Disorders Related With Nervous System
Table of Contents
Lack of Sensations
- Alexia. Failure to read,
- Aphasia. Failure to speak.
- Agraphia. Failure to write,
- Amnesia. Loss of memory
- Agnosia. Failure to recognize tactile agnosia (failure to recognize by touch), visual, and auditory agnosis.
- Analgesia. Insensibility to pain,
- Anesthesia. Loss of feeling,
- Coma. State of unconsciousness.
- Molecular Mechanisms of Nervous System Diseases
Some more disorders of the nervous system
Hydrocephalus
- The volume of CSF is abnormally high.
- The head may be enlarged.
- It develops due to malabsorption, or obstruction in the flow of CSF.
Meningitis
- It is inflammation of the meninges.
- It develops mainly because of bacterial infection (Meningococcus and Streptococcus bacteria)
- It produces severe headaches and stiffness in the neck. The CSF also becomes turbid.
Parkinson’s Disease (Paralysis agitans)
- It develops due to a deficiency of the neurotransmitter, Dopamine. Dopamine is not produced due to the gradual destruction of specific neurons.
- It produces muscle tremors, so-called ‘Shaking Palsy’.
- There is a lack of control and coordination of movements resulting in expressionless features and stooping posture which gradually produces physical disability.
Multiple Sclerosis
- It is due to demyelination of white matter in the brain and spinal cord.
- It is an autoimmune disorder and the susceptibility can be genetic also.
- It can cause abnormal sensation, muscular weakness, and lack of coordination.
Huntington’s Chorea
- It is a genetic disorder (dominant autosomal) that onsets after the age of 30 years.
- There develops a deficiency of the neurotransmitter, GABA, which causes rapid, involuntary, and uncoordinated ‘dancing’ movements. There is progressive dementia followed by death.
Alzheimer’s disease
- It was previously thought to be a ‘prion’ disease, but now, it is known to be produced by the deposition of abnormal amyloid (Tau) protein in the brain resulting in the generation of neurons.
- About 5-10% of the people above 60 yrs. are affected by this disease.
- It produces memory loss, dementia, confusion, (inability to judgment), and abnormal behavior. The death results within 10 years of the first onset of the disease.
- Due to the involvement of chromosome 21st, it is common amongst ‘Down syndromes’. The genes known for the disease produce the proneness or susceptibility.
In Focus
- Regulation means adjustment of the variables that determine the nature of physiological functions.
- The different physiological functions are not independent events rather all functional components are controlled and regulated.
- Neurons detect and receive innumerable bits of information from the different receptors and then for example rate all these to determine the mode of response.
- Sensory information is transmitted in the form of electrical impulses.
- Sponges lack neurons
- A nerve ring and a double ventral ganglionated nerve cord are the components of the nervous system of cockroaches.
- In the cockroach brain, a pair of circumoesophageal connective and pairs of suboesophageal ganglia constitute a nerve ring.
- Supra oesophageal ganglia constitute the brain. 3 and 6 ganglia are prevented in the thoracic and abdominal For example of ventral double nerve cord of cockroaches.
- A network of endocrine glands whose hormone production is controlled by the central nervous system constitutes the neuroendocrine system.
- A cluster of nuclei in the CNS is called nuclei and if such an action is present in the PNS, termed ganglia.
- Bundles of nerve fibers within CNS are called tracts whereas in the PNS termed nerves.
- Unipolar, bipolar, multipolar and pseudounipolar neuron are the kinds of neurons.
- Schwann cells are a type of glial cells that wrap around the axon of neurons, thus covering the axon with con-centric layers around the plasma membrane.
- Bundles of axons of neurons that are wrapped by a connective tissue sheath perineurium are called fascicles. Excitability and conductivity are two unique properties of nerve cells.
- The membrane has an electrical potential difference (voltage) across it known as the membrane potential.
- The different ion concentration across the membranes of the axon is the cause of membrane potential.
- Ion channels are the pores formed by proteins in the membrane of the axon which arc selectively pennene. The pioneer of voltage For example late ion channels provide of excitability to neurons
- The plasma membrane is more permeable to K+ as compared to Na+.
- Na+ and CP are the two ions that cannot move across the resting membrane of neurons.
- The resting membrane potential surface of the axon is positively charged relative to the interior and the electrical potential difference across the plasma membrane is called rest¬ing membrane potential.
- 40 to – 90 mV is the range of resting membrane potential in a neuron. A typical value is – 70 mV (minus sign indicates that inside is relative to outside).
- Na+ – K+ ion transmembrane pump maintains an electrochemical ion gradient.
- Na+– K+ exchange pump expels three Na+ to the outside for every two K+ imported.
- Four phases during the transmission of a signal by nerve fiber
- Initiation of impulse.
- Transmission along the nerve fiber.
- Transfer to target muscles or nerves.
- Effect on target.
- The close position of the axon of a neuron with the dendrites of the next neuron is called a synapse.
- As the Na+ moves rapidly inside the axon, the changed potential difference is termed depolarisation.
- 1 to 5 milliseconds (ms) is the time taken by depolarisation and repolarisation.
- 55 to – 60 mV (about 10 mV less than resting potential is the threshold stimulus to initiate depolarisation).,
- Saltatory conduction. The jumping of nerve impulses from one node of Ranvier to the next is called saltatory conduction.
Advantages of saltatory conduction
- Fast speed
- Less consumption of energy.
- The synaptic cleft is the gap between the lip of the axon and the target cell. It is about 10 – 20 nm.
Two kinds of synapsis
- Electrical
- Chemical.
Electrical synapses. These are specialized for rapid signal transmission so that the electrical signal (action potential) is passed on to the next post-synaptic membrane. Chemical synapsis. It consists of a synaptic knob or button which releases neurotransmitters and a postsynaptic membrane.
- 30 biochemicals and biogenic amines and derivatives of amino acid, 60 neuropeptides arc neurotransmitter,
- The brain reaches 75 to 80 percent of adult size within the first two years and its full size at the age of six years.
- 100 billion (10m) neurons may be present in the brain. The cerebral cortex is the outer part of the cerebrum, 2-4 mm thick formed of grey matter, and takes part in the interpretation, coordination, and response to various nerve impulses.
Action potential. It is the other name of nerve impulses. It propagates along the membrane from one point of the neuron to its farthest extension.
- The wave of reversed polarity along a nerve fiber is also called an action potential. Because different queens possess different densities of ‘.Nat ion channels, different neurons exhibit different lion potentials. However, for any one neuron, the action potential is always the same.
- Generation of nerve impulse. When a nerve fiber is stimulated by a mechanical, chemical, thermal, or electrical stimulus of adequate strength (equal or higher value than the threshold value), the stimulated area of the nerve fiber comes into a local excitatory state at the point of stimulation.
- In this area, the transmembrane potential increases and the membrane becomes several times more permeable to Na than to K+. Sodium ions rapidly diffuse from outside to intracellular fluid due to an electrochemical gradient so that the inside becomes positively charged concerning the outside which in diet increases the permeability of the membrane to Na.
- This reversal of polarity across two sides of the membrane is called depolarization and the membrane with reversed polarity is called depolarized nerve fibre. It is electropositive inside while electron outside. It lasts for less than 1/1.000 of a second. So a nerve fiber can conduct about 1.000 impulses per second.
Due to the rapid inflow of Na the potential increases first to zero, then rises to +45+50 mV and this newly developed potential difference is called action potential. This action potential travels as a wave of depolarization (reversed polarity) along the length of a nerve fiber in a particular direction and is called a nerve impulse.
- Axosomatic synapse. The synapse between the axon of one neuron with the cell body of the next neuron, c+Axo – the axonic synapse. Synapse between the axon of one neuron and with axon of another neuron.
- The movement of ions across the plasma membrane of the neuron is maintained.
Quanta To Memory
- Broca’s area center is present in the cerebrum and is associated with articulated speech.
- The brain uses about 20% of the body’s consumption of oxygen and 15% of its glucose utilization. So if the oxygen supply to the brain is blocked for just five minutes, it is permanently damaged.
- Synaptic delay. The difference in the rate of conduction of nerve impulses across a synapse than along a neuron is called synaptic delay (about 0.5 milliseconds). This delay is due to the period required for neurosecretion and neuroreception at the synapse.
- Satiety center. The sensory area in the hypothalamus has gluco receptor neurons and inhibits the intake of food.
- Appetite and satiety centers are also present in the hypothalamus.
- Synaptic fatigue. Exhaustion of neurotransmitters at the synapse due to repeated stimulation.
- At optic chiasma, only a few nerve fibers cross to another side while most of the nerve fibers remain on the same side of the brain.
- Glands of Swammerdam. These are calcareous bodies at the emerging sites of spinal nerves in frogs.
- Valve of Vieusseas. A band of nerve fibers joining optic lobes to the cerebellum.
- In the brain of mammals, the genu and splenium are associated with the corpus callosum to form the 5th ventricle or pseudocoel.
- Acetylcholine is affected in paralysis.
- Wernicke’s center is related to understanding speech and written language.
- Endorphins are the substances secreted by the brain. When released in blood they give the feeling of well-being.
- In Alzheimer’s disease, there are specific brain abnormalities. This disease is generally seen in old people.
- Generally, the dreams are seen during Rapid Eye movement (REM) sleep.
- The Vagus nerve provides a maximum number of parasympathetic fibers.
- The “Spike phase” of action potential is 2 milliseconds. In this duration, the sodium ions move first inside the axon and then outside it.
- An oscilloscope is used to record the transmission of nerve impulses.
- The disease tetanus occurs when the bacterium Clostridium tetani enters the body through a puncture wound and produces a neurotoxin that interferes with inhibitory synapses of motor neurons. This produces excessive contractions and spastic paralysis.
- The neurotransmitter serotonin, which is critical to the production and regulation of sleep, is derived from the amino acid tryptophan.
- The immediate covering of nerve fiber is called endometrium
- Basic cellular functions of neurons are performed by soma cyton or perikaryon cells.
- Brain damage is indicated by delta waves with E.E.G.
- The thalamus is a part of the forebrain (diencephalon).
- All muscular coordination is done by the cerebellum.
- During mental activity, beta waves are recorded in E.E.G.
- Skeletal muscles are controlled by Basal ganglia preset in the telencephalon.
- Sleep is induced by serotonin.
- Electro Encephalogram (EEG)
- An instrument that records the electrical impulses brain.
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