PHS 3341 Lecture 3 - Graded Potentials, Action Potentials and Synapses - Revised 2022- Student Copy

Graded Potentials

Local changes in membrane potential that can be either depolarizing or hyperpolarizing.

Action Potentials

Brief, rapid changes in membrane potential that allow for long-distance neural communication.

Synapses

Junctions between neurons where information is transmitted through the release and reception of neurotransmitters.

Excitatory Chemical Synapses

Synapses that increase the likelihood of an action potential in the postsynaptic cell.

Inhibitory Chemical Synapses

Synapses that decrease the likelihood of an action potential in the postsynaptic cell.

Synaptic Integration

The process by which multiple synaptic inputs are combined to determine whether an action potential will be generated in the postsynaptic cell.

Synaptic Strength

The effectiveness of a synapse in transmitting signals between neurons.

Neurotransmitter Release

The process by which neurotransmitters are released from the presynaptic neuron into the synaptic cleft.

Gated Ion Channels

Channels in the cell membrane that open and close in response to specific stimuli.

Chemically Gated (Ligand-Gated) Channels

Ion channels that open in response to the binding of a specific chemical, such as a neurotransmitter.

Voltage-Gated Channels

Ion channels that open and close in response to changes in membrane potential.

Mechanically Gated Channels

Ion channels that open and close in response to physical deformation of the membrane.

Depolarization

A decrease in membrane potential, making the inside of the membrane less negative.

Hyperpolarization

An increase in membrane potential, making the inside of the membrane more negative.

Receptor Potential

A graded potential generated in sensory neurons in response to a stimulus.

Postsynaptic Potential

A graded potential generated in the dendrites or soma of a neuron or muscle cell in response to synaptic input.

Absolute Refractory Period

A brief period after an action potential during which the neuron is unable to generate another action potential.

Relative Refractory Period

A period following the absolute refractory period during which a stronger-than-usual stimulus is required to generate an action potential.

Threshold Potential

The membrane potential at which an action potential is triggered, typically around -55 mV.1. Action Potential Propagation:The process of the electrical current from an action potential depolarizing adjacent membranes to the threshold potential.

Absolute Refractory Period

The period of time following an action potential during which the membrane is unable to generate another action potential.

Action Potential Conduction Speed

The speed at which an action potential propagates along an axon, which depends on the fiber diameter and whether the fiber is myelinated.

Saltatory Conduction

The rapid conduction of action potentials in myelinated axons, where the action potential "jumps" from one node of Ranvier to the next.

Graded Potentials

Changes in membrane potential that vary in amplitude and can be summed, unlike action potentials.

Action Potentials

All-or-none electrical signals that have a constant amplitude once the membrane is depolarized to threshold and cannot be summed.

Synapse

The point of communication between two neurons or a neuron and a muscle cell.

Chemical Synapse

A type of synapse where neurotransmitters relay information from the presynaptic cell to the postsynaptic cell across a synaptic cleft.

Electrical Synapse

A type of synapse where pre- and post-synaptic cells are joined by gap junctions, allowing for direct electrical communication.

Neurotransmitter Release

The process by which neurotransmitters stored in vesicles are released into the synaptic cleft in response to an action potential.

Postsynaptic Receptors

Proteins on the postsynaptic cell membrane that bind to neurotransmitters and initiate a response in the postsynaptic cell.

Excitatory Chemical Synapses

Synapses where the neurotransmitter glutamate causes depolarization of the postsynaptic membrane, bringing it closer to the threshold for generating an action potential.

Inhibitory Chemical Synapses

Synapses where the neurotransmitters GABA or glycine cause hyperpolarization of the postsynaptic membrane, moving it further from the threshold for generating an action potential.

Synaptic Integration

The process by which a neuron integrates the excitatory and inhibitory inputs it receives to determine whether or not to generate an action potential.

Axon Initial Segment

The region of the neuron where the action potential is initiated, which has a lower threshold for generating an action potential compared to the rest of the axon.

Modulation of Synaptic Strength

The mechanisms that can increase or decrease the strength of synaptic transmission, including changes in neurotransmitter release and receptor sensitivity.1. Release and degradation of the neurotransmitter:The process of releasing and breaking down the neurotransmitter inside the axon terminal.

Increased neurotransmitter release into the synapse

The action of increasing the amount of neurotransmitter released into the synapse.

Prevention of neurotransmitter release into the synapse

The act of stopping or inhibiting the release of neurotransmitter into the synapse.

Inhibition of synthesis of the neurotransmitter

The process of blocking or reducing the production of the neurotransmitter.

Reduced reuptake of the neurotransmitter from the synapse

The action of decreasing the reabsorption of the neurotransmitter from the synapse back into the axon terminal.

Reduced degradation of the neurotransmitter in the synapse

The process of decreasing the breakdown or degradation of the neurotransmitter in the synapse.

Agonists

Substances that evoke the same response as the neurotransmitter when they occupy the receptors.

Antagonists

Substances that block or inhibit the response to the neurotransmitter when they occupy the receptors.