martin chapter 6 Flashcards
what does the trigeminal system mediate?
somatic sensations (mechanosensations and the protective senses-temperature, pain and itch) from the face and head
how many pairs of cranial nerves do we have?
12
what do cranial nerves innervate?
face and head
where does the olfactory nerve (I) enter?
in the cerebral hemisphere. it mediates the sense of smell
where does the optic nerve (II) enter?
in the thalamus. it mediates vision
the other 10 cranial nerves enter and leave which structure?
the brain stem
which is the only cranial nerve located in the dorsal brain stem surface?
the trochlear nerve (IV)
in which part of the brain stem do the oculomotor (III) and trochlear (IV) nerve exit?
in the midbrain
how many cranial nerves does the pons contain?
4
which cranial nerve is located in the middle of the pons?
the trigeminal nerve (V). it consists of both sensory and motor functions->is characterized by both sensory and motor roots
the sensory root innervates the facial skin and mucous membranes of the oral and nasal cavities and the teeth.
The motor root contains axons that innervate jaw muscles
what does the abducens (VI) nerve innervate?
it is a motor nerve and innervates eye muscles
the facial nerve (VII)
-mixed nerve
-the motor root innervates the facial muscles that determine our expressions
-the sensory root innervates taste buds and mediates taste
what’s the name of the facial sensory root?
intermediate nerve
the vestibulocochlear nerve (VIII)
-sensory nerve
-2 separate components
vestibular component innervates the semicircular canals, utricle and saccule and mediates balance
chochlear component innervates the organ of Corti and serves hearing
the 4 cranial nerves associated with the pons
-facial (VII)
-Abducens (VI)
-Trigeminal (V)
-Vestibulocochlear (VIII)
how many cranial nerves does the medulla have?
4
name of the cranial nerves in the medulla
-glossopharyngeal (IX)->mixed nerve, major function is to provide the sensory innervation of the pharynx and to innervate the posterior 1/3 of the tongue. its motor function is to innervate a single pharyngeal muscle and peripheral autonomic ganglion.
-vagus nerve (X)->mixed nerve, myriad sensory and motor functions that include somatic and visceral sensation, innervation of pharyngeal muscles and much of the visceral autonomic innervation.
-spinal accessory (XI) and hypoglossal (XII) subserve motor functions innervating neck and tongue muscles respectively
Primary Sensory Neurons
the first neurons that receive the stimulus from the environment (touch, pain, temperature, proprioception) and send it towards the CNS (spinal cord or brainstem).
primary sensory neurons in cranial nerves can have 2 different types of morphologies:
pseudounipolar (2 axons) or bipolar (one axon and one dendrite)
most primary sensory neurons derive from?
neural crest cells, that derive from the dorsal region of the neural tube
the developing pons and medulla have 8 segments called
rhombomeres
how many categories of cranial nerve nuclei do we have ?
7
nuclei of each of these categories form discontinuous columns that extend rostrocaudally through the brain stem
the 7 functional categories are distributed through only 6 discrete columns, why?
2 of the sensory categories synapse on neurons in a single column but at separate rostrocaudal locations
where are the sensory columns disposed within respect to the motor columns?
sensory columns are lateral respect to the motor columns
what does the sulcus limitans represent in the adult brain?
an important anatomical landmark on the floor of the 4th ventricle that roughly divides the sensory columns from the motor columns
somatic sensations of the head, including the oral cavity, is carried by 4 cranial nerves:
trigeminal, glossopharyngeal, vagus and facial
the trigeminal innervates most of the head and the oral cavity and is the most important one out of the 4 nerves
the facial, glossopharyngeal and vagus innervates mucous membranes and organs of the body and small areas of the skin around the external ear.
where do the sensory fibers that innervate surface skin and oral mucosa project?
into central trigeminal nuclei
where do the sensory fibers that innervate the mucous membranes of the pharynx and larynx and other internal (visceral) structures project?
to the caudal portion of the solitary nucleus
these sensory fibers terminate into 2 of the trigeminal sensory nuclei
main trigeminal sensory nucleus and spinal trigeminal nucleus
mesencephalic trigeminal nucleus
third sensory nucleus
not a site of termination of primary sensory fibers
it is equivalent to a peripheral ganglion cause it contains the cell bodies of certain trigeminal primary sensory fibers
the ascending second order trigeminal fibers are called
trigeminal lemniscus
where in the thalamus do the ascending second order trigeminal fibers synapse?
in the ventral posterior medial nucleus in the thalamus
where do the axons of the ventral posterior medial nucleus in the thalamus project?
to the lateral part of the primary somatic sensory cortex, in the postcentral gyrus (via the posterior limb of the internal capsule).
from where do the secondary somatic sensory cortex and posterior parietal cortex receive their major input ?
from the primary somatic sensory cortex
the dorsal trigeminothalamic tract originates from?
the dorsal portion of the main trigeminal sensory nucleus
it ascends ipsilaterally to the ventral posterior medial nucleus and processes mechanical stimuli from the teeth and soft tissues of the oral cavity
what is jaw proprioception
the conscious awareness of how much we open our mouth
the spinal trigeminal nucleus has a rostrocaudal anatomical organization with three components:
- oral nucleus
- interpolar nucleus
- caudal nucleus
functions of the spinal trigeminal nucleus
similar to the functions of the dorsal horn of the spinal cord
plays an essential role in dental and facial pain, temperature sensation and itch.
a much lesser role in facial mehcanical sensations
what is the major ascending trigeminal pathway from the spinal trigeminal nucleus?
the trigeminothalamic tract
trigeminothalamic axons terminate in 3 principal locations in the thalamus:
- ventral posterior medial nucleus
- ventromedial posterior nucleus
- medial dorsal nucleus
where does the ventral posterior medial nucleus project?
to the primary somatic sensory cortex
where does the ventral medial posterior nucleus project?
insular cortex
where does the medial dorsal nucleus project?
the anterior cingulate gyrus
after entering the brain stem, the central branches of glossopharyngeal and vagal axons collect in what?
in the solitary tract of the dorsal medulla and terminate in the surrounding caudal solitary nucleus.
the caudal solitary nucleus is divided into 2 parts
a rostral portion for taste and a caudal portion that serves viscerosensory functions.
the trigeminal nerve consists of 3 sensory roots that innervate different regions and mucous membranes of the head. name the 3 divisions
-ophtalmic division
-maxillary division
-mandibular division
where are the cell bodies of the trigeminal sensory fibers?
in the trigeminal ganglion, a peripheral sensory ganglion.
where are the cell bodies of stretch receptors found in jaw muscles located?
in the CNS, in the mesencephalic trigeminal nucleus
what is the trigeminal dermatome?
the area of the skin of the face or head innervated by sensory fibers from a single trigeminal sensory nerve division
the cell bodies of the sensory fibers of the facial nerve are located in?
the geniculate ganglion
the cell bodies of the sensory fibers of the glossopharyngeal and vagus nerve are located in?
the superior ganglion of each nerve
which is the nucleus that contains the cell bodies of stretch receptors that signal jaw muscle length (key sensory signal for jaw proprioception)?
mesencephalic trigeminal nucleus, located in the rostral pons and in the midbrain
where is the spinal trigeminal nucleus located? and the main trigeminal sensory nucleus?
- medulla and caudal pons
- in the pons
the dorsal horn extends rostrally into the medulla as?
spinal trigeminal nucleus
the caudal nucleus (one of the 3 subdivisions of the spinal trigeminal nucleus) is also called?
medullary dorsal horn, cause very similar in structure to the spinal cord dorsal horn
the caudal nucleus extends from where to where?
from the first/second cervical segment of the spinal cord till the point in the medulla where the central canal opens to form the 4th ventricle
the inter polar nucleus extends from where to where?
from the rostral boundary of the caudal nucleus to the rostral medulla
the oral nucleus extends from where to where?
from the rostral boundary of the inter polar nucleus till the point in which the trigeminal nerve enters the pons
