cranial nerves

 Cranial Nerves

12 pairs of cranial nerves are peripheral nerves.

There are 12 pairs of cranial nerves originating from nuclei in inferior surface of brain, some sensory, some motor and some mixed.

They are called cranial as they arise from brain inside cranial cavity.

12 pairs cranial nerve are-

I- Olfactory nerves, sensory 

II- Optic nerves, sensory

III- Oculomotor nerves, motor

IV- Trochlear nerves, motor

V- Trigeminal nerves, mixed

VI- Abducens nerves, motor

VII- Facial nerves, mixed

VIII- Vestibulocochlear nerves, sensory

IX- Glossopharyngeal nerves, mixed

X- Vagus nerves, mixed

XI- Accessory nerve, motor

XII- Hypoglossal nerves, motor

I - Olfactory Nerve; Sensory

These are nerves of sense of smell, carry afferent impulses for sense of smell. The nerve's olfactory (hair) receptors are located within mucosa of nasal cavity, pass upwards through cribriform plate of ethmoid bone and then pass olfactory bulb. Area for perception of smell in temporal lobe of cerebrum.

Central connection- Olfactory bulb

Function- smell

Peripheral connection- Olfactory mucosa

Nerve type- sensory

II - Optic Nerve; Sensory

These are nerves of sense of sight, carry afferent impulse for vision.

The fibre originate in ratina of eye and they combine to form optic nerve, which passes through optic canal of orbit. They then pass through optic foramina of sphenoid into cranial cavity and join at optic chiasma.

Optic chiasma provide site for crossing over or desiccation of optic nerve fibers, terminating in opposite side of brain. The nerve proceed as optic track to lateral geniculate bodies of thalmus. 

Impulse pass from visual area in occipital lobe sight is perceived. In cerebellum impulse from eyes contribute to maintenance of balance posture and orientation of head in space.

III- Oculomotor nerve; motor

These nerves arise from nuclei near cerebral aqueduct they supply-

Four of six extrinsic muscles, which move eyeball.

Ciliary muscles, which alter shape of lens.

Circular muscles of iris, which constrict the pupil.

Levator palpebrae muscle, which raise movement of upper eyelids.

IV- Trochlear nerve; motor

These nerve arise from nuclei near cerebral aqueduct. They supply superior oblique muscles of eyes, which movement of eyeball.

V- Trigeminal nerve; mixed

Largest pair of cranial nerve, supplying the front part of head and dividing into-

Ophthalmic nerve; Supply lacrimal gland, conjunctiva of eyes, forehead, eyelids (sensory anterior aspect of scalp and mucous membrane of nose.)

Maxillary nerve; Supply cheeks, upper gums, upper teeth, lower eyelids (sensory).

Mandibular nerve; both sensory and motor fibers; mixed

Supply teeth and gums of lower jaw, pinnae of ear, lower lip and tongue.

They are chief sensory nerves for face and head (including oral and nasal cavities and teeth), receiving impulse of pain, temperature and touch.

VI- Abducens nerve (motor)

These nerve arise from nuclei lying underfloor of 4th ventricles.

They supply lateral rectus muscle of eyeballs causing abduction (movement of eyeball).

VII- Facial nerves; mixed

These nerves composed of both motor and sensory nerve fibres, arising from nuclei in lower part of pons.

Motor fibre supply muscles of facial expression.

Sensory fibres convey impulse from taste buds in anterior 2/3rd of tongue to taste perception area in cerebral cortex.

VIII- Vestibulocochlear; auditory nerve; sensory

These nerve composed of-

Vestibular nerves

Cochlear nerves

Vestibular nerves

Arise from semicircular canals of inner ear and convey impulses to cerebellum. They are associated with maintenance of posture and balance.

Cochlear nerves

Originate in organ of corti in inner ear and convey impulse to hearing areas in cerebral cortex where sound is perceived.

IX- Glossopharyngeal nerve; mixed

Motor fibres arises from nuclei in medulla oblongata and stimulate muscle of tongue and pharynx and sensory cells of parotid (salivary glands).

Sensory fibres convey impulses to cerebral cortex from pharynx and posterior tongue and from taste in tongue and pharynx.

These nerve are essential for swallowing.

Monitoring of blood pressure , O2 and CO2 in blood.

X- Vagus nerve (mixed)

The only cranial nerves to extend beyond head and neck region.

They pass down through neck into thorax and abdomen.

Fibres emerge from medulla.

These nerve form imprtant part of parasympathetic nervous system.

Sensory portion

Taste bud in epiglottis and pharynx.

Proprioceptors in muscles of throat and neck.

Baroreceptrors in arc of aorta and chemoreceptors in aortic bodies (for respiration) near arc of aorta.

Motor portion

Skeletal muscles in throat and neck.

Smooth muscles in esophagus, stomach, small intestine, large intestine, gallbladder.

Cardiac muscle in heart


Swallowing and voice production

Parasympathetic; smooth muscle contraction and relaxation in organ of gastrointestinal track, slowing heart rate

Secretion of digestive fluid

XI-  Accessory nerve; motor

These nerves arise from nuclei in medulla oblongata and in spinal cord.

The fibres supply sternocleidomastoid and trapezius muscles.

Branches join vagus nerves and supply pharyngeal and laryngeal muscles.


Movement of head and pectoral girdle, head rotating.

XII- Hypoglossal nerves ; motor

These nerves arise from nuclei in medulla oblongata.

They supply the muscles of tongue and muscles surrounding hyoid bone and contribute to swallowing and speech.

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