Brainstem-Gilland Flashcards
What does the brainstem consist of?
midbrain, pons, and medulla
The midbrain tectum is comprised of what?
- quadrigemminal bodies AKA superior and inferior colliculi
- the tectum forms the ROOF of the the MIDBRAIN
Where is the basal portion of the pons located?
ventral side
- basilar part of pons is the ventral part of the pons
- the dorsal part is known as the pontine tegmentum
The tegmentum is located in what areas of the brainstem?
it is located beneath the ventricles
midbrain and pons
-extends from the substantia nigra to the cerebral aqueduct
-forms the floor of the midbrain (mesencephalon)
The tegmentum (core) of the brainstem includes the cranial nerve nuclei, ascending sensory pathways, reticular formation, and periaqueductal gray matter and is involved in a variety of functions.
Anterior/Superior medullary velum
a thin, transparent lamina of white matter, which stretches between the superior cerebellar peduncles
It forms, together with the superior cerebellar peduncle, the ROOF of the upper part of the FOURTH VENTRICLE
Cerebellar peduncle
cerebellar peduncle is a nerve tract that permits communication between the cerebellum and the other parts of the central nervous system
superior, middle, and inferior cerebellar peduncles
Superior cerebellar peduncle is a paired structure of white matter that connects the cerebellum to the mid-brain.
Middle cerebellar peduncles connect the cerebellum to the pons and are composed entirely of centripetal fibers.
Inferior cerebellar peduncle is a thick rope-like strand that occupies the upper part of the posterior district of the medulla oblongata; bring sensory information about the actual position of body parts such as limbs and joints.
peduncles form the lateral border of the fourth ventricle, and form a distinctive diamond
Rhomboid fossa
a rhombus-shaped depression that is the ANTERIOR part of the fourth ventricle (So rhomboid fossa located on the dorsal side of the brainstem)
anterior wall, formed by the back of the pons and the medulla oblongata, constitutes the floor of the fourth ventricle.
It is covered by a thin layer of grey matter continuous with that of the spinal cord; superficial to this is a thin lamina of neuroglia which constitutes the ependyma of the ventricle and supports a layer of ciliated epithelium.
-projection of the nuclei of cranial nerves in the rhomboid fossa
Brainstem with 4th ventricle
exposed by severing cerebellar peduncles and cutting choroid roof away at the margins of the rhomboid fossa
- 4th ventricle has a diamond shape and is located in the upper portion of the medulla
- extends from the cerebral aqueduct (of Sylvius) to the obex and is filled with CSF
Cuneate (lateral) and Gracile (medial) tubercle, nuclei, and fasciculus
-tubercle is a swelling on the dorsal surface of the medulla caused by presence of nuclei
-fasciculus= bundle of nerve fibers
-ascending tracts: fasciculus gracilis
fasciculus cuneatus
The cuneate fasciculus carries information from vertebral level T6 and above, and the gracile fasciculus carries information from vertebral levels T7 and below. The two ascending tracts meet at the T6 level; pathway by which the sensory modalities of proprioception, vibration, discriminative touch and stereognosis are transmitted from the peripheral receptors of the upper/lower limb and trunk to the primary somatosensory cortex.
cuneate nucleus: cuneocerebellar tract (part of inferior cerebellar peduncle) originates here trigeminal tubercle trigeminal spinal tract (pain and temp) Chief Sensory Nucleus (touch) Nucleus of Solitary Tract (taste)
The trigeminal nerve originate from nuclei located where?
midbrain and medulla regions of your brainstem
The trigeminal nerve has both sensory and motor components. What do each branch into?
sensory root branches into ophthalmic, maxillary, and mandibular divisions
motor root branches into the mandibular division
The midbrain of the brainstem consists of what cranial nerve efferent nuclei?
Edinger-Westphal nucleus (parasympathetic of III)
Oculomotor nucleus (somatomotor nucleus)
Trochlear nucleus (somatomotor nucleus)
The pons of the brainstem consists of what cranial nerve efferent nuclei?
Trigeminal motor nucleus (upper pons)
Abducens nucleus (lower pons-somatomotor)
Facial motor nucleus (lower pons-branchiomotor)
Superior and Inferior Salivatory nuclei (parasympathetic VII and IX respectively)
The medulla of the brainstem consists of what cranial nerve efferent nuclei?
Dorsal vagal motor nucleus (parasympathetic of X)
Nucleus Ambiguus (branchiomotor; IX, X, XI)
IX: stylopharyngeus muscle
X: palatal muscles
XI: laryngeal muscles
Hypoglossal nucleus (somatomotor)
The superior and inferior salivatory nuclei are located in what region of the brainstem?
located in the pontine tegmentum in the brainstem which is the dorsal part of the pons, just above its junction with the medulla
What are the parasympathetic cranial nerve efferent nuclei of the brainstem?
- Edinger-Westphal nucleus (III)
- Superior salivatory nucleus (VII)
- Inferior salivatory nucleus (IX)
- dorsal vagal motor nucleus (X)
What are the branchiomotor cranial nerve efferent nuclei of the brainstem?
-trigeminal motor nucleus:
muscles of mastication, the tensor tympani, tensor veli palatini, mylohyoid, and anterior belly of the digastric
-Facial motor nucleus:
muscles of facial expression and the stapedius
-Nucleus Ambiguus:
IX: stylopharyngeus muscle
X: palatal muscles
XI: laryngeal muscles
all going to branchial arch muscles
What are the somatomotor cranial nerve Efferent nuclei of the brainstem?
- Oculomotor nucleus
- Trochlear nucleus
- Abducens nucleus
- Hypoglossal nucleus
all right near to the midline of brainstem, right under the ventricles, and right on top of medial longitudinal fasciculus axonal tract
Which cranial nerve Afferent nuclei of the brainstems consists of proprioceptive neurons projecting OUT of V2 and V3? What region of the brainstem is it located?
Trigeminal mesencephalic nucleus which is located in the midbrain and pons
Which cranial nerve Afferent nuclei of the brainstems consists of GSA, mainly fine TOUCH from V? What region of the brainstem is it located?
Trigeminal main sensory nucleus (chief sensory nucleus) which is located in the pons
-receives information about discriminative sensation and light touch of the face as well as conscious proprioception of the jaw via first order neurons of CN V
Which cranial nerve Afferent nuclei of the brainstems consists of GSA from V, VII, IX, and X? What region of the brainstem is it located?
Trigeminal spinal nucleus which is located in the pons and medulla
-receives information about deep/crude touch, PAIN, and TEMPERATURE from the ipsilateral face
Which cranial nerve Afferent nuclei of the brainstems consists of visceral fibers from VII, IX, and X? What region of the brainstem is it located?
Nucleus of tractus solitarius which is located in the medulla
- fibers conveying TASTE sensation project to the Nucleus of Solitary Tract
- Taste information from the facial nerve via the Chorda tympani (anterior 2/3 of the tongue), glossopharyngeal nerve (posterior 1/3) and vagus nerve (small area on the epiglottis)
Dorsal cochlear nucleus
Ventricular nucleus
Dorsal cochlear nucleus:
- there is also a ventral cochlear nucleus
- along with the ventral cochlear nucleus (VCN), it forms the cochlear nucleus (CN), where all auditory nerve fibers from the cochlea form their first synapses
Ventricular nucleus:
-vestibular nerve transmits sensory information transmitted by vestibular hair cells located in the two otolith organs (the utricle and the saccule) and the three semicircular canals via the vestibular ganglion
Reticular formation
fills in the spaces in between of the nuclei and axonal tracts
- a diffuse network of nerve pathways in the brainstem connecting the spinal cord, cerebrum, and cerebellum, and mediating the overall level of consciousness.
- don’t see much in cross-section
- involved with many functions including the sleep arousal (reticular activating) mechanism, the control of movement and the regulation of visceral activity.
Describe the open vs closed medulla oblongata.
- Open medulla is the upper portion of the medulla oblongata: consists the choroid plexus of the 4th ventricle
- Closed medulla is the lower portion of the medulla
What axonal tracts connect the cerebellum to the brainstem?
cerebellar peduncles: superior, middle, and inferior
Axonal tracts coming FROM the pons TO the cerebellum
middle cerebellar peduncle (INTO cerebellum)
Axonal tracts: output of the cerebellum going to the thalamus
superior cerebellar peduncle (OUT of cerebellum) through the midbrain
Axonal tracts going from spinal cord and brainstem to cerebellum AND leaving cerebellum and going to spinal cord and brainstem
inferior cerebellar peduncle (both OUT and IN of cerebellum)
Cerebral peduncle
- located outside of the midbrain; hide the midbrain from lateral view
- fiber bundle connecting the hemispheres down to brainstem and spinal cord
- The cerebral peduncles are involved in numerous functions including somatosensory perception, motor and autonomic control.
Inferior olivary nucleus
-close to the obex of the medulla
-inferior olivary nucleus plays an important role in the learning of new motor skills.
bulges out as it is made out of many nuclei
-precerebellar nucleus ????
Posterior to it: roots of CN IX, X, XI
Ventral to it: roots of Hypoglossal nerve
postcerebellar and precerebellar nuclei
The term postcerebellar and precerebellar nuclei refers to seven nuclei in the midbrain, pons, and medulla that constitute a functional part of the subcortical motor system of the cerebrospinal trunk. They include the red nucleus, ventral pontine gray, inferior olivary complex, lateral reticular nucleus, linear nucleus of the medulla, ventral paramedian reticular nucleus, and parasolitary nucleus. Functionally they are part of the subcortical motor system
4th ventricle begins and ends where?
begins from the trochlear nerve to the obex
-this area of margin contains the rhomboid fossa
What cranial nerves are found at the pontomedullary junction?
Cranial Nerve VI (abducens), VII (facial) and VIII (vestibulocochlear nerve)
What cranial nerves are located on the middle cerebellar peduncle?
Trigeminal nerve (CN V)
Trigeminal spinal tract
somatosensory nuclei mainly on the dorsal side of the medulla
Pyramids
descending fibers coming from the cortex
- physical manifestation of how cortex
- mediates voluntary motor control
-pyramid is a swelling formed by the corticospinal tract, which controls the speed and precision of skilled movements involving the distal muscles of the contralateral limbs, particularly those of the hands and fingers.
Where is the oculomotor cranial nerve located on the brainstem?
just below the inferior colliculus of the midbrain
Branchiomotor nuclei are always ________ to the somatomotor nuclei. Sensory nuclei are located more __________than all the other nuclei.
lateral
dorsally
How does the brainstem form embryologically?
neatly segmental structure
- embryonically midbrain and hindbrain neuroepithelium are divided up into a series neuroepithelial segments
- in the pons and medulla are called rhombomeres (rhomencephalon)
- you end up with a series of columns: somatic efferent and visceral efferent which make up the basal portion of the brainstem neuroepithelium; visceral afferent and somatic afferent column which make up the alar portion of the brainstem neuroepithelium
Reticular formation of the brainstem
everything in the brainstem that is not part of a motor nucleus, sensory nucleus, or precerebellar nucleus
- a garbage can to dump everything that is not in either one of nuclei
- not as densely packed as most of the motor and sensory nuclei
- the different parts of this system are not clearly anatomically defined so most of the parts are described in topographical terms
- a lot of the nuclei are modulatory meaning they are not in the direct processing train of information
- there are usually clustered near motor nuclei and receive lots of afferent information
The brainstem reticular formation is organized grossly in a series of neuronal cell columns running more or less continuously from what into the spinal cord? The columns are grouped as? How are the nuclei arranged in each column?
thalamus
The columns are grouped as:
- median (paramedian)
- medial (central)
- lateral
The nuclei are distributed rostro-caudally in a general segmental pattern with unique cellular and functional types located at particular axial levels of midbrain, pons, and medulla.
within the median reticular formation
this is the particularly in front there are modullary nucleli and most of them are the raphe nuclei which project extensively; include very long projections of serotonergic neurons; modulate motor, somatosensory, limbic, pain circuits;
serotonergic neurons
- part of the overall brainstem arousal system; includes cholinergic and dopaminergic reticular neurons that have strong influence on attention and sleep/wake cycles
- those located in the rostral raphe complex of mesencephalon and rostral pons project mainly to forebrain targets
- those located in caudal raphe complex of the caudal pons and medulla project to the brainstem and spinal cord;
raphe nuclei
- the ventral midline structure of the brain and spinal
- involved in analgesia and pain modulation
- Serotonergic neurons in nucleus raphe magnus are strongly involved in analgesia and pain modulation through direct projections to the spinal cord dorsal horn.
Nuclei of rostral raphe complex include
caudal linear, dorsal raphe and median raphe nuclei
Nuclei of caudal raphe complex include
raphe magnus, raphe obscurus and raphe pallidus nuclei
medial reticular column
- include numerous nuclei serving premotor functions to organize reticular types of movement
- in the midline is the oculomotor and trochlear nuclei; neurons that get lots of input from the vestibular and visual system surround them and help organize them in order of the muscles they control
- vertical gaze: mesencephalic reticular formation
- horizontal gaze: paramedian pontine reticular formation
- horizontal head movements: pontomedullary formation
together they form centers for chewing, facial movements, swallowing, etc.
major medial reticular nuclei
- cuneiform and subcuneiform nuclei
- oral pontine reticular nucleus
- caudal pontine reticular nucleus
- gigantocellular nucleus of medulla
need a premotor neuron to help power motor neuron activity
????
Lateral Reticular Column
Locus Coeruleus
Catecholamine nuclei
A number of noradrenergic and adrenergic nuclei are located in the lateral reticular formation of midbrain, pons and medulla
tracts
-bundle of axons traveling together like an information cable
medial longitudinal fasciulus (MLF)
right next to midline and runs up and down the brainstem and entire SC; important in control head and eye movements
- right near the midline and ventricle next to the central canal
- hypoglossal motor nucleus sit right on top of the MLF; they do not project into MLF!!; if you want to send info to the hypoglossal motor nucleus send your fibers through MLF
somatomotor nuclei sitting on the MLF (abducens, trochlear, oculomotor); get most of their input from fibers traveling in the MLF
-Longitudinal Fasciculus (MLF) – critical for controlling eye movements; note relationship to nuc. III, IV, VI, XII
pyramidal tracts
form the pyramids that run on ventral medulla; main tract for voluntary motor control; axon being in motor and premotor cortex and go to corticobulbar fibers in the brainstem
- corticobulbar projections going to hypoglossal nucleus
- many of the corticospinal fiber cross at the midline; decussation
- some stay uncrossed
- corticospinal tract is a clinically important descending motor pathway/control
- main tract for voluntary motor control, contains corticospinal and corticobulbar fibers, partially decussates in lower medulla
Medial Lemniscus
ascending somatosensory pathway
- in the upper medulla (open medulla)
- originates in dorsal medial column AKA originate in gracile and cuneate nuclei, forms internal arcuate fibers and decussates in lower medulla, ascends the brainstem to the contralateral thalamus
- fiber bundle that is spread out like a flat cable
- axons come out as internal arcuate fibers (meaning they begin dorsally go ventrally and then cross the midline of the brainstem meaning they decussate and go all the way to the contralateral thalamus)
-important in
upper limb and thorax movement
-medial lemniscus transmits sensations of discriminative touch, vibration, proprioception and stereognosis from the gracile and cuneate nuclei to the ventral posterior nucleus of the thalamus
lateral lemniscus
- ascending auditory pathway beginning down at the cochlear nuclei going to the inferior colliculi
- brainstem auditory pathway to inferior colliculus
- the lateral lemniscus transmits auditory information from the superior olivary and cochlear nuclei to the inferior colliculus.
Spinal Medullary junction (lower medulla)
- traditionally called the closed medulla
- right above the decussation of the pyramids = crossing of the corticospinal fibers
- a lot of nervous tissue above the roof the of the 4th ventricle and a ton of tracts below the ventricle (pyramidal tracts)
tract staining
???
all the nuclei will be light
This is how you relay somatosensory information
tracts of axons with information coming up from the spinal cord synapse in the dorsal column then project to the thalamus
the first thing they do is cross the midline by leaving the dorsal column nuclei as internal arcuate fibers and then enter into the medial lemniscus and turn rostrally and all those are part of the medial lemniscus and will eventually reach the CONTRALATERAL thalamus
Internal arcuate fibres carry tactile and proprioceptive data from the gracile and cuneate nuclei to join the contralateral medial lemniscus.
Trigeminal Spinal Tract
- incoming somatosensory info from all the cranial nerves synapse onto the trigeminal spinal nucleus
- axons run up to the thalamus as well
dorsal motor nucleus of vagus
- preganglionic parasympathetic nucleus
- visceral motor
solitary tract nucleus
the incoming axons of visceral sensory info from cranial mass from CN VII, IX, and X (all those would come in and run down as the solitary and synapse on cells clustered around these tracts AKA solitary tract nucleus
dorsal part of the closed medulla; below the roof of the 4th ventricle
region totally dedicated to visceral control
-deeply involved in regulation BP and HR
inferior olive
- huge nucleus
- refer to as the precerebellar nuclei
- gets input from a variety of places but has output goes mostly right to the cerebellum to help regulate neurons there
Nucleus Ambiguus
- branchiomotor nucleus of CN IX and X
- called this because it doesn’t show well on cross section
-in the ventro-lateral medulla which is heavily involved in respiration in concert with reticular formation
dorso-lower of closed medulla
visceral
dorsolateral of closed medulla
somatosensory
open medulla at the root of the vagus fibers
- there is a choroidal roof of the 4th ventricle
- above the gracile and cuneate nucleus
CN X root fibers
- in the open medulla
- dorsal lateral to the inferior olive
CN XII root fibers
- in the open medulla
- ventral to the inferior olive
vestibular nuclei
form a long pyramidal shaped structure ALWAYS dorsal in the brainstem and adjacent to the open port ventricle
incoming root fibers to the vestibular nerve (CN VIIII)
-organized similarly to the premotor system and project appropriately to motor systems to help control balance/posture/head and eye movements
inferior cerebellar peduncle
???
- all fibers from the SC and brainstem that want to go to cerebellum AND fibers that want to go from cerebellum to SC and brainstem
- sits on the lateral surface of the closed medulla
pontomedullary junction
???
caudal pons
- going through the middle cerebellar peduncle
- ependymal cells surrounding ventricles
-separate pyramids are hidden inside basilar pons
-
pontine nuclei
- in caudal pons
- gigantic relay btw cortex and cerebellum (cortex–>pons–>cerebellum)
transverse pontine (pontocerebellar fibers)
first thing they do is cross the midline (they project to the contralateral cerebellum)
middle cerebellar peduncle
giant bundle of pontine nuclei neurons forms
-continuous with inferior and superior cerebellar peduncle; can’t really distinguish them until you’ve gone through many sections
pontine tegmentum
???
abducens motor nucleus
in caudal pons
- sits lateral to the MLF
- somatomotor neurons
facial motor nucleu
- above nucleus ambiguus
- all the motor neurons that innervate stylohyoid, digastric, and all muscles of facial expression, adn stapedius are all in this nucleus
- then it does this CRAZY thing where the axons from these neurons don’t just pass ventrolaterally to go out of CN root; they instead ascend up towards the ventricle and form a great bundle that wraps around the abducens motor nucleus and make a great exit
- is reflective of the embryological migration pathway
rostral pons
- begin to see the superior cerebellar peduncle
- 4th ventricle is now narrowing down; see the cerebral aqueduct
- side walls of the 4th ventricle are made up of the superior cerebellar peduncle (leaving cerebellum going to the thalamus)
Trigeminal nucleus and Principal trigeminal nucleus
- lateral tegmentum of upper (ROSTRAL) pons
- tegmentum= area just below the 4th ventricle
caudal midbrain
trochlear nucleus and decussation of SCP fibers
- inferior colliculus
- above the basilar pons
- enormous fiber bundles on both sides
cerebral peduncle
-in caudal midbrain
-fibers from cortex going to pontine nuclei
(corticopontine fibers)
- other fibers form parts of the pyramidal tract running down the SC are corticospinal fibers located centrally of the cerebral peduncle
- other fibers are corticobulbar fibers running from cortex to motor nuclei of cranial nerves
- hide midbrain from lateral view
interpeduncular fossa
- space in between the between the cerebral peduncles
- where the root fibers of oculomotor come out
substantia nigra
- in caudal midbrain
- deep to the crus cerebri but part of cerebral peduncle
- substantia nigra plays an important role in the control of movement. It sends dopaminergic fibres to the striatum and when damaged, results in Parkinson’s disease.
periaqueductal gray
neurons surrounding the cerebral aqueduct
tectum
- roof of the midbrain
- consist of inferior and superior colliculus
-fibers of the inferior colliculus terminate auditory pathway coming up brainstem
trochlear motor nucleus
????
their axons exits dorsally
decussation of superior cerebellar peduncle fibers
-in caudal midbrain
can get bilateral deficit if you lesion exactly in the midline of crossing
rostral midbrain
-harder to distinguish MLF
-Edinger Wesphal nucleus
-oculomotor nucleus whose axons exit through the interpeduncular fossa
-red nucleus
medial geniculate nucleus (thalamus)
crus cerebri
corticospinal, corticopontine, and corticobulbar fibers together in the cerebral peduncle
red nucleus
- called this because they are red
- important in non-human mammals
- heavily involved in controlling movements of arms and hands
medial geniculate nucleus
- in the rostral midbrain
- gets its input for the inferior colliculus for AUDITORY to go to primary auditory cortex in the hemisphere
What are the cranial nerve efferent nuclei associated with CN III?
somatomotor nuclei: oculomotor nucleus
visceral (parasympathetic) nuclei: Edinger-Westphal nucleus
What are the cranial nerve efferent nuclei associated with CN IV?
somatomotor nuclei: trochlear nucleus
What are the cranial nerve efferent nuclei associated with CN V?
branchiomotor nuclei: trigeminal motor nucleus
What are the cranial nerve efferent nuclei associated with CN VI?
somatomotor nuclei: abducens nucleus
What are the cranial nerve efferent nuclei associated with CN VII?
branchiomotor nuclei: facial motor nucleus
visceral (parasympathetic) nuclei: superior salivatory nucleus
What are the cranial nerve efferent nuclei associated with CN IX?
Branchiomotor Nuclei: rostral part of nucleus ambiguus
Visceral (parasympathetic) Nuclei: inferior salivatory nucleus
What are the cranial nerve efferent nuclei associated with CN X?
Branchiomotor Nuclei: nucleus ambiguus
Visceral (parasympathetic) Nuclei: dorsal motor nucleus of vagus
What are the cranial nerve afferent nuclei associated with CN V?
Sensory Ganglia: Trigeminal ganglia
Somatosensory Nuclei: Principal trigeminal sensory nucleus
Visceral sensory Nuclei: Solitary nucleus
(nucleus of the solitary tract)
What are the cranial nerve afferent nuclei associated with CN VII?
Sensory Ganglia: Geniculate Ganglion
Somatosensory Nuclei: trigeminal spinal nucleus
(nucleus of the trigeminal spinal tract)
Visceral sensory Nuclei: gustatory portion
What are the cranial nerve afferent nuclei associated with CN IX?
Sensory Ganglia: Sup. & Inf. Sensory ganglia
Visceral sensory Nuclei: Abdominal Visceral portion
What are the cranial nerve afferent nuclei associated with CN X?
Sensory Ganglia: Sup. & Inf. Sensory ganglia
Visceral sensory Nuclei: Cardio-respiratory portion
What are the efferent nuclei related to cranial nerves?
Efferent Nuclei
Oculomotor nucleus Trochlear nucleus Trigeminal Motor nucleus Abducens nucleus Facial Motor nucleus Nucleus Ambiguus Hypoglossal nucleus Spinal accessory nucleus (in spinal cord)
What are the afferent nuclei and tracts related to cranial nerves?
Afferent Nuclei & Tracts
Trigeminal Sensory Nucleus
Trigeminal Spinal Tract & Nucleus
Mesencephalic Nucleus of Trigeminal
Solitary Tract & Nuclei
Cochlear Nuclei
Vestibular Nuclei
What are general somatic afferent nerves? Which cranial nerves carry them?
General somatic afferent fibers carry exteroceptive (pain, temperature, touch) and proprioceptive impulses. Cranial nerves for proprioception: III, IV, V, VI, XII; for pain, temperature, and touch: V, VII, IX, X.
What are general visceral afferent nerves? Which cranial nerves carry them?
General visceral afferent fibers carry impulses from the visceral structures, and cranial nerves IX and X contain these fibers.
What are special somatic afferent nerves? Which cranial nerves carry them?
Special somatic afferent fibers carry sensory impulses from the special senses (vision, hearing, equilibrium), and cranial nerves II and VIII contain these fibers.
What are special visceral afferent nerves? Which cranial nerves carry them?
Special visceral afferent fibers carry impulses from the olfactory and gustatory senses, and cranial nerves I (olfactory), VII, IX, and X (gustatory) contain these fibers.
What are general somatic efferent nerves? Which cranial nerves carry them?
General somatic efferent fibers carry motor impulses to somatic skeletal muscles. In the head, the tongue and extraocular muscles are of this type. Cranial nerves III, IV, VI, and XII carry these fibers.
What are general visceral efferent nerves? Which cranial nerves carry them?
General visceral efferent fibers carry parasympathetic autonomic axons. The following cranial nerves carry general visceral efferent fibers:
- Cranial nerve III (Edinger–Westphal nucleus): the preganglionic fibers from the Edinger–Westphal nucleus terminate in the ciliary ganglion, and the postganglionic fibers innervate the pupil.
- Cranial nerve VII (superior salivatory nucleus): the preganglionic fibers from the superior salivatory nucleus terminate in the pterygopalatine and submandibular ganglion. The postganglionic fibers innervate the lacrimal gland (from the pterygopalatine ganglion) and the submandibular and sublingual gland (from the submandibular ganglion).
- Cranial nerve IX (inferior salivatory nucleus): the preganglionic fibers from the inferior salivatory nucleus terminate in the otic ganglion, and the postganglionic fibers innervate the parotid gland.
- Cranial nerve X (dorsal motor nucleus): the dorsal motor nucleus innervates the abdominal viscera.
What are special visceral efferent nerves? Which cranial nerves carry them?
Special visceral efferent fibers innervate skeletal muscle derived from the branchial arches. They are carried by the following cranial nerves: V (muscles of mastication, first branchial arch), VII (muscles of facial expression, second branchial arch), IX (stylopharyngeus muscle, third branchial arch), X (muscles of the soft palate and pharynx, fourth branchial arch), and XI (muscles of the larynx/sternocleidomastoid (SCM)/trapezius, sixth branchial arch).
White matter vs. Gray matter
White matter: the paler tissue of the brain and spinal cord, consisting mainly of nerve fibers with their myelin sheaths
Gray matter: darker tissue of the brain and spinal cord, consisting mainly of nerve cell bodies and branching dendrites
Basilar Pons
The basis pontis is the ventral portion of the pons and contains several descending tracts (corticospinal, corticobulbar and corticopontine) , the pontine nuclei and the transversely oriented pontocerebellar tract
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