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Neuroanatomy II > 15 - Cranial Nerves I > Flashcards

15 - Cranial Nerves I Flashcards

1
Q

CN I

A

Olfactory nerve

Sense of smell

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2
Q

Olfactory epithelium

A
  • In roof and upper walls of nasal cavity.
  • In upper-most part of the nasal septum.
  • Contains the olfactory receptor cells (bipolar neurons), which are the first order neurons of the olfactory pathway, sustentacular (support) cells, and basal cells (stem cells).
  • Odorous substances dissolve in mucus, stimulating chemosensitive cilia of olfactory receptor cells.
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3
Q

Olfactory receptor cells - UNIQUE

A
  • are the only nerve cells that are exposed to the environment
  • are located in an epithelium instead of being enclosed in a ganglion, as other first order neurons of sensory pathways
  • are regenerated every 30 – 60 days throughout the lifetime of the organism
  • give rise to the slowest-conducting (unmyelinated) axons of the NS
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4
Q

Describe the axons of CN I

A
  • Axons form bundles called olfactory fila (L.atin for “threads”)
  • Collectively, all olfactory fila create Cranial Nerve I, on each side
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5
Q

Describe the pathway of fila

A
  • Fila pass through the perforations of the cribriform plate of the ethmoid bone
  • They then terminate and synapse in the overlying olfactory bulb in the anterior cranial fossa
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6
Q

Why do our nostrils open immediately above the orifice of the oral cavity?

A

Because the olfactory system serves as a last resort “alarm” system which protects us from ingesting food (or other substances) that might make us sick.

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7
Q

Olfactory bulbs contain two types of neurons

A

Second order neurons

Interneurons

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8
Q

Second order neurons of the olfactory bulbs

A

Second order neurons

a. Mitral cells
b. Tufted cells
c. Their axons run in olfactory tract and give off collaterals to the anterior olfactory nucleus (located within the olfactory tract).

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9
Q

Interneurons of the olfactory bulbs

A

Interneurons – modulate olfactory input.

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10
Q

Olfactory tracts divide into two stira

A

Medial olfactory stria

Lateral olfactory stria

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11
Q

Describe the lateral olfactory stria

A
  • It is the principal central projection of the olfactory system
  • It terminates in the primary olfactory cortex and the amygdala
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12
Q

The olfactory bulbs, tracts, and the medial and lateral olfactory striae are really…

A

extensions of the telencephalon which are not embedded within the brain

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13
Q

The olfactory projection consists of a sequence of only 2 neurons from receptor
to cortex as follows

A
  1. olfactory receptor cells (first order neurons)
  2. mitral and tufted cells (projection neurons in the olfactory bulb)

The olfactory system is the only sensory system which does NOT project to the thalamus prior to the cerebral cortex. Instead, it bypasses the thalamus and sends projections directly to the cortex.

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14
Q

Primary olfactory cortex projections

A

1 - hypothalamus
2 - amygdala
3 - cortical areas
4 - olfactory association cortex

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15
Q

Role of projections to the hypothalamus

A

integrates endocrine and autonomic functions

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16
Q

Role of projections to the amygdala

A

Amygdala of the limbic system - Limbic system is associated with the processing
of learning, memory, emotions and drives

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17
Q

Role of projections to the cortical areas

A

cortical areas associated with memory

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18
Q

Role of projections to the olfactory association cortex

A

olfactory association cortex: interprets the significance of a scent/odor

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19
Q

What is the olfactory cortex close to? Why is this significant?

A

The olfactory cortex is located close to the cortex associated with the processing
of memories.

For triggering memories , nothing beats the sense of smell.

The olfactory system is like a direct channel to our past. A scent may be enough to
relive an experience from years ago and to feel all the emotions associated with it.

Example: One whiff of formaldehyde years from now, will no doubt evoke memories of your first day in the gross anatomy lab.

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20
Q

How a lesion could occur to the olfactory receptor cells

A

During head trauma, the olfactory receptor cell axons may be damaged as a result of fracture of the ethmoid bone, or if the olfactory bulb moves from its normal position.

Note that the olfactory bulb lies in a depression of the ethmoid bone (the cribriform plate of the ethmoid bone) containing tiny holes. Movement of the olfactory bulb may cause a shearing force, injuring or damaging the olfactory receptor cell axons, as they pass through the perforations of the ethmoid bone, disconnecting the olfactory nerve fibers from the overlying olfactory bulb.

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21
Q

Can you recover from a lesion to the axons of olfactory receptor cells?

A

Once the axons of the olfactory receptor cells are severed following head trauma (from an automobile accident, a fall, or a blow to the nose), recovery of normal olfactory function is rare. There is no effective treatment.

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22
Q

Anosmia

A

Anosmia = Is the complete loss of the sense of smell.

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23
Q

Hyposmia

A

Hyposmia = Is the partial loss of the sense of smell.

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24
Q

Parosmia (dysomia)

A

Parosmia (dysosmia) = Is the distorted perception of odors

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25
Q

What diseases is olfactory dysfunction associated with?

A

Epileptics may perceive strange odors that are not really present, prior to an
epileptic seizure.

Olfactory dysfunction is also associated with neurodegenerative
diseases (during early stages of disease: Alzheimer, Parkinson, and Huntington).

Also schizophrenia, and Korsakoff psychosis.

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26
Q

CN II

A

Optic nerve

Vision

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27
Q

Receptors of visual pathway

A

Rods and cones in the retina are the receptors of the visual pathway.

28
Q

First order neurons of visual pathway

A

Bipolar cells in the retina are the first order neurons of the visual pathway.

29
Q

Second order neurons of visual pathway

A

Ganglion cells (the second order neurons of the visual pathway) residing in the retina, give rise to axons that exit the back of the eyeball and gather to form the optic nerve. The optic nerve is heavily myelinated.

30
Q

Path of the optic nerve

A

The optic nerve passes through the optic canal to enter the cranial vault.

31
Q

Formation of optic chiasm

A

The optic nerves converge to form the optic chiasm (G. chiasma, “optic cross”).

32
Q

Formation of optic tracts

A

The optic chiasm diverges to form the optic tracts.

33
Q

Termination of optic tract fibers

A
  • Most of the optic tract fibers terminate in the lateral geniculate nucleus (LGN) of the thalamus.
  • Some axons terminate in the superior colliculus
  • Other axons terminate in the pretectal area and the hypothalamus.
34
Q

Function of superior colliculus

A

Functions in the control of reflex head and eye movements in response
to visual, auditory or cutaneous stimuli

35
Q

Function of pretectal area

A

Associated with the pupillary constriction reflex in response to bright light

36
Q

Third order neurons of the visual pathway

A

The lateral geniculate nucleus (LGN) contains the third order neurons of the visual pathway.

These neurons give rise to axons that form the geniculocalcarine tract (optic radiation) which runs through the posterior aspects of the internal capsule, then the corona radiata to the primary visual cortex in the occipital lobe.

37
Q

Lesion of one optic nerve

A

total blindness in ipsilateral eye

38
Q

Lesion of only crossed fibers at optic chiasm

A

bitemporal (heteronymous) hemianopia

This is a type of partial blindness where vision is missing in the outer half of both the right and left visual field

39
Q

Lesion of only uncrossed fibers at optic chiasm on the right side only

A

ipsilateral (right) nasal hemianopia

vision is missing in the inner half of the right visual field

40
Q

Lesion of only uncrossed fibers at optic chiasm on both sides

A

binasal (heteronymous) hemianopia

vision is missing in the inner half of both the right and left visual field.

41
Q

Lesion of right optic tract

A

Left (homonyous) hemianopia

Visual field loss on the left side of the vertical midline

42
Q

Lesion of right lateral geniculate nucleus (LGN)

A

Left (homonymous) hemianopia

Visual field loss on the left side of the vertical midline

This is the same result as a lesion of the right optic tract

43
Q

Lesion of right optic radiation (both upper and lower divisions)

A

Left (homonymous) hemianopia

Visual field loss on the left side of the vertical midline

This is the same result as a lesion of the right optic tract or a lesion of the right LGN

44
Q

Lesion of right optic radiation (geniculocalcarine tract) upper division only

A

upper division only : to cuneus

Left lower (homonymous) quadrantanopia

The left lower quadrant of visual field is missing

45
Q

Lesion of right optic radiation (geniculocalcarine tract) lower division only

A

lower division only : (Meyer’s loop) : to lingual gyrus

Left upper (homonymous) quadrantanopia

The left upper quadrant of visual field is missing

46
Q

Thrombus occludes posterior cerebral artery

A

If a thrombus occludes the posterior cerebral artery it usually produces a lesion in the primary visual cortex (area 17), located in the medial surface of the occipital lobe on the banks of the calcarine sulcus

47
Q

Unilateral vascular lesion that damages the right visual cortex

A

left (homonymous) hemianopia with macular sparing

Visual field loss on the left side of the vertical midline

Macula is spared

48
Q

Macular sparing

A

Visual input from the macula occupies a substantial portion of the brain’s visual capacity. As a result, some forms of visual field loss can occur without involving the macula; this is termed macular sparing

49
Q

Cortical area that receives visual information from the macula

A
  • located in the posterior pole of the primary visual cortex
  • receives blood supply from the posterior cerebral artery (PCA)
  • also receives collateral blood supply contributed by the middle cerebral artery (MCA)
50
Q

Two factors that support macular sparing

A

1 - The dual blood supply of the visual cortex - If the PCA becomes occluded, the MCA nourishes the macular cortical region

2 - the macular cortical region is quite extensive, so it is rare that a single infarction (vascular lesion) will produce a lesion large enough to damage the entire cortical region that represents the macula

51
Q

CN XI

A

Accessory nerve

52
Q

CN XI function

A

1 - SVE/GSE: Skeletal motor to laryngeal muscles, SCM and trapezius muscles

  • GP: General proprioception (position sense) from SCM and trapezius muscles
53
Q

Aberrant vagal fibers

A

Arise from the nucleus ambiguus (SVE) (in medulla).

The lower part of the nucleus ambiguus contains the cell bodies of motor neurons (LMN’s) whose axons exit the nucleus.

These motor fibers are aberrant fibers of the vagus nerve that innervate the laryngeal muscles.

54
Q

Spinal accessory nerve origin

A

Arises from the spinal accessory nucleus of the spinal cord C1 – C5(6) levels (in anterior horn).

This nucleus is continuous superiorly with the nucleus ambiguus of the medulla.

Fibers arising from each of the above spinal cord levels gather to form the spinal accessory nerve.

55
Q

Pathway of spinal accessory nerve (including aberrant vagal fibers)

A
  • Ascends to the foramen magnum
  • Enters cranium
  • Meets aberrant vagal fibers, run together for a short distance
  • Exit cranium via the jugular foramen
  • Go their separate ways to distribute branches to various muscles in the neck
56
Q

Continuing pathway of aberrant vagal fibers

A

The aberrant vagal fibers join the main trunk of the vagus nerve and follow those fibers of the vagus to most of the intrinsic muscles of the larynx.

57
Q

Continuing pathway of spinal accessory nerve

A

The spinal accessory nerve courses inferiorly deep to the SCM to provide it with motor innervation.

It continues inferiorly in the posterior triangle to the deep aspect of the trapezius muscle to provide it with motor innervation.

58
Q

Is the accessory nerve a true cranial nerve?

A

In view of its embryologic origin, many neuroanatomists do not consider the accessory nerve to be a true cranial nerve, but instead, an unusual type of spinal nerve.

59
Q

Which sternocleidomastoid muscle (right or left) contracts as an individual turns his/her head to the right?

A

The left SCM contracts.

Turn your head and as you are turning, place your fingers over the SCM bilaterally. When you turn to the right, your left SCM contracts and feels firm. The SCM rotates the head so face turns upward toward the opposite side. It also approximates the ear to the shoulder

60
Q

Two different lesions can cause winging of the scapula. What are they?

A
  • CN XI lesion

- Long thoracic nerve lesion

61
Q

CN XI lesion scapula winging

A

Noticeable when arms are lateral to the trunk

More prominent during
abduction of the affected arm

62
Q

Long thoracic nerve lesion scapula winging

A

Noticeable when arms are lateral to the trunk

More prominent during
anterior elevation of the arms and pushing up against an immovable object
(ex: a wall or a piece of furniture)

63
Q

CN XII

A

Hypoglossal Nerve

64
Q

Function of CN XII

A
  1. GSE: Skeletal motor to intrinsic (transverse, longitudinal and vertical) muscle fibers and most extrinsic muscles (styloglossus, hyoglossus and genioglossus) muscles of the tongue. Mediates tongue movement
65
Q

Nucleus of CN XII

A

Hypoglossal nucleus (medulla)

Gives rise to fibers that emerge as rootlets in groove between the pyramid and olive. Fibers gather to form the hypoglossal nerve which projects to tongue

66
Q

LMN lesion to hypoglossal nucleus or to CN XII

A
  • Hemiparalysis (weakness on one side) of the tongue, ipsilateral to the lesion
  • Atrophy (wasting) of the tongue ipsilateral to the lesion (LMN lesion sign)
  • Fasciculations (twitching)
  • Furrowing
  • Upon protrusion of tongue, tongue deviates to side of lesion (weak side)
67
Q

Bilateral lesion of CN XII

A

Bilateral lesions result in difficulty in speaking and eating

Neuroanatomy II (10 decks)

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