Cranial Nerves_ Pons Flashcards
What are the 2 parts of the pons?
- tegmentum
2. basis points
Tegmentum =
- dorsal portion containing cranial nuclei and ascending and descending tracts.
Where does the tegmentum lie?
This region lies just below the fourth ventricle.
Basis points =
ventral portion containing pontine nuclei and crossing pontine fibers running transversely which will make up middle cerebellar peduncle.
This ventral portion is marked by large fascicles of fibers containing _________________________________________ axons. These axons are running in the _______________ direction.
corticospinal, corticobulbar and corticopontine
caudal
What are the 3 cerebellar peduncles:
inferior, middle and superior
Where are the 3 cerebellar peduncles located?
@ the pontine level
As a general principle, these allow for cerebellar afferents to enter (___________________) and exit (________________) the cerebellum.
inferior and middle
superior
What are the 4 cranial nerves associated with the pons:
CN VIII, VII, VI, V
vestibulocochlear, facial, abducens and trigeminal
Cochlear Division =
relay of auditory information from specialized receptor, the cochlea
Auditory information is distributed _________________ through brain stem and cortical auditory areas.
bilaterally
Therefore, unilateral lesions of CNS auditory structures do:
not result in unilateral deafness
Damage to the CN VIII or both cochlear nuclei will result in:
ipsilateral deafness
The entire system is ________________ organized (remember that other sensory systems are topographically organized).
tonotopically
(Ultimate goal is cerebral cortex.) Specifically, the superior surface of the _____________________ gyrus (within the lateral sulcus). Brodmann’s areas 41 and 42; primary auditory cortex; Transverse Temporal Gyri of ______________.
superior temporal
Heschl
Much cross-communication takes place between sides before arriving at cortex. The bilateral representation is complex and actual relay steps are unclear. It does however support the ability to:
localize sound to one side.
Cochlear Nerve:
- Consists of axons or central processes of neurons bringing afferent information from the ________________.
- Enters brainstem at _______________________, then bifurcates to synapse in both dorsal and ventral cochlear nuclei.
- Nuclei are superficial and located in rostral (open) medulla, adjacent to the base of the _______________________.
inner ear
cerebellopontine angle
inferior cerebellar peduncle
Name the 7 landmarks of the ascending system:
- Dorsal and ventral cochlear nuclei.
- Superior olivary nucleus.
- Lateral lemniscus.
- Nucleus of inferior colliculus.
- Brachium of inferior colliculus.
- Medial geniculate nucleus.
- Primary auditory cortex.
Protective auditory reflexes: Inferior colliculus >
superior colliculus
superior colliculus >
tectospinal tract
tectospinal tract =
reflex turning of head to sound
IMPORTANT for protection against loud noise. Superior olivary nucleus projects to CN VII - _____________ muscle which:
to CN V - tensor tympani muscle which:
stapedius muscle
dampens the noise at the stapes
dampens the noise at the malleus.
Acoustic Neuroma =
Tumor growing in the cerebellopontine angle, usually benign and beginning on the VIII nerve.
Vestibular component (of acoustic neuroma) =
irritative lesion; changes in perception of head position – spinning sensation, vertigo.
Tinnitus (ringing of the ears) –>
irritative lesion.
Which cranial nerves are also involved in acoustic neuroma?
CN VII, V, IX
Antibiotic toxicity =
Some antibiotics are toxic to the CNS (penicillin, streptomyocin). When given for ear infections, they can effect CN VIII specifically. This CN has a “weak” spot in the change from the meninges to the connective tissue component of a peripheral nerve.
Trigeminal Nerve CN V =
Mixed nerve for general sensation of the face and head area, as well as motor output to the muscles of mastication.
The sensory parts of this nerve (CN V) carry the same modalities as those carried in both the:
dorsal column system and the spinothalamic tract.
What 3 disctributed parts are involved with somatosensation of the anterior 2/3 of the face:
V1, V2, V3
V1 =
ophthalmic division; about the eye
V2 =
maxillary division; below the eye, about the mouth
V3 =
mandibular divisions; jaw
____________________ neurons innervating the muscles of mastication. Restricted to the ________________ division of CN V. (Motor nucleus of V). Also innervates a couple of other muscles, nerve to the mylohyoid (What muscles?) and tensor tympani.
Lower motor
mandibular (V3)
Facial Nerve CN VII: Lower motor neurons in motor nucleus of VII innervate _____________ muscles of facial expression, platysma and stapedius.
ipsilateral
REVIEW RELATION WITH CN VI.
Facial Nerve CN VII:
location -
exits at anterolateral part of tegmentum of lower pons.
Somatotopic organization of motor neurons in motor nucleus for muscles on half of face. Upper motor neuron innervation (_______________) is ___________ to upper part of face representation; ________________ only to lower part of face representation.
corticobulbar
bilateral
contralateral
motor neurons (of CN VII) are final common pathway, i.e., lower motor neurons, and therefore a lesion of the nucleus or the fibers result in lower motor neuron signs in the innervated muscles. WHAT ARE THE SIGNS OF LMN LESIONS? ARE THE SIGNS IPSILATERAL OR CONTRALATERAL?
?????
Preganglionic parasympathetic neurons =
located in the reticular formation in the caudal pons
tear production =
postganglionic cell bodies in pterygopalatine ganglion (lacrimal gland)
salivation =
postganglionic cell bodies in submandibular ganglia (submandibular and sublingual glands).
Taste from anterior 2/3 of tongue from ___________________.
chorda tympani
rostral part of the SOLITARY NUC. (NTS); NTS project ipsilaterally to ________; to gustatory area of cortex – _____________________.
VPM
parietal lobe and insula
What synapses in the caudal part of NTS?
???
Lesions of facial nerve CN VII: Bell’s Palsy =
Lower motor neuron deficit to muscles of facial expression.
Lesions of facial nerve CN VII: Upper motor neuron lesions =
deficit on contralateral lower face only.
WHY?
Name 5 symptoms of lesions:
- Lower motor neuron deficit of ipsilateral face.
- Dry cornea; ulcerated cornea.
- Loss of taste over ipsilateral ant. 2/3 of tongue.
- Inability to produce saliva.
- Hyperacusis - stapedius can’t dampen sound.
What is the only lower motor deficit of muscles of facial expression?
Bell’s Palsy
Corneal Blink Reflex (follow on schematic) innvervated by :
Trigeminal and Facial Nerve.
Blink reflex - touch the cornea and both eyes close.
- direct reflex =
- indirect or consensual response =
- direct reflex = closure of the touched eye.
2. indirect or consensual response = closure of the untouched eye.
Circuits of Blink Reflex: receptor =
free nerve ending in cornea (peripheral process of sensory neuron in the ophthalmic division of CN V (elicit with cotton wisp).
Circuits of Blink Reflex: afferent limb =
central process ends in main sensory nucleus of V.
Circuits of Blink Reflex: interneurons in main sensory nucleus V project _____________________________________
directly to ipsilateral facial motor nucleus and to RF interneurons.
Circuits of Blink Reflex: direct reflex efferent limb =
ipsilateral facial motor nucleus to orbicularis oculi - BLINK.
Circuits of Blink Reflex: indirect reflex efferent limb =
RF interneurons project to contralateral facial motor nucleus to activate contralateral orbicularis oculi - BLINK
Circuits of Blink Reflex: effects of lesions = Be able to identify whether the direct or consensual blink reflex is present with each of the identified lesions (A-E).
Be able to identify whether the direct or consensual blink reflex is present with each of the identified lesions (A-E).
