Cranial Nerves - V & VII Flashcards
What structures are innervated by general somatic efferent (GSE) fibres and which cranial nerves contain them?
- GSE fibres have their cell body within the brainstem and innervate skeletal muscles derived from somites
- found in III, IV, VI and XII
What is innervated by special visceral efferent (SVE) fibres and which cranial nerves contain them?
- they are functionally identical to GSE fibres and have their cell bodies within the brainstem
- they innervate skeletal muscle derived from pharyngeal (branchial) arches
- found in V, VII, IX, X and XI
What is the function of general visceral efferent (GVE) fibres and in which cranial nerves are they found?
- GVE fibres have their cell bodies within the CNS and innervate smooth muscles or glands
- This tends to be involuntary actions we are not aware of
- found in III, VII, IX and X
What are the general functions of CNs I, II, III and IV?
I - olfactory:
- part of the CNS - sense of smell
II - optic:
- part of the CNS - sense of sight
III - oculomotor:
- motor (GSE) to 4 extra-ocular muscles (inferior oblique, medial rectus, superior rectus, inferior rectus)
- parasympathetic (GVE) to sphincter pupillae and ciliaris
IV - trochlear:
- motor (GSE) to superior oblique muscle
What are the functions of CNs V and VI?
V - trigeminal:
- V1 - sensory to face and nasal/oral cavities
- V2 - sensory to face and nasal/oral cavities
- V3 - sensory to face and nasal/oral cavities AND motor (SVE) to muscles of mastication
VI - abducens:
- motor to lateral rectus
What are the general functions of CNs VII, VIII and IX?
VII - facial:
- sense of taste (GVA) to anterior 2/3 of tongue
- motor (SVE) to muscles of facial expression
- parasympathetic (GVE) to lacrimal, nasal, palatine, submandibular & sublingual glands
VIII - vestibulocochlear:
- involved in balance and hearing
IX - glossopharyngeal:
- sense of taste (SVA) to posterior 1/3 of tongue
- sensory to nasopharynx, oropharynx, auditory tube, middle ear, palatine tonsil
- parasympathetic (GVE) to parotid gland
What are the general functions of CNs X, XI and XII?
X - vagus:
- sensory to laryngopharynx and larynx
- motor (SVE) to muscles of soft palate, pharynx and larynx
- parasympathetic (GVE) to muscles of thorax and abdomen
XI - spinal accessory:
- motor (SVE) to trapezius and sternocleidomastoid
XII - hypoglossal:
- motor (GVE) to muscles of the tongue
What are general somatic afferent (GSA) fibres and which CNs are they found in?
- they carry sensory information relating to pain, touch, proprioception, pressure etc. from joints, tendons, skin and muscle
- cell bodies are outside of the CNS
- found in V, VII, IX and X
What are special somatic afferents (SSA) fibres and in which CNs are they found?
- similar to GSA fibres, but they carry information about special senses (vision / balance / hearing) to the brain
- found in I and VIII
What are special visceral afferents (SVA) and which CNs are they found in?
- similar to SSA fibres as they carry information about special senses to the brain
- they carry information from receptors associated with taste and smell
- these are visceral functions related to digestion
- found in I, VII, IX and X
Why are there more cranial nerve nuclei than there are cranial nerves?
- cranial nerve nuclei are associated with fibre type, rather than an individual cranial nerve
- each nucleus can receive inputs from a number of different cranial nerves, as long as they are all carrying the same fibre type
- each nucleus can send outputs to different cranial nerves
How can the location of cranial nerve nuclei within the brainstem be predicted?
- the sulcus limitans separates the basal (efferent) and alar (afferent) plates
- the more medial part of the brainstem contains efferent motor nuclei from the basal plate
- the more lateral part of the brainstem contains afferent sensory nuclei from the alar plate
- the nuclei immediately adjacent to the sulcus limitans on both sides tend to be visceral and have an autonomic function (SVE - SVA, GVA)
What is the typical 3 neurone chain involved in a CN sensory (afferent) pathway?
First order neurone:
- travels from sensory receptor in the periphery to the brainstem
- has cell bodies within a sensory ganglion
- synapses with second order neurone within the brainstem
Second order neurone:
- travels from CN nucleus within the brainstem to the thalamus
- crosses the midline
Third order neurone:
- travels from the thalamus to the postcentral gyrus
What is involved in the 2 neurone pathway of a typical CN motor (efferent) pathway?
Upper motor neurone (UMN):
- extends from the precentral gyrus to descend via the corticobulbar tract to the brainstem
- synapses with LMN within motor groups of CN nuclei
- UMN tends to send bilateral projections to CN nuclei on either side of the brainstem
Lower motor neurone (LMN):
- extends from the CN motor nucleus to innervate a specific muscle
- Corticobulbar tract generally provides bilateral innervation to H&N muscles (there are exceptions) as it projects bilaterally to both of the relevant CN nuclei in the brainstem*
What is meant by somatotopic organisation of the precentral and postcentral gyri?
- different body parts are represented in different regions of the postcentral and precentral gyri
- remember FATL - face, arm, trunk, legs
the face is represented more laterally, followed by the arm, trunk and then legs most medially
Which 4 cranial nerves contain GSA fibres carrying sensory information from the face?
Trigeminal (V):
- face, nose, scalp, dura
- anterior 2/3 of tongue
Facial (VII):
- external ear
Glossopharyngeal (IX):
- pharynx
- middle ear
- posterior 1/3 of the tongue
Vagus (X):
- auditory canal
- pharynx
- larynx
- oesophagus
ALL of these CNs carrying GSA fibres travel to the trigeminal sensory nucleus
What are the 2 nuclei associated with the trigeminal nerve and which fibres do they receive?
- the trigeminal nerve carries 2 modalities, and so has 2 nuclei associated with it
Trigeminal sensory nucleus:
- this receives GSA fibres
- primary neurone cell bodies within trigeminal ganglion (one exception)
Trigeminal motor nucleus:
- this receives SVE fibres
- it is located more medially than the sensory nucleus
Fibres travelling in which cranial nerves will reach the trigeminal sensory nucleus?
- V
- VII
- IX
- X
- these are all carrying GSA fibres (general sensation)
What are the 3 parts of the trigeminal sensory nucleus and which sensations do they receive?
Mesencephalic nucleus:
- receives GSA fibres relaying proprioception
Pontine (chief sensory) nucleus:
- receives GSA fibres carrying discriminative touch
Spinal nucleus:
- rostral part receives GSA fibres carrying simple touch / pressure
- caudal part receives GSA fibres carrying pain & temperature
What is different about the cell bodies of primary neurones related to the mesencephalic nucleus?
- the cell bodies of primary sensory neurones that relay the sense of proprioception are located within the mesencephalic nucleus
- these neurones are the only exception in which primary sensory cell bodies lie within the CNS opposed to peripheral ganglia
What is the tuberculum cinereum?
- a small bump on the dorsolateral surface of the medulla that is formed as a result of the underlying trigeminal spinal nucleus
- also called trigeminal tubercle
How can the trigeminal spinal nucleus be further divided?
- pars oralis
- pars interpolaris
- pars caudalis
- significance is unknown, but it is the pars caudalis that is important for processing pain & temperature information
Describe the pain & temperature pathway using the trigeminal nerve
First order neurone:
- GSA fibres carrying P&T information travel from the periphery in a branch of V
- This primary neurone has its cell body within the trigeminal ganglion
- The primary neurones descend in the spinal tract of V to reach the trigeminal spinal nucleus (pars caudalis)
- Primary neurone synapses with the second order neurone within the spinal nucleus in the medulla
Second order neurone:
- Second order neurone crosses the midline and ascends to the VPM nucleus of the thalamus via the trigeminothalamic tract
- Synapses with third order neurones within the VPM nucleus
Third order neurone:
- Travels from the VPM nucleus to the postcentral gyrus
Describe the discriminative touch pathway
First order neurone:
- GSA fibres travel from the periphery in V
- Their cell bodies are within the trigeminal ganglion
- Primary neurone travels to the pontine nucleus, and synapses with the secondary neurone here
Second order neurone:
- From the pontine nucleus, the secondary neurone crosses the midline to ascend to the VPM of the thalamus via the trigeminal lemniscus
- (trigeminal lemniscus is part of TTT)
- Synapses with tertiary neurone within the VPM nucleus
Third order neurone:
- travels from VPM nucleus to the postcentral gyrus
What is the ipsilateral pathway of the discriminative touch pathway?
Why is this significant?
- most information crosses the midline to travel from the pontine nucleus to the contralateral VPM nucleus
- some information passes from the pontine nucleus to the IPSILATERAL VPM nucleus via the dorsal trigeminothalamic tract (TTT)
- if there is an injury somewhere in the pathway, there will still be some sensation perceived due to this ipsilateral projection
Describe the UMN and LMN involved in the proprioception pathway
UMN:
- GSA fibres carrying proprioceptive information travel within the mandibular nerve (V3)
- They have their cell bodies within the mesencephalic nucleus
- V3 enters at the level of the pons, so GSA fibres must ascend to reach the mesencephalic nucleus via the mesencephalic tract of V
- From the mesencephalic nucleus, there are bilateral projections to the motor nuclei of V
- The UMN synapses with the LMN within the motor nucleus of V
LMN:
- From the motor nucleus of V, SVE fibres travel via the mandibular nerve (V3) to the muscles of mastication on both sides of the face
How does proprioceptive information reach the cortex?
- there are projections from the mesencephalic nucleus to a nucleus located adjacent to it
- from this nucleus, there is a projection to the CONTRALATERAL VPM nucleus of the thalamus
- a third order neurone then passes from the VPM nucleus to the postcentral gyrus
What reflex is associated with the proprioceptive pathway?
jaw jerk reflex
- when hit, GSA fibres travel to the mesencephalic nucleus, where bilateral projections are sent to the motor nuclei of V
- GVE fibres are sent via V3 to the muscles of mastication to elicit the reflex
What is involved in the motor pathway of V?
UMN:
- UMN travels from the precentral gyrus, through the internal capsule, to the motor nucleus of V
- UMN synapses with LMN within the motor nucleus of V
LMN:
- LMN travels within the mandibular nerve (V3) to reach the muscles of mastication on both sides of the face
- The LMN is carrying SVE fibres
What is the result of a lesion of the motor nucleus of V or LMN?
deviation of the jaw towards the side of the lesion
- as a result of the lesion, there will be ipsilateral atrophy of the jaw muscles
- upon jaw protrusion, there will be deviation towards the side of the lesion
What is the result of a lesion of the UMN involved in the motor component of V?
no damage
- the UMNs project to both motor nuclei of V
- the motor nucleus of V is still receiving information from the UMN on the opposite side to the lesion
Where does the facial nerve emerge from the brainstem?
How does it divide to innervate the muscles of facial expression?
- it emerges from the brainstem at the level of the cerebellopontine angle
- this is the junction between the cerebellum, pons and medulla
- there are 5 terminal branches of the facial nerve that carry SVE fibres to the muscles of facial expression
- temporal branches
- zygomatic branches
- buccal branches
- marginal mandibular branches
- cervical branches
What is the facial colliculus and how is it formed?
- the motor nucleus of VII is located more medially than the nucleus of VI
- fibres emerging from the motor nucleus of VII will wrap around the abducens nucleus to emerge from the cerebellopontine angle
- a bump on the dorsal surface of the pons is formed as a result of the motor fibres of VII wrapping around the nucleus of VI
- this bump is the facial colliculus
How many nuclei of the facial nerve are there and which fibre type are they associated with?
GSA fibres:
- associated with the trigeminal sensory nucleus
GVE fibres:
- assoicated with the superior salivatory nucleus
SVA fibres:
- associated with the rostral solitary nucleus
SVE fibres:
- associated with the motor nucleus of VII
What is meant by the nervus intermedius portion of the facial nerve?
- the nervus intermedius contains GSA, SVA and GVE fibres of the facial nerve
- the rest of the nerve is the motor part that carries SVE fibres
Describe the motor supply to the muscles of facial expression
How is innervation to the lower face different to that of the upper face?
Innervation to the upper face:
- UMN travels from the precentral gyrus and through the internal capsule
- UMN sends bilateral projections to the facial motor nuclei on BOTH sides of the brainstem
- LMN travels from both facial nuclei to innervate muscles of the upper face on BOTH sides
Innervation to the lower face:
- UMN travels from the precentral gyrus and through the internal capsule
- UMN crosses the midline to reach the CONTRALATERAL facial motor nucleus
- LMN travels from the facial nucleus to innervate muscles of the lower face
Innervation to the upper face is bilateral, whilst innervation to the lower face is contralateral only
What will result from a lesion to the facial nucleus or LMN innervating the muscles of facial expression?
What are some of the symptoms of this lesion?
there will be _paralysis of the entire *ipsilateral* side of the face_
- there is no motor supply reaching the upper or lower facial muscles on the side of the lesion
- symptoms include:
- inability to close the eyes
- inability to elevate the eyebrows
- weakness of the angle of the mouth
- this is Bell’s Palsy
What is a result of a lesion to the UMN supplying the muscles of facial expression (supranuclear lesion)?
this leads to _paralysis of the *contralateral* lower face_
- there is only paralysis of the lower facial muscles on the side opposite the lesion and there is forehead sparing
- even though there is loss of UMNs on one side, the upper facial muscles have bilateral innervation so are being supplied by neurones coming from the other side
Describe the afferent and efferent limb of the corneal blink reflex
Afferent limb:
- irritation to the cornea stimulates GSA fibres travelling within the ophthalmic nerve (V1)
- their cell bodies are within the trigeminal ganglion
- GSA fibres travel to the trigeminal sensory nucleus, where the primary neurone synapses
- from the sensory nucleus of V, there are interneurones projecting to the facial motor nuclei on BOTH sides of the brainstem
Efferent limb:
- Carried by the facial nerve
- SVE fibres travel from the facial motor nuclei on both sides to the orbicularis oculi muscles
- Stimulation of this muscle causes closure of BOTH eyes
What happens if there is a lesion in the afferent limb of the corneal blink reflex?
- if there is a lesion to the afferent limb (V1) then both eyes will remain open when the cornea is touched
- information related to sensation cannot reach the trigeminal sensory nucleus if V1 is damaged
What would happen if there was a lesion in the efferent pathway of the corneal blink reflex?
- lesion to the facial nerve leads to closure of the eye that has not been stimulated, but the eye that has been stimulated will remain open
What are the 2 divisions of the solitary nucleus and what fibres do they receive?
Caudal part:
- receives GVA fibres carrying information to the CNS about the condition of internal organs
Rostral part:
- receives SVA fibres carrying information about taste
Which 3 cranial nerves carry information about taste?
Facial nerve (VII):
- carries SVA taste fibres from anterior 2/3 of tongue
Glossopharyngeal nerve (IX):
- carries SVA taste fibres from posterior 1/3 of tongue
Vagus nerve (X):
- carries SVA taste fibres from vallecula & epiglottis
VII, IX & X all carry SVA taste fibres to the rostral solitary nucleus
Describe the pathway involved in taste sensation from the anterior 2/3 of the tongue
First order neurone:
- SVA fibres carrying taste sensation from the anterior 2/3 of the tongue travel in VII to the rostral solitary nucleus
- Their cell bodies are located in the geniculate ganglion
Second order neurone:
- secondary neurones travel from the rostral solitary nucleus to the VPM nucleus of the thalamus on the IPSILATERAL side
Third order neurone:
- travels from the VPM nucleus to the postcentral gyrus
SVA fibres coming from IX and X follow the same pathway
cell bodies are in the inferior ganglion of IX and inferior ganglion of X
How is the salivatory nucleus divided and what fibres does it receive?
Superior salivatory nucleus:
- located in pons region and receives GVE fibres from VII
Inferior salivatory nucleus:
- located in medulla region and receives GVE fibres from IX
Both nuclei are involved in salivation / lacrimation, which are both parasympathetic functions
Which structure initiates the pathway that leads to salivation / lacrimation?
Hypothalamus
the hypothalamus initiates these pathways as they are autonomic functions and the hypothalamus is the major autonomic centre
Describe the salivatory / lacrimal pathway involving the facial nerve
- Hypothalamus sends a stimulus which travels to the superior salivatory nucleus at the level of the pons
- GVE fibres travel from the superior salivatory nucleus via the facial nerve
- GVE fibres travelling to the submandibular or sublingual glands will synapse at the submandibular ganglion
- GVE fibres travelling to the lacrimal gland will synapse at the pterygopalatine ganglion
Describe the salivatory pathway involving the glossopharyngeal nerve
- Hypothalamus sends a stimulus that travels to the inferior salivatory nucleus
- GVE fibres travel from the inferior salivatory nucleus to the otic ganglion via IX
- GVE fibres synapse within the otic ganglion and postganglionic fibres travel to the parotid gland
