BSCI 353 Exam 2 | Questions and Answers

BSCI 353 Exam 2 | Questions and Answers What are the two types of synapses? Electrical synapses (gap junctions, fast, bidirectional) and chemical synapses (neurotransmitter-based, unidirectional, synaptic delay). What is the key structural feature of an electrical synapse? Gap junctions made of connexons, allowing direct ion flow between neurons. What is the main advantage of electrical synapses? Speed; they have almost no synaptic delay. What causes the delay in chemical synaptic transmission? The time required for neurotransmitter release, diffusion, and receptor activation (~1 ms). What triggers neurotransmitter release at a chemical synapse? Ca2+ influx through voltage-gated calcium channels in the presynaptic terminal. What are SNARE proteins, and why are they important? Synaptobrevin, SNAP-25, and syntaxin help dock and fuse synaptic vesicles for neurotransmitter release. How does botulinum toxin affect synaptic transmission? It cleaves SNARE proteins, preventing vesicle fusion and blocking neurotransmitter release. What are the two types of summation in neurons? Temporal summation: Multiple signals from the same synapse over time. Spatial summation: Inputs from different synapses combining on a neuron. What is the difference between excitatory and inhibitory synaptic inputs? Excitatory (EPSP): Depolarization (e.g., Na+ influx via glutamate receptors) Inhibitory (IPSP): Hyperpolarization (e.g., Cl- influx via GABA receptors) What role does synaptic vesicle recycling play? Prevents vesicle depletion by reforming vesicles after neurotransmitter release. How does α-latrotoxin (black widow toxin) affect synaptic transmission? It triggers massive neurotransmitter release by forming Ca2+-permeable pores in presynaptic neurons. What are the two main types of neurotransmitters? Small-molecule neurotransmitters (e.g., glutamate, GABA, acetylcholine) and neuropeptides (e.g., substance P, endorphins). Where are peptide neurotransmitters synthesized? Rough ER → processed in the Golgi apparatus → transported to synaptic terminals in large, dense-core vesicles. What are the two major types of neurotransmitter receptors? Ionotropic (ligand-gated ion channels) and Metabotropic (G-protein-coupled receptors, GPRCs). What is the main difference between ionotropic and metabotropic receptors? Ionotropic receptors act fast by directly gating ion channels, while metabotropic receptors act slowly via second messenger signaling. What are examples of ionotropic receptors? AMPA, NMDA (glutamate), GABA_A (GABA), nicotinic ACh receptor (acetylcholine). What are examples of metabotropic receptors? mGluRs (glutamate), GABA_B (GABA), muscarinic ACh receptors (acetylcholine), dopamine receptors. What are the major excitatory and inhibitory neurotransmitters in the CNS? Excitatory: Glutamate (depolarizes neurons via Na+ influx). Inhibitory: GABA & glycine (hyperpolarize neurons via Cl- influx). What enzyme synthesizes acetylcholine (ACh)? Choline acetyltransferase (ChAT). Which neurotransmitter is affected by sarin gas? Acetylcholine (sarin inhibits acetylcholinesterase, causing excessive ACh accumulation). What neurotransmitter do motor neurons release at the neuromuscular junction? Acetylcholine (ACh). What is the role of dopamine in the brain? Involved in reward, motivation, movement control (degeneration leads to Parkinson's disease). How do SSRIs (Selective Serotonin Reuptake Inhibitors) work? They block serotonin reuptake, increasing serotonin levels in the synaptic cleft. What type of receptor is a muscarinic acetylcholine receptor (mAChR)? Metabotropic GPCR (NOT ionotropic) Which statements about muscarinic ACh receptors are false? They do NOT control ligand-gated ion channels. They do NOT mediate rapid responses to ACh. They do NOT activate voltage-gated Na+ channels. They do NOT mediate neuromuscular junction effects (those use nicotinic ACh receptors). What are the three major types of cell signaling? Synaptic (fast, local), paracrine (local diffusion), endocrine (long-distance, via bloodstream). What are the three main components of intracellular signaling? Signal (ligand), receptor, intracellular transduction cascade. What are the three major types of neurotransmitter receptors? Ionotropic (ligand-gated ion channels), metabotropic (GPCRs), enzyme-linked receptors. What are G-protein-coupled receptors (GPCRs)? Metabotropic receptors that activate intracellular signaling cascades via G-proteins. What are the three types of G-protein subunits? Gα, Gβ, Gγ. What are the three types of Gα proteins and their functions? Gαs: Stimulates adenylyl cyclase → increases cAMP → activates PKA Gαi: Inhibits adenylyl cyclase → decreases cAMP. Gαq: Activates phospholipase C (PLC) → produces IP₃ & DAG → increases Ca²⁺ release & PKC activation. What is the effect of the cholera toxin on G-protein signaling? Cholera toxin locks Gαs in an active state, leading to increased cAMP and increased PKA activation. What is the effect of pertussis toxin? It inhibits Gαi, preventing it from decreasing cAMP levels. What are the second messengers involved in G-protein signaling? cAMP, cGMP, IP3, DAG, Ca2+. What enzyme produces cAMP? Adenylyl cyclase. What enzyme degrades cAMP? Phosphodiesterase (PDE) What is the function of protein kinase A (PKA)? Phosphorylates target proteins to regulate gene expression, metabolism, and ion channels. What is the function of protein kinase C (PKC)? Activated by DAG & Ca2+, regulates cell growth, gene expression, and neurotransmitter release. What is the role of Ca2+ in intracellular signaling? Activates calmodulin, PKC, and CaMKII to regulate neuronal function. What signaling steps do NOT amplify the signal? Activation of PKA by cAMP. Phosphorylation of target proteins by PKA. What are the two types of photoreceptors in the retina? Rods (light-sensitive, low-light vision) and cones (color vision, high acuity). What is the main function of rods? High sensitivity for nigh vision (scotopic vision), but low acuity. What is the main function of cones? High acuity and color vision (photopic vision). Where are cones most concentrated in the retina? The fovea (center of the retina), where they provide high visual acuity. Where are rods most concentrated in the retina? Peripheral retina, enhancing night vision and motion detection. What is rhodopsin? A G-protein-coupled receptor (GPCR) found in rods that detects light. What happens when light activates rhodopsin? Rhodopsin activates transducin (G-protein) → activates phosphodiesterase (PDE) → decreases cGMP → closes Na+/Ca2+ channels → hyperpolarization. What is the membrane potential of a rod in the dark? ~ -40 mV (depolarized due to open Na+/Ca2+ channels). What happens when a photoreceptor is exposed to light? The cell hyperpolarizes (~ -65 mV) because cGMP-gated Na+/Ca2+ channels close. What would happen if a drug increased cGMP levels in a photoreceptor? An attenuated hyperpolarization because Na+/Ca2+ channels would stay open longer. What is the difference between ON-center and OFF-center retinal ganglion cells? ON-center: Activated by light in center, darkness in surround. OFF-center: Activated by darkness in center, light in surround. What is the function of the fovea? Provides highest visual acuity (sharp vision) due to high cone density and minimal light scattering. Why are rods built for sensitivity? High convergence (many rods synapse onto one bipolar cell). More photopigment to capture light. Why are cones built for resolution? Low convergence (1:1 ratio of cones to ganglion cells in the fovea). Foveal specialization (no blood vessels blocking light). What is the blind spot, and why does it exist? The optic disc, where ganglion cell axons leave the retina (no photoreceptors present). What is mascular degeneration? Progressive loss of central vision due to damage to the macula (affects cone function). What are the two types of macular degeneration? Wet (exudative): Abnormal blood vessel growth under the retina. Dry (nonexudative): Gradual breakdown of photoreceptors and retinal pigment epithelium. What is retinitis pihmentosa? A genetic disorder causing progressive vision loss due to photoreceptor degeneration. What recording techniques are used to measure photoreceptor activity? Patch-clamp and voltage-clamp recordings measure ionic currents in photoreceptors. Which of the following best describes a basic property of synapses? a. Synaptic vesicles constitute important features for transmission in both chemical and electrical synapses. b. A postsynaptic neuron typically receives input from different presynaptic axons that are either excitatory or inhibitory, but it cannot receive inputs from both types. c. Synaptic delay is approximately the same for both chemical and electrical synapses. d. Neurotransmitter receptors can regulate the gating of an ion channel either directly (metabotropic receptor) or indirectly (ionotropic receptor). e. The mechanism of indirect gating of ions normally involves the activation of G-proteins.