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Asian American Medical Society

    The cranial nerves are a set of paired nerves in the back of your brain. Cranial nerves send electrical signals between your brain, face, neck and torso. Your cranial nerves help you taste, smell, hear and feel sensations. They also help you make facial expressions, blink your eyes and move your tongue.They are a key part of your nervous system.

    The cranial nerves emerge from the central nervous system above the level of the first vertebra of the vertebral column.

    The terminal nerves (0), olfactory nerves (I) and optic nerves (II) emerge from the cerebrum, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain.

    The cranial nerves are considered components of the peripheral nervous system (PNS),although on a structural level the olfactory (I), optic (II), and trigeminal (V) nerves are more accurately considered part of the central nervous system (CNS).

The Function of 12 cranial nerves:

Olfactory nerve (I)

The olfactory nerve is also known as the first cranial nerve. The olfactory nerve has only one job—making you able to smell thins.

When particles in the air enter ones nasal cavity, they interact wit the receptors on the olfactory nerve and a type of tissue called the olfactory epithelium, which is in several areas of the nasal cavity and contains millions of receptors. All those receptors send that information they’ve gathered to the central nervous system. Your brain then interprets that information as scent.

Optic nerve (II)

The optic nerve is the second cranial nerve. The optic nerve is critical to your vision. It’s an extension of your central nervous system, which includes your brain and spine. The optic nerve transmits electrical impulses from your eyes to your brain. Your brain processes this sensory information so that you can see. The perception of brightness, color perception, and contrast are all possible because of the optic nerve. The optic nerve is also responsible for the light reflex and the accommodation reflex.

Oculomotor nerve (III)

Oculomotor nerve is the third cranial nerve. As a mixed nerve, the oculomotor nerve supplies motor function and parasympathetic function. Motor function means movement, and the oculomotor nerve is responsible for much of the movement associated with your eyes. Parasympathetic function has to do with the parasympathetic nervous system, whose functions tend to oppose and balance those of the sympathetic nervous system.

Oculomotor nerve controls four of the six muscles that enable eye movement. CN III makes it possible to:

  • Elevate the upper eyelid
  • Focus the eyes
  • Respond to light by making the black center of the pupil smaller.
  • Move your eyes inward, outward, up and down and control torsion.

Trochlear nerve (IV)

Trochlear nerve is the forth cranial nerve. The trochlear nerve doesn't transmit sensory signals. It functions purely as a motor nerve.

In each eye, the superior oblique muscle functions as the trochlea. The trochlear nerve innervates this muscle to lift the eyes so you can look down. The nerve also enables you to move your eyes toward your nose or away from it.

Trigeminal nerve (V)

Trigeminal nerve is the fifth cranial nerve. It is one of a few nerves in human’s body that has both sensory and motor functions. The right and left trigeminal nerves each provide ipsilateral motor innervation and receive ipsilateral sensory input. This means that sensation travels from the right side of the face to the right trigeminal nerve and that motor function trvels from the right trigeminal nerve to the muscles on the right side of the head and face. The function of the right and left trigeminal nerves is symmetrical.

Although the trigeminal nerve has both sensory and motor functions, it primarily helps you feel. (sensory function)

The trigeminal nerves helps with:

  • Biting, chewing and swallowing
  • Facial and scalp sensations

Abducens nerve (VI)

Abducens nerve is the sixth cranial nerve. The function of the abducens nerve is quite simple and straightforward

  • It moves the eye outward(abduction) so you can look to the side.
  • Via the contralateral medial rectus muscle, it coordinates the simultaneous side-to-side movement of your eyes.

Facial nerve (VII)

Facial nerve is the seventh cranial nerve. The four components of the facial nerve include motor, sensory, taste, and parasympathetic function. Most of the branches of the facial nerve are motor branches that stimulate the movement of the facial muscles. The motor branches of the facial nerve activate muscles to move by releasing acetylcholine, a neurotransmitter that binds to the surface of muscle cells.The facial nerve detects sensation from the small area behind the ear described as the auricle. The sensory information from this area is transmitted through the facial nerve to the brainstem, then to the thalamus in the brain, and eventually to the cerebral cortex, where the brain can integrate and make sense of the sensation.

Vestibulocochlear nerve (VIII)

Vestibulocochlear nerve is the eighth cranial nerve. The function of the vestibulocochlear nerve is purely sensory. It has no motor function. The cochlear nerve is responsible for transmitting auditory signals from the inner ear to the cochlear nuclei within the brainstem and ultimately to the primary auditory cortex within the temporal lobe. The cochlea, the part of the inner ear where the cochlear part of the nerve originates, detects sound waves. These then travel from the spiral ganglion to the brain. The vestibular apparatus, where the vestibular part of the nerve originates, detects changes in the head’s position based on gravity. Then the position of the head communicates information about balance to the brain.

Glossopharyngeal nerve (IX)

Glossopharyngeal nerve is the ninth cranial nerve. The glossopharyngeal nerve serves a variety of functions in the head and neck through different types of nerve fibers and its various branches. The lingual branch performs the specialized task of transmitting taste information to your brain. It connects with the taste buds on the rear third of your tongue and down into the throat, and it also provides that area with general sensory information about things like touch, temperature, and pain.

Vagus nerve (X)

The vagus nerve is the tenth cranial nerve. The vagus nerve carries motor and important involuntary sensory information to different function of the body, including:

  • Digestion
  • Cardiovascular system, including heart rate, blood pressure
  • Respiration system
  • Immune system
  • Mood
  • Mucus and saliva production
  • Skin and muscle sensations
  • Speech

Accessory nerve (XI)

The accessory nerve is the eleventh cranial nerve.It has a similar function to the vagus nerve. It carries motor innervation to the pharyngeal constrictors, larynx, and muscles of the soft palate.

The accessory nerve is purely a motor nerve. It innervates both the trapezius and the sternocleidomastoid muscles.

Hypoglossal nerve (XII)

The hypoglossal nerve is the twelfth cranial nerve. The hypoglossal nerve is purely a motor nerve. This nerve and the muscles it serves are at least responsible for several important functions, including:

  • Talking and singing
  • Chewing
  • Swallowing

In addition, the hypoglossal nerve supplies movements that help you clear your mouth of saliva, aid unconscious movements involved in speech, and are involved in several automatic and reflexive motions.


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  • Cranial nerves anatomy
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