TYPES OF NERVE CELLS
1) Myelinated or Medullated or White neurons:
- When the axon is enclosed by the white fatty myelin cover it is called Myelinated or Medullated or White neurons.
- This forms the cerebral cortex of our brain.
2) Non- Myelinated or Non-Medullated or Grey neurons:
- This neuron is not enclosed by myelin sheath; so it appears greyish in colour.
- The axon is covered by only neurilemma and Schwann cells.
- This type of neuron is found in the white matter of cerebrum.
3) Unipolar neurons:
- The embryonic nervous tissue contains unipolar neurons.
- A unipolar neuron has a nerve cell body with a single process or fiber, which will act both as axon and Dendron.
4) Bipolar neurons:
- The sensory hair cells of the sense organs like rods and cones of the retina are made up of bipolar neurons.
- Each bipolar neuron has a cell body and two processes at the ends, one acting as axon and the other acting as Dendron.
4) Multipolar neuron: The cerebral cortex contains the multipolar neurons; each multipolar neuron has a cell body with many dendrites and an axon.
- The dendrites and the synaptic knobs of the axons of neighboring neurons are in physical contact with one another without fusing.
- This point of contact between the neighboring nerve cells is called synapse.
TYPES OF NEURON
Sensory neuron: These neurons receive signals from a sense organ.
Motor neuron: These neurons send signals to a muscle or a gland
Relay neurons: occur in the central nervous system (brain and spinal cord) where they serve as links between other neurons.
PATHWAYS: FROM STIMULUS TO RESPONSE
- There is coordination between eye and finger.
- Different pathways are taken by nerves to bring about this coordinated activity.
- On the basis of pathways followed, nerves are classified mainly into three different types.
- Afferent (or ferrying towards) which carry messages towards the central nervous system (spinal cord or brain) from nerve endings on the muscles of different sense organs that sense the change in surroundings are called stimulus detectors.
- These are also called ‘sensory nerves’.
- Efferent (or ferrying away) which carry messages from the central nervous system to parts that shall carry out the response or the effectors (nerve endings).
- They are also called ‘motor nerves.
ASSOCIATION NERVES: Association nerves, which link together the afferent and efferent nerves.