exam 2 - old study guide Flashcards
What is the neuromuscular junction and what kind of cells make this specialized synaptic connection?
The neuromuscular junction (NMJ) is a specialized synapse between a motor neuron and a muscle fiber.
The NMJ consists of presynaptic motor neuron terminals, the synaptic cleft, and the postsynaptic muscle cell membrane (sarcolemma).
The motor neuron releases neurotransmitters to stimulate the muscle cell.
What is the particular NT being released at this synapse? Is it a synapse in the CNS or PNS?
ACh acetylcholine - PNS because it connects motor neurons to skeletal muscles.
What does it mean for two cells to be “electrically coupled”?
Would those be electrical or chemical synapses between these cells?
they are directly connected via gap junctions, allowing ions to flow between them.
These connections form electrical synapses
Is the electrical activity of the two cells
synchronous if they are electrically coupled?
Are those synapses made of gap junctions?
Can ionic current move in both directions between the two cells via the gap junctions?
Is there any diffusion of neurotransmitters across a synaptic cleft at electrical synapses?
If two cells are electrically coupled, their electrical activity is typically synchronous because ion flow occurs almost instantaneously.
Gap junctions create low-resistance pathways for bidirectional ionic current movement.
Unlike chemical synapses, electrical synapses do not involve neurotransmitter diffusion across a synaptic cleft.
How do dense-core vesicles differ from synaptic vesicles (I have just a few differences listed on a slide or two)?
For example, which vesicles are larger and pack larger neurotransmitters?
Which ones are loaded with NT molecules in the axonal terminal?
Dense-Core Vesicles:
Larger
NT TYPE - Peptides (e.g., neuropeptides)
LOADED @ - Cell body (soma)
RELEASE - Require high-frequency stimulation
Synaptic Vesicles:
Smaller
Small molecule NTs (e.g., ACh, glutamate)
Axon terminal
Released during low- or high-frequency activity
What is the name of the precise area of presynaptic release (the area where vesicles are docked)?
What is an “active zone”?
Is that a pre-or a post-synaptic structure?
The active zone is the presynaptic region where synaptic vesicles are docked and primed for release.
It is a presynaptic structure where exocytosis occurs.
Know what the processes of exocytosis and endocytosis are:
Exocytosis: Process where synaptic vesicles fuse with the presynaptic membrane to release NTs into the synaptic cleft.
Endocytosis: Process where vesicle membranes are retrieved and recycled after neurotransmitter release.
What mediates exocytosis? Is exocytosis of vesicles dependent on a particular ion flowing into the active zone? What ion is it and what exact channels does it move through?
Exocytosis is calcium-dependent.
Voltage-gated calcium channels (VGCCs) in the active zone open in response to an action potential, allowing Ca²⁺ influx.
This triggers vesicle fusion and NT release.
How is NT loaded into synaptic vesicles?
Does that loading depend on a gradient of a certain ion across the membrane of the synaptic vesicle?
Who establishes that gradient (what membrane protein)?
Can you load NT without that particular ionic gradient?
NT loading into vesicles depends on an ion gradient.
Vesicular H⁺-ATPase (proton pump) establishes a proton gradient inside vesicles.
Vesicular neurotransmitter transporters use this gradient to load NTs into vesicles.
Without this proton gradient, NT loading cannot occur.
What particular process are the SNARE proteins involved in?
Do these proteins have to interact in order for vesicles to fuse with the plasma membrane?
Is there a protein in the terminal that acts as a calcium “sensor” and which one is it?
SNARE proteins (e.g., synaptobrevin, syntaxin, SNAP-25) mediate vesicle docking & fusion.
Synaptotagmin is the Ca²⁺ sensor that triggers exocytosis when Ca²⁺ binds to it.
Without SNARE interactions, vesicle fusion cannot occur.
How many pools of synaptic vesicles are there (the classic pool model)?
During normal function, immediate release of vesicles is mediated by what pool?
And which pool contains the largest number of vesicles that are believed to be rarely used for release?
Readily Releasable Pool (RRP) - Immediate release during normal activity
Recycling Pool -Replenishes RRP during sustained activity
Reserve Pool -
Largest, rarely used
Which one of the following will block exocytosis?
- Block of V-gated calcium channels
- Removal of extracellular calcium
- Genetic deletion of synaptotagmin
- Inhibition of SNARE protein interactions
- None of the above scenarios will affect exocytosis
- All of the above scenarios will block exocytosis
Blocking any of the following will prevent exocytosis:
✅ Block voltage-gated Ca²⁺ channels → No Ca²⁺ influx → No vesicle fusion
✅ Remove extracellular Ca²⁺ → No Ca²⁺ entry → No exocytosis
✅ Genetic deletion of synaptotagmin → No Ca²⁺ sensing → No exocytosis
✅ Inhibit SNARE interactions → No vesicle docking/fusion
Answer: “All of the above scenarios will block exocytosis.”
Blocking V-gated Na⁺ channels prevents action potential propagation, indirectly preventing exocytosis.
Which membrane receptor below is an example of an ionotropic receptor and which one is an example of a metabotropic receptor?
Ionotropic receptors have ion channels that open when bound to NTs.
Metabotropic receptors activate G-protein signaling.
To determine the receptor type, look for ion channels (ionotropic) or second-messenger cascades (metabotropic).
What are protein kinases and protein phosphatases?
Protein Kinase -
Phosphorylates proteins,
Activates ion channels(usually)
Protein Phosphatase -
Dephosphorylates proteins
Deactivates (usually)
What is responsible for the depolarized state of the photoreceptor membrane in the dark?
What channel?
Is it open or closed in the dark?
Why? What gates its activity?
Depolarized state is maintained by open cyclic nucleotide-gated (CNG) channels, allowing Na⁺ and Ca²⁺ influx.
What is the approx. value of the transmembrane voltage of a photoreceptor in the dark?
~-40 mV.
How do vertebrate photoreceptors respond to light?
Do they hyper- or depolarize in response to light?
Is this response an action potential or a graded potential?
Do they release more glutamate or less the more light there is?
Light → Hyperpolarization due to closure of CNG channels.
More light → Less glutamate release (graded response).
This response is a graded potential, not an action potential.
Does light activate or deactivate opsins?
Light activates opsins (e.g., rhodopsin in rods and photopsins in cones).
Does light activate or deactivate transducin?
Light activates transducin, a G-protein that initiates the phototransduction cascade.
Does light lead to activation or deactivation of PDE (phosphodiesterase)?
Light activates PDE, which breaks down cGMP.
Does activated PDE reduce or increase cGMP concentrations?
Activated PDE reduces cGMP concentrations by converting cGMP to GMP.
Does light activate or deactivate opsins? Does it activate or deactivate transducin? Does light lead to activation or deactivation of PDE? Does activated PDE reduce or increase cGMP concentrations? not answer!!!
ONLY THIS: How does that then affect the CNG channels? What does that all mean for the transmembrane voltage? How does that translate into changes in NT release?
How does that then affect the CNG (cyclic nucleotide-gated) channels?
Lower cGMP levels cause CNG channels to close, preventing Na⁺ and Ca²⁺ from entering the cell.
What does that all mean for the transmembrane voltage?
The photoreceptor hyperpolarizes (membrane potential becomes more negative).
How does that translate into changes in neurotransmitter (NT) release?
Less glutamate is released from the photoreceptor because NT release depends on depolarization.
What is the fovea?
The fovea is the central region of the retina specialized for sharp central vision and high visual acuity.
fovea - Is it important for central vision and highest visual acuity?
Yes, it is responsible for the sharpest vision and fine detail detection.
Is the fovea full of rods or cones?
Cones; the fovea has a very high density of cones and no rods.
fovea - Is it an area for central or peripheral vision?
Central vision.
fovea - Does it detect color?
Does it have high or low visual acuity?
Why are cells, other than photoreceptors, in the foveal pit displaced laterally?
Does it detect color?
Yes, because cones are responsible for color vision.
Does it have high or low visual acuity?
High visual acuity.
Why are cells, other than photoreceptors, in the foveal pit displaced laterally?
To minimize light scattering and allow direct access of light to the photoreceptors, improving visual clarity.
What is the optic disk? Where is the blind spot?
The region of the retina where axons from ganglion cells exit the eye to form the optic nerve.
located (blind spot) - At the optic disk, where there are no photoreceptors.
What is the structure that exits the retina and takes visual information to the brain?
The optic nerve (cranial nerve II).
What is myopia?
Nearsightedness; difficulty seeing distant objects clearly.
Where does the focus for distant objects lie in a myopic eye?
In front of the retina due to excessive corneal curvature or a longer eyeball.
What eye structure mediates the majority of the light refraction? Is it the cornea or the lens?
The cornea (it accounts for about 2/3 of the eye’s total refractive power).
Which photoreceptors are more sensitive to light?
Rods are more sensitive to light and function in dim conditions.
Are rods and cones evenly distributed across the retina?
No.
Rods are concentrated in the peripheral retina.
Cones are concentrated in the fovea (central retina).
Which type of photoreceptor is greater in number?
Rods (about 120 million) outnumber cones (about 6 million).
Which photoreceptors mediate color vision?
cones
Which photoreceptors mediate day- and night-time vision?
Rods = Night vision (scotopic vision).
Cones = Day vision (photopic vision).
How many types of cones are there in terms of color responses?
S-cones → Short wavelengths (blue light).
M-cones → Medium wavelengths (green light).
L-cones → Long wavelengths (red light).
Which cell type in the outer retina mediates lateral inhibition?
Horizontal cells mediate lateral inhibition in the outer retina.
What is the general definition of lateral inhibition, and is it observed only in the retina?
Lateral inhibition is a process where one neuron suppresses the activity of its neighbors, enhancing contrast in sensory perception.
It is observed in many sensory systems, not just the retina.
Do ganglion cells respond best to light contrast or absolute light levels?
Ganglion cells respond best to light contrast rather than absolute light levels.
Are ganglion cells subdivided into On- and Off-center types, like bipolar cells?
Yes, ganglion cells have On-center and Off-center subtypes.
What is phototransduction? Where does it take place?
Phototransduction is the process by which light is converted into electrical signals in the retina. It takes place in photoreceptor cells (rods and cones).
End result of phototransduction?
CNG channels close, leading to hyperpolarization of photoreceptors and decreased glutamate release.
General retinal connectivity (synaptic layers & major cells)?
Two major synaptic layers:
Outer plexiform layer: PRs → Bipolar cells & Horizontal cells
Inner plexiform layer: Bipolar cells → Ganglion & Amacrine cells
Major cells: Photoreceptors (PRs), Bipolar cells (BCs), Ganglion cells (GCs), Horizontal cells, Amacrine cells.
Which cells send axons out of the retina?
Ganglion cells.
Are cell bodies in distinct layers?
Yes, in the outer nuclear layer (PRs), inner nuclear layer (BCs, horizontal, amacrine), and ganglion cell layer (GCs).
Bipolar cell responses to light?
ON bipolar cells: Depolarize when light is shone onto the central cone (decreased glutamate release from the cone activates metabotropic receptors).
OFF bipolar cells: Hyperpolarize when light is shone onto the central cone (decreased glutamate reduces ionotropic receptor activation).
