Cerebral Cortex and Neuron Types PDF

**Cerebral Cortex and Neuron Types** 1. **Neuron Types in the Cortex**: - **Granular/Stellate Cells**: Short axons, responsible for intracortical connections and act as interneurons. - **Fusiform Cells**: Located in deeper layers, their axons form part of the white ma...

**Cerebral Cortex and Neuron Types** 1. **Neuron Types in the Cortex**: - **Granular/Stellate Cells**: Short axons, responsible for intracortical connections and act as interneurons. - **Fusiform Cells**: Located in deeper layers, their axons form part of the white matter, functioning as output cells. - **Pyramidal Cells**: Large, triangular neurons with axons projecting to the spinal cord, serving as both intracortical and output cells. - Other important cell types include **Horizontal Cells** and **Martinotti Cells**. - Despite being the largest, most accessible area detailed function not fully understood. - Functional area found in mantle (grey) 2 -- 5mm thick - Entire cortex has been mapped in terms cytoarchitecture & function and Brodmann classification is still extensively used (\~52 areas) - Entire cortex has been mapped in terms cytoarchitecture & function and Brodmann classification is still extensively used (\~52 areas) **Functional Areas of the Cortex** 1. **Primary, Secondary, and Association Areas**: - **Primary Areas**: - **Motor Cortex** (Precentral Gyrus): Controls discrete movements. - **Sensory Cortex** (Postcentral Gyrus): Responsible for specific sensory experiences, mapped by a **Homunculus**. - **Secondary Areas**: Interpret and make sense of signals processed in primary cortices (e.g., distinguishing the meaning of sound tones). - **Association Areas**: Involved in higher functions like voluntary movement planning, learning, and memory. - **Posterior Association Area**: Integrates signals from the somatosensory, visual, and auditory areas (e.g., **Wernicke\'s Area**). - **Anterior Association Cortex**: Involved in planning complex motor tasks and short-term memory. - **Limbic Association Cortex**: Controls behavior, emotions, and motivation. **Memory Formation** 1. **Memory Model**: - Memory is a cognitive process allowing the retention and retrieval of information. - Memories are caused by alterations in sensitivity, chemical characteristics and physical changes in circuits - - **Memory Types**: - **Sensory Memory**: Immediate retention of sensory information. - **Short-Term Memory (STM)**: Limited capacity (\~7 ± 2 items), decays rapidly unless encoded into long-term memory. STM can be: - **Presynaptic Facilitation/Inhibition**: Facilitator neuron activity prolongs neurotransmitter release.Due to maintained closure of K^+^ channel - Repolarisation is delayed as the NT + receptor causes ↑cAMP which results in ↑ PK\* levels. This phosphorylates channel proteins resulting in the K-channel remaining closed. - **Synaptic Potentiation**: Increased synaptic strength after repeated stimulation due to elevated **Ca²⁺** levels. - This is due to ↑ **\[**Ca^2+^**\]** in bulb/ button resulting in sustained NT release. Ca^2+^ levels eventually drop which is basis of decay - STM are therefore due to chemical changes hence difficult to evaluate in complex circuits eg cortex. - NB STM is labile - **Long-Term Memory (LTM)**: Involves structural changes in neurons, infinite retention capacity. - STMs are encoded to form LTMs (consolidation) Transfer attributed largely to hippocampi (no storage) - Encoding enhanced by rehearsal & prevented by factors such as concussion, etc - *Aplysia & Drosophilia* have served as good models in this area - Drugs preventing protein synthesis (eg anisomycin) - prevents formation of LTM! - - **Declarative (Explicit) Memory**: Memory of facts and events, consciously recalled, related to the medial temporal lobe. - **Procedural (Implicit) Memory**: Memory for skills and tasks, unconsciously recalled. 2. **Mechanisms of Memory**: - **Short-Term Memory**: - Chemical changes at synapses (e.g., closure of **K⁺ channels** due to increased **cAMP**). - Decay occurs due to the eventual drop in **Ca²⁺** levels. - **Long-Term Memory**: - Involves structural changes, such as increased presynaptic terminals, dendrites, vesicles, and neurotransmitter release. - **Protein Kinase M Zeta** is essential for maintaining long-term memory. Its absence can erase memories, similar to \"wiping a disk.\" - The **MAPK Pathway** promotes protein synthesis required for long-term memory formation. **Memory Consolidation** - STM is consolidated into LTM, primarily facilitated by the **hippocampi**, although they do not store memories. - Consolidation is enhanced by **rehearsal** and is disrupted by factors like **concussion**. - Drugs that inhibit protein synthesis (e.g., **anisomycin**) prevent LTM formation. These notes provide an in-depth overview of the brain\'s neuron types, cortical functions, and the processes underlying memory formation and retention.