Peripheral nerves:          

• Nerves which arise from the Central Nervous System.

On basis of their composition, they are:

1. Sensory or efferent nerve:

• Formed of only sensory nerve fibre.
• Conduct impulse from sense organ to CNS.

 

2. Motor or efferent nerve:

• Formed of only motor nerve fibres
• Conduct impulse from CNS to sense organ.

 

3. 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.

1. Olfactory nerve – sensory
2. Optic – sensory
3. Occulomotor – motor
4. Trochlear ­– motor
5. Trigeminal – mixed
6. Abducens – motor
7. Facial – mixed
8. Auditory – sensory
9. Glossophyarangeal – mixed
10. Vagus – mixed
11. Accesoory – motor
12. 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