The<unk>  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 vagus<unk> (X) provides sensory and autonomic (parasympathetic) supply to structures in the neck and also to most of the organs in the chest and abdomen. Terminal<unk> (0) The terminal<unk> (0) may not have a role in humans, although it has been implicated in hormonal responses to smell, sexual response and mate selection. Smell (I) The olfactory<unk> (I) conveys information giving rise to the sense of smell. Damage to the olfactory<unk> (I) can cause an inability to smell (anosmia), a distortion in the sense of smell (parosmia), or a distortion or lack of taste. Vision (II) The optic<unk> (II) transmits visual information. Damage to the optic<unk> (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 Eye movement (III, IV, VI) alt The oculomotor<unk> (III), trochlear<unk> (IV) and abducens<unk> (VI) coordinate eye movement. The oculomotor<unk> controls all muscles of the eye except for the superior oblique muscle controlled by the trochlear<unk> (IV), and the lateral rectus muscle controlled by the abducens<unk> (VI). This means the ability of the eye to look down and inwards is controlled by the trochlear<unk> (IV), the ability to look outwards is controlled by the abducens<unk> (VI), and all other movements are controlled by the oculomotor<unk> (III) Damage to these<unk>  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<unk> (III) can cause double vision and inability to coordinate the movements of both eyes (strabismus), also eyelid drooping (ptosis) and pupil dilation (mydriasis). Lesions may also lead to inability to open the eye due to paralysis of the levator palpebrae muscle. Individuals suffering from a lesion to the oculomotor<unk> 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<unk> (IV) can also cause double vision with the eye adducted and elevated. The result will be an eye which can not move downwards properly (especially downwards when in an inward position). This is due to impairment in the superior oblique muscle. Damage to the abducens<unk> (VI) can also result in double vision. This is due to impairment in the lateral rectus muscle, supplied by the abducens<unk>  Trigeminal<unk> (V) The trigeminal<unk> (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<unk> leads to loss of sensation in an affected area. Other conditions affecting the trigeminal<unk> (V) include trigeminal neuralgia, herpes zoster, sinusitis pain, presence of a dental abscess, and cluster headaches. The facial<unk> (VII) supplies the muscles of facial expression. Damage to the<unk> causes a lack of muscle tone on the affected side, as can be seen on the right side of the face here. Facial expression (VII) The facial<unk> (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. Most muscles are supplied by the cortex on the opposite side of the brain; the exception is the frontalis muscle of the forehead, in which the left and the right side of the muscle both receive inputs from both sides of the brain. Damage to the facial<unk> (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 most common cause of this is Bell's palsy, the ultimate cause of which is unknown. Patients with Bell's palsy often have a drooping mouth on the affected side and often have trouble chewing because the buccinator muscle is affected. The facial<unk> is also the most commonly affected<unk> in blunt trauma. Hearing and balance (VIII) The vestibulocochlear<unk> (VIII) supplies information relating to balance and hearing via its two branches, the vestibular and cochlear<unk> . 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<unk> transmits information from the cochlea, allowing sound to be heard. When damaged, the vestibular<unk> may give rise to the sensation of spinning and dizziness (vertigo). Function of the vestibular<unk> may be tested by putting cold and warm water in the ears and watching eye movements caloric stimulation. Damage to the vestibulocochlear<unk> can also present as repetitive and involuntary eye movements (nystagmus), particularly when the eye is moving horizontally. Damage to the cochlear<unk> will cause partial or complete deafness in the affected ear. Oral sensation, taste, and salivation (IX) alt The glossopharyngeal<unk> (IX) supplies the stylopharyngeus muscle and provides sensation to the oropharynx and back of the tongue. The glossopharyngeal<unk> also provides parasympathetic input to the parotid gland. Damage to the<unk> may cause failure of the gag reflex; a failure may also be seen in damage to the vagus<unk> (X). Vagus<unk> (X) The vagus<unk> (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<unk> (X) will lead to a loss of parasympathetic supply to a very large number of structures. Major effects of damage to the vagus<unk> may include a rise in blood pressure and heart rate. Isolated dysfunction of only the vagus<unk> 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<unk>  Damage to this<unk> may result in difficulties swallowing. Shoulder elevation and head-turning (XI) The accessory<unk> (XI) supplies the sternocleidomastoid and trapezius muscles. Damage to the accessory<unk> (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. Depending on the location of the lesion there may also be weakness present in the sternocleidomastoid muscle, which acts to turn the head so that the face points to the opposite side. Tongue movement (XII) The hypoglossal<unk> (XII) supplies the intrinsic muscles of the tongue, controlling tongue movement. The hypoglossal<unk> (XII) is unique in that it is supplied by the motor cortices of both hemispheres of the brain. Damage to the<unk> 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. The fasciculations of the tongue are sometimes said to look like a "bag of worms". Damage to the<unk> tract or nucleus will not lead to atrophy or fasciculations, but only weakness of the muscles on the same side as the damage.
Cranial nerves
Peripheral nervous system
Nervous system
Central nervous system
Autonomic nervous system
Integumentary system
Enteric nervous system
Somatosensory system