COMPARATIVE ANATOMY LECTURE NOTES
LECTURE 1
LECTURE 2
LECTURE 3
LECTURE 4
LECTURE 5
LECTURE 6
LECTURE 7
LECTURE 8
LECTURE 9
LECTURE 10
LECTURE 11
LECTURE 12
LECTURE 13
LECTURE 14
LECTURE 15
LECTURE 16
Origin and Diversity
Diversity and Phylogeny
Diversity and Phylogeny
Biological Design
Life History
The integument
Cranial skeletons
Post-cranial skeletons
Muscles
The Respiratory System
The Circulatory System
The Digestive System
The Urogenital System
The Endocrine System
The Nervous System
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
independent evolution
/convergence
different
evolution
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.
<back to top>
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
<back to top>
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
<back to top>
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.
<back to top>
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
<back to top>
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
<back to top>
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
<back to top>
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
<back to top>
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
<back to top>
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
<back to top>
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
<back to top>
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;
<back to top>
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
<back to top>
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
<back to top>
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
<back to top>