CNS Unit 9 Brainstem 1: Anatomy and CN Flashcards
What are the 3 structures of the Brainstem?
Midbrain, Pons and Medulla
What is the Rostral Limit of the brainstem?
Midbrain-Diencephalic Junction
What is the Midbrain-Pons junction?
What separates them?
Pontomesencephalic Junction
What is the Pons-Medulla junction?
What separates them?
Pontomedullary Junction
What is the Caudal Limit of the Brainstem?
Cervicomedullary Junction
When looking at the Dorsal View of the Brainstem, what makes up the Tectum “Roof”?
The Superior and Inferior Colliculi
When looking at the Ventral View of the Brainstem, what makes the Rostral End (Superior)?
The Midbrain is mostly formed by the Cerebral Peduncles, these are separated in the center by the Interpeduncular Fossa
When looking at the Vental View of the Brainstem, what may we find under the Pontomedullary Junction?
We’ll find the Pyramidal Decussation, and the Pyramids
When looking at the Lateral View of the Brainstem, what strucutres may we see?
- The Pons; In the Pons we’ll see the 4th Ventricle (This extends from the pons to the rostral/superior portion of the medulla), Superior/Middle/Inferior Cerebellar Peduncles
Which Cranial Nerves do not Emerge from the Brainstem?
- CN 1
- CN 2
*Although (in the pic) we can see it the Optic Nerve meet up at the Optic Chiasm forming the Optic tract, which wraps laterally around the midbrain to enter the LGN of the Thalamus *
Where do CN 3-12 Exit the Brainstem?
Either Ventrally or Ventrolaterally
- One exception is CN 4, which exits from the dorsal midbrain
Where does CN 3 Emerge from?
Oculomotor emerges ventrally from the Interpenduncular fossa of the Midbrain; usually between the SCA and the PCA
Carries parasympathetics to pupillary constrictor and cillary muscles of lens
Where does CN 4 Emerge from?
Trochlear Emerges dorsally from the inferior tectum of Midbrain
Where does CN 5 Emerge from?
Trigeminal emerges from the ventrolateral pons
- This then enters a small fossa called Meckel’s cave; It has a Trigeminal ganglion (sensory ganglion) that divides and they each have different exits in the skill.
Where does CN 6 Emerge from?
Abducens exits ventrally at the pontomedullary junction
Where does CN 7-10 Emerge from?
Facial, Vestibulocochlear, Glossopharyngeal, and Vagus all exit ventrolaterally from the pontomedullary junction and the Rostral Medulla
Where does CN 11 and 12 Emerge from?
Spinal Accessory arises laterally from muliple rootlets along the upper cervical cord
Hypoglossal exits the medulla ventrally between the Pyramid and Olive of the Medulla
Where in the skull does CN 1 exit?
Cribiform Plate
Where in the skull does CN 2 exit?
Optic Canal
Where in the skull do CN 3, 4, V1, and 6 exit?
Superior Orbital Fissure
Where in the skull does V2 exit?
Foramen Rotundum
Where in the skull does V3 exit?
Foramen Ovale
Where in the skull does CN 7 exit?
CN 7 Traverses subarachnoid space then enters Internal Auditory Meatus (Canal) to enter auditory canal then the main portions exits via Stylomastoid Foramen
Where in the skull does CN 8 exit?
Enters subarachnoid space to enter the Internal Auditory Meatus (Canal) to enter Auditory canal
Where in the skull does CN 9-11 exit?
Jugular Foramen
Where in the skill does CN 12 exit?
Hypoglossal canal
During Embryological Development, where do CN lie?
What happens when the nervous system matures?
Adjacent to the Ventricular System
As Nervous System matures, there are 3 motor and 3 sensory columns related to CN nuclei that run through the lenth of the brainstem (Pic on the Right)
What is the Function of CN 1 (Olfactory N.)?
Special Sensory
Smell
- Chemoreceptors detect odor and are located in Nasal Epithelium.
- Short olfactory nerves head up through the cribiform plate
- Then synapse in olfactory bulb, then information travels via olfactory tract to specific locations
What are the Dysfunction of CN 1?
- Anosmia: Olfactory Sensory Loss of smell
- With unilateral deficits, patients are rarely aware because the contralateral nostril compensates
- Bilateral deficits are accompanied with decreased taste
Dysfunction of CN 1
What may cause Anosmia?
Loss of smell
Head trauma, viral infections, PD, Alxheimer’s (Az), Intracrainial lesions
What is the pathway for vision?
- Retina
- Optic nerve
- Optic canal
- Optic chiasm
- Optic tract
- Lateral Geniculate Nucleus
- Visual cortex (Occipital Lobe)
Optic nerve travels from orbit to intracranial cavity via optic canal
What are the Functions of CN 3, 4 and 6?
They Control extraocular eye muscles
CN 3: - Motor to Superior/Inferior/Middle Rectus and
Inferior Oblique “Up and out” also elevates the eyelids
(This rotates the eyeball superiorly, inferiorly, and medially)
- As well as pupil constriction and accommodates lens of eye
CN 4: - Motor to Superior Oblique “Down and Out”
(This depresses, medially rotates and abducts eye)
CN 6: - Lateral Rectus {Abducts eye}
(This directs gaze laterally; looking lateral)
What are the Disorders of CN 3, 4, and 6?
CN 3: Loss of Pupillary reflex, Loss of constriction of the pupil in response to focusing near objects-no accomodation
CN 4: The patient will have a head tilt and chin tuck: the head will tilt away from affected eye (corrects extrosion), looking upward slightly (chin tuck) corrects hypertonia
CN 6: Left eye does not Abduct
With CN 3, 4, and 6, where are their nuclies located in the Brainstem?
- CN 3 and 4 nuclei are located in the midbrain
- CN 6 nucleus is in the Pons
What are the 3 division of CN 5 and where do they exit?
What is the function of CN 5?
3 division:
- Opthalmic (V1): Exits the inferior part of the Cavernous sinus to exit via Superior Orbital Fissure
- Maxillary (V2): Exits through Foramen Rotundum
- Mandibular (V3): Exits through Foramen Ovale
- V1 and V2 are sensory Nerves to the face
- V3 is a mixed nerve that does sensory to the face, Sensation to Anterior 2/3 of the tongue (Lingual) , as well as motor to the muscles of Mastication (small motor root)
What is a dysfuction of the Trigeminal Nerve (CN 5)?
With what population will you see this with?
What may cause this and what is the initial treatment?
This is referred to as Trigeminal Neuralgia, aka Tix Douloureux
- Recurrent episodes of brief severe pain last seconds to minutes (Most often involves V2 and V3 divisions)
- This is more commonly seen after the age of 35 and can be provoked by chewing, shaving, etc.
Sensation will be normal with this
- Causes are usually unknown, however can occur in MS patients, because of dymelination of CN 5 and the entry zone of the brainstem
- Initial treatment involves medication (Tegretol)
What would happen if there is a lesion of the Trigeminal Nuclei of the Brainstem?
This would cause Ipsilateal loss of facial sensation to pain and temperature because the primary sensory fibers do not cross before entering the nucleus
What is the Functions of CN 7?
Where is the Facial Nucleus found?
- Control muscles of facial expressions (Somatic motor)
- Lacrimation, salivation (Visceral Motor)
- Taste of anterior 2/3 of tonge (Special sensory)
- Skin over external auditory meatus (Sensory)
Facial nucleus located in Cuadal pons
What are the Dysfunctions of CN 7?
- Facial weakness: Consider both UMN and LMN
- UMN to the face invovles the primary motor cortex as well as contol of the LMN contralateral to the face
Superior regions of the face are controlled by projections descending from the ipsilateral and contralateral motor cortex
Facial Nerve Lesios
What is Bell’s Palsy? What are the clinical presentations, cause, and management?
Bell’s Palsy: Divisions of the CN 7 are impaired and then gradually recover
- Clinical Presentation: Unilateral LMN facial weakness, no affects of sensation
- Cause: Unknown; possible viral or inflammatory
- MRI: will yield normal results
- Medical Management: Oral steriods
~80% of pt. will have fully recovered within 3 weeks
This is the most common facial nerve disorder
During recovery, regenerating facial nerve fibers sometimes reach the wrong target:
- Synkinesis
- Crocodile Tear
With Bell’s Palsy, what is a common compaint and what may they suffer from?
Patients often initally complain of some retroauricular pain
- They may suffer from “dry eye”, resulting from decreased lacrimation with parasympathetic involvment
What is Corneal Reflex?
What are the roles of the Afferent and Efferent Limbs?
This is a reflex elicited by gental stroke of each cornea with a cotton swab or by applying a drop of saline; the response is eye closure
- The Afferent limb is conveyed by the Ophthalmic division to the chief sensory and spinal trigeminal nuclei
- The Efferent limb is then carried by the Facial nerve to reach the orbicularis oculi muscles causing eye closure
What is the Jaw Reflex?
This is elicited by tapping on the chin with the mouth slightly open; the jaw jerks forward in response.
- The monosynaptic pathway for this reflex consist of primary sensory neurons in the mesencephalic trigeminal nucleus, which send axons to the pons to synapse in the motor trigeminal ncleus.
- In Normal Individuals the Jaw Reflex is minimal or absent
What is the Purpose of the CN 8?
Dual Purpose: Hearing and Vestibular Sense from the inner ear
What is the Tensor Tympani innervated by?
What is the Stapedius innervated by?
Tensor Tympami: Trigeminal Nerve
Stapedius: Facial Nerve
What are the structures of the Inner Ear?
- Bony Labyrinth
- Membranous Labyrinth, which contains:
–Cochlea (Contains Organ of Corti)
–Vestibule (Saccule and Utricle)
–3 Semicircular Canals
Cochlea anatomy
With the Cochlea, what is Tonotopic Representation?
- Higher frequencies activate hair cells near oval window
- Lower frequencies activate hair cells near apex of cochlea
Cochlea anatomy
What does the Central Duct contain?
It contains the Organ of Corti: the Receptor organ for hearing
Cochlea anatomy
With our central pathways for hearing there are lots of collaterals. Where do these collaterals go?
- Lots of the collaterals cross to the other side (contralateral), some go to the Reticular Activating system, which projects to the cortex and some go to the spinal cord. This is the response to very loud sounds. These collaterals are also sent to the cerebellum in response to sudden noise.
There are also projections from the Inferior Colliculus to the Superior Colliculus to synapse with Tectospinal tract to mediate audiovisual reflex
Cochlea anatomy
What happens if there is damage to the Primary Auditory Cotex?
This reduces the sensitivity of our hearing
Cochlea anatomy
What happens if there was damage to one side of the Primary Auditory Cortex?
This has very little effect on our hearing, because of the significant amount of collateral/crossover connections from the Central Pathways
Cochlea anatomy
With hearing, what happens if there is damage to the Association Auditory Cortex (Wernicke’s)?
This does not affect hearing
- However it does affect the interpretation and meaning of sound that is being heard. Auditory comprehension is impaired.
Vestibular Anatomy
Where would you find the vestibular anatomy?
What supplies this?
The inner ear
Consist of the Peripheral Sensory Apparatus, Membranous/Bony Labyrith, and Hair cells
Supplied by the Labyrinthine Artery, a branch of AICA (sometimes off of basilar)
Vestibular Anatomy
What is the function of the Semicircular Canals?
They are our Dynamic Receptors; They respond to angular and/or rotational movement of our head and space
In the Membranous labrinth, what do the Urticles and Saccules do?
They are our Static receptors
- The Utricle signals the position of the head in space in response to gravity in the horizontal plane. (ex. when riding in a car)
- The Saccule response to gravity in the vertical plane (ex. riding in a elevator)
Vestibular Anatomy
What is inside both the Urticles and Saccules?
It has a primary sensory structure called the Macula. Embedded in the Macula are also hair cells
There are many more Macula in the Otolithic organs as compared to the Cupula and the Crista Ampullaris in the semicircular canals.
- Therefore, the otoliths are much more sensitive to the pull of gravity
Vestibular Anatomy
What do Hair Cells do?
Depolarizaton vs Hyperpolarizaton
Hair cells are sensors that convert displacement of head movement into neural firing fluid. These are found in the Ampulla of each semicircular canal and in the otoliths
- Depolarization is when the sterocilia is bent Towards kinocilia
- Hyperpolarization is when the sterocilia is bent away from kinocilia
Vestibular Anatomy
When referrencing the Ampulla of the Semicircular canal, what happens if the persons head were to rotate to the left?
The inertia of the endolymphatic fluid generates a force across the cupula (shifts to the right)
- The displacement induces either depolarization or hyperpolarization of the hair cells
- While displacement of the capula in the “normal” direction results in excitation of the hair cell, while displacement of the cupula in the reverse direction results in inhibition of the hair cell
The Patterns of excitation/inhibition of the hair cell are processed by our central pathways and are interpreted by neurons in the cerebellar an cerebral cortices for our sense of balance and equilibriun
Vestibular Anatomy
What is the role of the Cerebellum, relating to vestibular function?
It monitors vestibular performance (keeps everything in check)
The Cerebellum has direct afferent signals
- The cerebellum keeps everything in check by projecting back onto the vestibular nuclei with an inhibatory or dampening response
- The input goes to the Vermis and Flocculus
Vestibular Anatomy
What would happen if there is a problem with the Cerebellum?
What would happen if there was a lesion to the Vermis or the Flocculus?
The vestibular reflexes are going to be inefficient and ineffective
- If there is a lesion to the Vermis they will have gait ataxia and trunk instability
- If there is a lesion of the flocculus they will have issues with the gain of their VOR, further defined as the ration of eye movement to head movement
Vestibular Anatomy: Mechanisms for Motor Output
What is the purpose of VOR?
To keep vision while the head is being moved
Vestibular Anatomy: Mechanisms for Motor Output
What is the purpose of VSR?
To keep the head and body stabilized
What is Unilateral hearing loss caused by?
Disorders of external auditory canal, middle ear, cochlea, CN 8, or cochlear nuclei
What is Conductive Hearing loss?
What causes this?
This is abnormalities of external auditory canal or middle ear
- Causes include Otitis, Tympanic Membrane perforation
Typically the patient is not going to have the clinical presentation of unilateral hearing loss because the patient has all of that collateral communication that crosses over.
What is Sensorineaural Hearing loss?
What causes this?
This is a disorder of the cochlea or CN 8
- Caused by exposure to loud sounds, Menier’s disease or tumor
Ménière’s disease is a disorder of the inner ear that causes severe dizziness (vertigo), ringing in the ears (tinnitus), hearing loss, and a feeling of fullness or congestion in the ear.
What is Rinne Test?
Air conduction is compared to bone conduction
for each ear.
We measure air conduction by holding a vibrating tuning fork just outside each ear, and bone conduction by placing a tuning fork handle on each mastoid process.
Normal individuals hear the tone better by air conduction.
With the Rinne Test, if there is conduction hearing loss what would be greater bone or air conduction?
In conductive hearing loss, bone conduction is greater than air conduction because bone conduction bypasses problems in the external or middle ear.
With the Rinne Test, if there is sensorineural hearing loss what would be greater bone or air conduction?
In sensorineural hearing loss, air conduction is greater than bone conduction in both ears (as in normal hearing); however, hearing is decreased in the affected ear
What is Weber Test?
In the Weber test the tuning fork is placed on the vertex of the skull in the midline, and the patient is asked to report the side where the tone sounds louder. Normally, the tone sounds equal on both sides.
- In sensorineural hearing loss, the tone is quieter on the affected side.
- In conductive hearing loss, the tone is louder on the affected side,
What is the Difference between Dizziness and Vertigo?
- What can a true diagnosis of vertigo involve?
Dizziness is a very broad term that can be caused by many different things.
Vertigo is more of a vestibular pathology. With this, there can be lesions anywhere along the vestibular pathway
- A true diagnosis of vertigo can involve a lesion in the labyrinth, Vestibular nerve, vestibular nuclei, our cerebellum, and even the parietal cortex
What is the role of the clinician when it comes to vertigo?
To differentially diagnosis whether its a central or peripheral vestibular pathology.
- Peripheral pathologies involve the inner ear and it relates a lot to a deficit in the peripheral sensory apparatus
- Central pathologies usually indicative of some type of brain stem or cerebellum problem
Additional Pheripheral Vestibular Diagnoses
What is Vestibular Neuritis? What may this cause?
Inflammation of vestibular ganglion or nerve
- The patient is going to have intense vertigo for days, and loss of postural control for weeks to months, hearing is intact. At onset they are most likely going to be in bed
What is the clinical presentation of Vestibular Labyrinthitis?
The clinical presentation is similar to Vestibular Neuritis, the only difference is the presence of hearing loss
What is Meniere’s Disese?
What do they present as?
This is excess fluid and pressure in endolymphatic system
- These present as “Meniere’s Attacks”, these are recurrent episodes of vertigo accompanied by fluctuating loss and tinnitus (ringing of the ear)
What is Acoustic Neuroma?
Often referred as Vestibular Schwannoma
- This is the slowest growing tumor in our body; this often occurs unilaterally
- These patients will have hearing loss, tinnitus, vertigo and LOB
Since this tumor is slow growing, the patients will have annual MRIs to continue to estimate the size.
- Surgery isn’t generally indicated until the tumor is large enough and causing issues related to loss of postural control
What is the function of Glossopharyngeal?
- Taste and senation of Posterior 1/3 of tongue (Special Sensory)
- Supplies the stylopharyngeus muscle
- Conveys input from baroreceptors and chemoreceptors in carotid body
Addition functions include:
- Salivation, carotid body reflexes
What would happen if there was a lesion/disorder with Glossopharyngeal?
Decreased gag reflex and swallowing reflex
Where does Glossopharyngeal exit the brainstem and the skull?
- Exits the brainstem along the upper ventrolateral medulla between inferior olive and inferior cerebellar peduncle
- This nerve runs transverse the subarachnoid space and exits the skull via Jugular Foramen
What is the function of Vagus Nerve?
Vagus has the largest parasympathetic innervation to our organs
- Parasymp. fibers to heart, lungs, and digestive tract
- Motor fibers innervate pharyngeal and laryngeal muscles
- Sensation for the meninges, pharynx and external auditory meatus
What would happen if there was a lesion/disorder with Vagus Nerve?
- There would be difficulty swallowing and speaking, poor digestive due to decreased digestive enzyme and peristalsis movement
What is the function of Spinal Accessory Nerve?
- Innervates the SCM and Traps.
What would happen if a patient were to have a LMN lesion to the Spinal Accessory Nerve?
This would cause Ipsilateral weakness of the traps and it will not allow the patient to turn their head away from the side of the lesion
What is the function of the Hypoglossal Nerve?
Tongue movement
Except Palatoglossus, this is innervated by CN 10
What would happen if there was an UMN lesion to Hypoglossal Nerve?
There would be contralateral weakness of the tongue
What would happen if there was a lesion on the Hypoglossal nucleus or below (LMN pathology)?
There would be Ipsilateral weakness of the tongue
What is the difference between Dysarthria and Dysphagia?
Dysarthria is abnormal articulation of speech
Dysphagia is impaired swallowing
What are common causes of Dysarthria?
Infarct, MS, BS lesions, lesions of cerebellar and BG pathways
What are common causes of Dysphagia?
What are Red Flags for this?
Neoplasms, esophageal strictures, neural components
Red flags for PT/OT are aspiration pneumonia
This often occurs along Dysarthria
