Insect Muscular System - 2nd Term PDF

**7. MUSCULAR SYSTEM** [Movement] of the insect' body and its appendages is produced by an intrinsic system of musculature. Muscle contraction is facilitated by nerve impulses at nerve endings. The coordinated movement of muscles and appendages is critical to important activities like feeding,...

**7. MUSCULAR SYSTEM** [Movement] of the insect' body and its appendages is produced by an intrinsic system of musculature. Muscle contraction is facilitated by nerve impulses at nerve endings. The coordinated movement of muscles and appendages is critical to important activities like feeding, walking, jumping and flying. MUSCLES are made up contractile units called myosin filaments. These are striated fibers. striated = with light and dark bands (isotropid and anisotropid bands) made up of actin and myosin filaments; characterized by the presence of numerous nerve endings from a single axon (multiterminal innervation) Fibers = myofibrils situated in a matrix of multinucleated cytoplasm. Along with the myofibrils are mitochondria which contain enzymes for the oxidation process that release free energy for muscle reaction. [Myosin filaments] -- protein, long coiled chains of polypeptides \- Have lateral projections which interlink with actin filaments during contraction -With cross bridge, double helix **[MUSCLES]** -Occur or appear in antagonistic pairs: if there is a flexor, there is an extensor -Biological machines which convert chemical energy into mechanical work and into heat **[PRINCIPAL TYPES OF INSECT MUSCLES]** \- Based on the arrangement and number of myofilaments, nuclei and the way how the fibers are embedded in connective tissue 1\. Typical e. g. [honeybee larva] \- fibrils only slightly differentiated, enclosed in thick layer of superficial plasma; nuclei found within the plasma layer([fibrils]= a small filament or fiber) 2\. [MICROFIBRILLAR] e.g. leg muscles of [Orthoptera],, [Trichoptera] and [Lepidoptera] -fibrils closely packed, interspersed with columns of mitochondria; each fiber surrounded by sarcolemma; nuclei peripheral Sarcolemma -- plasma membrane Sarcoplasma -- plasma Sarcoplasm - cytoplasm 3\. [Lamellar] or [tubular] e.g. direct flight muscles; nuclei found only along the central portion forming a column and surrounded by alternating rows of mitochondria and fibrils; more mitochondria indicating the need for more energy [4. Fibrillar] \- of large diameter fibril surrounded by sarcolemma \- In between fibrils are mitochondria and sarcoplasm; nuclei peripheral \- Found in indirect flight muscles of very efficient fliers (located along dorsum, thorax) \- Presence of a large number of mitochondria indicating the use of a lot of energy during flight \- Lots of cytochrome C, glycogen; well tracheated and ventilated **[CATEGORIES OF MUSCLES OF INSECTS]** \- [Visceral muscles] \- Occur in circular, longitudinal or oblique bands around the digestive tract = produce peristaltic movements of the gut that moves food and wastes along its length \- Specialized muscles associated with the spiracles \- Others cause peristalsis or contractile movement of the heart \- [Segmental muscles] \- Series of bands that connect body segments \- Longitudinal bands connect the tergites and sternites in the abdomen \- Tergites to sternites of same segment are connected by oblique muscles on each side of the body \- In the thorax, predominant muscles are large cordlike bands moving the legs and wings [- Appendage muscles] \- Movable appendages have muscles either in them or attached to them [e.g. legs] = attachment for muscles housed in the body = attachment for muscles housed directly in the appendage \- Body muscles generally move the whole appendage, the segmental muscles move parts of the appendage **[LOCOMOTION IN INSECTS]** [A. WALKING] -- basic mode of locomotion of insects on land [TRIPOD MANNER] for adult insects 1 = 2 legs on the ground on one side 1 leg on the ground on the other side 2 = 3 other legs raised as 3 = grounded legs push backward Alternation of pushing tripods results in a slightly zigzag path of forward motion Maybe modified: \- Single-leg movements in very slow-walking insects \- In praying mantids, 1st pair of legs is not used for walking [B.CRAWLING] - basic mode of locomotion for worm-shaped immatures (larvae) As the caterpillar inches its way forward, longitudinal and dorsoventral muscles oppose each other in each segment Synchronized operation produces a wave of contraction down the body Fleshy prolegs on abdominal segments assist in anchoring the abdomen. This will prevent the body slipping backward and causes the body to move forward For loopers, crawling is accomplished in a sort of looping motion. Prolegs are brought forward and anchored causing a loop in the abdomen, followed by a straightening of the whole body [C. FLYING =] only adults can accomplish flight (exception: in [mayflies], weak flights may occur just before full sexual maturity) \- Muscles in the thorax are involved in flight: \- Indirect flight muscles attached to tergites and sternites \- Direct flight muscles attached to wing bases **[LOCOMOTION IN INSECTS FLYING]** \- In more primitive insects ([dragonflies], [roaches], [beetles]): \- up-and-down beat cycle \- Begins with contraction of the dorsoventral muscle (indirect flight muscles) 🡪 depression of the tergum forcing wing base down and the wing up, with the thoracic pleurite as fulcrum \- In the next cycle, contraction of basalar muscles (direct flight muscles) and relaxation of dorsoventral muscles (indirect flight muscles) forces the wing down, and the tergum is raised -In more advanced fliers, e.g. [honeybees] \- Up-and-down movement is produced only by indirect flight muscles (dorsoventral and dorsal muscles) that cause flexing of the thoracic segment and produce wing beat \- In addition, wings display a synchronized rotation \- Result: more surface on the downstroke than the upstroke pushing air backward to cause forward movement \- This is accomplished by muscles that distort the tergum and others that apply pressure alternately to the front and back of the wings **8. THE SENSES OF INSECTS** For insects to exist, they MUST SENSE the realities of the environment and govern their activities accordingly. They must locate food, find mates, avoid enemies, make nests and perform internal functions. They accomplish these tasks only by perceiving conditions and integrating this information to perform the appropriate behavior. Perception is achieved by a number of different sense organs, and behavior results from integration of information and stimulation by the nervous system. **THE SENSES OF INSECTS** **- BASIC SENSES** 1\. SIGHT 2\. SMELL (OLFACTION) 3\. TASTE (GUSTATION) 4\. TOUCH 5\. HEARING \- **GROUPS OF ORGANS/RECEPTORS** **(ECTODERMAL IN ORIGIN)** 1\. PHOTORECEPTORS 2\. CHEMORECEPTORS 3\. MECHANORECEPTORS 4\. AUDITORY ORGANS 5\. TEMPERATURE AND HUMIDITY RECEPTORS **[PHOTORECEPTORS]** \- Detect presence and quality of incident light; when images are produced it is called sight. \- e.g. eyes as the most complex photoreceptor involved in forming images \- COMPOUND EYES (CE) \- perceive images, color, movement \- not found in primitively wingless insects (have evolved along with flight); Lacking in immature of most advanced insects; Most insects with CE also have simple eyes \- Principal visual organ, characterized externally by the cornea being divided into hexagonal facets. Each facet is part of the individual sensory units called ommatidium. [NOTE:]... THE NUMBER OF FACETS TO A CE VARIES \- 20,000 in dragonflies \- 12,000 or more in Lepidoptera \- 4,000 in Musca (house flies) \- Fewer than a dozen in workers of certain ants [STRUCTURE OF THE CE/HOW THE CE WORKS] Light is gathered in ommatidium by lens or cornea The lens focuses light thru a crystalline cone (CC) to a light-receptor apparatus (LRA). \[The LRA comprises 6 -- 8 retinula cells (RC) which combine to produce a central light sensor (rhabdom). The CC and LRA are surrounded by pigment cells that isolate to various degrees, 1 ommatidium from another\] RC turn light into electrical energy which is carried to nerve fibers by the brain. Images produced by ommatidia are believed to result in an overall mosaic object, each ommatidium supplying only a piece of vision. [SIMPLE EYES/OCELLI] \- Present in many immatures of Endopterygota \- Also believed to perceive images although probably produce a less complete mosaic; some appreciation of color; perceive movement of objects in their vicinity; responsible for orientation to light \- Some insects with only simple eyes scan environment by moving head back and forth \- Structure varies among insects \- Some similar to individual ommatidia (caterpillars) \- Some with a single cornea overlying several retinula cells and rhabdoms [SIMPLE EYES] \- distinct from the CE thru the presence of a single corneal lens [2 classes:] \- Dorasl ocelli of imagines and nymphs \- 3 arranged in a triangle on frontal region of head or on the vertex \- Lateral ocelli of most endopterygote larvae \- No general uniformity of structure \- May occur singly (e.g.sawfly larvae) or in groups on either side of the head (e.g. [Lepidoptera larvae]) [NOTE:] SOME INSECTS HAVE NO EYES, THUS THEY DETECT LIGHT THRU THE CUTICLE (DERMAL PHOTORECEPTION) **[CHEMORECEPTORS]** \- Detect the presence of chemical substances in the air thru the sense of smell (OLFACTION) OR on substrates thru the sense of taste (GUSTATION) \- Based on the detection of certain molecules by receptor organs that subsequently produce a nerve impulse **[FORMS OF CHEMORECEPTORS]** \- short pegs or hairs on various body parts ([antennae],[palps]) [TASTE RECEPTORS] \- [Contact chemoreceptors] prevalent on surfaces of mouthparts, antennae (some [Hymenoptera)] and [tarsi] ([Lep], [Dip], [honeybees]); sensilla usually hairs or cones with 4 neurons \- Sense molecules from liquids \- Have fine nerve endings exposed to the environment at hair tips In general, wide differences in taste thresholds of different substances with a given species and for different species with the same substance happen sugar solution \] \[ preferred to distilled H2O dilute acid/salt soln\] more conc acid,salts soln \] 🡪 rejected \[ esters, alcohols,amino acids \] [SMELL RECEPTORS] \- Perceived by olfactory sensilla characterized by the presence of numerous pores \- Peglike; have greater number of nerve endings at the surface \- Most numerous on insect's antennae, also abundant on palpi of mparts \- More numerous on males: e.g last 8 antennal segments in male Apis about 30,000 sensilla compared to workers = 6,000 & queens = 2,000 \- Play an important role in the life of insects since many behavioral and developmental changes are caused by pheromones \- pheromones -- highly specific, volatile substances perceived thru the olfactory sensilla after being secreted by other members of the same species \- e.g. Scents produced by virgin females of some moth attract the males [MECHANORECEPTORS] Detect movements, vibrations, other mechanical disturbances [TOUCH] -- monitored by hair sensilla, innervated by a single neuron [HEARING -] perception of aerial vibrations by long, slender, trichoid sensilla \- [FOR THE TYMPANUM] to vibrate = perceived by chordotonal organs made up of scolopidia [Where is the tympanum?] -In grasshoppers, on 1st abdominal segment -In crickets, on tibiae -In moths, abdomen and metathorax [Johnston's organ] in the pedicel of adult insects responds to movements of antennae; maybe involved in hearing \- SENSILLA \_ COELONICA, CAMPANIFORMIA \- SENSILLA \_ CHAETICA \- SENSILLA \_ TRICHOIDEA \- SENSILLA - BASICONICA **[9. THE INTEGUMENTARY SYSTEM]** [INTEGUMENT OR BODY WALL] -Outer covering of the living tissues of insects; sclerotized for protection from abrasion as well as waterproofing -Composed of a [single layer] of cells called **EPIDERMIS** bounded on the inside by a **BASEMENT MEMBRANE** and on the [outside] by the **CUTICLE** \- epicuticle \- exocuticle \- endocuticle \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- **C**UTICLE \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- **E**PIDERMIS \-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- **B**ASEMENT MEMBRANE [INTEGUMENTARY SYSTEM] [- The CUTICLE] - - - [PRIMARY LAYERS OF THE CUTICLE] [EPICUTICLE] - When first laid on the surface, it is deeply folded and later, straighten after ecdysis (insect swallow air) [Layers:] - - - - [LAYERS OF THE CUTICLE] [EXOCUTICLE] - - - - - [ENDOCUTICLE] - [Basement membrane] - **[The integument of an insect]**  **[INTEGUMENTARY SYSTEM]** [CUTICULAR EXTENSIONS] 1. 2. 3. 4. - - - [3 separate cells form each seta] 1. 2. 3. - - make possible the [repair] of the [cuticle], [secretion of wax] and [release tanning agents.] - - **[Functions of the exoskeleton]** 1. 2. 3. 4. **MOLTING** E.g, [Cicada] (nymph), order (Homoptera) **EXUVIAE** \- Molted "skin" / Exoskeleton **MOLTING** [(casting of the old cuticle)] IS [TRIGGERED] BY [HORMONES] RELEASED WHEN AN [INSECT's GROWTH] REACHES the [PHYSICAL LIMITS] OF ITS **EXOSKELETON** [What happens during molting?] PHYSIOLOGY OF MOLTING/DISTINCT SEQUENCE OF EVENTS **[2 processes :]** **Apolysis** -- [cuticle] separates from the [epidermis] **Ecdysis** - [shedding off] of the [old skin] [1. Changes in epidermal cells] **EPIDERMAL CELLS** RESPOND TO [HORMONAL CHANGES] BY [INCREASING] THE [RATE OF PROTEIN SYNTHESIS] THAT QUICKLY [LEADING TO APOLYSIS (physical separation] of [epidermis] from [old endocuticle)] **[MOLTING]** [2. Secretion of molting fluid] **EPIDERMAL CELLS** (EC) [FILL] THE [RESULTING GAP] [WITH] AN [INACTIVE MOLTING FLUID] [3. Secretion of cuticulin layer] SECRETE A SPECIAL [LIPOPROTEIN (CUTICULIN] [LAYER)] THAT INSULATES AND PROTECTS THE EC FROM [MOLTING FLUID'S (MF)] DIGESTIVE ACTION. THE **CUTICULIN LAYER** BECOMES PART OF THE [NEW EXOSKELETON'S EPICUTICLE] [MOLTING] [4. Activation of molting fluid] AFTER THE FORMATION OF THE CUTICULIN LAYER, MF BECOMES ACTIVATED AND CHEMICALLY "DIGESTS" THE ENDOCUTICLE OF THE OLD EXOSKELETON. MOLTING 5\. [Absorption of the digested remains of old cuticle and start of secretion of new procuticle] BREAKDOWN PRODUCTS (AA AND CHITIN MICROFIBRILS) PASS THRU THE CUTICULIN LAYER WHERE THEY ARE RECYCLED BY THE EPIDERMAL CELLS AND SECRETED UNDER THE CUTICULIN LAYER AS A NEW PROCUTICLE =EXO AND ENDOCUTICLE (SOFT AND WRINKLED) [6. Formation of wax and cement layer] Wax line the pore canals for water retention and water loss mechanism PORE CANALS WITHIN THE PROCUTICLE ALLOW MOVEMENT OF LIPIDS AND PROTEIN TOWARD THE NEW EPICUTICLE WHERE WAX AND CEMENT LAYER FORM. 7\. [Ecdysis and expansion of the new cuticle] WHEN THE NEW EXOSKELETON IS READY, MUSCULAR CONTRACTIONS AND INTAKE OF AIR CAUSE THE INSECT'S BODY TO SWELL AND THE OLD E SPLITS OPEN ALONG LINES OF WEAKNESS (ECDYSIAL SUTURES) AND THE INSECT SHEDS OLD SKIN QUICKLY (ECDYSIS) AND CONTINUES TO FULLY EXPAND THE NEW ONE. 8\. [Sclerotization /Tanning] --processes by which the new cuticle is made more resistant to degradation, stiffer, less soluble. Processes by which cuticular proteins are cross-linked by the action of quinones, and therefore change the cuticle into dark, hard, insoluble material. [QUINONES]= t[anning subset for the cuticle] coming from tyrosine or para-OH phenylalanine in the hemolymph - - [9. Start of wax secretion] WAX STARTS TO BE SECRETED - - [PHYSIOLOGY OF MOLTING/DISTINCT] [SEQUENCE OF EVENTS] 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. **[CONTROL OF MOLTING AND]** **[ASSOCIATED PROCESSES]** 1\. [ **Ecdysone**] -- plays a vital role in [controlling the events of molting]; triggers the epidermal cells to change - 2.**[Bursicon]** -- [controls sclerotization] = necessary [for cuticle tanning] and endocuticle formation in flies 3\. A **hormone** released from the [corpora allata-corpora cardiaca] complex with [ecdysone] to control wax secretion. **[continuation: Control]** 4\. A hormone with ecdysone controlling endocuticle production 5\. **[Ecdepteroids]** [induce sclerotization] in [ligated abdomen of blowfly larvae] resulting to the [induction of de novo synthesis of enzyme dopa-decarboxylase] in the epidermal cells **[DIFFERENT TYPES OF CUTICLE]** The cuticle varies in nature in the different parts of the insect's body 1. Produced as a [result of tanning] in the [outer part of the procuticle] to [forming an exocuticle], but the extent of tanning, and hence the hardness of the cuticle varies - 2. [Flexible arthrodial membranes join] the [sclerites] and in these, the procuticle [remains untanned] - 3. e.g. those found in [elastic hinges] such as [wing-hinge ligament] lying between the pleural process and the 2nd maxillary sclerite **10. REPRODUCTIVE SYSTEM** **[COMPOSITION]** - - **[MODE OF REPRODUCTION IN INSECTS]** 1. 2. 3. **[MALE'S REPRODUCTIVE SYSTEM]** - - - - - - - **[Accessory glands]** - **[Functions: ]** 1. 2. **[FEMALE'S REPRODUCTIVE SYSTEM]** - - - **Oogonia** ([the first stage] in the differentiation of an [egg cell]) A group of [germ cells] near the distal end of each ovariole, dividing through mitosis, [increase in size] to form [oocytes] which are [produced regularly] within each [ovariole] during active **oogenesis** ([egg maturation]) **[Oocytes]** - - - **(vitellogenesis** = [deposition of] [yolk] in the [oocyte]) base of ovariole **(calyx)** [common oviduct opening] into a genital chamber (**BURSA COPULATRIX**) or **copulatory pouch** **[Female accessory glands]** - - - - - [The spermathecal gland produce:] - - **[REPRODUCTIVE SYTEM]** [Ovulation takes place] - - - - ### **Phases of Insect Development** 1. - - 2. - - **[ATYPICAL MODES OF REPRODUCTION]** 1\. **Parthenogenesis** \- Definition: Development from an [unfertilized egg]. **[- Types:]** \- **Thelytokous Parthenogenesis** \- [Females] produce only [female offspring.] **- Examples:** Certain species of Diptera [(flies)] and Coleoptera [(beetles)]. \- **Arrhenotokous Parthenogenesis** \- [Females] produce only [male offspring]. \- Examples: Hymenoptera ([bees], [ants, wasps]), scale insects, and whiteflies. \- **Amphitokous** or **Deuterotokous Parthenogenesis** \- [Females] produce both [male and female offspring]. \- Examples: Thysanoptera (thrips, which can undergo all types of parthenogenesis), aphids, and some species of wasps. ### **Types of Paedogenesis** 1. - - 2. - **NEOTENY** - - - - - - - - - **ATYPICAL MODE OF REPRODUCTION** ### **1. Hermaphroditism** - - - ### **2. Reproductive Process in Hermaphroditic Species** - - - - - **Reproductive Strategies: \"To Lay Eggs or Not to Lay Eggs\"** ### **1. Oviparity** - ### **2. Ovoviviparity** - ### **3. Viviparity** - ### ### **B. CORPORA ALLATA (CA)** #### **Overview** - - - #### **Function** - #### **Juvenile Hormone (JH) Functions** 1. - 2. - - 3. - 4. - 5. - ### **C. Thoracic/Prothoracic Glands** **Overview:** - **Anatomy:** - - **Function:** - #### **Ecdysone (Molting Hormone)** - - - - - - - - - - - **Other Hormones** ------------------ ### **1. Anterior Segment Refraction Factor (ARF)** - - - - ### **2. Puparium Tanning Factor (PTF)** - - - - [DEFINITION OF TERMS] **[ABSORPTION]** -- process by which a chemical crosses the various membrane barriers of a living organism and especially those processes by which a chemical is taken up from environmental media, including food and other ingested material. ### **Toxicity Overview** **Definition**:\ **[Toxicity]** refers to the [ability of a poison (e.g., pesticide) to produce adverse effects], which can range from mild symptoms like headaches to severe outcomes such as coma, convulsions, or death. It is the capacity of a substance to cause injury and is a measurable quantity.