**1. Introduction**

Neurodegeneration describes a complex and serious medical condition, which principally affects the neurons. Such a situation leads to disorders of the central nervous system.

Degenerative nerve affects various body activities such as balance, movement, talking, heart functioning, breathing, mood swing, poor coordination, seizure, confusion, and altered levels of consciousness in other words it affects day-to-day life. The basis of such dysfunction can be quite varied.

Neurological disorders can influence the entire neurologic pathway or a single neuron. Even a little disturbance to a neuron's structural pathway can result in dysfunction.

Neurological disorders can result from a number of sources that includes lifestyle, nutrition, environmental influences, physical injuries, infections including defective protein degradation and aggregation, free radical formation, oxidative stress and exposure to metal toxicity and pesticides.

The central nervous system consists of two types of cells, neurons and glial cells. Electrical impulses are not produced by glial cells, they are the supporting cells of neurons. These glial cells are superior to neurons in their function and cellular diversity. Glial cells including microglia, oligodendrocytes, and astrocytes, can regulate neuronal action.

Typically, the development of neurodegeneration initiates in the subcortical region as the disease progresses and extends to cortical regions [1]. Primary loss of neurons varies with the disease like striatal and cortical regions in HD, striatal regions in PD, spinal motor neurons and cortical regions in ALS, and hippocampal and cortical regions in AD [2–4].

Neurodegenerative diseases consider sharing a common pathogenic mechanism relating to aggregation and deposition of misfolded proteins, leading to unavoidable progressive worsening of the central nervous system. Misfolded proteins may create the most trouble as they form protofibrils. A number of methods have been described. In a few cases, these are particularly related to the type of protein, but in many other cases, they are nonspecific mechanisms shared by every misfolded protein disease. For a normal function, a protein must be properly synthesised and folded into its normal three-dimensional configuration. Nascent proteins are served in folding by molecular chaperones. Improperly folded proteins either damaged or otherwise beyond their functional lives are degraded by a ubiquitin-dependent proteasome protein degradation system.

In this system initially, the proteins are labelled for degradation by attachment of a polyubiquitin chain. Protein fragments and polyubiquitin are the end products of proteasome action. This polyubiquitin is then degraded and also recycled to the cellular ubiquitin pool, this process required enzymatic action by ubiquitin carboxyterminal hydrolase 1.

The subject of strong investigation is the cascade of pathogenic actions linking abnormal protein aggregation to cell death. Even though aggregates are the most striking physical change in surviving cells, the actual function of the aggregate remains a mystery. Mostly it is believed that the formation of aggregates may be a protective mechanism sequestering the wayward protein from vulnerable cell procedure.

There is an emerging proof that performed fibrils generated from the full length and truncated recombinant α-synuclein enter neurons, most likely by endocytosis, and act as "seeds" that stimulate the employment of soluble endogenous α-synuclein into soluble inclusions, resulting in progressive prion-like extend of neurodegeneration. The mutant protein may not be able to carry out a vital function or may obstruct the function of the wild-type protein. Mutant proteins may operate the apoptotic cascade. They may impede intracellular transport or other vital activities. They may restrain the activity of the proteasome, increasing protein aggregation. They may get in the way of mitochondrial function, making cells more exposed to excitotoxicity. Lysosomes play an essential role in ubiquitin–proteasome system in degrading intracellular proteins. When the function of the ubiquitin-proteasome system is not enough to clear the accumulating cellular protein, then the autophagy-lysosome pathway turns into the other main direction for the degradation of misfolded proteins as well as unwell mitochondria. For maintaining cellular health mitophagy is a highly recognised mechanism.

With the ageing of the population, the occurrence of neurodegeneration is escalating spectacularly in the absence of either effective therapeutic involvement or a clear understanding of the separate pathophysiology of neurodegenerative disease states.

Currently, a few hundred neurodegenerative diseases have been estimated and among these, many appear to overlap with one another pathologically and clinically, leaving their practical categorisation challenging to a certain extent. In diseases the issue is further complicated by multisystem atrophy where quite a lot of areas of the brain are affected, different combinations of lesions can give different clinical pictures. Moreover, the same neurodegenerative processes, in particular at the beginning, can affect different areas of the brain, making a known given disease appear very different from a symptomatic standpoint. In spite of these difficulties, the most

popular classification of neurodegenerative disorders is still o the bases of the predominant clinical feature or the topography of the predominant lesion, or frequently on a combination of both.

#### **2. Sleep and neurodegeneration**

Dementia is described by a progressive decline of reminiscence and cognition followed by language dysfunction, depression, hallucinations, other psychotic features, and sleep disturbance. In advanced phases, the patient turns out to be mute, bedridden and incontinent. The chief sleep disturbances in dementing illness include hypersomnia, insomnia, extreme nocturnal motor action, circadian sleep/wake rhythm disorders, respiratory dysrhythmias and "sundowning".

Synthesis of new extracellular matrix protein takes place in reactive astrocytes in the areas of neural degeneration that provide boundaries to segregate damaged axons from healthy axons, prevent hematogenous cells from invading the offended neural tissues, affect the survival of remaining axons, and prevent axonal regrowth.

#### **3. Classification and molecular characteristics of neurotraumatic disease**

Neurodegeneration is a complex multifactorial progression that causes neuronal death in the brain and spinal cord, resulting in brain and spinal cord injury and dysfunction. Neurodegeneration along with axonal transport shortage, oxidative stress, protein oligomerization, aggregation, mitochondrial dysfunction, calcium deregulation, DNA damage, irregular neuron-glial interactions, neuroinflammation and abnormal RNA processing.

Neurodegeneration happens in neurotraumatic, neurodegenerative, and neuropsychiatric diseases. These diseases occur due to neurochemical, structural and electrophysiological aberrations in the brain, spinal cord, and nerve bringing out muscle weakness, paralysis, seizures, uncertainty, poor coordination and soreness. Neurodegenerative diseases entail the accretion of misfolded proteins and the beginning of neurodegenerative diseases, some nutrients, oxygen and ATP are accessible to the neurons, ion homeostasis is maintained to a limited point, and neurodegeneration takes a longer time to die.

Neuropsychiatric disorders are schizophrenia, depression, autism, bipolar effective disorders, attention-deficit disorder, tardive dyskinesia, and chronic fatigue syndrome.

Neurodegeneration encircles multiple molecular ways and a complex interplay between different regulatory factors together with the epigenetic mechanism. Although traditional drugs target various etiological mechanisms in separation, one should concentrate on drugs which have multiple therapeutic objectives and can be given either as monotherapy or as adjunctive drugs for effective results.
