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The brain’s processing of sensory input & motor output is cyclical rather than linear
Sensations: stimulus to the brainPerceptions: interpretation of sensory info
Sensor Receptors:
• Exteroreceptors- detect stimuli outside the body- Heat- Light- Pressure- Chemicals
• Interoreceptors- detect stimuli within the body- Blood pressure- Body position
Sensory receptors transduce stimulus energy transmit signals to
the nervous system
• Sensory Transduction• Amplification• Transmission• Integration
• Chemoreception- Taste- Smell
• Electromagnetic receptors- Photoreceptors- Infrared receptors - Lateral line - Electroreception
• Nocioceptors• Mechanoreceptors:
- Hearing- Balance
• Thermoreceptors
respond to chemicals in an aqueous solutionfood dissolved in salivaairborne chemicals dissolved in mucous membrane
Taste and smell are involved with specific receptor cells called chemoreceptors
Salty- metallic ions
Sweet- sugarSweet- sugar
Sour- HSour- H++
Bitter- alkaloidBitter- alkaloid
Why are they important?
Gustatory pathway:Facial nerve (afferent) 2/3 anterior portion of tongueGlossophyngeal posterior 1/3 of tongueVagus nerve- few taste buds on epiglottis an pharynxThese afferent fibers synapse in medullathalamusgustatory cortex in parietal lobes and fibers to hypothalamus in limbic system
Jacobson’s organ: • The tongue flicks out, picking up odors
and carrying them to the roof of the mouth into contact this sensory receptor
Heat receptor:
• heat-detecting sensors concentrated as two large pits between their nostril and eyes
• Found in pit vipers, as well as some boas and pythons
• Detects small differences in temperature (as slight as 0.02 oC)
• Used to locate and capture warm-blooded prey at night.
A diversity of photoreceptors has evolved among invertebrates
• Eye cups are among the simplest photoreceptors– Detect light intensity and direction — no image
formation.– The movement
of a planarian is integrated with photoreception.
• Image-forming eyes.
– Compound eyes of insects and crustaceans.• Each eye consists
of ommatidia, each with its own light-focusing lens.
• This type of eye is very good at detecting movement.
• Single-lens eyes of invertebrates such as jellies, polychaetes, spiders, and mollusks.
– The eye of an octopus works much like a camera and is similar to the vertebrate eye.
Vertebrates have single-lens eyes
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• Is structurally analogous to the invertebrate single-lens eye.
Fig. 49.9
Vascular tunic- uvea: choroid, cilliary body, iris, pupil (middle layer)
Choroid- rich vascular nutritive layer; contains a dark pigment
that prevents light scattering within the eye
Cilliary body- lens is attached; contains muscles that change the
lenses shape
Iris- pigmented ring of muscular tissue composed of circular
and radial muscles
• reflex contraction of circular muscle in bright light (small dia of pupil)
• reflex contraction of radial muscle in dim light (large dia of pupil)
Pupil- central hole in iris
Sensory tunic- retina (inner most layer)
Photoreceptors:
• rods (dim light, contains pigment rhodopsin) and
• Cones (color vision, not evenly distributed, concentrated in fovea)
Optic disc- blind spot because its where optic nerve leaves the eyeball (no rods or cones)
Macula lutea- yellow spot, area of high cone
Fovea centralis- in center of macula lutea, contains only cones, area of greatest visual acuity
Vitreous humor- behind lens, gel-like substance with fine collagenic fibrils imbedded in as viscous ground substance- binds with water
• transmits light• supports the posterior surface of the lens and
holds the neural retina firmly against pigmented layer
• contributes to intraoccular pressure, helping to counter act the pulling force of the extrinsic eye muscles
Aqueous humor- in front of lens, anterior segment, watery fluid
• Supplies cornea and lens with nutrients• Helps to maintain the shape of the eye• Produced and renewed every 4 hrs by the
cilliary body
Lens- transparent biconvex structure, flexible• Attached by suspensory ligaments to cilliary
body• focuses image onto retina• changes lens thickness to allow light to be
properly focused onto retina
Coarse Fixed FocusingCoarse Fixed Focusing• Cornea ShapeCornea Shape
AccommodationAccommodation- adjust configuration of- adjust configuration of • Lens ShapeLens Shape• Pupil SizePupil Size
• Photoreceptors of the retina.
– About 125 million rod cells.• Rod cells are light sensitive but do not distinguish
colors.
– About 6 million cone cells.• Not as light sensitive as rods but provide color
vision.• Most highly concentrated on the fovea – an area of
the retina that lacks rods.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
The light-absorbing pigment rhodopsin triggers a signal-transduction pathway
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Rhodopsin (retinal + opsin) is the visual pigment of rods.
• The absorption of light by rhodopsin initiates a signal-transduction pathway.
Fig. 49.13
• Color reception is more complex than the rhodopsin mechanism.
– There are three subclasses of cone cells each with its own type of photopsin.• Color perception is based on the brain’s
analysis of the relative responses of each type of cone.
– In humans, colorblindness is due to a deficiency, or absence, of one or more photopsins.• Inherited as an X-linked trait.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
The retina assists the cerebral cortex in processing visual
information
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Visual processing begins with rods and cones synapsing with bipolar cells.
– Bipolar cells synapse with ganglion cells.
• Visual processing in the retina also involves horizontal cells and amacrine cells.
• Vertical pathway: photoreceptors bipolar cells ganglion cells axons.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Lateral pathways:
– Photoreceptors horizontal cells other photoreceptors.• Results in lateral inhibition.
– More distance photoreceptors and bipolar cells are inhibited sharpens edges and enhances contrast in the image.
– Photoreceptors bipolar cells amacrine cells ganglion cells.• Also results in lateral inhibition, this time of the
ganglion cells.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The outer ear includes the external pinna and the auditory canal.
– Collects sound waves and channels them to the tympanic membrane.
The mammalian hearing organ is within the ear
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• From the tympanic membrane sound waves are transmitted through the middle ear.
– Malleus incus stapes.
– From the stapes the sound wave is transmitted to the oval window and on to the inner ear.
– Eustachian tube connects the middle ear with the pharynx.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
external auditory
canal
tympanic membrane
eustachian tube
malleus
incus
stapes
round window
oval window
• The inner ear consists of a labyrinth of channels housed within the temporal bone.
– The cochlea is the part of the inner ear concerned with hearing.• Structurally it consists of the upper vestibular
canal and the lower tympanic canal, which are separated by the cochlear duct.
• The vestibular and tympanic canals are filled with perilymph.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Biology 100Biology 100Human BiologyHuman Biology
cochlea
saccule
utricle
semicircular canals
auditory nerve
– The cochlear duct is filled with endolymph.
– The organ of Corti rests on the basilar membrane.• The tectorial membrane rests atop the hair
cells of the organ of Corti.
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• From inner ear structure to a sensory impulse: follow the vibrations.
– The round window functions to dissipate the vibrations.
• Vibrations in the cochlear fluid basilar membrane vibrates hair cells brush against the tectorial membrane generation of an action potential in a sensory neuron.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Pitch is based on the location of the hair cells that depolarize.
• Volume is determined by the amplitude of the sound wave.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Behind the oval window is a vestibule that contains the utricle and saccule.
– The utricle opens into three semicircular canals.
The inner ear also contains the organs of equilibrium
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Fishes and amphibians lack cochleae, eardrums, and openings to the outside.
– However, they have saccules, utricles, and semicircular canals.
A lateral line system and inner ear detect pressure waves in most fishes and aquatic amphibians
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Statocysts are mechanoreceptors that function in an invertebrates sense of equilibrium.
– Statocysts function is similar to that of the mammalian utricle and saccule.
Many invertebrates have gravity sensors and are sound-sensitive
Fig. 49.21
• Sound sensitivity in insects depends on body hairs that vibrate in response to sound waves.– Different hairs respond to different frequencies.
• Many insects have a tympanic membrane stretched over a hollow chamber.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 49.22