Muscle Phys

Question 1

What are the 3 connective layers of mm (from in to out)

Answer 1

1. Endomysium- surrounds indv mm fibres
2. Perimysium- surrounds groups of mm cells (fasicles)
3. Epimysium- Surrounds entiraty of mm

Question 2

What are myofibrils and what are they made up of

Answer 2

Functional unit of the mm fibre

-Myofibrils are comprised of pro filaments called myofilaments which can be differentiated into thicc and thin filaments

Question 3

Myosin- characteristics, binding sites

Answer 3

Thick filament (creates pulling motion)

• has binding site for actin
• has binding site for ATP (for energy breakdown)

Question 4

What are the 3 protein subunits of actin

Answer 4

1. Actin- double helix along length of myofilament
2. Tropomyosin- Blocks actin binding sites when contraction isn’t supposed to happen
3. Troponin- located along tropomyosin (ensures tropomyosin stays in its blocking pos)

Question 5

What line borders each sarcomere

Answer 5

Z disc

Question 6

Where is titan located along the sarcomere, what does it act to do + disease that affects it

Answer 6

z disc to m line (acts to hold myosin in place for contraction to occur)

Tibial muscle dystrophy

Question 7

What does dystrophin connect and what is its function

Answer 7

connects actin filaments to the transmembrane pro B- dystroglycan which is located in sarcolemma

Question 8

What is in the A band

Answer 8

Formed by overlapping bands of actin/myosin

Question 9

What is the h zone

Answer 9

middle portion of myosin where there is no overlap

Question 10

What is the m line

Answer 10

small portion in h zone that is composed of m pro molecules that connect adjacent myosin

Question 11

What is the I band

Answer 11

Segment of the sarcomere that includes the z discs and the ends of the actin filaments

Question 12

What is the sarcolemma punctured by and the function of it

Answer 12

T tubules

-important for when the action pot needs to propagate along the mm

Question 13

Sarcoplasmic reticulum- how it is layed out, what does it do

Answer 13

chambers called terminal cisternae on either side of the t tubules and runs longitudinally along myofibril

-It stores ca when mm is not contracting

Question 14

What is the triad

Answer 14

A single t tubule with 2 surrounding terminal cisternea

Question 15

What are subneural clefts

Answer 15

numerous smaller folds in the mm membrane (greatly increases the surface area for which synaptic transmission can occur)

Question 16

Steps at neuromuscular junction

Answer 16

• Ap reaches and voltage gated Ca open
• aCH is released and binds to ligand channels
• NA comes in and triggers depolarization

Question 17

Where are volatage gated channels located in relation to ligand gated channels

Answer 17

Located very close in relation to ligaand gated- if membrane pot created by the ligand gated channels is great enough to reach threshold required by voltage gated AP will begin

Question 18

What type of feedback mechanism is voltage gated channels

Answer 18

Positive feedback mechanism (opening of voltage gated sodium channels allows more to keep opening)

Question 19

Where is dihydropyrindine receptor located and function

Answer 19

Located in walls of t tubules
- ca channels that are activated by depolarization which causes conformational change in ryanodine receptor which causes it to open and release ca into SR

Question 20

Once Ca is released into the SR what will it bind to

Answer 20

Will bind to troponic C, which pulls tropomyosin out of the way and exposing actin active sites

Question 21

How are cross bridges formed

Answer 21

form when myosin interact with exposed actin sites

- atp binds to myosin head and atpase breaks it down which puts myosin head in high energy state to bind to actin

Question 22

How is skeletal mm contraction ended

Answer 22

Ach removed by achesterase

• SR recaptures Ca off tropinin C (pumped back in by atp dependent Ca pump)
• Tropmyosin is brought back to cover actin sites

Question 23

Why does rigor mortis occur

Answer 23

Atp is depleted

-Without ATP Ca pumps cant work to detach myosin heads from cross bridges (mm will remain stiff)

Question 24

Myasthenia Gravis- pathophys

Answer 24

Autoimmune disease where body forms antibodies against ach receptors in motor end plate

Question 25

Myasthenia Gravis- age, clinical picture, tx

Answer 25

age- 20w, 60s m
clinical- Symetrical/asymetric weakness affecting smol mm first

Tx- anticholinesterase drugs (inhibits achesterase)

Question 26

Lambert eaton myasthenic syndrome- pathophys

Answer 26

autoimmune disorder that target presynaptic voltage gated calcium channels resulting in less ach released at NMJ

Question 27

Botulism- pathophys and when does occur

Answer 27

Inhibits/blocks release of ach from the nerve terminals

-occurs 6-48hrs after ingestion

Question 28

Tetanus- pathophys

Answer 28

Tetnus toxin travels retrograde axonal transport where it binds to presynaptic inhibitory neurons (blocks inhib nt release)

-net effect is disinhibition of spinal motor reflexes

Question 29

Tetanus- clinical pic

Answer 29

Sustained contraction of skeletal mm with periodic painfully mm spasms
-starts w small mm and moves to larger ones