IB biology HL: B3.3 - muscles and motility

motility

ability to move as a living organism

motile organisms

capable of independent movement; cheetah, tuna,, bacteria with flagellum

sessile organisms

unable to move independently; are anchored to a substrate; plants, corals, barnacles when adults, algae…

sarcomeres

repeating units made of two proteins - actin and myosin

actin

thin filaments making sarcomeres

myosin

a protein/filament, the thicker one, making up sarcomeres. 

when contracting,

motor unit

what causes muscle contraction

junction between he motor neuron and the skeletal muscle fibers

neuromuscular junction 

myofibrils

a series of sarcomeres

sarcoplasmic reticulum

specilised endoplasmic reticulum; they store calcium ions which they release when contracting the muscle fibers

what does a muscle contraction do

• actin slides next to myosin

• this shortens the sarcomeres

• muscle fiber gets shorter

skeletal muscles

voluntary control- contract or relax from signals of nervous systems

bundles of muscle fibers 

made of many myofibrils, made of sarcomeres, alternating actin ( anchored at Z line ) and myosin ( anchored at center of sarcomere on M line )

cross bridges of myosin filaments bind to binding sites on actin, allowing them to drag it towards each other

when muscles are relaxed, tropomyosin in binded on actin binding sites, preventing the bridges between the long and short fibers from being created 

when muscles contract, calcium ions are released from sarcoplasmic reticulum, which bind to the troponin, changing it’s shape and allowing the cross bridges to be created and making the actin move towards the M line 

muscles contracting

tropomyosin is a long fiber. it’s over the myosin binding site. when calcium ions come, they will bind to troponin, a protein attached to tropomyosin, which moves the tropomyosin away, and leaves the binding sites free.

active site exposure => cross brdge formation ( needs atp ) => myosin head pivots, moving actin => cross bridge gets detached ( needs atp ) => continues if ATP is available and calcium level is high

titin

it is a polypeptide, which acts like a spring

role of skeleton 

• nstructural support 

• muscles to anchor to 

• protection of internal organs

• bone marrow => blood cell productio

joints

each joint acts as a pivot point => act as levers

elbow joint

• hinge joint

• angular movement in only one dorection

• flexion + extension

radio ulnar joint 

• pivot joint 

• movement in all rotational directions 

hip joint

• ball and socket

• angular movement in many direction

• flexion, extension, abduction circumduction totation

range of motion of joints

• age

• estrogen

• muscles ( can get in the way