- Nerves which arise from the Central Nervous System.
On basis of their composition, they are:
- Sensory or efferent nerve:
- Formed of only sensory nerve fibre.
- Conduct impulse from sense organ to CNS.
- Motor or efferent nerve:
- Formed of only motor nerve fibres
- Conduct impulse from CNS to sense organ.
- Mixed nerve:
- Formed of both sensory and motor nerve fibres.
- Conduct impulse to and from CNS.
On the basis of their origin,
A. Cranial nerve
- Nerve arise from brain
- Made up of sensory neuron, motor neurons or mixed neurons.
- Reptiles, Birds, Mammals have 12 pairs of cranial nerve
- Fishes and amphibian have 10 pairs.
- Olfactory nerve – sensory
- Optic – sensory
- Occulomotor – motor
- Trochlear – motor
- Trigeminal – mixed
- Abducens – motor
- Facial – mixed
- Auditory – sensory
- Glossophyarangeal – mixed
- Vagus – mixed
- Accesoory – motor
- Hypoglossal – motor
11 and 12 are absent in lower vertebrates.
B. Spinal nerves
- Nerve which arise from spinal cord
- All spinal nerves are mixed neurons.
- This is 36 pairs in dog, 49- 51 pairs in cow, 50-56 pairs in horse, etc
|
Cervical vertebrae |
Thoracic vertebrae |
Lumbar vertebrae |
Sacral vertebrae |
Coccygeal vertebrae |
Sheep |
7 |
13 |
6-7 |
4 |
16-18 |
Ox |
7 |
13 |
6 |
5 |
18-20 |
Horse |
7 |
18 |
6 |
4 |
15-21 |
Pig |
7 |
14 |
6-7 |
4 |
20-23 |
Rabbit |
7 |
12 |
4 |
4 |
16 |
Dog |
7 |
13 |
3 |
3 |
20-23 |
Fowl |
13-14 |
7 |
14 |
– |
7 |