Skeletal and muscular physiology

Question 1

what is the smallest component of muscle fiber that is capable of contraction

Answer 1

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

Question 2

How is muscle contraction regulated

Question 3

outline how the muscle systems and skeletal systems work together to allow the cheetah to meet the challenges of its environment

Answer 3

• 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

Question 4

what is the function of the muscular system

Answer 4

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

Question 5

what are the different classifications of muscle and how are they classified

Answer 5

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

Question 6

outline the structure of a striated muscle

Answer 6

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

Question 7

What is a sacromere

Answer 7

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)

Question 8

what is a transient cross bridge

Answer 8

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

Question 9

How do transient cross bridges form

Answer 9

projections are present which go from the mysoin head and grab onto the actin before releasing
this grabbing actin allows filaments to slide

Question 10

Ryanodine receptors and dihyropyridine recpetors are named for the specific drugs which bind to them, but also physioloigcally, what is their function?

Question 11

outline the structure of thin filaments (actin)

Answer 11

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

Question 12

outline the structure of thick filaments (myosin)

Answer 12

• 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)

Question 13

outline the sliding mechanism theory

Answer 13

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

Question 14

outline the process of cross bridge cycling

Answer 14

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

Question 15

outline the difference between a relaxed and an active filament

Answer 15

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

Question 16

outline how calcium is regulated in the muscle system

Answer 16

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

Question 17

outline the entire process from the start of a muscle contraction to the relaxation of a muscle

Answer 17

1. Motor neurone AP stimulates release of
   acetylcholine, triggering AP in muscle fibre
2. AP moves through T tubules & triggers release
   of Ca2+ from sarcoplasmic reticulum
3. Ca2+ binds to thin filaments & tropomyosin
   moves away from myosin binding site
4. Myosin-actin cross bridges form
5. ATP driven power stroke & filament sliding
6. Cross bridge detaches & cycle repeats if Ca2+
   still present
7. When APs stop, Ca2+ is sequestered by
   sarcoplasmic reticulum, tropomyosin returns to
   block myosin binding sites & muscle fibres relax

Question 18

how does summation affect muscle tension

Answer 18

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

Question 19

what are the functions of the skeletal system

Answer 19

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

Question 20

what is the difference between an endo and exoskeleton

Answer 20

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

Question 21

outline the structure/form of bones

Answer 21

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

Question 22

what are the different types of bone cells and their function

Answer 22

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

Question 23

outline the process of bone remodelling performed by osteoblasts and osteoclast cells

Answer 23

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

Question 24

what affects the rate of bone remodelling

Answer 24

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

Question 25

how is calcium regulated in the skeletal system

Answer 25

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)

Question 26

what are the two ways PTH increases the mobilisation of calcium in the body

Answer 26

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)

Question 27

outline the negative feedback system PTH partakes in to increase calcium levels

Answer 27

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