list the four pairs of cranial nerves and their location
TELENCEPHALON (forebrain):
• olfactory, I
DIENCEPHALON (epithalamus, hypothalamus, thalamus):
• optic, II
MESENCEPHALON (midbrain):
• oculomotor, III
• trochlear, IV
RHOMBENCEPHALON (hind brain): • trigeminal, V • abducens, VI • facial, VII • vestibulocochlear, VIII • glossopharyngeal, IX • vagus, X • accessory, XI • hypoglossal, XII
which are the only two cranial nerves which don’t arise from the brainstem?
olfactory (I) and optic (II)
which is the only cranial nerve which does not arise from the basal surface of the brain?
trochlear (III)
classify four types of afferent sensory fibres
- General Somatic Afferent (GSA):
• similar to information carried in dorsal roots of the spinal cord => touch, pain, temperature, itch
• CN V - Special Somatic Afferent (SSA):
• special senses => vision, hearing and balance
• CN II, VIII - General Visceral Afferent (GVA):
• sensory feedback (usually pain but also tissue stretch and pressure) from e.g. organs or glands
• CN IX, X - Special Visceral Afferent (SVA):
• found in organs of special chemical sensing
=> taste and olfaction
• CN I, VII, IX and X
classify three types of efferent motor fibres
- General Somatic Efferent (GSE):
• like ventral roots; motor fibres that innervate the skeletal muscles of the head and neck, e.g. eye muscles, trapezius
• CN III, IV, VI, XII - General Visceral Efferent (GVE):
• fibres that belong to the autonomic nervous system and supply parasympathetic ganglia (e.g. smooth muscle around blood vessels and glands)
• CN III, VII, IX, X - Special Visceral Efferent (SVE):
• motor fibres that supply muscles of the pharyngeal arches; also referred to sometimes as ‘branchial efferents’ (BE)
• CN V, VII, IX, X and XI
which sulcus divides the alar (sensory) and basal (motor) plates during development?
sulcus limitans
which four cranial nerves contain parasympathetic fibres?
which ganglia do they synapse onto?
- oculomotor (III) → ciliary ganglion
- facial (VII) → pterygopalatine + submandibular ganglion
- glossopharyngeal (IX) → otic ganglion
oculomotor nerve (III):
– fibre type?
– origin and track?
– innervation?
- GSE and GVE fibres
- originates in midbrain (nuclei are medial)
- passes through superior orbital fissure
- innervates sup., med. + inf. rectus and inferior oblique
- innervates superior levator palpeprae (upper eyelid)
- innervates ciliary muscle and sphincter pupillae (GVE)
how does the eye respond to light?
PUPILLARY LIGHT REFLEX
when bright light enters one eye, the pupils of both eyes become smaller due to pupillary light reflex
- light enters through only one pupil
- optic nerve and optic tract transport the light signal
- collaterals from the optic tract synapse on neurones of the pretectal area
- neurones of the pretectal area project bilaterally to the Edinger-Westphal nuclei of the oculomotor nerve
- pretectal fibres cross contralaterally at the posterior commissure
- parasympathetic oculomotor fibres from the Edinger-Westphal nuclei innervate the sphincter pupillae muscle
- results in constriction of pupil
what is uncal herniation and what are the consequences?
herniation of the uncus due to high intercranial pressure
puts pressure on oculomotor nerve = pupil dilation
puts pressure on posterior cerebral artery = ischemia of the ipsilateral primary visual cortex
the tentorium can put pressure on the midbrain = lesion of pyramidal and sensory pathways
what occurs in oculomotor nerve palsy
downward and outward gaze for the affected (right) eye
dilated pupil and ptosis (drooping of the eyelid)
diplopia (double vision)
trochlear nerve (IV):
– fibre type?
– origin and track?
– innervation?
- GSE fibres
- only nerve to originate from dorsal part of midbrain
- innervates the superior oblique muscle of the eye
- tendon of the superior oblique muscle passes through a ottilaginous pulley, called trochlea (trochlear = “pulley”)
what is the consequence of a trochlear nerve lesion?
- Inability to rotate eye infero-laterally
- Gaze deviates upward and also slightly inward for the affected (right) eye;
- Diplopia (double vision)
abducens nerve (VI):
– fibre type?
– origin and track?
– innervation?
- GSE fibres
- originates from the anterior border of the pons and medulla oblongata (facial colliculus)
- passes through the superior orbital fissure to enter the orbit
- innervates the lateral rectus muscle of the eye which abducts the eye
what is the consequence of n abducens nerve lesion?
gaze deviates inwards (adduction)
trigeminal nerve (V): – fibre type? – origin and track? – innervation? – branches?
GSA + SVE fibres
originates from pons
contains three branches
V1: ophthalmic nerve
- sensory only
- supplies forehead, eyelid, eyebrow, nose
- supplies eye → afferent component for blink reflex (efferent motor part from CN VII)
- branches into frontal, naso-ciliary and lacrimal nerves
V2: maxillary nerve
- sensory only
- supplies skin of middle face
- major nerve continues as the infraorbital nerve
- several major branches in the pterygopalatine fossa
V3: mandibular nerve
- sensory + motor
- sensory innervation to skin of lower face, teeth of lower jaw and anterior 2/3 tongue
- motor innervation to muscles of mastication, muscles of middle ear, muscles of oral diaphragm, muscles of palate
thalamic relay for the sensory trigeminal
pathway is the ventral posterior medial nucleus (VPM)
what are the consequences of a trigeminal nerve lesion?
damage leads to flaccid, ipsilateral paralysis of muscles of mastication
slight deviation of the jaw to the side of injury
jaw-jerk reflex is absent.
with bilateral upper motor neuron lesions (above level of trigeminal nucleus), mandible will hang low, leading to difficulty in producing vowels, labial/lingual sounds
facial nerve (VII): – fibre type? – origin and track? – innervation? – branches?
SVA, SVE and GVE fibres
originates in pons
special visceral afferents:
• taste sensation from anterior 2/3 of the tongue (geniculate ganglion)
parasympathetic component:
• nasal gland, tear gland + salivary glands (submandibular and lingual)
motor component: • muscles of facial expression • muscles of scalp • posterior belly of digastric, stylohyoid and stapedius muscles • contributes to blink reflex
motor branches (to zanzibar by motor car)
1) temporal
2) zygomatic
3) bucal
4) marginal mandibular
5) cervical
what are the consequences of a lesion to the facial nerve
lesion to facial nerve = bell’s palsy
paralysis of facial muscles
loss of taste sensation
dry eyes + mouth
hyposalivation
hyperacusis:
lack of innervation of the stapedius muscle; stapedius muscle normally dampens the ear
drum and limits movement of the ossicles = normal sounds become very loud
what responds to rotation, gravity and movement?
semicircular canals
vestibulocochlear nerve (VIII): – fibre type? – origin and track? – innervation? – branches?
SSA fibres
fibers arise from the vestibular apparatus (balance) and cochlea (hearing) of the inner ear
travels through the internal acoustic meatus to enter the brainstem at the pons-medulla border
vestibular nerve:
• concerned position of head in relation to movement
• receives input from 3 semicircular canals, the utricle, and the saccule
• utricle and saccule detect gravity and linear acceleration
• semicircular ducts detect angular acceleration
cochlear nerve:
• hearing
glossopharyngeal nerve (IX):
– fibre type?
– origin and track?
– innervation?
SVA, GVA, SVE + GVE fibre types
fibres emerge from medulla and exit via the jugular foramen
special sensation:
• taste sensation from posterior 1/3 of tongue
general sensation:
• intraoral, pharynx and dorsal 1/3 of tongue
motor component:
• supplies stylopharyngeus muscle; from nucleus ambiguus
• motor component of gag reflex
parasympathetic component:
• from inf. salivatory nucleus; to parotid salivary gland via the otic ganglion
vagus nerve (X):
– fibre type?
– origin and track?
– innervation?
GSA, GVA, GVE, SVA, SVE fibres
general visceral sensory component:
• receptors in walls of viscera
special visceral sensory component:
• taste from he pharyngeal area
motor component:
• muscles of larynx, pharynx, upper esophagus
parasympathetic component:
• all visceral organs of the neck, thorax, upper abdomen, and parts of the intestine that are derived from the foregut and midgut
sensory component of gag reflex
what are the consequences of a vagus nerve lesion?
impaired reflexes for swallowing, gagging, coughing, sneezing, vomiting, breathing and heart rate
paralysis of the pharynx and soo palate –> swallowing difficulty
unilateral lesions may cause breathy voice and hoarseness, but ability to phonate is only minimally affected
bilateral lesions => aphonia; impaired air flow
