19 - Cranial Nerves V Flashcards
CN VIII
Vestibulocochlear nerve
Function of CN VIII cochlear nerve
Hearing (SSA)
Ganglion of CN VIII cochlear nerve
Spiral (cochlear) ganglion
Spiral (cochlear) ganglion of cochlear nerve
Spiral (cochlear) ganglion
a. contains bipolar sensory neurons (1st order neurons of the auditory pathway)
b. sensory
c. no synapses
Auditory pathway of cochlear nerve
- First order neurons
- Second order neurons
- Third order neurons
- Nuclei of the lateral lemniscus
- Inferior colliculus
- Medial geniculate nucleus (MGN)
- Auditory cortex
- Descending auditory projections
- Sound attenuation reflex
Auditory first order neurons
a. cell bodies: in cochlear ganglion
b. peripheral processes terminate in receptor hair cells of the organ of Corti
c. central processes (form root of cochlear nerve) enter pons, bifurcate and synapse in the dorsal cochlear nucleus and ventral cochlear nucleus
d. carry information from ipsilateral ear
Auditory second order neurons
a. are housed in the dorsal and ventral cochlear nuclei
b. axons from the ventral cochlear nucleus, form the ventral acoustic stria (trapezoid body), which terminates in a nucleus of the trapezoid body and the superior olivary nucleus. Others ascend in the lateral lemniscus (LL) to terminate in the nucleus of the LL and the inferior colliculus
c. axons from the dorsal cochlear nucleus form the dorsal acoustic stria, ascend in the LL to terminate in the inferior colliculus
d. carry information from the ipsilateral ear
Auditory third order neurons
From here on, each auditory pathway relays input from both ears…
a. are housed in the superior olivary nuclei which are involved in the localization of sound
b. carry information from both ears
Lateral lemniscus
Lateral lemniscus → inferior colliculus
a. is the main pathway of the auditory system
b. carries auditory information from both ears
Nuclei of the lateral lemniscus
Nuclei of the lateral lemniscus
a. process input from both ears
Inferior colliculus
Inferior colliculus
a. is a relay nucleus for hearing in the midbrain
b. processes input from the lateral lemniscus
c. projects to the medial geniculate nucleus (MGN)
Medial geniculate nucleus (MGN)
Medial geniculate nucleus (MGN)
a. is a relay nucleus for hearing in the thalamus
b. processes sound intensity and frequency
c. gives rise to the auditory radiation which projects to the primary auditory cortex
Auditory cortex - two areas
1 - Primary auditory cortex
2 - Secondary cortical areas
Primary auditory cortex
Primary auditory cortex
i. Brodmann’s areas 41 and 42
ii. transverse temporal gyri of Heschl
iii. role in localization of sound
iv. role in detection of alterations in pattern of sound
Secondary cortical areas of auditory cortex
Secondary cortical areas
i. multiple, difficult to locate
ii. interpretation of sound, voices, language, music
Descending auditory projections
Olivocochlear bundle
i. modulates the transmission of auditory input to the CNS
Last step in auditory pathway
Sound attenuation reflex
Two types of deafness
- Conduction deafness
- Sensorineural deafness
Sensorineural deafness
Sensorineural deafness
- cochlea
- cochlear nerve
- central auditory pathways
Other portion of CN VIII
Vestibular nerve
Function of CN VIII vestibular nerve
Equilibrium (balance) (SSA)
Ganglion of CN VIII vestibular nerve
Vestibular (Scarpa’s) ganglion
a. contains bipolar sensory neurons (1st order neurons of the vestibular pathway)
b. sensory
c. no synapses
CN VIII Vestibular Pathway
- First order neurons
- Second order neurons
- Third order neurons
- Afferents (input) to the vestibular nuclei
- Efferents (output) from the vestibular nuclei
First order neurons
First order neurons
a. cell bodies: in vestibular ganglion
b. peripheral processes terminate in receptor hair cells of the maculae of the utricle and saccule and the cristae of the semicircular canal ampullae
c. central processes (form root of vestibular nerve) enter pons, bifurcate and synapse in the vestibular nuclei. Some central processes pass into the inferior cerebellar peduncle to end in the ipsilateral flocculonodular lobe of the cerebellum
Second order neurons
Second order neurons
a. housed in the vestibular nuclei
b. their axons join the medial longitudinal fasciculus (MLF) to project to the
i. extraocular muscle nuclei
ii. reticular formation
iii. cervical spinal cord
c. other fibers terminate in the cerebellum and thalamus
Third order neurons
Third order neurons
a. are housed in the VPL and VPI nuclei of the thalamus
b. project to the primary vestibular cortex (Brodmann’s area 3a)
Afferents (input) to the vestibular nuclei
Afferents (input) to the vestibular nuclei from the
a. vestibular nerve
b. cerebellum
c. contralateral vestibular nuclei
d. spinal cord
Efferents (output) from the vestibular nuclei
Efferents (output) from the vestibular nuclei to the
a. extraocular muscle nuclei
b. contralateral vestibular nuclei
c. inferior olivary nucleus
d. cerebellum
e. spinal cord
f. vestibular labyrinth
g. brainstem reticular formation
CN IX
Glosopharyngeal nerve
Functional components of CN IX
- General visceral afferent
- Special visceral afferent
- General visceral efferent
- Special visceral efferent
- General somatic afferent
General Visceral Afferent (GVA)
General Visceral Afferent (GVA) from the
a. pharyngeal tube
b. palatine tonsils, fauces
c. pharynx
d. carotid sinus (baroreceptor)
Special Visceral Afferent (SVA)
Special Visceral Afferent (SVA) - taste from the
a. posterior 1/3 of tongue
General visceral efferent (GVE)
General Visceral Efferent (GVE) - parasympathetic (secretomotor) to the
a. parotid gland (salivation)
b. minor salivary glands in tongue and pharynx
Special Visceral Efferent (SVE)
Special Visceral Efferent (SVE) : skeletal motor to the
a. stylopharyngeus muscle
General Somatic Afferent (GSA)
General Somatic Afferent (GSA) from the
a. ear
b. ear canal
c. posterior 1/3 of tongue
Ganglia of CN IX
Two sensory
- Superior ganglion of teh glossopharyngeal nerve
- Inferior (petrosal) ganglion of the glossopharyngeal nerve
One parasympathetic
- Otic ganglion
Superior ganglion of the glossopharyngeal nerve
Pseudounipolar neurons (GSA) Their central processes descend in the spinal V tract to the spinal V nucleus
NOTE: CN IX sends its GSA fibers carrying nociception to the spinal V nucleus
Inferior (petrosal) ganglion of the glossopharyngeal nerve
Pseudounipolar neurons (GVA, SVA)
Their central processes join the solitary tract to terminate in the solitary nucleus
Parasympathetic ganglion - Otic ganglion
Otic ganglion
i. contains postganglionic parasympathetic neurons whose axons terminate in the parotid gland
ii. Frey’s syndrome
Nuclei of CN IX
1 - Inferior salivatory nucleus
2 - Nucleus ambiguus
3 - Solitary nucleus
Inferior salivatory nucleus
contains the cell bodies of preganglionic parasympathetic neurons (GVE), whose axons terminate in the otic ganglion
Nucleus ambiguus
contains the cell bodies of motor neurons (SVE)
Solitary nucleus
receives the central processes of GVA and SVA neurons
Lesion of the glossopharyngeal nerve
- loss of taste from posterior 1/3 of tongue
- decrease in salivary secretion
- diminished visceral sensation
- loss of the gag reflex
- loss of the carotid sinus reflex
CN X
Vagus nerve
Functional components of CN X
- General Visceral Efferent (GVE)
- Special Visceral Efferent (SVE)
- Special Visceral Afferent (SVA)
- General Somatic Afferent (GSA)
- General Visceral Afferent (GVA)
General Visceral Efferent (GVE)
parasympathetic to the thoracic and abdominal viscera
Special Visceral Efferent (SVE)
skeletal motor to most of the pharyngeal and laryngeal skeletal muscles
Special Visceral Afferent (SVA)
taste from the epiglottis, soft palate and upper pharynx
General Somatic Afferent (GSA)
from the outer ear, external auditory meatus, and the posterior third of the dura matter
General Visceral Afferent (GVA)
from the mucous membrane of the soft palate, pharynx, esophagus, larynx, trachea and carotid body (chemoreceptor)
Nuclei of CN X
1 - Dorsal motor nucleus of the vagus
2 - Nucleus ambiguus
3 - Solitary nucleus
Dorsal motor nucleus of the vagus
a. parasympathetic (visceral motor)
b. preganglionic parasympathetic neurons
Nucleus ambiguus
a. skeletal motor
b. skeletal muscles (larynx, pharynx)
Solitary nucleus
a. receives the central processes of the taste (SVA) and visceral sensory (GVA) neurons
b. is a sensory nucleus where fibers from the facial, glossopharyngeal and vagus nerves terminate
Ganglia of CN X
1 - Superior (jugular) ganglion of the vagus
2 - Inferior (nodose) ganglion of the vagus
3 - Parasympathetic ganglia
Superior (jugular) ganglion of the vagus
- sensory, no synapses
- pseudounipolar neurons (GSA)
Their central processes descend in the spinal V tract to the spinal V nucleus
NOTE: CN X sends its GSA fibers carrying nociception to the
spinal V nucleus
Inferior (nodose) ganglion of the vagus
- sensory, no synapses
- pseudounipolar neurons (GVA and SVA)
Their central processes join the solitary tract to terminate in the solitary nucleus
Parasympathetic ganglia
Parasympathetic ganglia located near viscera or within the wall of viscera in
thoracic and abdominal cavities to innervate cardiac muscle, smooth muscle and glands
a. Heart
b. Respiratory tract
c. GI tract
A unilateral lesion of the vagus nerve root as it exits the brainstem
- Flaccid paralysis or weakness of muscles of the
a. pharynx (dysphagia)
b. larynx (dysphonia)
c. soft palate - Dyspnea
- Loss of the gag reflex
- Loss of general sensation
- Cardiac arrhythmias
A bilateral lesion of the vagus nerve root as it exits the brainstem
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Case 15
A 70-year-old male has excruciating pain in the lower left part of his face. This began 1 month ago. He describes it as being like a jolt of lightning that radiates from his left ear, down to his jaw, and to the side of his mouth. These jolts of pain occur numerous times each day. Between attacks his face seems normal. He denies any numbness or tingling sensations. There is no hearing abnormality. The pain is triggered by talking, chewing, or touch of the lower left part of his face. He is unable to eat or brush his teeth, particularly on the left side, since he fears triggering another painful attack. He can only drink his meals through a straw and cannot lie in bed on his left side. He had the same symptoms about 2 years ago. At that time he was treated with a medication which helped; symptoms subsided, but he stopped taking the medicine. The pain is so distressing that the patient admits to contemplating suicide. The general and neurologic exam is normal, except that he withdraws and will not let anyone touch the left side of his face.
