pediagenosis: Nervous
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Showing posts with label Nervous. Show all posts
Showing posts with label Nervous. Show all posts

Wednesday, May 12, 2021

Neurochemical Disorders Affective Disorders

Neurochemical Disorders Affective Disorders


Neurochemical Disorders I: Affective Disorders
‘Affect’ refers to mood and affective disorders comprise of both a pathological lowering (depression) and elevation (mania) of mood. Bipolar affective disorder (manic-depression) refers to an oscillation between depression and mania. These conditions are not simply characterized by mood changes, however, and depression may comprise a number of characteristic features.
Both depression and mania may be accompanied by features of psychosis (delusions and hallucinations; see Chapter 58). The nature of the psychosis tends to be mood-congruent: in depression, the patient may believe that he or she is guilty of something or hear voices that are critical and unpleasant. Mania may be accompanied by grandiose delusions.

Neurochemical basis of depression

Depression
Aetiology
This is a common and mania disorder with a lifetime prevalence that has been estimated to be as high as 15%, with women affected more than men (approximately 2:1). It can occur in response to adverse circumstances (reactive depression), as well as for no apparent circumstantial reason (endogenous depression), although often the distinction between these two different types of depression is not that clear-cut. In both cases the depression probably arises through a combination of genetic and environmental factors.
Neurochemical Disorders Schizophrenia

Neurochemical Disorders Schizophrenia


Neurochemical Disorders II: Schizophrenia
Schizophrenia is a syndrome characterized by specific psychological manifestations, including auditory hallucinations, delusions, thought disorders and behavioural disturbances. It is a common disorder with a lifetime prevalence of 1% and an incidence of 2–4 new cases per year per 10 000 population. It is more common in men and typically presents early in life. Like all psychiatric disorders there is no diagnostic test for this condition, which is defined by the existence of key symptoms.
·       Positive symptoms:
      delusions: abnormal or irrational beliefs, held with great conviction and out of keeping with an individual’s sociocultural background;
      hallucinations: perceptions in the absence of stimuli.
·       Negative symptoms:
      blunting of mood, apparent apathy, lack of spontaneous speech and action;
      disordered speech.

Neurochemical Disorders II: Schizophrenia, delusions, hallucinations, The dopamine hypothesis of schizophrenia,

Aetiology
A distinction used to be made between type 1 and 2 schizophrenia but this has fallen out of fashion as it may relate more to the length of time that the individual has had the condition. The cause of schizophrenia is unknown but a number of aetiological factors have been suggested:

Monday, May 10, 2021

Neurochemical Disorders Anxiety

Neurochemical Disorders Anxiety


Neurochemical Disorders Anxiety
Anxiety is a normal emotional reaction to threatening or potentially threatening situations, and is accompanied by sympathetic overactivity. In anxiety disorders the patient experiences anxiety that is disproportionate to the stimulus, and sometimes in the absence of any obvious stimulus. There is no organic basis for anxiety disorders, the symptoms resulting from overactivity of the brain areas involved in ‘normal’ anxiety. Psychiatric disorders that occur without any known brain pathology are called neuroses.
Anxiety disorders are subdivided into four main types: generalized anxiety disorder, panic disorder, stress reactions and phobias. Many transmitters seem to be involved in the neural mechanisms of anxiety, the evidence being especially strong for γ-aminobutyric acid (GABA) and 5-hydroxytryptamine (5-HT). Because intravenous injections of cholecystokinin (CCK4) into humans cause the symptoms of panic it has been suggested that abnormalities in different transmitter systems might be involved in particular types of anxiety disorder. This remains to be seen.
Neurochemical Disorders III: Anxiety, Anxiety disorders,

There is some evidence for decreased GABA binding in the left temporal pole, an area concerned with experiencing and controlling fear and anxiety.
Neurodegenerative Disorders

Neurodegenerative Disorders


Neurodegenerative Disorders
Neurodegenerative disorders are those conditions in which the primary pathological event is a progressive loss of populations of CNS neurones over time. However, it is increasingly being recognized that most neurodegenerative disorders have an inflammatory component to them, and that inflammatory diseases of the central nervous system (CNS) (such as multiple sclerosis, see Chapter 62) will cause neuronal loss and degeneration.
Aetiology
There are a number of theories on the aetiology of neurodegenerative disorders, which may not be mutually exclusive. Of late there has been much work looking at the genetic risk factors for developing these disorders (see Chapter 63), and some common sets of genes are being found for them, e.g. genes involved with inflammation and immunity.

An infective disorder
Neuronal death with a glial reaction (gliosis) is commonly seen in infective disorders (typically viral) with inflammation in the CNS. However, in neurodegenerative disorders such a reaction is not seen, although the observation that human immunodeficiency virus (HIV) infection can cause a dementia has raised the possibility that some neurodegenerative disorders may be caused by a retroviral infection. Furthermore, the development of dementia with spongiform changes throughout the brain in response to the proliferation of abnormal prion proteins as occurs in Creutzfeldt–Jakob disease has further fuelled the debate on an infective aetiology in some neurodegenerative disorders (eg α-synuclein in PD).

Neurodegenerative Disorders, autoimmune process

An autoimmune process
Autoantibodies have been described in some neurodegenerative conditions, e.g. antibodies to calcium channels in motor neurone disease (MND). However, the absence of an inflammatory response would argue against this hypothesis, although neuronal degeneration with a minimal inflammatory infiltrate can be seen in the paraneoplastic syndromes (see Chapter 62) as well as the more recently described autoimmune disorders targeting ion channels and receptors.
Neurophysiological Disorders Epilepsy

Neurophysiological Disorders Epilepsy


Neurophysiological Disorders: Epilepsy
Definition and classification of epilepsy
Epilepsy represents a transitory disturbance of the functions of the brain that develops suddenly, ceases spontaneously and can be induced by a number of different provocations. It is the most prevalent serious neurological conditions, with a peak incidence in early childhood and in the elderly.
Patients may be classified according to whether:
·    the fit is generalized or partial (focal), i.e. remains within one small CNS site, e.g. temporal lobe;
·       there is an impairment of consciousness (if there is then it is termed complex);
·       the partial seizure causes secondary generalization.
Overall, 60–70% of all epileptics have no obvious cause for their seizures, and abouttwo-thirds of all patients stop having seizures within 2–5 years of their onset, usually in the context of taking medication.

Neurophysiological Disorders: Epilepsy, Definition and classification of epilepsy, Pathogenesis of epilepsy, Treatment of epilepsy, Mechanisms of action of anticonvulsants,

Pathogenesis of epilepsy
The aetiology of epilepsy is largely unknown, but much of the therapy used to treat this condition works by modifying either the balance between the inhibitory γ-aminobutyric acid (GABA) and excitatory glutamatergic networks within the brain or the repetitive firing potential of neurones.
Neuroimmunological Disorders

Neuroimmunological Disorders


Neuroimmunological Disorders
Central nervous system immunological network
The central nervous system (CNS) has relative immunological privilege compared with the peripheral nervous system (PNS) and most other parts of the body. The reasons for this are as follows:
Neuroimmunological Disorders, Acute disseminated encephalomyelitis, Other immunological diseases,
·   The blood–brain barrier (BBB) normally prevents most lymphocytes, macrophages and antibodies from entering the CNS (see Chapters 5 and 13).
    It has a very poorly developed lymphatic drainage system.
        There is only low level expression of major histocompatibility complex (MHC) antigens.
        There are no antigen presenting cells.

Wednesday, April 28, 2021

Neurogenetic Disorders

Neurogenetic Disorders


Neurogenetic Disorders
A large number of genetic disorders involve the nervous system, and some of these have pathology confined solely to this system. Recent advances in molecular genetics have meant that many diseases of the nervous system are being redefined by their underlying genetic defect.
Three major new developments have revolutionized the role of genetic factors in the evolution of neurological disease. First, genes encoded in the maternally inherited mitochondrial genome can cause neurological disorder; Second, a number of inherited neurological disorders have as their basis an expanded trinucleotide repeat (triplet repeat disorders); Third, the ability to use sophisticated genotyping of individual cases (exome sequencing) to find novel mutations is starting to yield new insights into diseases of the nervous system.

Neurogenetic Disorders

Disorders with gene deletions
Many different disorders within the nervous system result from the loss of a single gene or part thereof. For example, hereditary neuropathy with a liability to pressure palsies, in which the patient has a tendency to develop recurrent focal entrapment neuropathies in association with a large deletion on chromosome 17, which includes the gene coding for the peripheral myelin protein 22 (PMP 22).
Cerebrovascular Disease

Cerebrovascular Disease


Cerebrovascular Disease
Definition of stroke
A stroke or cerebrovascular accident (CVA) is typically an event of sudden onset (although it can occur over hours in some patients where a major vessel is slowly thrombosing). It is due to an interruption of blood supply to an area of the central nervous system (CNS) that causes irreversible loss of tissue at the core with a penumbra of compromised tissue around the area that may still be salvageable. If the disturbance in blood flow is temporary it causes a transient ischaemic attack or TIA. This is often a harbinger of a stroke. Stroke is common and its consequences depend on the vessel that has been occluded.

Cerebrovascular Disease

Investigation of stroke
·       History and examination
·       Computed tomography (CT)/magnetic resonance imaging (MRI)
·     Blood tests including full blood count, erythrocyte sedimentation rate, renal function, glucose and lipids
·   Electrocardiogram (ECG) which may be repeated and prolonged if a cardiac source for the stroke is suspected
Other investigation may include an ECHO cardiogram and imaging of the blood vessels and/or a CSF examination and this depends on the type of stroke (see Table 64.1).

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