pharmacology

Class Attendance and Resumption

  • Nine students checked in for the class meeting.

Review of Previous Topics

  • Recap of where the class left off: basic features and structures of neurons and glial cells.

  • Introduction of new topic: dendritic spines.

Dendritic Spines

  • Definition: Protrusions from the dendritic shaft; facilitate the reception of incoming information.

  • Function: Allow for neurochemical binding to receptors, converting that information into electrical messages.

  • Dynamic nature: Dendritic spines can grow and retract throughout the day, a concept illustrated using laser scanning confocal microscopy.

Real-Time Observation of Dendritic Spines

  • Example: Study using a living mouse observed over time.

    • Time Point Zero: Control condition, no significant activity.

    • After Drug Application:

      • Pilocarpine: Cholinergic agonist stimulating acetylcholine receptors.

      • Observations: Two hours post-application showed an increase in spine growth.

      • GABA A Antagonist (Bicyclidine):

      • Observations: Five hours later, evidence of spine retraction.

  • Conclusion: Inhibiting dendritic spine activity with the GABA A antagonist can negatively impact growth.

Advances in Microscopy Techniques

Electron Microscopy

  • Provides high-resolution images, aiding the understanding of neuronal structures.

  • Key structures identified:

    • Nodes of Ranvier: Segments of myelination separated (shown in panel g).

    • Axon Cross Sections: Myelination patterns in oligodendrocytes (CNS) vs. Schwann cells (periphery).

    • Synaptic Connectivity: Illustrated with proper labeling of presynaptic and postsynaptic membranes.

Myelination

Types of Myelination

  • Oligodendrocytes (CNS):

    • Wrap around axons multiple times, forming a myelin sheath.

  • Schwann Cells (peripheral nervous system):

    • Each Schwann cell myelinates a single segment of an axon.

  • Comparison of Structure:

    • Panel A (Periphery): Single Schwann cell wraps one segment.

    • Panel B (CNS): Oligodendrocyte with multiple end feet wrapping different segments.

Internal Support Structures

  • Mitochondria: Provide energy for ion transport within the axon.

  • Microtubules: Essential for molecular transport within the axon.

Importance of Synaptic Connectivity

  • The synapse consists of:

    • Presynaptic Membrane: Contains vesicles of neurotransmitters.

    • Postsynaptic Membrane: Contains receptor sites for neurotransmitters.

  • Electron-Dense Vesicles: Differentiate between neurotransmitters and neuromodulators.

Types and Functions of Glial Cells

  • Ependymal Cells:

    • Line cerebral ventricles; facilitate cerebrospinal fluid flow.

  • Astrocytes:

    • Multidimensional support functions, including metabolic support and nutrient transport.

  • Microglia:

    • Immune response; phagocytic activity, especially during trauma or disease.

Comparative Anatomy of Glial Cells

Astrocytic Structure Across Species

  • Different levels of complexity observed in glial cells across species (mice, monkeys, humans).

  • In higher-order species, astrocytic arborization is more extensive, reflecting advanced information processing capabilities.

Distinguishing Neurons from Glial Cells

Morphological Identification

  • Use of staining techniques, e.g., Nissl stain, to differentiate cell types in the brain (Garcia Cabezas et al. 2016).

  • Neuronal Features:

    • Defined nucleus and nucleolus, surrounding cytoplasm.

  • Glial Cells vs. Neurons:

    • Glial cells may appear similar to small neurons and require trained identification techniques.

Cellular Communication in Neuroscience

Action Potentials

  • Definition: Key electrical event within a neuron, propagating along the axon.

  • Mechanism:

    • Action potentials are initiated when the membrane reaches a depolarizing threshold.

    • Involvement of voltage-gated calcium channels: Calcium's role in neurotransmitter vesicle mobilization and release.

  • Synaptic Transmission:

    • Neurotransmitter release via exocytosis at the active zone of presynaptic membranes.

    • Postsynaptic receptors bind neurotransmitters for neuron-to-neuron communication.

Membrane Potential

  • Notation: Membrane potential represented as $V_m$.

  • Resting Membrane Potential: Typically around $-70$ mV.

  • When stimulated, a depolarizing current triggers action potential initiation when threshold is reached (around $-55$ mV).

  • Action Potential Characteristics:

    • All-or-nothing response; no variance in size once threshold is reached.

Local Potentials

  • Difference between local potentials and action potentials:

    • Local potentials are smaller, may not always reach the threshold.

    • Integration of excitatory (EPSP) vs. inhibitory signals (IPSP):

      • EPSPs increase likelihood of action potential initiation if they outweigh IPSPs.

      • Mixture of signals influences whether threshold is met at the axon hillock.

Conduction in Nervous System

Unmyelinated vs. Myelinated Axons

  • Unmyelinated Axons: Exhibit passive propagation of signals; typically has diminishing signal strength.

  • Myelinated Axons: Utilize saltatory conduction.

    • Conduction jumps from node of Ranvier to node, preserving signal strength.

    • Sodium current facilitates action potentials along the axon.

Summary of Potentials

  • Understanding differences between local potentials and action potentials is vital as they present distinct characteristics based on:

    • Originating stimuli.

    • Duration and amplitude of responses.

  • This information is crucial for grasping the neurophysiology underlying neuronal activity.

Conclusion

  • Review of the lecture content, highlighting important concepts detailed above.

  • Next class: Further exploration of neuronal communication and synaptic processes.