The Limbic System PDF

# The Limbic System ## The Limbic Cortex - Cingulate gyrus - Parahippocampal gyrus ## The Hippocampal Formation - The dentate gyrus - Hippocampus - Subicular Complex ## Other Structures - Amygdala - Septal area - Hypothalamus ## The Limbic System - Diagram This is a diagram of the Limbic Sy...

# The Limbic System ## The Limbic Cortex - Cingulate gyrus - Parahippocampal gyrus ## The Hippocampal Formation - The dentate gyrus - Hippocampus - Subicular Complex ## Other Structures - Amygdala - Septal area - Hypothalamus ## The Limbic System - Diagram This is a diagram of the Limbic System, showing the following components: - **Limbic Gyrus:** Cingulate gyrus, Parahippocampal gyrus - **Intralimbic Gyrus:** Septum Pellucidum - **Fornix & Inner Arc:** Fornix, Mamillary body, Fimbria, Hippocampus. ## Origin of the Limbic System - The limbic system is a complex network of brain structures that plays a role in emotion, motivation, and memory. - During embryonic development, the limbic system originates from distinct regions of the brain: - **Diencephalic components** include the hypothalamus, anterior thalamic nuclei, and habenular commissure. - **Telencephalic components** include cortical and subcortical areas: olfactory bulb, hippocampus, parahippocampal gyrus, fornix, fornix column, mammillary body, septum pellucidum, amygdala, cingulate gyrus, and entorhinal cortex. - **Mesencephalic components** receive visual, auditory, and somatosensory inputs and process these signals. ## Olfactory Bulb to Amygdala Pathway This pathway demonstrates the connection between the olfactory system and the amygdala: - Olfactory receptor neurons in the olfactory bulb transmit signals via the olfactory tract. - Signals reach the anterior olfactory nucleus and amygdala. - Input from the olfactory tract also projects to the hypothalamus and hippocampus. - The entire pathway is influenced by centrifugal fibres from neocortical areas. ## The Basolateral Amygdala - Consists of three major nuclei: - Lateral Nucleus - Basal Nucleus - Basolateral Accessory Nucleus - **Key Functions:** - Receives and processes sensory information (from sensory cortex, thalamus, and hippocampus). - Projects to the basal nucleus, basolateral accessory nucleus, and central nucleus. - Plays a key role in fear conditioning, associating memories with fear responses. ## The Centromedial and Cortical Amygdala - Consists of two nuclei: - Central Nucleus: - Receives input from the lateral, basal, and basolateral accessory nuclei. - Projects to the hypothalamus and brainstem. - **Key Functions:** - Controls physiological responses to stress and fear (including freezing, increased heart rate, and hormone release). - Plays a role in emotional processing and memory. - Medial Nucleus: - Receives input from the olfactory bulb and olfactory cortex. - Projects to the hypothalamus and preoptic area. - **Key Functions:** - Processes olfactory information. - Involved in reproductive behaviors. - Cortical Nucleus - Receives input from the olfactory bulb and olfactory cortex. - Projects to the medial nucleus and hypothalamus. - **Key Functions:** - Plays a role in olfactory processing and social behaviors. - Influences emotional responses to smell. ## The Cornu Ammonis (CA) - Comprises four subregions (CA1, CA2, CA3, and CA4) that differ in size, function, and vulnerability to damage. - **Subregions and Functions:** - **CA1:** - Large, densely packed pyramidal neurons. - Receives input from CA3 and the entorhinal cortex. - Crucial for long-term potentiation (LTP), a synaptic plasticity mechanism that underlies memory formation. - Vulnerable to ischemic damage and epilepsy. - **CA2:** - Small, sparsely populated pyramidal neurons. - Receives input from CA3 and the entorhinal cortex. - More resistant to ischemic damage than CA1. - Plays a role in social memory. - **CA3:** - Intermediate in size. - Has extensive recurrent collaterals, providing a potential for pattern completion and memory retrieval. - Receives input from the dentate gyrus and entorhinal cortex. - Relatively resistant to ischemic damage. - **CA4:** - Located in the dentate gyrus. - Receives input from the entorhinal cortex. - Site of neurogenesis (the formation of new neurons) in the adult brain. - Contributes to hippocampal plasticity and learning. ## The Amygdala **The Amygdala - A Complex System Involved in Fear, Emotion, and Memory** - A small, almond-shaped structure located in the medial temporal lobe of the brain. - Plays a critical role in processing and experiencing emotions, particularly fear and anxiety. - Also involved in: - **Memory formation:** The amygdala interacts with the hippocampus to help form and recall memories associated with emotionally significant events. - **Decision-making:** The amygdala influences our choices and behaviors based on past experiences and emotional learning. - **Social cognition:** The amygdala helps us process and interpret social cues, contributing to understanding the emotions and intentions of others.