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The central nervous system (CNS) is the part of the nervous system that includes the spinal cord and the brain. The CNS's primary function is to integrate all of the input it receives from other body components. It also plays an important role in the synchronization of body functions in order to improve the body's reaction to the information obtained.
As previously said, the CNS is made up of two main components: the spinal cord and the brain. The brain is protected by the cranium and is sealed within the skull. The brain is divided into two major parts namely the gray matter and the white matter (Canadian Cancer Society, 1). In addition, the gray matter is made up neurons (nerve cells) whose main duty is the transmission of all the information either in chemical and electrical forms to the brain. The transportation of the signal takes place through synapses. On the other hand, the white matter comprises of the oligodendrocytes (a form of neuroglia) whose main role is to insulate and offer support to the axons. Axons (nerve fibers) are components of the neurons, and their role is to ensure that information is transmitted across the various neurons successively.
The spinal cord emanates from the skull’s base and ends on the lumbar vertebra. The spinal cord consists of numerous spinal nerves whose role is to connect it to the muscles, joints and all other parts of the body. The spinal nerves play a significant role in transmitting any sensory information regarding any stimuli to the brains for either involuntary or voluntary measure to be adopted (which makes the body withdraw from any danger). All the spinal nerves transmit the motor and sensory information from the outer body to the sensory neurons that in turn transmit it (the information) to the CNS. However, the spinal nerves can also be used in the transmission of information from the CNS to the motor neurons that in turn transmit the data to the periphery.
Physiology of the CNS
The CNS works for hand in hand with the PNS (peripheral nervous system), which comprises of nerves that emanate from the spinal cord and are used in the transmission of information from the brains to the other parts of the body. The continuous interaction of the CNS and the PNS is what enables an individual to carry out his/her respective actions of daily living such as walking, eating, or even talking.
Physiology of the Brain
Figure 1: The central nervous system (CNS). Image location http://www.cancer.ca/en/cancer-information/cancer-type/brain-spinal/brain-and-spinal-tumours/the-brain-and-spinal-cord/?region=on
As illustrated by the diagram, above, the brain is made up of various parts key among them the cerebrum, which is the biggest part of the brain. The cerebrum is also divided into two major parts; the right cerebral hemisphere and the left cerebral hemisphere and the two are connected by a group of nerve fibers known as the corpus callosum (Canadian Cancer Society, 1). The gray matter is the outer surface of the cerebrum, and its role is the control the activities of the brain. The white matter (the inner part of the cerebellum) enhances the communication between the spinal cord and the brain through the axons. The cerebellum is further divided into four parts (lobes) namely the temporal, the occipital, the frontal, and the parietal. The occipital lobe is responsible for the control of an individual’s lobe. The parietal lobe maintains the control of the pain, pressure, and even sensation that may arise as a result of being touched and also controls an individual’s level of comprehending various shapes and sizes. On its part, the frontal lobe controls an individual’s movements, emotions, memory retention and even intelligence levels.
Figure 2: Parts of the cerebellum. Image location http://www.cancer.ca/en/cancer-information/cancer-type/brain-spinal/brain-and-spinal-tumours/the-brain-and-spinal-cord/?region=on
The cerebellum is the second largest part of the brain and is situated at the back side of the brain. It is also divided into two hemispherical parts, and its role is controlling the posture, balance, the reflex actions and the movement of a person. Also, the cerebellum takes charge of the complex activities done by an individual such as talking and is also responsible for the gathering of information from all over the body. The brain stem comprises of nerve tissues that join the spinal cord and the cerebrum and also transmits information between the brain and the body parts. The brain stem comprises of; the medulla oblongata, the midbrain, and the pons. The role of the brain stem is to control an individual’s blood pressure, heart beats, body temperatures, the rate of breathing as well as the thirst and hunger feelings.
The Spinal Cord
The spinal cord can be sub-divided into five major parts as follows;
The upper part is referred to as the cervical cord and emanates from the skull’s base and ends in the low area of the neck. The second part is referred to as thoracic part of the spine, which ends at the mid-back and starts at the shoulders’ area (Canadian Cancer Society, 1). The lumbar part of the spine is next, it ends at the hip and starts at the mid-back. The following part is referred to as the sacrum and is the base part of the spinal cord. Finally, the spinal cord has a coccyx, which is its end (the ‘tail-bone’).
Figure 4: The spinal cord. Image location http://www.cancer.ca/en/cancer-information/cancer-type/brain-spinal/brain-and-spinal-tumours/the-brain-and-spinal-cord/?region=on
The CNS and the Maintenance of the Body Homeostasis
Homeostasis refers to the maintenance of all chemical reactions in a body at a state of balance (an equilibrium point). Therefore, the components of the body have to keep on adjusting the body processes so as to ascertain that a state of equilibrium is maintained all through. One of the major components that take charge of the maintenance of homeostasis is the CNS. For instance, when an individual is feeling cold the skin receptors will garner the information that the temperatures are relatively low, hence, an individual is feeling sick. The neurons will, in turn, transmit the information to the brain, which triggers the hypothalamus – a part of the brain that is responsible for controlling homeostatic processes such as hunger and body temperatures – into action. The hypothalamus can dictate the pituitary gland to produce thyroxine, norepinephrine, and even epinephrine hormones that lead to an increase in the production of heat within the body. The heat produced may eventually make the person start sweating, which implies that the body temperatures would have been restored to the usual levels.
The CNS is also mandated to ensure that the glucose levels in the body remain stable all through. The neurons might transmit information to the brain regarding the long-term energy storage of the body as instigated by the leptin and insulin hormones. On the other hand, the information that is related to the short-term operations of the body is transmitted through signals that are related to the intake of glucose (Morton & Schwartz, 1). On receiving such information, the brain puts in place measures that are anchored on the regulation of the use of energy or food intake. To ensure that homeostasis is restored in case an individual is experiencing low energy levels, the brain may; limit the use of the available energy (by making an individual inactive), fasten the production of glucose within the body (endogenous production of glucose), or even dictate an individual to eat some food. Therefore, the brainstem might dictate one to consume more food to make sure that the required energy is produced (Morton & Schwartz, 1). On the other hand, if the energy level within the body is deemed to be high the brain will ensure that the body is activated to ore energy consuming activities such as walking, running among others. Also, the brain will also limit the potential of the secretion of the endogenous glucose and also influence the person to refrain from taking any food by ensuring that he/she feels completely satisfied.
Modifications of the CNS
Despite being a very sensitive part of the human body, the performance of the CNS can be improved through various actions. Scientists have proposed that the brain can be modified through a cognitive fitness process while the spinal cord can be modified by reflex conditioning.
The cognitive fitness process does not change the anatomy of the brain. However, it has been termed as a favorable form of improving and enhancing the welfare of the brain by making sure that at least almost all the important parts of the brain remain engaged at any one time (Goldberg, 249). In addition, scientists argue that mental exercises are also a favorable measure of protecting an individual from dementia. As they carried out the research, the scientists from Netherlands Institute for Brain Research in Amsterdam claimed that the mental exercises play a key role by ensuring that degeneration in the brain cells was delayed. They, thus, pointed out that just as physical fitness is deemed as a perfect way of boosting one’s physical well-being, cognitive fitness should also be adopted as a means of enhancing the well-being of an individual’s brain.
Brain modification through the cognitive process is also deemed as a favorable measure of enhancing homeostasis within the body. For instance, when an individual is having higher amounts of glucose within their body, the brain might dictate that exercising is the best way to restore the body to its normal condition. While exercising, the hippocampus (a part of the brain) actively responds to aerobic respiration. Since it is partly responsible for memory retention, exercising helps it to boost its memory potential. Since the body will be experiencing a shortage of oxygen supply, the brain stem will dictate the breathing muscles to relax and contract at a higher rate so as to increase the rate of oxygen supply within the body. The heart will also be pressured to increase its blood pumping rate so as to ensure that oxygen is supplied to all body parts at a faster rate. In the process the excess glucose within the body will be broken down into water and carbon dioxide, hence, leading to a restoration of the normal body glucose levels.
The reflex conditioning of the spinal cord is deemed as a favorable means of inducing spinal cord plasticity, which in turn improves locomotion. The technique is also termed as a favorable means of enabling people function as normal after suffering a spinal cord injury (Chen, Chen, Wang, Thompson, Carp Seal & Wolpaw, 1). Reflex conditioning may lead to long-term (or short-term changes) in the morphology of the spine as it may lead to the extinction of the dendritic spines. The spinal plasticity as led to the invention of the ‘homeostatic plasticity,’ which is a plasticity mechanism of regulating homeostasis. However, to enhance homeostasis, it is guided by the hypothalamus, which in turn dictates whether some activities (such as eating) should be performed so as to maintain the usual body condition.
To sum it all, the CNS – which is made up of the spinal cord and the brain – are key components of the body and are effective in the sustenance of homeostasis. The brain does so (maintain homeostasis) by dictating whether the body should carry out some activities. For instance, in case the blood sugar of a person is quite low, the brainstem might dictate that he/she takes some food so as to boost it or even refrain from engaging in activities that would lead to the consumption of high amounts of energy. Various modifications can also be done on the CNS to improve its functioning; the modifications can be done either through the cognitive fitness program (of the brain) or reflex conditioning of the spine.
Canadian Cancer Society. ‘Anatomy and physiology of the brain and spinal cord.’ Canadian Cancer Society, 2017, http://www.cancer.ca/en/cancer-information/cancer-type/brain-spinal/brain-and-spinal-tumours/the-brain-and-spinal-cord/?region=on. Accessed 7 May 2017
Chen, Xiang Yang, et al. "Reflex conditioning: a new strategy for improving motor function after spinal cord injury." Annals of the New York Academy of Sciences 1198.s1 (2010): E12-E21.
Goldberg, Elkhonon. The new executive brain: Frontal lobes in a complex world. Oxford University Press, 2009.
Morton, Gregory J., and Michael W. Schwartz. "Leptin and the central nervous system control of glucose metabolism." Physiological Reviews 91.2 (2011): 389-411.
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