USABO - USA Biology Olympiad Neurobiology and Sensory Systems Questions and Answers

Question 1

A single neuron receives multiple excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) simultaneously at various locations on its dendrites and soma.
Which of the following statements best describes how the neuron integrates these signals to determine whether to fire an action potential?

Accepted Answer

The integrated sum of all EPSPs and IPSPs at the axon hillock must depolarize the membrane to the threshold potential.

Answer

An action potential is fired if any single EPSP is strong enough to exceed the threshold potential on its own.

Answer

The neuron fires if the total number of incoming EPSPs is greater than the total number of incoming IPSPs, regardless of their magnitude.

Answer

Only EPSPs that arrive at the presynaptic terminal can trigger an action potential in the postsynaptic neuron.

Question 2

During the repolarization phase of an action potential, which of the following events is primarily responsible for the rapid decrease in membrane potential from its peak positive value back towards the resting potential?

Accepted Answer

The efflux of potassium (K+) ions through voltage-gated channels.

Answer

The influx of sodium (Na+) ions through voltage-gated channels.

Answer

The influx of chloride (Cl-) ions, causing hyperpolarization.

Answer

The closing of all ion channels and activity of the Na+/K+ pump.

Question 3

In the process of auditory transduction within the cochlea, the bending of stereocilia on hair cells is the critical mechanical event that opens ion channels. This bending is directly caused by the relative movement between which two structures?

Accepted Answer

The basilar membrane and the tectorial membrane

Answer

The oval window and the round window

Answer

Reissner's membrane and the basilar membrane

Answer

The tympanic membrane and the stapes

Question 4

When a photon of light strikes a photoreceptor (rod or cone) in the human retina, it initiates a signaling cascade. Which of the following correctly describes the state of a rod cell's membrane potential and its rate of glutamate release while in complete darkness?

Accepted Answer

Depolarized; high glutamate release

Answer

Hyperpolarized; low glutamate release

Answer

Hyperpolarized; high glutamate release

Answer

Depolarized; low glutamate release

Question 5

A patient is diagnosed with a demyelinating disease, where the myelin sheaths surrounding axons in the central nervous system are progressively damaged. Which of the following is the most direct physiological consequence of this loss of myelin on nerve impulse transmission?

Accepted Answer

The speed of saltatory conduction is decreased, potentially leading to transmission failure.

Answer

The refractory period of the action potential is eliminated.

Answer

The amplitude of the action potential at each node of Ranvier is significantly increased.

Answer

The resting membrane potential of the axon becomes unstable and hyperpolarized.

Question 6

The olfactory system possesses several unique characteristics when compared to other major sensory systems like vision or audition. Which of the following is a key distinguishing feature of the primary olfactory pathway?

Accepted Answer

It is the only major sensory system that does not first relay information through the thalamus before projecting to the primary sensory cortex.

Answer

Each olfactory receptor neuron expresses a wide variety of different odorant receptor proteins.

Answer

Sensory signals are first processed in the cerebellum for fine-tuning before reaching conscious awareness.

Answer

The sensory receptors are remarkably stable and are not replaced throughout an individual's lifetime.