Download Cranial Nerves

Cranial Nerves
• Lundy-Ekman
– Chapter 13
– Chapter 14
– Chapter 15
Objectives
1. Identify the 12 cranial nerves by name and
number, their major functions, and the site of
their connection with the brain
2. Describe the control of eye movements
3. Describe the control of the eye, including
pupillary, consensual and accommodation
reflexes
4. Describe the motor and/or sensory functions of
the cranial nerves
5. Identify the cranial nerves associated with
eating, swallowing and speech
6. Describe the loss of function associated
with damage to each of the cranial nerves
7. Describe the etiology and pathology of
Trigeminal Neuralgia and Bell’s Palsy.
Functions of Cranial Nerves
• Same overall functions as spinal nerves, though a
cranial nerve may not have all categories of
functions
– Motor
– Sensory
– Autonomic
• Some cranial nerves have special functions
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Smell
Vision
Taste
Vestibular
Three main functions
1. Motor innervation to muscles of face, eyes,
tongue, jaw and two neck muscles.
2. Somatosensory information from skin and
muscles of face and TMJ, and special sensory
information (olfactory, visual, auditory,
vestibular, taste, and visceral sensations)
3. Parasympathetic regulation of heart rate, blood
pressure, digestion, breathing, and some eye
muscles.
Lesions of Cranial Nerves
• Damage to cranial nerve in periphery (trauma,
inflammation)
– Ipsilateral deficits
• Damage to cranial nerve nuclei in CNS (stroke)
– Usually ipsilateral deficits
– Can help localize lesion in the brain
• Damage to upper motor neurons that control
cranial nerves (stroke)
– Usually do not see significant weakness due to bilateral
innervation of CN nuclei. (One significant exception)
Where Cranial Nerves Exit the
Brain
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Telecephalon – 1
Diencephalon – 1
Midbrain – 2
Pons – 1
Border between pons and medulla - 3
Medulla – 4
Page 358: location of cell bodies in
brainstem
Cranial Nerve I
Olfactory Nerve
• Sensory – Smell
• Olfactory receptors in nasal mucosa
– Axons travel through skull to the olfactory bulb
– Information travels to medial temporal lobe of
the cerebrum
• Damage – anosmia – loss of sense of smell
• How do we lose function in C.N. I
– Head injury – injure axons as they pass through
the skull
– Smoking
– Excessive nasal secretions
– Chemicals
• Loss of function
– Anosmia – loss of sense of smell
– Also decreases in taste
• These neurons can regenerate, and the sense
of smell may return
Cranial Nerve II
Optic Nerve
• Sensory - sight
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Retina
Optic Nerve - PNS
Optic chiasm - Diencephalon
Optic tract - CNS
Lateral geniculate body – thalamus
Primary Visual cortex
Retina
• Nasal retinal field
• Temporal retinal field
Optic Chiasm
• Some fibers cross
the midline
– From nasal retinal
field
• The LGN and visual
cortex receives
information from
the contralateral
visual field
Injuries to Visual System
• Injury to optic nerve
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• Injury to optic chiasm
– Which fibers are being injured?
– What visual field deficits will there be?
• Bitemporal hemianopsia
• Injury to Optic tract, LGN or visual cortex
– Homonymous hemianopsia
Cranial Nerves III, IV, and VI
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Primarily motor
III, IV: midbrain
VI: pons-medulla border (cell bodies in pons)
Extraocular muscles
Raise upper eyelid
Constrict pupil
Adjust shape of lens
Extraocular muscles
• Medial rectus – III
– Moves eye medially
• Lateral rectus – VI
• Medial and lateral rectus control horizontal
eye movements
• Superior rectus – III
– Eye looks up
• Inferior rectus – III
– Eye looks down
Oblique muscles
• Superior oblique – IV
– Eye abducted: Rotation
– Eye adducted: eye looks down
• Inferior oblique – III
– Eye abducted: Rotation
– Eye adducted: eye looks up
• Levator palpebrae superioris – III
– Elevates upper eyelid in part
• Pupillary sphincter muscle - III
– Constricts pupil
• Ciliary muscle - III
– Increases curvature of lens of eye
C.N. III
• Cell bodies
– Oculomotor nucleus
• Somatic motor
– Edinger-Westphal nucleus
• Parasympathetic fibers
– Ciliary ganglia behind the eye in the orbit
– Constrict pupil
– Change curvature of lens for near vision
» Accommodation
C.N. IV
• Cranial nerve IV
– Cell bodies
• In midbrain
– Axons leave dorsal surface of brainstem (only
one)
• Cranial nerve VI
– Cell bodies in pontine tegmentum
Cranial Nerve VI
Abducens nerve
• Motor
• Border between pons and medulla
• Lateral rectus muscle
– Action:
Reflexes involving the eye
• Pupillary reflex
• Consensual reflex
• Accommodation reflex
Pupillary reflex
• Stimulus:
• Response:
• Afferent nerve:
• Efferent:
Consensual Reflex
• Stimulus:
• Response:
• Afferent nerve:
• Efferent:
Pathways for the pupillary reflex
and the consensual reflex
• Retina  Pretectal nucleus in midbrain
•  parasympathetic nucleus of the
oculomotor nerve
•  Ciliary ganglion
•  Pupillary sphincter
Accommodation
• Reflex when we look at near objects
– Pupils constrict
– Eyes converge
• What muscle(s)
– Lens becomes more convex
• Requires visual cortex and frontal eye field
in the frontal lobe
Lesion of oculomotor nerve
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Ptosis – drooping of upper eyelid
Ipsilateral eye looks down and out
Difficulty moving eye medially
Double vision
Loss of reflexes
Pupillary dilation
Oculomotor nerve lesion
• Space-occupying lesions in the cerebrum
can compress the midbrain, interfering with
the functioning of the oculomotor nerve.
Trochlear Nerve
• Located in midbrain
• Superior oblique muscle
– If eye adducted, pupil down and in
– If eye abducted, rotates eye
Lesion of Trochlear Nerve
• Ipsilateral eye unable to look down and in.
• Double vision – can be reduced by tilting of
head.
Abducens Nerve
• Located between pons and medulla
• Lateral rectus mm.
– Abducts pupil
Lesion of Abducens Nerve
• Ipsilateral eye looks inward
• Unable to abduct eye past midline
• Double vision
Abducens Nerve Lesion (Right)
V - Trigeminal
• Enters at level of mid pons
• Sensory to skin of face, mucous membranes
of head, and meninges
• Motor to muscles of mastication
• Three main divisions
– Ophthalmic
– Maxillary
– Mandibular – only division with motor fibers
• Mesencephalic trigeminal nucleus –
midbrain
– Unconscious proprioception
• Chief sensory nucleus – mid pons
• Spinal trigeminal nucleus
– Caudal pons to upper cervical cord
Trigeminal Reflexes
• Corneal Reflex – ophthalmic division.
Facial nerve is efferent part of reflex.
• Masseter (Jaw Jerk) Reflex – mandibular
division
VII- Facial
• Pontomedullary border
• Cell bodies in pons
• Motor
– Muscles of facial expression
– Glands of head and neck
• Sensory
– Taste on anterior 2/3rd of tongue
Lesions
• If damage to nerve or nucleus, will see
deficits on whole ipsilateral face (Bell’s
Palsy affects axons of facial nerve)
• If damage to upper motor neurons (i.e.
cerebral stroke), deficits on lower
contralateral face. The forehead will be
spared.
VIII – Vestibulocochlear Nerve
• Pontomedullary border
• Cell bodies in pons
• Two Divisions
– Vestibular – posture and equilibrium
– Auditory - hearing
Deafness
• Conduction deafness
– Deficit in mechanism conveying vibrations
from air to the cochlea
• Sensorineural deafness
– Deficit in cochlea – transduction of sound
waves to action potentials
– Deficit in nerves
Vestibular Nerve
• Vertigo – sensation of movement
• Nystagmus – involuntary back and forth
movements of eyes
• Disequilibrium – loss of sense of balance
IX – Glossopharyngeal Nerve
• Medulla
• Sensory
– Posterior tongue
– Skin of external ear
– Mucosa of mouth – afferent limb of gag reflex
• Motor
– Muscles of throat
– Parotid gland
X - Vagus
• Medulla
• Cell bodies –medulla
• Main parasympathetic nucleus for head,
neck, thoracic organs, and superior
abdominal organs.
• Motor for muscles of larynx and pharynx
– Important in speech and swallowing
Effects of Vagus Nerve Lesion
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Difficulty speaking
Hoarseness
Difficulty with swallowing
Poor digestion – loss of parasympathetic
innervation to GI tract
XI – Accessory Nerve
• Medulla – nucleus extends into upper
cervical spinal cord
• Motor to trapezius and sternocleidomastoid
muscles.
XII – Hypoglossal Nerve
• Medulla
• Motor to intrinsic and extrinsic muscles of
ipsilateral tongue
Conclusion
Why are cranial nerves
important?
• Cranial nerves have important and unique
functions, especially somatosensation and motor
for the head and the special senses.
• Cranial nerves are important in speaking
(dysarthria)
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Larynx and soft palate – X
Jaws – V
Lips – VII
Tongue – XII
• Cranial nerves are important in swallowing.
– Mouth and jaw muscles – V, VII, IX, X, XII
– Pharynx, Larynx – IX, X
– Esophagus and GI tract – X
• Cranial nerves can indicate the level of a lesion to
the nervous system.
• Cranial nerve deficits can signal injury to other
regions of the nervous system.
– Pupilary reflex – increased intracranial pressure
– Bitemporal hemianopsia – pituitary tumor