Neurons and Nervous System Practice Questions
38 free Neurons and Nervous System practice questions for the Zoology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which part of the neuron is responsible for integrating incoming signals and 'deciding' whether or not to initiate an action potential?
- A Dendrites
- B Axon hillock
- C Nodes of Ranvier
- D Terminal buttons
Correct answer: Axon hillock
The axon hillock acts as the trigger zone of the neuron. It has a high density of voltage-gated sodium channels and sums up excitatory and inhibitory postsynaptic potentials to determine if the threshold is met.
During the depolarization phase of an action potential, which of the following events occurs?
- A Voltage-gated $K^{+}$ channels open, and $K^{+}$ leaves the cell
- B The $Na^{+}/K^{+}$ pump stops working entirely
- C Voltage-gated $Na^{+}$ channels open, and $Na^{+}$ enters the cell
- D The membrane potential becomes more negative than the resting potential
Correct answer: Voltage-gated $Na^{+}$ channels open, and $Na^{+}$ enters the cell
Depolarization is characterized by a rapid influx of sodium ions into the neuron. This occurs because the membrane potential reaches the threshold, causing voltage-gated $Na^{+}$ channels to open and move $Na^{+}$ down its electrochemical gradient.
What is the primary function of the myelin sheath in the nervous system?
- A To supply nutrients and metabolic support directly to the axon
- B To speed up impulse transmission via saltatory conduction
- C To act as a receptor surface for incoming neurotransmitters
- D To bundle multiple axons together into a compact peripheral nerve
Correct answer: To speed up impulse transmission via saltatory conduction
Myelin acts as an electrical insulator, preventing ion leakage across the axonal membrane. In myelinated neurons, the action potential 'jumps' from one Node of Ranvier to the next, which is significantly faster than continuous conduction.
At a chemical synapse, what triggers the fusion of neurotransmitter-filled vesicles with the presynaptic membrane?
- A The influx of $Na^{+}$ ions
- B The efflux of $K^{+}$ ions
- C The influx of $Ca^{2+}$ ions
- D The binding of ATP to the vesicle surface
Correct answer: The influx of $Ca^{2+}$ ions
When an action potential reaches the axon terminal, it opens voltage-gated $Ca^{2+}$ channels. The resulting rise in intracellular calcium concentrations signals the synaptic vesicles to undergo exocytosis.
Which of the following describes an Inhibitory Postsynaptic Potential (IPSP)?
- A A small depolarization that moves the membrane closer to threshold
- B A hyperpolarization that moves the membrane further from threshold
- C A permanent block of all future action potentials
- D The rapid reset of the resting membrane potential
Correct answer: A hyperpolarization that moves the membrane further from threshold
An IPSP occurs when neurotransmitters cause the opening of $K^{+}$ or $Cl^{-}$ channels. This makes the inside of the postsynaptic cell more negative (hyperpolarized), decreasing the likelihood of an action potential.
In a simple monosynaptic reflex arc, such as the knee-jerk reflex, how many synapses are involved in the spinal cord?
- A Zero synapses — direct electrical coupling
- B One
- C Two, via a single interneuron
- D Dozens, across multiple relay centers
Correct answer: One
A monosynaptic reflex involves a direct synapse between a sensory neuron and a motor neuron. There are no interneurons between them, resulting in a very rapid response to the stimulus.
What is the 'Absolute Refractory Period' of a neuron?
- A The time when a neuron is at its resting potential and fully excitable
- B Time when Na⁺ channels partially recover, allowing only strong stimuli to trigger an action potential.
- C The time during which no action potential can be initiated, regardless of stimulus strength
- D The time it takes for neurotransmitters to cross the synaptic cleft
Correct answer: The time during which no action potential can be initiated, regardless of stimulus strength
The absolute refractory period occurs when voltage-gated Na⁺ channels are either already open or in their inactivated state. During this window no second action potential can be triggered no matter how strong the stimulus, ensuring action potentials are discrete, unidirectional events.
Which type of glial cell is responsible for forming the blood-brain barrier (BBB)?
- A Oligodendrocytes
- B Microglia
- C Astrocytes
- D Schwann cells
Correct answer: Astrocytes
Astrocytes have 'end-feet' that wrap around capillaries in the brain. They stimulate the formation of tight junctions between endothelial cells, strictly regulating which substances can pass from the blood into the neural tissue.
The 'All-or-None' law of nerve conduction states that:
- A All neurons in a nerve fire at once
- B An action potential happens completely or not at all once threshold is reached
- C The strength of an action potential increases with the strength of the stimulus
- D Neurons either use $Na^{+}$ or $K^{+}$ but never both
Correct answer: An action potential happens completely or not at all once threshold is reached
The amplitude and speed of an action potential are independent of the stimulus intensity. As long as the threshold is reached, a full-sized action potential is generated; if not, no impulse is sent.
What is the role of Acetylcholinesterase in synaptic transmission?
- A To synthesize acetylcholine from choline and acetyl-CoA
- B To transport acetylcholine into synaptic vesicles
- C To break down acetylcholine in the synaptic cleft to terminate the signal
- D To act as the primary receptor for acetylcholine on the postsynaptic membrane
Correct answer: To break down acetylcholine in the synaptic cleft to terminate the signal
Acetylcholinesterase is an enzyme that rapidly hydrolyzes acetylcholine. This prevents continuous stimulation of the postsynaptic cell and allows the synapse to be ready for the next signal.
Which of the following is a characteristic of 'Electrical Synapses' compared to chemical synapses?
- A They are much slower
- B They utilize neurotransmitters like dopamine
- C They allow direct flow of ions through gap junctions
- D They are only found in the peripheral nervous system
Correct answer: They allow direct flow of ions through gap junctions
Electrical synapses feature gap junctions that physically connect the cytoplasm of two neurons. This allows for nearly instantaneous, bidirectional signal transmission, which is useful for synchronized activities like heart contractions.
In a reflex arc, which component is responsible for carrying the impulse from the CNS to the effector organ?
- A Sensory (Afferent) neuron
- B Interneuron
- C Motor (Efferent) neuron
- D Receptor
Correct answer: Motor (Efferent) neuron
The motor neuron carries the 'output' signal from the integration center (brain or spinal cord) to an effector, such as a muscle or gland, to produce a response.
Saltatory conduction occurs in:
- A Unmyelinated axons, where conduction is continuous
- B Myelinated axons
- C Dendrites only, not along the axon
- D Skeletal muscle fibers during contraction
Correct answer: Myelinated axons
Saltatory conduction refers to the 'leaping' of the action potential between the Nodes of Ranvier along a myelinated axon. It is much more energy-efficient and faster than the continuous conduction found in unmyelinated fibers.
What happens during the hyperpolarization (undershoot) phase of an action potential?
- A Sodium channels open widely, flooding the cell with Na⁺
- B Potassium channels stay open, letting K⁺ continue to leave
- C The Na⁺/K⁺ pump reverses direction and rapidly pushes ions back to resting levels
- D Calcium ions rush in through voltage-gated channels to stabilize the membrane potential
Correct answer: Potassium channels stay open, letting K⁺ continue to leave
Voltage-gated K⁺ channels are relatively slow to close. This leads to an excessive loss of positive ions, making the membrane potential even more negative than the resting state for a short period — the undershoot (hyperpolarization) phase.
The resting membrane potential of a typical neuron is approximately -70 mV. This is primarily established by:
- A Rapid influx of Na⁺ through voltage-gated channels at rest
- B High K⁺ permeability via leak channels plus the Na⁺/K⁺ pump
- C Large negatively charged intracellular proteins that dominate the resting potential entirely
- D Equal distribution of Cl⁻ ions across the membrane creating a Donnan equilibrium
Correct answer: High K⁺ permeability via leak channels plus the Na⁺/K⁺ pump
At rest, the membrane is much more permeable to K⁺ than to Na⁺. The outward leakage of K⁺ through leak channels, combined with the Na⁺/K⁺ pump (which exports 3 Na⁺ for every 2 K⁺ imported), maintains the negative interior at approximately −70 mV.
What is 'Temporal Summation' at a synapse?
- A Multiple different neurons stimulating a single postsynaptic cell simultaneously
- B A single presynaptic neuron firing repeatedly in quick succession
- C The breakdown of neurotransmitters over time
- D The movement of a signal from the axon to the dendrites
Correct answer: A single presynaptic neuron firing repeatedly in quick succession
Temporal summation occurs when a single presynaptic neuron generates multiple EPSPs so rapidly that they add together before the previous one has decayed, eventually reaching the threshold.
Which of the following is an example of a Polysynaptic Reflex?
- A Patellar reflex (knee-jerk), involving a single synapse
- B Withdrawal reflex (pulling hand away from a hot stove)
- C Stretch reflex mediated by muscle spindle afferents directly onto motor neurons
- D Monosynaptic reflex involving one direct sensory-to-motor connection
Correct answer: Withdrawal reflex (pulling hand away from a hot stove)
The withdrawal reflex involves at least one interneuron between the sensory and motor neurons. This allows for more complex processing, such as inhibiting the antagonistic muscle group (reciprocal inhibition).
What is the function of 'Nodes of Ranvier'?
- A They are the sites where synaptic vesicles fuse and neurotransmitters are released into the cleft
- B They are the only regions on a myelinated axon where ion exchange can occur
- C They serve as the connection point between the cell body and the initial dendritic branches
- D They slow the action potential to allow more reliable signal integration
Correct answer: They are the only regions on a myelinated axon where ion exchange can occur
In myelinated axons, voltage-gated channels are concentrated at the Nodes of Ranvier. This is the only place where Na⁺ and K⁺ ions can move across the membrane to regenerate the action potential, enabling rapid saltatory conduction.
Which neurotransmitter is the primary excitatory signal in the vertebrate Central Nervous System?
- A GABA
- B Glycine
- C Glutamate
- D Serotonin
Correct answer: Glutamate
Glutamate is the most abundant excitatory neurotransmitter. It usually works by opening cation channels that allow $Na^{+}$ or $Ca^{2+}$ to enter the postsynaptic cell, causing depolarization.
The 'Spatial Summation' of potentials refers to:
- A The total distance a signal travels along the axon before being fully attenuated by passive decay
- B Integration of simultaneous inputs from multiple presynaptic neurons
- C The physical size of the synaptic cleft between two neurons
- D The total count of neurons participating in a given reflex arc
Correct answer: Integration of simultaneous inputs from multiple presynaptic neurons
Spatial summation occurs when multiple presynaptic neurons fire simultaneously at different locations on the postsynaptic neuron. Their combined EPSPs and IPSPs are algebraically summed to determine the final membrane potential change and whether threshold is reached.
Which ions are primarily responsible for the rapid depolarization phase of an action potential in a typical vertebrate neuron?
- A Influx of Potassium ions (K+)
- B Efflux of Sodium ions (Na+)
- C Efflux of Chloride ions (Cl-)
- D Influx of Sodium ions (Na+)
Correct answer: Influx of Sodium ions (Na+)
Depolarization is triggered when voltage-gated sodium channels open, allowing Na+ ions to rush into the cell down their electrochemical gradient, making the interior more positive.
What is the specific role of 'Calcium ions (Ca2+)' at a chemical synapse?
- A To trigger neurotransmitter vesicle exocytosis
- B To hyperpolarize the postsynaptic membrane
- C To provide energy for the sodium-potassium pump
- D To bind to the dendrites of the presynaptic neuron
Correct answer: To trigger neurotransmitter vesicle exocytosis
When an action potential reaches the axon terminal, voltage-gated Ca2+ channels open. The resulting influx of calcium triggers the fusion of synaptic vesicles with the presynaptic membrane.
In the peripheral nervous system (PNS), which glial cells are responsible for the formation of the myelin sheath?
- A Oligodendrocytes
- B Microglia
- C Astrocytes
- D Schwann cells
Correct answer: Schwann cells
Schwann cells myelinate axons in the PNS, whereas oligodendrocytes perform this function in the Central Nervous System (CNS).
Which of the following describes 'Saltatory Conduction'?
- A An action potential jumping between the Nodes of Ranvier
- B The slow leakage of ions across a non-myelinated axon
- C The movement of neurotransmitters across the synaptic cleft
- D The simultaneous firing of many neurons in a reflex arc
Correct answer: An action potential jumping between the Nodes of Ranvier
In myelinated axons, the insulating sheath prevents ion flow except at the gaps (Nodes of Ranvier), allowing the signal to 'jump' and travel much faster than in unmyelinated fibers.
The 'Refractory Period' that occurs immediately after an action potential ensures that:
- A Action potentials travel in only one direction along the axon
- B The neuron can fire action potentials at an infinitely high frequency
- C Neurotransmitters are recycled and reused much more quickly than normal
- D Sodium channels remain open for a longer duration than usual
Correct answer: Action potentials travel in only one direction along the axon
During the refractory period, sodium channels are inactivated. This prevents the action potential from traveling backward toward the cell body, ensuring unidirectional propagation.
Which component of a reflex arc is located entirely within the Central Nervous System and connects sensory and motor neurons?
- A Receptor
- B Effector
- C Interneuron
- D Afferent fiber
Correct answer: Interneuron
Interneurons (or association neurons) process information within the spinal cord or brain, serving as the link between the sensory input and motor output in polysynaptic reflexes.
The 'Axon Hillock' is often referred to as the 'trigger zone' of the neuron because:
- A It contains the highest density of ribosomes for protein synthesis
- B It is the location where the myelin sheath is at its thickest point
- C It is the site where the threshold for an action potential is lowest
- D It secretes neurotransmitters directly into the bloodstream for transport
Correct answer: It is the site where the threshold for an action potential is lowest
The axon hillock integrates various EPSPs and IPSPs. Due to a high density of voltage-gated sodium channels, it is the site where action potentials are typically initiated.
Which neurotransmitter is specifically involved in the transmission of impulses at the 'Neuromuscular Junction' in vertebrates?
- A Dopamine
- B Serotonin
- C Norepinephrine
- D Acetylcholine
Correct answer: Acetylcholine
Acetylcholine (ACh) is the primary neurotransmitter released by motor neurons to stimulate skeletal muscle contraction.
The 'Knee-jerk' (Patellar) reflex is a classic example of which type of reflex?
- A Monosynaptic reflex
- B Polysynaptic reflex
- C Conditioned reflex
- D Autonomic reflex
Correct answer: Monosynaptic reflex
The patellar reflex involves a direct synapse between a sensory neuron and a motor neuron in the spinal cord, without the involvement of an interneuron.
Which of the following best defines 'Spatial Summation'?
- A Repeated stimulation of a single synapse in rapid succession
- B The simultaneous stimulation of multiple synapses on a single neuron
- C The movement of ions through a gap junction connecting adjacent cells
- D The active inhibition of a spinal reflex by descending signals from the brain
Correct answer: The simultaneous stimulation of multiple synapses on a single neuron
Spatial summation occurs when the postsynaptic neuron is stimulated at the same time by different presynaptic inputs, adding their effects together.
During the resting state of a neuron, the interior is negatively charged relative to the exterior. This is largely maintained by the Sodium-Potassium pump, which moves:
- A 3 Na+ in and 2 K+ out
- B 2 Na+ out and 3 K+ in
- C 3 Na+ out and 2 K+ in
- D 1 Na+ out and 1 K+ in
Correct answer: 3 Na+ out and 2 K+ in
The Na+/K+ ATPase pump actively transports three sodium ions out for every two potassium ions it brings in, contributing to the negative internal charge.
What happens to the 'Relative Refractory Period' of a neuron?
- A The neuron cannot fire regardless of stimulus strength
- B An action potential can be triggered by a stronger-than-normal stimulus
- C The cell membrane becomes permanently and completely depolarized instead
- D The sodium-potassium pump completely and permanently ceases working
Correct answer: An action potential can be triggered by a stronger-than-normal stimulus
During the relative refractory period, the cell is hyperpolarized. While an action potential is possible, it requires a larger stimulus to reach the threshold.
In a 'Chemical Synapse', the space between the presynaptic and postsynaptic membranes is called the:
- A Synaptic bulb
- B Synaptic cleft
- C Nodes of Ranvier
- D Ventricle
Correct answer: Synaptic cleft
The synaptic cleft is a small gap (approx. 20-50 nm) across which neurotransmitters must diffuse to reach the postsynaptic receptors.
Which of the following is an 'Inhibitory' neurotransmitter commonly found in the vertebrate brain?
- A Glutamic acid
- B Norepinephrine
- C Gamma-aminobutyric acid
- D Nitric oxide signaling molecule
Correct answer: Gamma-aminobutyric acid
Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the brain, working to reduce neuronal excitability throughout the nervous system.
The 'Withdrawal Reflex' (e.g., pulling your hand away from a hot stove) is faster than a conscious decision because:
- A It relies exclusively on very fast electrical synapses between neurons
- B The signal is processed in the spinal cord without traveling to the brain first
- C It does not involve any neurons or synaptic transmission at all
- D It relies entirely on hormones released into the bloodstream instead of nerve impulses
Correct answer: The signal is processed in the spinal cord without traveling to the brain first
Reflexes are involuntary and rapid because the neural pathway (reflex arc) bypasses the higher centers of the brain for immediate action.
The 'Equilibrium Potential' for an ion is the membrane potential at which:
- A The concentration of the ion is exactly equal on both sides
- B The net flux of that ion across the membrane is zero
- C The cell dies
- D The ion stops moving entirely
Correct answer: The net flux of that ion across the membrane is zero
At equilibrium potential, the electrical gradient and the chemical (concentration) gradient for a specific ion are equal and opposite, resulting in no net movement.
Which of the following glial cells act as the immune system of the Central Nervous System by phagocytosing debris and pathogens?
- A Astroglial cells
- B Ependymal cells
- C Microglial cells
- D Satellite cells
Correct answer: Microglial cells
Microglia are specialized macrophages that protect the CNS by removing damaged neurons and infectious agents.
Temporal Summation occurs when:
- A Multiple neurons fire once at different times
- B A single presynaptic neuron fires multiple times in rapid succession
- C An excitatory and an inhibitory postsynaptic signal cancel each other out
- D The neuron is in the absolute refractory period
Correct answer: A single presynaptic neuron fires multiple times in rapid succession
Temporal summation is the additive effect of several electrical impulses occurring at the same synapse at different times but close enough to build upon each other.