Biology - Muscle and motility

motile

can move from place to place

sessile

cannot move from place to place

skeletal muscles

muscles attached to skeletons that aid movement

striated muscle cells

• bundled into muscle fibre cells

• each muscle fibre contains:

• contractile proteins

• many nuclei

• sarcoplasmic reticulum

• sarcoplasm (specialised cytoplasm)

• mitochondria

• myofibrils

myofibrils

• thick filaments: myosin

• thin filaments: actin

• bundles of actin and myosin slide past each other during muscle contraction

myofibrils structure

• thick filaments: myosin, which are fibrous proteins with globular head

• fibrous part of myosin anchors into thick filament

• heads pointing away from M line

• thin filaments: actin

• globular proteins

• two twisted chains: one thin filament

• tropomyosin twisted around chain

• troponin attached at regular intervals

bands meaning

h band: only myosin filaments

i band: only actin filaments

A band: only myosin filaments + both

M line: attachment for myosin

Z line: attachment for actin

sarcomere: section between two z lines

muscle contraction

• myosin heads form cross-bridges by binding with sites on the actin filaments

• myosin heads cock/change orientation which pulls actin filaments so they slide next to myosin “power stroke”

• sarcomeres shorten as z lines are pulled closer together

antagonistic pairs

• muscles can only pull not push, so they often work in antagonistic pairs

• muscles maintain posture by antagonistic muscles both contracting at joints to keep it at the same angle

• muscle contraction without movement

titin protein

• muscle contraction and relaxation both rely on protein titin

• large proteins that joins ends of myosin filaments to z line

• the many folds in titin gives spring like properties

• in relaxed muscle, sarcomere lengthens and titin is stretched out

• titin stores chemical energy when stretched and prevents over stretching

• during muscle contraction, sarcomeres tighten and titin proteins recoil releasing chemical energy

• adds to force of contraction

skeletal muscle

• skeletal muscle contracts when it receives an impulse from motor neurone via the neuromuscular junction

• neuromuscular junctions are located between motor neurone and muscle cell

• all this = motor unit

bones

• provides anchorage for muscles to act as levers

• vertebrates have internal bones/endoskeleton

• invertebrates have external bones/exoskeleton

• provide support for body of organism and facilitate movement

• exoskeletons also provide protection

muscles and skeletons

• muscles are anchored to the skeleton either on inside (exo) or outside (endo)

• skeletons act as levers, transferring size and direction of force

• levers have point of effort, point of load, and fulcrum

synovial joint

• joint cavity filled with lubricating synovial fluid which reduced friction

• fluid is produced by synovial membrane, which surrounds the joint

• can exert: flexion, extension, rotation, abduction, adduction

human hip joint

• ball and socket synovial joint

• articulation is between bones of the femur (ball) and pelvis (socket)

• cartilage covers bones and provides surface to prevent bones rubbing against each other

• whole joint is encircled with ligaments to hold bone in place

• muscles connected to bone via tendons

antagonistic muscles in ribcage

as external intercostal muscles contract, internal intercostal muscles stretch, resulting in store potential energy in titin protein of sarcomere

reasons for locomotion

• foraging for food: guinea pigs, spend 70 percent of their time awake searching and eating plants

• escaping from danger: salticidae spiders, jump out of way from predators

• searching for a mate: salmon, ocean to fresh water rivers to mate

• migration: caribou dear, travel over 3000 miles a year between their southern and northern ranges

adaptations for swimming

• streamline shape of body to allow them to move with ease through viscous waters

• flippers for stearing

• tails form a fluke for propulsion

• change to airways by evolution of blowholes to allow periodic breathing between dive