(a)Healthy nervous system
Firstly, a nervous system is responsible for homeostasis. It is an interconnected system that has larger systems that are also made up of smaller systems that perform specific functions. The functions of any healthy nervous system is based on either integrative, motor or even sensitive functions. The sensory function of the system is that it makes use of several sensory receptors to assess the different changes that happen in and outside a person’s body. The changes are regarded as stimuli. The information that is acquired by the neurons in the sensory input. The healthy function based on integration is that the system processes then moves to the interpretation step of the input obtained by the neurons. What follows is the effectiveness of decisions on what one does at a specific time becomes the integration part. The third function is the motor function where information is sent to the effectors that respond correctly. The effectors would perform glandular secretions or even contract muscles.
The brain areas that pertain to coma include the cerebral cortex and areas located in the medial and upper thalamus. The RAS is responsible for the behavior on wakefulness and also maintaining the brain’s cerebral cortex (Tapia et al., 2013). Also, the brain regions of the RAS occur lesions causing the severe cerebral hemispheric damages when a coma happens. Suppression occurs on the thalamocerebral due to toxins or even drugs. The RAS is not affected by the lesions found in the cerebral hemispheres but may be affected by the mass of lesions on a single portion of the brain to cause a coma due to the compression of the upper brain stream.
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Functions of the spinal cord
The spinal cord extends from the brain (Bosma & Stroman, 2015). Messages are conveyed to the brain and returned through the spinal cord as it has nerves responsible for the messages. The nerve impulses that reach it are transmitted to the brain. Secondly, the spinal cord is responsible for automatic actions due to its reflex action. The reflex action is activated through a reflex arc that acts as its pathway. Also, the spinal cord is responsible for the upright posture of the human and ensures their flexibility.
(b) Description of Coma
Coma is the state of unconsciousness or a body’s unresponsiveness to any external stimuli. Coma is treated as an emergency that needs an intervention when the cause is unknown. Coma is unarousable unresponsiveness whereby a patient lies having closed their eyes and no nothing about their surroundings. The patient has a deficiency of sleep-wakefulness' cycles that is featured in a vegetative state (Huang et al., 2014). The result is due to the failure of the cortex and the RAS. Coma can occur also due to either the damages to the white matter or bihemispheric cortical to various axonal injury. Other causes that result in coma are such as trauma. When there are swellings to the brain due to trauma, then the brain fluid moves up against the person’s skull. Then the swelling causes the brain to malfunction and damage the RAS that takes responsibility for arousal and the body’s awareness. Even though the coma patients rarely wake up, they follow sleep patterns as usual. Automatic breathing occurs even though the mental ability faces suppression.
Additionally, coma can result due to the brain layers bleeding. The bleeding emerges from the blood pressure becoming high which affects the brain. Lack of proper amounts of oxygen causes coma. The cause is that the brain cells are deprived leading to their eventual collapse and then affects the brain tissues (Brogan & Provencio, 2014). The brain injury could arise from cardiac arrest, drug overdose or even direct poisoning. Different coma types are such as the locked-in syndrome where an individual is completely paralyzed yet stays awake with open eyes. A vegetative state is also common where the patient undergoes severe unconsciousness and cannot even move voluntarily (Huang et al., 2014). In the vegetative state, the patient has sleeping cycles and breathes. The assessment of the cognitive function of the comatose patients is hard as few voluntary movements are easily exhausted and not consistent. The brain’s activity quantification from the disorder would differ by an incomplete or a brief eye blink. Some causes of coma are based on infections related to either meningitis or severe encephalitis. Hyperglycemia is also a cause that results due to high diabetic nature of a patient or even hypoglycemia when the blood sugar is reduced (Wilinska et al., 2009). The result could lead to a coma.
(c and d) Structures affected by the disorder
Mechanisms that are responsible for the awareness and level of alertness are found in the RAS. If RAS dysfunctions, then it means that the alertness mechanisms have been damaged. When the damage to the patient’s brain is much, then brain herniation has led to the damages based on neurologic deterioration since it results in vascular and neuronal cell dysfunctions. Also, the brain tissues are compressed and the apoptosis autophagy pathways are activated. Since there is often the rigidity of the skull after infancy, swellings or the skull’s intracranial masses increases their pressure leading to brain tissues protrusion through the intracranial barriers such as the falx cerebri or the tentorial notch. The pressures lead to abnormalities. Other structures that are affected by coma are the posterior artery of the cerebral and the ipsilateral nerve. Later, the upper stem of the brain and the thalamus region peduncle due to the transtentorial herniation. During the subfalcine herniation, mass increment occurs around the cerebral hemisphere as the cingulate gyrus is moved beneath the falx cerebri. In the process, the anterior arteries of the cerebral are trapped leading to infarction related to the paramedian cortex. Another damage occurs when an upward herniation occurs that makes mesencephalon vasculature to distort as it compresses the cerebral vein. The figure shows the structure of the brain affected by the unconsciousness:
Fig 1: Brain structure
Overall effect on the Nervous System
Due to the damage of the upper stem of the brain, the pupils are unable to move and are mid locked with no responses to light reflexes. The reason is due to the metabolic or the patient’s disorder that leads to parasympathetic and the subsequent sympathetic pupillary state. The nervous system is unable to respond to eye positions due to the locked pupils. Moreover, there are cases of irregular oculovestibular reflexes and negative myoclonus. The nervous system cannot respond to breathing cycles accurately. The compression of the brain stem makes the nervous system fail to respond to the eye blinks leading to contralateral hemiparesis also. Lesions that happen to the brain stem makes the nervous system have abnormalities in the oculovestibular and oculocephalic reflexes (White, 1988). Decorticate rigidity occurs because of the upper lesions while decebrate rigidity occurs de to the pontine lesion. The stimuli response becomes ineffective. A patient at comatose may experience may lack or respond to different stimuli such as pain in either abnormal extension or flexion. Also, there could be cases of inappropriate conversations that lead to inappropriate responses from the patient. The patient’s eyes may be open though they blink at the eye’s baseline. Some patients may respond to different stimuli such as pain exerted at the sternum. Also, the nervous system may have responses such as early oculomotor and pupillary signs or even absent movements of the eyes.
(e) How the body compensates for the homeostatic imbalance
The body compensates for such homeostatic imbalances through the responses in lower consciousness levels, eye responses, tendon reflexes and the motor functioning. The consciousness of the patient is compensated through some verbal commands and noxious stimuli. The body attempts to respond to the supraorbital ridge pressure exertions. The pressure exerted to the region or the sternum is a measure taken by the patient to check the patients’ level or responsiveness. Additionally, the body would compensate the coma cases through the extraocular movements, neuro-ophthalmic reflexes or fundi (Moss et al., 2012). The body tries to compensate for the imbalances when fundi is examined. Intracranial pressure increment causes changes in the dilated capillaries and often disk hyperemia. If no reflexes happen, then the eyes would remain unmoved even if the head is moved. Additionally, the respiratory rate may have periodic breathing cycles. After some time, a respiratory arrest occurs during the homeostatic imbalance. The body tries to perform compensations through the cerebral flow of blood by vasoconstricting that would either lead to or avoid cerebral ischemia. During the coma state when serious prognostic measures are done, then the body would respond effectively. Such responses are speech returns even though incomprehensible, the patient may follow partially to certain commands and sometimes the eyes may or may not track movements.
References
Bosma, R. L., & Stroman, P. W. (2015). Spinal cord response to stepwise and block presentation of thermal stimuli: A functional MRI study. Journal of Magnetic Resonance Imaging, 41(5), 1318-1325.
Brogan, M. E., & Provencio, J. J. (2014). Spectrum of catastrophic brain injury: Coma and related disorders of consciousness. Journal of critical care, 29(4), 679-682.
Huang, Z., Dai, R., Wu, X., Yang, Z., Liu, D., Hu, J., ... & Wu, X. (2014). The self and its resting state in consciousness: an investigation of the vegetative state. Human brain mapping, 35(5), 1997-2008.
Moss, H. E., McCluskey, L., Elman, L., Hoskins, K., Talman, L., Grossman, M., ... & Liu, G. T. (2012). Cross-sectional evaluation of clinical neuro-ophthalmic abnormalities in an amyotrophic lateral sclerosis population. Journal of the neurological sciences, 314(1-2), 97-101.
Overview of Coma and Impaired Consciousness - Neurologic Disorders - MSD Manual Professional Edition. (2019). Retrieved from https://www.msdmanuals.com/professional/neurologic-disorders/coma-and-impaired-consciousness/overview-of-coma-and-impaired-consciousness
Tapia, J. A., Trejo, A., Linares, P., Alva, J. M., Kristeva, R., & Manjarrez, E. (2013). Reticular activating system of a central pattern generator: premovement electrical potentials. Physiological reports, 1(5).
White, A. (1988). Overdose of tricyclic antidepressants associated with absent brain-stem reflexes. CMAJ: Canadian Medical Association Journal, 139(2), 133.
Wilinska, M. E., Budiman, E. S., Taub, M. B., Elleri, D., Allen, J. M., Acerin, C. L., ... & Hovorka, R. (2009). Overnight closed-loop insulin delivery with model predictive control: assessment of hypoglycemia and hyperglycemia risk using simulation studies.
