B3.3 MUSCLE AND MOBILITY

outline the adaptions for movement as a universal feature of living organisms

• internal movement (movement that occurs within the body)

  • peristalsis: rhythmic contractions in gut for food transport

• locomotion: movement of entire body from one place to another

  • bar-tailed godwit: migratory wings for flight

• sessile organisms: remain fixed in one position

  • plants: roots anchor plants in soil’ rely on growth movements instead of migration

outline the structure of muscles

• each muscle is made up of groups of muscle fibers which contain multiple parallel myofibrils, made up of repeating sarcomeres 

  • sarcomeres are seperated by z-discs and consists of alternating light and dark bands

  • light bands: actin filaments only

  • dark bands: myosin filaments with overlapping actin

outline the structure and function of striated muscle fibers

• sarcolemma

  • contractile membrane that surrounds a muscle fiber

• myofibrils

  • contains sarcomeres which consist of light and dark bands

• sarcoplasmic reticulum

  • specialised endoplasmic reticulum which forms a network for the release of calcium ions into the sarcoplasm follow the stimulation from an action potential

• sarcoplasm

  • cytoplasm of muscle cells

outline the structure of a sarcomere

• a sarcomere is a unit of contraction, many sarcomeres are consisted in a single myofibril

• Z disks: boundaries of one sarcomere

• dark band: consists of myosin filaments and actin filaments

• light band: consists of only actin filaments

  • contain myosin binding sites for muscle contraction

• M line: the center of a sarcomere which anchors the myosin filaments

• titin: elastic protein which acts as a spring

outline the role of titin in muscle relaxation

• titin: giant/immense elastic protein which acts as a molecular spring (acts as elastic band tot prevent overstretching of relaxed muscle)

• one end is attached to Z disk while the other end is attached to the M line

• when a sarcomere is stretched, the titin is stretched and stores potential energy until the force is released and the energy is also released

  • this helps sarcomeres recoil after stretching

explain the silding filament theory (explain how a sarcomere contracts)

OVERVIEW: (outlining)

• actin filaments slide over myosin filaments towards the center of the sarcomere (towards the M line)

• Z disks are pulled closer together which shortens both the sarcomere and the muscle overall

IN DETAIL: (explaining)

1. calcium ion release

   • an action potential triggers the release of calcium ions from the sarcoplasmic reticulum into the muscle fiber

2. binding site exposure:

   • calcium ions bind to troponin, causing a conformational change that moves moves tropomyosin away from the myosin binding site

3. cross-bridge formation:

   • myosin heads bind to the exposed binding sites on actin, forming cross bridges

4. power stroke:

   • the myosin heads pivot, pulling the actin filaments towards the center of the sarcomere, the M line which is powered by the hydrolysis of ATP

5. detachment:/release of ADP and Pi:

   • after the power stroke, ADP and inorganic phosphate are released from the myosin head

6. resetting the myosin head:

   • once a new ATP molecule attaches to the myosin head, it causes the myosin to release from the actin filament

explain the role of the skeletal system

• skeletal system cannot move on its own, serves as an anchorage point for muscles

  • due to rigid nature they act as levers

    • joint is the fulcrum, contracting muscles create the force

• endoskeleton (internal skeleton)

  • vertebrates have this type

  • compromised of bone/cartilage

  • provides support/protection for the body

• exoskeleton (external skeleton)

  • arthropods have this type

  • possess rough exoskeleton made of chitin and jointed legs

  • provides protection from damage

explain the movement at the synovial joint

joints: where two or more bones meet, also known as articulation (allows and limits motion)

synovial joint:

• freely moveable joints which contain synovial fluid in a joint cavity that lubricates the joint to allow for smooth movement

• cartalige covers the ends of the nones to prevent friction and wear and tear

  • soft/spongy connective tissue

• joint capsule helps prevent wear and tear of the bones

ligaments:

• type of tissue that is tough/fibrous/slightly elastic

• connect bone to bone

tendons:

• strong, inelastic, fibrous bands of connective tissue which attach muscle to bone and allows muscles to pull on the bone

outline antagonistic muscles

• muscle pairs that have opposite actions, when one contracts, the other relaxes to allow for movement

  • muscular contractions only generate force in one direction

using internal and external intercostal muscles as an example, explain how they are antagonistic muscles

• external intercostal muscles (closest to the body)

  • run in downward and forward direction

  • diagonally towards the center of the chest

  • contraction of these movements cause the rib cage to move up and out

• internal intercostal muscles (deeper in the body)

  • run in upward and forward direction towards the center of the chest

  • perpendicular to the external intercostal muscles

  • contraction of these muscles cause the ribcage to move down and in

outline reasons for locomotion

• foraging for food

  • grazing on vegetation, actively hunting and capturing prey, searching for fruits/nuts etc

  • bees forage for nectar, pollen, water to bring back to the hive for the colony

• escaping from danger

  • quick behavious so animal can quickly avoid threats (jumping, flying, running)

  • elephants can detect infrasonic sounds

• searching for mate/reproduction

  • most animals will move to locations where members of opposite sex can be found

  • tigers have low pop density so they have limited opportunities with nearby females, as a result males have to cover large distances to find a mate

• migration

  • large scale seasonal movements of a group of animals from one place to another

  • young salmon migrate from rivers to sea, as adults migrate back to river to breed

outline the adaptations for swimming in marine mammals

• water is 1000x times denser than air, much more viscous

• streamlining bodies that minimise drag:

  • flippers and dorsol fin have elongated teardrop profile in transverse section

  • body surface is smooth due to even distribution of blubber and absence of hind legs

• forelimbs adapted to form flippers at the sides of usually long and narrow bodies

  • used to steer, generate upward force

  • contribute to streamlined shape

• adaptation of the tail to form a fat/wide fluke

  • can be used for steering and propulsion in the water with up and down movements

• changes to airways

  • allows for periodic breathing between dives (whales and dolphin blowholes)