Synapses and Neurotransmitters Practice Questions
20 free Synapses and Neurotransmitters practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which ion influx into the presynaptic terminal is directly responsible for triggering neurotransmitter release?
- A Sodium (Na+)
- B Potassium (K+)
- C Chloride (Cl-)
- D Calcium (Ca2+)
Correct answer: Calcium (Ca2+)
When an action potential reaches the presynaptic terminal, voltage-gated calcium channels open. The resulting influx of Ca2+ triggers the fusion of synaptic vesicles with the presynaptic membrane.
Which protein on the synaptic vesicle acts as the primary calcium sensor for exocytosis?
- A Synaptotagmin
- B Syntaxin
- C SNAP-25
- D Synaptobrevin
Correct answer: Synaptotagmin
Synaptotagmin is a specialized vesicle protein that binds calcium ions. This binding induces a conformational change that allows the SNARE complex to complete membrane fusion.
What is the primary mechanism for the termination of acetylcholine (ACh) action at the neuromuscular junction?
- A Active reuptake into the presynaptic terminal
- B Simple diffusion away from the synaptic cleft
- C Endocytosis of the entire ACh-receptor complex
- D Enzymatic degradation by acetylcholinesterase
Correct answer: Enzymatic degradation by acetylcholinesterase
Acetylcholinesterase is present in the synaptic cleft and rapidly hydrolyzes ACh into choline and acetate. This ensures that the muscle fiber is not continuously stimulated.
An Inhibitory Postsynaptic Potential (IPSP) is typically associated with the opening of which channels?
- A Ligand-gated Chloride channels
- B Ligand-gated Sodium channels
- C Voltage-gated Calcium channels
- D Voltage-gated Sodium channels
Correct answer: Ligand-gated Chloride channels
Opening of chloride channels allows Cl- to enter the cell, making the interior more negative (hyperpolarization). This moves the membrane potential further away from the threshold for an action potential.
Small-molecule neurotransmitters are typically synthesized in which part of the neuron?
- A Rough endoplasmic reticulum of the soma
- B Golgi apparatus
- C Nucleus
- D Cytosol of the axon terminal
Correct answer: Cytosol of the axon terminal
Unlike neuropeptides, which are synthesized in the cell body, small-molecule transmitters like GABA or Glutamate are synthesized by cytoplasmic enzymes located right in the axon terminals.
Electrical synapses differ from chemical synapses because they utilize:
- A Gap junction channels
- B Synaptic vesicles
- C Metabotropic receptors
- D Secondary messengers
Correct answer: Gap junction channels
Electrical synapses allow direct flow of current between cells through gap junction channels formed by connexins. This results in virtually instantaneous signal transmission without a synaptic delay.
Which of the following is the most common excitatory neurotransmitter in the Central Nervous System?
- A Acetylcholine
- B Glycine
- C Glutamate
- D Dopamine
Correct answer: Glutamate
Glutamate is the primary excitatory neurotransmitter in the brain. It acts on ionotropic receptors (like NMDA and AMPA) to cause depolarization via cation influx.
The 'synaptic delay' (usually 0.5 to 1.0 ms) is primarily caused by:
- A The speed of the action potential along the axon
- B The time required for calcium-induced vesicle release
- C The time required for neurotransmitter reuptake into the presynaptic terminal
- D The time required for the sodium-potassium pump to reset the resting potential
Correct answer: The time required for calcium-induced vesicle release
The delay is mostly due to the process of calcium entry and the subsequent machinery required for vesicle fusion and transmitter release. Diffusion across the narrow synaptic cleft is actually very rapid.
Which receptor type involves a G-protein and a second messenger system?
- A Ionotropic receptors
- B Metabotropic receptors
- C Nicotinic receptors
- D Voltage-gated ion channels
Correct answer: Metabotropic receptors
Metabotropic receptors are G-protein coupled receptors that trigger intracellular signaling cascades. Their effects are typically slower and longer-lasting than those of ionotropic receptors.
Spatial summation occurs when:
- A One single presynaptic neuron fires repeatedly at a very high frequency
- B Multiple presynaptic neurons fire simultaneously at different locations
- C The absolute refractory period of the neuron is shortened
- D Calcium levels in the presynaptic terminal remain elevated
Correct answer: Multiple presynaptic neurons fire simultaneously at different locations
Spatial summation is the additive effect of postsynaptic potentials originating from different synapses on the same neuron. If the sum reaches threshold at the axon hillock, an action potential is triggered.
Botulinum toxin causes muscle paralysis by which mechanism?
- A Blocking nicotinic acetylcholine receptors at the synapse
- B Inhibiting acetylcholinesterase
- C Cleaving SNARE proteins to prevent ACh release
- D Blocking voltage-gated sodium channels
Correct answer: Cleaving SNARE proteins to prevent ACh release
Botulinum toxin is a protease that cleaves specific SNARE proteins (like SNAP-25) in the presynaptic terminal. This prevents the docking and fusion of vesicles, effectively blocking neurotransmission.
Which of the following is a characteristic of Neuropeptide neurotransmitters?
- A They are stored in small, clear synaptic vesicles near the membrane
- B They are rapidly recycled via presynaptic reuptake mechanisms
- C They are synthesized in the cell body and moved by axonal transport
- D They act exclusively on fast ionotropic ligand-gated receptors
Correct answer: They are synthesized in the cell body and moved by axonal transport
Neuropeptides are synthesized as larger precursors in the soma and packaged into large dense-core vesicles. They are then moved to the terminal via fast axonal transport and are typically not recycled.
Glycine acts as a major inhibitory neurotransmitter primarily in the:
- A Cerebral cortex
- B Spinal cord
- C Basal ganglia
- D Hippocampus
Correct answer: Spinal cord
While GABA is the main inhibitor in the brain, glycine is the predominant inhibitory neurotransmitter in the spinal cord and brainstem. It increases chloride conductance in postsynaptic neurons.
Presynaptic inhibition typically involves a decrease in which of the following?
- A Postsynaptic receptor sensitivity to neurotransmitter
- B Calcium influx into the presynaptic terminal
- C Potassium efflux from the postsynaptic cell
- D The total number of available postsynaptic receptors
Correct answer: Calcium influx into the presynaptic terminal
Presynaptic inhibition usually occurs via an axo-axonal synapse where an inhibitory neuron reduces the opening of voltage-gated calcium channels in the target terminal. This reduces the amount of neurotransmitter released.
The 'quantal' nature of synaptic transmission refers to the fact that:
- A The size and amplitude of action potentials vary continuously
- B Neurotransmitter is released in discrete packets (vesicles)
- C Only one ion can pass through a channel at a time
- D Neurons can only release one type of neurotransmitter
Correct answer: Neurotransmitter is released in discrete packets (vesicles)
Each vesicle contains a relatively fixed amount of neurotransmitter, known as a 'quantum'. The total postsynaptic response is an integral multiple of the response to a single quantum.
Myasthenia Gravis is an autoimmune disorder characterized by the destruction of:
- A Voltage-gated Calcium channels
- B Acetylcholinesterase enzymes
- C Myelin sheaths on motor neuron axons
- D Nicotinic Acetylcholine receptors
Correct answer: Nicotinic Acetylcholine receptors
In Myasthenia Gravis, antibodies attack the nicotinic ACh receptors at the neuromuscular junction. This reduces the number of functional receptors, leading to muscle weakness and fatigue.
Which second messenger is commonly activated by the Alpha-s subunit of a G-protein?
- A Inositol triphosphate (IP3)
- B Diacylglycerol (DAG)
- C Cyclic GMP (cGMP)
- D Cyclic AMP (cAMP)
Correct answer: Cyclic AMP (cAMP)
The Gs protein activates the enzyme adenylyl cyclase, which converts ATP into cyclic AMP. cAMP then goes on to activate Protein Kinase A (PKA) to modulate cellular functions.
Cocaine exerts its stimulant effect primarily by:
- A Stimulating dopamine release
- B Inhibiting Monoamine Oxidase (MAO)
- C Activating dopamine receptors directly
- D Blocking the reuptake of dopamine
Correct answer: Blocking the reuptake of dopamine
Cocaine binds to and inhibits the dopamine transporter (DAT) on the presynaptic membrane. This prevents reuptake, causing dopamine to accumulate in the synaptic cleft and prolong its effects.
Post-tetanic potentiation is a form of synaptic plasticity caused by:
- A Accumulation of residual calcium in the presynaptic terminal
- B Depletion of synaptic vesicles after prolonged use
- C Upregulation of postsynaptic receptor density
- D Permanent structural changes within the synaptic connection itself
Correct answer: Accumulation of residual calcium in the presynaptic terminal
After a high-frequency burst of action potentials, calcium remains in the terminal longer than it can be sequestered. This 'residual calcium' enhances neurotransmitter release for subsequent stimuli.
Which of the following describes an EPSP?
- A A transient depolarization of the postsynaptic membrane
- B A transient hyperpolarization of the postsynaptic membrane
- C An all-or-none signal that travels down the axon
- D A signal that prevents the opening of sodium channels
Correct answer: A transient depolarization of the postsynaptic membrane
An Excitatory Postsynaptic Potential (EPSP) is a graded depolarization caused by the opening of cation channels. It brings the membrane potential closer to the threshold for firing an action potential.