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MHT-CET : Biology Entrance Exam

MHT - CET : Biology - Nervous Coordination Know More

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1.      On their way out, the nerve fibres from the motor areas of any side cross over to the opposite side of the region of the medulla oblongata. This means that the motor areas of the left hemisphere control the voluntary movements of the right side and vice versa. The motor neurons of the cerebrum are termed upper motor neurons, and those of the spinal cord, are called lower motor neurons. Damage to motor areas results in paralysis.

2.      The motor speech area controls the movements needed for speech. It is called Broca's area. It is peculiar because it develops in the left hemisphere in right-handed persons and in the right hemisphere in the left-handed persons.

3.      Unlike in other vertebrates, the boundary between the cerebrum and diencephalon is not very distinct in mammals.

4.      The spinal cord is protected within the neural arches of the vertebrae and also by the meninges and cerebrospinal fluid. The cord is suspended loosely in the spinal canal. Since its diameter is much less than that of the canal, there is no danger of it being injured by the ordinary movements of the vertebral column.

5.      Structure of Neuron

         The nervous system of man is made up of millions of nerve cells called neurons.

         Each nerve cell consists of a cell body called cyton.

         The cyton contains granular cytoplasm, called neuroplasm, surrounding a large nucleus.

         Scattered in the cytoplasm are found a number of long, delicate fibrils called neurofibrils.

         The neurofibril conducts nerve impulses.

         From the cyton arise two types of processes, viz. axon and dendron.

         The axon is a single, long process ending in many branches.

         The dendrons or dendrites are small processes. They are many in number and short or long in length. Each dendron is profusely branched at its tip.

         The dendrons conduct impulses towards the cyton, while the axons conduct impulses away from the cyton.

         According to the structure of the axon, two types of nerve fibres have been recognised. These are medullated and non-medullated nerve fibres.

         The medullated nerve fibres or myelinated nerve fibres are covered by a fatty sheath called medullary or myelin sheath. The non-medullated nerve fibres are not covered by myelin sheath.

         The myelin sheath of a nerve fibre is not continuous. Its continuity is broken at regular intervals, forming constrictions called nodes of Ranvier.

         The nodes of Ranvier are the points at which one Schwann's cell ends and the other Schwann's cell begins.

6.      Types of Neuron

         Depending on the number of processes they possess, neurons have been divided into three types, viz. unipolar, bipolar and multipolar.

         Unipolar Neuron: Neurons which have a single process dividing into a dendron and an axon are called unipolar. Such neurons are found in the dorsal ganglia of the spinal cord.

         Bipolar Neuron: Neurons having two processes arising from the opposite poles of the cyton are called bipolar. These neurons are found in the retina of the eye.

         Multipolar Neuron: Neurons having many processes arising from the cyton are called multipolar. Such neurons have a single axon and many dendrons. The great majority of neurons are of this type.

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