Understanding The Nervous System: Structure And Function Of The Brain And Spinal Cord Essay.

Components of the Nervous System

Nervous system is comprised of the spinal cord and brain, which forms the central nervous system. The spinal and cranial nerves, peripheral ganglia, constituting peripheral nervous system. Brain is covered by the hard bony skull. The most complicated system of all is the Brain. The spinal cord, brain, spinal and cranial nerves and peripheral ganglia are encased in hard connecting network like tissue. The safety sheaths around the spinal cord and brain are known as meninges. Meninges consists of three layers- Dura mater, pi mater and arachnoid membrane. There is a gap between the pia mater and arachnoid membrane referred to as subarachnoid space. The subarachnoid space is occupied with a liquid called cerebrospinal fluid (CSF).

The Brain is a large mass of neurons, glia and other supporting cells. These cells work together to perform on crucial job inside the nervous system. The Neurons gain support from glial cells structurally, maintaining the integrity of long-term neurons and neurons controlling glial cell behaviour. Glial cells are divided into several functions, like offering support to growth, structure, and insulation all around the axon. Neurons are responsible for receiving and sending messages to cells to other parts through delicate cellular expansions referred to as axons. Axons are spread over long and short distances for reaching their position, lastly connecting neurons with other tissues such as nerve, muscle tissue, or sensory organs. Axons are surrounded by Glial cells that compose a membranous sheath known as myelin, insulation of the axon. The transmission of information between neurons increases due to myelination, known as action potentials. Axons that are myelinated are unsheathed throughout their entire length. The length of the axons in mammalian ranging from 0.1 μm to 20 μm, whereas the unmyelinated axons range lesser than 2 μm and myelinated axons range higher than 1–2 μm in diameter (Giacci et al., 2018). Myelinated axons have greater diameters ranging more than 0.2 μm in the CNS. The myelinated axon appears to be a rounded profile encircled by a helical wound multilamellar sheath. A long-myelinated axon can be wrapped with myelin up to 250 to 300.

The brain structure is classified into three vital parts- the Forebrain, the midbrain and the hindbrain. The two crucial components of Forebrain are the (a) telencephalon (b) diencephalon. The telencephalon consists of the limbic system, cerebral cortex, and basal ganglia (Moseley, 2018). On the other hand, the diencephalon includes the thalamus and hypothalamus. The telencephalon is inclusive of two symmetrical cerebral hemispheres forming the cerebrum. The basal ganglia and limbic system are present below the cerebral cortex. “Cortex” means “bark”, and it covers the entire cerebral hemispheres. The surface area of the cortex is “2360 cm² (25ft²)”, and the diameter is 3mm approx. The cerebral cortex consists the cell bodies and glia cells, conjoined axons of neurons and dendrites. Cells that make up the cerebral cortex has a greyish brown presence is known as grey matter. The large concentration of myelin around axons provides the tissue a non-transparent white appearance- hence the term white matter (Safaiyan et al., 2021). Grey matter in the brain is associated with intelligence. In Human Brain, 40% is consists of grey matter, and 60 % is consists of white matter (Peer et al., 2017). Almost 94% of oxygen is absorbed by gray matter of the Brain. The cortex is classified into two cerebral hemispheres attached by a solid, tough stash of neural bodies referred to as corpus callosum (Abdelhafidh, 2016). Brain stem is present right before the cerebellum and conjoined with the spinal cord. The responsibility of the brain stem is to pass messages to cerebral cortex and different part of the body. The three main parts of the brain are: (a) Midbrain (b) Pons (c) Medulla Oblongata. Midbrain regulates the movement of eye, processing of auditory and visual information, whereas Pons is responsible for facial movements, beathing and transferring sensory information. Medulla oblongata acts as the central for controlling the functions of the heart and lungs. Any brain tumour could lead to acoustic neuromas or schwannomas. Acoustic neuroma stem from the schwann cells that covers the nerve and has a slow growth. Neurogenerative disorders could cause dementia, Huntington’s disease and Parkinson’s disease. Defect in brain functioning could lead to anxiety, depression, mood disorder and schizophrenia relating to hallucination and delusion. Damage to the parts of brain such as frontal lobe could give rise to impulsive behaviour.

Structure and Function of the Brain

The left hemisphere is responsible for the following functions- (a) Information Analysis, (b) Recognition of serial events, (c) Control sequence of behaviour, (d) Verbal functioning such as talking and understanding other people’s speech, (e) Reading and writing, whereas the right hemisphere is involved with (a) synthesis of information (b) emotional experience and expressions. Hemispheres are further subdivided into four lobes- (a) Frontal Lobe, (b) Temporal Lobe, (c) Parietal Lobe (d) Occipital Lobe. Damage to the Occipital lobe associated with the primary visual sensory area processing visual information could lead to partial or complete blindness even though the eyes function normally. Temporal Lobe is associated with the primary auditory association area (Berns et al., 2015). Damage to this area could result in Wernick’s Aphasia. Inability to understand the language of others, one can speak fluently, whereas the spoken words will be completely wrong. The frontal lobe is mainly responsible for higher mental cognitive activities, and the area is devoted to language (Leisman, Moustafa & Shafir, 2016). It allows in speaking smoothly and fluently. Broca’s aphasia is caused in the frontal lobe, which causes the inability to speak the language. The frontal lobe is also accountable for controlling emotions utilizing the connection to the limbic system.

In the beginning years of life, the human brain grows rapidly. During birth, it is only 25% of the adult’s brain size; however, within an age of 5 years, it grows up to an adult size of 90% (Gilmore, Knickmeyer & Gao, 2018). Along with the progressive brain development, changes take place in the capability of the youngsters to think, recognize and act. Lately, the occurrence of a field dedicated to developmental cognitive neuroscience that deals in learning the association between Brain and cognitive–behavioural development. PET and MRS are used to study the Molecules that are involved in signalling or processes connected with synaptic transmission can be studied. A suitable PET can help assess the specific receptor activity and receptor distribution. One added advantage for receptor activity is that it can directly associate with the activities of pharmacological agents in the Brain, while MRS can detect the bulk concentration of neurotransmitters and their modification in response to illness and pharmaceutical intervention. Neuroimaging techniques at the system level such as PET and MRI helps to access both the structure and physiology of the human Brain uninterruptedly. Brain activity is recorded with the help of techniques such as EEG or (Magnetoencephalography) MEG known to be functional imaging. However, the activity that can be observed are not functional genuinely, and data from neuroimaging should be viewed as brain dynamics from the start. Extracting functional brain activity from basic dynamics is a difficult yet often overlooked, procedure.

The study that is focused on hormones secreted by endocrine gland is known as Endocrinology. These secreted hormones from one body part, moving through the bloodstream, and have long-lasting impact on different body part — that are endured by a particular tissue receptor (Ponzi et al., 2020). Neuroscience have been dominated by the study of transmitting information and Electrophysiology that maps connectivity of neuroanatomy and the activities of neurones spiking and its inference for behaviour and cognition. The measuring of hormones and analysing the procedure of the production and the mechanism of signalling with which they have dominated endocrinology. In the course of pre or early postnatal life, the regulator of the neuro-endocrine immune system is neurotransmitters and systemic hormones which operate as Brain organizer. Thus, the number of systemic hormones and neurotransmitters throughout major phases of brain development, defines the characteristics, i.e., the response of the central nervous controllers, hence the range of tolerance and functioning provide feedback and controls the systems thought the entire life. The abnormal psychosocial and environmental environments cause unusual levels of neurotransmitters and systemic hormones that can operate as teratogens, causing irreversible psychological and physiological dysfunctions later in state of life (Bolte, Girdler & Marschik, 2019). As a result, many idiopathic, essential, cryptogenic, primary, or real aberrations and malfunctions in reproduction, metabolism, information processing, and immunity can be explained by faulty pre-and/or early postnatal psycho- and physiological processes. As a result, "functional teratology" (teratomorphology) was added to "structural teratology" (teratopsychophysiology). Improvement of the psychosocial and environmental surroundings as well as timely correction of inappropriate systemic hormones and neurotransmitter concentrations can often avoid deviations, dysfunctions, and diseases resulting from improper development of brain.

The Role of Hemispheres and Lobes

The developmental processing of brain begins around 2 weeks post conception and continues until early adulthood, around 20 years (Georgieff, Ramel & Cusick, 2018). The early months of prenatal are mostly influenced by genetical factors; however, the environment factors also play a role; for instance, it is widely recognized that a deficiency of nutrients such as folic acid and the existence of toxins like alcohol both can have negative effects on the developing Brain (Georgieff, Brunette & Tran, 2015). On the contrary, postnatal development of brain, is mainly based on experience and controlled by interaction of gene-environment. The principles of structural change are critical to the Brain's maturation and development. These mechanisms, are accountable for the evolution of a varied range of behaviours that characterize childhood. The increase accuracy and pace of coordinated movement in development of motor skills is performed by Myelination and Synaptic pruning. They are also responsible for maturation of cognitive skills. Synaptic remodelling, a procedure based on experience, is responsible for the improvement in the perception of sound of speech and face recognition. The Brain develops throughout the period of life. Researches conducted recently uncovered that with time there can be changes in brain, however not every time (for example, Seeing or hearing is not "learnt" by humans with their growing age). However, in early years, the occurring changes are highly significant as they act as the foundation block for all other development that will follow. There are evidences by cognitive processes and sensory system of perception that the higher order cognitive functions are dependent on lower-order cognitive functions. Before infants are born, their brains are pre-arranged for certain types of learning and experiences. The first sensitivity helps in development of subsequent language. Infants master to differentiate between sounds that are specified to the language they learnt from their environment they lived in their initial years of life. Infants are capable of distinguishing between sounds of any languages that is not learnt by six months of age. The Brain of a human being begins to exclusively specialize in detecting sounds of native language between the time period of 6 to 12 months; However, loses the ability to distinguish sounds in non-native languages (Ferjan Ramirez et al., 2017). There is a significance in lowering perceptual sensitivity as it is associated to development of language ability later in life.  The greater potential in discrimination of native language sounds anticipates improvement in language skills in life. The shift from infancy to adolescence is defined by the development of enhanced abilities in social cognition, as well as significant brain functioning maturation. Neurobiological mechanisms have significant contributions in promoting prosocial behaviour throughout the developmental stage. Early teenagers demonstrate more prosocial activity than children, according to one line of research implying that prosocial behaviour increases linearly with age. According to linear age trends of prosocial development, prosocial tendencies can emerge and keep on expanding from young age till maturity, owing to advancement in social-cognitive skills, promoting other-disposed considerations (van Hoorn et al., 2016). Another research has discovered distinction identified within the teenage years, along with early adolescents having more prosocial tendencies than late adolescents (Meuwese et al., 2015). Humans' altruistic behaviour is regarded to have biological foundations. However, there is evidence of significant variance in altruistic behaviour between individuals and civilizations Findings depicted that prosocial growth follows non-linear meaning quadratic age-relevant patterns, with early adolescents engaging in prosocial actions more frequently than children and mid-to-late adolescents. Individual differences in emotional reactivity to fear in others have recently been linked to variations in adults' altruistic conduct. Early adolescents, in particular, showed increased engagement of temporal pole, inferior frontal gyrus (IFG) and posterior superior temporal sulcus (pSTS) engagement) when delving into expensive prosocial behaviour in exchange for an award, whereas they elicited intensified pSTS and activation of dorsolateral prefrontal cortex when involving in inexpensive forms of prosocial behaviour. No age differences in prosocial conduct have been found, suggesting that early adolescent brain activation patterns are distinct, resulting in equal levels of prosocial behaviour (Do, McCormick & Telzer, 2019). Intimate partner violence (IPV) has the capacity to impact a child's neurological development and socio-emotional for a long time. The developmental repercussions of early childhood exposure to domestic violence have received less attention in research than the impact of IPV on mothers or older children. However, the brain of an infant and systems associated to stress are especially vulnerable to inputs from environment, crucial consequences are expected. The maturation of the areas of brain and Hypothalamus-Pituitary-Adrenal (HPA) involved in observing the auditory and visual cortex are all hampered when a born child is exposed to IPV during infancy (Mueller & Tronick, 2019).

It can be concluded from the above discussion that brain development goes through different stages, and it keeps on evolving throughout the life span. The structure, function and development of the Brain can stem from different behavioural patterns or functionalities. The biological development of the brain is a complicated process and has different layers to which various areas are nurtured, leading to the development of skills or problematic behaviour. Each part of the brain is accountable for proper functioning, and it can be studied by the usage of different neuroimaging such as fMRI, PET, EEG and others. However, environment and genes also play a role in brain development which affects human life.

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