Cranial nerve of scoliodon

Cranial Nerve of Scoliodon

            

There are ten pairs of cranial nerves in all the fishes.

 

Olfactory nerves:

The first pair of cranial nerves is the olfactory nerves which originate from the olfactory lobes and innervate the olfactory sacs. The terminal nerves are situated between the two olfac­tory lobes. These nerves emerge from the telencephalon and bear a ganglion called ganglion terminale near the origin.

These nerves supply the nasal septum and the external nostril.

 

Optic nerves

The second pair of cranial nerves is the optic nerves which, after the origin from the optic thalami, form the optic chiasma and supply the eyes.

 

Oculomotor nerve

The third cra­nial nerve is called oculomotor nerve which originates from the ventral surface of the mesencephalon and supplies the anterior, superior and inferior recti and the inferior oblique muscles of each eye ball.

 

Trochlear or pathetic:  

The fourth cranial nerve is called trochlear or pathetic nerve which arises from the dorsolateral surface of the midbrain and supplies the superior oblique eye muscle.

 

Trigeminal  

The fifth cranial nerve is the trigeminal which has three branches:

 

(1) Ophthalmicus superfi­cial which supplies to the skin of the snout.

 (2) The maxillaris which is divided into maxillaris superior supplying nerves to the skin of the upper jaw and maxillaris inferior inner­vating the posterior part of the upper jaw.

 (3) The mandibularis innervating the muscles of the lower jaw. Another nerve called ophthalmicus pro-fundus becomes secondarily associated with the trigeminal to supply nerves to the eye ball and the dorsal surface of the snout

 

Abducens:

The sixth cranial nerve is the abducens which supplies the posterior rectus muscle of the eye ball. The seventh cra­nial nerve is known as facial which divides into two branches:

 

(1) The ophthalmicus superficialis branch like that of the fifth cra­nial nerve.

 (2) A bundle of mixed nerves which subdivides into three routes:

 (a) A ramus buccalis innervating the infraorbital canal of the snout.

  (b) A ramus hyomandibularis supplying nerves to the lower jaw and throat.

 (c) A ramus palatinus giving nerve supply to the roof of the buccal cavity and the pharynx. The eighth cranial nerve is called auditory which gives the vestibular and saccular branches to the internal ear.

 

Glosso­pharyngeal:

The ninth cranial nerve is the glosso­pharyngeal which, in the region of the first gill cleft, divides into a small pretrematic nerve and a large posttrematic nerve. These nerves supply branches to the pharynx, pha­ryngeal muscles and the mucous membrane surrounding the first gill slit.

 

Vagus

The tenth cranial nerve is the vagus which arises by multiple roots and gives off many branches.

The branches are:

(i) the brachial nerves sup­plying the gills,

(ii) the lateralis supplying the lateral line sense organs and gives nume­rous branches along its course.

 

Spinal nerves:

(a) Ramus dorsalis,

(b) Ramus ventralis, and

(c) Ramus communicans to join with the autonomous nervous system.

 

 

 

Name of the nerve	Origin	Branches	Distribution	Physiological Nature
1. Olfactory	Olfactory lobe.	-	Olfactory epithelium of the nasal cavity.	Sensory
2. Optic	Optic lobe.	-	Retina of eye.	Sensory
3. Oculomotor	Ventrolateral side ofthe midbrain.	-	Anterior rectus, superior rectus, inferior rectus and inferior oblique muscles of the eye. Superior oblique muscle of the eye	Motor Motor
4. Trochlear	Dorsolateral aspect of the midbrain between the optic lobes and cerebrum.	-	Olfactory capsule and dorsal	Mixed
5. Trigeminal	Dorsally from the side of medulla oblongata below the corpora restiformes.	(i) Opthalmic profundus  (ii) Ophthalmicus superfi-cialis V  (iii) Maxillaris V (a) Superior (b) Inferior (iv) Mandibularis	skin of the snout. Skin of the snout. Skin of upper jaw Posterior part of upper lip. Muscles of the lower jaw.	Mixed Motor Mixed
6. Abducens	Midventrally from the floor of medulla oblongata	-	Posterior rectus muscle of the eye.	Mixed
7. Facial	From the side of medulla below the corpora restiformes in the form of a bundle.	(i)                   Opthalmicus super-ficialis VII   Ii Ramus buccalis (iii) Flyomandibularis (a)     Mandibularis externus (b) Mandibularis internus (c) Hyoidean (iv) Ramus palatinus	Sense organs; the lateral line system of snout. Infra-orbital lateral line canal and associated ampullae. Mandibular canal of lateral-line system. Mucous membrane of the floor of buccal cavity. Muscles of the roof of buccal cavity and pharynx. Roof of the pharyngeal and buccal cavity.	Mixed Mixed Mixed Mixed Mixed Sensory
8. Auditory	From the side of medulla close to the V and Vll cranial nerves.	(i) Vestibular (ii) Saccular	Membranous labyrinth of the internal ear	Sensory
9. Glossopharyn geal	From the ventro-lateral side of medulla.	(i) Pre-trematic (ii) Post-trematic	Mucous membrane of the first gill-cleft and the pharynx. The muscles of the pharynx Gills.	Sensory Mixed Mixed
10. Vagus	Side of Medulla.	(a) Branchialis (b) Visceralis (c) Lateralis	Viscera. Lateral-line system of the trunk.	Mixed Mixed Mixed