Neuroscience: Neurotransmission & Circuit Formation

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Questions and Answers

What type of neurotransmission involves neurotransmitters being released into the extracellular space?

Wired (correct)

Chemical

Synaptic

Electrical

The nonspecific effects produced by certain neural circuits primarily influence which of the following?

Global behavioral states (correct)

Sensory processing

Pain perception

Specific muscle control

Which of the following best describes the process of neurogenesis?

Relocation of newly formed cells

Formation of synapses

Cell proliferation and birth of neurons (correct)

Strengthening existing synapses

What occurs in the process of apoptosis during neural development?

Programmed cell death of excess neurons Signup and view all the answers

How do neurotransmitter effects differ in wired neurotransmission compared to hierarchical circuits?

Wired neurotransmitters have nonspecific outcomes. Signup and view all the answers

During the early stages of development, which layer consists of neuroepithelial cells that give rise to all neurons and astrocytes?

Ventricular zone Signup and view all the answers

What is the primary role of aggregation in neural development?

Grouping neurons for shared functions Signup and view all the answers

Which circuit disruption would most likely lead to nonspecific effects like changes in mood and personality?

Wired neurotransmission circuit Signup and view all the answers

What happens to the leading and trailing processes of migrating neurons before they differentiate?

They disappear. Signup and view all the answers

Which mutation is associated with enlarged lateral ventricles and diminished white matter?

Reelin mutation Signup and view all the answers

What characterizes the neuroblasts during their early stage after migration?

They are temporarily round and apolar. Signup and view all the answers

What do neuroblasts become after differentiation?

Multipolar neuroblasts with complex morphology. Signup and view all the answers

How do neurons that migrate without radial glial guides navigate?

By utilizing tissue, cellular, and molecular signals as cues. Signup and view all the answers

Which type of cells can oligodendrocytes derive from, aside from neuroepithelial cells?

Mesenchyme cells. Signup and view all the answers

What role does Reelin play in neuronal migration?

It signals the neuron to detach from the glia. Signup and view all the answers

What morphological change occurs in a neuroblast when it becomes bipolar?

Two processes develop on opposite sides of the cell body. Signup and view all the answers

What are the origins of microglia development?

From both mesoderm and neuroectoderm Signup and view all the answers

Which peptide hormone is crucial for establishing neuron identity?

Sonic hedgehog (Shh) Signup and view all the answers

Which condition is most commonly associated with a mutation in the SHH gene?

Holoprosencephaly Signup and view all the answers

What structure at the tip of an elongating axon aids in guiding its growth?

Growth cone Signup and view all the answers

What regulates the path and rate of axon growth?

Guidance cues and cytoskeletal signals Signup and view all the answers

How fast do axons typically grow per day?

3-4 mm Signup and view all the answers

What is the role of pioneer axons in axonal growth?

They serve as guides for the growth of later axons. Signup and view all the answers

What are the options available for a developing axon during growth?

Grow, turn, or stop Signup and view all the answers

What is a key characteristic of Horizontal gaze palsy?

Patients have limited ability to move their eyes horizontally. Signup and view all the answers

Which of the following events is NOT part of synapse formation?

Neural regulation Signup and view all the answers

What happens to the majority of neurons that are overproduced during development?

They undergo apoptosis and die. Signup and view all the answers

What role do neurotrophic factors play in neuronal survival?

They inhibit apoptosis in neurons. Signup and view all the answers

Which of the following neurotrophins was discovered first?

Nerve growth factor (NGF) Signup and view all the answers

What is the outcome if the target of spinal cord motor neurons is removed?

Increased cell death in the ventral horn Signup and view all the answers

What is the main function of signaling molecules in the process of target recognition during synapse formation?

To guide growth cones of axons to the appropriate target Signup and view all the answers

Which statement about synapse development in the CNS is correct?

It involves different molecules compared to NMJ. Signup and view all the answers

What principle is described by the phrase 'Cells that fire together, wire together'?

Hebb's theorem Signup and view all the answers

What happens to synapses that exhibit persistent uncorrelated activity?

They vanish or weaken Signup and view all the answers

Which area of the nervous system is primarily responsible for postnatal neurogenesis?

Hippocampus Signup and view all the answers

What type of activity strengthens the connection between presynaptic and postsynaptic neurons according to Hebb’s theorem?

Correlated activity Signup and view all the answers

What aspect of brain development primarily differentiates humans from other animals?

Cortical development Signup and view all the answers

Which of the following factors influences synaptic changes and dendritic extensions postnatally?

Learning and behavioral demands Signup and view all the answers

What is the result of molecular matching during embryonic development?

Establishment of default synaptic connections Signup and view all the answers

What can happen to branches of the presynaptic neuron when synapses lose correlated activity?

They may entirely disappear Signup and view all the answers

Study Notes

Wired Neurotransmission & Circuit Effects

Axon terminals release neurotransmitters into the extracellular space.
Serotonin is released from neurons in the raphe nuclei to various targets throughout the cerebral and cerebellar cortex.
Effects of these circuits are nonspecific, influencing global states like mood, arousal, and attention.
Lesions of these circuits lead to nonspecific changes in mood, pleasure, reward, personality, depression, and sleep.

Development of Neural Circuits

Neurogenesis: Proliferation and birth of neurons and glia.
Migration: Newly formed cells relocate to their final positions.
Aggregation: Similar neurons form groups called nuclei in the adult brain.
Differentiation: Neurons develop specific characteristics, including their neurotransmitter phenotype.
Synaptogenesis & Circuit Formation: Synapses are formed and connections are established.
Apoptosis: Programmed cell death of excess neurons.
Synapse Rearrangement: Maturation of synapses through strengthening and weakening.

Neurogenesis and Migration

Neuroepithelial cells, located in the ventricular zone of the neural tube, are responsible for generating neurons and astrocytes in the central nervous system.
Neuroepithelial cells divide, forming neuroblasts (immature nerve cells) and glioblasts (immature glial cells).
Migrating neurons rely on glial processes for guidance, using filopodia to move.
Mutations in migration genes can cause malformations of the cerebral cortex.
Reelin mutations lead to enlarged lateral ventricles, reduced white matter, and disrupted sulci and gyri.
Doublecortin (DCX) mutations result in dramatically enlarged ventricles, little subcortical white matter, and a smooth brain (lissencephaly).
Neurons destined for non-laminated structures migrate using tissue, cellular, and molecular cues.

Cell Aggregation and Differentiation

Neuroblasts, after migrating, undergo differentiation, developing two cytoplasmic processes: an axon and dendrites.
Glioblasts differentiate into astrocytes (protoplasmic in grey matter, fibrillar in white matter) and potentially oligodendrocytes.
Oligodendrocytes can also originate from mesenchyme cells.
Microglia develop from mesoderm or neuroectoderm, coinciding with vascularization of the CNS.
Glial cell fates can be altered by gene expression and signaling molecules.

Sonic Hedgehog (Shh) and Neurodevelopmental Disorders

Shh, a peptide hormone produced by the floor plate, is crucial for neuronal identity.
The Shh signaling pathway involves the Patched protein, Smoothened receptor, and the Gli1 transcription factor, all involved in gene regulation.
Mutations in the SHH gene can lead to holoprosencephaly, a malformation of the forebrain that disrupts the separation of the hemispheres and results in midline facial defects like cyclopia.

Synaptogenesis & Circuit Formation

Axonal growth involves elongation, target recognition (pathfinding), and synaptogenesis.
Growth cones, located at the tip of elongating axons, guide axonal growth using sensory-motor functions, filopodia, and chemical and morphological cues.
Axons grow at a rate of 3-4 mm/day.
Pioneer axons, reaching their targets first, guide subsequent axons.
Axon growth occurs in discrete steps, with decisions made at frequent intervals.
Horizontal gaze palsy, a disorder characterized by limited horizontal eye movement and difficulties in postural and motor control, is caused by impaired axonal connections in the brain.

Synapse Formation

Synapse formation involves target recognition, presynaptic differentiation, and postsynaptic differentiation.
Target recognition is facilitated by signaling molecules in the extracellular space.
Presynaptic differentiation transforms the growth cone into a nerve terminal and establishes transmitter release machinery.
Postsynaptic differentiation involves the elaboration of a postsynaptic apparatus with receptor accumulation at the active site.
Though CNS synapses develop similarly to neuromuscular junctions (NMJs), they differ in their molecular components.

Apoptosis: Living or Death

During development, there is overproduction of neurons, leading to cell death in approximately half of the neurons.
Cell death is an active and necessary process for development.
Target cells secrete neurotrophic factors, which promote neuronal survival.
The removal of a target leads to increased cell death of the innervating neurons.
Neurotrophins, such as NGF, BDNF, NT3, and NT4/5, are key factors in promoting neuronal survival.

Mechanism of Experience-Dependent Changes: Hebb's Theorem

Hebb's theorem (Hebbian rule) states that simultaneous activity of a presynaptic and postsynaptic neuron strengthens the synaptic connection between them ("cells that fire together, wire together").
Persistent correlated activity between neurons leads to synapse strengthening and branching, strengthening pre- and postsynaptic correlation.
Conversely, persistent uncorrelated activity weakens synapses and reduces branching.
Hebbian learning is the cellular basis for learning and memory and applies to long-term synaptic strength modifications.

Modification of Circuits During Development

Circuit modifications can involve changes in anatomical connectivity and synaptic strength.
Changes in anatomical connectivity include alterations in the number of synapses between neurons.
Changes in synaptic strength involve modifications at the presynaptic terminal and responses at the postsynaptic terminal, including changes in the number, type, and configuration of ion channels.

Postnatal Brain Development

Molecular matching dominates during embryonic development; activity and experience modify circuits after establishment.
Postnatally, significant changes occur in the cerebral cortex, which contains approximately 70% of CNS neurons.
Learning, behavioral demands, and sensorimotor training increase dendritic extensions and synapses in cortical pyramidal cells.
Neurogenesis occurs postnatally in specific brain areas, such as the hippocampus, contributing to its structural and functional integrity.
New hippocampal neurons may play a role in learning and memory.

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Description

Explore the intricacies of neurotransmission and the development of neural circuits. This quiz covers topics such as the role of neurotransmitters in mood and attention, as well as the processes involved in neurogenesis and synaptogenesis. Test your understanding of how brain circuits are formed and their implications on behavior.