Comparative anatomy lecture notes



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COMPARATIVE ANATOMY LECTURE NOTES
LECTURE 1 Origin and Diversity

LECTURE 2 Diversity and Phylogeny

LECTURE 3 Diversity and Phylogeny

LECTURE 4 Biological Design

LECTURE 5 Life History

LECTURE 6 The integument

LECTURE 7 Cranial skeletons

LECTURE 8 Post-cranial skeletons

LECTURE 9 Muscles

LECTURE 10 The Respiratory System

LECTURE 11 The Circulatory System

LECTURE 12 The Digestive System

LECTURE 13 The Urogenital System

LECTURE 14 The Endocrine System

LECTURE 15 The Nervous System

LECTURE 16 Senseory organs
Introduction, Origin and Diversity
Comparative anatomy is a subject about forms, their functions, and their evolution.





function

structures

similar

different

similar

phylogeny

/convergence

/parallelism


evolution

different

independent evolution

/convergence



nothing to compare

As Mayr put it, biology is a mixture of two quite distinct realms: functional biology is reducable to the level of physical sciences; while historical biology is not reducable; it has to be considered in terms of phylogeny, and the unique evolutionary history of the group being studied.

Generally, disciplines in biology belong to only one realm. Biochemistry, physiology, and molecular biology are examples of the functional biology; examples of historical biology are topics such as systematics, genetics, and evolution.

Comparative anatomy is one of the few disiplines whose explanations are partly functional and partly historical. A state found in an organism is determined not only by the physical aspects of the design, but is determined also by the history of the lineages. Physical part is a universal phenomenon, but the history of the organism is unique.


terms and concepts
phylogeny: inheritance

evolution: modification and inheritance

convergence: found in distantly related groups; evolved independently.

parallelism: found in closely related groups; evolved independently.

independent evolution/convergence: unrelated groups
Names and events:
1. evolution

Carolus Linnaeus (1707-1778): species unchanged; used characters to group organisms

Jean Baptiste de Lamarck (1744-1829): progressive change of characters (and species) dictated by use or disuse

Alfred Russel Wallace (1823-1913): survival of the fittest

Charles Darwin (1809-1882): survival of the fittest, tree of life
2. morphology/comparative methods

Georges Cuvier (1769-1832): form and function/comparative methods/species immutable

Richard Owen (1804-1892): archetypes/homology
Morphological concepts receive information from anatomy, physiology,

receive insights from phylogeny and paleontology


Functions and Biological Role
Preadaptation: structures evolve not with a purpose, but with a 'potential'
Remodeling: evolution is not about inventing new things, it is mainly about switching/alteration

pharyngeal slits: filter-feeding; gills: gas exchange

fins: balance; limb: propulsion; fore-limbs: grasping, making gestures
Phylogeny is based on cladistic methods. Phylogeny is not a fact, but a hypothesis that is constantly being challenged.

homology can be ancestral (primitive) or evolved (derived)

only shared derived homology (synapomorphy) diagnoses a monophyletic group
Analysis of vertebrate design, three steps
1. THE QUESTION: not so easy as it sounds. Use tools to help define the questions, such as dissection, taxonomy,
2. THE FUNCTION: detect and describe performance using various recording techniques
3. BIOLOGICAL ROLE: pronghorn's high speed not for escaping predator, but to move between scattered resources.

Diversity and Phylogeny
Chordate Phylogeny

determine primitive and derived characteristics

discover monophyletic groups

understand character evolution


Phylum Chordata

Urochordata

Cephalochordata

Craniata (Vertebrata)


Synapomorphies

Chordata: notochord, pharyngeal slits, endostyle, dorsal hollow nerve cord, postanal tail

Urochordata,

Cephalochordata

Craniata (Vertebrata): vertebral column(vertebral column is a new structure), head
Back-trace our ancestor From Homo sapiens:

Homo sapiens

Primates (other monkeys and apes added)

Mammalia (other hairy beasts added)

Amniota (reptiles added)

Tetrapoda (amphibians added)

Sarcopterygia (lungfish and coelacanth added)

Osteichthyes (actinopterygians added)

Gnathostomes (chondrichthyians added)

Vertebrates (lampreys added)

Craniata (hagfish added)

Chordata (cephalochordates and urochordates added)
Agnatha: a term for hagfish and lamprey combined

Gnathostomes

Chondrichthyes

Osteichthyes

Actinopterygii

Sarcopterygii

Actinistia

Choanata


Dipnoi

Tetrapoda

(early tetrapods)

Amphibia


Amniotes

Reptilia


Testudines

Diapsida


Archosauria (Croc and birds)

Squamates

Mammalia

Monotremes

Theria

Metatheria



Eutheria


Biological Design
Size:

relationships among length, area, and volume

surface area: chewing, intestinal absorption, breathing, capillaries

volume and mass: increase in mass compared to surface area


Shape:

alter length, area, and volume as animal change in size

allometry
Biomechanics

units and derived quantities

metric units

velocity, acceleration, force, power, work, pressure


torques and levers

life on land: gravity

life in fluid:

dynamic fluids: drag, boundary layer

Reynolds number: Re = ρlU / μ

ρ: density; l: shape and size; U: velocity through fluid; μ: viscosity

strength of material

forces acting on body: compression, tension, shear


Biomaterials response to stress, failure
Other physical processes important in anatomy

diffusion and exchange: pressures /partial pressure; countercurrent exchange

optics, depth perception, accommodation


Life History
ontogeny: from fertilization, to death of individuals
embryology: from fertilization to birth, hatching
1. fertilization: the union of sperm and egg

yolk contents differs: microlecithal, mesolecithal, macrolecithal


2. cleavage: cell division

cleavage pattern differs: holoblastic, meroblastic, discoidal

yolk contents affect cleavage patterns
3. Gastrulation and Neurulation

a. the formation of blastocoel

b. the formation of blastopore

c. the formation of gut (gastrocoel):

cell movements: epibody, involution, invagination, delamination, ingression

d. the formation of neural tube (spinal cord)

e. formation of three germ layers

f. the formation of coelom:


4. organogenesis

a. histogenesis: epithelium, connective tissue

b. organs

c. neural crest and ectodermal placodes


5. extraembryonic membranes (amniotes)

amnion, chorion(ectoderm), allantois, yolk sac (endoderm)


6. maturation and metamorphosis

heterochrony can explain many of the morphological diversity

a. peramorphosis

b. paedomorphosis


7. biogenetic law and von Baer's law

a. biogenetic law (recapitulation, Haeckel): ancestor's form reappears in the ontogeny of descedents

b. von Baer's law: the resemblance between embryos of ancestors and descendents.


The integument
the most prominent and important organ

the first defense

the most versatile organ

the most conspicuous


from ectoderm and mesoderm (dermatome)
dermal scales and unicellular glands

placoid scale, cosmoid scale, ganoid scale (only enamel), teleost scale (only lamellar bone)


epidermal scales and multicellular glands
keratinized structures
reptile scale

skin lack many glands


bird feather

uropygial gland


mammal hair and glands

glands: sebacous, wax, sweat, mammary lagnds


Teeth:
specializations of the integuments
a. nails, claws, hooves

b. horns and antlers

c. baleen

d. scales

e. dermal armor

f. mucus


g. color: melanophores, iridophores, erythrophores


Cranial skeletons
the skeletal system: exoskeleton and endoskeleton
skull (cranium): from different phylogenetic and embryonic sources

splanchnocranium (visceral skeleton)

chondrocranium: endochondral bone or cartilage

dermatocranium: dermal bones


chondrocranium: floor and lateral side of brain; mostly fused to other elements, occipital series remains
splanchnocranium: from branchial arches

arch: pharyngobranchial, epibranchial, ceratobranchial, hypobranchial, basibranchial


origin of jaws:

serial theory, from an original 7 arches, 1st becomes mandibular, 2nd becomes hyoid

composite theory: 10 or more arches, complex loss and fusion forms the jaws
types of jaw attachment: how mandible (lower jaw) is attached to the skull

paleostylic: agnathans, no attachment

euautostylic: placoderms and acanthodians; to skull

hyostylic: most groups; through hyoid arch and derivatives

caniostylic: mammals, to dermal bones
dermatocranium:

facial


orbital

temporal


vault

palatal


mandibular
Phylogeny of the Skull
Jawless vertebrates: well developed sense organs, not predaceous
Gnathostomes:

placoderms: predators, skull heavily ossified

Chondrichthyans: predators, mandible and upper jaw movement

Actinopterygians: head specialized for feeding

suspensorium: causing the jaw to protrude

Sarcopterygians

Tetrapods: internal nares, flattened skull

suction feeding, buccal pumping

Amniotes:

skull fenestra: for jaw movement and closing

skull kinesis

tongue in chameleon

mammals: turbinates, tongue, secondary palate, middle ear bones
functions of skulls

prey capture

in water: suction feeding and suspension feeding

in air: swallowing




Post-cranial skeletons
Axial skeleton: notochord and vertebral column combined to define the long axis of body; for

muscle attachment, prevent telescoping of the body, and support.


vertebrae:

general morphology: neural arch, interneural arch, centra, hemal arch

regionalization: atlas, axis, cervical, thoracic, lumbar, sacral, postsacral, caudal
Centrum: shape

an important structure for phylogenetic reconstruction


Ribs: between myoseptum

dorsal and ventral

bicipital: capitulum, to parapophysis, and tuberculum to diapophysis
sternum: endochondral
Gastralia: abdominal ribs
Phylogeny
regionalization, lateral processes
Appendicular system
Fins: pectoral, pelvic

fin rays: ceratotrichia (keratinized in elasmobranch), lepidotrichia (chondrified or bony in bony fish)


LImbs

stylopodium, zeugopodium, autopodium


Origin of paired fins

gill arch theory

fin-fold theory
Limbs and girdles
pelvic girdle: endochondral

pectoral girdle: dual origin, both endochondral and dermal




Muscles
movement, heat production, electric organs
classification of muscles
skeletal

cardiac


smooth
structures of skeletal muscles
muscle cells; muscle organ, tendons (aponeurosis, fascia)
Muscle contraction:

tension-length curve for single muscle fiber


properties of muscle fibers

1. color: myoglobin

2. tonic and twitch fibers (tab 10.1)
Whole muscle contraction: combination of passive and active tension
Graded force: by rate modulation, or selective contraction of motor units.
Maximum force proportional to cross section area of muscle
fiber orientation: parallel or pinnate muscles
velocity of shortening: long muscle fibers
distance of shortening:
Bone-msucle lever system: near point of rotation, for speed; away from point of rotation, for strength
Muscle homologies

attachment similarity

functional similarity

nervous innervation

embryology (?)
embryonic origins
1. mesenchyme: smooth muscles of blood vessel walls

2. hypomere: smooth muscle of guts, to cardiace muscles

3. paraxial mesoderm: skeletal muscles

somites: in the trunk

somitomeres: in the head
cranial musculature
jaw and pharyngeal: hypobranchial muscles fro trunk somites; and branchiomeric musculature from head somitomeres.
extrinsic eye muscles: three fomitomeres
Postcranial musculature

differentiation of epaxial and hypaxial muscles


appendicular musculature: dorsal and ventral muscles, all from myotome
tetrapod pectoral and forelimb muscles from

branchiomeric

axial musculature

dorsal muscles

ventral muscles
tetrapod pelvic muscles from dorsal and ventral muscles
Cranial musculature

branchiomeric musculature: mandibular, hyoid, and branchial arches

hypobranchial


The Respiratory System
diffusion not enough for large animals which have more oxygen demands.
The rate of diffusion depends on surface area, distance, and the resistance to diffusion by the tissue.
Also important is the partial oxygen pressure. In warm and stagnant water, the oxygen may come out of the body.
Respiratory organs:
Gills: internal gills: pharyngeal slits, interbranchial septum, operculum

external gills


Lungs: trachea, glottis, bronchi, bronchioles, dead space, tidal volume
Gas bladders: pneumatic duct
cutaneous respiration
accessory air-breathing organs:
ventilation mechanisms
cilia: not for ventilation, but for clearing tract and surface.
muscular mechanisms
1. water ventilation: dual pump

2. air ventilation: buccal pump

3. air ventilation: aspiration pump
Lamprey: ammocoete: velum ventilation; adults: in and out through gill openings

hagfish: velum movement, and then from nostril to pharynx

elasmobranchs: holobranch and hemibranch, spiracle

bony fish




The Circulatory System
cardiovascular system: from mesoderm

blood


blood vessels: arteries, veins, and capillaries
blood pessure and circulation

microcirculation

single and double circulation

heart: from mesoderm; self-contractile, promote the formation of vessels.


Phylogeny

ventral aorta, aortic arches, external carotids, dorsal aorta, internal carotids, aorta, caudal arteries (paired parietal arteries, subclavian, iliac, genital, renal

portal system: hepatic and renal

basic pattern: shark example

aortic arches

heart
venous system: systemic system: three pairs in embryos: vitelline veins, cardinals, lateral abdominals


hepatic portal system: from veins of the digestive tract
Heart:

sinus venosus, sinoatrial valve, atrium; atrioventricular valve; ventricle, conus arteriosus, semilunar valve

hagfish with heart (branchial heart) and other accessory hearts (caudal, portal, cardinal)

amphibians with spiral valves in conus


special circumstances

accessory air-breathing organs: to air bladder, gut

diving: bradycardia (decreased heart rate), anaerobic metabolism increases; microcirculation changes

embryo circulations:

umbilical vein: oxy blood away from placenta to liver, half to liver, other half to ductus venosus to hepatic vein. blood in the hepatic vain joins two cava to right atrium, not to pulmonary artery, most through ductus arteriosus to dorsal aorga; in heart, foramen ovale allows most blood to left atrium

at birth: placental circulation ceases, neonate lung expand,

rise in blood oxygen stimulate the contraction of muscle in ductus arteriosus and closing it and becomes ligamentum arteriosum.

more blood in lungs, and more blood returns to left atrium, closing of the septum of foramen ovale.

ductus venosus forms from the original umbilical vein.
heat transfer: dolphin, bear skin, sinus in ungulates and carnivores


The Digestive System
digestive tracts and digestrive glands
components

buccal cavity

palate

teeth


tongue

alimentary canal

esophagus

stomach


intestines

cloaca
specializations in the alimentary canal


glands

oral glands

liver

pancreas
functions



absorption

food processing

fermentation


The Urogenital System
Structure of the mammalian kidney

medulla, cortex, calyx, pelvis, ureter, to urinary bladder, urethra.

uriniferous tubule in cortex, loops and tubules in medulla
uriniferous tubules

nephron (nephric tubule):

glomerulus

renal capsule (Bowman's capsule)

proximal, intermediate, and distal tubules
collecting tubule:
Pronephros: transitional

mesonephros: embryos, in adult amphibians called opisthonephros

metanephros: adult kidney in amniotes, duct is the ureter.
kidney phylogeny
lampreys and hagfish: anterior aglomerular pronephros (to coelom); posterior glomerular tubules to pronephric duct (archinephric duct)

most fish: pronephros functional for some time, most fish's pronephros degenerate, adn replaced with a mesonephros and into opisthonephros


Tetrapods: opisthonephros:

amniotes: embryo kidney is the mesonephros,

only mammals and some birds have loops to produce urine with concentrations greater than blood

bird loops are independently evolved


Kidney function

removing nitrogeninous waste: uricotelism, ammonotelism, ureotelism

osmoregulation: water and salt: osmoconformer and osmoregulators

water elimination: hyperosmotic animals in freshwater: filtration kidney

water conservation: hot-dry and sea: eliminate filtration need (aglomerular kidney)
REPRODUCTIVE SYSTEM
Mammalian reproductive system

genital ridge from splanchnic mesoderm; germ cells form from extraembryonic endoderm. female in cortex, male in medulla


mesonephric duct: wolffian duct: vas deference

mullerian duct: oviduct


female reproductive system

ovary: hormone and ova, mesovarium

genital duct:

hag and lamprey: eggs into coelom and through secondary pores to cloaca or anus.

elasmobranchs: mullerian duct into funnel shell gland, isthmus, uterus; archinephric duct drains opisthonephric kidney

bony fish: most have a new ovarian duct, not from mullerian duct

amphibians: both ducts normal

amniotes: metanephric duct is the ureter; oviduct persist, arthinephric duct rudimentary

oviducts

uterus
Male reproductive system

testis, mesorchium

cyclostome: no ducts, archinephric duct only urine

elasmobranchs: rudimentary mullerian; accessory urinary duct for kieney; archinephric duct for sperm (vas deferens)

bony fish: archinephric duct for urine and sperm, but also a separate testicular duct for sperm

amphibians: some: archinephric duct for urine and sperm; most have accessory urinary duct. archi for sperm

amniotes: archinephric duct for sperm only; mammals have scrotum, via inguinal canal


copulatory organs: claspers, spermatotheca, penis, hemipenes
cloaca: coprodeum; urodeum; proctodeum;

The Endocrine System
thyroid

thyroxine (tetraiodothyronine, T4)

triiodothyronine, T3

lateral to trachea, with many follicles

principal cells: forms the walls of follicles, produce colloid in which the hormone is stored.
origin: as an outgrowth of the pharynx.

endostyle in amphioxus and lamprey is homologous

controlled by thyrotropin (thyroid-stimulating hormone, TSH, from pituitary)

function: inhibit metamorphosis in lampreys

metabolism: elevate oxygen consumption, and heat production of tissues (in endotherms)

growth and metamorphosis: salmon promote change to smolt; in amphibians, it arrest larval growth and promote metamorphosis

molt: promote sloughing and shedding of skin

reproduction: gonad maturation and oogenesis or spermatogenesis.

ultimobranchial body and parathyroid gland

two are antagonistic

ultimobranchial body secrete calcitonin (thyrocalcitonin): lower blood level of calcium

parathyroid secretes parathyroid hormone (parathormone): elevate calcium level


ultimobranchial bodies: from fifth pharyngeal pouches, separate and paired cell masses in the throat region (in fish, amphibians, birds, reptiles). cyclostomes do not have them. In mammals, they are dispersed among principal cells in the walls of thyoid follicles (parafollicular cells).

source is neural crest.


Parathyoid gland: ventral edges of the pharyngeal pouches. absent in fish and neotenic amphibians, so it is probably preceeded by gill cells.

chief cells are probably the source of parathormone; oxyphil cells of unknown function


low calcium level: muscle spasm

function of parathormone: promoting kidney retention of calcium and raise blood level of calcium; net effect is to cause bone removal, and free calcium. calcitonin has the opposite effect.

fish secrete somatolactin from the pars intermedia (pituitary), which influence calcium homeostasis. teleosts use scales instead of bone as calcium reservoirs.
adrenal gland: a composite organ from two sources.

adrenocortical tissue: produces corticosteroid hormones involves in (1) water resorption and sodium transport by the kidney (mineralcorticoids); (2) metabolism of carbohydrates (glucocorticoids); and (3) reproduction (estrogen, androgen, and progestogens). from splanchnic mesoderm.

chromaffin tissue or bodies: produce catecholamines (epinephrine and norepinephrine). from neural crests
function: as above.
pancreatic islets: composites of exocrine of acini; and pancreatic islets (islets of Langerhans). both differentiate within the pancreatic diverticulum, an outgrowth of gut
islets with four cell types:

B cells: insulin, controls the overall metabolism of carbohydrates, fats and proteins.: inhibit fat breakdown, promote fat synthesis, and lower blood level of fatty acids, inhibit breakdown of glycogen. most importantly, to bind to cell membranes and promote the entry of glucose into cells (esp. skeletal and cardiac muscles). low insulin cause diabetes mellitus

A cells: glucagon, mobilize stored products into usable chemicals. opposite to insulin.

D cells, somatostatin: inhibits secretion of insulin and glocagon.

PP cells: pancreatic polypeptides: controlling gastrointestinal activities as promoting the flow of gastric juice.
pituitary gland (hypophysis): two sources

infundibulum: an outgrowth from the diencephalon, retains connection to brain and becomes neurohypophysis

Rathke's pouch: a diverticulum from the stomodeum: no connection to stomodeum, and becomes the adenohypophysis.

can be recognized by tissue arrangements, staining properties, or anatomical position


three regions of adenohypophysis:

pars distalis: major portion of adenohypophysis; into lobes or subregions

pars tuberalis: ant to distalis, only in tetrapods, function ?, circadian rhythm, photoperiod

pars intermedia: remnant of lumen of Rathke's pouch

two regions of neurohypophysis:

pars nervosa

median eminence: more anterior
cells in neurohypophysis do not produce hormones (axons of hypothalamus secrete contents into it).

hypothalamus secrete neurohormones (releasing hormones or release-inhibiting hormones) through plexus to stimulate or inhibit cells of the adenohypothesis.


in neurohypophysis

vasopressin (antidiuretic hormone, ADH): synthesized by neurosecretory cells of the hypothalamus. acts on smooth muscles in the walls of peripheral arterioles, causing a rise in blood pressure. when dehydrated, ADH carried by blood cause the collecting ducts to become highly permeable to water, and produce concentrated urine. (diabetes insipidus: dilute urine, patient constantly thirsty)

oxytocin: target on myometrium (smooth muscle of the uterus) and myoepithelial cells of the mammary gland.

in adenohypophysis:

growth hormone (GH): target the liver, increased protein synthesis, mebilization of fatty acids, decreased utilization of glucose.

protactin (PRL): promotes development of mammary gland and lactation during pregnancy. stimulates lipid synthesis during premigratory fattening and support brooding behavior in birds. also crop milk, affect tail regeneration in lizards and growth in amphibians. in teleosts for osmoregulation (for migratory fish)

thyrotropin (TSH, thyroid-stimulating hormone): stimulate thyroid to synthesize and release of T3 and T4 into blood

gonadotropins (follicle-stimulating hormone, FSH; and luteinizing hormone, LH):

FSH induce development of ovarian follicles, also maintain spermatogenesis in males;

LH to finalize maturation of ovarian follicles. rise in LH promote ovulation and forming corpus luteum; in males to stimulates interstitial cells of the testis to secrete testosterone.

corticotropin (adrenocorticotropic hormone, ACTH): stimulate cortex of adrenal gland to release glucocorticoids.

melanophore-stimulating hormone (MSH): in pars intermedia; target on melanophores.


gonad

hormones support secondary sex characteristics. mainly estrogen and progestogens.


pineal gland (epiphysis): dorsal evagination of the midbrain. may involve in the release of ACTH from adenohypophysis, vasopressin secretion, inhibition of thyroid activity, or immune system
secondary endocrine organs

gastrointestinal tract

gastrin: stomach, stimulate the secretion of gastric juice

secretin: intestinal mucosa of duodenum: stimulate the pancreas to release pancratic juice (alkaline) to buffer the chyme

enterogastrone: inhibit furthur gastric secretion and mobility

cholecystokinin (CCK) of cholecystokinin-pancreozymin (CCK-PZ): from intestinal mucosa: stimulate relaxation of sphincter at the base of bile duct, the contraction of gallbladder, and ejection of bile. also stimulates the pancreas to secrete pancreatic juice containing enzymes.


kidney

renin (catalyzes the transformation of angiotensinogen in blood to angiotensin I, and to angiotensin II, in lungs. Angiotensin II is a vasoconstrictor that increase blood volume by stimulating the release of aldosterone from adrenal gland, aldosterone cause the distal tubules to reabsort more sodium, and then increase reabsorption of water

erythropoietin (EOP): reduced oxygen level in blood stimulates the production of EOP. stimulate red blood cell production.
Endocrine Coordination
1. mammalian reproduction
2. metamorphosis


The Nervous System
Central Nervous System (CNS): brain, spinal cord.

Peripheral Nervous System (PNS): all other nervous tissue.


Neuroglia are supporting, nourishing, and insulating cells in the nervous system.

Neurons are the cells for transmitting signals.


PNS

somatic vs visceral

afferent vs efferent

sensory vs motor

general vs special
1. Spinal nerves

dorsal root: afferent

ventral root: efferent

origin: neurons in the spinal cord, and from neural crest

each spinal nerve generally innervates a single somite.
2. Cranial nerves: roots in the braincase.

10, 12, 13 cranial nerves


dorsal: V, VII, IX, and X

ventral: III, IV, VI, XII


0. (terminal):

I. (olfactory)

II. (optic)

III. oculomotor

IV. trochlear

V. trigeminal

VI. abducens

VII. facial

VIII. octaval

IX. glossopharyngeal

X. vagus

XI. spinal accessory

XII. hypoglossal

(lateral line nerves: from medulla)

see tables 16.1 and 16.2 for functions and associated branchial arches in cranial nerves.
Functions of PNS

spinal reflexes

autonomic nervous system: motor neurons from brain and spinal cord; functions see Table 16.4

sympathetic:’thoracolumbar outflow’. preganglionic neuron short, postganglionic fiber long (acetylcholine)

parasympathetic: cranial nervesVII, IX, and X; and spinal nerves from the sacral region. long preganglionic neurons, ganglion on visceral organ (cholinergic)
CNS: receive sensory information from

interoceptors: e.g., proprioceptors

exteroceptors: touch, pressure, hearing, sight, smell, taste, etc.

memory:
Embryology of CNS

fusion of two neural folds into a hollow tube, with fluid-filled ventricles.

three regions are formed: prosencephalon, mesencephalon, and rhombocephalon


basic structures

outside the brain and spinal cord are meninges (mininx) with three layers, dura mater, arachnoid, pia mater.

blood vessels in pia mater

cerebrospinal fluid (CSF)

choroid plexus: small tufts of blood vessels project into ventricles at specific point, and is the source of CSF.
Spinal Cord:

gray matter: nervous cell bodies within the core

white matter: mainly fibers surrounding the gray matter

spinal tracts:

ascending tracts: carry ssensory impulse from spinal cord to medulla

fasciculus gracilis, fasciculus cuneatus in the dorsal region (proprioceptors, sensations)

spinocerebellar tracts: carry proprioceptive information to cerebellum

lateroventral spinothalamic tract: to thalamus about sensation of pain and temperature

descending tracts: from brain to spinal Cord

corticospinal tract: from cerebral cortex to motor neurons to the limbs

tectospinal tract: associated with optic and auditory (turn head, to neck)

rubrospinal tract: from midbrain to spinal cord and involved in initiating coordinated movements


Brain
Prosencephalon:

telencephalon: olfactory bulb, cerebral hemisphere

diencephalon: thalamus, pineal body, hypothalamus, pituitary

Mesencephalon: tectum (sensory) and tecmentum (motor)

Rhombencephalon:

metencephalon: cerebellum, pons,

mylencephalon: medulla oblongata
form and function
hindbrain

medulla oblongata: reflexes mainly

location of nuclei of cranial nerves V to X (in sharks) or VII to XII (mammals)

major routes for descending and ascending neural passways

center for visceral, auditory, and proprioceptive reflexes

pons: on the floor of the hindbrains in amniotes: pontine nuclei, convey information to cerebellar cortex from cerebral cortex

cerelellum: medial corpus and a paired lateral auricle

maintaining equilibrium; information of senses and motor input are processed here.

refinement of motor functions
midbrain

roof, tectum, receive sensory information, i.e., optic tectum and torus semicularis

floor: tegmentum, initiate motor output through IV and III nerves
forebrain

diencephalon

epithalamus: include pineal gland (biologicl rhythm, skin pigmentation), and habenular nucleus (function unclear)

hypothalamus: floor of diencephalon

mammillary bodies (part of the Papez circuit involved in reproductive behavior and short-term memory); responsible for homeostatis mechanisms

ventral thalamus: small area between the midbrain and the rest of the diencephalon

dorsal thalamus: nuclei receiving sensory input (relay center for sensory information going to cerebrum)
telencephalon: cerebral hemispheres and olfactory bulbs

gyri: rounded folds

sulci: grooves

fissue: deep sulcus seperating major surface regions of the cerebrum

commissure: bands of neurons transversely crossing the midline between respective brain regions

corpus collosum: commissure found only in eutherians


cerebrum has two regions

pallium dorsally and subpallium ventrally.

embryonic five regions: (Fig. 16.42) two in subpallium and three in pallium

lateral pallium: receives olfactory input via the lateral olfactory tract

dorsal pallium: receive visual, lateral line, thalamic and auditory stimuli

meidal pallium: exchange information between the hemispheres (?)

reptiles: cerebrum as a result of enlarged medial pallium

mammals: cerebrum as a result of enlarged dorsal pallium (isocortex)

hippocampus: mammalian medial pallium

septum (of subpallium): medial; receive info from medial pallium and to hypothalamus and tegmentum

striatum (of subpallium): lateral; with pallidum, are part of a nuclear group called basal ganglia. (contraol of movement
functional associations of parts of CNS
Limbic system: first described by Paul Broca, and later functions described by James Papez

“cerebral cortex immediately encircling the corpus callosum and brain stem” (including the deept parts of the cerebral cortex (cingulate gyrus) and medial surface of the temporal lobe of the cerebral cortex).


It includes thalamus, hypothalamus, amygdala, hipppocampus, cingulate gyrus, and septum; with the fornex connecting all nuclei of the system.

hypothalamus: contains nuclei affecting heart rate, respiration, the general visceral activity through the autonomic system

amygdala: active in the production of aggressive behavior and fear

hippocampus (medial pallium): damages causes loss of recent memory

cingulate gyrus: damage results in disruption of the order of compelx behavior
two main functions of the limbic system

regulates the expression of emotions

spatial and short-term memory
Reticular formation

in medulla and midbrain: diffused neurons and fibers without well-defined tracts or nuclei.

functions

arousal in action vis its awakening or stimulation of the cerebral cortex

filter: selecting information to be relayed to higher centers or down the spinal cord.

association neurons in the spinal cord




Senseory organs
Perception and sense

conscious sensations are subjective interpretation of the environments

all senses are sent to the nervous system by the same kinds of electrical impulses
A sensory organ

nerve fibes; dendrites connected to tissues that amplify the stimulus and translates energy from one kind (sound) to electrical.


General Sensory Organs

free sensory receptors: free nerve endings; tactile sensations in skin, cornea, oral cavity, etc.

encapsulated sensory receptors: sensory processes enclosed in a specialized structure; such as Meissner’s corpuscle, Pacinian corpuscles, etc.

associated sensory receptors: processes wrapped around another organ: muscle spindles, Golgi tendon organs


Special snsory organs

Chemoreceptors: smell and taste: on olfactory epithelieum and one body surface (aquatic)


olfactory system develops from olfactory placodes, invaginates to form respiratory epithelium (lateral wall) and sensory epithelium (center). Neurons grows out from the epithelium and reaches telencephalon to induce the brain to form olfactory bulb.
Mouth (taste buds): mainly terrestrial vertebrates.

tastes buds innervated by the facial, vagus, and glossopharyngeal nerves.


Radiation receptors: every species detects a limited range of the full electromagnetic spectrum. (most in the 380 to 760 nm range)
eye

sclera


uvea:

choroid: pigmented, and vascular (including tapetum lucidum in some nocturnal animals).

ciliary body: smooth muscle around the interior of the eyeball; attached to the lens through suspensory ligament.

iris: thin continuation of the uvea across the front of the eyeball.

pupil: not a structure!!

retina: three cell layers: photoreceptors (rods, cones); amacrine cells, ganglion cells


three chambers

anterior chamber: between iris and cornea (aqueous humor)

posterior chamber: between iris and lens (aqueous humor)

vitreal chamber: vitreous humor


eye developed from mesenchymes and optic placode.

start from the optic vesicles of the telencephalon, and induced the overlying ectoderm to form optic placodes, which invaginates to form lens primodium.

ectoderm: eyelids, cornea, and lens

mesenchymes: choroid and sclera

optic cup: iris and retina
pineal complex: roof of the diencephalon produces the parietal organ.

photorecoptors in anamniotes; endocrine organ in amniotes


four regions (from anterior): paraphysis, dorsal sac, parietal organ, and epiphysis.
Infrared receptors:
labial pits, facial pits in some snakes
Mechanoreceptors, hair cells (microvilli)
1. lateral line system

2. vestibular apparatus: endolymph and perilymph (from otic placode)

seimcircular canals and at least two connecting compartments (sacculus and utriculus)

vestibular epithelium in sacculus and utriculus (neuromast organs) (otolith receptor or macula)

cristae (sensory epithelium in semicircular canals
auditory system (lagena, cochlea): an enlargement of the sacculus and forming cochlea in mammals

organ of Corti: sensory receptors in the lagena.


external ear: pinna, external auditory meatus
middle ear: tympanum and ear ossicles
middle ear cavity, and the eustachian tube form from the first pharyngeal pouch

middle ear ossicles: stapes (columella) from the hyomandibular; in all tetrapods. incus (quadrate) and malleus (articular) onlyin mammals


inner ear:

vestibular apparatus and the surrounding perilymphatic spaces


Electroreceptors: fish head; specialized neuromast organs


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