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NLM2 > Cranial Nerves > Flashcards

Cranial Nerves Flashcards

0
Q

What makes up the olfactory association cortex?

A
  1. Parahippocampal Gyrus
  2. Anterior pole of the temporal cortex
  3. Posterior part of orbital gyri
    All contribute to interpretation of smells and olfactory memory
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1
Q

What forms the primary olfactory cortex?

A

The uncus and surrounding temporal cortex

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2
Q

Describe the journey of olfactory nerve

A

Olfactory receptors within the olfactory epithelium of the superior nasal conchae detect olfactory stimuli. Impulses travel through fibres via canals within the cribiform plate of the ethmoid bone. These then collect at glomeruli and synapse with dendrites of mitral cells. Axons of mitrial cells extend throughout the olfactory bulb and the olfactory nerve. The olfactory nerve travels posteriorly and separates into the medial olfactory striae and lateral olfactory striae at around the optic chiasm. The lateral o.s. go to the primary olfactory cortex.

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3
Q

Describe connections of olfactory association cortex with other cortical areas

A
  1. Extensive connections with the hypothalamus. This forms the basis for reflex visceral responses controlled by the ANS e.g vomiting to a bad smell / salivating to food smells
  2. Connections with the amygdala (emotion) and the hippocampus (associative memory). This is linking the olfactory cortex with limbic structures to aid memory association to aid survival.
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4
Q

What is the role of the medial olfactory striae?

A

-

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5
Q

Where are cell bodies of the optic nerve located?

A

The ganglionic layer of the retina

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6
Q

Why do 20% of fibres pass to the superior colliculus instead of the lateral geniculate nucleus of the thalamus?

A

So that visual stimuli can affect pupil constriction. This can be seen as visual reflexes. e.g. Pupillary light reflex (pretectal nucleus) / Accommodation reflex.
Also, this is to help smooth pursuit movements and fixation of gaze.

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7
Q

Describe the nuclei of the lateral geniculate nuclei.

A

There are 6 layers of nuclei.
Layers 1 and 2 receive contrast and movement information from M type retinal ganglion cells.
Layers 3, 4, 5 and 6 receive fine contrast and colour information from P type retinal ganglion cells.
Layers 1, 4 and 6 are from the contralateral eye
Layers 2, 3 and 6 are from the ipsilateral eye

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8
Q

Describe retinal projection onto the visual cortex.

A
  1. The macula projects to the posterior visual cortex for maximal discrimination. This is more central vision.
  2. Peripheral retina projects to the anterior visual cortex for peripheral vision. There is less cortex for this.
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9
Q

What forms Meyer’s loop and what is the consequence if there is an isolated lesion of M’sL?

A

Inferior geniculocalcerine fibres carrying superior retinal quadrants (the geniculocalcerine tract passes through the posterior limb of the IC). If lesioned there is contralateral superior quantrantanopsia.

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10
Q

What is the consequence of a lesion at each of the following? Give likely reasons for each lesion.

  1. Optic nerve
  2. Optic chiasm
  3. Optic tract
  4. Optic radiation
  5. Visual Cortex / Nearby Geniculocalcarine fibres
A
  1. Ipsilateral loss of vision e.g. Trauma, MS, Glaucoma
  2. Bitemporal hemianopsia e.g. Pituitary gland
  3. Contralateral homonymous hemianopsia e.g. Tumour
  4. Contralateral superior/inferior quadrantanopsia
  5. Contralateral homonymous hemianopsia with macular sparing e.g PCA stroke or Temporal / Occipital tumour
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11
Q

Where do the cell bodies of fibres of the oculomotor nerve originate?

A

Oculomotor nucleus and the Edinger-Westphal nucleus. Both are located within the periaquaductal gray mater of the midbrain at the level of the superior colliculus. The EW nucleus is dorsal to the III nucleus.

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12
Q

What muscles does the Oculomotor nerve supply? Also, what are the actions of these muscles?

A

Levator palpebrae superioris - Elevation of upper eye lid (superior branch)
Superior rectus - Elevation, Adduction, M.Rotation (superior branch)
Inferior rectus - Depression, Adduction, L.Rotation (inferior branch)
Medial rectus - Adduction (inferior branch)
Inferior oblique - Elevation, Abduction, L.Rotation (inferior branch)

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13
Q

What are the muscles that are not supplied by the Oculomotor nerve? What innervates them and what are the actions of these muscles?

A

Superior Oblique - Trochlear nerve. Depression, Adduction, M.Rotation
Lateral Rectus - Abducens nerve. Abduction.

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14
Q

Describe the pathway of Edinger-Westphal fibres that travel as part of the Oculomotor nerve.

A

Parasympathetic axons distrubute to the cillary ganglion of the nasocillary nerve, a branch of the opthalmic part of trigeminal. The preganglionic fibres synapse at the cillary ganglion. Postganglionic fibres pass through short cillary fibres to innervate the sphincter pupillae and cillary muscles to constrict the pupil.
Note: sympathetic innervation to dilate the pupils act via long cillary fibres.

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15
Q

Describe the pathway of the Oculomotor nerve.

A
  1. Cell bodies originate in the midbrain
  2. The III nerve passes through the cavernous sinus along the superior lateral wall
  3. Enters the superior orbital fissure and through the common tendinous ring
  4. It then separates into two branches, superior and inferior. The muscles that are innervated by each branch are explained previously.
16
Q

Where does the Trochlear nerve originate?

A

At the same area of the III nerve but at the level of the inferior colliculus. Also, the IV is the only cranial nerve to emerge from the dorsal aspect of the brain stem. The IV nerve decussates before emerging from the brain stem to supply the contralateral superior oblique muscle.

17
Q

Describe the journey of the Trochlear nerve.

A
  1. IV runs alongside the free edge of the tentorium cerebelli. The tentorium cerebelli is an extension of the dura mater to seperate the cerebellum from inferior occipital lobe.
  2. The IV runs along the lateral wall of the cavernous sinus.
  3. IV runs between the III and V1 nerves.
  4. The IV enters the orbit via the superior orbital fissure.
18
Q

Where are the nuclei of the Trigeminal nerve and what are they called?

A

Midbrain - Mesencephalic nucleus
Pons - Chief sensory nucleus V
Medulla oblongata - Spinal nucleus V

19
Q

Where does the abducens nerve originate?

A

Caudal pons near the floor of the 4th ventricle. Near the Medial Leminiscal pathway.

20
Q

Describe the journey of the abducens nerve.

A
  1. VI pierces the Dura Mater
  2. Enters the cavernous sinus
  3. Enters the superior orbital fissure
  4. IV can be seen on the medial aspect of the lateral rectus muscle
21
Q

Describe the abducens nerve within the cavernous sinus.

A
  1. The VI runs inferio-lateral to the internal carotid artery and runs in the body of the cavernous sinus.
  2. During it’s course it bends sharply over the crest of the petrosal bone.
22
Q

What may cause a lesion of the abducens nerve?

A

An aneurysm of the internal carotid artery may compress the abducens nerve within the cavernous sinus. Therefore, ipsilateral deficit of superior oblique function.

23
Q

Where are the nuclei of the facial nerve? Then what is the journey of the facial nerve fibres?

A
  1. Facial motor nucleus - in the lateral tegmentum of the caudal pons. There are two parts: one for the upper facial muscles and one for the lower facial muscles.
    - The VII nerve originates here and bends around the abducens nucleus before emerging between the pons and the cerebellar peduncles. ventrally.
    - The nerve then enters through the internal acoustic meatus and passes through the facial canal.
  2. Sensory & PNS nucleus - in the geniculate ganglion. Located within facial canal. Two branches are then given off: The greater petrosal nerve and the chorda tympani nerve.

The facial nerve then passes from the facial canal through the stylomastoid foramen, posterior to the stylomastoid foramen. Then through the parotid gland to innervate the muscles of facial expression (2nd pharnygeal arch musculature).

24
Q

What are the muscles of facial expression and what branches of the VII nerve innervate them?

A
  1. Frontalis - Temporal branch
  2. Obicularis Oculi - Zygomatic branch
  3. Buccinator - Buccal branch
  4. Obicularis Oris - Marginal Mandibular branch
  5. Platysma - Cervical branch
25
Q

What other muscles do the VII innervate?

A
  1. Stylohyoid
  2. Posterior belly of diagastric
  3. Strapedius
26
Q

What are all of the functions of the facial nerve?

A
  1. Muscles of facial expression and three others
  2. Parasympathetics to pterygopalatine ganglion (greater petrosal nerve - p ganglion - zygomaticotemporal nerve - lacrimal nerve) and submandibular ganglion (chorda tympani nerve - submandibular ganglion - lingual nerve)
  3. Anterior 2/3 general sensation and taste of tounge. This is carried back through the chorda tympani nerve.
  4. Sensation from ear, soft palate and pharynx
27
Q

Where are the nuclei of the vestibulocochlear nerve?

A

Vestibular fibres originate at the vestibular apparatus. There are four vestibular nuclei that form the vestibular complex.
Cochlear fibres originate from the organ of corti within the cochlear duct that then synapse at the cochlear / spiral ganglion.

28
Q

Describe the journey of the Vestibulocochlear nerve.

A
  1. The vestibulo and cochlear nerves join as they pass through the internal acoustic meatus.
  2. The VIII then passes through the subarachnoid space in the cerebellopontine angle. This is a region between the middle and inferior cerebellar peduncles.
29
Q

Describe the journey of Vestibular fibres within the VIII nerve.

A

Vestibulo fibres travel through the Vestibulospinal Tract for balance and posture. Also, the vestibular system acts on the cortex, cerebellum and spinal cord for conscious awareness of head position and movement.

30
Q

Describe the journey of Cochlear fibres after synapsing at the cochlear ganglion.

A
  1. Fibres travel through the lateral leminiscus to ultimately (after synapsing at other nuclei) reach the contralateral nuclei in the inferior colliculus
  2. Fibres project from here to the medial geniculate body of the thalamus. These then project to the auditory cortex.
  3. The cortex includes the primary auditory cortex and association auditory cortex (parts of Heschl’s gyrus and the superior temporal gyrus)
31
Q

Why is auditory information normally spared when there is a unilateral lesion?

A

The organ of corti bilaterally innervates cochlear ganglions. Therefore, only a bilateral lesion will cause permanent damage to hearing.
A unilateral lesion will cause temporary / minimal damage. This causes impairment to:
1. Localising direction
2. Localising distance on the contralateral ear

32
Q

What is the sole muscle that the Glossopharyngeal nerve innervates and what is the action of this muscle?

A

Stylopharyngeus - elevates the pharynx during swallowing and talking

33
Q

Describe the journey of the Glossopharyngeal nerve and explain its functions.

A
  1. IX emerges between the olives of the medulla and the inferior cerebellar peduncle and transverses the internal jugular foramen with the X.
  2. Passes deep to the stylomastoid process between the internal jugular vein and the internal carotid artery.
  3. Fibres pass to supply general sensation and taste for the posterior 1/3 tounge via lingual nerves that form part of the pharyngeal plexus
  4. The pharyngeal plexus is formed by the IX, X and cranial part of XI. The IX goes to the carotid body for baro and chemoreception.
  5. Branches from the pharyngeal plexus penetrate the pharyngeal wall to provide general sensation to the: soft palate, pharynx and fauces.
34
Q

Describe the pathway glossopharyngeal parasympathetic secretomotor fibres to the parotid gland.

A
  1. Through the jugular foramen
  2. Glossopharyngeal nerve enters the pharyngeal plexus
  3. Tympanic nerve branches off from the tympanic plexus
  4. The lesser petrosal nerve branches from the tympanic nerve and transverses the foramen ovalis
  5. Preganglionic PNS IX fibres synapse at the Otic ganglion
  6. Postganglionic fibres pass through the auriculotemporal nerve to the Parotid gland
  7. These fibres stimulate the parotid gland
35
Q

What are the divisions of the Accessory nerve and where do they originate?

A
  1. Cranial part - Nucleus ambiguus
  2. Spinal part - Ventral horn of grey mater at levels C1-C5 as a series of rootlets that ascend through the foramen magnum
36
Q

Describe the function and distribution of the spinal part of accessory.

A
  1. Rootlets ascend from the ventral horn of grey mater C1-C5 through the foramen magnum.
  2. As it then passes through the jugular foramen it communicates briefly with the cranial part of accessory.
  3. The nerve passes over the internal jugular vein to innervate the sternocleidomastoid.
  4. Then runs through the posterior triangle of the neck to innervate the trapezius.
37
Q

Describe the function and distribution of the cranial part of accessory.

A
  1. Originates at the inferior part of the nucleus ambiguus (X originates superiorly to XI)
  2. Enters the jugular foramen briefly communicating with the spinal part of accessory.
  3. The cranial part of accessory then joins the vagus nerve to distrubute to pharyngeal and palate musculature.
  4. This is done via the pharyngeal plexus. Cranial part of accessory supplies the vagal motor functions.

NLM2 (7 decks)

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