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The Muscular System - ANIM1020

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  • Course: Applied Animal Biology ANIM1020 The Muscular System

  • Dr Danielle Fitzgerald (Slides prepared by Dr Suresh Krishnasamy, Lecturer (Curriculum & eDesign) - School of Agriculture and Food Sustainability, Affiliate Academic - Institute for Teaching and Learning Innovation, University of Queensland

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  • Learning outcomes:

    • Highlight the importance of the skeletal system and its interplay with the muscular system.

    • Illustrate how muscular systems of different species are adapted for function.

  • Inspiration for this lecture comes from chapter 8 of the recommended textbook.

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  • Tour of the Muscles (extensive list across zones)

    • Zone 1: Zygomaticus; Temporalis; Sterno-occipitalis; Masseter; Levator anguli oculi medialis; External abdominal oblique; Latissimus dorsi; Sternomastoideus; Infraspinatus; Cleidocervicalis; Supraspinatus; Deltoid (spinal portion); Trapezius; Gastrocnemius; Achilles tendon; Peroneus longus; Flexor digitorum superficialis; Flexor digitorum profundus; Popliteus; Rectus abdominis; Pectoralis profundus; Triceps brachii (long head); Flexor carpi ulnaris (humeral head); Extensor digitorum ulnaris; Flexor carpi ulnaris; Tibialis cranialis; Flexor digitorum superficialis; Flexor digitorum profundus; Extensor digitorum longus; oculi; ELO; The University of Queensland affiliation marks; Malaris; Levator labii maxillaris; Levator nasolabialis; Caninus; Orbicularis oris; Buccinator; Sternocephalicus; Omotransversarius; Supraspinatus; Deltoid acromial portion; Cleidobrachialis; Pectoralis transversus; Pectoralis descendens; Triceps brachii (medial head); Brachialis; Brachioradialis; Extensor carpi radialis; Extensor digitorum communis; 3

    • Zone 2: (continuation of listed muscles across regions)

    • Zone 3: (continuation of listed muscles across regions)

    • Zone 4: (continuation of listed muscles across regions)

    • Zone 5: (continuation of listed muscles across regions)

  • Note: The slide includes multiple species references (e.g., Canis lupus familiaris) and broad regional lists; these illustrate major muscle groups across zones.

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  • Muscle Tissue - Recap (visual content)

  • Emphasis on the ubiquity of muscle tissue in animals and humans and its contractile function.

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  • What are Muscle Tissues?

    • Muscle tissue consists of cells with the ability to contract to produce movement.

  • Three muscle tissue types with distinct structures and functions:

    • Skeletal muscle: voluntary control via somatic nervous system.

    • Smooth muscle: involuntary control via autonomic nervous system.

    • Cardiac muscle: involuntary (rhythmic) control in the heart.

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  • Skeletal muscle characteristics:

    • Attached to the skeleton and responsible for voluntary movement of bones.

    • Fibres run in parallel tracts; multinucleated; heavily striated.

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  • Muscle fiber ultrastructure (as per Fig. 20.1):

    • Muscle fiber (cell) contains:

    • Sarcolemma (cell membrane)

    • Sarcoplasmic reticulum (SR)

    • Transverse tubules (t-tubules)

    • Terminal cisternae of SR

    • Myofibril with sarcomere organization:

    • A band; I band; H zone; Z disc; M line

    • Six myofibrils; mitochondrion noted

  • Key conceptual blocks:

    • Myofibrils are composed of repeating sarcomeres, the basic contractile units.

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  • Smooth muscle:

    • Location: lining internal organs (GI tract, uterus, blood vessels, eyes, etc.).

    • Function: involuntary constriction (peristalsis, vasoconstriction).

    • Morphology: spindle-shaped fibers with a single central nucleus; non-striated.

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  • Cardiac muscle:

    • Location: heart.

    • Function: rhythmic contraction (heartbeat).

    • Morphology: branching, intercalated discs, lightly striated, single nucleus per fiber.

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  • Summary: Types of Muscle Tissue

    • Skeletal, Smooth, Cardiac (as above).

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  • Terminologies (heading slide; content relates to muscle naming and concepts)

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  • Origins and Insertions:

    • Origin: the end of a muscle that moves the least.

    • Insertion: the end that moves the most.

    • Generally, the origin is the most proximal end, but this is not universal.

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  • Muscle contraction limits and antagonism:

    • Muscles can only contract and relax (they pull on bones).

    • Joints move because skeletal muscles come in antagonistic pairs.

    • Antagonistic muscle pairs enable opposite movements.

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  • Naming muscles (criteria):

    • Shape: e.g., deltoid (triangle-shaped).

    • Size: gluteus maximus/medius/minimus (maximus = largest; minimus = smallest).

    • Fibre direction: rectus (straight), obliques (angled), transverse (horizontal).

    • Number of origins: quadriceps, triceps, biceps (multi-origins).

    • Action: flexors, extensors, abductors, adductors.

    • Location: e.g., frontalis on the frontal bone; arm muscles named with -brachii; midline relations: lateralis vs medialis.

    • Attachments in names: origin named first (e.g., sternocleidomastoid has origins on sternum and clavicle and inserts on the mastoid process).

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  • Muscle shapes: Function follows form

    • Fusiform; Unipennate; Convergent; Bipennate; Parallel; Multipennate; Circular.

    • Example illustrations include Palmar interosseous, Pectoralis major, Rectus femoris, Rectus abdominis, Deltoid, Biceps brachii, Orbicularis oculi.

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  • Fusiform muscles:

    • Long and thin; often cross hinge joints; single direction of pull; primarily flexion/extension.

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  • Convergent muscles:

    • Single attachment at one end; broader attachment at the other; versatile movement around a single attachment.

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  • Pennate muscles:

    • Short fibers attached along greater lengths of bone; provide greater strength.

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  • Skeletal muscle fiber types:

    • General features:

    • Rich mitochondrial content; high myoglobin content; numerous blood vessels; red appearance; suited for endurance.

    • Type I (slow-twitch):

    • High oxidative capacity; fatigue-resistant; sustained activity.

    • Type IIX (fast-twitch, often labeled IIB/X):

    • Predominantly anaerobic glycolytic metabolism; high force but fatigue quickly; activated during high-intensity, short-duration activities.

    • Type IIA (fast-twitch but oxidative-glycolytic):

    • Faster contraction than Type I; can use both oxidative and glycolytic metabolism; moderate mitochondria/myoglobin; less fatigue-resistant than Type I but more than Type IIX; suited for activities needing both speed and endurance.

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  • Fiber typing imagery (myosin ATPase staining) illustrating Type I, IIA, IIX distributions in longissimus dorsi and semitendinosus muscles.

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  • Tour of the Muscles (overview slide)

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  • Muscles and their primary actions (selected examples):

    • Gluteals: extend hip

    • Gastrocnemius: extend lower leg

    • Sartorius: raises knee

    • Dorsals: twist and curl torso

    • Biceps femoris: flexes/bends leg

    • Oblique abdominals: hold in internal organs

    • Trapezius: draws shoulder up

    • Digital extensors: extend toes and claws

    • Jaw muscles: can exert enormous pressure

    • Deltoid: pulls shoulder forward

    • Triceps: straightens elbow

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  • Muscles of the Eye:

    • Each extraocular muscle has a primary function and limited secondary actions (adduction, abduction, intorsion, extorsion, elevation, depression).

    • The trochlea enables a primary function of intorsion for a specific muscle, with secondary depression and abduction.

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  • Head and Neck Muscles (selected):

    • Masseter: Elevates the mandible; controls facial expressions

    • Brachiocephalicus: Protracts the arm; aids leg and shoulder movement; acts as a lateral flexor in the neck

    • Trapezius: Keeps scapula in place and moves it forward/backward

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  • Arm and Shoulder Muscles (selected):

    • Latissimus dorsi: Major retractor of the arm

    • Deltoid: Protracts the upper arm

    • Deep Pectoral: Adducts the limb and pulls it caudally

    • Triceps Brachii: Extends the elbow and flexes the shoulder

    • Biceps Brachii: Flexes the forearm

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  • Vertebral Column Muscles:

    • Epaxial muscles: sit above the transverse processes; extend the spine

    • Hypaxial muscles: sit below the transverse processes; flex the neck and tail

    • Transverse process as an attachment point for spinal movers and stabilizing ligaments

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  • Abdominal Muscles:

    • External and internal obliques: compress abdomen and flex trunk

    • Rectus abdominis: supports abdominal wall and ventral flexion

    • Arranged in layers; left and right parts converge at the linea alba (ventral midline)

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  • Pelvis and Thigh Muscles (examples):

    • Tensor fasciae latae: extends the shank; protracts the thigh at the hip

    • Semitendinosus: assists biceps femoris in thigh retraction and shank flexion

    • Gastrocnemius and Soleus: flex knee/stifle; extend the tarsus

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  • Representative muscle lists by region (slide shows many names):

    • Includes Levator, Levator anguli oris, Caninus, Oculi, Temporalis, Masseter, Sternomastoideus, Cleidocervicalis, Omotransversarius, Trapezius, Latissimus dorsi, External abdominal oblique, Tensor fasciae latae, Gluteal fascia, Biceps femoris, Semitendinosus, Triceps, External abdominal oblique, Rectus abdominis, Pectoralis profundus, Gracilis, Extensor carpi radialis, Extensor digitorum communis, Flexor carpi ulnaris (humeral head), Extensor digitorum lateralis, Flexor digitorum profundus, Flexor digitorum superficialis, Orbicularis oris, (and more). The page also references various species and a range of forearm and limb muscles.

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  • Species-specific muscle lists (examples):

    • Macropus rufus (Red Kangaroo) – Gluteus medius; Gluteus superficialis anterior/posterior; Coccygeus; Semitendinosus; Semimembranosus; Biceps Femoris; Gastrocnemius; Sacrocaudalis dorsalis/ventralis; Pectoralis; Rectus Abdominis; Digastric; Masseter; Sternomastoid; Deltoid; Trapezius; Temporalis; Levator nasolabialis; Orbicularis oculi; Levator labii maxillaris; Caninus; Sternohyoid; Sternothyroid; Buccinator; Cleidomastoid; Triceps Brachii; Sartorius; Vastus lateralis; Tibialis cranialis; Soleus; Flexor carpi ulnaris; Peroneus longus; Extensor carpi ulnaris; Biceps brachii; Brachialis; Extensor carpi radialis; Extensor digitorum communis; Extensor digitorum lateralis; Flexor digitorum profundus; Orbicularis oris.

  • The slide shows broad cross-species muscle compilations.

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  • More muscles (species notes):

    • Coracoid; Scapula; Extensor metacarpi; Furcula; Pronator; Esophagus; Biceps brachii; Crop; Flexor carpi ulnaris; Flexor digitorum superficialis; Triceps brachii; Latissimus dorsi; External abdominal oblique; Sartorius; Iliotrochantericus; Iliotibialis; Radialis; Caudofemoralis; Semitendinosus; External abdominal oblique; Semimembranosus; Radius; Humerus; Metacarpals III/IV; Ulna; Supracoracoideus; Pectoralis; Keel of sternum; Pectoralis m.; Ligament; Forearm muscles; Biceps; Rope-and-pulley system (upper wing bone); Peroneus longus; Tibialis anticus; Gastrocnemius; Extensor brevis; Supracoracoideus; Pectoralis (pulls wing down); Keel; Knee; Triceps; Coracoid (shoulder); Thigh; Lower leg muscles; Supracoracoideus (raises wing); False Knee; Pectoralis (pulls wing down); Keel. (This slide integrates multiple Musce lists across species like Canis, Macropus, etc.)

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  • Forelimb and pectoral muscle architecture (diagram-rich slide):

    • Coracoid, Scapula, Extensor metacarpi, Furcula, Pronator, Esophagus, Biceps brachii, Latissimus dorsi, External abdominal oblique, Sartorius, Iliotrochantericus, Iliotibialis, Radialis, Caudofemoralis, Semitendinosus, Semimembranosis, Radius, Humerus, Metacarpals, Ulna, Supracoracoideus, Pectoralis, Keel of Sternum, Pectoralis m.; Forearm muscles; Rope-and-pulley system (upper wing bone); Supracoracoideus (raise wing); Pectoralis (pulls wing down); Keel; Knee; Triceps; Coracoid (shoulder).

  • The slide emphasizes cross-species anatomical relationships in flight adaptions (keel, supracoracoideus, pectoralis).

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  • Growing Pains (section header/intro)

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  • Growth basics:

    • All animals have a genetically controlled potential size (mature weight) that they can reach if unconstrained.

    • Birth weight relates to birth weight; Growth defined as an increase in structure, not merely weight; progressive increase in size towards full development.

    • Source for growth definition cited: https://dogsbestlife.com/dog-breeds/big-dogs/

    • Key terms: mature weight; birth weight.

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  • Growth curves and slaughter points (illustrated):

    • Growth curves show Muscle, Fat, Bone components over time.

    • Slaughter point for optimal carcass tissue proportions occurs when the majority of animals reach the following weights:

    • 1300\text{ lb} for cattle,

    • 280\text{ lb} for swine,

    • 120\text{ lb} for lamb.

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  • Compensatory growth:

    • Natural phenomenon where cattle, after dietary restriction, exhibit accelerated growth and improved feed efficiency when nutrition improves.

    • Strategy: reduce energy density of winter feed to induce compensatory growth during the following grazing season.

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  • Marbling:

    • Definition: visible intramuscular fat within muscle and between muscle fibre bundles.

    • Composition: polyunsaturated, monounsaturated, and saturated fats.

    • Significance: marbling positively affects eating quality (tenderness, juiciness/moisture, flavour) by making meat softer and easier to chew due to lower relative muscle fibre and collagen per unit volume, aiding faster breakdown and flavour release.

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  • Growth Hormones and meat quality:

    • A comparative image shows meat from a pig with bovine growth hormone genes vs a normal pig, illustrating reduced fat content in the transgenic pig at the same rib area.

    • Captioned as: NORMAL GRASS FED COW vs GROWTH HORMONE + ANTIBIOTICS + CORN FED.

    • Physiologic effects of Growth Hormone include direct effects on adipose tissue and liver IGF-1 production, and indirect effects via systemic growth regulation.

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  • Muscular Adaptation (intro):

    • Adaptation is the process by which organisms become better suited to their habitat.

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  • Locomotion styles and muscular adaptations (overview):

    • Aerial Locomotion; Arboreal Locomotion; Aquatic Locomotion; Cursorial Locomotion; Saltatorial Locomotion; Fossorial Locomotion.

    • Focus questions:
      1) Specific muscular adaptations?
      2) How these adaptations support their respective modes of locomotion?

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  • Aerial locomotion examples:

    • Eagles: powerful pectoral muscles (notably pectoralis major) enable strong wingbeats for take-off and sustained flight; support long gliding to conserve energy.

    • Hummingbirds: highly developed flight muscles (supracoracoideus and pectoralis major) comprising a significant portion of body weight; enable rapid, continuous wing beating and hovering to feed on nectar.

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  • Arboreal locomotion examples:

    • Squirrels: strong, flexible limb muscles (forelimbs and hindlimbs) for climbing and leaping; robust forelimb muscles for gripping and pulling up trunks.

    • Orangutans: powerful shoulder and arm muscles (deltoid and latissimus dorsi) enabling branch-to-branch swinging; long, strong arms for controlled movement in trees.

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  • Aquatic locomotion examples:

    • Sharks: powerful myotomal muscles arranged in W-shaped blocks for wave-like body undulations propelling through water.

    • Dolphins: highly developed epaxial and hypaxial muscles along spine and tail powering up-down movements of the caudal fin (fluke) for high speed and maneuverability.

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  • Fossorial locomotion examples:

    • Wombats: strong shoulder and forelimb muscles (deltoids, triceps) for extensive burrowing; short, muscular limbs for moving soil.

    • Naked mole-rats: strong jaw muscles (masseter and temporalis) adapted for digging with incisors.

    • Source: Cox & Faulkes (2014) Digital dissection of the masticatory muscles of the naked mole-rat, PeerJ.

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  • Saltatorial locomotion examples:

    • Kangaroos: powerful elongated hind limb muscles (quadriceps, gastrocnemius) for explosive hopping; enables long-distance movement.

    • Grasshoppers: large hind leg extensor muscles in the femur; store elastic energy during flexion and release explosively for leaps.

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  • Cursorial locomotion examples:

    • Greyhounds: long, lean hind muscle groups (gluteals, quadriceps) for explosive acceleration and sustained high-speed running.

    • Pronghorns: well-developed thigh and lower leg muscles (gastrocnemius and large thigh muscles) for speed and endurance to outrun predators across open plains.

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  • Intraspecies Differences (muscle composition):

    • Quarter Horse vs Arabian

    • Racing/ridden performance correlates with a lower proportion of Type I fibers in horses conditioned for speed and short bursts (racing/rodeo) vs higher proportion of Type I fibers in endurance-focused activities.

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  • Practice Question prompt:

    • Compare muscular adaptations in frogs and rabbits for jumping versus rapid running; discuss structural and functional aspects of these muscles.

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  • Practice Question prompt (restate):

    • Frogs and rabbits: Overview of muscular adaptations for explosive jumping (frogs) vs speed and agility (rabbits).

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  • Suggested answer outline for the frog vs rabbit question:

    • Frogs:

    • Powerful hind limb muscles (e.g., gastrocnemius, semimembranosus) for explosive jumps.

    • Elastic tendons in hind limbs store and release energy to boost jump power.

    • Excellent hind limb and body muscular coordination for precise, powerful leaps.

    • Fast-twitch fibers contribute to rapid power production.

    • Rabbits:

    • High proportion of fast-twitch fibers in hind limbs for quick bursts of speed and agility.

    • Strong hind limb muscles (quadriceps, hamstrings) for powerful pushes.

    • Spinal flexibility aids in absorbing impact and enabling rapid direction changes during running.

    • Shared theme: Both groups rely on specialized hind limb muscles, but frogs emphasize energy storage in tendons for explosive power, while rabbits emphasize rapid, powerful contractions via fast-twitch fibers for speed.

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  • Closing details:

    • Thanks to Suresh Krishnasamy, Associate Lecturer (Curriculum and e-Design) – School of Agriculture and Food Sustainability; Affiliate Academic - ITaLI, University of Queensland.

    • Contact: Suresh.krishnasamy@uq.edu.au; 07 5460 1186; CRICOS code 00025B