L13 - Motor Pathways I: Muscle

Question 1

Key words: Perimysium, Fascicle, Muscle fiber, T-Tubules and nuclei

Answer 1

Connected to bones by connective tissue.

P: Connective tissue outside

F: bundle

MF: unit of muscle (contains myofibrils, which are composed of myofilaments

T: lead into the interior of the muscle fibre (high SA)
wraps around the myofibrils special part of SR - terminal cistern

Multiple nuclei – unique to skeletal

Question 2

H zone, A band, I band, Z line and M line

Answer 2

H - thick filaments not overlapping thin

Z - boarders (alpha actinic)

A band - Thick (myosin and titin)

I band - thin (actin and nebula)

M - center

Question 3

What is the optimal length?

Answer 3

Max no. go interactions

Question 4

Composition of myosin? (6)

Answer 4

Diverse motor proteins

Hexameter

ATPase

Skeletal (myosin 2)

2 light chains

4 heavy (2 reg/2 essential)

Question 5

Composition of actin (3)

Answer 5

Polymer

Globular - G (Filamentous)

F - Helical and single stranded.

Question 6

Composition of Tropomyosin (3)

Answer 6

Runs along actin (1 T per 7 actin monomers)

2 alpha helixes

Rest = blocks myosin binding

Question 7

Composition of Troponin (4)

Answer 7

Tetramer (1 per per 1 tropomyosin)

T: bind to tropomyosin

I: bind to actin and inhibit contraction

C: binds to calcium

Question 8

Stages of contraction (6)

Answer 8

1. Myosin bonds to actin
2. ATP binds = dissociation of bond
3. ATPase activity = conformational change in myosin (cocked)
4. New cross bride - down 2 actin monomers
5. Phosphate dissociates = POWER STROKE (uncocked)
6. ADP released = back to start

Question 9

Where is calcium stored?

Answer 9

Sarcoplasmic reticulum

Question 10

What happens when an AP happens?

Answer 10

Travels down T- Tubules to triad

Question 11

Calcium in muscle cells (5)

Answer 11

High outside

100nM inside

High in SR

Move into SR by SERCA (ATPase)

VSCC - not really letting calcium in

Question 12

Where does the calcium come from to trigger contraction? (5)

Answer 12

T tubules has VGCC (acts as voltage sensor)

Spring connection to T tubules and SR

Ryanodine receptor

AP down T tubule – activates VGCC – pulls receptor open on SR.

PRIMARY MECHANISM

Question 13

The DHP Receptor Tetrad

Answer 13

4 DHP = Tetrad

Interact with each ryanodine receptor.

Also L-type calcium receptor

Question 14

Restoring Calcium Balance

Answer 14

SERCA – uses ATP to pump calcium back into SR