Association Cortices (W2L2)

Today's Topic: The session will primarily serve as a review of previous topics, reinforcing the understanding of fundamental concepts vital for upcoming materials.
Interactive Approach: Students are encouraged to ask questions throughout the lecture for clarity and deeper comprehension of the material.

Neurotransmitter Dynamics: The presynaptic neuron fires and releases glutamate, which is an excitatory neurotransmitter. Glutamate binds to ionotropic receptors on the postsynaptic neuron, leading to the influx of sodium ions. This sodium influx generates excitatory postsynaptic potentials (EPSPs), which contribute to the overall excitability of the neuron. Additionally, GABA, an inhibitory neurotransmitter, is also released and binds to its respective receptors, allowing chloride ions to enter. This action effectively 'shunts' the excitatory signal.
Signal Integration: The balance between EPSPs and inhibitory postsynaptic potentials (IPSPs) determines whether the neuron will reach the action potential threshold, underscoring the importance of both excitatory and inhibitory neurotransmitters in neuronal communication.

Receptor Types: There are two major types of neurotransmitter receptors: ionotropic and G-protein coupled receptors (GPCRs). Ionotropic receptors facilitate fast (milliseconds) synaptic transmission by conducting ions directly, such as glutamate receptors. In contrast, GPCRs activate slower (minutes to hours) signaling pathways that involve more complex processes.
Signal Transduction: When neurotransmitters bind to GPCRs, they activate G-proteins, which initiate intracellular changes through secondary messengers like cyclic AMP, leading to a cascade of signaling events that modulate neuronal activity.

Mechanism: A small quantity of neurotransmitter can lead to a significant effect on the postsynaptic neuron due to the amplification process involved in signal transduction pathways.
Role of Enzymes: Key enzymes such as kinases, which add phosphate groups to activate proteins, and phosphatases, which remove phosphate groups to inactivate proteins, play critical roles in these pathways, affecting the overall physiological responses of the neuron.

Directional Terms in Neuroscience: In the context of four-legged mammals (e.g., rodents), anatomical terms include: anterior (toward the nose) and posterior (toward the tail), corresponding to rostral (anterior) and caudal (posterior). For positioning, dorsal means top and ventral means bottom; medial indicates toward the center, while lateral refers to the sides.

Sectional Planes: The brain can be sectioned into three major planes: sagittal (divides the brain into left and right), horizontal (divides it into top and bottom), and coronal (divides it into front and back). Understanding these sections is essential for interpreting neuroanatomical research and clinical imaging.
Pathway Classification: Distinction between afferent (incoming) pathways, which bring sensory information into the central nervous system, and efferent (outgoing) pathways, which convey motor commands from the central nervous system to the body, is crucial for understanding neurophysiology.

Gray Matter vs. White Matter: Gray matter consists predominantly of neuron cell bodies, typically appearing gray in color; it often refers to a localized structure called a nucleus. In contrast, white matter is composed of myelinated axons, which appear white due to the light-reflective properties of myelin. Understanding these two types of brain matter is fundamental in neuroscience.
Tracts: These refer to bundles of axons that connect different areas of the brain, such as the corticospinal tract which is essential for motor control.

Roots Functionality: Dorsal roots are responsible for carrying sensory information into the central nervous system (afferent), whereas ventral roots carry motor commands out, contributing to muscle movement and function (efferent).
Role of Sensory Cortices: Primary sensory cortices receive sensory input through pathways originating from the body, traveling through the spinal cord to the brain via relay stations like the thalamus. Notably, evolutionary adaptations are reflected in the differences observed in sensory cortices between humans and rodents.
Motor Cortex: The motor cortex is essential for generating motor responses, sending commands to muscles through descending pathways that coordinate movement.

Higher-Level Processing: Higher-level cognitive functions and processing occur in association cortices, which integrate information across different modalities and sensory inputs. These cortices play a significant role in complex behaviors and decision-making. Next week’s lectures will delve deeper into understanding these areas and their significance in brain function.

Final Encouragement: Students are encouraged to reach out with any questions or concerns before the weekend to ensure comprehensive understanding and preparation for future topics.