Question 1

Apoptosis that occurs in motor neurons during vertebrate development can be postponed by

Accepted Answer

Stopping electrical activity in motor neurons can postpone apoptosis during vertebrate development. This is because the survival of developing neurons, including motor neurons, often depends on their activity and the receipt of survival signals that are activity-dependent.

Question 2

Unlike in adult rats, muscle fibers in newborn rats

Accepted Answer

In newborn rats, muscle fibers are initially innervated by multiple motor neurons, a condition that changes as they mature, with each fiber eventually being innervated by a single motor neuron.

Question 3

The elimination of polyneuronal innervation in the neuromuscular junction is mediated by

Accepted Answer

Polyneuronal innervation refers to multiple motor neurons innervating a single muscle fiber in the neuromuscular junction. Competitive synapse refinement is the process by which the weaker synapses are eliminated and stronger synapses are reinforced. In the neuromuscular junction, this process leads to the elimination of polyneuronal innervation and the establishment of a single, strong connection between a motor neuron and a muscle fiber. Apoptosis is programmed cell death and is not directly involved in the establishment of neuromuscular connections. Axon branch retraction is a process by which axon branches are withdrawn during development, but it is not a random process. Synchronous activation of motor neurons can lead to increased muscle activation, but it is not directly involved in the elimination of polyneuronal innervation.

Question 4

What type of activity in motor neurons drives the elimination of polyneuronal innervation in the neuromuscular junction?

Accepted Answer

Asynchronous activity in motor neurons drives the elimination of polyneuronal innervation in the neuromuscular junction by causing each axon terminal to release neurotransmitters independently of other terminals, leading to competition for the limited number of available receptors on the muscle fiber. This competition ultimately results in the elimination of excess connections and refinement of the synaptic pattern.

Question 5

Sympathetic and parasympathetic neurons typically have _______ effects on their target organ.

Accepted Answer

Sympathetic and parasympathetic neurons have opposing effects on their target organ. Sympathetic neurons cause an increase in heart rate, while parasympathetic neurons cause a decrease in heart rate. Sympathetic neurons cause the dilation of airways, while parasympathetic neurons cause the constriction of airways. Sympathetic neurons cause the release of glucose from the liver, while parasympathetic neurons do not have a significant effect on glucose release.

Question 6

Sympathetic and parasympathetic neurons have different effects on a target organ because they

Accepted Answer

Sympathetic and parasympathetic neurons release different neurotransmitters, which bind to different receptors on the target organ and produce different effects. For example, sympathetic neurons release norepinephrine, which tends to stimulate the organ, while parasympathetic neurons release acetylcholine, which tends to inhibit the organ.

Question 7

In developing autonomic ganglia,

Accepted Answer

Afferent inputs compete for synaptic space on the target neuron, which is a key process in the development of autonomic ganglia.

Question 8

A Hebbian synapse becomes _______ when it causes the _______ neuron to fire.

Accepted Answer

A Hebbian synapse strengthens when it causes the postsynaptic neuron to fire, which is known as Hebb's rule or the "fire together, wire together" principle. This strengthening of the synapse is thought to underlie learning and memory processes in the brain. Therefore, the correct answer is C, as a Hebbian synapse becomes stronger when it causes the postsynaptic neuron to fire.

Question 9

Subjecting neurons in the perforant pathway to tetanus stimulation strengthens activity in the dentate gyrus, indicating that

Accepted Answer

The strengthening of activity in the dentate gyrus after tetanus stimulation suggests the occurrence of long-term potentiation, which is a form of synaptic plasticity involving changes in the strength of synapses, and is one of the mechanisms believed to underlie learning and memory. The phenomenon of strengthening synapses based on their simultaneous activation, known as Hebbian plasticity, is one of several mechanisms implicated in long-term potentiation. Therefore, the fact that tetanus stimulation can induce lasting changes in synaptic strength indicates that synapses in the brain are capable of Hebbian plasticity.

Question 10

Which neurotransmitter does the hippocampus primarily use?

Accepted Answer

The hippocampus primarily uses the neurotransmitter glutamate, which is involved in processes related to learning and memory. A and B are both involved in learning and memory processes, but glutamate is the primary neurotransmitter in the hippocampus. C and D are not primarily used by the hippocampus.

Question 11

Long-term potentiation in the hippocampus is mediated by

Accepted Answer

Long-term potentiation (LTP) in the hippocampus is mainly mediated by ionotropic glutamate receptors, specifically the NMDA receptor. Activation of this receptor leads to a cascade of signaling events that results in the strengthening of synaptic connections between neurons, which is the basis of LTP. While other neurotransmitters and receptors may also have a role in LTP, ionotropic glutamate receptors are the primary mediators.

Question 12

AMPA receptors produce stable excitatory responses at _______ rates of stimulation, and NMDA receptors produce increased synaptic responses at _______ rates of stimulation.

Accepted Answer

AMPA receptors respond quickly to low-frequency stimulation, providing stable excitatory responses, while NMDA receptors are activated by high-frequency stimulation, leading to increased synaptic responses due to their role in synaptic plasticity.

Question 13

When hippocampal afferents are stimulated at a slow rate,

Accepted Answer

When hippocampal afferents are stimulated at a slow rate, NMDA receptors are blocked by magnesium ions. This is because NMDA receptors require both glutamate binding and partial depolarization of the postsynaptic membrane to displace the magnesium ion and allow calcium ions to enter the cell. At slow stimulation rates, there is not enough depolarization to displace the magnesium ion, resulting in NMDA receptor blockage.

Question 14

In long-term potentiation, pre-synaptic glutamate release can be increased by

Accepted Answer

A retrograde messenger released from the postsynaptic cell can signal the presynaptic cell to release more glutamate, enhancing synaptic strength in a process involved in long-term potentiation (LTP). This is part of the mechanism by which synaptic communication is modified during learning and memory formation.

Question 15

In vertebrates, the right visual cortex receives information from the

Accepted Answer

In vertebrates, the right visual cortex processes information from the left visual field, and the left visual cortex processes information from the right visual field. This is due to the partial crossing of optic nerve fibers at the optic chiasm, allowing each hemisphere of the brain to receive visual information from the opposite visual field.

Question 16

By which pathway does visual information travel to be interpreted by the vertebrate brain?

Accepted Answer

Visual information first travels from the retinal ganglion cells to the optic tract, then to the lateral geniculate nucleus, and finally to the visual cortex for interpretation.

Question 17

In what way is the organization of the lateral geniculate nucleus and layer IV of the adult primary visual cortex similar?

Accepted Answer

Both the lateral geniculate nucleus and layer IV of the primary visual cortex are organized into regions that receive input from only one eye, maintaining segregation of input from each eye.

Question 18

Ocular dominance bands appear in layer IV of the visual cortex in mice even before rods and cones in the retina can respond to light, suggesting that _______ required for the segregation of input from the two eyes.

Accepted Answer

Ocular dominance bands form before the retina can respond to light, indicating that visual experience is not necessary for their formation.

Question 19

The segregation of input from the two eyes in the developing lateral geniculate nucleus is driven by

Accepted Answer

Spontaneous neuronal activity is crucial for the segregation of input from the two eyes in the developing lateral geniculate nucleus, even before visual experience can influence development.

Question 20

In visual system development, axons travel from the retina to their approximate correct position in the lateral geniculate nucleus by

Accepted Answer

Axonal pathfinding mechanisms guide the axons of retinal ganglion cells to the correct location in the lateral geniculate nucleus. This is achieved through a combination of attractive and repulsive signals from various molecules in the surrounding environment.

Quiz 8: Activity-Guided Neural Development