action potentials Flashcards
What are dendrites?
Receptive or input region of a neuron that convey incoming messages (graded potentials) toward the cell body
What is the role of axons?
Generate nerve impulses and transmit them away from the cell body along the axolemma
Where is the nerve impulse generated in motor neurons?
At the axon hillock (or trigger zone)
What is the function of the myelin sheath?
Makes conduction faster
What happens when an impulse reaches the axon terminals?
Causes neurotransmitters to be released into the synaptic space
What is facilitated diffusion?
A process for molecules that are not lipid-soluble or small enough for simple diffusion to cross the membrane
What is the resting potential?
The electrical potential difference across the plasma membrane of a cell when the cell is at rest
What two factors contribute to the resting membrane potential?
Different concentration of Na+ and K+ on either side of the membrane, and the different permeability of the membrane to Na+ and K+
What is the typical resting potential for a motor neuron?
Around -70mV
What is depolarization?
A change in membrane potential that makes it more positive
What is hyperpolarization?
A change in membrane potential that makes it more negative
What is the threshold potential?
The critical level to which a membrane potential must be depolarized to initiate an action potential
What are graded potentials?
Short-lived, localized changes in membrane potential that can vary in strength
What are the two types of alteration that can change resting potential?
- Altering the permeability of the membrane to Na+ and K+
- Altering the concentration of Na+ and K+ inside and/or outside of the cell
What is the relationship between graded potentials and action potentials?
Graded potentials are essential in initiating action potentials
What is an all-or-none phenomenon in relation to action potentials?
An action potential either happens or it doesn’t; if threshold is reached, the action potentials are always the same size
What is the absolute refractory period?
A period during which an action potential cannot be initiated
What is the relative refractory period?
A period during which another action potential can be fired, but a bigger stimulus is needed
What factors affect the propagation velocity of action potentials?
- Axon diameter
- Degree of myelination
What are the two types of conduction in myelination?
- Continuous conduction
- Saltatory conduction
What is a synapse?
A junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell
What is the difference between pre-synaptic and post-synaptic neurons?
- Pre-synaptic neuron: conducts the impulse to the synapse
- Post-synaptic neuron: receives the impulse and transmits it away from the synapse
What are the two types of synapses?
- Electrical synapses
- Chemical synapses
What occurs during pre-synaptic events?
- Action potential arrives at presynaptic end bulb
- Opens voltage gated Ca2+ channels
- Ca2+ flows into cell
- Exocytosis of synaptic vesicles
- Neurotransmitter released into cleft
What is an EPSP?
Excitatory post-synaptic potential that brings the potential closer to threshold
What is an IPSP?
Inhibitory post-synaptic potential that brings the potential further from the threshold
What is the function of neurotransmitters?
They mediate communication between neurons
What are the classifications of neurotransmitters?
- Functionally: inhibitory or excitatory
- Chemically: direct- or indirect-acting
What effect does caffeine have on nervous transmission?
Lowers the threshold level of the nerve, increasing the possibility for a stimulus to result in an action potential
What effect does alcohol have on nervous transmission?
Increases the nerve threshold level, decreasing the possibility of a stimulus to result in a nerve action potential
What is the role of local anesthetics like novocaine?
Prevent the opening of sodium gated channels, inhibiting generation of nerve action potentials
What is the role of acetylcholinesterase?
Inactivates acetylcholine
Acetylcholine is a neurotransmitter involved in muscle activation and other functions.
What condition can result from the inactivation of acetylcholinesterase?
Tetanus (paralysis)
Tetanus refers to muscle stiffness and spasms due to prolonged muscle contraction.
What is the resting potential range for all cells?
Between -50 and -90mV
What do neurons use to communicate?
Action potentials
What can changes in resting potentials generate?
Graded potentials
What are graded potentials?
Short-lived and short distance signals that can vary in intensity
How do action potentials differ from graded potentials?
All-or-none changes in resting potential used for long distance signal propagation
Which channels are responsible for initiating an action potential?
Voltage-gated Na+ channels
Which of the following does not translate into a short-distance, short-lived change of potential in the cell membrane?
Action potential
Action potentials are long-distance signals.
Where is the velocity of a nerve impulse conduction greatest?
Heavily myelinated, large diameter fibers
What do local anaesthetics block?
Voltage-gated Na+ channels
What do general anaesthetics activate?
Chemically-gated Cl- channels
What specific process do anaesthetics impair?
Nerve impulse transmission
Fill in the blank: Changes in resting potentials can also generate _______.
graded potentials
True or False: Graded potentials are long-lived signals.
False
