 The reticular activating system is a collection of nuclei and thus neurons in the brain stem that have a critical purpose - it helps to "gate" or "filter" information passed through the brainstem to the cortex and from the eyes and ears (see the diagram). The reticular activating system also helps gate outgoing motor output. Deficits in neurotransmitters in ADHD cause differences in the function of the reticular activating system which underlies some of the differences in behaviour we see in people with ADHD.
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 The Ventral Tegmental Area (VTA) is the second major dopamine production site in the brain (the other one here adjacent in blue - the SNpc - we talked about last week. The key difference is obvious - the SNpc projects to the midbrain whereas the VTA projects to the cortex - thus its role in reward learning, depression, obsession, and a myriad of other things!
 The substantia nigra pars compacta (SNpc) control some of the dopamine production in the brain. As such - it plays a role in a range of activities from motor control to learning to emotion. When it is damaged, or its projections are damaged, it leads to clinical issues such as Parkinson's Disease.
 The Primary Motor Cortex essentially controls the muscles of the body. When the region of the Primary Motor Cortex corresponding to the right bicep muscle fires, then a neural pathway fires that ends up with the alpha motor neuron of the right bicep muscle contracting (bear in mind there are literally tens of thousands of neurons dedicated to controlling this one muscle). Also - note that the left Primary Motor Cortex controls the right hand side of the body, and the right Primary Motor Cortex controls the left hand side of the body. Finally, note the image below. The number of neurons in the Primary Motor Cortex dedicated to a given body region corresponds to the amount of fine control needed. So, the face requires a lot of fine motor control - think of the array of facial expressions needed - whereas the hip does not to the same extent. So, fine motor control means more neurons means a larger portion of the Primary Motor Cortex dedicated to control.   Broca's Area is the motor speech area of the brain. What does that mean? Your brain works with language in what is called "a verbal code" amongst other things - its basically just the way that your brain represents language. When you want to "speak" Broca's Area translates the verbal code into motor commands which then can be used to contracts the muscles needed to produce speech. People with Broca's Aphasia have damage to this area and are unable to comprehensible speech - but they can produce sounds that have no meaning. It is also important to realize that Broca's Area is also a part of the overall language process and works with areas like Wernicke's Area for speech comprehension and production.
 Wernicke's Area is located in the superior temporal cortex near the temporal - parietal junction. Wernicke's Area was originally discovered by Dr. Carl Wernicke who observed that people with damage to Wernicke's Area had trouble producing speech that was intelligible and also had trouble with speech comprehension. Based on that observation, Dr. Wernicke proposed that this region was responsible for speech comprehension - translating the audio code sent from the primary auditory cortex into language. It turns out this is not true entirely - more on this next week!
 The Hypothalamus is a midbrain structure that is a part of the Limbic System. The best way to summarize that the Hypothalamus does is to think of it as a low level management system for some of your bodies natural responses and functions. Some of the things that the Hypothalamus does:
1.Control of the Pituitary gland and Thyroid gland and to control blood pressure 2.Autonomic control- The Sympathetic and pParasympathetic nervous systems. 3.Temperature regulation 4.Fluid balance: Drinking control 5.Eating control: Feeding centre and satiety centre 6.Sleep and wake regulation (Supra-chiasmatic nucleus) 7.Sexual responses 8.Linkage to other parts of the Limbic system  The best way to think of the Thalamus is that it is a relay station - incoming signals go through the thalamus to the cortex and outgoing signals go through the thalamus to the motor system and other regions of the peripheral nervous system.
Now, another key thing to understand about the Thalamus is that it is not a single structure, but it is a name for a collection of nuclei, each of which is a "mini" relay station. For example, incoming visual information from the eyes goes through the Pulvinar nucleus of the Thalamus to the Primary Visual Cortex. Thalamic Nuclei (and their role) Anterior Nucleus Memory and Emotion Dorsomedial Nucleus Executive Function Ventral Posterolateral Nucleus Relays information about pain, temperature, and touch Ventral Posteromedial Nucleus Sensory information from the face Ventral Anterior Nucleus. Relays information from the muscles about movement Ventrolateral Nucleus Relays motor information Lateral Posterior Nucleus Attention - helps prioritize sensory information Pulvinar Nucleus Visual processing Medial Geniculate Nucleus Processes auditory information Lateral Geniculate Nucleus Visual processing Reticular Nucleus Sort of controls the Thalamus as a whole - the outer layer  The Brain Stem
The brain stem plays a key role in controlling basic body functions such as balance, blood pressure, breathing, facial sensations, hearing, heart rhythms, and swallowing. The brain stem consists of three primary structures - the Midbrain, the Pons, and the Medulla Oblongata. The Midbrain is crucial for controlling eye movements. The Pons controls facial movements, hearing, and balance. The Medulla Oblongata controls breathing, heart rhythms, blood pressure, and swallowing. The Brain Stem also contains the Reticular Activating System which governs your sleep and wake cycles.   The human hippocampus. Very easy to see in the cartoon picture, in real life on an MRI scan very hard to see - the highlighting is artificial of course.
The hippocampus plays a big role in the formation of new memories - in particular explicit memories such as our knowledge of facts (semantic memories) and events (episodic memories). The hippocampus also plays an important role in consolidation - when the various parts of a memory are "tied" together so they have a relationship. Thing of your memory for last night - you need to consolidate the sights, smells, location, etc into one memory. The hippocampus also plays a key role in spatial navigation. |
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