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This page contains abridged crux of lecture topics covered during the course.
Brain Anatomy
The brain is the concentrated mass of billions of neurons in the body. It processes signals from the environment consciously and unconsciously and splits the processing into regions that are specialized for specific functions. Specifically there are four lobes in the brain: frontal, parietal, occipital, and temporal. These lobes contain structures that connect to form various systems. One of the systems, the nervous system, is composed of a neural network of nerve tracts (nerve fiber bundles) connecting the regions of the brain. Since neurons don’t divide, supportive cells are needed to protect, help the neurons, and maintain the microenvironment, including astrocytes, microglia, ependymal, and oligodendrocytes.
Senses, Perception and Movement
The sensory cortex involves different parts of the brain and processes sensory stimuli, including visual, olfactory, auditory, and gustatory information. One of the senses, vision, is processed when light passes through the cornea and enters the eye through the pupil. The iris then regulates the amount of light entering the eye by changing the pupil size accordingly. The lens bends the light to focus on the retina and the electrical signals are then processed by the retina’s specialized cells (such as photoreceptors) and travel to the primary visual cortex for interpretation and perception via the optic nerves. For visual disorders, such as blindness in which the photoreceptors lose function (or genetic defects are involved), gene therapies and restoration of photoreceptors are possible treatments.
The central nervous system is responsible for movement, including voluntary movements, involuntary movements (reflexes). The autonomic nervous system controls involuntary movements such as reflexes, and the somatic nervous system controls voluntary movements.
Learning, Encoding, Retrieval and Discrimination of Memories
Memory is the ability to retain learned information through intact synapses of past events and to retrieve that information. Therefore, repetition of information helps an individual deeply understand the information and remember it since more connections/ engagement with more synapses are made within the brain. There are many types of memory based on the aspects of the information: working vs. long term, episodic vs. generic, explicit vs. implicit, and procedural vs. declarative. The encoding and storage of the memory depends on the following factors: time spent in working memory, rehearsal, attention and engagement, connection to past knowledge, and depth of processing. Furthermore, there are memory disorders such as anterograde amnesia in which new memories are unable to be formed after the brain injury (ex: Alzheimer's) and retrograde amnesia is the inability to retrieve old memories before the brain injury.
Aging and Memory
A process that continues throughout our lives is the brain’s continuous change. As used synaptic connections between regions of the brain get strengthened and unused synaptic connections are pruned, the aging process begins in the brain as early as 30 years of age but is noticed at 50 years of age. When processing speed reduces with age due to changes in the speed of neurotransmission, working memory also declines and the prefrontal cortex loses cells and mass. On a beneficial note, aging also strengthens an individual's ability to remember emotionally positive and personally relevant memories, allowing the ability to see the larger topic rather than focusing on only the details.
Neuronal cell determination & Brain development
Neuronal cell determination refers to how the neural system develops in terms of the development of specialized cell types (differentiation) after committing to a cell fate. There are two levels of commitment: specification and determination, meaning the degree that the cell can commit to a certain cell fate. Specification is reversible and means that the cell can differentiate autonomously when placed in a neutral environment. Determination may be irreversible and means that the cell can differentiate autonomously when placed into a different region.
Brain development can include synaptic pruning in which unused connections in the brain are pruned/removed, occurring in early childhood and adulthood (as we age). Most of the brain development occurs in the early stage of gestation since organogenesis is also occurring in the same period of time. Adolescence is the second critical stage since during this period, the brain’s complex functions develop depending on the surrounding environment.
Homeostasis
Homeostasis refers to maintaining the balance and equilibrium of the body’s tissues and organs, involving the cerebellum and hypothalamus. For instance, one’s circadian rhythm which consists of neurons in the hypothalamus coordinates daily life and keeps activity in sync with individualized day and night cycles. Furthermore, the neuroendocrine system refers to the connection between the nervous system and the endocrine system, in other words, the brain’s involvement in secreting hormones through the glands. In a chronic stress response, the adrenal glands release epinephrine and glucocorticoid hormones that could have negative effects due to overexposure, including an effect on development.
Childhood disorders
Childhood disorders include autism spectrum disorder (ASD), attention deficit hyperactivity disorder (ADHD), down syndrome, dyslexia, and epilepsy. ASD is diagnosed in an individual based on two main evaluation criteria which are impaired social communication and repetitive behaviors/narrow interests, and is due to partially genetic factors (rare mutations) and environmental factors. The diagnosis can be evaluated using a gaussian distribution which scales behavioral characteristics. ADHD is the most common childhood disorder, characterized by inattentiveness and hyperactivity. Individuals with down syndrome possess a third copy of all or part of chromosome 21 with symptoms including hearing loss, heart defects, and specific physical traits. Dyslexia is the most common learning disability, characterized by a clear difficulty in reading. In epilepsy, seizures occur without a medical condition and result from overactivity in the brain (overfired signals). Thus, further research is being done regarding how epigenetics can play a role in the development of childhood disorders, specifically, how the environmental factors may influence gene expression.
Psychiatric disorders
Psychiatric disorders include anxiety disorders, post-traumatic stress disorder (PTSD), obsessive-compulsive disorder (OCD), schizophrenia. and mood disorders such as major depression and bipolar disorder. Psychiatric disorders can result from genetic factors and environmental factors such as life circumstances. Medical conditions, and personal relationships. Anxiety disorders are characterized by uncontrollable anxiety, including PTSD and OCD and are seen most commonly in women. More specifically, OCD is uncontrollable thoughts followed by repeated compulsions due to signaling errors between the basal ganglia and the brain. PTSD is caused particularly by traumatic events that cause symptoms such as flashbacks, nightmares, memory loss, etc. Moreover, major depression is characterized by symptoms such as sadness, loss of appetite, irritability, sleep issues, and weight change, and additionally, bipolar disorder is characterized by intense mood changes from manic to depressive episodes.
Neurodegenerative Disease
Neurodegeneration is the gradual loss of nerve structure and function over time. Neurodegenerative diseases can include Alzheimer's disease, Parkinson's disease, Huntington's disease, Multiple Sclerosis, and Amyotrophic Lateral Sclerosis (ALS). Parkinson’s disease is characterized by symptoms including depression, sleep problems, increased sweating, hypotension, and respiratory problems. This disease also causes the death of neurons, including those that release dopamine which affects reward centers and movement. Huntington’s disease is primarily a genetic disease due to the dominant gene on chromosome 4, which codes for the huntingtin protein that has a role in the brain. ALS arises due to neuronal death, specifically, the loss of upper and lower motor neurons. This disease is characterized by head and neck, respiratory, upper body, and lower body symptoms such as weakness and paralysis.
Genetics of Neurological Disease
Nervous system disorders have been attributed to genetic risk factors. Monogenic risk score is when one gene contributes to the risk of developing the disease, whereas polygenic risk scores is when multiple genes contribute to the risk of developing the disease. Some genetic risks may or may not be expressed due to incomplete dominance, known as incomplete penetrance of genetic factors. Such occurrences along with high rates of risk factor mutations in genes result in a genetic explanation for neurodegeneration that is multi-factorial, meaning that to study the genetic risk factors, a large sample study done over a long period of time needs to be conducted. Therefore, to study the genetic components, future directions include employing a decentralized approach to conduct a wider range of research with a larger sample size.
Molecular Neuroscience
Molecular neuroscience is the branch of neuroscience that investigates the molecular biology of the nervous system.
Research in this field primarily focuses on signaling pathways in the brain and molecular neuroanatomy, including firing patterns of neurons and synaptic connections. Such molecular insight can help to understand neurodegenerative diseases and neuropsychiatric disorders.
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