This platform is to present my introduction to neuroscience course summary, shorts notes and solutions that were useful during the course., Feel free to send your comments and suggestions the the github issuse pages for this site.
The nervous system can be divided into 2 major subdivisions:
1. The central nervous system (CNS)
2. The peripheral nervous system (PNS)
NB: The peripheral nervous system(PNS) connects the CNS to the rest of the body.
The sympathetic part of the autonomic nervous system is considered a “flight and fight” system basically because it is organized to mobilize the body for activity. Upon the perception of a threat, the nerve fibers of the autonomic system get activated and the part of the brain that is involved in emotional processing; the amygdala is “informed”. The images and sound are interpreted by the amygdala, and should this signal be perceived as danger; a distress signal is quickly sent to the hypothalamus. The hypothalamus, via the nervous system, then sends a signal to the adrenal glands. The adrenal glands in response, pump adrenaline into the bloodstream.
The circulation of adrenaline in the blood instigates several physiological changes. Adrenaline in the blood stimulates the release of glucose and fats that have been stored in various sites of the body. This creates a surge of nutrients in the blood which makes available energy to all parts of the body to either fight or flee the threat.
Characteristic of this fight/flight response is tachycardia (an increase in heart rate), increased blood glucose concentration, anxiety, increased perspiration rate, tremor, and opening of the small airways of the lungs which increases the amount of oxygen breathed in. With this increased oxygen in the system, alertness becomes sharper. When the initial adrenaline in circulation reduces, the HPA axis (hypothalamic-pituitary axis) is activated. This axis keeps flight-and-flight response activated. Should the threat persist unabated, corticotropin-releasing hormone (CRH) gets activated. CRH then travels to the pituitary gland to stimulate the release of cortisol, keeping the body alert. When the threat is abated, the parasympathetic nervous system which acts to calm the body down or return the body to a normal state kicks in.
One inhales the virus, and it gets into the mucous membrane of one’s throat. The virus then moves down the respiratory tract which includes airways of the lungs, nose and throat. These airways have the ACE2 receptor which is known to be the functional receptor of SARS-CoV. The observed breathing defects seen in COVID patients can be attributed to two main lung complications.Pneumonia and bronchitis. In the case of COVID-19 pneumonia, both lungs are affected. The air sacs in the lungs become filled with fluid. This thus, reduces the ability of the lungs to take in oxygen which leads to shortness of breath. When there is COVID bronchitis, there is an excess amount of sputum that is produced in the airways. This buildup of sputum narrows the airways, leads to congestion in the chest and consequently, difficulty in breathing. Sonu et. al, 2020 in their paper: “Is the Collapse of the Respiratory Center in the Brain Responsible for Respiratory Breakdown in COVID-19 Patients?” Have suggested a possible mechanism of viral infection of the cardiorespiratory center in the brainstem. According to this study, using SARS-CoV-2, the main route of entry of the virus is through the olfactory mucosa
of the upper nasal cavity. The virus then gets through to the olfactory axons, and projects to the olfactory epithelium and olfactory bulb. The virus then moves deeper into the brain areas such as the brainstem and thalamus via a trans-synaptic migration to target the pre-Botzinger complex. The pre-Bötzinger complex (preBötC) is a neural network responsible for inspiration during respiratory activity (Smith et. al,1991). This in effect causes the breakdown of the respiratory center of the brain which leads to death in some cases.
The enteric nervous system (ENS) is a division of the autonomic nervous system whose component neurons lie within the walls of the digestive organs (esophagus, stomach, intestines, pancreas, gall bladder, and pancreato-biliary ducts). The enteric nervous system contains entire nerve circuits for digestive organ control and can function autonomously (Furness, 2007). The main argument in support of the position that the enteric nervous system is our second brain is that it functions independently of the brain and spinal cord. In that, it has been found to contain more neurons than the entire spinal cord and has its own web of neurons it interacts
with. The other argument in support of the ENS as our second brain is that it functions similarly to the neural networks in the brain and spinal cord. The basis for this position is that the neurons in the ENS communicates similarly to how the neurons in the brain communicates.
COVID-19 is predominantly characterized by respiratory symptoms including fever, cough, and dyspnea (Diao et al., 2020). A study by Song et al. in 2020 revealed that some COVID-19 patients experience digestive symptoms. Angiotensin-converting enzyme 2 (ACE2) is known to be the functional receptor of SARS-CoV. It is reported that the expression of ACE2 is approximately a 100-fold higher in the gastrointestinal tract than in the respiratory system. This discovery presents a strong support for the position that SARS-COV2 affects the digestive system and thus SARS-CoV2 not only to be breathable but also swallowable. When one takes up that virus through serval means and it ends up in the mouth, it infects saliva. With the vast amount of ACE2 receptors in the digestive system, it consequently becomes a breathing ground for the virus. This then disrupts the intestinal immune balance. This disruption of the intestinal immune balance further triggers the release of pro-inflammatory cytokines, expanding the state of excessive inflammation and eventually leading to death (Jin
X. et al., 2020).
Case: Terri Schiavo case
Terri Schiavo was a 41-year-old female found in a persistent vegetative state. She fell into this state in 1990 and remained in this state for 15 years. This case was at the center of a political, legal , and media tempest over the removal of a feeding tube (Quill, 2005). The husband and parents could not find common ground in deciding on whether or not to continue her sustenance through hydration and nutrition and sought resolution in a court of law. A persistent vegetative state (PVS) is used to describe a condition where there is a disorder of
consciousness that patients with severe brain damage find themselves in a state of partial arousal as opposed to full, true awareness. Patients with PVS have no cerebral cortical function (they are unconscious and unaware) but exhibit irregular circadian sleep-wake cycles with either full or partial hypothalamic and brainstem autonomic functions and persisting reflexes (Scully, 2014). She had an eating disorder that resulted in hypokalemia consequently triggering a cardiac arrest. She further developed hypoxic-ischemic encephalopathy and later lost her higher cortical function. What marked her persistent vegetative state was her periods of wakefulness which alternated with sleep, some reflexive responses to light and noise as well as some basic gag and swallowing responses. She however had no signs of emotion, any will activity , or cognition.
Diao K, Han P, Pang T, et al. HRCT imaging features in representative imported cases of 2019 novel coronavirus pneumonia. Precision Clin Med 2020;3(1):9–13.
Furness, J. B. (2007). Enteric nervous system. Scholarpedia, 2(10), 4064. Jin, X., Lian, J.-S., Hu, J.-H., Gao, J., Zheng, L., Zhang, Y.-M., et al. (2020). Epidemiological, clinical and virological characteristics of 74 cases of coronavirus-infected disease 2019 (COVID-19) with gastrointestinal symptoms. Gut 69, 1002–1009. doi: 10.1136/gutjnl-2020-320926
Quill, T. New England Journal of Medicine (2005) 352(16) 1630-1633
Scully, C. (2014). Scully's Medical Problems in Dentistry (Seventh Edition) (Vol. 13). (C. Scully, Ed.) Churchill Livingstone.
Smith, Jeffrey C., et al. "Pre-Bötzinger complex: a brainstem region that may generate respiratory rhythm in mammals." Science 254.5032 (1991): 726-729.
Song Y, Liu P, Shi XL, et al SARS-CoV-2 induced diarrhoea as onset symptom in patient with COVID-19Gut 2020;69:1143-1144.
Sonu Gandhi, Amit Kumar Srivastava, Upasana Ray, and Prem Prakash Tripathi
ACS Chemical Neuroscience 2020 11 (10), 1379-1381DOI:10.1021/acschemneuro.0c00217
Assume that the lesion destroyed all cell bodies, including those that project to the median eminence. Choose two major systems that would be affected and identify all hormones that might be involved, the neuroendocrine circuit, and their functions. When you describe the neuroendocrine circuit, please list all parts/cells involved. Also, how does the circuit communicate?
The arcuate nucleus (ARC) of the hypothalamus is particularly regarded as a critical platform that integrates circulating signals of hunger and satiety reflecting energy stores and nutrient availability. A lesion in the arcuate nucleus could principally result in obesity. Two major systems that might be affected are feeding and the reproduction system. In that, GnRH secretion will be impacted which consequently will affect the production of the follicle-stimulating hormone (FSH), luteinizing hormone (LH), and then inhibit the downstream production of the gonads. Hence, the production of the sex hormones (testosterone and estrogen) will also be affected. Feeding will be affected because the ARC has a high density of orexigenic peptide-producing neurons. The arcuate nucleus secretes GnRH and prolactin would ultimately be affected. These two hormones might be affected by a lesion in this area. Prolactin regulates lactation and as a result, a lesion in the ARC consequently would affect milk production as no signal will be sent for its release. GnRH causes the pituitary gland in the brain to make and secrete the luteinizing hormone (LH) and follicle-stimulating hormone (FSH). It is responsible for the production of testosterone in males
Assume that the lesion destroyed all cell bodies, including those that project to the median eminence. Choose two major systems that would be affected and identify all hormones that might be involved including the neuroendocrine circuit, and their functions. When you describe the neuroendocrine circuit, please list all parts/cells involved. Also, how does the circuit communicate?
A lesion in the Paraventricular nucleus (PVN) could lead to hyperphagia, polydipsia, poly urea and obesity as PVN neurons are important for the inhibitory control of food intake. In that, the PVN secretes oxytocin and vasopressin that increases the amount of solute-free water reabsorbed back into the circulation from the filtrate in the kidney tubules of the nephrons will not release and solute-free water will not be reabsorbed
back into circulation from the filtrate in the kidney tubules of the nephron, polyurea. Poly urea will then lead to polydipsia. When the PVN is lesioned, two major systems that might be affected are the circulatory system and reproductive systems. The hormones that might be involved in the circulatory system is vasopressin and that which is involved in the reproductive system is oxytocin. Oxytocin is known to stimulate uterine wall contractions and stimulate milk let-down in the mammary glands, thus affects the reproductive system. Vasopressin also constricts arterioles, which increases peripheral vascular resistance and raises arterial blood
pressure (Caldwell & Young, 2006), thus affects the circulatory system. These hormones are then stored in the secretory granules transported via the stalk to the pars nervosa. Oxytocin and vasopressin are finally released to the body.
Leptin and insulin are considered anorexigenic (appetite suppressant).
i. Leptin is secreted by adipose cells in proportion to overall body fat mass. A well-fed state leads to increase fat which in turn leads to an increased leptin secretion. Leptin enters the central nervous system and initiates a JAK or STAT second messenger pathway in the hypothalamus. It maintains homeostasis in response to high-fat levels through the following effects: Decrease food intake, increase metabolic rate, activity level , and temperature , and the inhibition of insulin synthesis and release. Leptin levels thus, indicate overall fasting or feeding state over many days. Leptin further, inhibits the stimulation of the lateral hypothalamus which in
effect inhibits the effects of ghrelin. The main effect(target) of leptin is the arcuate nucleus.
ii. Insulin is secreted by the pancreas, and it exerts its effect on olfactory bulbs and arcuate nucleus. When there is an increase in insulin secretion, the NPY-secreting cells of the arcuate nucleus are inhibited which consequently suppresses food intake.
ghrelin and peptide YY3-36 are considered orexigenic (appetite stimulant) hormones.
i. Ghrelin is released when the blood sugar level gets low, prior to feeding. It is released by the P/D1(distinctive endocrine cells) cells in the fundus of the stomach, targets the GHSR-1a (ghrelin/growth hormone secretagogue
receptor) , and acts in antagonism to leptin. An empty stomach activates its secretion. Upon its secretion, it exerts its orexigenic effects by binding to GHSR- alpha which is on the ventromedial nuclei. These nuclei as a result function to increase food intake.
ii. peptide YY3-36 is produced by the small and large intestines. After food intake, the concentration of peptide YY3-36 in the blood increases. Its thus, targets the arcuate nucleus and acts by inhibiting the appetite-stimulating NYP-secreting neurons of the arcuate nucleus.
The hypothalamus integrates feedback loops from target organs. Give an example of positive feedback and an example of negative feedback. Name the hormones involved in each and completely describe the anatomical circuits including releasing factors or neural inputs, pituitary cells/hormones, and target cells. Also, describe the general function of each of the two feedback circuits that you chose.
The release and response of oxytocin during childbirth is an example of a Positive feedback. The onset of the contraction of the uterus signals the body to release oxytocin. Oxytocin then travels to the uterus where it further stimulates contraction. The resulting contractions signals for the release of more oxytocin which stimulates contractions the more. which stimulates more contractions. This feedback loop continues until the baby is born which then stops contractions. This signals the body to stop the release of oxytocin.
The TRH-TSH-thyroxine system is an example of negative feedback. Negative feedback occurs when the output(s) of a pathway inhibits the inputs to the said pathway. An example of negative feedback is the control of the secretion of the thyroid hormone. In this, feedback loop, the hypothalamus contains neurons that secrete the thyroid-releasing hormone (TRH). The TRH then stimulates cells of the anterior pituitary to consequently secrete the thyroid-releasing-hormone. The TSH then binds to the receptors on the epithelial cells in the thyroid gland which stimulates the synthesis and secretion of thyroid hormones. This continues until a point when the concentration of thyroid hormones in the blood increases to a threshold. With the thyroid hormones at this concentration, TRH-secreting neurons in the hypothalamus become inhibited and stop the secretion of TRH.
. Caldwell HK, Young WS III (2006). "Oxytocin and Vasopressin: Genetics and Behavioral Implications" (PDF). In Lajtha A, Lim R (eds.). Handbook of Neurochemistry and Molecular Neurobiology: Neuroactive Proteins and Peptides (3rd ed.). Berlin: Springer. pp. 573–607. ISBN 978-0-387-30348-2.
Gil-Campos M, Aguilera CM, Cañete R, Gil A. Ghrelin: a hormone regulating food intake and energy homeostasis. Br J Nutr. 2006 Aug;96(2):201-26. doi: 10.1079/bjn20061787. PMID: 16923214
A. Two processing pathways originate from the primary visual cortex. Please name and describe each pathway, discuss the processing stages and divisions in each pathway, discuss the properties of neurons at various stages and identify functions associated with them. Finally, identify two clinical syndromes that are associated with damage to each pathway (a total of four).
The two processing pathways are:
. The ventral stream or “What pathway”
. The dorsal stream or “Where pathway”.
The ventral stream or “what pathway”, so-called due to its role in identifying objects is located at the junction of the occipital and temporal lobes. It carries information from the primary visual cortex to the temporal lobe.
The neurons in the parietal association cortex and superior and middle temporal visual association cortex (posterior parietal lobe and middle superior temporal gyrus and the superior part of the posterior inferior and middle temporal gyrus) have binocular receptive fields and process P-channel information about object location and M-channel information about object movement.
The dorsal stream or “Where pathway”, is so-called because of its involvement in analyzing the movement of identified objects. This pathway is thought to be involved with perceiving motion and spatial relationships between objects in the visual field. It comprises several cortical areas, including the medial temporal area (MT or V5), the medial superior temporal area (MST), and the ventral and lateral intraparietal areas (VIP and LIP).
At early stages in the ventral stream pathway, neurons are sensitive to specific types of visual stimulation. At later stages, neurons are increasingly sensitive to illusory contours which are implied by combinations of visual stimulation. At higher tiers of processing, silent areas surrounding the receptive fields of neurons augment the activity of stimuli in the receptive field – (i.e., figure/ground segregation). Neurons in the anterior 2/3rds of IT are sensitive to complex feature arrangements like objects and faces. Face selective neurons (patches) can be found in the lower bank of the STS in primates
B. Two clinical syndromes associated with damage to the Ventral Stream pathway are Agnosia and alexia. Two clinical syndromes associated with damage to the dorsal Stream pathway are Balint’s Syndrome and akinetopsia.
A. The difference between the exogenous and endogenous attentional systems.
The endogenous attentional system is driven by internal motivations and processes; our ability to voluntarily monitor information at a given location. It is of two types: covert and overt. The covert type is indirect, when you look at something from the corner of your eye without directly looking at it. Overt on the other hand is direct when you focus your attention on a target or location.
The exogenous attentional system on the other hand is driven by response to stimulus characteristics when something commands one’s attention; an involuntary, automatic orienting response to a location where a sudden stimulation has occurred. It is of two types: automatic and effortful. The automatic type refers to stimulus that grabs one’s attention. An example is something that really stands out. Effortful on the other hand, is when you look hard and search for something in the field of stimuli. It requires a lot of energy.
A. Describe Papez Circuit in terms of its anatomical divisions.
The Papez circuit begins and ends with the hippocampus. The entorhinal cortex (in the anterior parahippocampal gyrus) projects to the hippocampus. The hippocampus projects via the fornix to the mammillary nuclei. The mammillary nuclei project to the anterior thalamic nuclei via the mammillothalamic fasciculus. The anterior thalamic nuclei project to the cingulate gyrus. Finally, the cingulate gyrus projects back to the entorhinal cortex via the cingulum to close the Papez circuit loop.
Fisch, A. (2012). Neuroanatomy: Draw It to Know It. United Kingdom: Oxford University Press, USA.
The Oxford Handbook of Attention. (2014). United Kingdom: OUP Oxford.
This process can be divided into three phases;
Planning (of the idea)
Initiation
Execution.
In the planning phase, the movements (abstract thoughts) are planned in the cortex, as well as the basal ganglia and part of the cerebellum. In the initiation phase, the commands are then relayed via the corticospinal tracts (from the cortex to the spinal nerves) and the corticobulbar tracts (from the cortex to the cranial nerves) to the lower motor neuron that supplies the muscle.
Finally, for the execution phase, as the movement occurs, receptors in the muscle, the muscle spindle, Golgi tendon organ, joint receptors, and those in the skin are stimulated. This feed-back information is relayed back via sensory nerves to the cerebellum and the motor cortex, and the movements are adjusted to make it smooth and precise.
Decorticate and decerebrate posturing are abnormal posturing responses typically to noxious stimuli.
In decortication, there is decorticate posturing in which:
a. Upper limbs are flexed
b. lower limbs are extended with toes pointed slightly inward
c. The head is extended.
In decerebration, there will be decerebrate posturing in which:
a. Lower extremities are extended with toes pointed inward.
b. Upper extremities extended with fingers flexed and forearms pronate.
c. The neck and head are extended.
Historically, the cerebellum has been considered a motor structure. In that, a cerebellar damage leads to a marked impairments of motor control. The cerebellum works with other motor structures to modify the motor commands of the descending pathways to make movements more adaptive and accurate. The first thing required of the cerebellum is a “motor plan”. This involves the muscle that needs to contract, along with information about the needed intensity, duration, and strength to contract the muscle in question to do a given movement. The motor areas of the cerebral cortex, via relay nuclei in the brain stem, notify the cerebellum of their intent to initiate voluntary muscle contractions. At the same time, the cerebellum receives information from proprioceptors throughout the body (regarding tension in the muscles and tendons, and joint position) and from visual and equilibrium pathways. The cerebellum uses this information to evaluate the body’s position and
momentum (where the body is and where it is going). The cerebellar cortex then calculates the most optimal way to coordinate the force, direction, and extent of muscle contraction to prevent an overshoot, maintain posture, and ensure smooth, coordinated movements.
Finally, through the superior peduncles, the cerebellum dispatches to the cerebral motor cortex, its "blueprint" for coordinating movement. Cerebellar fibers also send information to brain stem nuclei, which in turn influence motor neurons of the spinal cord.