WEEK 8 CRANIAL NERVES FINISHED Flashcards
How many pairs of cranial nerves are there?
12
In what order are they named in according to position?
From anterior to posterior
Why are cranial nerves called cranial nerves?
1 - they emerge through the foramina of the cranium/skull
2- they are covered by sheaths made out of cranial meninges
What sections of the brain are included in the brain stem?
The medulla oblongata, the pons and the midbrain (mesencephalon)
What is the brain stem?
The connecting link between the remainder of the brain and the spinal cord
What are the 5 main functional components of cranial nerves?
Motor:
- Somatic motor (efferent)
- Visceral motor (efferent parasympathetic)
Sensory:
- General sensory (afferent) (touch, pain, temperature)
- Visceral sensory (afferent)
- Special sensory (hearing, sight, smell etc)
What are the 12 cranial nerves in order?
CN I - Oh OLFACTORY
CN II - Oh OPTIC
CNIII - Oh OCCULOMOTOR
CN IV - To TROCHLEAR
CN V - Touch TRIGEMINAL
CN VI - And ABDUCENS
CN VII - Feel FACIAL
CN VIII - Virgin VESTIBULOCOCHLEAR
CN IX - Girls’ GLOSSOPHARYNGEAL
CN X - Vaginas VAGUS
CN XI - And ACCESSORY
CN XII - Hymen HYPOGLOSSAL
CN I - Composed of? Originates and ends?
What type of functional component(s) does it have?
OLFACTORY NERVE
Functional type: special sensory - smell/olfaction
Approx 20 olfactory nerves on each side, composed of both neurons and receptors.
Originates - cell bodies and dendrites are within the olfactory mucosa of the nasal cavity
Ends - olfactory bulb, continue to the olfactory area in the cerebral cortex through the cribriform plate of the ethmoid bone
Describe how and where the nerves from CN I pass into the cranium.
The olfactory nerve fibres pass through the foramina of the cribriform plate of the ethmoid bone. They pierce the dura and arachnoid mater of the brain and enter the olfactory bulb in the anterior cranial fossa. They synapse with the fibres in the bulb then become the olfactory tract as they pass through to the brain.
CN II -
Originates?
Ends?
What type of functional component(s) does it have?
OPTIC NERVE
Functional type: Special sensory - sight
Originate: Eyeball
Exit skull: Through optic canal
Arises from the retinal cells in the back of the eye.
Begins where the axons of these cells pierce the sclera (the external fibrous coat of the eyeball). The optic nerve conducts impulses from the photoreceptors (cones/rods) in the retina.
The nerve passes posteriorly /medially in the orbit or the eye socket and exits through the optic canal. In the middle cranial fossa the optic nerve forms the optic chiasm.
What the CN II ‘claim to fame’?
The largest cranial nerve
What is the optic chiasm? What is the optic nerve called after it has passed through as the optic chiasm?
Where the fibres from the medial half of each retinal cross over and join the uncrossed lateral fibres from each retina.
After this point they become the optic tracts and then continue on to the visual cortes within the occipital lobe.
What nerve is the paired extension of the forebrain?
CN II
What fibres form the right optic tract? Explain how this is relevant in terms of the various places the optic nerve can be damaged
The right optic tract is formed by the fibres from the ride side of each retina. This would mean the right optic tract is made up by the nasal fibres from the right eye and the peripheral fibres from the left eye. (remember that nasal fibres come from the nose and hit the lateral side of the eye, where as the peripheral fibres come from the periphery and hit the medial side of the eye).
If the right optic nerve was damaged before it formed the optic chiasm, the person would lose all sight in the right eye. If the optic chiasm was split through the middle the person would have nasal vision in each eye but no vision from the peripheral portion. If the damage occurred in the right optic tract, the person would lose peripheral sight in the left eye and nasal sight in the right eye. Therefore they would be unable to see to the right at all.
What does visual field mean?
What is seen by a person with both eyes wide open and looking straight ahead.
CN III - Originates? Ends? What type of functional component(s) does it have? What does it do/functions?
OCCULOMOTOR NERVE
Originates: in the midbrain
Exits skull: through the superior orbital fissure.
Functional type:
- Somatic motor nerves
- Parasympathetic visceral motor nerves
Functions:
- Motor control over 4 of the 6 extraoccular muscles (superior rectus, inferior rectus, medial rectus, inferior oblique)
- Motor to the upper eyelid muscles (levator palpebrae superioris)
- Parasympathetic to the pupillary sphincter (constricts pupil) and cillary muscles of the lens (accommodation)
What is olfaction?
The sensation of odours that results from the detection of odorous substances aerosolised in the environment.
CN IV - Originates? Ends? What type of functional component(s) does it have? What does it do/function?
TROCHLEAR NERVE
Originates: From the midbrain, BUT it emerges from the posterior surface of the midbrain and winds around the brainstem.
Ends: Leaves the skull via the superior orbital fissure.
Functional type: Somatic motor
Function: innervates superior oblique muscle to the eye as well as proprioception
What is the CN IV ‘claim to fame’?
Only CN to emerge from the posterior surface of the midbrain, ALSO, the smallest CN but has the longest intracranial course.
CN V - Originates? Ends/ exits the skull? What type of functional component(s) does it have? What are the different divisions?
TRIGEMINAL NERVE
Originates: from the pons, one small root, one large root
Functional types: Somatic motor fibres and somatic sensory fibres
Divisions
- Ophthalmic (V1) nerve
- Maxillary (V2) nerve
- Mandibular (V3) nerve
Ends:
Ophthalmic nerve - SOF
Maxillary nerve - Foramen rotundum
Mandibular nerve - Foramen ovale
What is the CN V ‘claim to fame’
The second largest Cranial Nerve
What are the functional components and functions of the divisions of CN V?
Ophthalmic (V1)
- Sensory
Maxillary (V2)
- Sensory
Mandibular (V3)
- Sensory and motor nerve
What are the functions of the trigeminal nerve?
Motor:
Muscles of mastication (masseter, temporalis, medial and lateral pterygoids)
Mylohyoid muscles
Anterior belly of digastric
Tensor veli palatini
Tensor tympani
Sensory:
Principal general sensory nerve for the head
Face, teeth, mouth, nasal cavity, dura
CN VI - Originates? Exit from the skull? What type of functional component(s) does it have? What does it do/function?
ABDUCENS NERVE
Origin: pons, between the pons and medulla
Exits the skull: through the SOF
Functional type: somatic motor
Function: lateral rectus muscle
CN VII - Originates? Course? Ends/ exits the skull? What type of functional component(s) does it have?
FACIAL NERVE
Origin: Emerges from the junction of the pons and medulla
Course: passes through the internal acoustic meatus, facial canal within the temporal bone and exits through the stylomastoid foramen. Enters the parotid gland where it gives rise to the terminal branches which supply the muscles of facial expression.
Exits: through the stylomastoid foramen.
Functional types: Special sensory (taste) Somatic sensory Somatic motor Visceral motor (parasympathetic)
What are the 2 roots of CN VII?
Larger motor root - muscles of facial expression
Smaller intermediate root - carries special sensory (taste), somatic sensory, visceral motor (parasympathetic)
CV VII functions:
Taste to the anterior 2/3 of the tongue and soft palate
Sensory to the external ear
Motor to:
- mm of facial expression
- throat (posterior belly of digastric, stylohyoid)
- middle ear (stapedius)
- proprioception to the above muscles
Parasympathetic to the submandibular and sublingual glands, lacrimal gland, glands of the nasal cavity and palate
What is CN VII ‘claim to fame’
The longest intraosseous CN
What are the nerves of the CN VII?
Greater Petrosal Nerve (to the lacrimal gland)
Nerve to the Stapedius and the Chorda Tympani (to the submandibular and sublingual gland, taste to the anterior 2/3 of the tongue)
What holes does CN VII enter and exit?
Transverses the internal acoustic meatus then the facial canal within the temporal bone
Exits through the temporal bone through the stylomastoid foramen.
What are the terminal branches of CN VII?
Posterior auricular Temporal Zygomatic Buccal Mandibular Cervical
Describe the parotid gland (innervation?)
Largest of 3 salivary glands, supplied by the glossopharyngeal nerve CN IX, sympathetic by cervical plexus
CN VIII - Originates? Course? Ends/ exits the skull? What type of functional component(s) does it have? Functions?
VESTIBULOCOCHLEAR NERVE
Originates: Junction between the pons and medulla
Ends/exits the skull: Enters the internal acoustic meatus. but then doesn’t exit the skull
Functional type - special sensory
Functions:
Vestibular nerve = Equilibrium
Cochlear nerve = hearing
What is CN VIII’s ‘claim to fame’
The only CN to not exit the skull
CN IX -
Originates?
Ends/ exits the skull?
What type of functional component(s) does it have?
GLOSSOPHARYNGEAL NERVE
Originate: Medulla
Exits cranium: through jugular foramen.
Functional types and functions:
- Special sensory: taste
- Somatic sensory
- Visceral sensory
- Somatic motor
- Visceral motor (parasympathetic)
What are the functions of CN IX?
Sensory:
Special - taste to the posterior 1/3 of tongue
Sensory:
Somatic - mucosa of the pharynx and palatine tonsils
- Posterior 1/3 of tongue, auditory tube, middle ear, carotid body and sinus.
Motor:
- stylopharyngeus
Proprioception:
- stylopharyngeus
Parasympathetic:
- parotid gland and glands of the posterior 1/3 of the tongue
CN X -
Originates?
Ends/ exits the skull?
What type of functional component(s) does it have?
VAGUS NERVE
Origin: Series of rootlets from the medulla
Exits skull: through the jugular foramen
Functional types:
- Somatic sensory
- Visceral sensory
- Special sensory
- Somatic motor
- Visceral motor
What is the CN Xs ‘claim to fame’?
The longest CN with the most extensive course
What are the functions of CN X?
Somatic sensory:
- Inferior pharynx
- Larynx
Visceral sensory:
- Thoracic and abdominal organs
Special sensory:
- Taste in the root of the tongue and taste buds of the epiglottis
Somatic motor and proprioception:
- soft palate
- pharynx
- intrinsic laryngeal muscles
- palatoglossus
Visceral motor/parasympathetic
Parasympathetic fibres to the thoracic and abdominal viscera as far as the left colic flexure
CN XI -
Originates?
Ends/ exits the skull?
What type of functional component(s) does it have?
ACCESSORY NERVE
Originates:
- has a cranial root - medulla
- and a spinal root - upper C5-C6 segments
Exits the skull: through jugular foramen
Functional types:
Somatic motor
Functions:
Motor: soft palate (muscles, movable posterior 1/3 of the palate suspended from the posterior border of the hard palate), pharynx
Motor: SCM, trapezius
CN XII -
Originates?
Ends/ exits the skull?
What type of functional component(s) does it have?
HYPOGLOSSAL NERVE
Origin: Medulla
Exits skull: hypoglossal canal
Motor: most of the muscles of the tongue, both intrinsic and extrinsic
Proprioceptive fibres to the above muscles
Skull exits of all cranial nerves?
I - Foramina in the cribiform plate of the ethmoid bone II - Optic Canal III - SOF IV - SOF V - V1 - SOF, V2 - foramen rotundum, V3 - foramen ovale VI - SOF VII - Internal acoustic meatus to stylomastoid foramen VIII - does not exit the skull IX - Jugular foramen X - Jugular foramen XI - Jugular foramen XII - Hypoglossal canal
Claims to fame for all CNs
I - None II - Largest cranial nerve III - None IV - Smallest CN but longest intracranial course, only CN to emerge from the brainstem dorsally V - Second largest CN VI - None VII - Longest intraosseous CN VIII - Only CN to not exit the skull IX - None X - Longest CN with the most extensive course XI - Has a spinal and CN root XII - None
