23 - sense organs
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Lecture 23 Sense OrgansKardong Chapter 17, Hildebrand Chapter 19
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Sense OrgansSense organs are transducers that translate energy from one form into another,
i.e., to an electric signal in the nervous system. By doing so, they provide
information to guide movement, away from danger or toward food or mates.Special sense organs include theolfactory epithelium, the eyes, and the earsand lateral line. These are unique to vertebrates, ie., comparable organs in other
phyla are analagous, not homologous.
General sense organs are widely distributed over the body, both internally(interoceptors) and externally (exteroceptors).
KK 17.2, H&G 19.1KK 17.3, H&G 19.2
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Chemoreceptors or Taste Buds
Taste buds distinguish four basic
chemical signals*. While concentratedon the tongue in mammals, they are
generally distributed in the mouth of
non-amniotes as well as on their skin.
*For the latest:
Chandrashekar, J. et al. 2006. Thereceptors and cells for
mammalian taste. Nature 444:288-294
KK 17.5
KK 17.15, H&G 19.6
KK 17.15
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Special Sense Organs - Olfactory EpitheliumThe chemoreceptors of the olfactory
epithelium can discriminate among a
greater diversity of chemicals andoften at much lower concentrations
than taste buds.
Shark Nasal Cavity, KK 17.9b. H&G 19.4KK 17.7
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Vomeronasal OrgansVomeronasal organs are patches of olfactory
epithelium in a chamber on the palate, ratherthan in the nasal chamber. They are present in
many tetrapods. In mammals with this organ,
it is connected to the mouth via the
nasopalatine duct in the secondary palate. In
many reptiles, the tongue is used to collectscent molecules and deliver them to the
vomeronasal organ.
Like the optic nerve (II), the olfactory nerve
(I) that serves the olfactory organs is not
serially homologous with the dorsal root
spinal nerves, and can be considered part of
the brain.
KK 17.14, H&G 19.5
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Development of the Eye
The vertebrate eye
has an interesting
compound
development,
beginning with
lateral evaginations
of the embryonic
midbrain that
induce formation of
the lens placodes on
the ectoderm.
KK 17.18, H&G 19.16
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The neurectoderm of the optic vesicle eventually produces the optic nerve, retina,
pigment layer, and iris. The conjunctiva, cornea and lens are from ectoderm. The
capsule around the eye, or schlera, plus the choroid layer and ciliary body, are from
mesenchyme. Extrinsic eye muscles are from myotomes.
KK 17.18d, H&G 19.12
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The sensory cells of the eye are rod
and cone cells, the conespredominating near the fovea
(centre) and the rods at the
periphery and in nocturnal animals.
Cones sense different colours, but
need more light.
The pigment layer captures stray
light, but in nocturnal animals it
may be replaced by a reflective
tapetum lucidum.
Note the short bipolar sensory
neurons between the nerve cells and
optic nerve.
Ciliary receptors?
KK 17.17, H&G 19.14
Structure of the retina
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Lateral lines
and Inner EarsWhile lateral lines and ears seem an
odd combination of things to include
under one heading, they have a
common developmental origin and
very similar mechanoreceptors calledhair cells. As with rods and cones, the
sensitive part of the sensor is a cilium.
In lateral the line, these hair cells are
organized into sense organs called
neuromasts that lie in the lateral line
canal and are sensitive to currents or
vibration.
KK 17.31, H&G 19.7
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Lateral Line SystemsKK 17.32, H&G 19.7
Lateral lines are found in fish and in some Amphibia, particularly larval forms and
aquatic salamanders.
They consist of a groove or tube with pores. Along the tube or groove are sense
organs called neuromasts. These contain sensitive cilia enclosed in a gelatinous
cupula.
The neuromast organs can detect current or vibrations in water. Fish use them to
detect movement of water or movement of other animals.
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The Inner Ear or Vestibular ApparatusKK 17.33,H&G 19.8
The inner ear is serially
homologous with the lateral linesystem; one of a series of
ectodermal placodes generating the
lateral line system sinks deeply into
the head, under the influence of the
hindbrain, to produce the vestibularapparatus.
Patches of sense organs (cristae) at
the bases of the semicircular canals
are very similar in their
morphology to neuromasts. Cristaesense water movements, thereby
providing information on rotation.
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The Inner Ear or Vestibular Apparatus 2KK 17.33,H&G 19.8
The chambers below the semicircular
canals are called the utriculus and thesacculus, and contains patches of sense
organs called maculae.
The maculae, rather than having a
gelatinous cupula, support mineral
concretions called otoliths. Theseearstones are particularly large in
fishes that live in turbid environments,
like the freshwater drum. They bend
the cilia of the hair cells in response to
change in orientation with respect togravity or acceleration.
In fishes and other vertebrates that can
hear with the vestibular apparatus, that
sense is due to a part of the the sacculus
called the lagena.
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Inner Ear of TetrapodsIn tetrapods, the inner ear is similar and has the same functions in respect of the
utriculus and saccule. But the ventral extension of the sacculus, called the
lagena in fish and lower tetrapods, is much larger in vertebrates with acutehearing and is now called the cochlea.
This ventral extension, whether lagena or cochlea, is the organ of hearing. Its
length reflects the range of pitch that can be detected, low notes being detected
in the distal portion.
Mammal
KK 17.34, 17.36, H&G 19.8
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1.Tympanum picks up sound waves
2.Ear ossicles translates soundwaves to oval window on thespace housing of the inner ear.
3.Sound waves travel through thescala vestibuli to the tip of thecochlea and back through the scala
tympani. The hair cells of theorgan of Corti lie in a separatechamber, the scala media, betweenthese two, with their ciliaembedded in the tectorialmembrane. Vibration of thetectoral membrane is registered bythe Organ of Corti and stimulatesa branch of the auditory nerve(VIII).
The Mammalian EarKK 17.44,45, H&G Fig. 19.10Echolocation?
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Directional Hearing....
Owls are able to use their
sensitive hearing to detectprey. Their facial disk
helps gather sound waves
to the auditory canal, and
that is assymetric to assist
in using differential
hearing to pinpoint theirprey.
Bats and marine
mammals take this
further, producing their
own sounds and usingthese to detect silent prey
and other objects by
echolocation.
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Course Summary(i.e., what I hope you remember after the final)
1. Vertebrates evolved from a common ancestor and show many similarities.
Despite the morphological and functional diversity of vertebrates, major organs
are homologous, and differences represent adaptation.
2. Some adaptations have occurred independently, in parallel, in different groups.
3. Vertebrates are more than 500 million years old, but taxa come and go relatively
rapidly. The fauna of the earth is dynamic.
4. The relatedness of vertebrates is most apparent in the their development;
vertebrate embryos have features that echo (recapitulate) their evolutionary
history.
5. Reconciling the present vertebrate fauna of the earth with the fossil record anddevelopmental biology represents one of the major achievements of science. The
big picture is largely roughed in, but progress is ongoing.
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