Olfaction & visual systems Flashcards
olfactory pathway
Up through cribriform plate → olfactory bulb → olfactory tract → olfactory cortical areas
**No relay through the thalamus
general brain parts/functions
hippocampus - memory
hypothalamus - homeostasis/autonomic response
amygdala and limbic - emotion
epithalamus - coordination
ventral striatum - decision making and reward-related behavior
entorhinal cortex: connects memories and smells
medial geniculate nucleus
lateral geniculate nucleus
medial = hearing lateral = vision
VPM
somatic sensation for face/head
VPL
somatic sensation for the rest of the body
fracture of anterior cranial fossa - anosmia
lack of smell
fracture of anterior cranial fossa - CSF rhinorrhea
Leakage of CSF from subarachnoid space into nasal cavity
Route for bacteria to enter brain - can cause infection
type of receptor cells present in olfactory system
Specialized bipolar neurons (1st order neurons)
Chemoreceptors / Exteroreceptors
location of receptor cells in olfactory system
Located in mucous membrane in nasal cavity
Hairs/cilia react to odors
NO relay through thalamus
constant turnover of cells
replaced every 60 days
functions of visual system
Focus images on back of retina
Adjust dark/light intensity; different degrees of light
Color detection
Shape and movement detection (processing)
Localize visual stimuli
orbit
Socket: contains eyeball, blood vessels, nerves
Fractures cause visual disturbances
eyelids
Protect eyes
Orbicularis oculi – closes eylid (CN VII)
Lesion in nerve or facial motor nucleus in pons (Bell’s Palsy) leads to inability to close eyelid
Levator palpebrae superioris – opens eyelid (CN III)
Lesion in nerve or oculomotor nucleus in midbrain leads to Ptosis (drooping eyelid due to weakness)
Lacrimal Glands
Keep eye lubricated (produce tears)
Innervated by CN VII
Lesion to nerve or motor nuclei can result in inability to tear/dry eye (BP)
Puts cornea at risk with foreign objects entering eye
Eyeball - cornea
Light refraction and focusing image
Sensory innervation by CN V
Reflex by CN V (afferent, brainstem to facial motor n.) and CN VII (efferent, to orbicularis oculi)
Lesions in CN V, CN VII, or facial motor nucleus in pons will impair/lose corneal blink reflex to touch
Eyeball - iris
Pupil is hole in iris that constricts and dilates in response to light Parasympathetic Innervation cell bodies of neurons in Edinger Westphal nucleus in midbrain Axons leave midbrain in CN III Action = constrict pupil Lesion – dilated pupil Sympathetic Innervation Dilates pupil
Eyeball - Ciliary body
Change shape for proper focus (smooth muscle attach to lens – contract and change)
Ciliary muscles innervated be Edinger-Westphal nucleus in midbrain (CN III)
Important in focusing image for looking at close objects
Lesions: difficulty focusing
Eyeball - photoreceptors
Sit in retina
Rods: highly sensitive to light for night vision; no color (monochromatic); do not help with visual acuity
Cones: for colors (trichromatic) and visual acuity; low sensitivity to light
corneal blink reflex
Blink reflex is a protective mechanism in response to touch
When something is touching eye, CN V sends signal to brainstem to facial motor nucleus
CN VII transmits signal to the orbicularis oculi and you blink
how corneal blink reflex can be lost
Can be lost due to lesions to CN V or CN VII or their nuclei
vision pathway
Light through cornea → Lens → Retina → Photo receptors → Ganglion Cells → Optic Nerve → Optic Chiasm → Optic Tract → Lateral Geniculate Nucleus → Optic Radiation → Primary Visual Cortex
lesion in optic nerve
ipsilateral blindness (blind in that eye)
lesion in optic chiasm
Tunnel Vision: cuts off nasal retinas so we lose peripheral vision
lesion in optic tract
ipsilateral temporal retina, contralateral nasal retina and visual field, homonymous hemianopsia
lesion in visual cortex
cortical blindness (partial or complete)
left visual field
nasal retina from left eye, temporal retina from right eye
right visual field
nasal retina from right eye, temporal retina from left eye
to have complete perspective of L/R visual fields you have to …
get information from both eyes
hypermetropia
farsighted
- cannot focus well on near objects
- caused by misshapen lens or cornea or eyeball sizes and shapes that produce refractive errors.
myopia
nearsighted
- cannot focus well on far away objects
- caused by misshapen lens or cornea or eyeball sizes and shapes that produce refractive errors.
presbyopia
reduction in visual acuity due to aging in which individuals have trouble focusing on near objects
cataracts
age-induced
clouds the lens reducing vision in the eye
glaucoma
due on an increase in intra-ocular pressure which damages the retina; early sign is tunnel vision
macular degeneration
familial
saccades
rapid movement of the eye between fixation points
components of saccades
the oculomotor system: moves the eyes in the orbits
head-movement system: moves the eye sockets
visual association cortex (PCA) is responsible for
association: needs info to tell you what you are seeing
object agnosias and prospoagnosias
limbic system is responsible for
emotional responses to light
seasonal affective disorder
CN VII (facial) is responsible for
blink in response to light
another form of blink reflex where the stimuli to blink is light rather than touch
superior colliculus and the spinal cord is responsible for
Visual discrimination and integration occur in superior colliculus with somatosensory and auditory input to help orient eyes
motor response of head and body in response to visual input
hypothalamus is responsible for
circadian rhythms
Pretectum and Edinger Westphal Nucleus (CNIII) is responsible for
constricting pupil in response to light
visual fields are made up of
nasal and temporal retina
focal point
far side of each eye and medial corner of each eye
lesion in optic radiation
similar to tract but bigger section so less of an impact; partial visual field loss
pupillary light reflex
shine light in one eye, both pupils restrict
light received by Edinger Westphal nucleus (acc. to oculomotor n) → ciliary ganglion → pupils constrict
frontal eye field
NOT the same as visual field
portion of the brain that helps control the direction eyes move
lesion: eyes drift in the direction of the lesion
PPRF (paramedian pontine reticular formation) and lesion
segment of brainstem that helps coordinate abducens and oculomotor nuclei
lesion: eyes drift to opposite side
