The olfactory epithelium lines the roof of nasal cavity. Olfactory epithelium lines the inferior surface of cribriform plate of ethmoidal bone (roof of the nasal cavity). The latter is related to the inferior surface of the brain.

1. Dr / Ahmed Salah Ashour(Ph.D.)
Associate professor of human anatomy
Dr.Ahmedashour@gmu.ac.ae
USMLE Clinical Anatomy

2. CRANIAL
NERVES

3. ILOs
• Describe the deep origin of 1st and 2nd cranial nerves

5. OLFACTORY (I)
Special somatic afferent column
Special Somatic Afferent (SSA): These nerves carry sensory information related to all special senses (except taste)

6. Attachment to brainstem

7. Responsible for the sense of smell.
It is related to anterior surface of the brain. 1

8. Fact:
The olfactory epithelium lines the roof of nasal cavity.
Olfactory epithelium lines the inferior surface of cribriform plate of ethmoidal bone
(roof of the nasal cavity). The latter is related to the inferior surface of the brain.
cribriform plate of ethmoidal bone

9. Fact:
UNI-POLAR BI-POLAR

10. Human have 6 to 10 million olfactory
sensory neurons distributed along a
surface area of 2.5 cm. Sense of smell is
around 10000 times more sensitive than
sense of taste.

11. Course

12. First order neuron
Olfactory nerve cells: are bipolar calls with body embedded within olfactory
epithelium. The peripheral processes terminate in cilia directed to nasal cavity. The
central processes are grouped and pass through the cribriform plate of ethmoidal
bone to end in the olfactory bulb cells (anterior olfactory nuclei).
Anterior olfactory nuclei
Central processes
Olfactory nerve cells
Peripheral processes
cilia
Olfactory bulb
Cribri. plate ethmoid.
Olfactory epithelium
Nasal cavity

13. Fracture base skull
Fracture of the cribriform plate may be
associated with tear of the meninges and
a leakage of CSF fluid into the nasal
cavity and provide a route of infection
from the nose to the brain.
Clinical Insight

14. It is estimated that the
olfactory epithelium can
respond to a trillion different
scents!

15. Second order neuron
anterior olfactory nuclei are located at olfactory bulb: It is oval mass and overlies
the cribriform plate of ethmoidal bone. Axons of anterior olfactory nuclei are
grouped to form the olfactory tract at the base of brain.
Anterior olfactory nuclei
Central processes
Olfactory nerve cells
Peripheral processes
cilia
Olfactory bulb
Cribri. plate ethmoid.
Olfactory epithelium
Nasal cavity
Axons of anterior olfactory nuclei olfactory tract

16. Lesions olfactory epithelium
Lesions of the olfactory
epithelium do not affect the
ability to sense pain from the
nasal epithelium
[this is because pain from the
epithelium which lines the
nose is carried to the central
nervous system by the
trigeminal nerve].
Clinical Insight
olfactory nerve
trigeminal nerve branches

17. Olfactory tract:
It is a narrow-elongated band.
It divides into the lateral, and medial
striae.
These striae connect the olfactory tract to
the olfactory cortex.
Olfactory bulb
Olfactory tract
Lateral olfactory stria
anterior perforated
substance

18. Olfactory cortex (Rhin-encephalon):
Primary: anterior perforated substance
Secondary: entorhinal area 28, 34
olfactory stria
anterior perforated substance
entorhinal area 34
entorhinal area 28

19. Comprehensive experience of flavor
The olfactory and gustatory systems both
send signals to the brain, where they are
integrated to form a unified perception of
flavor. This integration occurs primarily
in the orbitofrontal cortex, where inputs
from different sensory modalities are
combined. This area is crucial for
processing and integrating information
related to taste and smell. Neurons in the
orbitofrontal cortex respond to the
combination of olfactory and gustatory
stimuli, contributing to the overall flavor
experience.
Clinical Insight

20. Lesions of olfactory pathway
Etiology:
• Meningitis
• Tumors of the frontal lobe of the
brain.
These injuries often lead to a reduced
ability to taste and smell.
Clinical Insight

21. OPTIC (II)
Special somatic afferent column
Special Somatic Afferent (SSA): These nerves carry sensory information related to all special senses (except taste)

22. Attachment to brainstem

23. Involved in vision. The optic nerve of both sides will
unit forming the optic chiasm, which is related to
anterior base of the brain.
2

24. Course

25. First order neuron
Rods and cones cells
• Cell bodies are located at retina and
receive information from the visual
fields
• Axons, transmit this input to second
order neuron [retinal ganglion cells].
Rods and cones
Ganglion cells

26. Second order neuron
Ganglion cell
• Cell body is located in the retina
• Axons converge and leave the
posterior pole of the eye as the optic
nerve.
Rods and cones
Ganglion cells
optic nerve

27. Optic nerve
Origin: Is made up of the axons of the cells
in the ganglionic cell layer of the retina.
retina
Optic nerve

28. Op<c nerve
Exit from the eyeball:
emerges from the eyeball 3 or 4 mm
nasal to its centre.
Length: 4 cm
• 25 mm intraorbital
• 5 mm intra-canalicular
• 10 mm intracranial.
Intraorbital part
Intra-cranial part

29. Course
• Runs backwards and medially
• Passes through the optic canal to enter the middle
cranial fossa
• It joins the nerve of the opposite side to from the
optic chiasma
optic chiasma
Optic nerve

30. Relations
Surrounded by the recti muscles.
Op<c nerve
Intraorbital part
Intra-cranial part
Recti muscles

31. Chiasma and optic tract
• Axons from the
ganglionic cells located
at nasal halves of each
retina cross to
contralateral optic tract.
• Axons from the
ganglionic cells located
at temporal halves
remain uncrossed and
run at the ipsilateral
optic tract .

32. Optic radiation contains
• Temporal fibers of the same
side
• Nasal fibers from the
opposite side.

34. Third order neuron
• Cell bodies are located at
the lateral geniculate body
• Axons travel posteriorly as
optic radiation which end
into the visual cortex.
Optic radiation contains
• Temporal fibers of the same
side
• Nasal fibers from the
opposite side.
Optic radiation

35. Visual cortex:
The primary visual area
(area 17)
The secondary visual area
(area 18, 19)
This functional MRI (fMRI) was obtained during presentation of
a visual stimulus to the subject in the MRI unit.

36. Visual field test
is an eye examination that can detect dysfunction in central and peripheral vision
which may be caused by various medical conditions.
Clinical Insight

37. The nasal part of the retina is
responsible of receiving the
light from the temporal half of
the visual field and vise versa.
Temporal
Nasal
Clinical Insight

38. Optic nerve lesions
Aetiology:
• Optic atrophy
• Traumatic avulsion
• Acute optic neuritis etc.
Manifestations:
• Ipsilateral blindness ( loss of vision in
the affected eye)
Clinical Insight

39. Chiasmal lesions
Aetiology:
• Intrinsic causes – Lesions which produce
thickening of chiasma [Gliomas, multiple
sclerosis]
• Extrinsic causes – Compressive lesions.
[Pitutary adenoma]
Pituitary
Chiasma
Clinical Insight

40. Chiasmal lesions
Manifestations:
1.Central chiasmal lesion
Bitemporal hemianopia:
partial blindness where vision is missing in
the outer half of both the right and left visual
field.
Clinical Insight

41. Chiasmal lesions
2.Lateral chiasmal lesion
Binasal hemianopia:
par>al blindness where vision is missing
in the inner half of both the right and
le? visual field.
Clinical Insight

42. Optic tract lesions
Aetiology:
• Demyelinating diseases and infarction
and Compressive lesions (adenomas,
tumours)
Manifestations:
Contralateral homo-nymous hemianopia
(visual field loss on the same side of both
eyes)
Clinical Insight

43. Clinical Insight

44. Lateral geniculate nucleus lesions
Aetiology:
• Extrinsic causes – Compressive
lesions
Manifestations:
Contralateral homo-nymous hemianopia
Clinical Insight

45. Optic radiations lesions
Aetiology:
• Vascular occlusions
• Tumours
• Trauma
Manifestations:
Contralateral homonymous hemianopia
Clinical Insight

46. Clinical Insight

47. Clinical Insight

48. Agnosia
Patients with damage to the visual association
cortex may complain of inability to recognize
[familiar faces or to observed objects, patient can
use other senses to recognize objects.
Clinical Insight

52. Formative Quiz

53. Q1 A young boy is brought to the clinic. He appears quite small for his age and
complains of not being able to see as well as he used to. Visual field examination
reveals an impaired peripheral vision in the outer temporal halves of the visual
field. You suspect a tumor located near which of the following?
A. Pituitary gland and stalk
B. Calcarine sulcus
C. Parieto-occipital sulcus
D. Nucleus of crania) nerve III
E. Pineal gland

54. Q2 A patient comes to the office because of decreased vision. You discover that she
has visual field defects involving the lateral (temporal) visual fields in both eyes.
Which of the following is the most likely cause of her vision problem?
Optic neuritis
Parietal lobe lesion
Pituitary tumor
Posterior cerebral artery infarct
Temporal lesion

55. Q3 A 56-year old man has a stroke in branches of the posterior cerebral artery,
which affects the majority of his Brodmann's area 17. What major problem do you
expect this individual to exhibit?
Difficulties in the comprehension of speech
Difficulties hearing
Disruptions with the perception of pain and temperature
Disruptions in visual processing
Disruptions in voluntary motor output

56. Q4 A 71-year-old woman comes into your office for a standard check-up. She says
she has no complaints other than decreased hearing. Her exam shows no
abnormalities in her ear and suggests a nerve lesion. Which cranial nerve is
responsible for her sensory complaints?
CN I
CN II
CN VII
CN VIII
CN XI

57. Q5 What part of the ventricular system is closest to the optic radiations?
A. Aqueduct.
B. Posterior horn of the lateral ventricle.
C. Fourth ventricle.
D. Third ventricle.
E. Frontal horn.

58. Q6 What is the difference between the optic nerve and tract?
A. One has oligodendrocytes and the other Schwann cells.
B. One has third order axons and one has second order axons.
C. One has only ipsilateral axons and the other has both ipsilateral and
contralateral axons.
D. One is central nervous system tissue and the other is peripheral
nervous system tissue.

59. Q7 A patient presents with the inability to recognize familiar faces, even those of
close family members, while retaining the ability to see and describe the individual
facial features. Which type of agnosia is most likely affecting this patient?
Prosopagnosia
Auditory agnosia
Tactile agnosia
Anosognosia

60. Q8 In a patient with homonymous hemianopia, where vision is lost in the same
visual field of both eyes, what part of the visual pathway is likely affected?
Optic nerve
Optic chiasm centrally
Optic tract
Optic chiasm peripherally

61. Q9 Your patient, a 25-year-old woman, tells you that 6 months ago she had balance
problems and numbness in her right hand, but the numbness subsided after a week
or so. She is a secretary and thinks that she may have carpal tunnel syndrome.
Today,you note that she has decreased vibratory sense in both the right hand and
right leg, decreased pinprick sen- sation in the right lower limb, and that both of her
right limbs are weak. Analysis of cere- brospinal fluid following lumbar tap reveals
heterogeneous immunoglobulin G staining with oligoclonal banding. Which of the
following might also be seen in the patient?
(A)Bilateralptosis
(B) Blurry vision
(C) Clawhand
(D) Ticdouloureux
(E) Foot drop

62. Q10 A 20-year-old man is brought to the emergency department 1 hour after he was
involved in a motorcycle collision. He was not wearing a helmet. Physical
examination shows clear fluid dripping from the nose. X-rays show a fracture of the
cribriform plate of the ethmoid bone. This patient is at greatest risk for impairment
of which of the following senses?
Balance
Hearing
Olfaction
Taste
Vision

63. Q1 Pituitary gland and stalk
Q2 Pituitary tumor
Q3 Disruptions in visual processing
Q4 CN VIII
Q5 Posterior horn of the lateral ventricle
Q6 One has only ipsilateral axons and the other has both ipsilateral and contralateral
axons.
Q7 Anosognosia
Q8 Optic tract
Q9 Blurry vision
Q10 Olfaction

64. List of Texts and Recommended Readings
• Last's Anatomy, Regional and Applied. Chummy S. Sinnatamby. 12th edition 2011, ISBN:13 - 978 0 7020 3394 0
(Available in ClinicalKey: https://www.clinicalkey.com/#!/browse/book/3-s2.0- C2009060533X)
• Estomih Mtui, Gregory Gruener and Peter Dockery. Fitzgerald's Clinical Neuroanatomy and Neuroscience. 7th
edition; 2016, ISBN: 13 - 978-0-7020- 6727-3 (Available in ClinicalKey:
https://www.clinicalkey.com/#!/browse/book/3-s2.0- C20130134113
• Drake, Richard L. Gray's Anatomy for Students, Third Edition, Elsevier Saunders 2015. ISBN-13: 978-0702051319
(Available in ClinicalKey: https://www.clinicalkey.com/#!/browse/book/3- s2.0-C20110061707).
• Sobotta Atlas of Human Anatomy. F. Paulsen. Vol.1, 15th Edition; 2013, ISBN: 9780702052514 (Available in
ClinicalKey: https://www.clinicalkey.com/#!/content/book/3- s2.0-B9780702052514500067)
• Sobotta Atlas of Human Anatomy. F. Paulsen. Vol.2, 15th Edition; 2013, ISBN:13 - 978-0-7020-5252-1 (Available in
ClinicalKey: https://www.clinicalkey.com/#!/browse/book/3- s2.0-C20130046919)

65. Recap