Behavioral Neuroscience Exam 2 Review

Synapse

A specialized junction where one neuron communicates with another cell, such as a neuron, muscle cell, or gland.

Synaptic Cleft

The small gap (approximately 200 angstroms wide) between the presynaptic and postsynaptic cells where neurotransmitters diffuse.

EPSP (Excitatory Postsynaptic Potential)

A depolarizing postsynaptic potential that increases the likelihood of an action potential.

IPSP (Inhibitory Postsynaptic Potential)

A hyperpolarizing postsynaptic potential that decreases the likelihood of an action potential.

Temporal Summation

The process of adding together synaptic inputs that occur at different times to reach the threshold for an action potential.

Spatial Summation

The process of adding together synaptic inputs that occur at different locations on the neuron to reach the threshold for an action potential.

Axodendritic Synapse

A synapse where the axon terminal of one neuron connects to the dendrite of another; the most common type in the brain.

Axosomatic Synapse

A synapse where the axon terminal connects directly to the soma (cell body) of the postsynaptic neuron.

Axoaxonic Synapse

A synapse where one axon terminal connects to another axon, typically regulating neurotransmitter release.

Dendrodendritic Synapse

A less common synapse where one dendrite connects to another, often found in local circuits and interneurons.

Type I (Asymmetric) Synapse

Usually excitatory synapses with round vesicles and a thick postsynaptic density, typically producing EPSPs.

Type II (Symmetric) Synapse

Usually inhibitory synapses with flattened vesicles and a thin postsynaptic density, typically producing IPSPs.

Ionotropic Receptor

A type of postsynaptic receptor that directly opens an ion channel upon binding with a neurotransmitter.

Metabotropic Receptor

A type of postsynaptic receptor that activates second messenger systems upon binding with a neurotransmitter.

Charles Scott Sherrington

The scientist who provided the first experimental evidence for synapses by observing delays in spinal reflexes.

Otto Loewi

The scientist who proved chemical neurotransmission by transferring fluid from a stimulated frog heart to an unstimulated one.

Acetylcholine (ACh)

The first neurotransmitter discovered; it is the primary transmitter of the parasympathetic nervous system.

Presynaptic Terminal

The swollen ending of an axon that contains synaptic vesicles and releases neurotransmitters.

Postsynaptic Density

A protein-rich region on the postsynaptic membrane that anchors receptors and organizes signaling machinery.

Seven Steps of Neurotransmission

Synthesis, storage, release, autoreceptor regulation, postsynaptic receptor binding, reuptake, and enzymatic degradation.

Action Potential Integration

The process by which a neuron combines excitatory and inhibitory inputs to determine whether to trigger an action potential.

Spontaneous Firing Rate

The baseline rate at which a neuron generates action potentials in the absence of specific synaptic input.

Neural Circuitry

The organization of neurons into chains, convergent networks, or divergent networks to integrate and distribute information.

Voltage-gated Calcium Channels

Channels in the presynaptic terminal that open in response to an action potential, triggering neurotransmitter release.

Convergent Network

A neural circuit structure where multiple neurons send signals to a single postsynaptic neuron.

Divergent Network

A neural circuit structure where one neuron sends signals to multiple postsynaptic neurons.

Asymmetric synapses (Type I)

Synapses with a thick postsynaptic density and round synaptic vesicles; typically excitatory and located on dendritic spines.

Symmetric synapses (Type II)

Synapses with a thinner postsynaptic density and flattened or ellipsoidal vesicles; typically inhibitory and located on the soma.

Non-synaptic chemical communication (Volume transmission)

The release of neurotransmitters into the extracellular space to diffuse and affect multiple nearby neurons, rather than a single point-to-point synapse.

Excitatory postsynaptic potential (EPSP)

A graded depolarization of the postsynaptic membrane that increases the likelihood of an action potential.

Inhibitory postsynaptic potential (IPSP)

A graded hyperpolarization of the postsynaptic membrane that decreases the likelihood of an action potential.

Modulatory signals

Signals that do not directly cause immediate firing but alter how a neuron responds to other inputs, often via metabotropic receptors.

Ionotropic receptors

Ligand-gated ion channels that open immediately upon neurotransmitter binding to allow rapid, direct ion flow.

Metabotropic receptors

G-protein-coupled receptors that trigger intracellular signaling cascades, resulting in slower, longer-lasting, and amplified effects.

Second messenger

An intracellular signaling molecule activated by a metabotropic receptor that carries the signal to internal targets like ion channels or enzymes.

Autoreceptors

Receptors on the presynaptic neuron that detect neurotransmitter levels and provide negative feedback to regulate further release.

Neurotransmitter-dependent ion channels

Ligand-gated channels that open in response to neurotransmitters, allowing specific ions to flow based on their electrochemical gradients.

Sodium (Na+) channels

Channels that allow Na+ to enter the cell, typically causing depolarization and EPSPs.

Potassium (K+) channels

Channels that allow K+ to leave the cell, typically causing hyperpolarization and IPSPs.

Chloride (Cl-) channels

Channels that allow Cl- to enter the cell, typically causing hyperpolarization and inhibition.

Calcium (Ca2+) channels

Channels that allow Ca2+ to enter the cell, contributing to depolarization and activating intracellular signaling pathways.

What is the primary function of adhesion proteins at the synapse?

They stabilize the structure and align the two cells precisely to ensure efficient transmission.

What is the typical functional difference between asymmetric and symmetric synapses?

Asymmetric synapses are generally excitatory, while symmetric synapses are generally inhibitory.

What brain states are often regulated by non-synaptic communication?

Overall brain states such as mood, arousal, and attention.

How do excitatory signals increase the probability of an action potential?

By causing depolarization through the opening of ion channels that allow positive ions like sodium (Na+) to enter the cell.

How do inhibitory signals decrease the probability of an action potential?

By causing hyperpolarization, usually through allowing chloride (Cl-) to enter or potassium (K+) to leave the cell.

What is the role of G-proteins in metabotropic signaling?

They are activated by the receptor and trigger a signaling cascade that can open ion channels, activate enzymes, or modify gene expression.

Why is signal amplification possible with metabotropic receptors?

Because one receptor activation can generate many second messenger molecules, leading to a broader effect inside the cell.

What is the purpose of the negative feedback provided by autoreceptors?

To maintain balance in neural communication and prevent excessive neurotransmitter release.

What determines whether a postsynaptic potential is excitatory or inhibitory?

The specific type of ion channel that opens, which dictates the direction of ion flow and the resulting change in membrane potential.

Why are postsynaptic potentials considered 'graded'?

Because their size and impact depend on the number of receptors activated at the synapse.

Axon hillock

The integration zone of the neuron where incoming EPSPs and IPSPs are summed to determine if an action potential will be triggered.

Threshold potential

The membrane potential (approximately -55 mV) that must be reached to open voltage-gated sodium channels and trigger an action potential.

Peptide neurotransmitters

Neurotransmitters synthesized from a DNA template in the soma, processed in the rough ER and Golgi, and transported down the axon via microtubules.

Small-molecule neurotransmitters

Neurotransmitters (e.g., dopamine, serotonin, acetylcholine) synthesized from precursor molecules directly in the axon terminal by local enzymes.

Synaptic vesicles

Membrane-bound structures that store neurotransmitters in the axon terminal until they are released via exocytosis.

Kiss-and-run

A mode of vesicle release where the vesicle briefly fuses with the membrane, releases its contents, detaches, and is reused.

Merge-and-recycle

A mode of vesicle release where the vesicle fully collapses into the presynaptic membrane and is later retrieved and recycled.

Bulk endocytosis

A mode of vesicle release where large portions of the presynaptic membrane are retrieved during periods of high neuronal activity.

Readily releasable pool

A pool of synaptic vesicles docked at active zones, available for immediate release upon stimulation.

Recycling pool

A pool of synaptic vesicles that functions to replenish the readily releasable pool.

Reserve pool

A large backup supply of synaptic vesicles mobilized only during periods of strong stimulation.

Quantum (in neurotransmission)

The very small postsynaptic response produced by the release of neurotransmitters from a single vesicle.

Reuptake

The process of clearing neurotransmitters from the synaptic cleft by transporting them back into the presynaptic neuron via specialized transporter proteins.

Enzymatic degradation

The process of inactivating neurotransmitters in the synaptic cleft by breaking them down using specific extracellular enzymes.

Acetylcholinesterase (AChE)

An enzyme in the synaptic cleft that breaks down acetylcholine into acetate and choline to terminate its signal.

Neural circuit

A network of interconnected neurons that process and transmit information to perform specific functions like movement or sensation.

Neural chain

The simplest type of neural circuit where neurons are connected in a linear, step-by-step sequence.

Exocytosis

The calcium-dependent process by which synaptic vesicles fuse with the presynaptic membrane to release neurotransmitters into the synaptic cleft.

Divergent Circuitry

A circuit where one presynaptic neuron synapses onto multiple postsynaptic neurons, amplifying signals and coordinating activity across multiple brain regions.

Convergent Circuitry

A circuit where multiple presynaptic neurons synapse onto a single postsynaptic neuron, allowing for the integration of information from different sources.

Drug

An exogenous chemical, not an essential nutrient, that significantly alters cell function at low doses.

Exogenous

A substance that originates from outside the body.

Psychoactive Drug

A drug that specifically alters mood, thought, or behavior.

Blood-Brain Barrier (BBB)

A barrier that drugs must cross to affect the brain; lipid solubility is the most important factor for determining if a drug can pass through it.

Pharmacokinetics

The study of how the body processes a drug over time, specifically the processes of absorption, distribution, metabolism, and excretion (ADME).

Half-life

The time required for the concentration of a drug in the body to decrease by half.

Metabolism

The process, usually involving liver enzymes, by which the body breaks down a drug into metabolites for elimination.

Metabolites

The products resulting from the metabolism of a drug; they may be inactive or biologically active.

Pharmacodynamics

The study of what a drug does to the body, including its physiological and behavioral effects.

Affinity

A measure of how strongly a drug binds to its target, such as a receptor.

Efficacy

The ability of a drug to activate a receptor and produce a physiological effect after binding.

Oral Administration

A route of drug delivery involving swallowing pills or liquids; it is the most common route but produces slower effects.

Intravenous Injection

A peripheral injection route where a drug is delivered directly into a vein, resulting in rapid and strong effects.

Intrathecal Injection

A direct nervous system injection route where a drug is delivered into the cerebrospinal fluid.

Intracerebroventricular Injection

A direct nervous system injection route where a drug is delivered into the brain ventricles.

Intraparenchymal Injection

A direct nervous system injection route where a drug is delivered directly into brain tissue.

Sublingual Administration

A route where a drug is placed under the tongue for rapid absorption into the bloodstream.

Subcutaneous Injection

A peripheral injection route where a drug is delivered under the skin.

Intramuscular Injection

A peripheral injection route where a drug is delivered into a muscle.

Intraperitoneal Injection

A peripheral injection route where a drug is delivered into the abdominal cavity.

Lipid Solubility

The primary factor determining a drug's ability to cross the blood-brain barrier, as lipid-soluble molecules pass through cell membranes easily.

Summation

The process enabled by convergent circuitry where multiple inputs are integrated to determine if a postsynaptic neuron reaches the threshold to fire an action potential.

ADME

An acronym for the four processes of pharmacokinetics: Absorption, Distribution, Metabolism, and Excretion.

What defines a good therapeutic drug in terms of receptor interaction?

A good therapeutic drug typically has both high affinity (binds well) and high efficacy (produces the desired effect).

What is the primary difference between an agonist and an antagonist?

An agonist mimics or increases the actions of a neurotransmitter, while an antagonist blocks or decreases those actions.

Does an agonist always excite a neuron?

No. Agonists increase neurotransmitter effects, but they can produce inhibitory effects depending on the system (e.g., morphine).

How does a competitive antagonist function?

It binds to the same receptor site as the neurotransmitter, competing directly; its effects can be overcome by increasing neurotransmitter concentration.

What characterizes a noncompetitive antagonist?

It binds to a different site on the receptor, changing its shape or function so the neurotransmitter cannot activate it; its effects are generally not overcome by increasing neurotransmitter levels.

What is an irreversible antagonist?

A drug that permanently binds to or modifies a receptor, rendering it inactive until the neuron produces new receptors.