Neuroscience

Neuroscience Oral Exam

Introduction

  • Understanding brain functions is complex and multifaceted, with no simple or universally accepted description.

Evolution of the Nervous System

  • Porifera (sponges): These primitive organisms lack a complex nervous system but possess independent effectors like myocytes, enabling them to perform basic activities such as slow and non-coordinated movements.

  • Nerve Nets: The neurophysiology of organisms across the animal kingdom shares similarities; however, the organization and complexity of the nervous system vary drastically, suggesting evolutionary adaptations to environmental and functional demands.

  • Sensorimotor Neurons: While simple reflexes are biologically essential, they are surprisingly rare in simpler organisms like cnidaria (e.g., jellyfish).

Advantages of Neurons

  • Divergence: The branching nature of neurons allows a single neuron to relay information to multiple target neurons, enhancing communication within the nervous system.

  • Convergence: Numerous neurons can synapse onto a single neuron, allowing for the integration of diverse signals and producing a coordinated response.

  • Coordination of Effectors: Neurons enable integration across various body movements, ensuring smooth and coordinated actions.

  • Rapidity of Transmission: Neuronal signals travel rapidly, a significant advantage over slower means such as hormonal diffusion.

  • Localized Patterns: Neurons can establish specific patterns of activity that facilitate localized control, crucial for fine motor movements.

  • Amplification: Neural circuits can produce substantial physiological responses from minimal stimuli, emphasizing the efficiency of signal propagation.

Neuron Types

  • Sensory and Motor Neurons: These neurons facilitate independent regulation of body functions, exhibit avalanche conduction properties, and contribute to complex neural networks.

  • Human Neuron Count: The human brain contains an estimated 86 billion neurons (8.6 x 10^10), contributing to its intricate functional capacity.

Reasons for Large Brains

  • Large brains facilitate exploration and control of extensive areas, enhancing sensorimotor computation and adaptability.

  • They support complex physiological functions necessary for survival in dynamic environments.

  • Larger brains allow for anticipatory physiological regulation, crucial for preparing the organism for future events.

General Design Principles

  • Energetic Cost of Action Potentials: Action potentials consume approximately 20% of the total energy utilized by the brain, underlining the metabolic consequences of neural activity.

  • Energy-Saving Strategies: To mitigate energy costs, brains may shorten axons and wiring, transmit only necessary signals, and minimize action potential rates when feasible.

Amacrine Extensions

  • These extensions are critical for synaptic reciprocation, allowing gradual signal propagation and fine-tuning within vertebrate neural circuits.

Interneurons

  • Interneurons provide additional control over local circuits, showing dynamic excitatory and inhibitory interactions, which are vital for rhythm generation.

Centralization and Cephalization

  • This process enhances efficient neural processing by organizing nervous tissue; ganglia and nerve structures concentrated at the organism's head exemplify this principle.

  • Neuropil Structures: These are networks of interconnecting neuronal processes, commonly seen in invertebrates, with unipolar interneurons being typical, contrasting with the more complex multipolar structure found in vertebrates.

Components of the Nervous System

  • Insects exhibit a unique ventral cord complex system alongside a dorsal brain, highlighting the diversity of nervous system architectures.

  • In contrast, human neural circuits are more complex, showcasing evolutionary advances in neural processing.

College 2: Cell Types and Signals

  • Dale’s Principle: This principle states that all synapses formed by a single neuron will release the same neurotransmitter, establishing foundational concepts in neurobiology.

  • Major Cell Types: The central nervous system (CNS) and peripheral nervous system (PNS) contain various cell types, including:

    • Neurons: Highly diverse in function and structure.

    • Macroglia: Comprising astrocytes, oligodendrocytes, and Schwann cells (found in the PNS).

    • Microglia: Act as the immune defense within the CNS.

    • Ependymal Cells: Line the ventricles and central canal of the spinal cord, contributing to cerebrospinal fluid circulation.

Oligodendrocytes and Schwann Cells

  • Oligodendrocytes: These cells do not have the ability to proliferate easily and are particularly vulnerable to autoimmune attacks.

  • They can myelinate up to 50 axons, with myelin forming nodes of Ranvier which facilitate saltatory conduction.

  • Oligodendrocytes exhibit an active response to injury, which allows limited regeneration in peripheral nerves.

Astrocytes

  • Astrocytes: These star-shaped glial cells play crucial roles in nutrient transport, structural support, and the maintenance of the blood-brain barrier (BBB).

  • GFAP (Glial Fibrillary Acidic Protein): This protein is vital for astrocyte function and is involved in cellular responses to injury or damage.

Cytoskeletal Elements

  • Microtubules: Essential for forming spindle structures during cell division and axonal transport processes.

  • Microfilaments: Facilitate changes in cell shape and contribute to the motility of growth cones during development.

  • Neurofilaments: Provide structural support, maintaining axonal shape and contributing to growth processes.

Neuronal Specificity

  • There exists a vast diversity among neurons in terms of size, shape, physiological properties, and subcellular organization, allowing for specialized functions in different brain regions.

Voltage-Gated Ion Channels

  • These channels are crucial for controlling membrane potentials and ionic gradients, playing key roles in initiating and propagating action potentials.

College 3: Axonal Transport

  • Anterograde Transport: Involves the movement of materials from the neuron’s cell body to its synapses, transporting neurotransmitters and membrane proteins essential for cell signaling.

  • Retrograde Transport: Returns materials from the synapses back to the cell body, facilitating the retrieval of larger organelles and growth factors necessary for neuronal health and plasticity.

Dendrite Transport

  • mRNA transport within dendrites is a significant mechanism that allows for local protein synthesis, which is critical for synaptic plasticity and function.

College 4: CSF and Blood-Brain Barrier

  • Cerebrospinal Fluid (CSF): Vital for nutrient transport and the removal of waste products from the brain, contributing to overall neural health.

  • Blood-Brain Barrier (BBB): Essential for maintaining homeostasis, regulating ion concentrations, and allowing selective nutrient exchange within the CNS.

Astrocytic Regulation of BBB

  • Astrocytes play a pivotal role in maintaining the integrity and functionality of the BBB through the release of various signaling factors that influence endothelial cell behavior.

Neurovascular Unit

  • Comprised of endothelial cells, basal lamina, and pericytes, which together regulate BBB function and cerebral blood flow, illustrating the interdependence of neuronal and vascular systems.

Solute Carriers in BBB

  • Include transporters for glucose and amino acids, along with ion exchange mechanisms that are crucial for nutrient uptake in the brain.

Blood-Brain Barrier in Pathology

  • Disruption of the BBB can lead to significant pathological conditions and influences the strategies developed to facilitate drug delivery into the CNS for disease treatment.

College 5: Astrocyte Functions

  • The brain contains a mix of cells predominantly made up of microglia (approximately 20%) and macroglia (about 80%), which is primarily composed of astrocytes and oligodendrocytes.

  • Distinct astrocytic subtypes serve specialized functions in supporting synaptic activities and maintaining biochemical homeostasis in the brain.

College 6: Experimental Approaches

  • Various experimental methodologies exist for investigating CNS functions, including classic subcellular preparations, dissociated cell studies, acute brain slice techniques, and organotypic cultures, each providing unique insights into neural mechanisms.

College 7: Metabolic Features of Brain Cells

  • The brain is a metabolically demanding organ, relying heavily on the continuous availability of glucose and oxygen to sustain its high energy demands, particularly for action potential generation and neurotransmitter release.

  • The mechanisms for nutrient uptake are accurately adjusted depending on the energy needs of different brain regions during varying activities.

Sensory Systems and Processing

  • Different sensory modalities such as vision, hearing, and touch are processed using distinct neural pathways, each employing specialized mechanisms for encoding sensory information.

  • Areas of focus include visual processing pathways, sensory integration mechanisms, and the implications of these processes for perception and cognition.