chapter- cranial nerves Flashcards

1
Q

In the brain stem- motor nuclei are located ventrolaterally.
Sensory nuclei are located dorsolaterally.
Midbrain contains: tectum- roof( superior and inferior colliculi).
Tegmentum forms the bulk of the midbrain.
Cereberal peduncle - contains the corticospinal and corticobulbar fibers.

A

Midbrain structures:
Medial: peri-aquaductual grey matter.
Mesencephalic trigeminal nucleus and tract.
Edinger westphal and oculomotor nucleus.
Medial longitudinal fasiculus.
Hebinulointerpeduncular nucleus- retroflexus nucleus.

Lateral: red nucleus, medial laminscus, anterolateral laminscus trigeminal laminscus.

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2
Q

Midbrain section: superior colliculus- red nucleus and oculomotor.
Inferior colliculus- conjuctivum brachium( decussation of the superior cerebellar peduncle) and the tochlear.

A

Midbrain : at the level of the inferior colliculus.
Torchlear nucleus and fascicle.
Raphe nucleus ( median and dorsal).

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3
Q

pons: there are three levels: upper- middle and lower.
Nuclei: median and dorsal raphe nucleus.
locus curelus- the nucleus is located in the mid bonse.

A

Upper pons: cerebral aquaduct- locus cerulous AND raphe nucleus.
Mid pons: has the fourth ventricle. Locus cerulus nucleus, superior vestibular nucleus ,
mesencephalic trigeminal, principle sensory nucleus of the trigeminal nerve. MLF.
Lower pons:
the medial longitudinal fasiculus becomes more medial. lateral to it, is the doral longitudinal fasiculus. trapezoid body, and the paramedian pontine reticular formation.

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4
Q

Rostral medulla: fourth ventricle and inferior olivary complex.
Caudal medulla: contains the dorsal column and the dorsal column nucleus and the central canal of the spinal cord.
Rostral medulla contains the solitaory nucleus, hypoglossal nucleus, dorsal motor nucleus of vagus nerve, nucleus ambiguous.

A

There are three motor nuclei and three sensory nuclei.
oculomotor, abducens, trochlear, hypoglossal.
MLF connects the 3, 4,6 and 8th Vestib nerve.
Facial nerve nucleus forms the facial collicus located in the floor of the fourth ventricle in mid to lower pons.
Hypoglossal nerve forms the hypoglossal trigones in the floor of the fourth ventricle. The three motor nuclei ( somatic motor)that run along the fourth ventricle is the hypoglossal- dorsal motor nuceli and solitary nucleus.

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5
Q

branchial motor:
1- trigeminal- mid ponse, ventral to the principle trigeminal sensory nucleus.
2- Facial nerve: lower pons forming a loop fiber around the 6th nerve-
3- nucleus ambiguous is difficult to distinguish from surrounding.
4- spinal accessory nucleus: in the upper cervical spine

A

parasympthatic nuclei: 1- edinger westphal nucleus.
2- superior and inferior salivatory nucleus.
3- dorsal motor nucleus.

Edinger westphal- midbrain.
Superior and inferior salivatory nucleus: midbrain tegmentum.
Dorsal motor nucleus: from rostral to caudal medulla lateral to the hypoglossal nucleus- forms the vagal trigon.

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6
Q

Somatic sensory input from the V, VII, IX,X goes to the trigeminal nuclear complex.
Midbrain: mesencephalic- periaqueductal grey matter- PROPRIOCEPTION.
chief or principle sensory nucleus is in the mid to lower pons- just DORSOLA TO TERALTHE MOTOR NUCLEUS OF THE TRIGEMINAL.
trigeminal spinal nucleus- is an extension of the dorsal horn of the spinal cord. - discriminative touch.

A

Special somatic sensory: VIII- hearing and vestibular.
Hearing: the dorsal and ventral cochlear nuclei.
Then it will synapse with the trapezoid and the SUPERior olivary complex, then ascend to the lateral laminscus then to the inferior colliculus through the brachium to the medial geniculate to the hearing center in the cortex.

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7
Q

There are four vestibular nuclei.
Superior, inferior, medial and lateral.
They are located in the lateral wall of the fourth ventricle of the pons and rostral medulla.
the medial and lateral vestibulospinal tract are important for posture and muscle tone.
Largest vestibular nuclei is the medial one.
The inferior vestibular nucleus is identified by checkboard appearance because the lateral l fibers cross it.

A

MLF runs in from the midbrain to the pons. It connects the fibers from superior and medial vestibular nucleus to the oculomotor, abducens, trochlear to mediate the vestibule-ocular reflex.
MLF is highly myelinated located in the midline below the floor of the fourth ventricle in the pons and the oculomotor, trochlear in the mibrain.
solitary nucleus is located in the rostral medulla- special visceral.
GENERAL AND SPECIAL VISCERAL AFFERENT- NUCLEUS SOLITARIOUS.
ON CROSS SECTION AT THE LEVEL OF LOWER PONS- IT HAS DONUT SHAPE BECAUSE OF HEAVY MYLEINATED CENTER AND PALE SURROUNDING.
Rostral nucleus solitaries is for taste. CAUDAL nucleus solitaoris is for cardiorespiratory and GI ( IX and X).

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8
Q

Tracts:
corticospinal and corticobulbar- located in the middle third of the cereberal peduncle.
They decussate at the cervicomedullary and ascent as the anterior corticospinal fibers.

The posterior column: nucleus gracilus and nucleus cunetous.
Gracillus- lower ext
Cunetus- the upper ext. they cross as the internal arcuate fibers and ascend as the medial laminscus.
fine touch, proprioception and vibration.
Anterolateral system is for crude touch, pain and temp.

A

locked in syndrome: due to lesion of the ventral pons affecting corticospinal and corticobulbar tract.

Vertical eye movements are controlled by the tegemntium of the rostral midbrain.
The horizontal eye movements are controlled by the pontin circuit.

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9
Q

cerebellar connection with the brain stem:
superior cerebellar peduncle- it is the major cerebellar output. connects at the level of the midbrain- red nucleus up to the premotor and motor cortex.
Middle cerebellar peduncle: major input to the cerebellum from the pontine nuclei.
Inferior cerebellar peduncle is the major cerebellar input from the spinal cord.

A

The red nucleus ( rostral midbrain) through the central tegmental tract then to the inferior olive nucleus at the level of the rostral medulla then through the inferior cerebellar peduncle it goes back to the cerebellum- lesion here causes palatal myoclonus.

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10
Q

Reticular formation:
It extends from the mesencephalon to the intermediate zone of the spinal cord.
It is divided into upper- from mesencephalon to mid pons for the consciousness.
Mid pons and medulla to spinal cord for reflex, motor and autonomic function.

A

The neurotransmitters of arousal:
Acetylcholin: it is a neuromodulator.
It arises from pedunclopontine tegmental nucleus and the dorsolateral tegmental nucleus. this does not project to the cereberal cortex.
Acetylcholin projections to the cerebral cotex and hypo thalamus come from medial septal nuclei, nucleus basalis of meynert and nucleus of diagonal band.
medial septal nuclei and nucleus of diagonal band are important for hippocampal memory formation. Hippocampal theta rhythm.
Acetaylcholin is good for attention, memory and learning.

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11
Q

The dopamine system:
Main sources are ventral tegmental area of the midbrain and the substantia nigra parsa compacta.
There are three systems:
Mesolimbic: connects with the limibic system and reward, positive symptoms of schizophrenia.
mesostrital: caudate and putamen. primarily the substantia nigra.
mesocortical: prefrontal- behavior, attention. primarily from ventral tegmental.

A

Norepinephrine: important for mood, sleep wake cycle and attention.
It is located in the locus cerulus( blue spot) located in the rostral pons close to the floor of the fourth ventricle and the lateral tegmental area. .
It can be excitatory and inhibitory. It is mainly excitatory of the thalamus

Serotonine:
raphe nucleus that is located from the midbrain to the medulla.
There is rostral raphe nucleus that projects to the thalamus and cortex.
Caudal raphe nucleus that projects to the medulla, spinal cord - pain modulation, arousal and motor function.

Other neurotransmitters for alertness and consciousness are:
OREXINE- OR HYPOCRETIN- FROM POSTERIOR LATERAL HYPOTHALAMUS- FOR WAKEFULLNESS.
Adenosine- unknown source but is important for circadian rhythm.

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12
Q

sleep cycle:
VLPO- located in the anterior hypothalamus. ventrolateral preoptic area send inhibitory signals to the ascending activating system of the forebrain that promotes nonREM sleep.

Non- REM sleep control center:
VLPO which is located in the anterior hypothalamus, releases GABA and GALANIN that inhibits the ascending activating system, and norepi,serotonine, histamine and cholinergic.
It also inhibits the orexin or hypocretine from the lateral posterior hypothalamus.

In REM sleep: the REM on cells located in the PONTINE reticular system inhibit the serotonin, NE and promote the cholenrgic activity. The acetylcholine increased its effect on hypothalamus promoting REM sleep.
The combination of GABA and INHIBITION FROM VLPO cause reduced NE, serotonine.

PONTO-GENICUL-OCCIPITAL- PRODUCE DREAMS.

A

Decreased muscle tone: the glutamate on cells in the pontin reticular formation releases glycine that inhibits causes inhibitory effect on the lower motor neurons. Damage to this area in parkinsion causes loss of inhibitory effect leading to REM sleep behavior.

The melanin concentration neurons are found mostly in REM SLEEP.

Narcolepsy:
It is proposed to be secondary to defect in flip flop switch.
This results from decreased orexine.
Excessive day time sleepiness.
hyponogoni, and hypmopomic hallucination.
cataplexy
sleep paralysis.

COMA:
the EEG has less than 2 microvolets of amplitude.
Vegetative state: restoration of sleep wake cycle.
Persistent vegetative state: duration of 1 month.

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13
Q

Reticular formation control of other functions.

Respiration control:
pre-botzinger complex- in the medulla- pace maker of respiration.
different patterns of breathing:
Ataxic breathing- lesion of the medulla. causes eventual respiratory arrest.
Apneustic breathing: 2 to 3 second pause in full inspiration. LESION in the MEDIAL PARABRACHIAL fuse center.
Neurogenic hyperventilation: midbrain lesion.
Chyne stock can occur anywhere.

A

Arterial blood supply to the brain stem:
Vert comes of the subclavian artery. The bilateral verts join at the pontomedullary junction to give the basilar that runs along the pons, then bifurcates to form the PCA at the top connecting with the PCOMM to anterior circulation.
Medulla:
Medial medulla:
Caudal- ASA penetrating arteries.
Rostral- vert penetrating arteries.
Lateral medulla:
PICA and small penetrating branches of basilar.
Pons: basilar
Medial: paramedian pontine.
Lateral: circuferential penetrating( long is caudal and short is rostral)
Most caudal- lateral: AICA.
Most rorstral dorso-lateral: SCA.

Midbrain:
medial- PCA and penetrating branches of the basilar.
Lateral- PCA only.

Oculomotor nerve runs between SCA and PCA.

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14
Q

Long and short circumferential arteries supply the lateral aspect of the brain stem.

Artery of percheron- supply medial midbrain and thalamus.
Bilateral cereberal peduncle infarction can give locked in syndrome but with sparing of the vertical and horizontal eye movements.

A

Medial medullary syndrome: artery- paramedian perforation of ASA and vertebral artery,
affects: corticospinal, medial laminscus and hypoglossal nerve.
Contralteral hemiparesis sparing the face, contralateral loss of vibration and proprioception and ipsilateral tongue deviation.
simulate cervical cord lesion as it spares the face.
The tongue is involved in 50% of the cases.

Lateral medullary syndrome: PICA and vert penetrating arteries.
No weakness of minimal weakness.
Inferior cerebellar peduncle- ataxia.
Vestibular nuclei- vertigo, horizontal and rotatory nystagmus.
nucleus soliatrious- taste on the ipsilateral tongue.
nucleus ambiguous of X- hoardness and dysphagia.
Ipsilateral face loss of pain, and temp and contralateral body. Can have hypesthesia or paresthesia on acute onset.
They have a sense or vertical orientation- the room was upside down.

medulla localization is because of nucleus soliatrous and nucleus ambigues.

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15
Q

Pontine strokes:
usually due to the basilar artery thrombosis, tenosis, lacunar infract or atherosclerosis.
The infarction of the median pons can cause pure motor hemiparesis, or ataxic hemiparesis by involvement of the pontocerebellar fbers or hemiparesis with dysarthria.
If the infarction extends to the tegmentum and facial colliculus it can cause 6th nerve palsy with ipsilateral horizontal gaze palsy, ipsilateral facial weakness and contralateral hemiparesis( frovill’s syndrome).
Ipsilateral facial weakness and contralateral hemiparesis causes millard gubler syndrome.

A

AICA causes a syndrome similar to PICA but they have associated unilateral hearing loss and does not cause hoarseness or loss of taste.

SCA causes ipsilateral ataxia.

Midbrain lesions:
1- weber- ipsilateral third nerve and contralateral hemiparesis.
2- calude- ipsilateral third and contralateral ataxia.
3- Benneditt’s: ipsilateral third, contralateral hemiparesis, tremor and abnormal movements.

top of basilar syndrome:
ocular abnormalities, ataxia, vivid dream- pedunculus hallucination.

Basilar scrape syndrome which occurs when an embolus travels across the basilar causing multiple transient symptoms.

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