23 - Sense Organs

7/27/2019 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.

23 - Sense Organs

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