NBB 1 Part 2 Flashcards
Describe the ventricular spaces associated with each of the subdivisions of the brainstem
- Cerebral aqueduct of Sylvius between 3rd and 4th ventricles is in the midbrain
- 3rd ventricle is in the diencephalon
- 4th ventricle dorsal to pons, shared between pons and rostral medulla (which has choroid plexus on dorsal side at caudal end of 4th ventricle)
What are the exit points for CSF circulation in the brainstem?
Where does CSF go afterwards? What are the cisterns
- Foramen of Magendie (medial)
2 + 3. Foramina of Luschka (lateral)
Drains into cisterna magna (second place you can obtain CSF fluid, after spinal tap) –> subarachnoid space –> drained via arachnoid granulations –> venous sinus
Cisterns: magna, prepontine, interpeduncular, and quadrigeminal
Differentiate between the levels of the brainstem (medulla, pons, midbrain) and explain the basis for their gross anatomical differences:
1. Medulla
- Medulla:
A. Ventral side of rostral medulla: anteromedial fissure for anterior spinal artery
-Most medial - pyramid
- then olive - covers the inferior olivary nucleus (winding snake like appearance)
- then inferior cerebellar peduncle
B. Dorsal side of rostral medulla:
-4th ventricle, plus choroid plexus
C. Ventral side of caudal medulla:
-pyramidal decussation of corticospinal tract (motor tract for body from primary somatosensory cortex)
D. Dorsal side of caudal medulla:
-gracile tubercle (2nd order synapse of axons from lower limbs from sensory DCMLS)
-cuneate tubercle (2nd order synapse of axons from upper limb from sensory DCMLS)
Review DCMLS and STT pathways and where they pass through the medulla
DCMLS: vibration, proprioception, soft touch
1st order in DRG, 2nd is gracile and cuneate nuclei of caudal medulla, decussation as internal arcuate fibers of lower medulla, ascends via medial lemniscus, 3rd order is VPL of thalamus
-travels through medial medulla
STT: pain, temperature, crude touch
1st order in DRG, 2nd order is Lissauer’s tract in dorsal horn, decussates at anterior white commissure and ascends for 2 spinal cord levels, ascends via anterolateral system, 3rd order is VPL of thalamus
-travels through lateral medulla
- Name the motor and sensory pathway that synapse in the medulla
- Name the motor and sensory pathway that travel through the medulla
1A.Corticobulbar (synapse with CN LMNs)
B. DCMLS (ipsilateral cuneate/gracilis nucleus then decussates as internal arcuate fibers)
2A. Corticospinal (pyramidal decussation then synapse in anterior horn of spinal cord)
B. Spinothalamic (synapse in Lissauer’s tract and decussate at anterior white commissure of spinal cord)
- What is the difference between a nerve and a tract?
- Define functions of the types of motor nuclei:
A. Somatic efferent nuclei
B. Visceral efferent nuclei - general
C. Visceral efferent nuclei - special
3. Define functions of the types of sensory nuclei: A. Somatic afferent nuclei - general B. Somatic afferent nuclei - special C. Visceral afferent nuclei - general D. Visceral afferent nuclei - special
- Both are bundles of axons
Nerve is in touch with periphery, tract with CNS - A. Somatic efferent nuclei GSA: framework of body e.g. skeletal muscles that originate from embryonic somites
B. Visceral efferent nuclei- general GVE: parasympathetic fibers for smooth muscles (viscera)
C. Visceral efferent nuclei - special SVE: activates striated muscle (from embryonic branchial arches i.e. jaw, face, larynx, pharynx, trap, sternocleidomastoid) - Somatic afferent- info about changes in environment from framework of body (receptors)
A. General GSA- impulses that begin near the body surface e.g. pain, temp, touch pressure
B. Special SSA- highly specialized sensory systems e.g. vision (light) and hearing (sound)
Visceral - impulses arising in/around the viscera or organs
C. General GVA- receptors from mucous membrane or in organ walls - physical (distension) or chemical composition
D. Special SVA- specialized chemical stimuli i.e. smell, taste
Describe distribution of cranial nerves throughout the brainstem and medially/laterally
Rule = 2:2:4:4 (out:Md:Po:Me)
I and II - outside the brainstem
II and IV - in midbrain
V, VI, VII, VIII - in pons
IX, X, XI, XII - in medulla.
Motor CNs are more medial, sensory more lateral e.g. VIII is most lateral
Medulla - most medial is hypoglossal nucleus, then parasympathetic dorsal motor nucleus of X, then sulcus limitans line, then sensory nuclei (spinal trigeminal, nucleus solitarius, vestibular nuclei)
CN XII (Hypoglossal) I. Which part of the brainstem does it travel through? II. What are its functions? III. Lesion of UMN (corticobulbar tract) vs LMN (hypoglossal nerve) vs bilateral lesion
I. XII is between olive and pyramids in the medulla (ventral side)
hypoglossal trigone on the floor of the 4th ventricle (dorsal side) –> visual aspect of the hypoglossal nucleus, which is a cell column –> LMNs extend the full length of the medulla
II. Innervated by:
A. Voluntary movements/articulation
- UMNs form corticobulbar pathway from cerebral cortex –> crossed/contralateral innervation (e.g. R cortex to L hypoglossal nucleus)
-LMNs from hypoglossal nucleus innervate all extrinsic and all but one (palatoglossus - CN X) extrinsic tongue muscles
-GSE - ipsilateral tongue muscles –> controls movement of tongue, maintains muscle tone
B. Reticular neurons for automatic/reflex movements - control of movements while eating and swallowing
III. Corticobulbar tracts usually bilateral, BUT are contralateral for XII
UMN lesion –> tongue deviates to opposite side of damage (e.g. if you lesion L corticobulbar tract –> affects R hypoglossal nerve –> tongue deviates to R side)
LMN lesion –> tongue deviates to same side of damage (e.g. if you lesion L hypoglossal nerve –> tongue deviates to L side) + severe muscle atrophy
Bilateral lesion –> disability speaking, swallowing food; due to motor neuron disease, demyelination (ALS), bleeding, tumors of medulla / base of skull
CN XI (Spinal Accessory) I. Which part of the brainstem does it travel through? II. What are its functions? III. What happens with lesion?
I. Lateral to XII in the medulla, one part from medulla (Accessory nucleus), other part is ventral motor horn of cervical spinal cord
II. CN XI = motor
A. SVE Branchial motor part –> innervates ipsilateral sternocleidomastoid and trapezius muscles (neck and shoulder) Special visceral efferent
B. Visceral motor part –> control of larynx, joins CN X
III. Lesion:
- cannot rotate head towards healthy side (away from lesion) against pressure
- ipsilateral shoulder drop
- weakened voice or hoarseness
CN X (Vagus) I. Which part of the brainstem does it travel through? II. What are its functions? III. What happens with lesion?
I. Efferent fibers exit medulla between olive and inferior cerebellar peduncle on ventral side; vagal triangle is also on the floor of the fourth ventricle on dorsal side, overlies the dorsal motor vagal nucleus adjacent to hypoglossal nucleus
-Although LMNs from multiple nuclei inside brainstem – axons come together to form single bundle at CNX level of medulla
II. CN X is mixed
A. Motor components:
1. general visceral efferent (dorsal vagal nucleus)–> preganglionic parasympathetic –> ganglia for heart, lungs, GI to splenic fixture
2. special visceral efferent /branchial efferent (nucleus ambiguus) –> pharyngeal muscles (swallowing), laryngeal muscles (vocalization)
B. Sensory components:
- GSA (joins nucleus of CN V) - touch, pain, pressure from small parts of face –> pharynx, meninges, small region of external ear (conscious)
- SVA (rostral nucleus solitarius)- taste for small part of mouth –> epiglottis and posterior pharynx
- GVA (caudal nucleus solitarius)- from chemoreceptors and baroreceptors from aortic arch (subconscious)
III. bilateral lesion is fatal !
Unilateral lesion - motor affected first –> contralateral uvula deviation, ipsilateral vocal muscle paralysis
CN IX (Glossopharyngeal) I. Which part of the brainstem does it travel through? II. What are its functions? III. What happens with lesion?
I. Exits upper medulla rostral to vagus nerve (bw olive and cerebellar peduncle)
II. CN IX is mixed
A. Motor components:
1. GVE (inferior salivator nucleus in the pons) - pregang parasympathetics for parotid gland
2. SVE / branchial efferent (nucleus ambiguus) - stylopharyngeal muscle –> elevates pharynx during talking and swallowing
B. Sensory components:
- GSA- touch pain pressure from small parts of face –> pharynx, posterior 1/3 tongue, middle ear, small region of external ear (conscious)
- SVA (rostral nucleus solitarius)- taste from posterior 1/3 tongue
- GVA (caudal nucleus solitarius)- chemoreceptors and baroreceptors from carotid body (subconscious)
III. problems with coughing, saying “Aah”, blowing out cheeks; due to polio, ischemic lesions, motor neuron disease, etc.
Differentiate between the levels of the brainstem (medulla, pons, midbrain) and explain the basis for their gross anatomical differences:
2. Pons
- Pons
A. Ventral side - 2 corticospinal tracts on ventral side, one CN trying to reach cerebellum
B. Dorsal side - facial colliculus, 3 cerebellar peduncles - superior, middle (made of contralateral pontine nuclei fibers), inferior; 4th ventricle
CN V (Trigeminal) I. Which part of the brainstem does it travel through? II. What are its functions and motor/sensory nuclei? III. What happens with lesion?
CN V (Trigeminal) I. Small motor part exiting on dorsal side but large sensory part coming in through middle cerebellar peduncle
- innervations are ALL ipsilateral
- V3 includes anterior 2/3 tongue (taste for that region comes from VII
II. Mixed - 4 nuclei
A. Motor components:
1. SVE/branchial motor (trigeminal motor nucleus)- muscles of mastication + tensor tympani muscle + bilateral corticobulbar projections for voluntary chewing
*more medial to the principal sensory nucleus, fibers leave from dorsal side
B. Sensory components:
- GSA - crude touch, pain, and temp + noxious stimuli/ nociception from V1-V3 (spinal nucleus) –> trigeminothalamic tract
- GSA - fine touch and pressure from V1-V3 (chief/ principal sensory nucleus) –> trigeminal lemniscus tract e.g. afferent aspect of c
- GSA - unconscious proprioception and bite strength (mesencephalic nucleus) –> NO tract to thalamus; only primary sensory neurons already in CNS, in the mesencephalic nucleus –> goes from pons to the midbrain
III. Lesion
- atrophy and chin deviation on side of lesion
- trigeminal neuralgia - idiopathic, brief severe pain in V2-V3 but facial sensation normal
- loss of jaw jerk reflex
CN V.
Describe the trigeminothalamic pathway (i.e. Trigeminal Chemosensory pathway)
Trigeminothalamic pathway - conveys pain and temperature from the head and face to thalamus for CN V (general sensory afferent)
*conveys nociception / noxious stimuli detection (eg chili peppers, vinegar) - separate pathway from CN I
1st order neuron - trigeminal ganglion outside the pons
fibers go downwards from pons
2nd order neuron - ipsilateral spinal nucleus of V (medulla) or in the spinal cord
ascends and decussates at the pons and medulla (at 2 levels) –> create trigeminothalamic fibers
3rd order neuron - VPM nucleus of thalamus
*Spinal Nucleus V also receives afferents that enter brainstem with
IX - sensation for back of ear, posterior 1/3 tongue, upper pharynx
X - sensation for pharynx, larynx, external ear
CN V.
Describe the trigeminolemniscal pathway
Trigeminolemniscal pathway - conveys touch and pressure from head and face to thalamus for CN V (General sensory afferent)
1st order neuron - trigeminal ganglion outside the pons
fibers enter and synapse right away
2nd order neuron - principal sensory nucleus of V in the pons –> decussation only at pontine level
3rd order neuron - VPM of thalamus
CN VII ( Facial) I. Which part of the brainstem does it travel through? II. What are its functions and motor/sensory nuclei? III. What happens with lesion?
CN VII
I. Ventral pons - nerve exits laterally to VI at the ponto-medullary junction
Dorsal pons - facial colliculus on floor of 4th ventricle - consists of fasicles of facial nerve looping around abducens nucleus
II. CN VII - Mixed
A. Motor components:
1. SVE - muscles of facial expression - stapedius muscle and part of digastric muscle motor parts of corneal, sucking, and blinking reflexes
2. GVE - pregang parasympathetic for salivatory gland (lacrimal, sublingual, submandibular) EXCEPT parotid (IX)
B. Sensory components:
- GSA - sensation from small region near outer ear (also IX, X)
- SVA - taste from anterior 2/3 tongue (sensory is from CN V, posterior 1/3 is CN IX) –> joins other taste fibers (IX, X) at the nucleus solitarius
- GVA - mucous membrane of nasopharynx
III. Lesions
A. UMN (corticobulbar tract) lesions - bilateral for upper face and contralateral for lower face –> only lower face weakness
refers to voluntary facial paresis; emotional expression comes from anterior cingulate cortex and hypothalamus –> joins corticobulbar tract at facial nucleus LMNs
B. LMN (CN VII) lesion e.g. Bell’s Palsy - ipsilateral for upper and lower face –> unilateral facial weakness, dry eye, loss of taste
Differentiate between the levels of the brainstem (medulla, pons, midbrain) and explain the basis for their gross anatomical differences:
3. Midbrain
- Midbrain
A. Ventral side - cerebral peduncles (axons) with interpeduncular fossa in between (interpeduncular cistern) and CN III oculomotor nerve exiting *CN III between superior cerebellar artery (SCA) and posterior cerebral artery)
B. Dorsal side (back side) - trochlear CN IV exits; cerebral aqueduct; quadrigemina composed of paired superior (visual) and inferior (auditory) colliculi (collection of cell bodies) –> quadrigeminal cistern
Midbrain contributes one tract to medial motor system (superior colliculus –> tectospinal - head movement) and one to lateral (red nucleus –> rubrospinal - voluntary contralateral flexors)
Describe the vascular supply of the midbrain and conditions that arise if it is compromised
Posterior cerebral artery - covers the cerebral peduncles where all the motor pathways (corticobulbar, corticopontine), and sensory pathways (anterolateral, spinothalamic, trigeminal thalamic, trigeminal lemniscus) are together
-covers substantia nigra, red nucleus, descending sympathetic fibers
Describe the development of the eye.
What are clinical implications of eye development?
Eyes form as an outgrowth the CNS (other sensory systems formed peripherally)
- Optic vesicle induces overlying ectoderm to differentiate into lens epithelium
- Optic vesicle folds in on itself and pulls in the forming lens
- Lens separates from ectoderm
- Outer layer differentiates into retinal pigmented epithelium; inner layer becomes neural retina –> retinal layer
- Surrounded mesenchyme becomes sclera (tough outer layer) and uvea (vascular layer)
optic nerve –> optic sheath –> subarachnoid space where CSF flows through –> dura
so increased intracranial pressure –> compresses optic nerve –> impairs venous return –> papilledema (optic nerve swelling that can be visualized through the pupil)
*swelling of optic nerve due to other causes = intraocular optic neuritis
What are the 3 distinct layers of the eye and their functions?
What are the segments of the eye?
3 layers (ie spheres lying inside one another):
I. tough outer layer –> sclera and cornea
II. vascular layer –> uvea with choroid posterior and ciliary body/lens and iris anterior
III. third inner layer –> retina, incomplete sphere with only posterior aspect
Fluid-filled segments:
1. Posterior segment - from retina to back of lens, filled with vitreous humor –> slow turnover
2. Anterior segment - from lens to cornea, filled with aqueous humor –> constantly replenished
A. Anterior chamber - in front of iris
B. Posterior chamber - behind iris
- Describe process of closing/opening eye
- Describe process of lacrimation
A. Dry eyes stimulation
B. lacrimation stimulation
1A. Opening eye - levator palpebrae superioris (CN III) and superior tarsal (sympathetic from superior cervical ganglion)
B. closing eye - obicularis oculi (CN VII) - orbital and palpebral portions motor limb of corneal reflex
- Lacrimation - lacrimal gland is superior and lateral –> produces tears which flow across eyes –> drain into lacrimal ducts near caruncle –> drain into inferior nasal meatus
sympathetic and parasympathetic (via CN VII) innervation:
A. dry eye signaled via afferent limb CN V to chief/principal sensory nucleus of trigeminal nerve
B. lacrimation stimulated via efferent limb of CN VII (parasympathetic fibers from superior salivary nucleus travel through greater petrosal nerve –> synapse on pterygopalatine ganglion –> innervate lacrimal gland)
I. Describe how the eye regulates light intensity.
II. Describe normal light and consensual reflexes
III. Differentiate bw light reflex results with II vs III lesion
I. Iris has 2 opposing muscle groups that regulate pupil diameter:
- Sphincter pupillae (parasympathetic via CN III; Edinger-Westphal nucleus) –> lesion leads to mydriasis “blown pupil”
- Dilator pupillae (sympathetic) –> dilates by pulling on sphincter muscle –> lesion leads to miosis
II. Light stimulus leads to constriction of stimulated (“direct”) and contralateral (“consensual”) pupils
Pathway: light –> afferent is II (i.e. optic nerve)–> information goes to prectal nucleus –> bilaterally to Edinger-Westphal nucleus (outer part of CN III nucleus)–> efferent limb is III –> synapses in parasympathetic ciliary ganglion –> postganglionic parasympathetic innervation to sphincter pupillae
III. Complete CN II lesion –> no direct or consensual reflex
Partial II lesion/ relative afferent pupillary defect / Marcus Gunn pupil –> decreased constriction in affected eye appears as dilation, use “swinging flashlight” test
III lesion –> no direct reflex, but consensual reflex still exists
Describe how the eye focuses light.
Describe role of lens in this process
What happens with presbyopia?
Light entering the eye is refracted by the cornea (bending) and the lens (fine tuning) to focus rays on the retina –> image is rotated 180 degrees
- myopia = image focused anterior to retina
- hypermetropia (far-sighted) = image focused posterior to retina
Lens changes thickness depending on object distance
- Distant objects: Ciliary muscle relaxed, Zonules (Suspensory ligaments) pull on lens –> lens is elongated and flattened (overcomes lens capsule force)
- Near objects: Ciliary muscle (parasympathetic innervation via Edinger-Westphal nucleus, part of ciliary body) contracts, Zonules relaxed –> lens capsule takes over and squeezes on the muscle –> lens becomes round
- -> this muscle tension during accommodation is why eyes get tired after reading
Presbyopia - lens hardens with age –> capsule still works but no matter how hard it squeezes, cannot get lens in rounder shape –> far-sighted
I. Describe the retinal layers
II. Describe the interdependence of retinal pigmented epithelium and photoreceptor cells
I. Retina began as 2 layers separated by actual space –> mature retina has 3 neural sub-layers and one epithelial outer layer
Retinal layers in order of looking in through pupil:
1. retinal ganglion cells (RGCs) –> only axons that leave the eye, form optic nerve
synapses on inner plexiform layer
2. inner nuclear layer (interneurons)
synapses on outer plexiform layer
3. outer nuclear layer (photoreceptors i.e. rods for B/w and cones for color)
4. Retinal pigmented epithelium (RPE)
II. Apex of outer segment of all photoreceptor cells is buried in the RPE –> crucial for function and survival
A. Rod outer segments contains stacked discs studded with photopigments that absorb light and convert into neural signals, these discs are pushed towards the apex and phagocytized by RPEs
B. Cones have sinusoidal plasma membrane with embedded photopigments