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In unit one of neurology, the main topics discussed are the lobes of the brain, communication pathways, subcortical structures, cerebrovascular supply, and the anatomy of a neuron. The lobes include the frontal, temporal, parietal, and occipital lobes, each playing a role in different aspects of speech and language. Communication pathways such as the corpus callosum and archaeophysiculus allow for the exchange of information between language centers. Subcortical structures like the limbic system, hippocampus, amygdala, thalamus, hypothalamus, basal ganglia, and cerebellum have various functions related to emotions, memory, sensory processing, and motor movement. The cerebrovascular system supplies blood to the brain, with important arteries like the middle cerebral artery supporting speech and language regions. Neurons are the basic unit of the nervous system and transmit information through electrical signals called action potentials. Action potentials involve depolarization and repol Okay, so I'm going to start with unit one neurology, so basically we're going to talk about the lobes, the communication pathways, the subcortical structures, the cerebrovascular supply, and then the anatomy of a neuron, action potential, and how all this Down syndrome impacts all these areas. So the lobes, so the four lobes are the frontal lobe, the temporal lobe, the parietal lobe, and the occipital lobe. The frontal lobe is an area that's essential for speech production and language processing, especially because this lobe has Broca's area. Broca's area is responsible for speech production, and it is the motor programming for articulation. It's definitely very important because if it's damaged, it will cause impaired slow speech, which is known as Broca's aphasia. Other parts of the frontal lobe are the precentral gyrus and the prefrontal lobe. The precentral gyrus is the motor cortex, and the prefrontal lobe is for personality insight and foresight. Moving on to the temporal lobe, the temporal lobe is essential for auditory processing and understanding language. This lobe has Wernicke's area, which is responsible for language comprehension of spoken and written language. It is also extremely important for speech because of the language comprehension portion, and if Wernicke's area is damaged, it results in speech that is fluent but has poor content, which would be Wernicke's aphasia. This means that what they are saying is coherent, so let's say I said a sentence, you'd be able to know what words I am saying and it sounds right, but it does not make sense, so the context of it would not be like a full story that connects. And also part of the temporal lobe is the Heschel's gyrus, which is the primary auditory cortex. All of the auditory information is projected here. The next lobe is the parietal lobe, which plays a role in processing and understanding language, especially regarding sensory information. The postcentral gyrus and the angular gyrus and the supramarginal gyrus are also parts of the parietal lobe. The postcentral gyrus is a sensory cortex, the supramarginal gyrus is a symbolic integration for writing, and the angular gyrus is a symbolic integration for reading. The last lobe is the occipital lobe, which honestly does not have much of a direct connection to speech and language, but controls our visual cortex, which helps us perceive and understand things like shapes and colors. So yeah, it is the primary visual cortex. Moving on to communication pathways, the communication pathways are the corpus callosum and the archaeophysiculus. The corpus callosum is a pathway between the two hemispheres of the cerebral cortex and it allows communication between language centers in both hemispheres. The archaeophysiculus is a neural pathway that connects Broca's area and Warnke's area, which helps communicate between the speech and comprehension regions. You need that bridge, obviously, to make sure that you are comprehending the speech and language to be able to produce your own speech. So moving on to the subcortical structures, there's the limbic system, the hippocampus, the amygdala, the thalamus, the hypothalamus, the basal ganglia, and the cerebellum. So the limbic system is a set of structures that regulates emotional responses and behavioral motivations. It also contains our short-term memory. It is where subcortical structures meet the cortical structures. So the hippocampus, it's an X structure, it's a consolidation of new memories of information and a consolidation of information that is associated with the memory function. It is very important because damage to it makes it difficult to form new memories. Its information comes from both cortical and subcortical structures. So for example, sometimes you can smell something and it triggers a past memory. So that can be part of the consolidation of memories in the hippocampus. The amygdala is an X structure. The amygdala is the emotional and behavioral center and it is located in the medial temporal lobe. It inhibits behaviors and participates in memory formation. The next one is the thalamus, which is a sensory realization. It's for all senses except for smell. It's a paired structure with the hypothalamus and together they are called the diencephalon. It is the primary bridge because it is a sensory realization, which is the final location of the information. The hypothalamus is actually what monitors the limbic system. It's the gatekeeper of it and it controls our automatic nervous system, which is fight or flight or rest and digest, which can refer to our hunger, adrenaline, et cetera. Any damage to the hypothalamus, you may not feel hunger or thirst or handle situations specifically dangerous or anxiety-inducing ones the same way or recover from them the same way. And the next structure is the basal ganglia. This is a group of cell bodies or nuclei that controls motor movement and tone. And without this, our motor movement cannot be in check. So it could either be excessive movement, which is, it helps to regulate this so there's not an excessive movement. Any damage to basal ganglia can cause dyskinesia, so that would be an uncontrolled involuntary movement disorder, so it's not voluntary and you have no control over it. The cerebellum is the last structure we're going to look at, which is the mini-brain and it contains two hemispheres. It sits inferior to the cerebrum and posterior to the brainstem and it compares afferent and efferent information. Afferent is motor and efferent is sensory. Next looking at the cerebrovascular supply, the cerebrovascular system maintains constant circulation, which is required of the nervous system. The blood supply is O2 and glucose and the two sources of blood from heart to brain are the carotid artery and the vertebral artery. One of the most important arteries for speech and language is the middle cerebral artery because it provides blood to the temporal lobe, Broca's area, Wernicke's area, the motor strip and the sensory reception regions. All those regions are very, very important and major to speech and language. And also the circle of Willis, which is made up of the anterior cerebral artery, the middle cerebral artery and the posterior cerebral artery and also the anterior and posterior communicating arteries. It promotes the equal distribution of blood, which also can help with speech and language. So messages travel in the brain through the neuron and looking at the anatomy of the neuron, it's the basic unit of the nervous system and its purpose is to communicate or transmit information. The nervous system has about 100 billion neurons and can be efferent, so motor nerves, or afferent, which are sensory nerves. The structure itself is of a cell body, which contains the nucleus, dendrites, which transmit info towards the cell body, the axon, which conducts information away from the cell body, myelin sheath, which covers axon and speeds up neural conduction and is important because it saves energy for the neuron and helps regenerate damaged or severed axons. And the nose of Renvier is areas between myelinated segments on an axon and are important in conduction. And synaptic vesicles contain neurotransmitters, which are responsible for activating the next neuron in a chain, so the neurotransmitters are released from synaptic vesicles and bind to the receptors of postsynaptic neurons. So when the neuron is stimulated, the ion channels open and allow ions to enter. When the ions are allowed to enter, it leads to firing of that neuron, which can be excitatory or inhibitory. Moving on to action potential, so change in electrical potential that occurs when the cell's membrane is stimulated adequately to permit ion exchange is what action potential is. At the start of the membrane, at the start, the membrane is completely polarized and when action potential is initiated, it depolarizes the region of the brain, which in turn spreads the depolarization to the adjacent regions. So once the adjacent region is depolarized to its threshold, an action potential then starts and the repolarization occurs due to the outward flow of potassium ions. The depolarization spreads forward, which triggers the action potential. The depolarization spreads forward and repeats the process. The sodium is always on the inside of the axon, but it's moved to the other side of the axon when the potassium enters. Action potential also has hyperpolarization at the end because the potassium leaks into open channels that are still open, but action potential ends when the gates are closed. There's also the all-or-none theory, which is the strength by which a nerve or muscle fiber responds to a stimulus and is not dependent on the strength of the stimulus. So as long as the stimulus exceeds a certain threshold, a full action potential is initiated along the nerve fiber. So basically, if the stimulus is below the threshold, there won't be an action potential because the neuron or muscle fiber either fires completely or not at all in response to a stimulus. It helps explain the consistent nature of neural signaling, where the strength of the signal is not figured out by the size, but rather the frequency of the action potential is fired by the neuron. The absolute refractory period is another portion, which refers to a period where the neuron is not capable of generating another action potential. So even if there's a big strength of an incoming stimulus, it won't generate another action potential because when a neuron fires an action potential, it goes through a sequence of events that changes the ion channels, and basically, the depolarization phase leads to the opening of sodium channels that causes a big group of sodium ions to trigger the action potential. And the refractory period is initiated for neurons after depolarization. And the depolarization phase is divided into the two periods, absolute and relative. And the absolute period is when the neuron is briefly and completely insensitive to another stimulus, so it's literally impossible for a neuron to fire again. All of this has an impact on Down syndrome. All of this is impacted by Down syndrome, sorry. Down syndrome often affects brain development, so this includes the actual structures of the different lobes, so the structures themselves can have alterations in size and shape, which could potentially impact the speech and language functions, because if the structures of the lobes are not the right size and shape, then there could be potential damage. The structural differences in the brain of the individuals with Down syndrome might affect the development of the neural pathways, too, like the arcuate, fasciculus, and the corpus callosum, because if the shape and size of the regions are different, then the pathways could also be damaged. So this could be the challenges in communication, like between the different language-related portions of the brain. According to Renata Varsaghi in the article Brain Circuit Pathology in Down syndrome, from Neurons to Neural Networks, they conducted many studies to review the impact DS has on neurons and neurotransmitters, and all of the results showed that DS causes alterations in neuronal biophysical properties, organization of excitatory and inhibitory systems, and synaptic plasticity. And this leads to the question regarding the outcome of these alterations to overall signal processing in the neuronal networks, which is not something that we can figure out on humans. It's been tested on animals, but it's just not a process that is capable to do, or is not possible to do on humans. So that's kind of up in the air for that. Some individuals also who have Down syndrome may have an increased risk to certain medical conditions, which include cardiovascular issues. That could indirectly impact the cerebrovascular supply to the brain regions, which is obviously involved in language processing. While the basic structure of the neurons remain intact, alterations in brain development might affect the connectivity of the neurons, and impacts how information is transmitted between the cells, which in turn obviously would affect your speech and language. Individuals with Down syndrome often experience a lot of different degrees of cognitive and developmental delays, which can affect language and speech abilities. So they might encounter challenges in expressive and receptive language skills, even without other areas affecting it. So moving on to Unit 2 of respiration. So respiration is a fundamental, it's fundamental for sustaining life, and also for speech production. The two halves of the cycle of respiration breath are inhalation and exhalation. Inhalation is when the diaphragm contracts and moves downward, and the intercostal muscles expand the ribcage. The diaphragm is the primary muscle of respiration, and it helps generate the consistent airflow for sustained speech, and maintaining the intensity and duration of speech, and having that control. The external intercostals assist in expanding of the ribcage, which can help with a more forceful inhalation that you need to seek for speech. So when the increasing of the lung volume happens, it provides a good amount of airflow for louder speech or the sustained speech. When the diaphragm and the external intercostals make these movements, the volume of the thoracic cavity increases. So when the increased volume happens in the thoracic cavity, the air pressure decreases within the lungs. This causes air to flow in from the atmosphere through the nose or mouth into the lungs, because oxygen moves from an environment of high pressure to an area of lower pressure. So that's why it moves into the lungs. This is according to Boyle's Law, which states that as volume increases, pressure decreases, and vice versa. Within respiration, there is also a pleural lining that covers the lungs and lines the chest cavity. It helps to maintain the separation between the lungs and the chest. So this allows the lungs to expand and contract during respiration, and in speech, it makes sure that there's a smooth movement of the lungs, so they're not rubbing up against each other because there's this little lining blocking it, and it maintains the necessary pressures for effective speech breathing. So for a full breath cycle, I talked about inhalation, but exhalation also needs to occur. And it's when the diaphragm and the intercostal muscles relax and allow the chest cavity to decrease in volume. When the cavity decreases inside, the pressure within the lungs becomes higher than the atmospheric pressure, so it forces air out of the lungs through the nose or mouth. This relates to speech because you need breath support for speech and pronation, and articulation can't occur without the respiration. So effective speech requires controlled exhalation, using the air during exhalation to create a sound. So the muscles involved in respiration work together to regulate the airflow for speech production. For pronation, the airflow initiated is essential for the creation of the sound in the larynx. The vocal folds vibrate as air passes through, producing sounds, so like the airflow passes through the vocal tract, where the speech sounds are shaped by the movement of the tongue, lips, and the other articulators. The airflow is modulated to produce different speech sounds. So this speech breathing is different than rest breathing because during rest breathing, inhalation and exhalation are more relaxed and are normally driven by the diaphragm. In speech breathing, there is a more active and controlled inhalation and exhalation, and it's not just the diaphragm that's engaged, but all of the other accessory muscles as well. So this is to regulate airflow for speech production. Speech breathing requires more precise control over the duration, the force, and the regulation of exhalation to produce speech sounds of all different lengths and volumes and intensities. When I think about respiration, I think about when I dance, how I need to have constant inhalation and exhalation of air to keep myself from losing energy so I can continue dancing for as long as my personal lung capacity will give. And looking at this with individuals with Down syndrome, there are some impacts to respiration. Some people with DS have narrowed airways, and that would be from structure abnormalities such as a smaller oral cavity, an enlarged tongue, and a narrowed nasal passage, which can contribute to airway obstruction. So another common abnormality in Down syndrome is hypotonia. In an article by Mark Latosh et al., he states, well, they state, virtually all papers on motor control, motor development, and motor learning in Down syndrome mention low muscle tone or hypotonia as a major contributor to the typical differences between movements performed by persons with and without Down syndrome. So hypotonia is when they have reduced muscle tone, and it can affect muscles involved in breathing, so that could lead to weaker respiratory muscles and then potentially affect the ability to maintain the proper airflow that you need. There are also specific respiratory issues that are prevalent among individuals with DS, like obstructive sleep apnea and respiratory infections. OSA is a condition when upper airway obstruction during sleep leads to pauses in breathing and disturbs sleep patterns. So according to breathing in the population with Down syndrome, there is a long list of risk factors, which are several congenital and acquired airway abnormalities, and they seem to be pretty common. The respiratory infections are due to individuals with DS being more susceptible to them because of their weakened immune system, because all people with DS happen to just have a weakened immune system. So this can further compromise the respiratory function in general. Due to the individuals with DS having compromised respiratory function, they're also at a higher risk for developing pulmonary issues, which could be like pulmonary hypertension or respiratory issues that are recurrent, like pneumonia or bronchitis. Pulmonary hypertension is a condition where high blood pressure affects the arteries in the lungs, which in turn could possibly impact breathing efficiency. So there are a lot of different risk factors and a lot of different issues that could be had from having Down syndrome. Moving on to Unit 3, phonation. So the larynx sits at the top of the trachea and below the pharynx, so it is part of the upper respiratory tract. Respiration and phonation are sequential stages of the speech chain because respiration begins with inhalation, involving the intake of the air through the nose and the mouth, which is passing through the larynx and trachea into the lungs. Phonation follows respiration, so like respiration happens first and then phonation follows directly after. And it involves the production of sound through the vibration of the vocal cords, which is within the larynx. So the respiration and phonation work together to create the vocal sounds. The larynx plays an essential role in speech production because it controls the vibration of the vocal cords, which in turn produces sounds based off of how the muscles and cartilages adjust. And within the larynx to produce the sound, so muscles and cartilages that are involved with producing voice, this is the vocal cords, the thyroid-retinoid muscle and the cricothyroid muscle and also the epiglottis, arytenoid, and thyroid cartilages. So for the vocal cords, they are the primary structures involved in sound production and they consist of muscles and ligaments within the larynx. And the thyroid-arytenoid muscle controls tension in the vocal cords. The cricothyroid muscle is responsible for adjusting the length and tension of the vocal cords. And the epiglottis, arytenoid, and thyroid cartilages help in controlling the position and the tension of the cords. So now we're going to move into what the stages of phonation are. There are three stages, which are initiation, sustained, slash continuation, and termination. So for initiation, there are three different types of vocal attacks, which a vocal attack itself is a movement of the vocal folds into the airstream for the purpose of initiating phonation. There's a simultaneous vocal attack, which is a coordination of adduction and expiration so they can occur simultaneously. There is a breathy vocal attack, which is where the airflow starts prior to adduction. And the glottal attack, which is the expiration that occurs after adduction. And so moving on to the second stage, which is sustained phonation, the vocal folds are held in place during the sustained phonation through the muscles of adduction and the thyrovocalis and thyromuscularis provides stability of the vocal folds during sustained phonation. These muscles are different from the muscles of adduction. It's a steady state phonation to control the fundamental frequency and stabilize the intensity. And it is not due to repeated adduction or abduction. It is maintenance of laryngeal posture. And the last stage is termination, which refers to the movement at the moment, sorry, the vocal folds stop vibrating and the sound production stops. So this occurs when the muscles controlling the vocal folds relax, which causes them to separate and stop vibrating. And the duration of the stage depends on the speech or vocal adjacent that's being produced. It all depends. Moving on to some of the principles. So there's the Bernoulli's effect and the myeloelastic aerodynamic principle. So Bernoulli's effect describes the velocity of airflow between the vocal cords, which causes a decrease in air pressure. The decrease in air pressure pulls the vocal cords together. And this effect contributes to the vibration of the vocal folds, vocal cords during phonation. So an example of this is how an airplane flies. So as air flows over the wings of the plane, it travels faster, like over the curved upper surface compared to the flat lower surface. So the faster moving air results in lower pressure and the pressure above the wing becomes relatively lower than the pressure beneath it, which creates the lift. It's the principle that helps the plane overcome gravity and fly. So I have a quote here from one of our PowerPoints about Bernoulli's effect. It says, given a constant flow of air or fluid at a point of constriction, there will be a decrease in air pressure perpendicular to the flow and an increase in velocity of the flow. And then looking at the myeloelastic aerodynamic principle. So this explains how the interaction between muscular tension and the flow of air leads to the vibration of the vocal cords. So muscles control the tension of the cords and airflow through them causes vibration, which generates the sound. An example of this would be like if I was producing the vowel sound E, like in the word beat. So when someone articulates this sound, the vocal folds and the larynx come together and then air passes through the little gap, which sets the vocal cords into the vibration due to the aerodynamic forces of the airflow. And then this vibration creates sound. So that is how we are able to make the E sound in beat. And moving on to the last part of how Down syndrome impacts these areas. So individuals with Down syndrome may experience certain physiological differences, which can affect their speech production, including aspects related to the larynx and the phonation. So the reduced muscle tone, which we talked about earlier in hypotonia, is common in Down syndrome. And this can affect the muscles involved in phonation as well, not just for respiration. So it can lead to weaker control and coordination of the muscles responsible for regulating the vocal fold tension and the movement during phonation. So obviously, since DF can impact the respiratory system, it can affect the airflow necessary for the vocal fold vibration during phonation. According to Mary T. Lee et al. in the article Intonation and Phonation in Young Adults with Down syndrome, based on acoustic analysis, young adults with Down syndrome demonstrate a reduced overall pitch range, OPR, compared to typical speakers. So this means that the individuals with Down syndrome tend to have a more limited variety or variation between their highest and lowest pitches when they speak. This article also mentions a reduced lexical pitch range, OPR, which indicates that within their speech, the pitch variation used across different words or phrases is somehow narrower compared to what they might observe in people without Down syndrome. So what they found indicates that there might be a limitation or reduced variability in the pitch range and variation used by individuals with Down syndrome during speech, which can impact the intonation and phonation aspects of their communication. And then for my references, I just want to make sure that I have said all of them. I know I didn't really say them throughout this, but I want to include them at the end. I do have my reference page, but Bhartisaghi, I have her article, which is Brain Circuit Pathology in Down syndrome from Neurons to Neural Networks. We have Feeley, Monica Feeley, who has the article Cardiovascular Complications of Sleep Disordered Breathing in the Population with Down syndrome. We have Li, which is the Intonation and Phonation in Young Adults with Down syndrome. I also had a page that was from the National Down Syndrome Society, just to learn more about Down syndrome portion of this project. And then I obviously included all of my citations of Professor Differding's lectures and PowerPoints. So thank you so much.
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