BISC 4140 Unit 4 (Thalamus, Auditory & Vestibular, Visual, Taste & Olfaction)

epithalamus

pineal gland, habenula, pre-tectal area

subthalamus

subthalamic nucleus (STN), zona incerta

the septum —> habenula via

stria medullaris

thalamus function

• all sensory info (except olfaction) from basal ganglia, cerebellum, limbic structures

• motor function

internal medullary lamina (IML)

divides medial from lateral thalamus

intralaminar n.

• located along IML

• fxn. alertness, arousal (global control), pain system

anterior n.

• fxn. limbic

• relay via mammilothalamic tract

input = mammillary body

outputs = cortex, hypothalamus, cingulate (Papez Circuit)

dorsomedial n. (DM)

• fxn. affect, foresight

• damage: Phineas Gage-like symptoms

inputs: amygdala, olfactory cortex, basal ganglia

outputs: prefrontal cortex

dorsal tier nuclei (3)

• lateral dorsal (LD) n.

• lateral posterior (LP) n.

• pulvinar

lateral dorsal (LD) n.

• projects to cingulate

• fxn. limbic

lateral posterior (LP) n.

• continuous with pulvinar

• parietal-occipital-temporal association ctx.

• inputs from visual system + association ctx.

pulvinar

• fxn. visuospatial/somatosensory processing

• inputs from sup. colliculi

• outputs to frontal/parietal/insular lobes, cingulate, amygdala, parahippocampal, parieto-occipital

ventral tier (3 nuclei)

• ventral anterior (VA)

• ventral lateral (VL)

• ventral posterior (VP) —> VPL, VPM

ventral anterior (VA) & ventral lateral (VL) nn.

motor control (cerebellum and basal ganglia)

ventral posterior (VP) n.

ascending sensory from medial lemniscus, trigeminothalamic, spinothalamic tracts

• divided into lateral and medial (VPL, VPM)

ventral posterolateral (VPL) n.

ascending sensory from body

ventral posteromedial (VPM) n.

ascending sensory from head (+ CN V)

lateral geniculate n. (LGN)

fxn. visual relay

• retinogeniculate striate pathway

retinogeniculate striate pathway

retinal cells —> CN II —> LGN —> BA 17

medial geniculate n. (MGN)

fxn. auditory relay

• inferior colliculus pathway

auditory relay pathway

inferior colliculus —> MGN —> BA 41

thalamic reticular n.

fxn. thalamic regulation (does not project to ctx.)

internal capsule

major output pathway of thalamus

thalamic syndrome

hemisensory loss —> thalamic pain syndrome (over time)

• symptoms: behavioral changes, inattention, thalamic aphasia, anterograde amnesia, chorea, etc.

thalamic aphasia

• sounds like Wernicke’s

• dependent on attentiveness

hemisensory loss

“pure”, often head to toe loss (pure sensory or sensorimotor)

outer ear

air-filled

• auricle (pinna)

• external auditory meatus

middle ear

air-filled

• ossicles (malleus, incus, stapes)

• oval window covered by stapes

• round window

inner ear

fluid-filled (endolymph)

• cochlea

cochlea

snail-shaped structure that processes sound, tonotopically arranged

• contains 3 scala (ramps)

scala media

component of the cochlea containing spiral ganglion; communicates sound to brain

cilia

tips of hair cells bathed in endolymph fluid

tip links

small structures that connect hair cells; amplification of sound

auditory pathway

hair cells (receptor) —> spiral ganglion

1° spiral ganglion (in scala media)

2° cochlear nuclei —> lateral lemniscus (most cross contralateral, some ipsilateral)

3° inferior colliculus —> MGN (thalamus)

4° auditory ctx. (BA 41)

damage to auditory pathway results in…

• not full hearing loss (bilateral innervation/compensation)

• loss of foreground/background

• loss of localization of sound

air conduction

sound via outer and middle ear

bone conduction

sound directly to spiral ganglion/cochlea through bone

conductive hearing loss

damage to outer or middle ear (obstruction, infection)

sensorineural hearing loss

damage to inner ear - hair cells, spiral ganglion, or cochlear nuclei

Rinne test

air vs bone test

• normal = air > bone

• conductive = bone > ear

• sensorineural = air > bone (diminished)

Weber test

directional test

• normal = equal both sides

• conductive = louder on affected side

• sensorineural = louder on normal side

vestibular labyrinth components

• semicircular canals (3)

• vestibule (saccule, utricle)

semicircular canals

3 “hula hoops” of vestibular system; orthagonally arranged (90° angles)

ampulla

internal component of semicircular canals; contains crista and cupula

• fxn. angular acceleration (rotation)

crista

layer of hair cells with cilia; inside ampulla

cupula

gelatin layer above crista; cilia extend upwards into gel to detect rotation

vestibule

• saccule and utricle

• fxn. linear acceleration

saccule

linear acceleration (up and down - gravity)

utricle

side-to-side, back and forth acceleration

otoliths

calcium carbonate stones on top of gelatinous layer of vestibule

fxn. move/push cilia based on vestibular information

vestibular nuclei (4)

• medial/inferior vestibular n.

• lateral vestibular n.

• superior vestibular n.

medial/inferior vestibular nn.

• descending

fxn. head/neck position

lateral vestibular n.

• descending

fxn. posture and extensor tone

superior vestibular n.

• ascending to MLF

• fxn. eye movement (vestibulo-ocular reflex)

• inputs: cerebellum, spinal cord, brainstem

• outputs: cerebellum, thalamus, vestibular nn.

caloric reflex test

• induced nystagmus by cold water in one ear and warm water in the other

• “COWS”

layers of the eye (3)

• sclera/cornea

• uvea

• retina

sclera

whites of eyes

cornea

front outer portion of sclera

uvea

middle layer of eye

• choroid

• choroidal pigment

• ciliary body

• ciliary epithelium

• iris

choroid (uvea)

contains blood vessels that supply eye tissues

choroidal pigment (uvea)

fxn. scattering and absorption of light

ciliary body

front middle layer; contains ciliary muscle, ciliary epithelium, and iris

retina

inner layer of eye

retinal pigment epithelium (RPE)

contains photoreceptors; supplied by choroid vessels

iris

melanated cells in ciliary body

• protection from light (in dark eyes)

• contains pupillary sphincter and pupillary dilator muscles

aqueous humor

fluid secreted by ciliary epithelium cells (posterior chamber) —> anterior chamber

vitreous humor

gelatinous substance that forms bulk of eye

fovea

area of highest visual acuity; bright light, color vision

macula

surrounds fovea; high visual acuity, low-light no color vision

optic disc

gathering of axons as CN II; located on medial (nasal) side of eye; blind spot

rods

low-light, no color conditions; poor spatial/temporal resolution; most abundant photoreceptor

cones

bright light, highest acuity photoreceptors; high spatial/temporal resolution; least abundant

retinal field pathway

photoreceptors (rods/cones) —> bipolar/horizontal cells —> ganglion/amacrine cells —> optic nerve

the direction of ____ is front to back, but the direction of ____ is back to front

light; information flow

horizontal cells

receives input from photoreceptors; links multiple bipolar cells according to signal

amacrine cells

receives input from bipolar cells; links (+/-) multiple ganglion cells depending on signal

ganglion cells

only cell type going to optic nerve

retinogeniculocortical pathway

retina —> optic nerve —> optic tract —> LGN —> optic radiations —> BA 17

the visual field in comparison to the retinal field is…

reversed and inverted

Meyer’s loop

inferior optic radiations that sweep into temporal lobe before running back to occipital

calcarine fissure

separates upper and lower banks of visual ctx.

lower bank

superior visual field, inferior retinal field, inferior optic radiation (Meyer’s loop)

upper bank

inferior visual field, superior retinal field, superior optic radiation

extra-geniculate pathways

• retina —> hypothalamus (suprachiasmatic n.) master biological clock

• retina —> superior colliculus (diverse connections: LGN, pulvinar, cortex, somatosensory, auditory, RF, spinal cord)

monocular scotoma

small area of dead photoreceptors on one side

monocular vision loss

loss of vision in one eye; lesion at optic nerve

bitemporal hemianopia

loss of outer (temporal) visual fields; lesion at optic chiasm

contralateral homonymous hemianopia

same sided-loss in each eye; lesion of one side optic radiations (all), optic tract, or upper+lower bank

contralateral superior quadrantanopia

loss of ½ superior visual field (¼ of whole eye) in each eye; lesion at one side Meyer’s loop or lower bank

contralateral inferior quadrantanopia

loss of ½ inferior visual field (¼ whole eye) in each eye; lesion at one side superior radiation or upper bank

taste pathways

• visceral chemoreceptors (glucose, O2, hormones)

• gustatory receptors

• olfactory receptors

• chemosensitive receptors (menthol, chili pepper, ammonia)

papillae

bumps on surface of tongue; contain taste buds —> taste cells

taste pores

receptors based on type (salty, sweet, bitter, sour, umami)

taste pathway (main)

1° CN VII, IX, X

2° NTS

3° thalamus —> gustatory ctx. (insula)

taste pathway (reflexes)

NTS (2°) —> DMX, RF

• fxn. = salivation, swallowing, coughing, gag reflex

gustatory ctx. to…

• frontal operculum

• orbital ctx.

• amygdala

mix of olfactory w/ taste

olfactory epithelium

contains mucus to capture odorants —> receptor cells detect odorants

olfactory fila

bundle of olfactory receptor cells heading to olfactory bulb

glomerulus

collection of single olfactory cell type, heading to mitral/tufted cells

olfaction pathway

1° olfactory receptor cell

2° tufted/mitral cells