L72- Muscles Flashcards
what are the different types of muscles?
- skeletal muscle
- controlling skeletal muscle
- smooth muscle
what are the 5 functions of the skeletal muscle?
- Movement: attach to bones to allow us to move
- Posture: muscle tension holds our skeleton in place eg head
- Soft tissue support: abdominal wall supports internal organs
- Guards entrance/exits: digestive and urinary tract are controlled by voluntary muscles for control
- Maintains body temperature: contractions use energy and produce heat
why is the sarcoplasmic reticule important in muscles?
plays a role in storing Ca2+ required for contraction
what are transverse tubules?
are continuations of the plasma membrane (the sarcolemma) which dip into the cell and allow effective propagation of an action potential
what is a muscle made from?
unit of fibres
what is myosin?
Myosin is a protein which makes up thick .Heads make up myosin cross-bridges – sites of attachment to thin actin filaments (actin binding site). Myosin head binds ATP and acts as an ATPase
what is actin?
makes up the thin filament, I is globular.
what is tropomyosin?
is a thread-like molecule that lies next to actin molecules.
- controls access to the cross-bridge binding sites - held in place by the troponin complex
- movement is regulated by calcium
what is troponin?
3 polypeptide units that bind to actin, tropomyosin and calcium
what is the neuromuscular junction?
is a specialised synapse between an α-motor neuron and a skeletal muscle fibre at the motor end plate
what are the properties of a-motors?
neurons are fast, myelinated neurons
what happens during contraption( power stroke)?
- myosin cross bridge attaches to the acts myofilament.
- myosin head pivots and bends as I pulls on he actin filament sliding it toward the M line.
- As new ATP ATTACHES TO THE MYOSIN HEAD THE CROSS BRIDGES DETACHES.
- as ATP is split into ADP and Pi cocking of the myosin head occurs.
what is the Z lines?
the 2 ends of the sarcomere.
what is the M line?
the centre line
what is the H band?
space between the 2 myosin molecules in the middle
what is the I band?
the space between the z line and the myosin filament at the ends
what is the sliding filament theory of contraction?
- increase in ca+ starts sliding filament
- as sliding happens z lines pull closer, sarcomere shortens
- decrease in ca+turns off sliding
how is relaxation of muscles controlled?
by reducing Ca2+, removed from cytoplasm
• Also need to remove ACh from the Neuromuscluar Junction – enzyme-mediated breakdown by acetylcholinesterases
• Once the stimulation is removed there is no action potential
how does the whole muscle contraction happen?
- acetylcholine released by axon crosses cleft binds to receptor.
- action potential generated on response moves down T tubules of muscle cell.
- this riggers Ca2+ released from sarcoplamic reticulum
- Ca2+bind to tropomyosin and move it to uncover cross bridge binding sire on actin.
- mysin cross bridge attaches to actin this pulls actin towards centre of sarcomere engird from ATP.
- Ca2+ taken up by sarcoplasmic reticulum when no local action potential
- with no Ca2+bound to troponin, tropomyosin slips back to blocking the binding site, and actin slides back to resting potential.
what are the major groups of smooth muscle?
- vascular
- gastrointestinal
- urinary
- respiratory
- reproductive
- ocular
where are smooth muscles found ?
in walls of hollow organs and tubes
what don’t smooth muscles have that controlling muscles do?
• Smooth muscle is not striated, no myofibrils, no
sarcomeres
• Fewer mitochondria
• Contract and relax slower
how does smooth muscles work?
- Increase in [Ca2+]i can be generated via ion channels or receptors or release from sarcoplasmic reticulum
- Ca2+ signals through Ca2+-binding proteins such as calmodulin
- Binds 4 calcium ions and then activates further target proteins – e.g. MLCK
what does removal of Ca2+ do to smooth muscles?
inactivates MLCK myosin light chain kinase
hows does smooth muscle contraption happen?
- Ca2+ increases and enters cell via t tubes released from SR.
- Ca2+ binds to calmodulin (CaM).
- Ca2+- calmodulin activates myosin light chain kinase
- MLCK phosphorylates light chain in myosin heads and increases myosin ATPase activity.
- active myosin cross bridges slide along actin and create muscle tensions.
