between the time the neurotransmitter is released and the time the postsynaptic potential is produced?
Synaptic delay
What is the term for the type of receptors that contain a neurotransmitter binding site and an ion channel?
Ionotropic receptors
What is the effect of graded potentials on the membrane potential?
A small, localized change in the membrane potential
Which of the following is NOT a mechanism of neurotransmitter removal from the synaptic cleft?
Synthesis of new neurotransmitters
What is the term for the sum of the effects of multiple excitatory and inhibitory postsynaptic potentials?
Summation
What is the purpose of the axon hillock?
To generate action potentials
What is the primary effect of a neurotransmitter agonist on neurotransmission?
Mimicking the action of endogenous neurotransmitters
What is the primary mechanism of action of neuromodulators?
Influencing the release or reuptake of neurotransmitters
What is the threshold potential for depolarization?
Above -70mV
Which of the following drugs is an example of a neurotransmitter antagonist?
Haloperidol
What is the sequence of events in an action potential?
Depolarization, repolarization, hyperpolarization, return to resting state
What is the significance of the refractory period?
It's the time period during which the neuron cannot generate another action potential
What is the primary effect of opioids on their target neurons?
Making the neurons more difficult to excite
What is the purpose of temporal and spatial summation?
To increase the strength of graded potentials
Study Notes
Neurotransmitters and Their Effects
- Same neurotransmitter can have different effects depending on the receptor it binds to
- Acetylcholine (Ach) binds to ionotropic and metabotropic receptors:
- Ionotropic receptors (e.g., nicotinic acetylcholine receptors) allow influx of positively charged ions, leading to depolarization and excitatory effects
- Metabotropic receptors (e.g., muscarinic acetylcholine receptors) trigger intracellular signaling cascades, leading to inhibitory effects
Neurotransmitter Removal
- Neurotransmitters can be removed from the synaptic cleft by:
- Diffusion
- Enzymatic degradation
- Uptake into cells (reuptake or uptake into neighboring neuroglia)
Action of Drugs on the Chemical Synapse
- Drugs can:
- Increase leakage of neurotransmitter from vesicle to cytoplasm
- Increase neurotransmitter release into the cleft
- Block neurotransmitter release
- Inhibit transmitter synthesis
- Block neurotransmitter reuptake
- Block cleft enzymes that metabolize neurotransmitters
- Bind to receptors on the post-synaptic membrane
- Inhibit or stimulate second-messenger activity in the post-synaptic cell
Neurotransmitter Agonists and Antagonists
- Neurotransmitter agonists:
- Mimic the action of endogenous neurotransmitters
- Enhance neurotransmission
- Bind to receptors on the post-synaptic neuron, leading to an excitatory response
- Examples: L-DOPA (levodopa) for treatment of Parkinson's disease
- Neurotransmitter antagonists:
- Block the action of endogenous neurotransmitters
- Bind to receptors, preventing the neurotransmitter from exerting its usual effect
- Result in inhibitory responses
- Examples: Haloperidol for treatment of Schizophrenia
Neuromodulators
- Modulate synaptic transmission by influencing the release or reuptake of neurotransmitters
- Examples: Opioids, which can alter the electrical properties of target neurons and induce pain relief, euphoria, and other effects
Ion Channels
- Types of ion channels:
- Leak channels
- Ligand-gated channels
- Mechanically-gated channels
- Voltage-gated channels
- Ion channels open and close due to "gates" that can seal the channel pore shut or open it up
- Ion channels allow specific ions to move across the plasma membrane down their electrochemical gradient
Resting Membrane Potential
- Determined by:
- Unequal distribution of ions across the plasma membrane
- Selective permeability of the neuron's membrane to Na+ and K+
- Na+/K+ pump
- Net flux of ions across membranes depends on both the concentration gradient and the electrical difference (electrochemical gradient)
Graded Potentials
- Small, transient changes in membrane potential confined to a small region of the plasma membrane
- Provide signaling in short distances
- Can be depolarizing (excitatory) or hyperpolarizing (inhibitory)
- Magnitude of the transient changes in membrane potential can vary
- Dependent on changes in membrane permeability to ions (ligand-gated ion channels)
Action Potentials
- Sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarization) and eventually restore it to the resting state (repolarization)
- Large changes in membrane potential of excitable cells only
- Membrane potential can change from -70mV to +40mV
- Depolarization, overshoot, repolarization, hyperpolarization, and return to resting membrane potential
Mechanism of Action of Action Potentials
- Initiated at the axon hillock (trigger zone)
- All-or-none event
- Depolarization needs to exceed the threshold potential
- CNS physiology and electrical signals in neurons
Electrical Signals in Neurons
- Information is carried within neurons and from neurons to their target cells by electrical and chemical signals
- Excitable cells communicate with each other via action potentials or graded potentials
- Action potentials allow communication over short and long distances, while graded potentials allow communication over short distances only
Synapse
- Anatomically specialized junction between two cells
- One single neuron can synapse onto many other post-synaptic cells (divergence)
- Many synapses from different presynaptic neurons can synapse with a single cell (convergence)
- Functional anatomy of the nervous system synapse:
- Electrical synapse (gap junction)
- Chemical synapse (operates through the release of neurotransmitters)
This quiz covers the basics of electrical signals in neurons, including action potentials and graded potentials, and their role in communication within and between neurons.
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