Cranial Nerves Flashcards
What is the function of the olfactory nerve?
1 The olfactory nerve enables us to receive sensation of smell.
2 Olfactory sensations also stimulates responses the digestive function through connections of the brain with the vagus nerve.
3 Emotional responses and memories are also activated through connections with the lambic system and associated areas of the brain.
4 increases the sense of taste thanks to the capacity of the nose to distinguish hundreds of substances even in minute quantities.
Describe the pathway of the olfactory nerve
- receptors within the olfactory mucosa in the upper part of the nasal cavity receive sensation of smell
- fibres travel up through the cribriform plate of the ethmoid bone
- fibres emerge onto the surface of the ethmoid bone and enter the olfactory bulbs (extensions of the forebrain lying on the surface of the cribriform plate and they sinapse
- neurological impulses are transmitted posteriorly from the olfactory bulbs along the olfactory tracts to the forebrain
What could be the causes of anosmia?
^Fracture of the cribriform plate with damage of the olfactory fibres passing through it
^displacements or restrictions of the ethmoid or its adjoining bones, including frontal bone, sphenoid and vomer
^membranous tension impinging on the olfactory fibres as they pass through the dura on the superior surface of the cribriform plate
^congestion in the nasal cavity blocking receptors
^blockage of the nasal passage due to cold or nasal allergy can cause transient anosmia
^ eccessive dryness of the nose can also cause transient anosmia
What is another important function of the olfactory nerve pathway apart from carrying olfactory sensations?
It provides the most significant pathway for drainage of the cerebrospinal fluid.
Other outlets of cerebrospinal fluid are:
Arachnoid villi
Spinal nerve exit
Cranial nerve exit
What type of nerve is the olfactory nerve?
Purely sensory
What type of nerve is the optic nerve?
Purely sensory
What are the symptoms of vagal dysfunction?
Vagotonia and underactivity of the vagus
What are the symptoms of vagotonia?
Hypotension Bradycardia Cold hands and feet Cold and clammy skin Severe fatigue
What are the symptoms of under active vagus?
Reduced activity of stomach (gastroparesis)
Nausea
Heartburn
Abdominal pain
Stomach spasms
Disturbance of the awareness of hunger and digestion
and the symptoms of overactive sympathetic system:
Arrhythmia, increased heart rate, shortness of breath, difficulty with swallowing and speech
What is the effect of healthy level of vagal tone?
Lowering blood pressure Lowering heart rate Reduced risk of stroke and cardiovascular diseases Improved digestion Enhanced blood sugar regulation Enhanced stomach acid secretion Enhanced digestive enzymes production Reduced sympathetic stimulation
What is low vagal tone associated with?
Cardiovascular conditions and stroke Depression Diabetes Chronic fatigue Cognitive impairment Inflammatory conditions like: rheumatoid arthritis, inflammatory bowel disease, endometriosis Autoimmune thyroid conditions Lupus
What are the natural ways to stimulate the vagus nerve?
Deep breathing Relaxation Yoga Submerging the tongue Cold water face immersion Healthy diet Probiotics Social interaction Soft gentle contact to the eyeballs
With which other cranial nerve and part of the brain does the olfactory nerve connect?
With the vagus nerve, stimulating digestion
With the lambic area stimulating emotional responses and memories
How does the process of vision work?
The light enters the lens, the aqueous humour and the vitreous humour of the eyeball, is focused by the lens onto the receptors.
What are the receptors of the retina?
Rods for the light and dark vision 125 millions in the retina
Cones for the color vision 7 millions
Where are the central vein and central artery of the retina?
They travel through the centre of the optic nerve
How many fibres does an optic nerve have?
Around 1 million
What’s the pathway of the optic nerve?
The optic nerve travels posteriorly from the back of the eyeball
Passes through the optic canal (between the body and the lesser wing of the sphenoid) and emerges medial to the anterior chinois process of the sphenoid, anterior to the pituitary gland.
Here the 2 optic nerves come together to form the optic chiasm in which medial fibres from each optic nerve decussate (cross over to the other side) and continue posteriorly as the optic tract
With which cerebral structures does the optic tract connect?
It gives off branches to the geniculate body of the thalamus enabling visual reflexes
Continues as optic radiation to the visual cortex in the calcarone fissure of the occipital lobe
What is particular about the optic nerve?
The optic nerve is considered an extension of the brain as the eyeball is completely enveloped within the meninges, the sclera (white) of the eye being a continuation of the meningeal membrane
How do you know the site of neurological damage within the optic pathway?
Damage to the optic nerve, between the eyeball and the chiasma, would cause a loss of sight in the affected eye
Damage to the centre of the optic chiasma (ex: pituitary tumor)may lead to tunnel vision (dysfunction of medial fibres on both sides, which carry information from the lateral part of the visual field)
Damage in the optic tract would lead to loss of vision in the medial fibres of one eye and lateral of the other, reducing the visual field on the opposite side
What would a damage to the optic nerve cause?
If it’s located between the eyeball and the chiasma, would cause loss of vision in the affected eye
What would damage to the optic chiasma cause?
If the centre of the chiasma is affected, there will be tunnel vision, as the dysfunction will affect the medial fibres of both sides (ex: pituitary tumor) which perceive the lateral part of the visual field
What would be the effect of damage to the optic tract?
Loss of vision of the medial side of the eye and lateral vision of the opposite eye
What can be the source of disturbance of the optic nerve function?
Cranial bone displacement (particularly involving the sphenoid)
Nerve compression (particularly optic canal and sella turcica)
Membranous tension
Neuritis
Why are cranial nerve III IV and VI often described together?
Because their main function is the movement of the eyeball and they coordinate their activity when directing the gaze in different directions
What is the function of cranial nerve III oculomotor?
Movement of the eye (up, middle, down, up and out)
Rising of the upper eyelid
Control of intrinsic muscles of the eye for pupil constriction and lens accommodation
What’s the pathway of cranial nerve III?
Oculomotor nerve emerges from the anterolateral midbrain
Runs on the floor of the middle cranial fossa
Passes through the cavernous sinus
Enters the orbit through the superior orbital fissure
Passes through the tendinous ring and
Gives branches to the superior rectus, inferior rectus, medial rectus, inferior oblique muscles and to the levator palpebrae superioris muscle
The parasympathetic fibres branch away from the main nerve within the posterior orbit to synapse with the ciliary ganglion, and they continue into the eyeball as short ciliary nerves to control the intrinsic muscles of the eye for pupil constriction and lens accommodation.
What’s the pathway of cranial nerve IV?
The trochlear nerve emerges from the posterolateral midbrain
Runs along the floor of the middle cranial fossa
Passes through the cavernous sinus
Enters the orbit through the superior orbital fissure
Goes directly to the superior oblique muscle which directs the gaze down and out, without passing through the tendinous ring
What’s the pathway of cranial nerve VI?
The abducent nerve emerges from the anterolateral pons
Runs along the floor of the middle cranial fossa
Enters the orbit through the superior orbital fissure
Passes through the tendinous ring and goes to the lateral rectus muscle to control the moment of the eye in order to look laterally
What is the clinical effect of an injury to the Oculomotor nerve?
Injury may lead to strabismus (squints) and diplopia (double vision) on looking in whatever direction which involves the use of the superior, inferior and medial rectus muscles.
The affected eye can only move laterally and downward and will tend to be directed laterally since the lateral rectus muscle will now act unopposed.
Injury affecting the levator palpebrae superioris may lead to ptosis (drooping) of the eyelid, but because the eyelid is also supplied by the sympathetic fibres to the tarsal muscle, the effect will be only partial.
Injury affecting also the parasympathetic branch of the nerve will lead to a persistently dilated pupil on the affected side, potentially causing photophobia, and may affect accommodation of the eye to near and far vision
What is the effect of injury on the parasympathetic component of oculomotor nerve?
Injury affecting the parasympathetic branch of the nerve will lead to a persistently dilated pupil on the affected side, potentially causing photophobia, and may affect accommodation of the eye to near and far vision
What’s the clinical effect of injury to the trochlear nerve?
Injury may lead to strabismus (squint) and diplopia (double vision) on trying to look down and out to the affected side as one eye will move in that direction whilst the other will continue to look forward, up or down.
What’s the clinical effect of an injury to the abducent nerve?
Injury may lead to strabismus (squint) and diplopia (double vision) on trying to look laterally to the affected side as one eye will move in that direction whilst the other will not turn, but rather continue to look straight ahead, leading to transient diplopia, to the point that usually patient will adapt by turning the head instead of the eyes.
The eye will tend to be directed medically (convergent strabismus) since the medial pull of the medial rectus will now be unopposed by the paralysed lateral rectus muscle.
What would be the craniosacral treatment for squints?
Squints are often addressed through an operation at an early age. This may resolve the squints successfully, but will not address the other imbalances that may be contributing to the squint.
When there are clearly evident cranial or membranous distortions, the cases are very responsive to cranio sacral integration.
Craniosacral treatment involves:
Clear understanding of the nerves, muscles and other structures involved and identification of the dysfunction
Accurate diagnosis of the location and source of disturbance by tracing the nerve pathways with informed awareness
Craniosacral balancing of the orbit, cranium, membranes and any other structure involved
Identify and address patterns throughout the body that may be contributing to the disturbance in the eye
Addressing birth trauma
What are the functions of the Trigeminal nerve?
The Trigeminal nerve is primarily associated with receiving sensation from the face: skin of the face from the top of the head to the lower jaw and throat, eyeball, conjunctiva, lacrimal gland, ear, external auditory canal, nasal cavity, oral cavity, sinuses, teeth, TMJ, anterior tongue, nasopharynx, meningeal membranes of anterior and middle cranial fossa, including parts of the tentorium.
Proprioceptive input from the muscles of mastication, of facial expression, extrinsic muscles of the eye and eyeball.
The motor branch supplies the muscles of mastication enabling chewing and other movements of the lower jaw, and several small muscles:
Tensor tympani, tensor veli palatini, anterior belly of the digastric, mylohyoid.
Where il the Trigeminal nerve emerging?
It emerges from the pons
Where is the trigeminal ganglion located?
It bulges out of each side of the pons, and it is contained within the cavum Trigeminale, a membranous cave encapsulating the ganglion and its roots, at the apex of the petrous portion of the temporal bone.
What is the function of the trigeminal ganglion?
It is the site of synapse for sensory fibres travelling in from the periphery. Preganglionic fibres of the three sensory divisions of the trigeminal nerve: ophthalmic, maxillary and mandibular nerves pass into the ganglion, where they synapse before relaying their sensory input into the brain stem via postganglionic fibres.
What are the sensory divisions of the Trigeminal nerve?
Ophthalmic, maxillary, and mandibular division
What is the pathway of the ophthalmic division of Cr.V?
After emerging from the pons and synapsids in the trigeminal ganglion, the ophthalmic division
Travels along the floor of the middle cranial fossa together with CIII CIV and CVI,
Passes through the cavernous sinus together with CIII CIV and CVI,
Enters the orbit through the superior orbital fissure together with CIII CIV and CVI,
Within the orbit it gives off
a sensory branch to the lacrimal area (lacrimal branch)
a sensory branch to the cornea, iris, ciliary muscles and pupil dilator muscles, that travels further on to the nasal cavity and passes to the frontal, ethmoidal and sphenoidal sinuses (nasociliary branch)
a main sensory branch which emerges at the supraorbital notch and receives sensation from the frontal area: forehead and frontal sinuses.
Where does the ophtalmic division receive sensation from?
From the upper portion of the face, the forehead, the eyes, upper eyelids, lacrimal glands, nose, nasal cavity and frontal, ethmoidal and sphenoidal sinuses
What is the pathway of the maxillary division of the trigeminal nerve?
After emerging from the trigeminal ganglion,
It travels anteriorly along the floor of the middle cranial fossa
Turns inferiorly through the floor of the cranium via the foramen rotundum
Emerges to the inferior surface of the cranium and turns anteriorly to enter the orbit through the inferior orbital fissure
Passes along a groove on the floor of the orbit until it deepens to become a tunnel
It gives off an alveolar branch to the upper teeth
A branch to the maxillary sinus
And emerges at the surface of the face through the infraorbital foramen, below the inferior rim of the orbit
Where does the maxillary division of the Trigeminal nerve receive sensation from?
It receives sensation from the middle portion of the face:
From the lower eyelid to the upper lip, including the side of the nose
From the mucous membranes of nose and nasopharynx,
From the maxillary sinus
From the roof of the mouth and the upper teeth
What is the pathway of the mandibular branch of the trigeminal nerve?
After emerging from the trigeminal ganglion,
It turns downward through the foramen ovale
Gives off a recurrent meningeal branch which passes back up to the meninges of the middle and anterior cranial fossa through the foramen spinosum (together with the middle meningeal artery) as well as to the mastoid air cells
At the inferior surface of the cranium, the mandibular branch divides in 4 branches:
Auriculo-temporal branch to the skin of the external ear, external auditory canal, tympanic membrane and temporal area
Buccal branch to the buccinator muscle
Lingual branch to the anterior 2/3 of the tongue
Inferior alveolar branch which enters the mandibular foramen on the medial surface of the ramus of the mandible, travels inside the mandible giving off alveolar branches to the lower teeth and emerges at the mental foramen on the anterior surface of the mandible
The motor division also travels with the mandibular branch
Where does the mandibular branch receive sensation from?
From the lower portion of the face including the mandible,
From the lower teeth, gums and lip
The anterior 2/3 of the tongue
TMJ
Mastoid air cells
Skin of the ear, external auditory canal and tympanic membrane
Temporal area
What are the branches of the mandibular division?
Recurrent meningeal nerve Auriculo-temporal nerve Buccal nerve Lingual nerve Inferior alveolar nerve
Where does the auriculo-temporal nerve receive sensation from?
Auriculo-temporal nerve receives sensation from the skin of the external ear, external auditory canal, tympanic membrane and temporal area
Where does the buccal nerve receive sensation from?
Buccal nerve receives sensation from the buccinator muscle
