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
CN V TEST
- Sensory – sharp, dull, and light touch over the face
- Strength of jaw clenching and movements of the jaw
Cranial Nerve VII Functions:
- Facial movements OTHER THAN the tongue, eye muscles, and
muscles of mastication (somatic motor) - Taste from the anterior 2/3 of the tongue (special sense →
taste) - Autonomic motor input to glands (“autonomic” motor)
▪ Salivary and tears
▪ Nasal glands (nasal secretions) - Somatic sensation from the ear canal (somatic sensory)
Cranial Nerve VII Exits
simplified: Exits/enters the pons → passes through the internal
acoustic meatus and facial canal, exits through the
stylomastoid foramen
Cranial Nerve VIII Function
Hearing and balance (special senses)
From inner ear → internal acoustic meatus → pons
From pons it passes through the thalamus and synapses in the
temporal lobe for the perception of sound
See page for How it works
CN Nerve VIII Test
▪ Whisper to patient to test for auditory acuity
▪ Tuning forks – allow you to tell if there’s a problem with the nerve
or with the ear canal → ear drum → cochlea pathway
Tuning forks can be “heard” by conduction of the tuning fork
vibration through the bones of the skull
- If you “hear” the tuning fork better when it’s sending vibrations
through your skull (versus being held up to your ear) →
▪ have a problem with sound conduction through the ear
canal, ear drum, or the tiny bones of your middle ear
SLide 23
Cranial Nerve IX
- Swallowing – (somatic motor)
- Sensation from the pharynx, part of the external ear
(somatic sensory) and from chemoreceptors/baroreceptors
in the carotid body (“autonomic sensory”) - Taste from posterior 1/3 of tongue (special sensory)
- Innervation of a salivary gland – parotid (“autonomic
motor”)
Cranial Nerve IX Exit
Nerve enters/exits through the jugular foramen in the skull and
projects to/leaves the medulla
CN IX - TEST
▪ Stimulate the posterior aspect of the pharynx (careful – this causes a
gag reflex)
▪ The soft palate and tongue elevate (CN X) when stimulation is
detected (CN IX)
▪ Not the most helpful test – many healthy people have a diminished
gag reflex
Cranial Nerve X - Why is it considered “vagus”?
It projects to a wide variety of organs such as the lungs, heart,
liver, and gastrointestinal tract (among others)
- vagus nerve (“vagus” means “wanderer”)
Cranial Nerve X Functions
▪ Pharyngeal muscles –swallowing - and laryngeal muscles -
vocal cords (somatic motor)
▪ Parasympathetic nervous system input to the visceral organs
discussed above (“autonomic motor”)
* “Rest and digest” aspect of the autonomic nervous system
▪ Sensation from the visceral organs it impacts (“autonomic
sensory”) and some of the pharynx and external ear (“somatic sensory”)
▪ Sensory input from aortic baroreceptors and chemoreceptors
(“autonomic sensory”)
Cranial Nerve X - TEST
▪ Usually by listening to the patient’s voice – if hoarse,
then it may be due to damage of the vagus motor input
to the vocal cords
▪ Ask the patient to say “ahhhh” → elevation of the palate
is part of the somatic function of the vagus nerve
▪ We don’t usually test the function of parasympathetic
nervous system at the vagus nerve level
Cranial Nerve XI Function
– innervation of the sternocleidomastoid
and trapezius (somatic motor)
CN XI isn’t really a true cranial nerve – the neuronal cell
bodies are actually located in the cervical spinal cord
Cranial Nerve XI travels into the skulls via …. and then back out again via ….
- this nerve travels into the skull (foramen magnum)…
- and then back out again (jugular foramen)
Cranial Nerve XI TEST
▪ Turning the head against resistance
▪ Shrugging the shoulders
Cranial Nerve XII Function
Function – innervation of the tongue (somatic motor)
▪ Key for speech and swallowing
Cranial Nerve XII Exits
Exits the medulla and passes through the hypoglossal
canal
Cranial Nerve XII TEST
▪ Ask the patient to stick out her tongue, and move it side
to side
- If the tongue is deviated or the patient can’t follow these
instructions, then damage could be at the level of the
nerve, medulla, or motor cortex
The special senses are all carried via the cranial nerves
– all will eventually project to the ____
▪ Vision – _________ lobe
▪ Sound – _________lobe
▪ Taste and smell –_________ frontal lobes
▪ Vision – occipital lobe
▪ Sound – temporal lobe
▪ Taste and smell – inferior-lateral frontal lobes
The other senses – pain, touch, vibration, proprioception, temperature – all project to the ______________ in the parietal lobe
postcentral gyrus in the parietal lobe
▪ Touch, vibration, proprioception – ____________
lemniscal system
▪ Pain, temperature – _________ tract
– column-medial lemniscal system
– spinothalamic tract
Dorsal column-medial lemniscal system
Neurons that receive sensory input (first order neurons) send their axons to the dorsal horn (gray matter of spinal cord) and then project into the dorsal columns
(white matter of spinal cord)
▪ These axons stay on the same side until they enter the
medulla
- After entering the medulla, they synapse on another
neuron →
The next neuron (second-order neuron) crosses to the
other side of the medulla, and then synapses with
another neuron in the thalamus (third order neuron) →
The third order neuron projects to the post-central gyrus
Spinothalamic Tract
Neurons that receive sensory input (first order neurons)
send their axons to the dorsal horn (gray matter of
spinal cord) →
- and then synapse with another cell in the dorsal horn
(second-order neuron)
The axon of the second order neuron crosses over in the
gray matter, then sends its axon up to the brain in the
lateral and anterior white matter of the spinal cord →
▪ The second-order neuron synapses with another neuron
in the thalamus (third-order neuron) →
- Third order neuron synapses with a neuron in the postcentral gyrus
Each spinal nerve collects information from a part of
the body and sends it to the thalamus and to the __________
prefrontal gyrus
Loss of sensation can be at the level of the spinal nerve, the
spinal cord, the thalamus (rare) or at the level of the cortex. How doe we test these?
We “map out” neurologic deficits in sensation by testing
“dermatomes”
Specific dermatomes _____ (aren’t/are) always the same among
individuals
aren’t
some areas of the body will be supplied by one spinal nerve
in one person and a totally different spinal nerve in someone
else
C2 and C3 area
C2 scalp
C3 front of neck
C4, C5 area
shoulder
C8, T1 area
little finger
T4 area
nipple
T10 area
Umbilicus
L2 area
Thigh
L4 area
malleoli, medial anterior lower leg
L5 area
Malleoli, lateral anterior leg
S1 area
Lateral posterior leg, lateral plantar foot
S3, S4, S5 area
Perineal area
