vision
What are the four main layers of the eyeball, and what are their functions?
1) Sclera --> white of eye, extra ocular muscle attachment, protective function as well
2) Choroid/uvea --> vascularized, contains ciliary body that produces aqueous humor, absorbs light
3) Retinal Pigment Epithelium --> absorbs light, sustains neural retina
4) Neural Retina --> photoreceptors, fovea, and neural projections to rest of visual pathway
*note: there is a potential space between RPE and NR, becomes real in a retinal detachment
A blind child is able to read braille. What is the mechanoreceptor responsible for this ability?
- Merkel-neurite cell complex. Aβ fibers allow for sensing texture and form
*also know other types of mechanoreceptors and their functional roles.
compare and contrast symptoms of upper motor neuron (UMN) damage versus lower motor neuron (LMN) damage.
UMN: spastic paralysis, increased tone, hyperreflexia, positive babinski reflex
LMN: flaccid paralysis, decreased tone, hyporeflexia, fasciculations (only in early stages of LMN loss)
compare vestibulocollic/vestibulocervical versus vestibulospinal reflexes.
Vestibulocollic: stabilizes head in relation to body movement via MVST (traveling through MLF)
Vestibulospinal: stabilizes body in relation to head movement via LVST
You're playing baseball and the pitcher throws the ball straight at your head; it hits your head, right at the bridge of your nose. Months later you still can't smell. Explain what happened.
- head trauma from baseball --> sheared olfactory nerve processes traveling through cribriform plate on their way to the olfactory tract.
- this is a form of sensorineural anosmia (total loss of smell due to nerve damage)
compare and contrast nasal and temporal hemiretina, and their visual fields they're responsible for.
temporal hemiretina: remain ipsilateral straight to LGN; they are responsible for the medial visual fields of each eye.
nasal hemiretina: decussate at optic chiasm before synapsing in LGN; are responsible for lateral visual fields of each eye.
What general "rule" of neuroanatomy does the mesencephalic nucleus of CN V not follow? Hint - think CNS vs PNS
What information is carried to this nucleus?
- primary sensory afferent cell bodies found in CNS (NOT PNS)
- these are proprioceptive fibers for jaw muscles of the head
You're in middle school and notice you can't read the front of the board anymore during class, but when you sat closer to the board you could read it again. Your mom takes you to the eye doctor and you end up getting glasses. What type of corrective lens will you get, and what type of visual refractive error do you have?
You have myopia (short-sightedness), and receive a concave lens to help correct it.
compare and contrast ascending MLF versus descending MLF.
Ascending MLF : carries information for VOR, and coordinates other eye movements.
Descending MLF : carries MVST for coordinating vestibulocollic reflex and neck muscle movements
Compare the differences between papillae on the tongue based on region and innervation. Also compare the different types of taste cells that papillae contain.
Papillae Types:
- Fungiform papillae: anterior 2/3 of tongue, innervated by CN VII
- Foliate papillae and circumvallate papillae: posterior 1/3 of tongue, innervated by CN IX (foliate is lateral, circumvallate is medial)
- pharynx and upper epiglottis: no papillae here, but taste sensation by CN X
taste cells: made by basal cells
type I: supportive, possibly salty taste
type II: sweet and umami (GPCR T1R2 and T1R3), bitter (GPCR T2R)
type III: sour (and possibly salty taste) and integrative (have synapses)
What layers of the lateral geniculate nucleus carry ipsilateral information? From which hemiretina (temporal/nasal)? What about contralateral information?
ipsi: layers 2,3, and 5; temporal retinal projections
contra: layers 1,4,6; nasal retinal projections
*all of these fibers then project to the primary visual cortex into ocular dominance columns in layer four of the visual cortex.
compare and contrast the brachium of the superior colliculus versus the brachium of the inferior colliculus in terms of pathway and function/modality.
brachium of superior colliculus: carries visual, reflexive information TO the superior colliculus from the optic tract
brachium of inferior colliculus: carries auditory information AWAY from the inferior colliculus towards the medial geniculate nucleus
A stroke occurs in the middle cerebral artery, specifically the branch supplying the pars opercularis and pars triangularis of the inferior frontal gyrus. What symptoms might you expect to see in that patient?
-Pars opercularis and triangularis --> Broca's area
- symptoms of Broca's aphasia: broken but sensible speech, difficulty producing words and halts often while talking, poor grammar
What's direction is the VOR for a right head turn?
Left SCC: hyper polarized, inhibitory signals to right lateral rectus and left medial rectus muscles
Right SCC: depolarized as endolymph pushes stereo cilia towards kinocilium, releasing glutamate onto vestibulocochlear nerve. Sends processes to synapse at ipsilateral vestibular nuclei. From there, fibers travel contralaterally to left abducens nucleus which sends axons releasing Ach onto left-side lateral rectus muscle. Abducens nucleus also has fibers that cross back to the right side into the oculomotor nucleus. Fibers from this nucleus then excite the medial rectus muscle on the left side. This ultimately causes the eyes to slowly shift left as the head turns to the right.
Your friend is complaining of ipsilateral hearing loss. Their level of their damage can be no farther than what neuroanatomical structure in the auditory pathway?
Cochlear nucleus (in superior medulla brainstem level). If lesion occurs beyond this point in the auditory pathway, there would be partial/total hearing loss bilaterally, since information travels bilaterally after this point in the auditory pathway.
An aneurysm of the right anterior choroidal artery (supplies optic tract) leads to what visual deficits?
- anterior choroidal artery: supplies optic tract
- optic tract: contains ipsilateral temporal retina and contralateral nasal retina; lesion results in left visual field deficits in both eyes
What's the function of the lateral cuneate nucleus? Describe the entire pathway surrounding this nucleus (modality, ultimate target, origin of the tract, if it crosses midline, etc)
- Like nucleus dorsalis/thoracic nucleus of clarke but for upper body unconscious proprioception
- unconscious proprioceptive fibers traveling in fasciculus cuneatus synapse in the lateral cuneate nucleus --> higher order neurons carry upper body proprioceptive information to the cerebellum via the inferior cerebellar peduncle
- NEVER crosses midline
An embolus gets lodged in the superior basilar artery, blocking blood flow to downstream vessels. What brainstem level(s) would be severely impacted by this, and which level(s) would be largely unimpacted?
heavily impacted: pons and midbrain (primary blood supply for pons is basilar artery, and midbrain is supplied by SCA, a branch off of basilar, as well as some PCA)
minimal impact: medulla (supplied by PICA, anterior spinal artery, and vertebral arteries, all of which are located below level of embolus and thus blood flow would be unimpacted)
A young man is taken into the emergency room after a motorcycle crash, with a lesion of the left vestibular nuclei. What symptoms will you see?
- look away from lesion, lean towards lesion.
- Look away: without firing of the left vestibular nucleus in VOR, the right vestibular nucleus becomes hyperactive. Thus, it is interpreted as a constant head turn to the right --> slow phase deviates eye to the left, but fast (corrective) phase snaps eye focus to the right --> right beating nystagmus (look away from lesion on the left side)
- Lean towards: vestibular nuclei carry information ipsilaterally. If the left vestibular nucleus is damaged, there would be loss of vestibular innervation to antigravity and postural muscles within vestibulospinal and vestibulocollic reflexive pathways. This lack of innervation, coupled with the contralateral side continuing to have baseline firing of antigravity muscles from that vestibular nucleus causes the body (and head) to lean towards the lesion.
You walk into the new bakery in town and smell your Grandma's best pumpkin pie, giving you a warm feeling of childhood nostalgia. Explain how this happened using the olfactory transduction pathway.
odorous stimulus binds to receptor proteins on olfactory receptor cells (ORCs) --> excites the cell --> creates electrical signal carried through cranial nerve I (olfactory) to specific glomeruli in the olfactory bulb --> synapses and travels to ipsilateral piriform cortex, amygdala, and hippocampus --> hippocampus is responsible for recalling those childhood memories!
*ONLY pathway that doesn't have a thalamic relay nucleus
A patient comes to the ER after a motor vehicle accident, featuring a contrecoup injury heavily impacting the left posterior cerebral artery. What visual deficits will they have?
- Left posterior cerebral artery damage --> left occipital lobe (primary visual cortex) damage --> RIGHT visual field deficits in both eyes
*also know about Meyer's loop and how visual deficits would present if there was a lesion there (answer in lab 8)
Compare the spinal/descending nucleus of V, principal nucleus of V, mesencephalic nucleus of V, and motor nucleus of V in terms of function, and how they interact with each other.
Spinal: slow somatosensation for the head only, sends axons to contralateral VTT to go to thalamus
Principal nucleus: fast somatosensation for head, sends axons to contralateral VTT and joins with fibers that are coming up from the spinal tract of V
*at level of principal nucleus and above, VTT carries fast AND slow somatosensory fibers
Mesencephalic nucleus: contain cell bodies of primary sensory afferents for proprioception of the head. Has projections to principal nucleus (then to VTT), but also unconscious projections to motor nucleus for reflexes (ex. jaw jerk reflex)
Motor nucleus: has projections to jaw muscles. receives proprioceptive input from mesencephalic nucleus (jaw jerk reflex), as well as conscious motor input for chewing and jaw movements.
A patient comes in with an incomplete brain stem injury, shown in the following image. What sensory symptoms might they have?
- Brain stem level: large fourth ventricle + pontine nuclei = inferior pons
- left sided lesion
left ML damaged: right-side fast ss deficits for body
left VTT damaged: right-side slow and fast ss deficits for head
left ALS damaged: right-side slow ss deficits for body
left ICP/restiform body damaged: left-side unconscious proprioception deficits for body
left spinal trigeminal nucleus/tract damaged: left slow ss deficits for head
left solitary nucleus damaged: taste loss on left side
left vestibular nuclei damaged : ipsilateral vestibular sense deficits, ataxic gait towards left side
*while not labeled in Haines, principal, mesencephalic, and motor nucleus of V are visible on contralateral side so one can assume these nuclei would also be damaged on the left side, leading to ipsilateral (left) fast somatosensory loss, including proprioceptive, reflexive fibers from mesencephalic nucleus, and motor neurons for jaw from the motor nucleus.
two patients come into the ER with stroke-like symptoms and you determine for patient #1 the stroke is in the posterior spinal artery, while patient #2's stroke was located in the posterior inferior cerebellar artery. Compare and contrast the symptoms for these patients, specifically in the context of ataxia.
Patient #1: sensory ataxia
- posterior spinal artery supplies the dorsal columns, responsible for fast somatosensation of the body; loss of the function of DCML causes sensory ataxia.
- symptoms of sensory ataxia: 'stomping' gait, positive Romberg test, use of visual input to aide in walking and balance
Patient #2: motor (cerebellar) ataxia
- PICA supplies aspects of the cerebellum, so without it, one would develop motor ataxia (end of the dorsal spinocerebellar tract)
- symptoms of motor ataxia: intention tremor, gait and balance not improved with visual input
You and your friends go to a haunted corn maze in town to begin the spooky season festivities. When a scare actor jumps out from the corn stalks at you, your friend lets out a high-pitched scream. Follow this high-frequency sound wave through your auditory pathway until it reaches your primary auditory cortex.
1) Outer Ear: Gathering sound
- The sound wave is funneled into the auditory canal via the pinna
2) Middle Ear: Amplifies sound
- sound vibrations hit tympanic membrane which then pushes on ossicles, both which amplify sound vibrations
3) Inner Ear: cochlear transduction
- Amplified sound vibrations finish traveling through the stapes and enter the cochlea.
- perilymph of Scala vestibuli moves due to pushing of stapes, which then moves endolymph of Scala media
4) transduction pathway in cochlear duct
- prestin proteins in OHCs cause tectorial membrane to shake which helps move endolymph of Scala media (amplify signal going to IHCs)
- higher frequency stimulus from the scream will vibrate the more narrow and stiff base of the basilar membrane
- inner hair cells depolarize when stereocilia moved to tall side, sends neural signal via CN VIII
5) Neural pathway:
- Branch of CN VIII auditory nerve carries signal to ipsilateral cochlear nucleus then bilateral to: superior olivary nucleus --> inferior colliculus (via LL) --> medial geniculate nucleus (via brachium of IC) --> transverse temporal gyrus (primary auditory cortex)