Midterm 2 shit ton of cards

What is a synapse?

The site where nerve impulses are transmitted between two neurons or between a neuron and an effector such as a muscle or gland cell.

What are the two cells involved in a synapse called?

Presynaptic cell = sends the signal; postsynaptic cell = receives the signal.

What is an effector?

A specialized, non-neuronal cell that responds to a stimulus to produce a specific change; examples include muscle cells and gland cells.

What is a neuromuscular junction (NMJ)?

A synaptic connection between a motor neuron and a muscle fiber.

What are the two main types of synapses?

Chemical synapses and electrical synapses.

What happens at a chemical synapse?

Electrical activity in the presynaptic cell causes release of a neurotransmitter, which crosses the synaptic cleft and binds receptors on the postsynaptic cell.

Why do chemical synapses create directionality?

Neurotransmitter is released from the presynaptic cell and receptors are located on the postsynaptic cell, so information normally flows in one direction.

What are the two possible effects of a chemical synapse?

It can be excitatory or inhibitory.

What determines whether a chemical synapse is excitatory or inhibitory?

The interaction between the neurotransmitter/receptor and the postsynaptic cell, particularly which ion channels are opened.

What is an electrical synapse?

A direct electrical connection between cells through gap junction channels.

Are neurotransmitters involved in electrical synapses?

No. Current flows directly from one cell to another through gap junctions.

What determines current flow through an electrical synapse?

The voltage difference (driving force) between the two cells.

What structure connects cells at an electrical synapse?

Gap junctions, which form channels between the cells.

What is the main difference between chemical and electrical synapses?

Chemical synapses use neurotransmitters; electrical synapses allow direct current flow through gap junctions.

Where are motor neurons that innervate skeletal muscle located?

In the ventral horn of the spinal cord.

What type of axons do motor neurons have?

Heavily myelinated axons that project from the spinal cord to muscle fibers.

How does a motor neuron stimulate muscle contraction?

It releases acetylcholine (ACh), which activates receptors on the muscle fiber.

Are most synapses in the body neuromuscular junctions?

No. Most synapses are between neurons.

What is an axodendritic synapse?

A synapse where the presynaptic axon contacts a dendrite of the postsynaptic neuron.

What is an axosomatic synapse?

A synapse where the presynaptic axon contacts the soma of the postsynaptic neuron.

Why can axosomatic synapses have a large influence?

They are located directly on the soma, close to the site where the neuron integrates inputs and generates an action potential.

What is an axoaxonic synapse?

A synapse where one neuron's axon contacts the axon of another neuron.

What is the typical function of an axoaxonic inhibitory synapse?

It can modulate action-potential propagation or neurotransmitter release in the target axon.

What is an EPSP?

An excitatory postsynaptic potential; a depolarizing postsynaptic potential that makes the neuron more likely to reach threshold.

What is an IPSP?

An inhibitory postsynaptic potential; a postsynaptic potential that makes the neuron less likely to reach threshold.

What happens when an excitatory presynaptic neuron spikes?

It can produce a depolarizing EPSP in the postsynaptic neuron.

What happens when an inhibitory presynaptic neuron is activated?

It can produce an IPSP, often involving hyperpolarization or shunting inhibition.

Are EPSPs and IPSPs action potentials?

No. They are graded postsynaptic potentials.

How are EPSPs/IPSPs different from action potentials?

EPSPs/IPSPs are graded and decremental and can summate; action potentials are all-or-none.

What happens if the presynaptic stimulus is too weak to generate an action potential?

In the basic chemical synapse model, no action potential means no normal neurotransmitter release and therefore no postsynaptic potential.

What is the temporal profile of an EPSP/IPSP?

It rises and then gradually decays rather than behaving like a brief all-or-none action potential.

What is temporal summation?

The addition of postsynaptic potentials occurring close together in time.

Why can EPSPs undergo temporal summation?

Because an EPSP lasts long enough that another EPSP can occur before the first has completely decayed.

What happens if a presynaptic neuron fires rapidly multiple times?

Multiple EPSPs can stack on top of one another, producing a larger depolarization.

Does the second EPSP start from the resting membrane potential?

No. It begins from the membrane potential remaining after the first EPSP.

Why is it called temporal summation?

Because the EPSPs are summed based on their timing in relation to one another.

What happens if summed EPSPs reach threshold?

The postsynaptic neuron can generate an action potential.

What is the sequence from presynaptic activity to a postsynaptic action potential?

Presynaptic action potential → neurotransmitter release → postsynaptic receptor activation → EPSP/IPSP → summation → threshold → postsynaptic action potential.

What is temporal synaptic summation?

The summation of multiple postsynaptic potentials produced by repeated activity at the same synapse over a short period of time.

What is spatial synaptic summation?

The summation of postsynaptic potentials produced by activation of multiple synapses at different locations on the neuron at the same time.

How does spatial summation occur in dendrites?

EPSPs generated at different synapses passively propagate through the dendrites and sum when they converge, producing a larger integrated EPSP.

What happens to a summed EPSP as it travels toward the soma?

It continues to passively propagate and attenuates with distance.

Why is the soma important for synaptic integration?

The soma receives and integrates many EPSPs and IPSPs arriving from different parts of the dendritic tree.

What is the basic sequence of spatial summation?

EPSP 1 + EPSP 2 → traveling EPSPs → integrated/larger EPSP → propagation toward soma.

What is a neurotransmitter?

A small signaling molecule released by a presynaptic cell that crosses the synaptic cleft and binds receptors on the postsynaptic cell.

What determines whether a neurotransmitter is excitatory, inhibitory, or modulatory?

The type of receptor it activates and the resulting effect on the postsynaptic cell.

What are the three broad functional categories of neurotransmitters?

Excitatory, inhibitory, and modulatory.

What is the major excitatory neurotransmitter in the vertebrate CNS?

Glutamate.

What neurotransmitter is used at the neuromuscular junction?

Acetylcholine (ACh).

What is the major inhibitory neurotransmitter in the vertebrate CNS?

GABA.

What is another major inhibitory neurotransmitter?

Glycine.

What are examples of modulatory neurotransmitters?

Serotonin, norepinephrine, dopamine, ATP, and in the CNS, acetylcholine.

What are the major neurotransmitter families?

Amino acids, purines, biogenic amines, and peptide neurotransmitters.

What are examples of amino acid neurotransmitters?

Glutamate and GABA.

What is an example of a purine neurotransmitter?

ATP.

What are examples of biogenic amine neurotransmitters?

Dopamine, norepinephrine, epinephrine, and serotonin.

What are peptide neurotransmitters?

Neurotransmitters made as peptides by ribosomes; many function as longer-lasting neuromodulators.

What is the postsynaptic cell at the neuromuscular junction?

A skeletal muscle fiber.

What happens when the motor axon at the NMJ is stimulated?

An action potential travels to the presynaptic terminal, causing ACh release and an excitatory endplate potential in the muscle fiber.

What is an endplate potential (EPP)?

The depolarizing postsynaptic potential produced at the neuromuscular junction by ACh.

What happens if the EPP reaches threshold?

Voltage-gated Na+ channels open and the muscle fiber generates an action potential.

How does the muscle action potential lead to contraction?

The action potential travels along the sarcolemma and T-tubules, triggering Ca2+ release/entry that ultimately causes muscle contraction.

How does ACh initiate the muscle action potential?

ACh binds nicotinic ACh receptors, opening ligand-gated cation channels and producing an inward current and depolarization.

What is iontophoresis?

A technique that uses electrical current in a micropipette to eject a charged molecule, such as ACh, onto a cell or tissue.

Why is atropine sometimes used in classic NMJ experiments?

Atropine blocks muscarinic ACh receptors and can prevent certain effects of ACh; it is not the primary blocker of skeletal muscle nicotinic receptors.

What controls neurotransmitter release from the presynaptic terminal?

Ca2+ entry through voltage-gated Ca2+ channels.

Where does Ca2+ enter during synaptic transmission?

Through voltage-gated Ca2+ channels in the presynaptic terminal.

What opens presynaptic voltage-gated Ca2+ channels?

Depolarization of the presynaptic terminal caused by the arriving action potential.

What are Ca2+ microdomains?

Small local regions near open Ca2+ channels where Ca2+ concentration rises rapidly and locally.

Why is presynaptic Ca2+ necessary for synaptic transmission?

Ca2+ binds the release machinery and triggers synaptic vesicle fusion and neurotransmitter release.

What happens if a Ca2+ chelator such as BAPTA is introduced into the presynaptic terminal?

It rapidly binds incoming Ca2+ and greatly reduces Ca2+-triggered neurotransmitter release, even though the presynaptic action potential can still occur.

What does the BAPTA experiment demonstrate?

Ca2+ entry into the presynaptic terminal is necessary for neurotransmitter release.

What is quantal neurotransmitter release?

The release of neurotransmitter in discrete packets called quanta, with each quantum generally corresponding to the contents of one synaptic vesicle.

What is a quantum?

The amount of neurotransmitter released from approximately one synaptic vesicle.

Why are neurotransmitters released in discrete quanta?

Because neurotransmitters are stored in individual synaptic vesicles, and each vesicle releases its contents as a discrete event.

Why are experiments often performed in low extracellular Ca2+ when studying quantal release?

Low Ca2+ reduces the probability of vesicle release, allowing individual quantal events to be distinguished.

What happens to EPPs when extracellular Ca2+ is reduced?

They become smaller and more variable, and many stimuli may produce no detectable release.

What is a miniature endplate potential (mini EPP)?

A small spontaneous EPP produced by the spontaneous release of neurotransmitter from approximately one synaptic vesicle.

Do miniature EPPs require stimulation of the presynaptic neuron?

No. They can occur spontaneously in the absence of an action potential.

What does the amplitude of a mini EPP approximately represent?

The postsynaptic response to one quantum of neurotransmitter.

What does a quantized distribution of EPP amplitudes look like?

It shows discrete peaks corresponding approximately to 0, 1, 2, 3, etc. quanta of release.

Why does normal extracellular Ca2+ make individual quanta harder to distinguish experimentally?

High Ca2+ produces many simultaneous release events, causing quantal responses to overlap and produce larger, less discrete EPPs.

Where are synaptic vesicles concentrated for neurotransmitter release?

At specialized presynaptic regions called active zones.

What happens when a synaptic vesicle fuses with the presynaptic plasma membrane?

The vesicle membrane merges with the plasma membrane and its neurotransmitter is released into the synaptic cleft.

What is the fusion pore?

The initial connection between the lumen of a synaptic vesicle and the extracellular space that forms during vesicle fusion.

How can you identify the presynaptic side of a chemical synapse using electron microscopy?

It contains numerous synaptic vesicles clustered near the active zone.

What is resolution in microscopy?

The shortest distance between two points that can still be distinguished as separate.

What limits the resolution of light microscopy?

The wavelength of visible light; conventional light microscopy has a resolution on the order of hundreds of nanometers.

How does electron microscopy achieve higher resolution?

It uses accelerated electrons with much shorter effective wavelengths than visible light.

What is the approximate resolution of electron microscopy?

It can reach approximately 0.1–1.2 nm depending on the technique.

What is the basic sequence of chemical synaptic transmission?

Action potential → presynaptic depolarization → opening of voltage-gated Ca2+ channels → Ca2+ entry → synaptic vesicle fusion → neurotransmitter release.

What are major approaches used to study the molecular basis of vesicle fusion?

Biochemical purification, yeast genetics, biochemical reconstitution, genetic tests, and studies of toxins that block neurotransmitter release.

What are the three major questions about the molecular basis of synaptic fusion?

What mediates membrane fusion, what makes fusion Ca2+-dependent, and what ensures the speed of release?