Module 7 (ET muscle) Flashcards
Types of muscles
Skeletal, cardiac and smooth
Striated muscle
Skeletal and cardiac; highly ordered contractile system leading to a banded appearance with bands occurring with a periodicity of about 2um
Non-striated muscle
Smooth muscle
Voluntary muscles
Skeletal; responsible for the movement of limbs; attached to bones which act as levers to provide a greater range of movement
Involuntary muscles
Cardiac for pumping blood; smooth for lining blood vessels and hollow organs, responsible for altering their dimensions; may have intrinsic contractile activity whose amplitude and/or frequency is modulated by nervous system input (myogenic); others may be quiescent and their contraction initiated by autonomic nervous system input
Motor unit
A group of muscle cells which are innervated by a single motor neuron
Structure of skeletal muscle
Most highly ordered of muscles; attached to bones via tendons; the cells (muscle fibres) are up to 35cm long and 0.1cm wide; cells composed of fibrils which run the length of the cell and contain highly organised contractile filaments; SR surrounds the fibril and stores calcium, releases it to activate contraction
Fibrils in skeletal muscle
Run the length of the cell; made up of alternating bands of myosin and actin filaments which interdigitate
Sarcomere
Basic contractile element; consists of an array of thick and thin filaments, attached to Z-discs at each end; t-tubules invaginate the surface membrane of the cell (sarcolemma) and are surrounded by the SR
Thin actin filaments
Globular proteins that form thin filaments within the cell; may have accessory proteins attached to them which regulate their activity (such as troponin and tropomyosin)
Thick myosin filaments
High molecular weight protein that is formed from two high molecular weight sub-units which each have a tail that wind around each other in a double helix and a globular head able to hydrolysed ATP; accessory proteins regulate this ability
A-band
Thick filaments run the entire length; some thin filament
I-band
Thin filaments run length
Z-disc
Coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another
H-zone
Lighter mid-region where filaments do not overlap
M-line
Line of protein myomesin that holds adjacent thick filaments together
T-tubules
Deep invaginations continuous with the sarolemma (cell membrane) and circle each sarcomere at each of the junctions of the A and I bands; allows APs to be carried deep within the cell
SR
Sarcoplasmic reticulum; calcium storage site; terminal cistenae lie close to the T-tubules
Sliding filament theory
Sarcomere shortens as the thin filaments are pulled over the thick filaments; Z-line pulled toward M-line; I band and H zone become narrower
Cross-bridge cycle
Cross-bridge formation; power stroke; detachment; energisation of myosin head
Cross-bridge formation
Myosin binds to the actin binding site to form a cross-bridge; can only occur in the presence of calcium when the myosin biding site on actin is exposed; the myosin head has already hydrolysed ATP so ATP needs to be available
The power stroke
ADP is released; myosin head rotates to its low-energy state (about 45degrees to the actin) pulling with it the thin filament; result is shortening of the sarcomere
Detatchment
A new ATP molecule bind to the myosin; the actin-myosin bond is weakened and the myosin detaches; if there is no ATP, rigor mortis (stiffness) will occur because there is no energy available and the myosin stays attached to the actin
Energisation of the myosin head
Myosin head hydrolyses the ATP to ADP and Pi; the myosin head moves back to its high energy (cocked) conformation about 90degrees to the actin