ZOO301 Handouts
ZOO301 Handouts
ZOO301 Handouts
12 Hydrostatic skeleton
Four cell types contribute to movement:
1. Amoeboid cells
2. Flagellated cells
3. Ciliated cells &
4. Muscle cells
Earthworm:
Longitudinal and circular muscles contract alternately creating a rhythm that moves the earthworm.
Hydro skeleton keeps the body from collapsing when the muscles contract.
13 Exoskeleton
Exoskeleton is a rigid external frame-work of the body.
Functions:
• Provides site for muscle attachment.
• Supports and protects the body like a shield.
• Prevents internal soft tissues from drying out.
• Provides protection from enemies.
Exoskeleton in Arthropods:
• Cuticle waterproofs the body.
• It limits the animal growth.
• Periodic shedding of exoskeleton.
• At the joint regions the cuticle is flexible, where the antagonistic muscles function.
• At wing joints, a protein, resilin, stores energy on compression and then releases energy to produce
movement.
• This is reason for success of arthropods.
14 Endoskeleton
Introduction:
Endoskeleton is the internal framework of the body.
Examples:
Spicules in Sponges.
Calcareous plates (ossicles) in echinoderms
Bones in vertebrates.
15 Mineralized tissues in vertebrates
What are mineralized tissues?
Tissues in which inorganic calcium carbonate crystals are embedded in the collagen matrix.
About two-third of the living species that contain mineralized tissues are invertebrates.
Examples:
• Gastropods
• Lower chordates
16 Skeletal System of Vertebrates: Cartilage, Bone.
Introduction:
Skeletal System of Vertebrates is an endoskeleton enclosed by other tissues.
The endoskeleton consists of cartilage and bone.
Cartilage is a specialized type of connective tissue that provides:
• Support
• Helps in movement at joint
• Site for muscle attachment.
Histologically it consists of:
1. Cells (chondrocytes)
2. Fibers
3. Cellular matrix
Bone or Osseous tissue has the following functions.
• Provides a point of attachment for muscles.
• Support the internal organs of the animal.
• Store reserves calcium and phosphate.
• Manufactures blood cells.
• Bone cells also called osteocytes are located in minute chambers called lacunae, which are arranged in
concentric rings around the osteonic canals.
• These cells communicate with nearby cells through small channels called canaliculae.
17 Skeleton of fishes
Bone cells also called osteocytes are located in minute chambers called lacunae, which are arranged in
concentric rings around the osteonic canals.
These cells communicate with near by cells through small channels called canaliculae.
25 Fish musculature
• In fish the musculature consists of segmental myomeres.
• The myomeres are arranged along the vertebral column in 3D ‘W’ shaped blocks separated by
collagenous sheaths called myosepta.
• Embedded in the myosepta are distinct tendons.
• Within teleosts these tendons often ossify.
• These ossified myoseptal tendons are homologous to inter muscular bones.
• These intermuscular bones are of various shapes, some are Y shapes, some are brush like etc.
• Fish movements are based on myomere contraction.
• These myomeres cause the lateral undulations of the trunk and the tail.
• These undulations bring about fish locomotion.
26 Structure of Skeletal muscle I
Skeletal muscle consists of a bundle of long fibers running the length of muscle.
Each muscle fiber is a single cell with many nuclei below the cell membrane, the sarcolemma.
This reflects its formation by the fusion of many embryonic cells.
Each muscle fiber is surrounded by connective tissue called Endomycium.
Perimycium is connective tissue that wraps bundles of muscle fibers.
Epimycium wraps the whole muscle.
Each muscle fiber is itself composed of smaller myofibrils arranged longitudinally.
The myofibrils, in turn , are composed of myofilaments, which are
i) Thin and
ii) Thick
Each muscle fiber is itself composed of smaller myofibrils arranged longitudinally.
Skeletal muscle is also called striated muscle because of repeating pattern of light and dark bands.
Each repeating unit is called a sarcomere.
Sarcomere is a basic functional unit of the muscle.
The borders of sarcomere is called Z-line.
The Z-lines of adjacent myofibrils contribute to the striations visible with light microscope.
Thin filaments are attached to Z lines and project towards the center of the sarcomere They are 7-8 nm in dia.
Thick filaments are centered in the sarcomere and are 16nm in diameter.
Forebrain:
The vertebrate fore brain has changed a great deal during evolution.
The forebrain has two main parts- and telencephalon and diencephalon.
Telencephalon, the front part of the fore brain expanded rapidly in size and complexity
Telencephalon consists of :
a. Cerebrum,
b. Olfactory bulb,
c. Limbic system and
d. Corpus Striatum
Cerebrum is divided by a deep groove into Rt and Lt Cerebral hemispheres.
In mammals, the outer most part of cerebrum is called cortex.
Telencephalon consists of :
a. Cerebrum,
b. Olfactory bulb,
c. Limbic system and
d. Corpus Striatum
Cerebrum is divided by a deep groove into Rt and Lt Cerebral hemispheres.
In mammals, the outer most part of cerebrum is called cortex.
Telencephalon consists of :
a. Cerebrum,
b. Olfactory bulb,
c. Limbic system and
d. Corpus Striatum
Cerebrum is divided by a deep groove into Rt and Lt Cerebral hemispheres.
In mammals, the outer most part of cerebrum is called cortex.
The diencephalon expanded slowly as compared to telencephalon.
Diencephalon contains-thalamus. Hypothalamus,
Pineal gland and
Pituitatory gland,
The thalamus relays all the sensory information to higher brain centers.
The hypothalamus regulates many functions, sexual drive, Carbohydrate metabolism,
hunger and thirst.
Pituitary gland is a master endocrine gland and produce about 9 hormones.
50 Anatomy of vertebrate brain II
Mid Brain:
Mid brain contains reticular formation, which is a relay center connecting hind brain with
the fore brain.
Mid brain did not change in size. The roof of the mid brain is a thickened region of grey
mater that integrates visual and auditory signals.
Hind Brain:
Hind brain is continuous with the spinal cord and includes:
a. Pons ,
b. Cerebellum and
c. Medulla oblongata
Pons is a bridge of transverse nerve tracts from cerebrum to cerebellum.
Cerebellum:
It is an outgrowth of medulla oblongata.
In tetrapods the cerebellum is laterally expanded.
They provide locomotor control of muscles of appendages.
Cerebellum is much larger in birds and mammals.
Medulla oblongata:
MO is the enlargement where the spinal cord enters the brain.
It contains reflex centers for breathing, swallowing, cardiovascular .
It is well developed in jawed vertebrates.
52 Cranial nerves I
I. Olfactory nerve:
Olfactory Nerve is the first cranial nerve and conveys special sensory information related
to smell. It is the shortest of the cranial nerves and passes from its receptors in the nasal
mucosa to the forebrain.
II. Optic nerve:
It transmits visual information from the retina to the brain.
III. Occulomotor:
It enters the orbit and innervates muscles that enable most movements of the eye and that
raise the eyelid.
IV Trochlear:
It innervates only single superior oblique muscle of the eye. Controls the downward
movement of the eye ball.
V Trigeminal:
A nerve responsible for sensation in the face and motor functions such as biting and
chewing.
Its three major branches are:
a. Ophthalmic nerve
b. Maxillary and
c. Mandibular
V Trigeminal:
A nerve responsible for sensation in the face and motor functions such as biting and
chewing.
Its three major branches are:
a. Ophthalmic nerve
b. Maxillary and
c. Mandibular
Mandibular division Supplies Scalp, skin of jaw, lower teeth, lower gum and lower lip.
VI Abducens:
It is motor nerve.
Supplies jaws, floor of mouth and eye muscles.
Olfactory and optic are sensory nerves.
Occulomotor and Trochlear are motor.
Trigeminal is mixed and Abducens is motor nerve.
53 Cranial nerves II
VII Facial:
It emerges from Pons of the brainstem.
Controls the muscles of facial expression, taste receptors of anterior 2/3 of tongue, tear
glands and salivary glands.
Inflammation or damage of this nerve cause Bell’s Palsy
VIII Vestibulocochlear:
It has two branches -Vestibular and Cochlear.
The vestibular nerve innervates the vestibular system of the ear.
It is responsible for equilibrium.
Cochlear supplies the inner ear and serves the sense of hearing.
XI Accessary Nerve:
Has two branches-
a) Cranial branch
b) Spinal branch
Innervates soft palate, pharynx and larynx. It is motor nerve.
XII Hypoglossal:
It is a motor nerve.
Innervates tongue muscles.
Facial nerve is a mixed nerve and
Vestibulocochlear is a sensory nerve.
Glossopharyngeal and Vagus nerves are mixed nerves.
Accessory and Hypoglossal are motor nerves.
54 Introduction of Autonomic NS
Autonomic nervous system (ANS) is the part of peripheral nervous system.
PNS also includes Somatic Nervous System (SNS).
The SNS consists of motor neurons that stimulate skeletal muscles.
In contrast, the ANS consists of motor neurons that control smooth muscles,
cardiac muscles and
glands.
In addition, the ANS monitors visceral organs and blood vessels.
In the ANS, the connection between the CNS and its effector consists of two neurons—
the preganglionic neuron and the postganglionic neuron.
The synapse between these two neurons lies outside the CNS, in an autonomic ganglion.
The ANS is further divided into the sympathetic nervous system and the parasympathetic
nervous system.
54 Sympathetic and Parasympathetic NS
Autonomic NS is divided into divisions:
Sympathetic and
Parasympathetic NS.
These two divisions generally make synaptic contacts with the same organ but usually
produce opposite effects.
Sympathetic NS:
It consists of ganglia, nerves and plexues that supply involuntary muscles.
This NS arise from middle portion of spinal cord and terminate in ganglia.
This system is important during emergency situation.
‘Fight and flight”
However neither kind of nerve is exclusively excitatory or inhibitory,
For example, the sympathetic fibers increase heart beat but inhibit intestinal peristaltic
movements.
Parasympathetic NS:
This system consists of nerves some of which emerge from brain and others from sacral or
pelvic region of the spinal cord.
PS division is associated with non stressful activities e.g. resting, eating, digestion &
urination.
Retards heartbeat.
55,56 Introduction of sensory reception
In human five senses- sight, smell, hearing, taste and touch are commonly known.
Apart from these there are other senses also found in animals
For example: Invertebrates possess the following sensory receptors:
i) Tactile receptors that sense touch.
ii) Hygroreceptor that detect content of air.
iii) Georeceptors That sense pull of gravity.
iv) Proprioceptors- that respond to compression, stretching, bending, and tension.
v) Phonoreceptors- That are sensitive to sound
vi) Baroreceptors- that respond to pressure changes.
vii) Chemoreceptors- that are sensitive to air and water borne chemicals.
viii) Photoreceptors-that are sensitive to light.
ix) Thermoreceptors- that are sensitive to temp changes.
vi) Baroreceptors- that respond to pressure changes.
vii) Chemoreceptors- that are sensitive to air and water borne chemicals.
viii) Photoreceptors-that are sensitive to light.
ix) Thermoreceptors- that are sensitive to temp changes.
Sensory receptors convert stimuli into nerve impulse.
All receptors are tranducers i.e. that convert one form of energy into another.
Different types of receptors convert different kinds of stimuli into local electrical potential
called generator potential.
When the GP reaches the neuron threshold potential, it causes the channels in plasma
membrane to open and creates an action potential.
The impulse then travels along the axon towards a synaptic junction and becomes
information going to the CNS.
The nature of the nerve impulse is the same.
How then action potential give rise to different sensations?
Animals that have, nerve signals from specific receptors always end up in a specific part
of brains for interpretation.
For example a stimulus that goes to the optic center is interpreted as visual sensation. And
so on.
57 Invertebrate sensory receptors
An animal’s behavior is largely a function of its responses to environmental information.
Invertebrates possess a variety of receptors through which they receive information about
their environment.
(a) Baroreceptors
(b) Chemoreceptors
(c) Georeceptors
(d) Hygroreceptors
(e) Phonoreceptors
(f) Photoreceptors
(h) Tactile receptors
(i) Thermoreceptors
58 Baroreceptors
Baroreception
A barometer is a scientific instrument used to measure air pressure.
Pressure tendency can forecast short term changes in the weather.
The Zoologists have not identified any specific structures for baroreception in
invertebrates.
Nevertheless responses to pressure changes have been identified in ocean swelling
copepod crustaceans, Ctenophores, jelly fishes medusa and squids.
Some crustaceans that live between the tides respond to water pressure changes and
coordinate with daily tidal movements.
59 Chemoreceptors
Chemoreceptors are sensitive to chemicals.
Chemoreception is the oldest and most universal sense in animal kingdom.
Examples:
Protozoans show avoiding response to acid, alkali and salt stimuli.
Specific chemical attract predatory ciliates to their prey
Location of chemoreceptors:
In aquatic invertebrates they are located in pits or depressions, through which water
carrying the specific chemicals may be circulated.
In arthrpods, the receptors are usually located on the antennae, mouthparts, and legs in
the form of hollow hairs called Sensilla containing chemosensory neurons.
The types of chemicals to which invertebrates respond are closely associated with their
life styles.
For example: chemoreceptors are sensitive to humidity; pH, prey tracking, food
recognition, and mate location.
With respect to mate location the antennae of male silkworm moth detect one bombykol
molecule in over a trillion molecules of air.
Female silk moth secrete bombykol as a sex attractant.
This enables a male to find a female at night from several miles down wind.
Occurrence of georeceptors:
They are found in various gastropods, cephalopods, crustaceans, nemertines, polychaetes
and scyphozoans.
Burrowing animals can not rely on photo for orientation instead they rely on georeceptors
within he substratum.
Planktonic animals orient in their environment using statocysts.
They are important at night and deep waters.
Most of aquatic insects detect gravity from air bubbles entrapped in tracheal tubes, which
stimulate sensory bristles that line the tubes.
61 Hygroreceptors
Hygroreceptors are sensitive to water content of air.
Some insects have hygrorecptors that can detect small changes in the ambient relative
humidity.
There hygroreceptors are have been identified on the antennae, palps, underside of the
body and near the spiracles.
Hygroreceptors enables the insects to seek an environment with a specific humidity to
modify their physiology or behavior with respect to humidity.
Drosophila detect air humidity through hygroreceptors located in a sac like invagination
of the antenna.
These receptors rapidly respond to a puff of dry air, potentially alerting the animal to the
fact that dangerous dry conditions are looming.
Swarming, in termite is humidity dependent.
62 Phonoreceptors (tympanal organ)
Phonoreceptors are the receptors that respond to sound.
They have been identified only in insects, archnids and centipedes.
Some other invertebrates seem to respond to sound- induced vibrations of the substratum.
Crickets, grasshoppers posses phonoreceptors called tympanic or tympanal organs.
This organ consists of tough, flexible tympanum that covers internal sac. The sensory
neurons are attached to the tympanum.
When sound waves strike the tympanum it vibrates.
When sensory neurons are stimulated by these vibrations generator potential is produced.
Most arachnids possess phonoreceptors in their cuticle called slit sense organs that are
sensitive to vibrations.
Centepedes have organs of Tomosvary, which are sensitive to sound.
However, the physiology of these organs i.e. the organs of Tomosvary and slit like organs
are poorly known.
63 Photoreceptors (Ocellus) I
Photoreceptors are sensitive to light.
All photoreceptors possess light-sensitive pigments e.g. rhodopsin and carotenoids.
These pigments absorb photons of light energy and then produce generator potential.
This is basic commonality.
Photoreceptors in various organisms:
Euglena:
Stigma (mass of bright red granule containing carotenoid.
Actual photoreceptor is the swelling at the base of the flagellum.
Stigma serves as a shield, which is essential if the receptor is to detect light.
Thus the photoreceptor plus stigma enable euglena to orient itself so that its receptor is
exposed to light.
This helps the protozoan maintain itself in the region where sufficient light is available.
In earthworm Lumbricus, simple unicellular photorecepter cells are scattered over the
epidermis or concentrated in particular areas of the body.
Other animals possess multicellular photoreceptors that can be classified into:
ocilli,
compound and
complex eyes.
Ocellus is simply a small cup lined with light sensitive receptors (retilunar cells) and
backed by light absorbing pigment.
The retilunar cells contain photosensitive pigments.
Stimulation by light causes a chemical change in the pigment.
This stimulation leads to generator potential then action potential that sensory neurons
carry.
This type of visual system gives animal an information about the direction and intensity of
light only but no image.
Ocelli are common in phyla such as Annelida, Mollusca and Arthropoda.
64 Photoreceptors (compound eye) II
This stimulation leads to generator potential then action potential that sensory neurons
carry.
This type of visual system gives animal an information about the direction and intensity of
light only but no image.
66 Proprioreceptors
Proprioceptors commonly called stretch receptors.
Located internally.
Sensitive to mechanically induced changes caused by stretching, bending compression or
tension.
These receptors give an animal information about the movement of its body parts and
their position relative to each other.
Proprioceptors are associated with appendage joints and body extensor muscles.
In these animals the sensory neurons may be attached to the muscles, elastic connective
tissue fibers or various membranes that span joints.
As shape changes, generator potential starts.
67 Tactile Receptors
Tactile receptors are generally derived from modifications of epithelial cells associated
with sensory neurons.
Most tactile receptors of animals involve projections from the body surface.
These projections include: bristles, spines, setae and tubercles.
When an animal comes in contact with an object in the environment, these receptors are
mechanically deformed.
These deformations activate the receptors, which in turn activates underlying sensory
neuron initiating generator potential.
Most tactile receptors are also sensitive to mechanically induced vibrations propagated
through water or a solid substrate.
Examples:
Tube swelling Annelids bear receptors that allow them to retract quickly from their tubes
in response to any movement in surroundings.
Web-building spiders have tactile receptors that can sense struggling prey in webs through
vibrations of the web threads.
68 Thermoreceptors
Web-building spiders have tactile receptors that can sense struggling prey in webs through
vibrations of the web threads.
Leeches and ticks possess heat sensing mechanism that can recognize warm blooded
hosts.
Certain insects, some crustaceans, and the horseshoe crab (Limulus) can also sense
thermal variations.
In all of these cases, however, specific receptor structures have not been identified.
69 Vertebrate Sensory Perception
Vertebrate sensory receptors reflect adaptations to the nature of sensory stimuli in
environment.
The environment has chemical and physical characteristics that affect the kinds of energy
and molecules that carry sensory information.
For example, our external environment consists of the media that surrounds us: the earth
that we stand on and the air that we breathe.
Other animals may have different external environments: a trout may be immersed in the
cool, clear water of a mountain stream.
A turtle may be submerged in the turbid water of a swamp; and a salmon may be
swimming in the salty water of the sea.
70 Lateral line system
The lateral line system is electrical sensing that occur both in jawless and jawed fishes and
some amphibians, along the sides of head and body
It consists of sensory pores in the epidermis of the skin that connect to canals leading into
electroreceptors called ampullary organs.
These organs can sense feeble electrical field produced by organisms living in
surrounding water.
This ability to detect these fields help a fish to find mate, capture prey or avoid predators.
This is especially valuable sense in deep, turbulent or murky water where vision is of little
use.
In fact, some fishes actually generate fields and then use their electroreceptors to detect
how surrounding objects distort the field.
This allows these fishes to navigate in murky or turbulent waters.
71 Lateral line system & Mechanoreception
Mechanoreceptor also called Neuromasts are the part of Lateral Line system.
These receptors are fund in cyclostomes, sharks, aquatic amphibians and some advanced
fishes.
Neuromasts are located in pits along the body but not in head region.
Neuromasts are responsive to local water disturbance.
When water near the lateral line moves, water in the pits also moves.
This movement disturbs hair like cells of the neuromasts causing the generator potential in
the associative sensory neurons.
This helps the animal to detect the direction and force of water currents and thus the
movement of other animals in the vicinity and become alert from the predators.
For example this sense enables a trout to orient the head upstream in water.
72 Hearing and Equilibrium in air
Hearing is important to vertebrates as a mechanism to:
a) become alert against nearby or faraway dangerous activity.
b) become important for the location of food communicated by other animals e.g. Crows.
c) respond the calls for mating e.g. cats, cows.
Hearing and Equilibrium are the sensations that occur together in the same vertebrate
organ, ear.
For hearing it is the Auditory organ and for equilibrium and posture, the Vestibular
apparatus.
The main part of auditory apparatus which is involved with hearing is the cochlea.
The part of the ear which is involved with equilibrium are the semicircular canals.
Sound results when waves transmit energy through some medium such as air or water.
Adaptation of hearing in air resulted from the evolution of an acoustic transformer that
incorporates a thin membrane that is exposed to air.
73 Tympanum in Amphibians
Tympanum or the ear drum first evolved in Amphibians.
Ears of Anurans consists of :
a) Tympanum
b) Middle ear and
c) Inner ear
Tympanum is modified integument stretched over cartilaginous ring.
93 Functioning of eye
The retina is a thin layer of tissue that lines the back of the eye on the inside.
The retina is a light-sensitive layer which is composed of pigmented epithelium, that
covers the choroid layer.
Nervous tissue that contains photoreceptor cells lies on this basement layer.
The photoreceptor cells are called rod and cone cells.
Rods are sensitive to dim light whereas cones respond to high intensity light and involved
in color perception.
With the help of the cornea and crystalline lens, image is formed on the retina which
transforms it into nerve impulses and sent to the brain.
Chemistry of Vision:
Visual perception in humans occurs through the absorption of electromagnetic radiations
by photoreceptors in the retina.
When rhodopsin, a pigment in rod cells, absorb light energy.