Download - Scales
Skin Scales and Skeletal MusclesContents:
ScalesTypes of Scales:Are all scales the same size? Can scale type vary with sex? Slime and Spots Functions of ScalesHow old is a fish scaleFish skinFunctionSkin StructureFish and Mammalian skinSkin PropertiesHormonal control of Skin
Skeletal MusclesTypes of MuscleSkeletal Muscles functionProperties of MuscleStructureMyosin (Thick) MyofilamentActin (Thin) MyofilamentsSliding Filament Model of ContractionNeuromuscular JunctionMotor Unit:Contractile Machinery: SarcomeresCrossbridge formation and movemen
Scales
A rigid plate out of an animal's skin to provide protection.
Evolved multiple times with varying structure and function.
Classified as an organism's integumentary system.
scales usually not eaten.
Types of scales
Ganoid Leptoid PlacoidCosmoid
Scales of Rohu (Labeo
rohita)
Ganoid Scales
Diamond-shaped, shiny, and hard.
gars (family Lepisosteidae), reed fishes (family Polypteridae), Sturgeons and Paddlefish
Similar to cosmoid but ganoin lies over the cosmine layer
Leptoid scales
Leptoid believed to derived from ganoid scales by the loss of ganoin layer
Single layer of bone.
Two forms:cycloid (circular) and ctenoid (toothed)
As they grow,add concentric layers.
Overlaping in a head-to-tail direction, like roof tiles
Leptoid scales
Jungle Perch Kuhlia rupestris
Paradise Fish, Macropodus opercularis
Leptoid scales
Cycloid scales
smooth outer edge,
primitive fish salmon, carp, trout, smelt, herrings and minnows
Ctenoid scales
a toothed outer edge,
derived fishes bass, crappie and perch
Kardong, Kenneth V. (1998).
Placoid scales
also called dermal denticles, tooth like structure sharks and raysconsists of an upper layer of enamel like substance called vitrodentine, a lower layer of dentine, a pulp cavity, and a disk like basal plate embedded in the skin.
Placoid scales
Do not increase in size, new scales must be added as a shark grows
Homologous with teeth in all vertebrates.
Broadnose Sevengill Shark
Cosmoid scales
primitive coelacanth (Latimeria chalumnae) or as fossils.
a four-layered bony scale.
1. upper layer is enamel like vitrodentine
2. the second layer is a hard, dentine like called cosmine
3. the third layer is spongy bone, and
4. the lowest layer is dense bone
Cosmoid scales
In lungfishes, but highly modified, single-layered form.
Similar in structure to placoid probably arose from fusion of placoid scales
Queensland Lungfish
Cosmoid scales
scales of bony fishes evolved a long time ago
they had four layers,
one of dense bone,
one of spongy bone,
one of dentine and
one of enamel.
Are all scales the same size?
No sizes vary between species.
freshwater eels and tunas tiny embedded scales,
Coral Snappers medium sized,
of Tarpon, Megalops cyprinoides to be used in jewelry.
In Indian Mahseer, reach over 10 cm in length.
Can scale type vary with sex?
Yes. In flatfishes, males have ctenoid and females have cycloid scalesSole have ctenoid scales on the 'eyed' side and cycloid scales on other side. Sea Perches, have ctenoid scales above the lateral line and cycloid belowNot all species have scales,clingfishes are scale less. Protected by a thick layer of mucous,
Function of Slime and Spots
Hydrodynamic function to reduce water friction and resistance to forward motion
Enzymes and antibodies as a defensive system
Spots size fluctuate according to nervous stimuli.
The arrangement imbricate or mosaic
General Functions
To calculate a fish’s age
Dried scale of a Barramundi showing annuli.
Times of migration, periods of food scarcity and illness
How old is a fish scale?
As scales increase in size, growth rings called circuli visible.
Cooler months scale grows slowly and circuli are closer leaving a band called an annulus.
Source and reservoir of calcium.
Fish skin
Barrier, strong, tough and watertight,
Ion- and water balance
The scales lie in the Dermis of skin
Skin Structure
Two layers, the Epidermis (outer) layer and the Dermis.
Epidermis is made up of epithelial cells
Inter-spaced between epithelial cells are slime cells produce mucous secretions
Dermis consists of two layers:stratum spongiosum & stratum compactum.
Hypodermis
Comparison of Fish and Mammalian skin
Skin Properties
Mucus→fatty acid+phospholipids
Pigment cells (chromatophores) under hormonal or nervous system control
Effector organ
Respond to hormones & neurotransmitters via receptors
Xanthophores,erythrophores and melanophores
Hormonal control of Skin
Melanin-concentrating hormone (MCH)
Neurotransmitter or neuromodulator
Sensory organs
Nerve endings and receives tactile, thermal, and pain stimuli e.g. teleost fish
Blood vessels
Collagen fibers
Types of Muscle
Three types of muscle:
Skeletal muscle
Smooth muscle
Cardiac muscle
Skeletal Muscles function
Two groups – the axial and appendicular muscles.
Main function is to support the body viscera.
Without them animal could neither move or eat or bear young.
Body movement (Locomotion)
Maintenance of posture
Constriction of organs and vessel
Types of Muscle fiber
Red muscles with capillary network mitochondria and myoglobin
White muscles produce tensions operative for short periods
pink
Nervous Control
Each myomere is controlled by a separate nerve.
Properties of Muscle
Excitability: capacity of muscle to respond to a stimulus
Contractility: ability of a muscle to shorten with force
Extensibility: muscle can be stretched to its normal resting length and beyond to a limited degree
Elasticity: ability of muscle to recoil to original resting length after stretched
Structure
Muscles are layered rather than bundled as in other vertebrates
Myomere or myotome, Septa,epaxial & hypaxial
Structure
Muscle cells long and cylindrical and have many nuclei.
Actin and myosin with controlling proteins
In other vertebrates muscles connected to bone through a tendon.
In fish, arranged vertically throughout whole length of fish.
Muscle Fiber Anatomy
Sarcolemma - cell membraneSurrounds the sarcoplasm (cytoplasm of fiber)
Contains oxygen-binding protein myoglobinPunctuated by openings called the transverse tubules (T-tubules)
Narrow tubes that extend into the sarcoplasm Filled with extracellular fluid
Myofibrils -cylindrical structures within muscle fiberAre bundles of protein filaments (=myofilaments)
– When myofibril shortens, muscle shortens (contracts)
Sarcomere
repeating functional units of a myofibrilAbout 10,000 sarcomeres per myofibril, end to endEach is about 2 µm long
Differences in size, density, and distribution of thick and thin filaments gives the muscle fiber a striated appearance.
A bands: a dark band; length of thick filamentsM line - protein to which myosins attachH zone - thick but NO thin filaments
I bands: a light band; from Z disks to ends of thick filamentsThin but NO thick filamentsExtends from A band of one sarcomere to A band of the next sarcomere
Z disk: filamentous network of protein. Serves as attachment for actin myofilamentsTitin filaments: elastic chains of amino acids; keep thick and thin filaments in proper alignment
d) myofibril c) muscle fibre b) muscle fibre bundle a) Muscle belly
Components of skeletal muscle
Nerve and Blood Vessel Supply
Motor neurons: stimulate muscle fibers to contract. Nerve cells with cell bodies in brain or spinal cord; axons extend to skeletal muscle fibers through nervesAxons branch so that each muscle fiber is innervatedCapillary beds surround muscle fibers
Muscles require large amts of energyExtensive vascular network delivers oxygen and nutrients and carries away metabolic waste produced by muscle fibers
Myosin (Thick) Myofilament
elongated molecules like golf clubs. Single filament contains 300 moleculesMolecule consists of two heavy myosin wound together to form a rod and two heads that extend laterally. Myosin heads1. Can bind to active sites on the
actin molecules to form cross-bridges. (Actin binding site)
2. Attached to the rod portion by a hinge region that can bend and straighten.
3. Have ATPase activity:
Actin (Thin) Myofilaments
Thin Filament: 3 major proteins1. F (fibrous) actin2. Tropomyosin3. TroponinTwo strands of fibrous (F) actin form a double helix extending the length of the myofilament; attached at either end at sarcomere.
Composed of G actin monomers each of which has a myosin-binding site Actin site can bind myosin during muscle contraction.
TropomyosinTroponin three subunits:
Tn-A : binds to actinTn-T :binds to tropomyosin,Tn-C :binds to calcium ions.
Sliding Filament Model of Contraction
Thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree
In the relaxed state, thin and thick filaments overlap only slightly
Upon stimulation, myosin heads bind to actin and sliding begins
Sliding Filament Model of Contraction
Each myosin head binds and detaches several times during contraction, acting like a ratchet to generate tension and propel the thin filaments to the center of the sarcomere
As this event occurs throughout the sarcomeres, the muscle shortens
Neuromuscular Junction
The neuromuscular junction is formed from:
Axonal endings, which have small membranous sacs (synaptic vesicles) that contain the neurotransmitter acetylcholine (ACh)
The motor end plate of a muscle, a specific part of sarcolemma that contains ACh receptors and helps to form the neuromuscular junction
Axonal ends and muscle fibers are always separated by a space called the synaptic cleft
Neuromuscular Junction
Figure 9.7 (a-c)
Motor Unit: The Nerve-Muscle Functional Unit
A motor unit is a motor neuron and all the muscle fibers it supplies
The number of muscle fibers per motor unit can vary from a few (4-6) to hundreds (1200-1500)
Motor Unit: The Nerve-Muscle Functional Unit
Figure 9.12 (a)
Contractile Machinery:
Sarcomeres
Contractile units
Organized in series ( attached end to end)
Each myosin is surrounded by six actin filaments
Projecting from each myosin are tiny contractile myosin bridges
Longitudinal section of myofibril
(a) At rest
Contractile Machinery:Crossbridge formation and movement
Cross bridge formation: - a signal comes from the motor nerve activating the fibre
- the heads of the myosin filaments temporarily attach themselves to the actin filaments
Cross bridge movement: - similar to the stroking of the oars and movement of rowing shell- movement of myosin filaments in relation to actin filaments- shortening of the sarcomere
b) Contraction
Longitudinal section of myofibril
Contractile Machinery:Optimal Crossbridge formation
Sarcomeres should be optimal distance apartoptimal distance is (0.0019-0.0022 mm)At this an optimal number of cross bridges is formed
If stretched farther apart : - fewer cross bridges can form
less force produced
If the sarcomeres are too close together:
- cross bridges interfere with one another less force produced
Longitudinal section of myofibril
c) Powerful stretching
d) Powerful contraction
Any questions ……..Don’t shy