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


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


c) Powerful stretching

d) Powerful contraction

Any questions ……..Don’t shy

Scales

Technology

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