Clin Phys 6 Flashcards
Nerves that “emerge from the brain” and exit via skull foramina
cranial nerves
- All other nerves exit the spinal cord and travel through the
intervertebral foramina
Cranial nerves carry a wide variety of information:
▪ Special sensory information
▪ Somatic motor information
▪ Somatic sensory information
▪ Motor and sensory information to/from structures that we cannot control or perceive
Olfactory (CN I) – projects to
cortex
Optic (CN II) projects to
thalamus
CN III and IV nuclei are found
nuclei are
found in the midbrain
CN V, VI, VII, and VIII nuclei are found
in the pons
CN IX, X, XI, XII
nuclei are (mostly) found in the medulla
Cranial Nerve I Function
sense of smell (special sense)
From the superior part of the nasal cavity → olfactory bulb → many different locations in the temporal and frontal lobes
CN I Skull entry/exit point:
Axons penetrate the skull via the
tiny holes in the cribriform plate (ethmoid)
How do we test CN I
▪ Ask the patient to identify a couple of distinctive smells
(eyes closed if necessary)
▪ i.e. coffee, peppermint
▪ Loss of sense of smell = anosmia
* Infections (COVID is famous for it), head injuries
CN II Function
vision (special sense)
From the retina (back of the eye) → thalamus → occipital
lobe (cortex)
There are other connections between the optic nerve and the
brain other than through the thalamus – mostly for mediating
reflex eye and head movements
CN II Exit Point
optic foramen (canal)
CN II Test
▪ The Snellen eye chart (central vision)
▪ Peripheral field tests (peripheral vision)
▪ Observation of the back of the eye (ophthalmoscope)
* Assesses the retina (the “light sensor”)
▪ Others – pupillary movements, rapid involuntary eye
movements
Cranial Nerve III, IV, VI function
Main Function: Eye movements (somatic motor)
CN III Location
from the midbrain → muscles around the eye
As well, CN III projects to your pupillary muscles (dilation,
constriction) and your levator palpebrae superioris
muscle (helps elevate your eyelid)
CN IV Location
from midbrain → one of the muscles around your eye
(superior oblique)
CN VI Location
from the pons → one of the muscles around your eye
(lateral rectus)
Cranial Nerve III, IV, VI Skull entry/exit point for all
superior orbital fissure
CN III function
most eye movements and control of pupils
CN IV function
directs your gaze down and outwards
CN VI function
– directs gaze laterally (abducts eyeball)
Cranial Nerves III, IV, VI: How do we test them?
You can see that these nerves innervate very small, quick, coordinated muscles that help us to control our eye movements
TEST
1. Ask patient to “follow your finger with their eyes”
- Move your finger so that you draw a big “H” in the air
in front of them
* Eyes should smoothly follow your finger - Shine a light into the patient’s eyes and hold an object
close to patient’s eyes
* Pupils should constrict in response
Cranial Nerve V Functions (2)
- Sensation over the face, scalp, nasal cavity and cornea (somatic sensation)
- Sensations include touch, pain, proprioception for facial
muscles and tongue
- Cornea = clear, tough outer part of the eye that overlies the
iris - Motor function (somatic motor) for the muscles of mastication (chewing) and some neck, middle ear muscles
▪ Main muscles – temporalis, masseters, pterygoids
Cranial Nerve V Sensation Exit:
Exits from the pons, leaves skull through:
* Superior orbital fissure: cornea, forehead, scalp, eyelids,
nasal mucosa (upper face, scalp)
- Foramen rotundum: face over the maxillary part of the
face, including maxillary teeth (mid-face) - Foramen ovale: lower jaw, proprioception for tongue
(lower face, mouth – but NOT taste)
Cranial Nerve V Motor Exit:
▪ Main muscles – temporalis, masseters, pterygoids
▪ Exits through the foramen ovale