Neuro4 Flashcards
What is the structure that houses the auditory and vestibular sense organs called?
The bony labyrinth (petrous portion temporal bone)
Where is the membranous labyrinth of the Auditory System?
Inside the bony labyrinth
- of the petrous portion of the temporal bone
What type of fluid fills the inside of the membranous labyrinth?
Endolymph
What fluid lies between the bony and membranous labyrinths?
Perilymph
Is the perilymph inside the membranous labyrinth?
NO.
It is just outside the membranous portion.
What comprises the auditory apparatus within the labyrinth?
the Cochlea
What comprises the vestibular apparatus within the cochlea?
Three semicircular canals/ducts
as well as the utricle and saccule
How does sound enter the ear?
Via outer ear and external auditory meatus and Tympanic Membrane
What is the middle ear filled with?
Air and 3 small bones
What are the 3 ossicles of the middle ear called?
Malleus (hammer)
Incus (anvil)
Stapes (stirrup)
Trace the structures involved through the inner ear beginning with the Tympanic Membrane:
Tympanic Membrane
Malleus
Incus
Stapes
(this makes up the connection between the inner and outer ear)
Is air pressure of the inner ear normally equal to atmospheric pressure?
Yes.
connected by the auditory (eustachian) tube
What connects the Stapes to the Cochlea?
The Oval Window
What are the 3 scalae (fluid filled compartments) of the inner ear?
Scala Vestibuli (superior) Scala Tympani (inferior) Scala Media (between)
Where do the scala vestibuli and the scala tympani meet?
Helicotrema
the end of the ducts
What are the scala vestibuli and scala tympani filled with?
Perilymph
What is the scala media filled with?
Endolymph
What windows open up on to the scala vestibuli and scala tympani
Scala vestibuli - Oval Window (stapes connection)
Scala tympani - Round Window
What structure houses the Organ of Corti (the sound sensing organ), and what fluid lines it?
Scala media (aka Cochlear duct) Endolymph
Trace the vibration through Cochlea, starting with stapes
Stapes > Oval window > scala vestibuli > scala tympani > Round window
What stimulates the (Basilar Membrane) hair cells of the organ of Corti?
oscillations in both the scala vestibuli and scala tympani
Why does the input to the Cochlea necessitate amplification through the ossicles?
(and amplification through concentration of sound from tympanic membrane to oval window - which is much smaller)
Fluid has a higher impedence than air
What is responsible for the transduction of mechanical vibrational energy to neural activity?
Hair cells in the cochlea
What happens when the basilar membrane moves?
Causes stereocilia to bend and change shape in relation to their FIXED tips (in tectorial membrane)
This mechanical deformation opens ion channels in the hair cells. Cation influx, generates receptor potential.
Hair cell then releases neurotransmitter > depolarizes CN VIII
Where are the cell bodies of CN VIII?
Where do their central processes synapse?
Spiral Ganglion
Cochlear nuclei
The organ of Corti lies between what two structures?
The inferior chamber (Scala Tympani) and the Scala Media
At the base of the cochlea, next to the Oval Window, the basilar membrane is ______, which optimizes sensing ______ sounds
Narrow
High frequency sounds
At the end of the cochlea, next to the helicotrema, the basilar membrane is _______, optimizing hair cells for ________ sounds.
Thick
Low Frequency
High frequency sounds (15000 Hz) have their peak amplitude near the ______, which low frequency sounds (100 Hz), have their peak amplitude near the ______.
Base
Apex
T/F
Not only is the basilar membrane thin and stiff near the oval window, but so are the ciliary hair cells (same with basilar membrane/ciliary cells being thicker/longer near the apex)
True
How many inner and outer rows of hair cells are there, and which one can alter its hair length?
1 inner 3 outer (alters - thought to selectively tune to important sounds)
Central Auditory Pathway, aka…
8CSLIMA
What does 8CSLIMA stand for?
8 - CN VIII
C - Cochlear nuclei
S - Superior Olivary nuclear complex
L - Lateral Lemniscus
I - Inferior colliculi
M - Medial geniculate
A - Primary auditory cortex (lateral temporal lobe)
How are dorsal and ventral cochlear nuclei organized, and where are they found?
Tonotopically
Medulla
Where does the central auditory pathway decussate?
Lower Pons
between the C & S in 8CSLIMA
What percentage of ascending fibers in the central auditory pathway cross at the pons and synapse on the superior olivary nucleus?
What % DON’T cross in the pons and synapse on the Reticular Formation?
about 80%
20%
What does the A in 8CSLIMA stand for, and where is it?
primary Auditory cortex
Superior Temporal Gyrus
Why would a unilateral lesion of the central auditory pathway cause more pronounced hearing loss to one side?
Which side?
The 80/20 split in the Pons, with majority crossing.
If lesion is above pons, more hearing loss opposite to lesion
If lesion below pons, more hearing loss same side of lesion
What is special about Brodmann’s areas 41 and 42
Site of the primary auditory cortex (Heschel’s gyri) in the transverse temporal lobe
Within the central auditory pathway, what are the functions of the:
Primary auditory cortex
Superior olivary nuc. and Inf. Colliculus
Reticular formation
?
Conscious hearing
Orientation/Localization of sound (Batman!)
CNS activation
What is the function of the descending efferent of CN VIII
descending auditory pathway
More inhibitory than excitatory
dampens extraneous noise - like crowd noise and background
What are the two middle ear muscles?
What is their innervation?
What is their function?
Tensor Tympani - CN V (inserts malleus)
Stapedius - CN VII (inserts stapes)
Both dampen vibration in response to loud noise (protective function)
What is Conductive Deafness, and what are 3 examples?
Interruption of sound passage
- Obstruction (foreign object)
- Otosclerosis (fixation of Stapes - excessive bone growth)
- Otitis Media (middle ear inflammation - common in children)
What is the most common cause of meningitis and the most common cause of brain abscesses?
Otitis Media
What structure and in what bone are the auditory and vestibular receptors located?
Inner ear
Temporal Bone
What is the term for nerve/perceptive deafness caused by diseases (Rubella, syphilis), drugs (aspirin, quinine), or toxins?
Sensorineural deafness
What is the degenerative hearing loss that occurs with ageing (involving degeneration at the base of the Organ of Corti), that disproportionally affects perception of high frequency sounds?
Presbycusis
What tumor, located where, can result in unilateral deafness and tinnitis?
Acoustic neuroma (aka “schwannoma”)
located at cerebellopontine angle
What causes Hyperacusis?
Damage to V or VII
- affecting Tensor Tympani or Stapedius
What is the general term (with multiple causes) for abnormal sounds of ringing, buzzing, etc.?
Tinnitus
What is the disease caused by an overproduction of endolymph (endolymphatic hydrops) or inability to absorb endolymph, resulting in tinnitus and vestibular disturbances?
(this is all caused by an increased pressure in the labyrinth)
Meniere’s Syndrome
Why won’t lesions in the 8CSLIMA pathway cause bilateral deafness?
The 80/20 cross at the pons
Do lesions of the Auditory cortex affect the ability to perceive sound frequency?
No.
Batman.
They disrupt the ability to localize the sound
T/F
Taste evolved to detect whether food is toxic/non-toxic.
True
What are the 5 main tastes, what is their primary stimuli and function?
Sweet - Sugar - (carbs=calories)
Sour - HCl or Citric acid - (acids/bacteria)
Bitter - caffeine/nicotine - (poisons)
Salty - NaCl - (water homeostasis)
Umami - L-glutamate - (peptides/proteins)
What are the 4 types of papillae?
Which ones have taste buds?
Circumvallate
Foliate
Fungiform
Filiform (most numerous - only one without taste buds)
How many types of gustatory receptor cells are there?
What are they responsive to?
I, II, III, IV
II - sweet, bitter, umami, possibly salty
III - sour
Taste receptor division of the tongue?
Ant 2/3 - VII
Post 1/3 - IX
Epiglottic - X
New terms:
Where are the 1st order sensory neurons for taste?
Geniculate Ganglion (VII - this isn't new) Petrosal Ganglion (IX) Nodose Ganglion (X)
Where is the 2nd order sensory neurons for taste? (where do they begin?)
Nucleus Solitarius - Medulla
What/where is the 3rd order sensory neurons for taste?
Ventral Posteromedial nucleus (VPM)
located in the Thalamus
What are 4 taste disorders?
Hypogeusia - reduced ability to taste
Ageusia - complete loss
Dysgeusia - distorted taste (foul tastes may persist)
Phantogeusia - phantom, unpleasant, lingering
Can third molar and middle ear surgery cause taste disorders?
Yes.
as can middle ear infections, radiation, head injury, poor oral hygiene
What divides the Aqueous and Vitreous humor?
The lens
What is the thin, watery fluid found anterior to the lens?
Aqueous humor
What is the thick, jelly-like semifluid found posterior to the lens?
Vitreous humor
Outer layer:
What is the white part of the eye?
Clear portion of the eye?
Sclera
Cornea
Name 4 structures in the middle layer of the eye.
Choroid (has vessels and nerves)
Ciliary body (involuntary muscles)
Lens (suspended and connected to ciliary body)
Iris (pigmented portion)
Do the nerves in the choroid sense light?
No. sense physical touching to eye
What CN is involved in pupillary constriction?
What is involved in pupillary dilation?
CN III (parasympathetic) T1-T2 sympathetic
What does a lesion of T1 and T2 result in?
Horner’s Syndrome
What suspends the lens from the ciliary body?
Zonula fibers
Adjustment of the shape of the lens to a more rounded shape (by the ciliary body) is called ________, and it degrades with age.
Accommodation
What is the light sensing part of the eye?
Retina
What are 3 interneurons within the retina?
Amacrine cells
Bipolar cells
Horizontal cells
What do Rods do and what are they important for?
Black and white
important for night vision
What photoreceptor is optimized for color and high visual acuity?
Cones
Where are rods and cones located?
Behind cell layers that neither absorb nor distort light
What are the most anterior cells of the Retina?
What do they form?
Retinal Ganglion cells
they eventually form CN II
T/F
The rods/cones send out graded potentials, which may or may not fire retinal gangion
True
Where is the Natural Blind Spot?
Site of optic nerve called the Optic Disk
no photoreceptors here
What is in the center of the Macula Lutea, and what does it contain?
Fovea
only Cones
site of highest visual acuity (sharp and straight ahead)
The visual map on the Retina is…
Upside down and backwards
What decussates at the Optic Chiasm?
The fields coming from the Nasal (medial) portion of the Retina
Where is the optic tract, what fibers does it contain, and where does it synapse?
Posterior to Optic Chiasm
fibers containing ganglion from Left temporal/Right nasal or Right temporal/Left nasal.
LGN (lateral geniculate nucleus - a relay nuc.)
From the eye, trace the optic signal.
Optic nerve > Optic Chiasm > Optic Tract > LGN > Optic Radiations > Primary visual cortex
On what structures in the primary visual cortex do the optic radiations terminate?
Cuneus (sup. structure, receives input from Inf. Visual Field) Lingual gyrus (inf. structure, receives input from Sup. Visual Field)
(these are separated by the Calcarine sulcus)
Primary visual cortex pathway aka:
Retinogeniculostriate pathway
What are the initially anteriorly directed axons leaving from the LGN called?
Where will they terminate and what info are they carrying?
Meyer’s Loop
Lingual gyrus
superior visual field
What will a lesion of Meyer’s loop cause?
Contralateral superior quadrantanopia
How are neurons in the visual cortex categorized?
Ocular dominance columns
Orientation columns
Color blobs
T/F
There is a high specificity of information received in the primary visual cortex?
True
From the visual cortex, what two pathways does the information take?
Dorsal “where” pathway
Ventral “what” pathway
What does the Retinotectal Pathway do, and what does it connect, and what pathway is it part of?
Visual attention and Detection of Movement
connects the Retina to the Superior Colliculus
Tectospinal Pathway (novel stimulus/movement)
What nucleus is involved in the body’s Master Clock system that is also involved in sympathetic pupillary dilation?
Where is it?
What pathway is this part of?
Suprachiasmatic nucleus
This is prior to the Optic Chiasm in the Hypothalamus
Retinohypothalamic Pathway
In the pupillary constriction reflex (parasympathetic), what is the response of the eye the light shines into?
Other eye?
Direct light response (reflex)
Consensual light response (reflex)
Explain the pathway of the pupillary constriction reflex.
Light in eye > Pretectal nucleus > bilateral Edinger-Westphal nucleus > CN III parasympathetic constricts pupils (mm. of iris) bilaterally
Explain the pathway for Pupillary Dilation: (involved in Horner’s)
Sympathetic from Hypothalamus > Intermediolateral cell column (lateral horn) of T1-2 > up to Superior Cervical Ganglia > pupillary dilator m. in the iris
What is the pathway of the Accomodation-Convergence Reflex?
visual stimulus close > superior colliculus > Edinger-Wesphal nucleus > ciliary ganglion > ciliary body > rounds lens
Also, medial rectus and pupil constriction involved (both CN III)
What are the terms for dividing the retina both vertically and horizontally?
temporal and nasal hemiretinas
superior and inferior hemiretinas
What will a craniopharyngioma bisecting the optic chiasm result in?
Bitemporal heteronymous hemianopsia
tunnel vision
What will interruption of the non-decussating optic fibers result in?
Ipsilateral nasal hemianopsia
nasal visual field lost on one side
What does a lesion in the cuneus result in?
Contralateral lower quadrantic anopsia
What causes cortical blindness?
Any lesion that interrupts signal from getting to primary visual cortex
Temporal lesions may cause
contralateral homonymous superior quadantonopia
What causes dilated pupils and eyes to go down and out?
Uncal herniation (through tentorial notch) by increased supratentorial cranial pressure
(takes out CN III)
Presbyopia
loss of accommodation due to ageing
What causes diabetic retinopathy?
leaky vessels and causes clouded vision
How does glaucoma work?
excessive aqueous humor pushes lens back, which pushes on retina.
can cause blindness
Can oxygen cause blindness?
yes
What does scotoma often accompany?
migraines
scintillating photoscotoma is the dancing bright light
What does detached retina look like to a pt?
floating curtain
What is the membranous labyrinth filled with?
Endolymph
What fluid lies outside the membranous labyrinth?
Perilymph
- space between bony and membranous labyrinths
What does the auditory apparatus consist of?
Vestibular apparatus?
Cochlea
3 semicircular canals and
a pair of otolith organs: the utricle and saccule
What two important pieces of information does the Vestibular System supply to the nervous system?
VOR - vestibulo-ocular reflex (reflex of eye movements)
VSR - vestibulospinal reflex (reflex of upright posture)
In what 3 planes can the semicircular canals detect acceleration?
horizontal
anterior
posterior
Where do both ends of each semicircular canal terminate?
Utricle
What is the enlargement in the semicircular canals?
Ampulla
What are the specialized receptor cells of the Ampulla?
Vestibular hair cells
surrounded by gelatinous mass called CUPULA
What is vestibular transduction based on ?
Inertia
Endolymph moves and puts pressure on the Ampulla, and creates pressure gradient across the Cupula. this causes bending of hair cells
T/F
Vestibular hair cells are only activated by acceleration
True
What is the one large hair in the vestibular hair cell called? What about the small cells?
1 large - Kinocilium
40-70 small - stereocilia
What does bending of stereocilia toward kinocilum cause?
what does bending away from kinocilium cause?
depolarization (fires VIII)
hyperpolarization (decrease VIII)
What does the depolarization/hyperpolarization coupling do for the brain?
guarantees these semicircular canals work in concert and the brain receives TWO signals - when one side of the brain is depolarized, other side hyperpolarized
What 2 types of information is provided by the Otolith organs (utricle and saccule)
linear acceleration and head position with respect to gravity
What do hair cells of the Utricle respond to?
Saccule?
Linear acceleration (and tilting head forward/backward)
Vertical displacements
What are the hair cells of the Utricle and Saccule covered with?
gelatinous substance containing Otoliths (otoconia), tiny stones that make them heavier than surrounding fluid
What directly stimulates the hair cells of the utricle and saccule in response to movement?
otoliths
What are the 4 vestibular nuclei?
Lateral (Deiter’s)
Medial
Sup.
Inf. vestibular nuclei
What does the SVN join with and participate in?
inputs?
ascending component of the MLF
vestibulo-ocular reflex (head and eye stabilization)
many inputs
What does the LVN (Deiter’s Nucleus) give rise to?
inputs?
The LVST (lateral vestibulospinal tract)
antigravity reflex (maintains balance and upright posture)
Utricle input
What is the main input of the MVN?
What does it join with?
What reflex does it participate in?
ampullae and semicircular ducts
descending and ascending MLF
Vestibulo-ocular reflex (along with SVN)
What 2 nuclei participate in the vestibulo-ocular reflex?
SVN
MVN
What is the IVN’s input and function
Input: all vestibular components and the vermis (cerebellum)
integration and postural control
Which vestibular nucleus sends output to the cerebral cortex?
occulomotor nuclei?
spinal cord?
LVN
SVN/MVN
LMV/MVN/IVN
What is the type of vertigo, not associated with tinnitus, that is due to the dislodging of utrical otoliths to the cupula, particularly the posterior semicircular canal (aka cupulolithiasis)?
(otoliths may free-float in semicircular canal - canalithiasis)
Benign Paroxysmal Positional Vertigo
What is Acoustic Neuroma (vestibular Schwannoma) a hallmark of?
neurofibromatosis 2
What are the 3 parts of the Brainstem?
Midbrain
Pons
Medulla
What are the two ways to divide the anatomy of the brainstem?
Midbrain, pons, medulla
Basilar (anterior), Tegmentum (posterior), Tectum (posterior midbrain/rostral pons only)
What are the 3 main functional components of the brainstem?
Cranial nuclei
white matter tracts
Reticular formation
4 somatic motor nuclei of cranial nn.
III - occulomotor
IV - trochlear
VI - abducens
XII - hypoglossal
4 branchial motor nuclei
V - trigeminal motor nuc.
VII - FACIAL NUC.
IX, X - Ambiguous
XI - spinal accessory
4 visceral motor/parasympathetic cranial nuclei
III - Edinger westphal
VII - Superior Salivatory
IX - Inferior Salivatory
X - Dorsal Motor Vagus
General sensory nucleus ALL go to:
Trigeminal nuc. (V, VII, IX, X)
Visceral and special sensory:
Nucleus Solitarius
What is the Reticular Formation?
Central core of nuclei runs through length of brainstem
What are the 2 main divisions of the Reticular Formation?
Rostral
Caudal
Where is the Rostral Reticular Formation (aka pontomesencephalic reticular formation) and what does it regulate?
Midbrain, upper pons
regulates alertness (think neurotransmitters), state of consciousness, sleep/wake cycle
What is the ARAS, and what is it part of, and where does it go?
Ascending Reticular Activating System
Rostral Reticular Formation
numerous cortical regions via Thalamic nuclei
Pathology ARAS?
classic cause of coma
What does the Caudal Reticular Formation (aka pontomedullary reticular formation) do?
Important motor, reflex, and autonomic functions
includes respiration, heart rate, bp, involuntary movements - coughing, hiccuping, etc.
A lesion in the Rostral Reticular Formation will induce ______, while a lesion in the Caudal Reticular Formation will induce _______.
Coma
death (usually stop breathing)
