Nervous tissue: Neuron and Neuroglia




Nervous tissue: Neuron and Neuroglia

  • Nervous tissue contains densely packed nerve cell ( neuron),which are specialized for nerve impulse conduction.
  • Origin- ectoderm
  • Nervous tissue consists of
  1. Neuron or nerve cell (functional unit of Nervous system)
  2. Neuroglia (glial cell)

Neuron:

  • About 100 billions of neurons are present in nervous system.
  • They are Specialised type of cell, they vary in shape and size, all neurons contains three principle parts- cell body, dendrites and an axon

Cell body

  • Has a large nucleus, which contain prominent nucleolus, as well as other several structures (Nissl bodies, ER,lysosome, mitochondria, neuroflament), responsible for metabolism, growth and repair of neuron
  • Nissl bodies- made up of RNA, RER and free ribosome, help in protein synthesis
  • Neurofilament and neurotubules are thread like protein, runs parallel to long process
  • Neurofilament- semisolid structure that provide skeletal framework to axon
  • Neurotubules- transport intracellular proteins between cell body and the processes

Dendrites-

  • Many thread cytoplasmic extension arises from cell body called dendrites
  • It conducts nerve impulse toward the cell body
  • They are myelinated and have Nissl’s granule and neurofibril

Axon-

  • Usually one of the cytoplasmic extension is long and unbranched called axon.
  • It is covered by lipid sheath called myelin sheath
  • Myelin sheath is formed by specialized non-neural cell called schwann cell (neurolemmocytes) in PNS and by Oligodendrocytes in CNS. The outer sheath of these cell is known as neurolemma
  • It conduct nerve impulse away from cell body
  • It lacks nissl’s granules

Types of neuron:

I. Types of neuron based on structure-

  1. Unipolar- have single processes, very common sensory neuron in PNS,
  2. Bipolar- two processes- a dendrires and an axon, eg. Retina, cochlea, smell receptor
  3. Multi polar-many processes- many dendrites but one axon eg. Brain and spinal cord

II. Types of neuron based on function-

  1. General somatic afferent (sensory)- carry sensory impulse from skin, skeletal muscles, joints and connective tissue to CNS
  2. General visceral afferent- impulse from visceral organ to CNS
  3. General somatic efferent(motor)- CNS to skeletal muscles
  4. General visceral efferent- CNS to visceral organs
  5. Special visceral efferent- brain to muscles of jaws, pharynx, facial expression, larynx
  6. Special afferent- receptor cell (olfactory, optics, auditory, vestibule, gustation) to CNS

 

2. Neuroglia

  • Glial cells are non conducting cells that protect and nurture as well as support cells of nervous tissue.
  • There are 4 types of neuroglia cells

i) Astrocytes

  • largest,most numerous glial cell, with long star like processes, help form the blood –brain barrier.
  • Function: structural support, transport of substance between blood vessels and neurons, mop up excess ions (k) and neurotransmitters.

ii) Oligodendrocytes-

  • relatively small, with several branching processes,found in grey and white matter of CNS,
  • function: produce myelin sheath

iii) Microglial cell

  • smallest glial cell, cuboidal or columnar shaped, it is a macrophage, engulf damaged neuron

iv) Ependymal cell-

  • elongated cell, arranged in single layer in inner lining of spinal cord and ventricle of brain.

Nervous tissue: Neuron and Neuroglia