The cranial nerves

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The cranial nerves
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The cranial nerves

• These are twelve pairs and numbered from before
  backward.
• All the nerves are distributed in the head and
  neck except the tenth which supply structures in
  the thorax and abdomen.
• Sensory
• 1st, 2nd and 8Th.
• Motor
• 3rd, 4th, 6th, 11th and 12th.
• Mixed
• 5th, 7th, 9th and 10th.

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The cranial nerves Overview

• Cr VII Facial
• Cr VIII Vestibulocochlear
• Cr XI Glossopharyngeal
• Cr X Vagus
• Cr XI Accessory
• Cr XII Hypoglossal

• Cr I Olfactory
• Cr II Optic
• Cr III Oculomotor
• Cr IV Trochlear
• Cr V Trigeminal
• Cr VI Abducent

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The cranial nerves

• The first two are merely an outdrawn part of the
  CNS rather than nerves.

• Olfactory (Sensory) Cr I

• Optic (sensory) Cr II

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Olfactory (Sensory) Cr I

• Fibers originate in the upper part of the nose.
• They are unique in being the central processes
  not peripheral ones

• Clinically
• Bilateral anosmia CSF leak
• are common signs of head
• injuries with anterior cranial
• fossa fracture.

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Optic (sensory) Cr II

• Leaves the orbital cavity through the optic canal
  They join each other to form the chiasma.

• Clinically
• Section through the optic nerve
• causes epsilateral blindness.
• Lesions behind the optic chiasma
• (pituitary gland tumors) lead to
• contro-lateral blindness.

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Oculomotor nerve (motor) Cr III

• Oculo Eye Motor mover
• Somatic nerve to four of the six muscles of that
  moves the eye and the muscle that raises the
  eyelids
• Enter the orbit through superior orbital fissure

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Oculomotor nerve (motor) Cr III

• Clinically
• Inability to look up, down or medially.
• Dilatation of the pupil.
• Ptosis (drooping of the eyelid paralysis
• of LPS)

• Supply all the orbital muscles, except the
  superior oblique, lateral rectus and levator
  palpebrae superioris
• Supply parasympathic fibers to the constrictors
  of the pupil.

9
Trochlear nerve (motor) Cr IV

• Enter through the superior orbital fissure
• supply the superior oblique muscle

• Clinically
• Unable to look downward and
• inward.
• Difficulty in walking downstairs

10
Trigeminal Nerve (mixed)
Cr V

• Motor nucleus (branchial) in the upper pons, for
  the muscles of the first branchial arch.
• Sensory nucleus (somatic) divided into three
• Mesencephalic
• Main
• Spinal

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Trigeminal Nerve (mixed)
Cr V

• Mesencephalic
• extend through the midbrain
• First order neurons
• mediate proprioceptive impulses
• Main sensory
• upper pons lateral to the motor
• second order neurons
• mediate touch
• Spinal
• extend from lower pons, medulla to spinal cord
• second order neurons
• mediate pain temperature

12
Trigeminal Nerve (mixed)
Cr V

• Ophthalmic division
• It is the nerve for the frontonasal process
• emerging through the superior orbital fissure
• divide into three branches
• 1-Lacrimal nerve. 2-Frontal nerve.
  
• 3-Nasociliary nerve.

13
Trigeminal Nerve (mixed)
Cr V

• Maxillary division
• It is the nerve to the maxillary process, leaves
  the skull through foramen rotundum and have a
  very short course.
• Ganglionic branches
• zygomatic nerve
• posterior superior alveolar nerve
• Infraorbital nerve

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Trigeminal Nerve (mixed)
Cr V

• Mandibular division
• It is the nerve for the first pharyngeal arch,
  very short and emerges through foramen ovale
• Accompanied by the motor root of the trigeminal
  nerve
• divide into
• Anterior division
• all motor except one
• Posterior division
• all sensory except one

15
Trigeminal Nerve (mixed)
Cr V

• Nerve to medial pterygoid muscle
• Anterior branches
• nerves to lateral pterygoid, masseter and two
  deep temporal
• the long buccal nerve S.
• Posterior branches
• Auriculotemporal
• inferior alveolar (nerve to mylohoid M)
• the lingual nerves

16
Trigeminal Nerve (mixed)
Cr V

• Clinically
• Fracture midface, zygoma or mandible might lead
• to anaesthesia to light touch and other
  modalities.

• Lesions of the entire nerve leads to
• anaesthesia and paralysis and atrophy
  
• of the muscles of mastication.

• Trigeminal neuralgia
• Herpes zoster

17

• Abducent (motor)
• Cr VI

• Somatic, leave the brain through the superior
  orbital fissure
• Supply the lateral rectus muscle.

• Clinically
• Strabismus and diplopia
• on lateral gaze

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• Facial (mixed)
• Cr VII

• Joined by the nervus intermedius, sensory root,
  in the facial canal in the temporal bone before
  it emerges through the stylomastoid foramen.
• Passes into the parotid gland and divides into
  five motor
• Branchial motor branches
• supply the muscles of the facial expression (from
  second pharyngeal arch)

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• Facial (mixed)
• Cr VII

• Visceral efferent
• Secretomotor to submandibular sublingual
  salivary gland
• Sensory fibers
• Visceral afferent
• Taste buds anterior two third of tongue soft
  palate
• Somatic afferent
• skin of external auditory meatus and tympanic
  membrane

• Clinically
• Bells Palsy
• Loud sound,
• paralysis of stapidus muscle

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• Vestibulocochlear (sensory)
• Cr VIII

• A special sensory nerve, consist of two kinds of
  fibers, the vestibular and the cochlear
• Mediate sound reception and balance.

• Clinically
• Deafness
• vertigo

21

• Glossopharyngeal Nerve (mixed)
• Cr IX

• Sensory
• Special
• taste from the posterior 1/3 of tongue.
• General sensation
• from the back of the tongue wall of the pharynx
  and the middle ear.
• Chemoreceptor pressure
• Carotid sinus concerned with regulation of
  respiration and circulation

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• Glossopharyngeal Nerve (mixed)
• Cr IX

• Motor
• To the stylopharyngeus muscle of the pharynx.
• Parasympathetic fibres
• to the otic ganglion, the postganglionic fibres
  travel with the auriculo-temporal nerve to the
  parotid

• Clinically
• Neuralgia.
• Loss of gagging reflex

23
Vagus nerve mixed Cr X

• Has the most extensive distribution of all the
  cranial nerves, supply the heart and the major
  part of the respiratory and alimentary tract.
• Has one sensory and two motor nuclei in the
  medulla.
• Leave the cranial cavity through the jugular
  foramen.
• passes vertically down the neck within the
  carotid sheath.

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Vagus nerve mixed Cr X

• Have 4 types of fibres
• Motor fibres to the striated muscles of larynx
  and pharynx.
• Paralysis of soft palate, dysphagia and aphonia
• Visceral-motor fibres carry impulses to thoracic
  and abdominal viscera
• Sensory fibres
• for pain from external auditory meatus
• Visceral fibres
• Taste buds in the epiglottis
• Stretch receptors in the heart, aorta and common
  carotid bifurcation (Blood Pressure and heart
  rate)
• Stretch receptors in the lung and upper G-T I
  (rate and depth of respiration

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Accessory nerve (Motor) Cr XI

• A small cranial root which is distributed to the
  muscles of the palate, pharynx and larynx.
• A large spinal root to the sternocleidomastoid
  and trapezius muscles.

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Accessory nerve (Motor) Cr XI

• Clinically
• Paresis of the laryngeal and pharyngeal muscles
  leading to dysphonia and dysphagia.
• Paresis of the trapezius and sternocleidomastoid
  muscle following neck dissection for tumour
  surgery.

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Hypoglossal nerve (Motor)
Cr XII

• Leave the posterior cranial fossa via the
  hypoglossal canal in the occipital bone.
• Supply the intrinsic and the extrinsic muscles of
  the tongue with the exception of the palatoglossus

• Clinically
• Unilateral lingual paresis
• hemiatrophy of the tongue
• Dysarthia.