week 4: muscular production of movement

Question 1

state the heirarchy of structural organisation of a muscle?

Answer 1

myosin and actin filament
sacromere
myofibrils
muscle fibre
muscle fasicles
muscle
skeletal muscle

Question 2

heirarchy of structural organisation of enwrapping connective tissue?
and its purpose?

Answer 2

enwrapping tissue provides a framework for the concept of series and parralell elements within a muscle
muscle mass = 85% fibres, 15% CT

• epimysium: enwraps muscle
• perimysioum: enwraps fasicle
• endomysium: enwraps muscle fibres
• sacrolema: specialised cell membrane of muscle cells, contains elastin therefore in heirachy

Question 3

function of epimysium

Answer 3

• it is the outermost CT layer
• enwraps entire muscle
• enables muscle to retain structural integrity when contracting and lengthening
• keeps entire muscle discete from other structures

Question 4

function of perimysium

Answer 4

• enwraps fasicles
• fasicular organisation allows nervous system to recruit fibres housed within a fasicle with greater specificity

Question 5

inner CT/ endomysium function

Answer 5

• enwraps individual fibres
• surrounds and supports the cell extracellular matrix, whcih contains important stuctural componenents

Question 6

sacrolema

Answer 6

• plasma membrane of each muscle cell
• has elastic properties

Question 7

what is the function of connective tissue as a whole?

Answer 7

permit force transmission to produce movement

• when a muscle contracts it creates tension
• this tension is transferred sequentially to each layer of tendon, concentrated at the MTJ
• via the tendon the force is transferred to the periosteal layer of bone, pulling on bone and moving skeleton

Question 8

what are the elements of a single muscle fibre that also contribute to muscle contraction?

Answer 8

• General chemical composition
• Nuclei/ ‘Myonuclei’
• Sarcolemma and Basement Membrane/ Basal Lamina
• Sarcoplasm
• Mitochondria
• Sarcoplasmic Reticulum (SR), and its Terminal Cisternae
• T-Tubule Network
• Myofibrils/ Myofibrillar Proteins

Question 9

how does the general chemical composition of a muscle, specialised for muscle contraction?

Answer 9

• 75% h20
• 20 % protien
• 5% inorganic compounds

Question 10

how is nuclei specialised in muscle cells for muscle contraction

Answer 10

• muscle cells are multi-nuclear
• ## loacted at the periphery of the muscle fibre/cells between the myofibrils and sacrolemma

Question 11

how are sarcolemmas (cell membrane) specialised for motor function?

Answer 11

• specialised, extendible cell membrane of fibres
• can be excitied electrically by AP from motor nueron
• it has a layered structure including: phospholipids, membrane bound receptors and transport molecules, structural proteins

Question 12

how are basement membranes specialised?

Answer 12

• also known as basal lamina
• they are immediatly external to sacrolemma
• extracellular deposition of protiens to form a membrane
• it is an ECM ‘coat’ that anchor the fibre as well as supporting cell development, reintergation, and cell signalling

Question 13

sarcoplasm (cytoplasm) specialisations?

Answer 13

• specialised cytoplasm of muscle fibres
• suspends myofibular proteins and organelles
• contents: ions, enzymes, ATP, phosphages, glycogen, lipid droplets, metabolic molecules

Question 14

mitochondria specialisations

Answer 14

• it is the powerhouse of intercellular space
• the density and size of mitochondria in muscles are larger and higher
• there is peroipheral and intermyofibular mitochondria

Question 15

sarcoplasmic reticulum (ER) and its terminal cisternae

Answer 15

SR:
- specialised smooth ER that stores, releases and retrives calcium ions
- calcium is fundemental for contraction

TC:
- a region of the SR in close proximity to, and surrounding the transverse tubercles
- stores calcium ions

Question 16

transverse tubules

Answer 16

• invaginations of the sacrolemma that extend inwards towards the centre of the cell
• retain proximity to SR and have key role in excitation-contraction coupling
• communicate iwth outside cell membrane to deep muscle

Question 17

myofibrils/myofibule protiens

Answer 17

• give structure and function
• suspended by sarcoplasm and run the length of fibre
• myofibrils are made up of connected sarcomeres

Question 18

sarcomere

Answer 18

• smallest functional unit within a skeletal muscle
• made of specialised contractile, regulatory and structural protiens

as a functional unit:
- contraction leads to individual contraction of muscle fibres, leadig to entire muscle contraction

Question 19

what is the structure of a sarcomere

Answer 19

• contain thick myosin and thin actin filaments
• the region of a sarcomere is between 2 Z discs
• M line is structural protein myosin, that anchors the thick myosin filaments in the center of the sarcomere
• A band in middle is dark bc of thick myosin overlap
• an I band anchors thin filaments either side of the sarcomere
• I band on either side is light becuase of thin filaments

Question 20

describe the structure of a thick filament

Answer 20

• made of myosin

2x MHC, 2xMLC
- MHC= tail region, hinge region, head that contains binding sites for ATP and Actin
- MLC: is the regulatory protein located at hinge region

• the globular head on myosin are referred to as “cross bridge” region, which contain myosin and ATPase (related to splitting ATP, speeding and providing energy)

Question 21

describe the structure of a thin filament?

Answer 21

made of 2x actin chains
- actin filaments are consecutive, linked actin protiens
- each single unit has a binding site for myosin
- troponin and tropomyosin span the actin chain and have a regulatory role determining actin binding availability

Question 22

what is the role of titin, and where is it?

Answer 22

• each titin molecule extends from z disk to M line
• part of titin molecule is associatied with thick filament
• rest of molecule is springing and changes length with sacromere
• therfore provides elasticity and stabilises myosin