cranial nerves

The eye's blind spot is a result of the

absence of photoreceptors in the area of the retina where the optic nerve leaves the eye.

optic nerve produces irreversible

blindness

Cranial nerves IV and VI also participate in control

of eye movement. Cranial nerves III, IV, and VI are usually tested together.

The specialized olfactory receptor neurons of the olfactory nerve are located in the

olfactory mucosa of the upper parts of the nasal cavity

all cranial nerves are part of the PNS excet

CN 1 and 2 which are part of the CNS

glossopharyngeal nerver

Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus (The stylopharyngeus is a muscle in the head that stretches between the styloid process and the pharynx). Some sensation is also relayed to the brain from the palatine tonsils. Located in the jugular foramen.

Since the oculomotor nerve controls most of the eye muscles, it may be easier to

detect damage to it

trochlear nerve

the fourth cranial nerve, also called the fourth nerve which is a motor nerve that innervates a single muscle: the superior oblique muscle of the eye

. Damage to the vestibulocochlear nerve may cause the following symptoms:

Hearing loss Vertigo False sense of motion Loss of equilibrium in dark places Motion sickness

the optic nerve is encased in

all three meningeal layers dura, arachnoid, and pia mater so it is considered part of the peripheral nervous system rather than the epineurium, perineurium, and endoneurium found in peripheral nerves

the vestibulocochlear nerve or auditory vestibular nerve is the

eighth of twelve cranial nerves. This senses sound, rotation, and gravity (essential for balance and movement). More specifically, the vestibular branch carries impulses for equilibrium and the cochlear branch carries impulses for hearing. Located in the internal acoustic canal.

Its name trigeminal = tri or three, derives

from the fact that each trigeminal nerve, one on each side of the pons, has three major branches: the opthalmic nerve (V1), the maxillary nerve (V2), and the mandibular nerve (V3).

The olfactory nerves do not form

two trunks as do the remaining cranial nerves. Rather, they consist of a collection of many sensory nerve fibers that extend from the olfactory epithelium to the olfactory bulb, passing through the many openings of the Cribriform plate of the Ethmoid bone, a sieve-like structure.

abducens nerve

The abducens nerve or abducent nerve the sixth cranial nerve, also called the sixth nerve is a nerve that controls the movement of a single muscle, the lateral rectus muscle of the eye, in humans. Located in the superior orbital fissure.

spinal nerves

The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. Humans have 31 left-right pairs of spinal nerves, each roughly corresponding to a segment of the vertebral column: 8 cervical spinal nerve pairs (C1-C8), 12 thoracic pairs (T1-T12), 5 lumbar pairs (L1-L5), 5 sacral pairs (S1-S5), and 1 coccygeal pair. The spinal nerves are part of the peripheral nervous system (PNS).

the optic nerve transmits

visual signals from the retina of the eye to the brain

the trigemina nerve

(the fifth cranial nerve, also called the fifth nerve, or simply CNV or CN5) is a nerve responsible for sensation in the face and certain motor functions such as biting, chewing, and swallowing

hypoglossal nerve

Provides motor innervation to the muscles of the tongue (except for the palatoglossus, which is innervated by the vagus nerve) and other glossal muscles. Important for swallowing (bolus formation) and speech articulation. Located in the hypoglossal canal.

vagus nerve

Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles (except the stylopharygeus, which is innervated by the glossopharyngeal). Also provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure. Receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance and the soft palate. Symptoms of damage: dysphagia (swallowing problems), velopharyngeal insufficiency. Located in the jugular foramen.

By observing the eye movement and eyelids, the examiner is able to obtain more information about the

extraocular muscles, the levator palpebrae superioris muscle, and cranial nerves III, IV, and VI.

The examiner typically instructs the patient to hold his head still and

follow only with the eyes a finger or penlight that circumscribes a large "H" in front of the patient.

the opthalmic and maxillary nerves are purely

sensory

the mandibular nerve has both

sensory and motor functions

the oculomotor nerve also controls

the constriction of the pupils and thickening of the lens of the eye. This can be tested in two main ways. By moving a finger toward a person's face to induce accommodation, as well as his going cross-eyed, his pupils should constrict.

the trochlear nerve is unique among the

the cranial nerves in several respects. It is the smallest nerve in terms of the number of axons it contains. It has the greatest intracranial length. Other than the optic nerve (cranial nerve II), it is the only cranial nerve that crosses to the other side before innervating its target. Finally, it is the only cranial nerve that exits from the dorsal aspect of the brainstem.

the optic nerve is

the second of twelve paired cranial nerves but is considered to be part of the central nervous system

the facial nerve is

the seventh VII of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the taste sensations from the anterior two-thirds of the tongue and oral cavity. Its main function is motor control of most of the muscles of facial expression

the olfactory nerve is

the shortest of the twelve cranial nerves and only one of two cranial nerves (the other being the optic nerve) that do not join with the brainstem.

oflactory nerve

transmits the sense of smell from the nasal cavity. The sense of smell (olfaction) arises from the stimulation of olfactory receptors by small molecules of different spatial, chemical, and electrical properties that pass over the nasal epithelium in the nasal cavity during inhalation These interactions are turned into electrical activity in the olfactory bulb, which then transmits the electrical activity to other parts of the olfactory system and the rest of the central nervous system via the olfactory tract.

cranial nerves

I - Olfactory nerve II - Optic nerve III - Oculomotor nerve IV - Trochlear nerve/pathic nerve V - Trigeminal nerve/dentist nerve VI - Abducens nerve VII - Facial nerve VIII - Vestibulocochlear nerve/Auditory nerve IX - Glossopharyngeal nerve X - Vagus nerve XI - Accessory nerve/Spinal accessory nerve XII - Hypoglossal nerve

Tic douloureux or trigeminal neuralgia

is a severe, stabbing pain to one side of the face. It is the largest of the cranial nerves

the oculomotor nerve

is the 3rd of 12 paired cranial nerves. It enters the orbit via the superior orbital fissure and controls most of the eye's movements, including constriction of the pupil and maintaining an open eyelid by innervating the levator palpebrae superioris muscle.

accessory nerve

Controls the sternocleidomastoid and trapezius muscles, and overlaps with functions of the vagus nerve (CN X). Symptoms of damage: inability to shrug, weak head movement. Located in the jugular foramen.

Located in and runs through the internal acoustic canal to the facial canal and exits at the stylomastoid foramen. There are five major facial branches - from top to bottom:

Temporal Branch Zygomatic Branch Buccal Branch Mandibular Branch Cervical Branch

somatic nervous system

The somatic nervous system is the part of the peripheral nervous system associated with the voluntary control of body movements via skeletal muscles. The somatic nervous system consists of efferent nerves responsible for stimulating muscle contraction, including all the non-sensory neurons connected with skeletal muscles and skin.