Cranial Nerve Pathways Flashcards
Describe the Cranial Nerve pathway for the: Olfactory Nerve CN I
1) Smell is picked up by smell receptors in olfactory mucosa.
2) Olfactory nerves pass up through Cribriform Plate of Ethmoid & synapse in Olfactory Bulbs.
3) Travel posteriorly along olfactory tracts into Forebrain.
Describe the Cranial Nerve pathway for the: Optic Nerve CN II
1) Visual images are received by the Retina.
2) Images are transmitted from back of eyeball along Optic Nerve.
3) Passes through optic canal to Optic Chiasma (in front of pituitary gland).
4) 2 optic nerves meet at Optic Chiasma and decussate, medial fibres cross, lateral fibres don’t.
5) Optic fibres continue as the Optic Tract and Optic Radiation to the visual cortex in Occipital Lobe to be processed.
Describe the Cranial Nerve pathway for the: Oculomotor Nerve CN III
Oculomotor; Trochlear & Abducent -
1) EMERGE from Midbrain (3,4), Pons (6)
2) Travel forward together along floor of MIDDLE cranial fossa, each side of SPHENOID BODY.
3) Pass through CAVERNOUS SINUS
4) ENTER orbit through SUPERIOR ORBITAL FISSURE with CN V - Trigeminal - Ophthalmic Branch
5) Branch out in different directions:
Oculomotor supplies - MOTOR fibres to EXTRINSIC MUSCLES of eye =
Superior Rectus - eyes up
Inferior Rectus - eyes down
Medial Rectus - eyes towards the middle
Inferior Oblique - eyes down and out
Levator Palpbrae Superioris - Raises upper eye lid
Oculomotor supplies - PARASYMPATHETIC fibres to INTRINSIC MUSCLES of eye =
Pupil constriction &; Lens accommodation
Describe the Cranial Nerve pathway for the: Trochlear Nerve CN IIII
MOTOR NERVE
Oculomotor; Trochlear & Abducent -
1) EMERGE from Midbrain (3,4), Pons (6)
2) Travel forward together along floor of MIDDLE cranial fossa, each side of SPHENOID BODY.
3) Pass through CAVERNOUS SINUS
4) ENTER orbit through SUPERIOR ORBITAL FISSURE with CN V - Trigeminal - Ophthalmic Branch
5) Branch out in different directions:
Trochlear Nerve supplies MOTOR fibres to
EXTRINSIC MUSCLE of eye =
Superior Oblique - eyes down and out
Describe the Cranial Nerve pathway for the: Trigeminal Nerve CN IV
SENSORY = receiving sensation from face and x3 sinuses (not maxillary)
OPTHAMALMIC DIVISION -
1) Emerges from PONS via TRIGEMINAL GANGLION
2) Along floor of MIDDLE cranial fossa
3) ENTERS orbit through SUPERIOR ORBITAL FISSURE (with CN III, IV and VI)
4) Divides into 3 BRANCHES
A) = Lacrimal branch to lacrimal glands
B) = Nasociliary branch (iris, ciliary muscles), penetrates nasal cavity and passes to x 3 sinuses (not maxillary)
C) = Frontal branch - EMERGES SUPRAORBITAL NOTCH to supply frontal area, receives info from forehead and frontal sinus.
SENSORY = receiving sensation from middle face, upper teeth & maxillary sinuses, sides of nose
MAXILLARY DIVISION -
1) Emerges from PONS via TRIGEMINAL GANGLION
2) Along floor of MIDDLE cranial fossa
3) Passes down through Foramen ROTUNDUN
4) ENTERS orbit through INFERIOR ORBITAL FISSURE
5) ALVEOLAR branch to UPPER teeth
6) Main nerve travels along groove in orbit
7) EXITS at INFRAORBITAL FORAMEN in MAXILLA
MANDIBULAR DIVISION -
SENSORY = receives sensation from lower face, lower teeth, anterior 2/3 tongue, TMJ, skin of ear, temporal area
1) Emerges from PONS via TRIGEMINAL GANGLION
2) Along floor of MIDDLE cranial fossa
3) Passes through Foramen OVALE
4) RECURRENT MENINGEAL branch turns up to pass through the Foramen SPINOSUM to the Meninges (along with MENINGEAL ARTERY and MENINGEAL VEIN)
4) Mandibular division ENTERS MANDIBULAR FORAMEN (medial wall of ramus) to travel through mandible.
5) Gives off alveolar branches to lower teeth.
6) EXITS at MENTAL FORAMEN
MOTOR division of Mandibular division = supplies Muscles of Mastication
1) also passes through Foramen OVALE with the sensory division
2) To supply the muscles of mastication & TENSOR TYMPANI and TENSOR VELI PALATINI
NB - tensor tympani - muscle contracts when chew, speak, or hear loud sounds = tenses the tympanic membrane which holds the malleus bone and dampens vibration and therefore sound. Opens Eustachian tube with Tensor Vali Palatini. Muscle can be held in permanent contraction due to anxiety; whiplash; upper cervical spine; TMJ.
NB - tensor veli palatine muscle - also opens Eustachian tube. When this tiny muscle goes into spasm, it closes off the eustachian tube and produces symptoms that mimic middle-ear problems eg tinnitus. Also tenses soft palate and prevents food going down nasopharynx while swallowing.
DYSFUNCTION OF TRIGEMINAL NERVE - MANDIBULAR
1) Middle ear infections and glue ear - relationship with tensor tympani and tensor veli palatini muscle
2) Hearing disorders/ LD in relation to noise and sensations
3) Hyperacusis - sensitivity to noise
4) Trigeminal Neuralgia - causes = pressure on nerve; latent herpes simplex virus; tumour or MS damaging nerve. Usually affects Mandibular or Maxillary division.
Describe the Cranial Nerve pathway for the: Abducent Nerve CN VI
Oculomotor; Trochlear and Abducent -
1) EMERGE from Midbrain (3,4), Pons (6)
2) Travel forward together along floor of MIDDLE cranial fossa, each side of SPHENOID BODY.
3) Pass through CAVERNOUS SINUS
4) ENTER orbit through SUPERIOR ORBITAL FISSURE with CN V - Trigeminal - Ophthalmic Branch
5) Branch out in different directions:
Abducent supplies MOTOR to:
Lacteral Rectus Muscle - eyes side to side (abducts)
Describe the Cranial Nerve pathway for the: Facial Nerve CN VII
MOTOR - to muscles of face (expressions) and glands (not parotid)
SENSORY - from anterior tongue 2/3; hard and soft palate and external ear and mastoid region.
PARASYMPATHETIC - to the glands of the face = lacrimal, nasal, sublingual, submandibular NOT parotid.
1) EMERGE from PONS
2) ENTERS INTERNAL AUDITORY MAETUS (with CNVIII)
3) Travels through Temporal Bone in Facial Canal
4) In facial canal it gives off sensory branches to the anterior tongue AND parasympathetic supply to the glands of the face.
5) Main MOTOR branch EXITS at the STYLO-MASTOID FORAMEN
6) Travels forward to the PAROTID GLAND (but does not supply it) and branches out to muscles of face.
NB
Nasal glands = produce mucus
Lacrimal glands = produce tears
Sublingual glands = (under tongue) = produce saliva for mastication, swallowing, digestion
Submandibular glands = (floor of mouth) = produce saliva for mastication, swallowing, digestion.
So Facial Nerve (parasympathetic division) regulates supply of saliva, mucus, tears.
If parasympathetic nerve is restricted = may overstimulate glands = mucus = lead to sinusitis
OR may inhibit secretions = dry mouth; dry eyes; dry nose = inflammation of mucus membranes
DYSFUNCTION =
1) Bells Palsy = flaccid paralysis of face on 1 side; muscles droop, expressionless; eye droops, food can get stuck in cheek; crooked smile; tears trickle from affected eye, saliva from affected side. Cause = stroke; mumps; surgery; middle ear infection; head injury; nerve damage or inflammation.
Describe the Cranial Nerve pathway for the: Vestibulocochlear CN VIII
SENSORY - hearing and equilibrium
1) Nerve travels from INNER EAR
2) Through INTERNAL AUDITORY MAETUS (with CN VII)
3) ENTER LOWER PONS
4) COCHLEAR DIVISION = Sound waves travel through external auditory meatus to tympanic membrane. Vibrations travel through malleus; incus; stapes to cochlea of inner ear. Vibrations turn into neurological stimuli to PONS via cochlear division of nerve.
5) VESTIBULAR DIVISION = vestibular sensations - balance and equilibrium) are picked up by hair receptors in vestibular division. Neurological impulses are transmitted via the nerve. Fibres synapse at the ganglion inside internal auditory meatus.
DYSFUNCTION COCHEAR = deafness; tinnitus
DYSFUNCTION VESTIBULAR = dizziness; vertigo; motion sickness
CAUSE of damage = inner ear infection; Meniere’s; Meningitis; Loud noise;
Describe the Cranial Nerve pathway for the: Glossopharyngeal Nerve CN IX
SENSORY - from tongue, throat, pharynx, middle ear cavity and Eustachian tube, skin behind ears, back 1/3 of tongue.
MOTOR - to a small muscle = stylo-pharyngeus (raises and opens pharynx when swallowing and speaking).
PARASYMPATHETIC - to PAROTID gland to secrete saliva
1) EMERGES from MEDULLA
2) Travels through JUGULAR FORAMEN (with Vagus; SP; Internal Jugular Vein)
3) Sensory Ganglia are located in Jugular Foramen
4) Sympathetic branch to parotid gland
5) Sensory branch to pharynx, larynx, palate and tongue
6) Carotid branch which influences breathing and blood pressure.
DYSFUNCTION = affecting swallowing; speaking, saliva secretion, touch and taste (bitter and sour) from back 1/3 of tongue.
Describe the Cranial Nerve pathway for the: Vagus Nerve CN X
PARASYMPATHETIC - to heart; respiratory and digestive tract and abdominal viscera.
SENSORY - from viscera, heart, lungs, throat, epiglottis
MOTOR - to pharynx, larynx, palate and tongue
1) EMERGES MEDULLA
2) Passes out through JUGULAR FORAMEN with Spinal Accessory; Glossopharyngeal; Internal Jugular Vein,
3) MOTOR branch to pharynx and larynx
4) SENSORY branch to the tongue
5) Main branch passes down the neck within the CAROTID SHEATH (with Carotid Artery and Internal Jugular Vein).
6) To supply THORACIC viscera (heart, lungs, oesophagus)
7) Left and Right vagus meet to form anterior and posterior vagus
8) Continue through Oesophageal opening in diaphragm
9) To ABDOMINAL viscera (stomach, liver, gallbladder, spleen, pancreas).
10) AS far as 1st half of LARGE COLON (Not adrenals)
5 ways to disrupt the vagus nerve =
1) Injury/ restriction along pathway - compressive forces on brainstem and cranial base
2) Inflammation, sclerosis, impingement on carotid sheath, disturbances to sympathetic plexi and diaphragm.
3) Through sensory feedback via GIT
4) Toxicity - botox
5) ANS imbalance - sympathetic overstimulation
What is the carotid sheath? - fascial tube - restrictions anywhere in fascia will pull carotid artery, internal jugular vein and vagus nerve. Will affect arterial blood to head and venous drainage from head. Fascial unwinding of neck can help with carotid sheath restrictions.
VAGAL symptoms =
1) OVERSTIMULATION of vagus = tired, listless, unwell, vagal exhaustion
2) OVERACTIVE vagus = VAGOTONIA = ANS imbalance towards PARASYMPATHETIC division. Symptoms = LBP; slow heart rate; cold hands and feet; cold and clammy skin, severe fatigue; bladder control; fainting; digestive complaints.
3) UNDERACTIVE vagus = nausea; heartburn; SOB; difficulties swallowing.
Healthy vagal tone = fluent function of body and response to stress
LOW vagal tone = strokes; depression; diabetes; inflammatory conditions - endometriosis, arthritis.
What to advice for low vagal tone =
deep breathing; tongue and face submerging in cold water, relaxation, breathwork. Cold water stimulates Trigeminal Nerve and massages heart rate to conserve oxygen. Can apply pressure to eyeball to stimulate parasympathetic oculomotor.
Sympathetic Splanchnic nerves come from - T7 to L2 to join celiac; superior mesenteric plexus; inferior mesenteric plexus and superior hypogastric plexus.
Parasympathetic Splanchnic nerves come from S234 (pelvic splanchnic nerves) and found on the walls of abdominal organs (terminal ganglia).
AUTONOMIC PLEXI - contain sympathetic and parasympathetic fibres. They surround the aorta and form branches =
Aortic plexus - round ABDOMINAL aorta
Celiac plexus - greater and lesser splanchnic nerves and vagus
Hepatic plexus - round hepatic artery and from celiac p
Renal plexus - round renal arteries and fibres from celiac and aortic plexus and least splanchnic nerve
Superior Mesenteric Plexus
Inferior Mesenteric Plexus
Superior Hypogastric Plexus
Left and Right Inferior Hypogastric Plexus - found on sides of rectum, cervix and bladder. Parasympathetic from Pelvic Splanchnic Nerves.
Vagus supplies 1st half of colon
2nd half - pelvic splanchnic nerves
RIGHT side of abdomen = ascending colon = ileo-caecal valve dysfunction (T10-T11) - may involve vagus and can be traced back to JF and medulla.
LEFT side of abdomen = descending colon = left sided IBS = would not involve vagus but would involve splanchnic nerves from sacrum S234.
Describe the Cranial Nerve pathway for the: Spinal Accessory Nerve CN XI
MOTOR ONLY
SPINAL DIVISION
EMERGES from C4 to C1 and bunch together to travel inside the VERETEBRAL CANAL
Through the FORAMEN MAGNUM with VERTEBRAL ARTERIES to ENTER cranium
To join the Cranial Division
CRANIAL DIVISION
EMERGES from the MEDULLA
Joins the Spinal Division
They BOTH EXIT the cranium through the JUGULAR FORAMEN along with the Glossopharyngeal Nerve and Vagus Nerve and Internal Jugular Vein.
SPINAL DIVISION = MOTOR supply innervates TRAPEZIUS and STERNOCLEIDO MASTOID MUSCLES
CRANIAL DIVISION = Travels with the VAGUS nerve to MOTOR supply the pharynx, larynx and palate.
DYSFUNCTION =
NB - 3 WAY INTERACTION between: Vagus; Sternocleidomastoid muscles and Jugular Foramen.
= tension in SCM muscles can compress OM suture and JF (NB SCM attaches both sides of the sutures - to both occipital and temporal bone). Causes vicious circle because - a restricted JF = compression of SA Nerve and Vagus nerve = tension and overstimulation of SCM muscle.
BI-LATERAL tension in SCM muscles and Trapezius = common tension and emotional holding.
UNILATERAL tension in SCM muscles and Trapezius = Birth Trauma.
= Torticollis as baby = neck bending to one side and head rotating to opposite side (from compression and physical twisting forces during birth)
= Torticollis as adult = WRY NECK = severe spasm, pain, head bending to one side and rotating to opposite side. Neck unwinding effective to release SA nerve, JF and Cervical Neck area (for spinal division).
Autism - often find severe restriction in cranial base from compression (if not genetic).
C2 - direct innervation for SCM muscle
C3 and C4 - direct innervation to trapezius muscle
So disturbances to upper spine will affect these muscles
Behaviour disorders/ ADHD may have cranial base compression.
Describe the Cranial Nerve pathway for the: Hypoglossal Nerve CN XII
MOTOR to supply intrinsic and extrinsic tongue muscles and some supply to supra-hyoid muscles of throat.
Function - stick out tongue and move it using intrinsic and extrinsic muscles.
1) EMERGES MEDULLA
2) Passes through HYPOGLOSSAL CANAL in Occiput
3) EXITS cranial base in front of occipital condyles
4) Passes below angle of mandible to MOTOR supply muscles of the tongue.
5) Small branch to ANSA CERVICALIS which with C1 to C4 provides motor supply to SUPRA-HYOID muscles to throat.
