Neuro 4 Flashcards
Lateral zone - RF
reflux machinery and more.
Substantia nigra
really a part of basal ganglia
PAG
continuous with hypothalamus
GSA, General somatic afferent
Origin CNS: Spinal & main sensory nuclei
Mesencephalic nucleus
Peripheral origin or termination:
Skin & deep tissues of head, dura
Muscle spindles and other mechanoreceptors
SVE, Special visceral efferent
CNS: Trigeminal motor nucleus
PNS: MOM and the tensor twins”, etc (muscles of mastication)
Trigeminal Nerve
Three divisions:
Opthalmic:Upper face
Sensory only
Maxillary division: Middle face
Sensory only
Mandibular division: Lower face
Sensory and Motor
V motor components
Branchial motor Cell bodies: Trigeminal motor nucleus Terminates in: Muscles of mastication Lesion (injury): Jaw closure is weakened Opened jaw will deviate toward side of lesion
Supratrigeminal nucleus
Near V motor nucleus
Actually part of reticular formation (node)
Pattern generator for masticatory rhythm
V Mesencephalic nucleus
Sensory Afferent
Cell bodies: Trigeminal mesencephalic nucleus down to pons.
Centrally directed process terminates in:
Trigeminal motor nucleus - jaw jerk reflex
Supratrigeminal nucleus - chewing movements
Senses: proprioception; spindles in muscles of mastication, mechanoreceptors in gums, teeth and hard palate
Mesencephalic nucleus: Proprioception
Receptors:
Neuromuscular spindles of mastication muscles
Pressure/tension receptors in periodontal ligaments
Cell body of origin:
Unipolar cell bodies
Trigeminal mesencephalic nucleus
Projects to:
Trigeminal motor nucleus
Supratrigeminal nucleus (masticatory generator - rhythm)
Controls distance between mandible and maxilla
Occlusal vertical dimension (vertical dimension of occlusion
In pontine tegmentum
most to supratrigeminal, some to motor or main sensory nuclei
V3
MOM stretch receptors (spindles) Stretch receptors (Ruffini endings) in suspensory, periodontal ligaments of teeth
V2
Stretch receptors (Ruffini endings) in suspensory, periodontal ligaments of teeth
V Sensory Nuclei
The sensory nuclei form a column of cells the is almost continuous through the brainstem.
Main sensory nucleus is at about mid-pons and is a bit later to the trigeminal motor nucleus
Spinal nucleus extends caudally into the medulla
Mesencephalic nucleus extends into midbrain. It is rather thin and is accompanied by the mesencephalic trigeminal tract. The mesencephalic nucleus is odd in that is contains pseudounipolar neurons as seen in dorsal root ganglia of the cord, so it is as if a bit of a ganglion somehow got incorporated into the CNS. Myelinated processes from these pseudounipolar neurons form the mesencephalic tract. The peripheral processes go to spindles of muscles of mastication, mechanoreceptors of teeth, gums and hard palate.
Nuclei ascend
trigeminal thalamic tract goes up. Sometimes referred to as trigeminal lemniscus.
VPM
ventral posteriormedal nucleus. From here, they send to primary central cortex in parietal lobe.
Ventral posteriolateral nucleus
end of medial lemniscus
Cortical Representation V
Parietal lobe
Postcentral gyrus
Brodmann’s Areas 3, 1, 2
V: : Main Sensory Nucleus
Sensory afferent Region served: Face, head Oral cavity, teeth Meninges Cell bodies: Trigeminal ganglion Terminates in: Main/ principal trigeminal sensory nucleus Discriminative touch & vibration
V main/principal sensory nucleus
Homologue of posterior column nuclei
Discriminative tactile (face & oral cavity) and some proprioception (jaw position)
Two ascending pathways:
Crossed pathway joins medial lemniscus on its way to VPM
Uncrossed, dorsal trigeminal tract, inside of mouth represented to VPM (ends near uncrossed taste pathway
V: Spinal trigeminal nucleus
Sensory afferent Region served: Face Oral cavity, teeth Meninges Cell bodies: Trigeminal ganglion – just like main sensory nucleus Terminates in: Trigeminal spinal nucleus Pain, crude touch, temperature
Spinal trigeminal
pain – not very myelinated.
Spinal trigeminal
Afferents descend thru spinal trigeminal tract and synapse in caudal nucleus
Second order neurons send axons across midline, ascend and join spinothalamic tract, terminates in VPM – tend to have longest axons.
Third order neurons are the ones that have cell bodies in VPM and go to cortex.
Vast majority is in caudal part of trigeminal spinal – pain and temp nucleus is here.
Mesencephalic nucleus
Heavily myelinated fibers
Posterior column homologue– medial lemniscus system
Proprioception
Main/ principal sensory nucleus
Heavily myelinated fibers- tactile descrimination.
Posterior column homologue – medial lemniscus system
Discriminative touch
Spinal nucleus
Lightly myelinated fibers
Homologue of anterolateral system
Pain, crude touch, temperature
From: Trigeminal spinal nucleus
Contralateral projection to: (not ipsilateral)
Ventral posteromedial nucleus of thalamus (VPM)
Internal capsule
Postcentral gyrus parietal lobe (Brodmann’s Areas 3,1,2)
From: Main/ principal trigeminal sensory nucleus
Bilateral projection to:
Ventral posteromedial nucleus of thalamus (VPM)
Internal capsule
Postcentral gyrus parietal lobe (Brodmann’s Areas 3,1,2)
Trigeminal nerve: major connections
Peripheral branches of mesencephalic neurons innervate masseter muscle spindles and other mechanoreceptors
Tactile afferents
Motor neuron fibers: muscles of mastication – descends.
Pain-temperature afferents
Pars Caudalis
Laminar structure
Blends with posterior horn of cervical cord
Somatotopic organization
Inverted representation of face
‘Onion Peel’ representation – rostral (oral) to caudal (peripheral face)
Primarily pain fibers
Substantia gelatinosa (Lamina II)
Contains excitatory and inhibitory interneurons
Receives raphe spinal tract fibers (serotonin)
Receives afferents from cranial nerves
VII, IX & X – all for area near ear
GSA, General somatic afferent VII
CNS: Spinal trigeminal nucleus
Geniculate ganglion
PNS: Skin of outer ear
SSA, Special sensory afferent VII
CNS: Nucleus of solitary tract
Geniculate ganglion
PNS: Taste buds anterior 2/3 of tongue, Parts of nasal cavity and soft palate
GVE, General visceral efferent VII
CNS:Superior salivatory nucleus
Submandibular & Pterygopalatine ganglia
PNS: Submandibular and sublingual glands, nasal and palatine glands, lacrimal glands
SVE, Special visceral efferent (a.k.a branchial motor) VII
CNS: Facial motor nucleus
PNS: Muscles of facial expression, stapedius (Arch 2)
Actions of VII
Motor Muscles of facial expression: Closes eye, closes lips Stapedius muscle: Modulates sound volume Sensory: Skin of outer ear Geniculate ganglion Palatine tonsil & posterior nasal cavity Geniculate ganglion - Solitary nucleus Taste: Anterior 2/3 of tongue Salivation Lacrimation: Lubricates cornea
VII: Somatic sensory
Skin of outer ear
Fibers enter spinal trigeminal tract, dorsomedially situated
Act exactly as trigeminal afferents
Facial motor nucleus & corticobulbar pathway
Motor neurons to lower facial muscles mainly innervated by contralateral cortex, but upper facial muscles innervated bilaterally
Unilateral damage to corticobulbar pathway (e.g. in cerebral peduncle)
Results in: inability to smile or bare teeth symmetrically; but ability to wrinkle forehead is unaffected
Selective weakness of lower facial muscles
Corticobulbar gateway lesions:
Selective weakness of lower facial muscles
A) Muscles on left side of face are weak…… but can raise eyebrows symmetrically.
Trigeminal neuralgia
Brief, episodes of excruciating pain in distribution of one (can be more) division of the trigeminal nerve
Mandibular division 70%
Ophthalmic division < 5%
No sensory trouble between attacks
Often a tactile stimulus triggers an attack
A number of cases due to trigeminal compression by a vessel, tumor etc.
Often responds to medications. How could surgery help?
Surgical procedures include cutting nerve root, introducing a lesion in trigeminal ganglion
Result: loss of all tactile sensation not just pain to the area
Microvascular decompression
Branches of the superior cerebellar artery are most frequently involved in cases of trigeminal neuralgia that are due to vascular cause
Bell’s palsy
Type of unilateral (<1% bilateral) facial paralysis due to VII dysfunction
Most common cause of acute facial nerve paralysis (>80%)
Some denture wearers experience discomfort
Cause unknown, by definition
Believed to be an inflammatory condition resulting in facial nerve swelling in facial canal
Commonly shows rapid onset with partial or complete paralysis; can occur overnight
Usually improves over time and function restored to normal or near-normal most of the time, steroids improve outcome
Corneal blink reflex
Touch cornea and both eyes blink
Afferent limb: Vi to SpV tract
Efferent limb: VII elicited by bilateral projection from SpV nucleus/ reticular formation
Clinical test of V, VII & central connections
Jaw opening & closing reflexes
Jaw closing reflex
Food in contact with oral membranes
Jaw opening reflex
Periodontal afferents activated by dental occlusion
Pain afferents from mucosal membranes
Input (V) from:
Jaw muscles (proprioception – trigeminal mesencephalic nucleus)
Tactile information (food in mouth – trigeminal main nucleus)
Pain information (trigeminal spinal nucleus)
Output (V) to:
Muscles of mastication
Jaw-jerk reflex
Monosynaptic reflex
Downward tap on chin, stretches masseter
Afferent limb: mesencephalic V neuron innervating masseter spindle
Efferent limb: V motor neuron
Nervus Intermedius
Aligns with VII nerve distal to genu
intermediate nerve
Taste pathways in the CNS
Gustatory afferents reach nucleus of the solitary tract via the solitary tract
Second order fibers do 2 things:
Reflex activities: swallowing, salivation
Project uncrossed to thalamus (VPM), then to gustatory cortex (insula, medial surface of frontal operculum)
Gustatory cortex projects to orbitofrontal cortex, integrated there with olfactory info, reaches amygdala, from there to limbic system & hypothalamus
