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.
