Exam 5 - Myocardial Contraction Flashcards
1
Q
Skeletal muscle
A
- contraction via nervous system
- Ach is neurotransmitter
- long, striated w/ multiple nuclei
- voluntary movement
2
Q
Smooth muscle
A
- contraction via nervous system (ANS) , hormonal stim (Epi/NE), muscle stretch
- found in hollow organs and arterioles
- can stimulate and inhibit contraction
- long, spindle shaped w/ single nuclei
3
Q
Cardiac muscle
A
- contraction via specialized cardiac cells
- branching, striated, fused at plasma membrane
- single nuclei
- function is to pump blood
4
Q
Organization of fibers
A
- Muscle fiber -> myofibril -> myofilaments
5
Q
Sarcolema
A
- plasma membrane enclosing muscle fiber
6
Q
How many ATP needed to move 1 myosin head
A
1 ATP
7
Q
Sarcoplasm
A
- cardiac muscle cell cytoplasm
- contains numerous mitochondria
- large number of myofibrils running parallel
8
Q
Intercalated discs
A
- hold fibers together
- aid in conduction
- unique to cardiac muscle cells
9
Q
Sarcoplasmic Reticulum
A
- surrounds each myofibril
- network of tubes and sac with high [Ca]
- similar to smooth ER in other cells
- Ca here used in plateau phase
- HUGE in cardiac muscle cells
10
Q
T tubules
A
- Cross SR at right angles and communicate to outside
- Move AP from exterior to interior
- Fluid inside tubules is interstitial fluid
- Bring extra cellular environment to interior of cell
11
Q
Sarcomere
A
- one z-line to another z-line
- fundamental unit of muscle contraction
12
Q
I-Band
A
- Thin actin strands alone
- actually cuts across two adjacent sarcomeres
- gets smaller during contraction
- from end of myosin to next myosin
13
Q
Z-line
A
- Anchors actin filaments
- composed of proteins
14
Q
A-band
A
- overlapping myosin and actin
- the length of the myosin filaments
- stays same length during contraction
15
Q
H-zone
A
- area within A-band
- contains only myosin filaments
- gets smaller during contraction
16
Q
M-line
A
- Middle of H-zone
- connects adjacent myosin strands
17
Q
Titin molecule
A
- framework for sarcomere
- keeps acting and myosin aligned
- very large protein (3,000,000 daltons)
- one end anchored to the myosin…other to z-line
- very springy….can change length with contraction/relaxation
18
Q
Z-line to z-line distance
A
- 2 microns
19
Q
Anatomy of Actin
A
- 1 micron long
- 3 strands….2 F-actin and 1 Tropomyosin (70,000 D)
- Basic unit of F-actin is G-actin molecule (42,000 D)
- each G has one ADP attached…x-bridge attachment site - During resting phase (phase 4)…tropomyosin blocks active G sites
20
Q
Anatomy of Tropomyosin
A
- Spaced along are 3 proteins
- Troponin I: affinity for actin
- Troponin T: affinity for tropomyosin
- Troponin C: affinity for Calcium - I and T hold tropomyosin to actin
21
Q
Relationship of contractility and [Ca]
A
- higher [Ca] = more x-bridges = more contractility = stronger contraction
22
Q
Anatomy of myosin
A
- fiber = 200 myosin molecules
- 480,000 D
- Each head is an ATPase enzyme
- made of 2 heavy chains / 4 light chains
- heavy chains wrap around each other to form tail
- at end of wrap…heavy chains fold on self to create head
- each head gets 2 light chains on it (total of 4)
23
Q
Pre-load
A
- volume in ventricle at end of diastole
- more preload = better cardiac performance
- this affects INTRINSIC contractility
- EXTRINSIC would be like shifting starling curve
24
Q
Contraction of Sarcomere
A
- Ca enters cells and interacts with Troponin C
- This causes change in Troponin I…exposing binding site
- X-bridges begin to form
- head moves and pulls like oars on boat
25
How long does each power stroke move
- 5 nm
26
Power stroke movement process
- ATP binds to head... causing release of head and actin site
- ATP is hydrolyzed and energy stored in head (cocking it)
- ADP and phosphate still bound to head
- Energy filled head form weak bond with new binding site
- causes phosphate to be released
- release of phosphate tightens bond and power stroke occurs
- power stroke causes loss of bound ADP and into rigor stage
- process will repeat if Ca present
27
How Ca enters cardiac muscle cell
- AP triggers release of Ca into cell through T-tubules
- 90% of Ca that binds to Troponin C comes from SR
- Ca entering cell from outside (10%) is just trigger Ca for SR
- In regular muscle cells...Ca comes from outside...not SR
28
How Ca removed from cardiac muscle cell
- 90% pumped back into SR via ATP pump
- Phospholamban helps with this
- 5% pumped out of cell via Ca ATP pump
- 5% pumped out via Na/Ca pump
- Also a Na/K pump that helps build gradient for Na/Ca pump
29
Isotonic
- tension stays same...muscle length decreases
- tension built up is only enough to move...then you get change in length
- here you get max rate of shortening
30
Isometric
- length stays same....tension builds
- can build up MAX tension
- Pre-load determines resting muscle stretch
- also acts as muscle antagonist (like bicep/tricep)
31
Resting vs Active tension
- Resting: tension created by stretching
- Active: tension created by stimulation
- difference between resting and peak isometric tension
- resting tension is only one we can change
32
Measured systolic pressure
- Max pressure seen in systole
33
Measured diastolic pressure
- minimum pressure seen in diastole
| - pressure that must be overcome to open aortic valve
34
Two types of work the heart does
- Pressure build up: to overcome aortic valve pressure and open
- Ejection of blood: to overcome SVR
35
Why we don't develop max tension/velocity
- No max tension: can't have shortening
| - No max velocity: only get minimal tension
36
Length of optimal sarcomere
- 2-2.2 microns
- develops max tension and interaction of actin and myosin
- perfect amount of overlap
37
Muscle length and SV
- As afterload increases...ability of muscle to shorten decreases
- This will decrease SV
38
Why cardiac muscle cells arranged circumferentially
- creates twisting/ squeezing of ventricle from bottom-up
39
Law of Laplace
T = P x r
T: wall tension
P: intraventricular pressure
r: ventricular radius
