09 Control and Coordination - part 03 - Neural tissue

 

09 Control and Coordination - part 03 - Neural tissue

9.3 Neural tissue
  • The neural tissue consists primarily of two types of cells viz - 
  1. Neurons and 
  2. Neuroglia or glial cells. 
  • A nerve is bundle of axons
  • The word ‘nerve’ is used for a bundle of axons outside the CNS while inside the CNS for the same, word ‘tract’ is used. 
  • Nerves may be - 
  1. Sensory type
  2. Motor type or 
  3. Mix type i.e. having both the types - sensory and motor fibres.
  • All these along with nervous organs make up the nervous system of the higher animal and bring about coordination and control of various activities of the body. 
  • This is done through the receptors which bring in sensory inputs towards the central nervous system. 
  • Processing is carried out in the CNS and then through the motor commands, the response is sent out. 
  • The nerves arising from the cytons of the CNS, travel throughout the body transmitting the nerves impulses to or from the CNS.
Neurons/Nerve cells : 
  • Structural and functional units of the nervous system.  
  • Each multipolar neuron has three parts - 
  1. Cyton or cell body
  2. Dendron and 
  3. Axon. 
1. The cyton :
  • has a distinct central nucleus with a nucleolus and neuroplasm. 
  • A clear film of cytoplasm surrounds the nucleus around which there are - 
  1. Nurofibrils
  2. Nissl’s granules and 
  3. Other cell organelles.
  • Nissl’s granules are riboprotein components. 
  • They play an important role in the synthesis of the enzyme required for formation of the neurotransmitter. 
  • Neurofibrils play an important role in transmission of nerve impulse. 
2. Dendrons :
  • Are many small conical processes arising from the cyton. 
  • These are highly branched into fine dendrites. 
  • Nissl’sgranules and neurofibrils both can be seen at the base of the dendrons. 
  • They transmit message towards the cyton. 
3. Axon :
  • Single long, usually unbranched process arising from the cyton at the axon hillock. 
  • It consists of a bundle of neurofibrils. 
  • Nissl’s granules are absent. 
  • Terminally, the axon gives out branches called telodendrons. 
  • Carry the messages away from the cytons. 
  • May give out lateral branches called collaterals.
  • Terminal branches attach to a muscle, gland, skin or telodendrites of another neuron.
  • The interconnection between two neurons or neuron with motor organ is called synapse. 
  • It is usually axo dendronic or may be axo axonic ,axo somatic or dendro dendronic

  • Cytons are generally found 
  1. Inside the brain
  2. Spinal cord (CNS) and 
  3. In the ganglia.
  • Small groups of cell bodies inside the white matter of brain are called basal nuclei. 
  • A bundle of axons called nerve may be covered only by neurilemma in the non-medullated nerve.
  • In the medullated nerves it is covered both by medullary sheath and on the outside by neurilemma. 
  • Conduction of impulse by the medullated nerves is 50 times faster than in the non-medullated nerves. 
  • The connective tissue covering around the nerve fascicule is called endoneurium. 
  • Few nerve fasciculi with endonurium are surrounded by connective tissue, called perineurium.
  • A still large bundle of nerves is covered on the outer side by epineurium. 
  • Blood is supplied to all the nerves to provide oxygen and nutrients.
Neuroglial cells :
  • The neuroglial cells are far greater in number than the neurons. 
  • Most of the supporting cells of the nervous system are derived from the same embryonic tissue layer (ectoderm) that produces neurons. 
  • The term neuroglia refers to the supporting cells of the Central Nervous System (CNS) and Peripheral Nervous System (PNS).

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