2 - comparative vertebrate anatomy (1)

7/30/2019 2 - Comparative Vertebrate Anatomy (1)

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2 - Comparative Vertebrate

Anatomy

Descriptive morphology - the study of the

structure of vertebrates

Functional morphology study of the functional

significance of structure

includes:

ontogenesis- development of individuals and

phylogenesis- ancestral histories of individuals


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Comparative Vertebrate Anatomy

Involves: ecology

embryology

genetics

molecular biology

biodiversity

paleobiology


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Comparative Vertebrate Anatomy

FOCUS: * organs and organ systems

* their roles in survival

* their embryogenesis

* their historical background

in geological time


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The Phylum Chordata: The Big Four

Notochord

skeleton at the back

Dorsal hollow central nervous system

Postanal tail

Endostyle a glandular groove in the floor of the

pharynx

Chordatesare animals that have a notochord in the embryo stage at least.

Craniatesare chordates with a neurocranium.

Vertebratesare chordates with vertebrae.


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The Craniate Body: GeneralPlan

I. Regional DifferentiationTypical regional components: HEAD, TRUNK, and POSTANAL

TAIL

a. Head= with special sense organs (monitor externalenvironment);

brain (receive & process information, & provide appropriatestimuli to body musculature);

jaws (acquire, retain, macerate food);

gills in fishes (respiration)

= greater degree of cephalization in craniates than in any

other group of animals


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b. Trunk= with coelom - house most of viscera

body wall - surrounds coelom

consists chiefly of muscle, vert. column, ribs)

paired pectoral and pelvic appendages (fins or limbs)in many craniates


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neck - narrow extension of trunk ofamphibians, reptiles, birds, mammals

- consists primarily of vertebrae, muscles,spinal cord, nerves, elongated tubes(esophagus, blood vessels, lymphatics,

trachea) that connect structures of headwith trunk

With 2 pairs of appendages

pectoral andpelvic) supported by internal skeleton

- sometimes vestigial or completely lost


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c. Tail= starts at anus or vent (postanal);consists of caudal continuation of body wallmuscles, axial skeleton, nerves, & blood

vessels

=absent in some adult craniates but present inall embryos (e.g. swimming larvae of frogs,toads, & wormlike amphibians have tails but are losturing metamorphosis

= modern bird tails reduced to nubbin

= humans have vestigial postanal tail early inembryonic life; its remnant in adults is the

tailbone orcoccyx


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II. Bilateral Symmetry and

Anatomic Planes

3 principal body axes in craniates:

1. LONGITUDINAL (ANTEROPOSTERIOR)

AXIS)

2. DORSOVENTRAL AXIS

3. LEFT-RIGHT AXIS (bilateral symmetry)


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3 principal anatomic planes:

2 axes define a plane

1. Cross section = a cut in thetransverse plane established by the

left-right and the dorsoventral axes

2. Frontal section = a cut in the frontalplane established by the left-right and

longitudinal axes

3. Sagittal section = a cut in the sagittalplane established by the longitudinal

and dorsoventral axes

=section parallel to sagittal is parasagittal


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III. Metamerism

the serial repetition of structures in thelongitudinal axis of the body

clearly manifested in craniate embryos &is retained in many adult systems


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no external evidence in most adult reptiles,

birds, & mammals

but internally a series of muscle segments

are visible

- serial arrangement of vertebrae, ribs,spinal nerves, embryonic kidney

tubules, segmental arteries & veins)


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CRANIATE CHARACTERISTICS(Morphological Features)

a. Cranium

b. 3-part brain

c. Neural crest and its derivatives

d. Paired external sense organs (e.g., olfactory, optic,

otic with a single semicircular canal, & lateral linesystem with unicellular sense organs)

e. Cartilage


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VERTEBRATE

CHARACTERISTICS

1. a vertebral column (primitively seen as isolatedelements associated with an unrestrictednotochord)

2. two semicircular canals

3. electroreception

4. lateral line system with multicellular neuromasts

5. a number of additional soft tissue specializations


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STRUCTURES COMMON TO CRANIATES(notochord, pharynx, dorsal hollow cns

1. Notochord and Vertebral Column

Notochord= the 1st skeletal structure to appear in

craniate embryos

Vertebrae= consists of a

centrum(depositedaround notochord),

neural arch(forms over

spinal cord), and various processes


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Fate of notochord during development:

Head regionincorporated into floor ofskull

Trunk and tailsurrounded bycartilaginous or bony vertebrate


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Fate of the notochord in adults:

Fishes and amphibiansnotochord persists the

length of the trunk and tail but is constricted

within the centrum of each vertebra

Reptiles, birds and mammalsnotochord

almost disappears during development

Protochordatesnotochord remains as the chief

axial skeleton


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2. Pharynx common to hemichordates & chordates: pharynx

perforated by openings ( slits) to either the

exterior or an atrium (reflecting commonancestry)

it is the vital part of craniate embryo that

produces:* gills of fishes (permanent slits)

* lungs of tetrapods (temporary slits)

* skeleton & musculature of jaws


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* endocrine glands that regulate metabolic

rates in all body cells & maintain

appropriate calcium levels in bones

* other tissues & circulating blood


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gives rise to middle ear cavity of tetrapods

provides initial cells of immune system

during fetal life & shortly after(in humans)


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Pharyngeal Pouches & Slits

Pouches

* arises as diverticula of endoderm of

foregut; grow toward the surface of animal

* establish the limits of pharynx


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* maximum no. in jawed craniates: 8 (e.g. basalshark); 15 (living agnathans)

* Ectodermal groove grows toward each pouch;branchial plate separates groove from pouch

* A passageway (pharyngeal slit) is formedbetween pharyngeal lumen and exterior ofanimal, if & when, branchial plate ruptures


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Slits

* May be permanent (in fishes, exits forrespiratory water from gills) ortemporary (in most tetrapods)

* Temporary if animals is going to live onland


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Pharyngeal Arches

A column of tissue which separates eachembryonic pharyngeal pouch or slit fromthe next

Typically has 4 components or blastemasfrom which these components develop:

1. Supportive skeletal elements

2. Striated muscles that operate the arch


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3. Branches of 5th, 7th, 9th, and 10th cranial nerves

w/c innervate muscles & provide sensory input

to brain

4. An aortic arch that connects the ventral & dorsal

aortas

Pharyngeal (visceral) skeleton

= skeleton of pharyngeal arches

Branchiomeric = muscles of the arches


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3. Dorsal Hollow CNS

Consists ofbrain and spinal cord

Contains neurocoel (central lumen)

Typically arises as longitudinal neural groove

(becomes the dorsal surface of embryo)


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Dorsal Hollow CNS

Neural groove closes over or rolls up,sinks beneath the surface to become ahollow neural tube (dorsal tonotochord)


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Neurulation neural tube formation

Wider anterior portion of tube becomes thebrain with its ventricles
http://embryology.med.unsw.edu.au/notes/images/neuron/st10neural.jpg


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Some Features Common to other

members of other Phyla

1. Bilateral symmetry

2. Metameric

3. Possess a true body cavity or coelom

4. Lined with mesoderm

5. Cephalization conc. of nervous tissue andsense organs in or toward the head


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COMPARISON OF ANIMAL PHYLA

Symmetry Germ

layers

Coelom Organs Segmenta-

tion

Mollusks Bilateral 3 Present Present Unsegment-

ed

Annelids Bilateral 3 Present Present Segmented

Arthropods Bilateral 3 Present Present Segmented

Echinoderms Radial(adult)

3 Present Present Unsegment-ed

Chordates Bilateral 3 Present Present Segmented


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2 - comparative vertebrate anatomy (1)

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