The Brainstem and Cranial Nerves Flashcards
What are the rostral and caudal margins of the brainstem?
Extends from the mamillary bodies rostrally to the pyramidal decussation caudally
What are the characteristic anatomical features of the midbrain, pons and medulla on their dorsal aspects?
Midbrain: superior and inferior colliculi
Pons: facial colliculi (formed by abducens nucleus and fibres of CNVII)
Medulla: Dorsal columns (composed of nuclei-gracile and cuneate tubercle)
Describe the position of the pons
Limited by the 4th ventricle and linked with the cerebellum via large fibre tracts
What are the superior and inferior colliculi involved in?
Movement control and hearing
What are the characteristic anatomical features of the midbrain, pons and medulla on their ventral aspects?
Midbrain: cerebral peduncles with interpeduncular fossa
Pons: superior, middle and inferior cerebellar peduncles
Medulla: inferior olivary nuclei (rostrally), pyramids
What is the structural role of the cerebellar peduncles?
Link the pons to the cerebellum dorsolaterally
What is the tectum and where is it found?
The tectum (composed of the colliculi) forms a “roof” over the 3rd and 4th ventricles and is found only in the midbrain
Describe the dorsal and ventral organisation of the brainstem
Dorsal brainstem usually contains the cranial nerve nuclei and structures involved in their regulation
Ventral brainstem usually contains structures related to motor function
Where is the tegmentum found and what does it contain?
The tegmentum is found throughout the brainstem and is continuous with the spinal cord
It contains cranial nerves and nuclei, and the reticular formation
What is the role of the basis/basilar part?
Descending motor control (contains tracts, and attachments to the cerebellum and to other nuclei)
Where do the spinal nerves begin?
At the level of C2
How are the cranial nerves organised in terms of their exit from the brainstem?
Exit the brainstem in numerical order rostrally to caudally
CNI-IV exit above the pons
CNV-VIII exit at the pons
CNIX-XII exit at the medulla
All except IV exit via the ventral surface
Which cranial nerves are exclusively motor?
III, IV, VI (oculomotor, trochlear, abducens; for control of eye movements)
XI, XII (accessory, hypoglossal)
Which cranial nerves are exclusively sensory?
I, II, VIII (olfactory, optic, vestibulocochlear; involved in special senses)
Which cranial nerves are mixed?
V, VII, IX, X (trigeminal, facial, glossopharyngeal, vagus)
Describe the embryological development of the cranial nerve nuclei
Cranial nerve nuclei lie adjacent to the ventricular system (sensory nuclei develop from the alar plate; motor nuclei develop from the basal plate)
The ventricle pushes the alar plate to the lateral sides as it develops
Motor nerve nuclei are found closer to the midline than sensory nerve nuclei
How are cranial nerve nuclei positioned within the brainstem?
Found within columns, with 6 columns lying either side of the midline
Motor nerve nuclei are found closer to the midline than sensory nerve nuclei
List the 6 different cranial nerve nuclei columns from medial to lateral
General somatic (motor) Branchial (motor) General visceral (motor) General and special visceral (sensory) General somatic (sensory) Special somatic (sensory)
What structures is the reticular formation continuous with rostrally and caudally?
Rostrally: certain nuclei in the thalamus
Caudally: intermediate grey matter of the spinal cord
What are the functions of the reticular formation and what regions are these functions localised to?
At the midbrain and upper pons: maintains alert conscious state
At the pons and medulla: variety of important motor reflex and autonomic functions (in conjunction with cranial nerve nuclei and spinal cord)
What structures are contained within the rostral component of the reticular formation and how are they defined?
Structures contributing to modulation of forebrain activity in the rostral part of the reticular formation consist of long projection systems (the "ascending reticular activating system") defined by their neurotransmitters, and include: Locus cereleus (NA) Substantia nigra (DA) Dorsal raphe nuclei (5HT) Certain cholinergic nuclei (ACh)
List 3 regions of the caudal reticular formation and their roles
Ventrolateral medullary reticular formation: regulates visceral functions of CNX including GI responses, respiratory activities and CV responses
Lateral medullary and pontine reticular formation: chewing
Region surrounding facial nucleus: crying, smiling
What are the 2 major ascending tracts traversing the brainstem?
Dorsal column-medial lemniscus system
Anterolateral system
What does the dorsal column-medial lemniscus system detect and where does it cross?
Detect fine touch (tactile) and vibration
Crosses to the medial lemniscus in the medulla
What does the anterolateral system detect and where does it cross? Where does each of its 3 pathways terminate?
Detects pain
Crosses in the spinal tract
Terminates in thalamus, midbrain or reticular formation
What is the name of the descending tract traversing the brainstem and what is its role? Where does it cross?
Corticospinal tract
Controls motor function
Crosses at the pyramidal decussation
What structures in the basis of the midbrain, pons and medulla have a role in regulating control of the descending motor pathways?
Midbrain: cerebral peduncles, substantia nigra, red nuclei
Pons: cerebellar nuclei, middle cerebellar peduncle
Medullar: inferior olivary nuclei
What is locked-in syndrome?
Generally caused by injury to the ventral pons with preservation of the survival centres (reticular formation) in the medullar
The patient is aware but cannot move or communicate verbally due to complete paralysis of all voluntary muscles in the body except the eyes
List all 12 cranial nerves in order
I: olfactory II: optic III: oculomotor IV: trochlear V: trigeminal VI: abducens VII: facial VIII: vestibulocochlear IX: glossopharyngeal X: vagus XI: accessory XII: hypoglossal
Which nuclei are located within the somatic motor column of the brainstem?
Extra-ocular muscles (movers of the eyeball; CNIII, CNIV, CNVI)
Muscles of the tongue (CNXII)
Which nuclei are located within the branchial arch column of the brainstem?
Muscles of mastication (CNV3)
Muscles of facial expression (CNVII)
Muscles of pharynx and larynx (nucleus ambiguus; CNIX innervating stylopharyngues, CNX innervating levator palati)
Where is the nucleus ambiguus located?
Within the medulla behind the inferior olive
Which nuclei are located within the visceral efferent column of the brainstem?
Edinger-Westfal nucleus (CNIII)
Superior salivatory nucleus (CNVII)
Inferior salivatory nucleus (CNIX)
Dorsal motor nucleus of CNX
Which nuclei are located within the visceral afferent column of the brainstem?
Nucleus solitarius: Gustatory nucleus (rostral; CNVII, CNIX, CNX) Visceral sensory division/autonomic (caudal; CNIX, CNX)
What kind of information is transmitted through the visceral sensory division of the nucleus solitarius?
CNIX: baroreceptors and chemoreceptors from carotid body and sinus
CNX: afferents from heart and abdominal viscera
Which nuclei are located within the somatic sensory column of the brainstem?
Sensation to face, forehead, mucosa of nose and mouth, most of cranial dura (CNV)
Skin behind ear and lining of external auditory meatus (CNVII, CNIX, CNX)
Which nuclei are located within the special sensory column of the brainstem?
Smell (CNI)
Vision (CNII)
Hearing and equilibrium (CNVIII)
Where does CNI exit the skull?
Cribiform plate
How is visual information transmitted to the visual cortex?
The optic nerve is formed from the axons of the ganglion cells of the retina
Some axons cross within the optic chiasm and then travel to the ganiculate nucleus within the thalamus
Neurons travel from the thalamus to the visual cortex in the occipital lobe
Which extra-ocular muscles are controlled by CNIII?
Superior rectus
Inferior rectus
Medial rectus
Inferior oblique
Which extra-ocular muscles are controlled by CNIV?
Superior oblique
Which extra-ocular muscles are controlled by CNVI?
Lateral rectus
Describe the passage of CNIII, CNIV, CNVI
Through the cavernous sinus, exiting at the superior orbital fissue
CNIII and CNVI go through the common tendinous ring
What are the motor functions of CNIII?
Extra-ocular muscles SR, IR, MR, IO
Levator palpebrae superioris
PS innervation to iris (pupils) and ciliary muscle (for focussing)
What forms the superior orbital fissure?
Greater and lesser wings of the sphenoid
Where does CNII exit the skull?
Optic canal
Where do CNVII and CNVIII exit the skull?
Internal acoustic meatus
Where do CNIX, CNX and CNXI exit the skull?
Jugular foramen
Where does CNXII exit the skull?
Hypoglossal foramen
What inputs and outputs are involved in the pupillary reflex and what is used to assess?
Sensory input to the brain from the retina via CNII
Motor outputs to sphincter pupillae in the iris via PS fibres of CNIII (EW nucleus)
Used to assess midbrain function
What are the 3 main functions of CNV?
Sensory input from the face, parts of the ear, meninges and inside of the face
Motor to muscles of mastication and tensor tympani in the inner ear
What are the 4 nuclei of CNIV? Where are they located and what is their role?
Mesencephalic in midbrain for proprioception
Chief sensory in pons for fine touch
Spinal trigeminal nucleus in medulla/spinal cord for pain and temperature
Motor nucleus in pons for muscles of mastication and tensor tympani
Which ascending systems do the chief sensory and STN of CNV mimic, respectively?
Chief sensory: dorsal column-medial lemniscus system
STN: anterolateral system
Where does the motor component of CNV run?
With the mandibular division of the sensory component
What are the 3 sensory components of CNV?
V1: opthalmic
V2: maxillary
V3: mandibular
Where do the 3 sensory divisions of CNV leave the skull?
V1: superior orbital fissure
V2: foramen rotundum
V3: foramen ovale
What inputs and outputs are involved in the corneal reflex and what is it used to assess?
Sensory input via CNV1
Motor outputs to eyelid (orbicularis oculi muscle) via CNVII
Used to assess pontine function
What are the 2 main divisions of CNVII and what are their functions?
Facial nerve proper: innervates muscles of facial expression, stapedius (ear) and part of the digastric
Nervus intermedius: PS to lacrimal, sublingual and submandibular salivary glands, taste from anterior 2/3 tongue and soft palate, and sensation from small region near external auditory meatus
Describe the course of CNVII
Exits via the internal acoustic meatus
Gives off the greater petrosal nerve to the lacrimal gland
Gives off branch to stapedius
Gives off chorda tympani to the tongue
Travels through the stylomastoid foramen
Gives off terminal branches including the temporal, zygomatic, buccal, mandibular, cervical and posterior auricular nerves
What is the function of the stapedius muscle?
Sound dampening
Where are the nuclei for CNVIII located?
Dorsal and ventral cochlear nuclei, and 4 vestibular nuclei, all located In the brainstem at the border of the pons and medulla
What are the 4 main functions of CNIX?
Sensory from tongue (posterior 1/3), pharynx, middle ear and carotid body
Taste from posterior 1/3 of tongue
PS innervation to the parotid
Motor to the stylopharyngeus
Describe the course of CNIX
Exits via jugular foramen lateral to and in front of CNX and CNXI
Superior and inferior ganglia follow the stylopharyngeus to reach the oropharynx and tongue
What are the 4 main functions of CNX?
Motor to soft palate, pharynx, larynx, upper oesophagus, palatoglossus
PS innervation from pharynx to upper abdomen
Sensory from pharynx, larynx and oesophagus
Visceral input from baroreceptors and chemoreceptors of the aortic arch
What inputs and outputs are involved in the gag reflex and what is it used to assess?
Sensory inputs to pharynx via CNIX
Motor outputs to pharynx via CNX
Used to assess medulla function
What is the role of CNXI?
Motor output to sternocleidomastoid and upper part of trapezius
Describe the route of CNXI
CNXI nucleus is located in the upper 5-6 cervical spinal cord
Nerves enters the cranium via foramen magnum
Nerve travels with CNX roots and exits jugular foramen
What is the main function of CNXII?
Provides motor innervation to intrinsic and extrinsic muscles of the tongue, except palatoglossus
What is a symptom of CNXII dysfunction?
Atrophy of the tongue muscles
If unilateral, the tongue deviates to the atrophied side
