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Refraction. Light rays are bent refractive index = ratio of light in a vacuum to the velocity in that substance velocity of light in vacuum=300,000 km/sec Light year 9.46 X 10 12 km Refractive indices of various media air = 1 cornea = 1.38 aqueous humor = 1.33 lens = 1.4

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  • Light rays are bent
  • refractive index = ratio of light in a vacuum to the velocity in that substance
  • velocity of light in vacuum=300,000 km/sec
    • Light year 9.46 X 1012 km
  • Refractive indices of various media
      • air = 1
      • cornea = 1.38
      • aqueous humor = 1.33
      • lens = 1.4
      • vitrous humor = 1.34
refraction of light by the eye
Refraction of light by the eye
  • Refractive power of 59 D (cornea & lens)
    • Diopter = 1 meter/ focal length
      • Convex lens expressed as + diopters
      • Concave lens expressed as - diopters
  • central point 17 mm in front of retina
  • inverted image- brain makes the flip
  • lens strength can vary from 20- 34 D (Δ 14)
    • Ability to increase refractive power ⇓ with age
      • 14 (age 10) 8 (age 30) 2 (age 50)
  • Parasympathetic + increases lens strength
    • Greater refractive power needed to read text
  • Increasing lens strength from 20 -34 D
    • Parasympathetic + causes contraction of ciliary muscle allowing relaxation of suspensory ligaments attached radially around lens, which becomes more convex, increasing refractive power (illustration)
      • Associated with close vision (e.g. reading)
        • In addition, eyes roll in and pupils constrict
    • Presbyopia- loss of elasticity of lens w/ age
      • decreases accommodation
errors of refraction
Errors of Refraction
  • Emmetropia- normal vision; ciliary muscle relaxed in distant vision
  • Hyperopia-“farsighted”- focal pt behind retina
      • globe short or lens weak ; convex lens to correct
  • Myopia- “nearsighted”- focal pt in front of retina
      • globe long or lens strong’; concave lens to correct
  • Astigmatism- irregularly shaped
      • cornea (more common)
      • lens (less common)
visual acuity
Visual Acuity
  • Snellen eye chart
    • ratio of what that person can see compared to a person with normal vision
  • 20/20 is normal
  • 20/40 less visual acuity
    • What the subject sees at 20 feet, the normal person could see at 40 feet.
  • 20/10 better than normal visual acuity
    • What the subject sees at 20 feet, the normal person could see at 10 feet
visual acuity6
Visual acuity
  • The fovea centralis is the area of greatest visual acuity
    • it is less than .5 mm in diameter (< 2 deg of visual field)
    • outside fovea visual acuity decreases to more than 10 fold near periphery
    • acuity for point sources of light 25 sec of arc (angle of 25 seconds)
  • point sources of light two  apart on retina can be distinguished as two separate points
fovea and acute visual acuity
Fovea and acute visual acuity
  • Central fovea-area of greatest acuity
    • composed almost entirely of long slender cones
      • aids in detection of detail
    • blood vessels, ganglion cells, inner nuclear & plexiform layers are displaced laterally
      • allows light to pass relatively unimpeded to receptors
depth perception
Depth Perception
  • Relative size
    • the closer the object, the larger it appears
    • learned from previous experience
  • Moving parallax
    • As the head moves, objects closer move across the visual field at a greater rate
  • Stereopsis- binocular vision
    • eyes separated by 2 inches- slight difference in position of visual image on both retinas, closer objects are more laterally placed
formation of aqueous humor
Formation of Aqueous Humor
  • Secreted by ciliary body (epithelium)
    • 2-3 ul/min
    • flows into anterior chamber and drained by Canal of Schlemm (vein)
  • intraocular pressure- 12-20 mmHg.
  • Glaucoma- increased intraocular P.
    • compression of optic N.-can lead to blindness
    • treatment; drugs & surgery
  • Peripheral extension of the CNS
  • Processing of visual signal
  • Photoreceptors
    • Rods & Cones
  • Other Cells
    • bipolar, ganglion, horizontal, amacrine
    • Only retinal cells that generate action potentials are the ganglion cells
  • Rods & Cones
  • Light breaks down rhodopsin (rods) and cone pigments (cones)
  •  rhodopsin   Na+ conductance
  • photoreceptors hyperpolarize
  • release less NT (glutamate) when stimulated by light
retinal responses



↑ NT

Hyperpol Depolarize






Depolarize Hyperpol


Retinal responses
bipolar cells
Bipolar Cells
  • Connect photoreceptors to either ganglion cells or amacrine cells
  • passive spread of summated postsynaptic potentials (No AP)
  • Two types
    • “ON”- hyperpolarized by NT glutamate
      • Invaginating bipolars
    • “OFF”- depolarized by NT glutamate
      • Flat bipolars
ganglion cells
Ganglion Cells
  • Can be of the “ON” or “OFF” variety
    • “ON” bipolar + “ON” ganglion
    • “OFF” bipolar + “OFF” ganglion
  • Generate AP carried by optic nerve
  • Three subtypes
    • X (P) cells
    • Y (M) cells
    • W cells
p x ganglion cells
P (X) Ganglion Cells
  • Most numerous (55%) G cells
  • Receive input mostly from bipolar c.
  • Slower conduction velocity (14 m/sec)
    • Sustained response-slow adaptation
  • Small receptive field
    • signals represent discrete retinal location
  • Respond differently to different 
    • Responsible for color vision
  • Project to Parvocellular layer of lateral geniculate nucleus (thalamic relay)
m y ganglion cells
M (Y) Ganglion Cells
  • Receive input mostly from Amacrine
  • Larger receptive field
  • Transient-fast conduction velocity
    • respond best to moving stimuli
  • Not sensitive to different 
  • More sensitive to brightness
  • Project to magnocellular LGN
  • Black & White images
w ganglion cells
W Ganglion Cells
  • smallest, slowest CV (8 m/sec)
  • 40% of all ganglion cells
  • many lack center-surround antagonistic fields
    • they act as light intensity detectors
  • some respond to large field motion
    • detect directional movement
  • Broad receptive fields
    • Receive most of their input from rods
    • Important for crude vision in dim light
horizontal cells
Horizontal Cells
  • Non spiking inhibitory interneurons
  • Make complex synaptic connections with photorecetors
  • Hyperpolarized when light stimulates input photoreceptors (just like receptor)
  • When they depolarize they inhibit photoreceptors
  • Maybe responsible for center-surround antagonism
amacrine cells
Amacrine Cells
  • Receive input from bipolar cells
  • Project to ganglion cells
  • Several types releasing different NT
    • GABA, dopamine
  • Transform sustained “ON” or “OFF” to transient depolarization & AP in ganglion cells
center surround fields
Center-Surround Fields
  • Receptive fields of bipolar & gang. C.
  • two concentric regions
  • Center field
    • mediated by all photoreceptors synapsing directly onto the bipolar cell
  • Surround field
    • mediated by photoreceptors which gain indirect access to bipolar cells via horizontal cells
center surround cont
Center-Surround (cont)
  • Photoreceptors contributing to center field of one bipolar cell contributes to surround field of other bipolar cells
  • Because of center-surround antagonism, ganglion cells monitor differences in luminance between center & surround fields
center surround cont23
Center-surround (cont)
  • If center field is on, surround is off
  • If center field is off, surround is on
  • Simultaneous stimulation of light of both fields gives no net response
    • antagonistic excitatory & inhibitory inputs neutralize each other
  • When surround is illuminated, the horizontal cells depolarize the cones in the center (opposite effect of light)
receptive field size
Receptive field size
  • In fovea- ratio can be as low as 1 cone to 1 bipolar cell to 1 ganglion cell
  • In peripheral retina- hundreds of rods can supply a single bipolar cell & many bipolar cells connected to 1 ganglion cell
dark adaptation
Dark Adaptation
  • In sustained darkness reformation of light sensitive pigments (Rhodopsin & Cone Pigments)
  •  of retinal sensitivity 10,000 fold
  • cone adaptation<100 fold (1st 10 min.)
  • rod adaptation>100 fold (50 min.)
  • dilation of pupil
  • neural adaptation
  • 3 populations of cones with different pigments-each having a different peak absorption 
  • Blue sensitive (445 nm)
  • Green sensitive (535 nm)
  • Red sensitive (570 nm)
color blindness
Color Blindness
  • Sex-linked trait carried on X chromosome
  • Occurs almost exclusively in males but transmitted by the female
  • Most common is red-green color blindness
    • missing either red or green cones
loss of cones
Loss of Cones
  • Loss of Red Cones- Protanope
    • decrease in overall visual spectrum
  • Loss of Green Cones- Deuteranope
    • normal overall visual spectrum
  • problems distinguishing green, yellow, orange & red (Ishihara Chart)
  • Loss of Blue Cones- rare but may be under-represented “Blue weakness”
visual pathway
Visual Pathway
  • Optic N to Optic Chiasm
  • Optic Chiasm to Optic Tract
  • Optic Tract to Lateral Geniculate
  • Lateral Geniculate to 10 Visual Cortex
    • geniculocalcarine radiation
additional visual pathways
Additional Visual Pathways
  • From Optic Tracts to:
    • Suprachiasmatic Nucleus
      • biologic clock function
    • Pretectal Nuclei
      • reflex movement of eyes-
        • focus on objects of importance
    • Superior Colliculus
      • rapid directional movement of both eyes
      • Orienting reactions
primary visual cortex
Primary Visual Cortex
  • Brodman area 17 (V1)-2x neuronal density
    • Simple Cells-responds to bar of light/dark
    • above & below layer IV
    • Complex Cells-motion dependent but same orientation sensitivity as simple cells
    • Color blobs-rich in cytochrome oxidase in center of each occular dominace band
      • starting point of cortical color processing
    • Vertical Columns-input into layer IV
      • Hypercolumn-functional unit, block through all cortical layers about 1mm2
visual association cortex
Visual Association Cortex
  • Visual signal is broken down & sent over parallel pathways
    • Visual analysis proceeds along many paths in parallel- at least 30 cortical areas processing vision
      • Parvo-interblob
        • High resolution static form perception (B & W)
      • Blob
        • Color (V4)
        • Achromatopsia
      • Magno
        • Movement (MT) & Stereoscopic Depth
old vs new visual system
Old vs. New visual system
  • Old pathway projects to the superior colliculus
    • Locating objects in visual field, so you can orient to it (rotate head & eyes)
    • Subconscious
    • Blindsight
  • New pathway projects to the cortex
    • Consciously recognizing objects
  • Some patients who are effectively blind because of brain damage can carry out tasks which appear to be impossible unless they can see the objects.
    • For instance they can reach out and grasp an object, accurately describe whether a stick is vertical or horizontal, or post a letter through a narrow slot.
    • The explanation appears to be that visual information travels along two pathways in the brain. If the cortical pathway is damaged, a patient may lose the ability to consciously see an object but still be aware of its location and orientation via projections to the superior colliculus at a subconscious level.
  • How the brain learns to see video
cortical fixation areas
Cortical fixation areas
  • Voluntary fixation mechanism (anterior)
    • Person moves eyes voluntarily to fix on an object
    • Controlled by cortical field bilaterally in premotor cortex
  • Involuntary fixation mechanism (posterior)
    • Holds eyes firmly on object once it has be located
    • Controlled by secondary visual areas in occipital cortex located just in front of primary visual cortex
    • Works in conjunction with the superior colliculus
      • Involuntary fixation is mostly lost when superior colliculus is destroyed.
control of pupillary diameter
Control of Pupillary Diameter
  • Para + causes  size of pupil (miosis)
  • Symp + causes  size of pupil (mydriasis)
  • Pupillary light reflex
    • optic nerve to pretectal nuclei to Edinger-Westphal to ciliary ganglion to pupillary sphincter to cause constriction (Para)
horner s syndrome
Horner’s Syndrome
  • Interruption of SNS supply to an eye
    • from cervical sympathetic chain
      • constricted pupil compared to unaffected eye
      • drooping of eyelid normally held open in part by SNS innervated smooth muscle
      • dilated blood vessels
      • lack of sweating on that side of face
function of extraoccular muscles
Function of extraoccular muscles
  • Medial rectus of one eye works with the lateral rectus of the other eye as a yoked pair to produce lateral eye movements
  • The superior& inferior recti muscles elevate & depress the eye respectively and are most effective when the eye is abducted
  • The superior oblique muscles lower the eye when it is adducted
  • The inferior oblique muscle elevates the eye when it is adducted
innervation of extraoccular muscles
Innervation of extraoccular muscles
  • Extraoccular muscles controlled by CN III, IV, and VI
  • CN VI controls the lateral rectus only
  • CN IV controls the superior oblique only
  • CN III controls the rest
  • Units of Sound is the decibel (dB)
  • I (measured sound)
  • Decibel = 1/10 log --------------------------
  • I (standard sound)
  • Reference Pressure for standard sound
      • .02 X 10-2 dynes/cm2
  • Energy is proportional to the square of pressure
  • A 10 fold increase in sound energy = 1 bel
  • One dB represents an actual increase in sound E of about 1.26 X
  • Ears can barely detect a change of 1 dB
different levels of sound
Different Levels of Sound
  • 20 dB- whisper
  • 60 dB- normal conversation
  • 100 dB- symphony
  • 130 dB- threshold of discomfort
  • 160 dB- threshold of pain
frequencies of audible sound
Frequencies of Audible Sound
  • In a young adult
  • 20-20,000 Hz (decreases with age)
  • Greatest acuity
  • 1000-4000 Hz
tympanic membrane ossicles
Tympanic Membrane & Ossicles
  • Impedance matching-between sound waves in air & sound vibrations generated in the cochlear fluid
  • 50-75% perfect for sound freq.300-3000 Hz
  • Ossicular system
    • reduces amplitude by 1/4
    • increases pressure against oval window 22X
      • increased force (1.3)
      • decreased area from TM to oval window (17)
ossicular system cont
Ossicular system (cont.)
  • Non functional ossicles or ossicles absent
  • decrease in loudness about 15-20 dB
  • medium voice now sounds like a whisper
  • attenuation of sound by contraction of
    • Stapedius muscle-pulls stapes outward
    • Tensor tympani-pull malleous inward
attenuation of sound
Attenuation of sound
  • CNS reflex causes contraction of stapedius and tensor tympani muscles
  • activated by loud sound and also by speech
  • latency of about 40-80 msec
  • creation of rigid ossicular system which reduces ossicular conduction
  • most effective at frequencies of < 1000 Hz.
  • Protects cochlea from very loud noises, masks low freq sounds in loud environment
  • System of 3 coiled tubes
    • Scala vestibuli
    • Scala media
    • Scala tympani
scala vestibuli
Scala Vestibuli
  • Seperated from the scala media by Reissner’s membrane
  • Associated with the oval window
  • filled with perilymph (similar to CSF)
scala media
Scala Media
  • Separated from scala tympani by basilar membrane
  • Filled with endolymph secreted by stria vascularis which actively transports K+
  • Top of hair cells bathed by endolymph
endocochlear potential
Endocochlear potential
  • Scala media filled with endolymph (K+)
    • baths the tops of hair cells
  • Scala tympani filled with perilymph (CSF)
    • baths the bottoms of hair cells
  • electrical potential of +80 mv exists between endolymph and perilymph due to active transport of K+ into endolymph
  • sensitizes hair cells
    • inside of hair cells (-70 mv vs -150 mv)
scala tympani
Scala Tympani
  • Associated with the round window
  • Filled with perilymph
    • baths lower bodies of hair cells
function of cochlea
Function of Cochlea
  • Change mechanical vibrations in fluid into action potentials in the VIII CN
  • Sound vibrations created in the fluid cause movement of the basilar membrane
  • Increased displacement
    • increased neuronal firing resulting an increase in sound intensity
      • some hair cells only activated at high intensity
place principle
Place Principle
  • Different sound frequencies displace different areas of the basilar membrane
    • natural resonant frequency
  • hair cells near oval window (base)
    • short and thick
      • respond best to higher frequencies (>4500Hz)
  • hair cells near helicotrema (apex)
    • long and slender
      • respond best to lower frequencies (<200 Hz)
fourier analysis by the cochlea
Fourier analysis by the cochlea
  • Any complex wave can be broken down into its component sine waves with differing phases, frequencies, & amplitudes
    • Fourier analysis
  • Cochlea behaves like a Fourier analyser
    • Acts a kind of auditory prism
      • Sorting out vibrations of different frequencies into different positions along the membrane
central auditory pathway
Central Auditory Pathway
  • Organ of Corti to ventral & dorsal cochlear nuclei in upper medulla
  • Cochlear N to superior olivary N (most fibers pass contralateral, some stay ipsilateral)
  • Superior olivary N to N of lateral lemniscus to inferior colliculus via lateral lemniscus
  • Inferior colliculus to medial geniculate N
  • Medial geniculate to primary auditory cortex
primary auditory cortex
Primary Auditory Cortex
  • Located in superior gyrus of temporal lobe
  • tonotopic organization
    • high frequency sounds
      • posterior
    • low frequency sounds
      • anterior
  • S.Q.U.I.D
    • changes in central sensitivities
air vs bone conduction
Air vs. Bone conduction
  • Air conduction pathway involves external ear canal, middle ear, and inner ear
  • Bone conduction pathway involves direct stimulation of cochlea through the vibration of the skull as the cochlea is imbedded in the petrous portion of the temporal bone
  • reduced hearing may involve:
    • ossicles (air conduction loss)
    • cochlea or associated neural pathway (sensory neural loss)
differentiating a hearing loss
Differentiating a hearing loss
  • If there is a known bad ear
  • Weber test (512 Hz) tunning fork placed on midline of the skull
    • If sounds louder in bad ear- conduction loss in bad ear. (external canal or ossicles involved)
    • If sounds louder in good ear- sensory neural loss in bad ear
  • Rinne test- confirms results of Weber
    • air conduction > bone- sensory neural
    • bone conduction > air- air conduction loss
sound localization
Sound Localization
  • Horizontal direction from which sound originates from determined by two principal mechanisms
    • Time lag between ears
      • functions best at frequencies < 3000 Hz.
      • Involves medial superior olivary nucleus
        • neurons that are time lag specific
    • Difference in intensities of sounds in both ears
      • involves lateral superior olivary nucleus
exteroceptive chemosenses
Exteroceptive chemosenses
  • Taste
    • Works together with smell
    • Categories (Primary tastes)
      • sweet
      • salt
      • sour
      • bitter (lowest threshold-protective mechanism)
      • Umami (savory/pungent)
  • Olfaction (Smell)
    • Primary odors (100-1000)
taste receptors
Taste receptors
  • May have preference for stimuli
  • influenced by past history
    • recent past
      • adaptation
    • long standing
      • memory
      • conditioning-association
primary sensations of taste
Primary sensations of taste
  • Sour taste-
    • caused by acids (hydrogen ion concentration)
  • Salty taste-
    • caused by ionized salts (primarily the [Na+])
  • Sweet taste-
    • most are organic chemicals (e.g. sugars, esters glycols, alcohols, aldehydes, ketones, amides, amino acids) & inorganic salts of Pb & Be
primary sensations of taste66
Primary sensations of taste
  • Bitter- no one class of compounds but:
    • long chain organic compounds with N
    • alkaloids (quinine, strychnine, caffeine, nicotine)
  • Umami/Savory
    • Flavor associated with MSG
    • Receptor responds to amino acids
  • Taste sensations are generated by:
    • complex transactions among chemical and receptors in taste buds
    • subsequent activities occuring along the taste pathways
  • There is much sensory processing, centrifugal control, convergence, & global integration among related systems contributing to gustatory experiences
taste buds
Taste Buds
  • Taste neuroepithelium consists of taste buds distributed over tongue, pharynx, & larynx.
  • Aggregated in relation to 3 kinds of papillae
    • fungiform-blunt pegs 1-5 buds /top
    • foliate-submerged pegs in serous fluid with 1000’s of taste buds on side
    • circumvallate-stout central stalks in serous filled moats with taste buds on sides in fluid
  • 40-50 modified epithelial cells grouped in barrel shaped aggregate beneath a small pore which opens onto epithelial surface
innervation of taste buds
Innervation of Taste Buds
  • each taste nerve arborizes & innervates several buds (convergence in 1st order)
  • receptor cells activate nerve endings which synapse to base of receptor cell
  • Individual cells in each bud differentiate, function & degenerate on a weekly basis
  • taste nerves:
    • continually remodel synapses on newly generated receptor cells
    • provides trophic influences essential for regeneration of receptors & buds
adaptation of taste
Adaptation of taste
  • Rapid-within minutes
  • taste buds account for about 1/2 of adaptation
  • the rest of adaptation occurs higher in CNS
cns pathway taste
CNS pathway-taste
  • Anterior 2/3 of tongue
    • lingual N. to chorda tympani to facial (VII CN)
  • Posterior 1/3 of tongue
    • IX CN (Petrosal ganglion)
  • base of tongue and palate
    • X CN
  • All of the above terminate in nucleus tractus solitarius (NTS)
cns pathway taste cont
CNS pathway (taste cont)
  • From the NTS to VPM of thalamus via central tegmental tract (ipsilateral) which is just behind the medial lemniscus.
  • From the thalmus to lower tip of the post-central gyrus in parietal cortex & adajacent opercular insular area in sylvian fissure
  • Least understood
    • smell is subjective
    • hard to study in animals
    • rudimentary in humans
      • Humans are microsmatic
        • Poorly developed sense of smell
the nose
The Nose
  • 3 conchae bilaterally
    • Highly vascularized organs covered with erectile tissue
      • Fxns to moisten and warm incoming air
      • Limit loss of heat & H2O in expired air
    • Engorged with blood when you have a cold
      • Block air from reaching olfactory receptors
        • Partial loss of smell
  • Olfactory cleft at the top
    • Olfactory epithelium
      • Associated with the olfactory receptors
      • Normally only a small portion of air reaches here
        • Sniffing  the % by creating turbulence around conchae
vomeronasal organ
Vomeronasal organ
  • Aka Jacobson’s organ
  • Located medially on septum in lower part of nasal cavity
  • Appears to contribute to olfaction
  • Probably more receptive than olfactory epithelium to phermones which have profound effects on behavior
olfactory membrane
Olfactory Membrane
  • Superior part of nostril
  • Olfactory cells
    • bipolar nerve cells
    • 100 million in olfactory epithelium
    • 6-12 olfactory hairs/cell project in mucus
    • react to odors and stimulate cells
cells in olfactory membrane
Cells in Olfactory Membrane
  • Olfactory cells-
    • bipolar nerve cells which project hairs in mucus in nasal cavity
    • stimulated by odorants
    • connect to olfactory bulb via cribiform plate
  • Cells which make up Bowman’s glands
    • secrete mucus
  • Sustentacular cells
    • supporting cells
characteristics of odorants
Characteristics of Odorants
  • Volatile
  • slightly water soluble-
    • for mucus
  • slightly lipid soluble
    • for membrane of cilia
threshold for smell
Threshold for smell
  • Very low
  • methyl mercaptan
    • 1/25 billion of mg/ml of air can be detected
    • mixed with natural gas so gas leaks can be detected
stimulation of olfactory cells
Stimulation of Olfactory Cells
  • Odorant binds to receptor protein
  • Inside of protein is coupled to a G-protein
    • 3 subunits
  • G-protein activates adenyl cyclase
    • Adenyl cyclase converts ATP  cAMP
      • cAMP causes protein gated Na+ channels to open
      • Ca++ enters as well which opens choride channels
        • High Cl- concentraction inside olfactory receptors (unusual)
          • Efflux of Cl- prolongs depolarization
  • At every step the effect is amplified
primary sensations of smell
Primary sensations of smell
  • Anywhere from 100 to 1000 based on different receptor proteins
  • odor blindness has been described for at least 50 different substances
    • may involve lack of a specific receptor protein
olfactory receptor
Olfactory Receptor
  • Resting membrane potential when not activated = -55 mv
    • 1 impulse/ 20 sec to 2-3 impulses/ sec
  • When activated membrane pot. = -30 mv
    • 20 impulses/ sec
  • Prolongation of response in response to +
    • Na+ and Ca++ influx during depolarization
      • Ca+ influx binds to and opens Chloride channel protein
        • High Chloride content intracellularly (atypical), therefore when stimulated, Cl- efflux will prolong depolarization
glomerulus in olfactory bulb
Glomerulus in Olfactory Bulb
  • several thousand/bulb
  • Connections between olfactory cells and cells of the olfactory tract
    • receive axons from olfactory cells (25,000)
    • receive dendrites from:
      • large mitral cells (25)
      • smaller tufted cells (60)
cells in olfactory bulb
Cells in Olfactory bulb
  • Mitral Cells- (continually active)
    • send axons into CNS via olfactory tract
  • Tufted Cells- (continually active)
    • send axons into CNS via olfactory tract
  • Granule Cells
    • inhibitory cell which can decrease neural traffic in olfactory tracts
    • receive input from centrifugal nerve fibers
  • Periglomerular Cells
    • Inhibitory cells between glomerulus
cns pathways
CNS pathways
  • Very old- medial olfactory area
    • feeds into hypothalamus & primitive areas of limbic system (from medial pathway)
    • basic olfactory reflexes
  • Less old- lateral olfactory area
    • prepyriform & pyriform cortex -only sensory pathway to cortex that doesn’t relay via thalamus (from lateral pathway)
    • learned control/adversion
  • Newer- passes through the thalamus to orbitofrontal cortex (from lateral pathway)
    • - conscious analysis of odor
medial and lateral pathways
Medial and Lateral pathways
  • 2nd order neurons form the olfactory tract & project to the following 1o olfactory paleocortical areas
    • Anterior olfactory nucleus
      • Modulates information processing in olfactory bulbs
    • Amygdala and olfactory tubercle
      • Important in emotional, endocrine, and visceral responses of odors
    • Pyriform and periamygdaloid cortex
      • Olfactory perception
    • Rostral entorhinal cortex
      • Olfactory memories