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 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
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
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
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.
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,
