Cranial nerves and its function pdf
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The cranial nerves are 12 pairs of nerves that can be seen on the ventral bottom surface of the brain. Some of these nerves bring information from the sense organs to the brain; other cranial nerves control muscles; other cranial nerves are connected to glands or internal organs such as the heart and lungs. Can't remember the names of the cranial nerves?
Cranial nerve , in vertebrates, any of the paired nerves of the peripheral nervous system that connect the muscles and sense organs of the head and thoracic region directly to the brain. Lower vertebrates fishes, amphibians have 10 pairs. A 13th pair, a plexus branching network known as the terminal nerve CN 0 , is sometimes also recognized in humans, though whether it is a vestigial structure or a functioning nerve is unclear. Cranial nerves are made up of motor neurons , sensory neurons, or both. They are named for their function or structure; for example, the trigeminal nerve consists of three primary branches, while the vestibulocochlear nerve serves the organs of equilibrium and hearing.
Table of cranial nerves
Cranial nerves are the nerves that emerge directly from the brain including the brainstem , of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck , including the special senses of vision , taste , smell , and hearing.
The cranial nerves emerge from the central nervous system above the level of the first vertebrae of the vertebral column. There are conventionally twelve pairs of cranial nerves, which are described with Roman numerals I—XII. Some considered there to be thirteen pairs of cranial nerves, including cranial nerve zero.
The numbering of the cranial nerves is based on the order in which they emerge from the brain and brainstem, from front to back. 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 cranial nerves are in contrast to spinal nerves , which emerge from segments of the spinal cord.
Most typically, humans are considered to have twelve pairs of cranial nerves I—XII , with the terminal nerve 0 more recently canonized. Cranial nerves are generally named according to their structure or function.
For example, the olfactory nerve I supplies smell, and the facial nerve VII supplies the muscles of the face. Because Latin was the lingua franca of the study of anatomy when the nerves were first documented, recorded, and discussed, many nerves maintain Latin or Greek names, including the trochlear nerve IV , named according to its structure, as it supplies a muscle that attaches to a pulley Greek : trochlea.
The trigeminal nerve V is named in accordance with its three components Latin : trigeminus meaning triplets ,  and the vagus nerve X is named for its wandering course Latin : vagus. Cranial nerves are numbered based on their position from front to back rostral-caudal of their position on the brain,  as, when viewing the forebrain and brainstem from below, they are often visible in their numeric order.
Cranial nerves have paths within and outside the skull. The paths within the skull are called "intracranial" and the paths outside the skull are called "extracranial". There are many holes in the skull called "foramina" by which the nerves can exit the skull.
All cranial nerves are paired , which means they occur on both the right and left sides of the body. The muscle, skin, or additional function supplied by a nerve, on the same side of the body as the side it originates from, is an ipsilateral function. If the function is on the opposite side to the origin of the nerve, this is known as a contralateral function. Grossly , all cranial nerves have a nucleus.
With the exception of the olfactory nerve I and optic nerve II , all the nuclei are present in the brainstem. Because each nerve may have several functions, the nerve fibres that make up the nerve may collect in more than one nucleus. For example, the trigeminal nerve V , which has a sensory and a motor role, has at least four nuclei. With the exception of the olfactory nerve I and optic nerve II , the cranial nerves emerge from the brainstem.
The olfactory nerve I and optic nerve II emerge separately. The olfactory nerves emerge from the olfactory bulbs on either side of the crista galli , a bony projection below the frontal lobe , and the optic nerves II emerge from the lateral colliculus, swellings on either side of the temporal lobes of the brain.
The cranial nerves give rise to a number of ganglia , collections of the cell bodies of neurons in the nerves that are outside of the brain. These ganglia are both parasympathetic and sensory ganglia. The sensory ganglia of the cranial nerves, directly correspond to the dorsal root ganglia of spinal nerves and are known as cranial nerve ganglia. Sympathetic ganglia supplying the head and neck reside in the upper regions of the sympathetic trunk , and do not belong to the cranial nerves.
The ganglion of the sensory nerves, which are similar in structure to the dorsal root ganglion of the spinal cord , include: .
Additional ganglia for nerves with parasympathetic function exist, and include the ciliary ganglion of the oculomotor nerve III , the pterygopalatine ganglion of the maxillary nerve V2 , the submandibular ganglion of the lingual nerve , a branch of the facial nerve VII , and the otic ganglion of the glossopharyngeal nerve IX. After emerging from the brain, the cranial nerves travel within the skull , and some must leave it in order to reach their destinations.
Often the nerves pass through holes in the skull, called foramina , as they travel to their destinations. Other nerves pass through bony canals, longer pathways enclosed by bone. These foramina and canals may contain more than one cranial nerve and may also contain blood vessels.
The cranial nerves are formed from the contribution of two specialized embryonic cell populations, cranial neural crest and ectodermal placodes. The components of the sensory nervous system of the head are derived from the neural crest and from an embryonic cell population developing in close proximity, the cranial sensory placodes the olfactory, lens, otic, trigeminal, epibranchial and paratympanic placodes.
The doble-origin cranial nerves are summarized in the following Table: . Abbreviations: CN, Cranial Nerve; m, purely motor nerve; mix, mixed nerve sensory and motor ; NC, neural crest; PA, pharyngeal branchial arch; r, rhombomere; s, purely sensory nerve. The cranial part of the accessory nerve sends occasional branches to the superior ganglion of the vagus nerve.
The cranial nerves provide motor and sensory supply mainly to the structures within the head and neck. The sensory supply includes both "general" sensation such as temperature and touch, and "special" senses such as taste , vision , smell , balance and hearing. The terminal nerve 0 may not have a role in humans,  although it has been implicated in hormonal responses to smell, sexual response and mate selection. The olfactory nerve I conveys information giving rise to the sense of smell.
Damage to the olfactory nerve I can cause an inability to smell anosmia , a distortion in the sense of smell parosmia , or a distortion or lack of taste. The optic nerve II transmits visual information.
Damage to the optic nerve II affects specific aspects of vision that depend on the location of the damage. A person may not be able to see objects on their left or right sides homonymous hemianopsia , or may have difficulty seeing objects from their outer visual fields bitemporal hemianopsia if the optic chiasm is involved.
Inflammation optic neuritis may impact the sharpness of vision or colour detection . The oculomotor nerve controls all muscles of the eye except for the superior oblique muscle controlled by the trochlear nerve IV , and the lateral rectus muscle controlled by the abducens nerve VI. This means the ability of the eye to look down and inwards is controlled by the trochlear nerve IV , the ability to look outwards is controlled by the abducens nerve VI , and all other movements are controlled by the oculomotor nerve III .
Damage to these nerves may affect the movement of the eye. Damage may result in double vision diplopia because the movements of the eyes are not synchronized. Abnormalities of visual movement may also be seen on examination, such as jittering nystagmus.
Damage to the oculomotor nerve III can cause double vision and inability to coordinate the movements of both eyes strabismus , also eyelid drooping ptosis and pupil dilation mydriasis. Individuals suffering from a lesion to the oculomotor nerve may compensate by tilting their heads to alleviate symptoms due to paralysis of one or more of the eye muscles it controls.
Damage to the trochlear nerve IV can also cause double vision with the eye adducted and elevated. This is due to impairment in the superior oblique muscle. Damage to the abducens nerve VI can also result in double vision. The trigeminal nerve V and its three main branches the ophthalmic V1 , maxillary V2 , and mandibular V3 provide sensation to the skin of the face and also controls the muscles of chewing.
Damage to the trigeminal nerve leads to loss of sensation in an affected area. Other conditions affecting the trigeminal nerve V include trigeminal neuralgia , herpes zoster, sinusitis pain, presence of a dental abscess , and cluster headaches.
The facial nerve VII controls most muscles of facial expression, supplies the sensation of taste from the front two-thirds of the tongue, and controls the stapedius muscle. Damage to the facial nerve VII may cause facial palsy. This is where a person is unable to move the muscles on one or both sides of their face. The vestibulocochlear nerve VIII supplies information relating to balance and hearing via its two branches, the vestibular and cochlear nerves.
The vestibular part is responsible for supplying sensation from the vestibules and semicircular canal of the inner ear , including information about balance , and is an important component of the vestibuloocular reflex , which keeps the head stable and allows the eyes to track moving objects. The cochlear nerve transmits information from the cochlea , allowing sound to be heard. When damaged, the vestibular nerve may give rise to the sensation of spinning and dizziness vertigo.
Function of the vestibular nerve may be tested by putting cold and warm water in the ears and watching eye movements caloric stimulation. The glossopharyngeal nerve IX supplies the stylopharyngeus muscle and provides sensation to the oropharynx and back of the tongue.
Damage to the nerve may cause failure of the gag reflex ; a failure may also be seen in damage to the vagus nerve X. The vagus nerve X provides sensory and parasympathetic supply to structures in the neck and also to most of the organs in the chest and abdomen. Loss of function of the vagus nerve X will lead to a loss of parasympathetic supply to a very large number of structures. Major effects of damage to the vagus nerve may include a rise in blood pressure and heart rate.
Isolated dysfunction of only the vagus nerve is rare, but - if the lesion is located above the point at which the vagus first branches off - can be indicated by a hoarse voice, due to dysfunction of one of its branches, the recurrent laryngeal nerve.
Damage to this nerve may result in difficulties swallowing. The accessory nerve XI supplies the sternocleidomastoid and trapezius muscles. Damage to the accessory nerve XI will lead to weakness in the trapezius muscle on the same side as the damage.
The trapezius lifts the shoulder when shrugging , so the affected shoulder will not be able to shrug and the shoulder blade scapula will protrude into a winged position. The hypoglossal nerve XII supplies the intrinsic muscles of the tongue, controlling tongue movement. Damage to the nerve may lead to fasciculations or wasting atrophy of the muscles of the tongue.
This will lead to weakness of tongue movement on that side. When damaged and extended, the tongue will move towards the weaker or damaged side, as shown in the image. Damage to the nerve tract or nucleus will not lead to atrophy or fasciculations, but only weakness of the muscles on the same side as the damage. Doctors, neurologists and other medical professionals may conduct a cranial nerve examination as part of a neurological examination to examine the cranial nerves.
This is a highly formalised series of steps involving specific tests for each nerve. A cranial nerve exam starts with observation of the patient, as some cranial nerve lesions may affect the symmetry of the eyes or face. Visual field testing may be used to pin-point structural lesions in the optic nerve, or further along the visual pathways.
The sensation of the face is tested, and patients are asked to perform different facial movements, such as puffing out of the cheeks. Hearing is checked by voice and tuning forks. The patient's uvula is examined. After performing a shrug and head turn, the patient's tongue function is assessed by various tongue movements.
Smell is not routinely tested, but if there is suspicion of a change in the sense of smell, each nostril is tested with substances of known odors such as coffee or soap. Intensely smelling substances, for example ammonia , may lead to the activation of pain receptors of the trigeminal nerve V located in the nasal cavity and this can confound olfactory testing. Nerves may be compressed because of increased intracranial pressure , a mass effect of an intracerebral haemorrhage , or tumour that presses against the nerves and interferes with the transmission of impulses along the nerve.
Summary of the Cranial Nerves
The names of the cranial nerves relate to their function and they are also numerically identified in roman numerals I-XII. There are twelve cranial nerves in total. Figure 1 — The location of the cranial nerves on the cerebrum and brainstem. Figure 2 — Superior view of the skull base showing the foramina and which cranial nerves pass through them. They are the only cranial nerves to pass through canals. See table 1 for a summary of the cranial nerves, their modalities and functions.
The cranial nerves are a set of twelve nerves that originate in the brain. Each has a different function for sense or movement. Each nerve has a name that reflects its function and a number according to its location in the brain. When a person inhales fragrant molecules, olfactory receptors within the nasal passage send the impulses to the cranial cavity, which then travel to the olfactory bulb. Specialized olfactory neurons and nerve fibers meet with other nerves, which pass into the olfactory tract. The olfactory tract then travels to the frontal lobe and other areas of the brain that are involved with memory and notation of different smells. When light enters the eye, it hits the retina, which contains rods and cones.
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Your cranial nerves are pairs of nerves that connect your brain to different parts of your head, neck, and trunk. There are 12 of them, each named for their function or structure. This is based off their location from front to back. Their functions are usually categorized as being either sensory or motor. Sensory nerves are involved with your senses, such as smell, hearing, and touch.
V 1 ophthalmic nerve is located in the superior orbital fissure V 2 maxillary nerve is located in the foramen rotundum. V 3 mandibular nerve is located in the foramen ovale. From Wikipedia, the free encyclopedia.