Skeletal and muscular physiology Flashcards
what is the smallest component of muscle fiber that is capable of contraction
The functional unit, a sacromere
a functional unit is defined as any part of an organ which is the smallest component that can perform all the functions of that organ
How is muscle contraction regulated
outline how the muscle systems and skeletal systems work together to allow the cheetah to meet the challenges of its environment
- flexible long spine
- long tail which acts as a rudder
both allow increased agility - large powerful leg muscles allowing increased speed and locomotion of skeletal muscles
both systems work together
what is the function of the muscular system
1) locomotion
- attached to skeletal system by tendons
2) external mechanical work
- e.g. lifting
3) structural support
- posture and body form
4) movement through the vessels
- smooth muscle
5) Heat production
- shivering
what are the different classifications of muscle and how are they classified
1) Skeletal = voluntary (somatic nervous system), striated (sacromeres) parallel muscle fibres
2) Smooth = involuntary (ANS), unstriated, covers walls of internal organs
3) Cardiac = involuntary (ANS), striated, branched muscles fibres
outline the structure of a striated muscle
MUSCLE = made up of thick branches of muscle fibres
MUSCLE FIBRE = made up of bundles of fibres (a single muscle cell)
MUSCLE CELL = made up of parallel branches of microfibrils with dark and light bands
DARK BANDS= interlocking filaments of thick filament (myosin ) and thin filament (actin)
LIGHT BANDS = known as the Z line and is just thin filament actin
What is a sacromere
The area between two Z lines (thin filament actin) which is a functional unit of skeletal muscle and made up of interlocking thick and thin filaments bound by z lines
contains M lines in the centre (mitochondrial rich, high ATP increasing contractions)
what is a transient cross bridge
the attachment formed between the myosin heads and the actin filaments during contractions
transient cross-bridges occur repeatedly during muscle contraction and allow for the sliding of actin and myosin filaments, leading to the shortening of muscle fibers and generation of force
How do transient cross bridges form
projections are present which go from the mysoin head and grab onto the actin before releasing
this grabbing actin allows filaments to slide
Ryanodine receptors and dihyropyridine recpetors are named for the specific drugs which bind to them, but also physioloigcally, what is their function?
outline the structure of thin filaments (actin)
monomeric units of globular actin (G-actin) which polymerase to form an actin helix (F-actin)
each monomer has a specific binding site for the attachment of the myosin cross bridge
filamentous protein tropomyosin allowing with globular troponin complexes bind to the grooves in the actin polymer covering the myosin binding sites so they aren’t accessible
outline the structure of thick filaments (myosin)
- complexes made up of three different myosin proteins; myosin heavy, light and regulatory chains
Tails = made up of 2 coiled heavy myosin chains
Head = made up of a heavy chain, two light chains and a regulatory chain
on the myosin head there are two binding sites, one for actin and one for ATPase (muscle contraction)
outline the sliding mechanism theory
refers to the cyclic attachment and detachment of actin and myosin (cross bridge theory) , interlocking regions remain the same length but non-overlapping H zones (sarcomere) and I bands (light filaments) shorten
outline the process of cross bridge cycling
outline the events which occur during muscle contracting and is part of the sliding mechanism theory
1) ATP is split by myosin ATPase into ADP +Pi and remain attached to myosin acting as stored energy in cross bridges
2) Binding of calcium released by excitation removes inhibitory influence from actin enabling it to bind with cross bridge- no calcium means actin cant bind so muscle fibres remains at rest
3) power stroke of cross bridge triggers on contraction between myosin and actin cause Pi during and ADP after power stroke
4)linkage between actin and myosin is broken as fresh molecule of ATP binds to myosin cross bridge so it forms original conformation and ATP hydrolysed back to ADP +pi
5) if no fresh ATP formed (death) actin and myosis remain bound and muscle remains contracted = rigamortis
outline the difference between a relaxed and an active filament
RELAXED = there is no bridge between myosin and actin as the binding site of actin is covered by the filamentous protein tropomyosin and the globular complex troponin
ACTIVE= cross bridge is formed and tryponin and trypomyosin move away due to binding to calcium molecules released from action potentials and the binding site binds to the myosin head
outline how calcium is regulated in the muscle system
Muscles cells have a type of endoplasmic reticulum known as a sarcoplasmic reticulum which stores calcium
transvers tubules in the membrane of muscle cells are stimulated by action potentials which travel down the tubules
the tubules have two voltage gated receptors; dihydropyridine and ryanodine which couple allowing the release of calcium from the sarcoplasmic reticulum to the cell allowing contraction
outline the entire process from the start of a muscle contraction to the relaxation of a muscle
- Motor neurone AP stimulates release of
acetylcholine, triggering AP in muscle fibre - AP moves through T tubules & triggers release
of Ca2+ from sarcoplasmic reticulum - Ca2+ binds to thin filaments & tropomyosin
moves away from myosin binding site - Myosin-actin cross bridges form
- ATP driven power stroke & filament sliding
- Cross bridge detaches & cycle repeats if Ca2+
still present - When APs stop, Ca2+ is sequestered by
sarcoplasmic reticulum, tropomyosin returns to
block myosin binding sites & muscle fibres relax
how does summation affect muscle tension
increases muscle tension
- if the duration of a muscle contraction stops before a new action potential then only a small twitch occurs
- if it lasts until a new action potential the tension is stronger
- this continues until reaching maximum muscle tension known as tetanus
what are the functions of the skeletal system
1) locomotion
2) structural support
3) protection e.g. skull, ribs and pelvis
4) blood cell production = bone marrow
5) mineral storage e.g. caclium
what is the difference between an endo and exoskeleton
exo = made up of chitin in arthropods and carbonate in molluscs, cant support large body sizes, variable protection, replaced (moulting), no blood supply
endo = develops from mesodermal tissue, made from bone and cartilage, supports large body sizes, strong protection, slow repair and has a blood supply
outline the structure/form of bones
Top = spongey bone with red bone marrow for RBC production
Middle = hard bone with yellow bone marrow surrounded by a matrix made from collogen and calcium
matrix called the osteon which is a series of different layers of bone matrix surrounding a central blood vessel
what are the different types of bone cells and their function
1) osteocytes = brown cells surrounding units which are a mature bone cell and maintain bone function by recycling calcium and minerals
2) Osteogenics = immature bone cells called stem cells
3) osetoblast = forms the bone matrix from collogen and calcium
4) osteoclast = breaks down and reabsorbs bone tissues
outline the process of bone remodelling performed by osteoblasts and osteoclast cells
1) osteoclasts derived from macrophages secrete hydrochloric acid and enzymes which dissolve the bone matrix
2) osteoblasts move into the voids created by osteoclasts and secrete osteoid (matrix of collogen and calcium) to replace the bone
what affects the rate of bone remodelling
the balance between the activity between osteoblasts and clasts maintained by two chemicals
1) RANK Ligands = RANK receptors are present on both macrophages and osetoclasts and when bound it stimulates macrophages to differenciate into mature osetoclasts and stops osetoclasts breaking down by apotosis = INCREASES ACTIVITY
2) OPG= is a decoy receptor which binds to RANK ligand stoping them from binding to macrophages and osetoclasts preventing action therefore decreasing osteoclast activity
how is calcium regulated in the skeletal system
there are 2 hormones involved
1) parathyroid hormone (PTH) = increases calcium (mammals primarily rely on this)
2) Calcitonin = decreases calcium (less in mammals and more in fish)
what are the two ways PTH increases the mobilisation of calcium in the body
1) rapid exchange: caclium ATP pumps
- ATP driven pumps responsive to the hormone to increase the pumping of calcium into the blood plasma
2) chronic exchange
- breakdown of mineralised bone tissues which increases RANK ligand activity decreasing overall integrity of bone (bad)
outline the negative feedback system PTH partakes in to increase calcium levels
less calcium causes increased PTH
causes increased mobilisation of calcium from the kidney tubules reabsorbing more, increased vitamin D activation which acts on the gut to increase calcium uptake
