Cranial Nerves Flashcards
1
Olfactory
The olfactory nerve transmits sensory information to your brain regarding smells that you encounter.
When you inhale aromatic molecules, they dissolve in a moist lining at the roof of your nasal cavity, called the olfactory epithelium. This stimulates receptors that generate nerve impulses that move to your olfactory bulb. Your olfactory bulb is an oval-shaped structure that contains specialized groups of nerve cells.
From the olfactory bulb, nerves pass into your olfactory tract, which is located below the frontal lobe of your brain. Nerve signals are then sent to areas of your brain concerned with memory and recognition of smells.
2
Optic
The optic nerve is the sensory nerve that involves vision.
When light enters your eye, it comes into contact with special receptors in your retina called rods and cones. Rods are found in large numbers and are highly sensitive to light. They’re more specialized for black and white or night vision.
Cones are present in smaller numbers. They have a lower light sensitivity than rods and are more involved with color vision.
The information received by your rods and cones is transmitted from your retina to your optic nerve. Once inside your skull, both of your optic nerves meet to form something called the optic chiasm. At the optic chiasm, nerve fibers from half of each retina form two separate optic tracts.
Through each optic tract, the nerve impulses eventually reach your visual cortex, which then processes the information. Your visual cortex is located in the back part of your brain.
3
Oculomotor
The oculomotor nerve has two different motor functions: muscle function and pupil response.
Muscle function. Your oculomotor nerve provides motor function to four of the six muscles around your eyes. These muscles help your eyes move and focus on objects.
Pupil response. It also helps to control the size of your pupil as it responds to light.
This nerve originates in the front part of your midbrain, which is a part of your brainstem. It moves forward from that area until it reaches the area of your eye sockets.
4
Trochlear
The trochlear nerve controls your superior oblique muscle. This is the muscle that’s responsible for downward, outward, and inward eye movements.
It emerges from the back part of your midbrain. Like your oculomotor nerve, it moves forward until it reaches your eye sockets, where it stimulates the superior oblique muscle.
5
Trigeminal
Sensory: All three divisions (ophthalmic, maxillary & mandibular) of the Trigeminal nerve innervate the skin of the face and scalp, mucous membrane of the eye, oral cavity, nasal cavity and paranasal sinuses. This nerve is responsible for transmitting general sensation from these structures to the sensory cortex in the CNS.
General sensory to front 2/3 of tongue.
Motor: The mandibular division of the trigeminal nerve (CN V3) is responsible for the motor innervation of the muscles of mastication (Temporalis, Masseter, Medial/Lateral Pterygoid). In addition, the other muscles innervated by the CN V3 are: mylohyoid, anterior belly of digastric, tensor veli palatini (soft palate), and tensor tympani (middle ear).
Some of the terminal branches of all three divisions of trigeminal nerve carry parasympathetic nerve fibres from other cranial nerves (CN III, CN VII, & CN IX) to ciliary ganglion, lacrimal, nasal, paranasal sinuses, parotid, submandibular, sublingual glands and minor salivary glands.
The trigeminal nerve has three sensory nuclei, and a motor nucleus. It emerges from the pons with a large sensory root that forms the trigeminal ganglion (sensory ganglion) and a smaller motor root. The trigeminal ganglion divides in to three divisions the ophthalmic (V1), maxillary (V2) and mandibular (V3) and they exit the skull through the superior orbital fissure, foramen rotundum and foramen ovale. The motor root bypasses the ganglion and joins the mandibular root before it enters the foramen ovale.
6
Abducens
The abducens nerve controls another muscle that’s associated with eye movement, called the lateral rectus muscle. This muscle is involved in outward eye movement. For example, you would use it to look to the side.
This nerve, also called the abducent nerve, starts in the pons region of your brainstem. It eventually enters your eye socket, where it controls the lateral rectus muscle.
7
Facial
Sensory: Facial nerve transmits general sensation from a small area of the concha of auricle of the ear.
Special Sensory: Taste sensation to the anterior 2/3 of the tongue via its chorda tympani branch which joins the lingual nerve of CN V3.
Motor: Innervates all muscles of facial expression. In addition it is motor to posterior belly of digastric, stylohyoid and stapedius (middle ear) muscles.
Parasympathetic: Secretomotor supply to submandibular, sublingual, lacrimal and minor salivary glands of oral cavity and glands in the nasal mucosa and paranasal sinuses.
5 divisions in parotid (supra to infra): Temporal, zygomatic, buccal, marginal mandibular, cervical.
8
Vestibulocochlear
Your vestibulocochlear nerve has sensory functions involving hearing and balance. It consists of two parts, the cochlear portion and vestibular portion:
Cochlear portion. Specialized cells within your ear detect vibrations from sound based off of the sound’s loudness and pitch. This generates nerve impulses that are transmitted to the cochlear nerve.
Vestibular portion. Another set of special cells in this portion can track both linear and rotational movements of your head. This information is transmitted to the vestibular nerve and used to adjust your balance and equilibrium.
The cochlear and vestibular portions of your vestibulocochlear nerve originate in separate areas of the brain.
The cochlear portion starts in an area of your brain called the inferior cerebellar peduncle. The vestibular portion begins in your pons and medulla. Both portions combine to form the vestibulocochlear nerve.
9
Glossopharyngeal
Motor: Innervates the stylopharyngeus muscle.
General Sensory: Innervates the oropharynx, posterior 1/3 of the tongue, soft palate and tonsils.
Special Sensory: Taste sensation to the posterior 1/3 of the tongue.
Parasympathetic: Parasympathetic innervation to the parotid gland.
Originates in the medulla oblongata, exits cranium via jugular foramen.
3 nuclei in medulla: Main motor, parasympathetic, sensory
10
Vagus
Main motor nucleus: The main motor nucleus is nucleus ambiguus. Innervation to most of the muscles of the soft palate, pharynx, and larynx.
Parasympathetic: The parasympathetic nucleus forms the dorsal vagus nucleus. It receives afferents from hypothalamus via descending autonomic pathways and from glossopharyngeal nerve (from carotid sinus). The efferent fibres innervate involuntary muscles of bronchi, heart, and gastrointestinal system from oesophagus to transverse colon.
Special Sensory nucleus: This is the nucleus of the tractus solitarius for sensation of taste from taste buds on epiglottis.
General Sensory: Sensory innervation to the skin of the external acoustic meatus and meninges of posterior cranial fossa ends in the spinal nucleus of trigeminal nerve.
The vagus nerve arises from the medulla oblongata and exits the cranium via the jugular foramen. In the neck:
Pharyngeal branches – innervates most of the muscles of the pharynx and soft palate.
Superior laryngeal nerve – innervates the cricothyroid muscle of the larynx and sensation to the laryngopharynx and superior larynx.
Recurrent laryngeal nerve - innervates most of the muscles of the larynx
11
Accessory
Your accessory nerve is a motor nerve that controls the muscles in your neck. These muscles allow you to rotate, flex, and extend your neck and shoulders.
It’s divided into two parts: spinal and cranial. The spinal portion originates in the upper part of your spinal cord. The cranial part starts in your medulla oblongata.
These parts meet briefly before the spinal part of the nerve moves to supply the muscles of your neck while the cranial part follows the vagus nerve.
12
Hypoglossal
Your hypoglossal nerve is the 12th cranial nerve which is responsible for the movement of most of the muscles in your tongue. It starts in the medulla oblongata and moves down into the jaw, where it reaches the tongue.
Purely Motor
Hypoglossal nucleus is located in the medulla oblongata of the brainstem, emerges on its anterior surface, and leaves the cranium via the hypoglossal canal. The hypoglossal nucleus receives corticonuclear fibres from both cerebral hemispheres, but the neurons responsible for genioglossus (largest muscle of tongue) only receive fibres from the opposite hemisphere. Has one main motor nucleus.
Sense of taste
Front 2/3 of tongue: Facial (7)
Back 1/3 of tongue: Glossopharyngeal (9)
Root of tongue/Epiglottis: Vagus (10)
Blink (Corneal) reflex
Afferent/Sensory: Trigeminal (5) Opthalmic
Efferent/Motor: Facial (7)
CN 7 Lesions
In lower motor lesion the ipsilateral half of the face will be paralysed. In an upper motor lesion the contralateral lower quadrant of the face will be paralysed whilst the both upper quadrants (forehead) and the ipsilateral lower quadrant will be spared.
UMN L: Lower opposite quadrant
LMN L: Ipsilateral, half of face
