Muscle Contraction

Question 1

thick filaments; describe composition.

Answer 1

made up of many MYOSIN molecules that have PROTRUDING HEADS at opposite ends of filament
- connect with THIN STRANDS of ACTIN to form CROSS BRDIGES - for MUSCLE CONTRACTION
“pulling motion”

Question 2

thin filaments; describe composition.

Answer 2

has TWO STRANDS of ACTIN with a TWISTED HELIX STRUC.
- TWO REGULATORY PROTEINS: TROPONIN & TROPOMYOSIN
- has SPECIFIC MYOSIN ATTACHMENT SITES
*look like little blueberries :)

Question 3

troponin

Answer 3

aids greatly in MUSCLE CONTRACTION in SKELETAL & CARDIAC MUSCLE

Question 4

tropomyosin

Answer 4

aids in the CONTRACTION of SKELETAL MUSCLE

Question 4

Titin

Answer 4

helps hold the THICK FILAMENTS in PLACE, helps with the RECOIL/GREATER RESISTANCE

Question 5

dystrophin

Answer 5

aids with the LINKING OF FILAMENTS TO PROTEINS of the SARCOLEMMA

Question 6

sarcoplasmic reticulum

Answer 6

• a basic network of SMOOTH ENDOPLASMIC RETICULUM that surrounds each MYOFIBRIL
• helps with the REGULATION of INTRACELLULAR Ca2+ LEVELS

Question 7

triad

Answer 7

composed of T TUBULES & TERMINAL CISTERNS of the SR

Question 8

terminal cisterns

Answer 8

• a given PATHeAY/SUBWAY for CALCIUm to allow for MUSCLE CONTRACTION

Question 9

t tubules

Answer 9

a TUBE that is FORMED by the PROTRUSION OF SARCOLEMMA DEEP into CELL INTERIOR

Question 10

what is the sliding contract mechanism?

Answer 10

this is where we begin to see CHANGES within the I BAND & H ZONE - during MUSCLE CONTRACTION
- where MYOSIN BEGINS TO PULL ACTIN (making the SARCOMERE SHORTEN - Z DISCS MOVE TOWARDS EACH OTHER

Question 11

what is the sliding filament model of contraction? name each step!

Answer 11

(***remember to note where our CALCIUM COMES FROM first - released by the SR due to ACTION POTENTIAL from the NMJ)

PHASE TWO
1. AP first TRAVELS across the entire SARCOLEMMA
2. AP TRAVELS along the T TUBULES
3. SR RELEASE of CALCIUM which BINDS TO TROPONIN (TROPONIN+CALCIUM)
4. TROPONIN PULLS TROPOMYOSIN - EXPOSED ACTIN BINDING SITES
5. MYOSIN HEAD BIND TO ACTIN (CROSS-BRIDGING)
6.’‘SWIVELING” MOTION - creation of the “POWER STROKE” **sliding filament action
7. COMPLETED POWER STROKE - ATP attachment again to MYOSIN/BACK TO ORIGINAL POSITION

*this process is repeated all over again as ATP is broken down by ATPase
*important - CALCIUM + ATP

Question 12

the 4 steps of describe muscle contraction.

Answer 12

1. begins always with NERVE STIMULATION within the NEUROMUSCULAR JUNCTION
2. ACTION POTENTIAL CREATED in NMJ
3. PROPAGATED AP through EC COUPLING (excitation-contraction coupling)
4. Intracellular CALCIUM LEVELS must rise briefly

Question 13

describe the nerve stimulus and the events that occur during the NMJ.

Answer 13

[context. always heavily getting stimulations from our skeletal muscles - sends then through alpha motor neurons all the way to the NMJ]

PHASE 1
1. AP arriving at AXON TERMINAL of MOTOR NEURON
2. VOLTAGE GATED CALCIUM enters AXON TERMINAL
3. CALCIUM ENTRY causes ACH (acetylcholine) RELEASe through EXOCYTOSIS (vesicles)
4. DIFFUSION of ACh in the SYNAPTIC CLEFT - binding of SARCOLEMMA RECEPTORS
5. PASSAGEWAY OF SODIUM-POTASSIUM PUMPS (3 sodiums in, 2 potassiums in) - creation of END PLATE POTENTIAL (also changes POLARITY of CELL
*local DEPOLARIZATION that helps DIFFUSE AP to PHASE 2

Question 14

role of acetylcholinesterase

Answer 14

the breakdown of ACh is due to the enzyme acetylcholinesterase & stops contractions

Question 15

muscle twitch

Answer 15

the SIMPLEST CONTRACTION due to MUSCLE FIBER’S RESPONSE to a SINGLE AP from MOTOR NEUTRON

• muscle fiber CONTRACTS QUICKLY + RELAXES
• can be seen through MYOGRAM

Question 16

what are the myogram phases?

Answer 16

1. LATENT PERIOD
   - events of excitation-contraction coupling; NO MUSCLE TENSION
2. PERIOD OF CONTRACTION
   - cross-bridge FORMATION; tension INCREASES
3. PERIOD OF RELAXATION
   - Ca REENTRY into SR - TENSION DECLINES to ZERO

*phases can vary from SIZE of muscles, or other METABOLIC NEEDS

Question 17

wave (temporal) summation

Answer 17

results from 2 DIFFERENT STIMULI recieved from the MUSCLE due to RAPID SUCCESSION
*not enough time to RELAX - creation of MORE TENSION

Question 18

tentanic contraction/fused (complete) tetanus

Answer 18

• seen in HIGHER STIMULUS FREQUENCIES; NO RELAXATION B/W STIMULI
  or aka MUSCLE CRAMP :(

Question 19

muscle tone

Answer 19

the CONSTANT, SLIGHTLY CONTRACTED STATE OF ALL MUSCLES
- gets input from stretch receptors in muscles - keeping muscles FIRM, HEALTHY, & RESPONSIVE

Question 20

what is excess postexercise oxygen consumption (EPOC) or oxygen debt?

Answer 20

this is where if you continue to BREATHE HEAVILY for a long time
- replenishing of CP reserves
- conversion of lactate to pyruvate
- lactic acid to pyruvic acid
- reloading of oxygen into myoglobin

Question 21

what are the type of stimulus?

Answer 21

1. SUBTHRESHOLD STIMULUS
   - stimulus is NOT STRONG ENOUGH *doesn’t reach threshold
2. THRESHOLD STIMULUS
   - stimulus is STRONG ENOUGH for SOME CONTRACTION *reaches threshold
3. MAXIMAL STIMULUS
   - the STRONGEST STIMULUS - all MOTOR UNITS ARE RECRUITED

*range of MOTOR UNITS depending on stimulus (goes from small, medium, to large fibers)