0827 - The Trigeminal System Flashcards
What is the function of the trigeminal system?
Sensory system for the head and motor system for muscles of mastication.
What are the branches of the trigeminal nerve? where do they arise? Where do they leave the skull
Arise at Semilunar ganglion.
Vi - Ophthalmic division - superior orbital fissure.
Vii - Maxillary division - Foramen rotundum to pterygopalatine fossa
Viii - Mandibular division - Foramen ovale to infratemporal fossa
What are the branches of the ophthalmic division of CNV? What does it innervate? Where does it leave the skull?
Pure Sensory - Superior Orbital Fissure
Frontal nerve - Forehead and medial eyelid.
Lacrimal - lacrimal gland and lateral eyelid, also receives parasympathetic from CNVII, allowing lacrimal secretions.
Nasociliary - Eye (incl cornea), nose, nasal cavity and ethmoidal sinuses. Also carries SY for dilator pupillae.
What are the branches of the Maxillary division of CNV? What does it innervate? Where does it leave the skull?
Pure Sensory - Foramen Rotundum
Supplies skin on cheeks, oral cavity, upper teeth.
Branches - Anything ‘zygomatic, and infra-orbital. Also important for communications - greater petrosal (VII paras), and deep petrosal (SY from cav sinus) going to pterygopalatine ganglion and lacrimal gland.
What are the branches of Mandibular division of CNV? Where do they arise? Where do they leave the skull?
Mixed motor-sensory. Leaves via foramen ovale.
Motor branches - innervate the muscles of mastication and tensor tympani. Carry proprioceptive information from jaw muscles.
Sensory branches - Innervate lower teeth, anterior ⅔ of tongue. Lingual branch also carries (for VII) taste fibres to anterior ⅔ and preganglionic paras to submandibular ganglion for sublingual/submandib glands.
Meningeal/N Spinosum - carries pain fibres from dura of anterior and middle cranial fossae.
Explain the communications of CNV with the parasympathetics of CNVII
Preganglionic parasympathetic. As greater petrosal nerve, hitches with deep petrosal nerve (SY) to pterygopalatine ganglion (V2). Synapses there and proceeds to lacrimal nerve (V1).
Submandibular G - Preganglionic paras from VII travel to submandibular ganglion for submandib/sublingual glands.
Explain the communications of CNV with the sympathetic system.
Deep petrosal - Travels from superior cervical SY ganglion to pterygopalatine G (V2) to innervate submandib/sublingual glands.
Ciliary - SY fibres from cavernous sinus travel via V1 and III (ciliary G) to dilator pupillae.
Describe the approximate locations of the 4 trigeminal nuclei in the brainstem, and explain the functional significance of each.
Motor - Mid-pons at entry of nerve - Muscles of mastication and jaw jerk.
Mesencephalic - close to 4th ventricle and motor - Homologue of dorsal root ganglion for jaw mm and teeth and gums.
Principal sensory - Mid-pons, lateral to motor nucleus - Homologue of dorsal column nuclei (touch and proprioception)
Spinal trigeminal - Extends from mid-pons to C3 - N. Caudalis is Homologue of dorsal horn (pain and temp processing)
Describe the approximate location of the trigeminal motor nucleus in the brainstem, and explain its functional significance.
Located at mid-pons, at level of entry of the nerve.
Mediates a jaw jerk reflex, and receives bilateral corticobulbar input from motor cortices.
Describe the approximate location of the mesencephalic nucleus in the brainstem, and explain its functional significance.
Located close to 4th ventricle and trigeminal motor nucleus. Surrounded by mesencephalic tract
Only nucleus where cell bodies of sensory nerves are contained within the brain (analogous to dorsal root ganglion).
Provides proprioception from jaw mm, and mechanoreceptor information from teeth, gums (and tongue?) - protective against biting yourself.
Describe the approximate location of the principal sensory nucleus (trigeminal) in the brainstem, and explain its functional significance.
Located at mid pons, at level of entry of nerve, lateral to motor nucleus.
Homologue of a dorsal column nuclei. Relays information about discriminative touch and proprioception, carried by fast, myelinated fibres.
Describe the approximate location of the spinal trigeminal nucleus in the brainstem, and explain its functional significance.
Extends from mid-pons to C3, in lateral aspect of cord.
Has 3 parts, main one is n. caudalis in the closed medulla. This is a homologue of the dorsal horn/substantia gelatinosa in that it processes pain and temperature from V1, V2, V3. It ultimately blends into the spinal cord, becoming Lissauer’s tract.
Compare the trigeminal system with the dorsal column.
The principal nucleus is analagous to the dorsal column, with large calibre, myelinated fibres synapsing there. Second-order neurons (except from mouth) then cross the midline, joining the medial lemniscus and enter VPM.
Compare the trigeminal system with the spinothalamic pathway
Pain and temperature fibres form spinal trigeminal tract, and terminate within nucleus caudalis, analagous to the dorsal horn (with V3 dorsal, V1 ventral, medial rostral, lateral caudal).
Explain the role of the trigeminal spinal nucleus in mapping sensory information from all of the head and neck territories, including the dura, particularly in relation to pain in the head and neck region.
All pain from head and neck will go to CNV spinal nucleus. This is C2, C3 dermatomes and myotomes, CNn VII, IX, X, and all of CNV. They synapse in spinal trigeminal nucleus and are mapped in primary sensory centre (homunculus). It means that pain in any of these areas can be perceived as headache.
