Structure of a typical neuron
- Nissle granule is a RER
- Neurofibrils in the cytoplasm
- Consist of microfilaments and microtubules
- Produced and maintained by centrioles
- At the axon hillock.
- Location where the action potential starts
- This occurs because there are about seven times more voltage-gated Na+ channels there, so it depolarizes much easier than the soma
- Neurites
Axons | Dendrites |
Single | Multiple |
Long | Short |
Thin process of a nerve cell | Tapering processes of the nerve cell |
Terminates away from the nerve cell body | Terminate near the nerve cell body |
Axon ends by dividing into many fine processes called axon terminals | Dendrites are highly branched to form a dendritic tree |
It has uniform diameter and smooth surface It is free of Nissl granules | The thickness of dendrite reduces as it divides repeatedly Nissl granules are present in dendrites |
The nerve impulses travel away from the cell body | The nerve impulses travel towards the cell body |
Classification of Neurons
- Variation in the shape of neuronal cell bodies:
- Stellate (star-shaped)
- Pyramidal
- Polarity
- Unipolar
- Single process arising from cell body
- Eg
- Posterior root ganglia of spinal nerves,
- Sensory ganglia of cranial nerves
- Bipolar
- One axon and one dendrite arising from cell body
- Eg
- Retina
- Sensory ganglia of cochlear and vestibular nerves
- Multipolar
- Multiple processes arising from cell body
- Most common
- Eg
- Motor neurons of anterior grey column of spinal cord,
- Autonomic ganglia
- Variations in Axons size:
- Golgi type I (long axons)
- Pyramidal cells of cerebral cortex
- Golgi type II (short axons)
- Stellate cells of cerebral cortex
Neural Stem Cells
- Previously thought that neurons are incapable of regeneration might not be fully true
- Cell capable of forming new neurons as well as glial cells found in (adult neurogenic zone)
- Subventricular zone of lateral ventricle and
- Hippocampal gyrus
Neurobiotaxis
- A law governing the arrangement of neuronal cell bodies and their fibres during life
- Neuronal cell body migrates towards the greatest density of stimuli
- E.g. facial nerve nuclei migrate towards trigeminal nucleus to complete the reflex arc.
- Neuronal cell body has a tendency for centralization and encephalization,
- E.g. an evolutionary process by which functions that were governed by lower centres (in lower animals) are progressively being controlled by the higher centres.
- Neuronal processes with similar function run together
- E.g.
- In the brainstem
- Descending fibres run in basilar part;
- Ascending fibres in tegmentum.