Defect Of Nervous System

Nervous System of Class 11

Ataxia : Lack of muscle coordination due to damage of cerebellum.

Dyslexia : Inability of a person to comprehend written language.

Aphasia : Inability to coordinate the understanding of speech and producing sound, due to defect of Wernicke’s area.

Parkinson’s disease : Also known as paralysis agitans is caused due to lack of dopamine; characterised by (i) rigidity of musculature (ii) involuntary tremors when person is in resting state (iii) serious difficulty in initiating movement called akinesia; Treated by the drug L-dopa.

Schizophrenia : Caused by excess secretion of dopamine; characterised by incoherent speech, broken ideas, abnormal sequence of thoughts, often withdrawn, abnormal posture, intense fear, unreal feelings etc.

Huntington’s chorea : A hereditary disease that generally begins after 30-40 years of age characterised by flicking movements at points then progressive distortional movements of entire body, dementia also develops with motor dysfunction. This occurs due to loss of GABA and acetylcholine secreting neurons in many parts of brain. The abnormal gene has many times repeating codon CAG that code for multiple glutamine.

Multiple Sclerosis : It is a kind of autoimmune disease that causes the damage of myelin sheath of nerve cell, this results in neuron death leading to numbness, slurred speech and paralysis.

Epilepsy : Characterised by periodic seizures when a large number of neurons fire spontaneously, accompanied by involuntary spasm of skeletal muscle. In most cases there is no structural abnormality in the parts of brain. But, in some case it may be due to brain damage at birth, severe head injury or inflammation of brain.


Sir Charles Sherrington was the first person who used the term synapse. The process of chemical transmission across synapse was discovered by Henry Dale. Physiological importance of synapse for transmission of nerve impulse was established by Mc Lennan.

Acetylcholine was the first neurotransmitter to be isolated and obtained by Otto loewi from the endings of parasympathetic neurons of vagus nerve in frog heart.

GABA ( Gamma amino butyric acid) is released by synaptic knobs of fibres of some interneurons in CNS. It inhibits postsynaptic regeneration of action potential, hence it is called inhibitory neurotransmitter.

Nervous system is found only in animals, it is absent in plants.

Nervous system is ectodermal in origin .

CNS in mainly made up of association neurons .

Neopallium forms dorsal wall of cerebrum in mammals and it indicates the development of intelligence in mammals.

Lamina terminali is a delicate membrane which forms the boundary of third ventricle in rabbit.

Brain stem is the part of brain which is continuous with spinal cord as medulla oblongata, mid-brain & pons. Diencephalon may or may not be included.

Telechoroidea is the term used for epithalamus and piamater fused (choroid plexus).

Olfactory sense in highly developed in shark (dog fish). The name dog fish is on the basis of well developed olfactory lobes.

Ataxia means lack of muscle cordination . Damage to cerebellum is characterized by ataxia. Dyslexia involves an inability to comprehend written language.

First pair of spinal nerves in frog is Hypoglossal. The last pair of cranial nerves of mammals has the same name.

Association neurons are also called interneurons or internuncial neurons.

Autonomic or visceral nervous system was discovered by Langley.

ANS is regulated by centres in brain like cerebral cortex, hypothalamus & medulla oblongata.

Total number of sympathetic ganglia in rabbit is 18 pair.

Sympathetic nervous system increases defence system of body against adverse conditions. It is active in stressfull

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