28. motor mechanisms Flashcards
what are the three main functions of animal skeletons?
support, protection and movement
how does a hydrostatic skeleton provide support and allow movement?
it provides support by body fluids held under pressure in a closed body compartment.
allows movement by muscles changing the shape of fluid filled compartments
how do insects and molluscs grow inside an exoskeleton?
insects grow by shedding their chitin cuticle (epidermis). its jointed so the areas for protection have a hardened cuticle and areas needing flexibility (leg joints) have a thin cuticle.
molluscs secrete more cuticle from the mantle as it grows larger, adding onto the exoskeleton
what is the difference between endoskeletons and exoskeletons?
endoskeletons are hard elements buried inside soft tissue whereas exoskeletons are on the epidermis
what is the order from largest to smallest to make up a muscle?
muscle
long muscle fibres
muscle cell with multiple nuceli
a bundle of small myofibrils
myofibril is a cylinder with myofilaments
what are the two types of myofillaments myofibrils are composed of? what protein are they made from?
thin filaments (actin) and thick filaments (myosin)
what does a relaxed and a contracted sacromere look like?
Relaxed sarcomeres contain myosin heads that have released their pull on the thin filaments. This allows them to return back to their relaxed state and causes the I bands and H zones to appear.
The myosin heads pull on the thin filaments as a muscle contracts causing the disappearance of the I bands and H zones
what is the structure of a sacromere?
Z lines
thin filaments
thick filaments
I band
A band
H zone
the Z lines which is the outer boarder.
thin filaments are attached to Z lines horizontally to go to the centre of the sacromere
thick filaments are horizontal in the middle of the sacromere
I band is on the edge of the sacromere - only thin filaments reach
A band is the lenghth the thick filaments reach
H zone is the area in the centre of the A band (only thick filaments reach)
how does the sacromere shorten (muscle contraction) without the thick and thin filaments shortning?
the filaments slide past each other so theres more overlap. the I bands and H bands shrink in lengh. the sliding filament model
what is the role of calcium in muscle contraction?
when calcium binds to another set of regulatory proteins on thin filaments (troponin complex), myosin binding sites on the thin filament are blocked by tropomyosin
what are the 7 steps of muscle contraction (action potential)
- acetylcholine from motor neuron triggers an action potential in muscle fibre
- action potential travels along plama membrane and down T tubules
- action potential triggers release of calcium from sarcroplasmic reticulum
- calcium ions bind to troponin complex, moving tropomyosin and uncovering the myosin binding site on the thin filament
- myosin alternately forms and breaks cross bridges with actin pulling the thin filament towards the centre of the sacromere. ATP powers sliding of the filaments
- calcium is removed from the cytosol back to the sarcroplasmic reticulum
- tropomyosin covers myosin binding sites on thin filament. contraction ends and the muscle fibre relaxes
study image!
describe two ways the nervous system controls how strongly a muscle contracts
the amount of motor units are activated
using large or small motor units
what are thetwo subdiisions of striated muscle in vertebrates? what do they do?
skeletal muscle - under voluntary control, wont produce AP unless stimulated by a motor neruon
cardiac msucle - similar to skeletal muscle but only found in the heart. dosent need the nervous system for AP.
why dosent smooth muscle have a striated appereance? (found in blood vessels, digestive tract and airways)
its not under volnatary control, because actin and myosin are not regulary arranged. the irregular arrangement of myofilaments means the muscle contracts slowly
