Lecture 19 Muscle Physiology 2 Flashcards Preview

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Flashcards in Lecture 19 Muscle Physiology 2 Deck (30)
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1
Q

Neuromuscular junction

A

synpase between motor neuron and muscle fiber

motor neuron AP-> ACH release -> synaptic transmission-> EPP -> muscle AP

2
Q

Muscle action potential

A

formed along the sarcolemma, similar to axon membrane

3
Q

Excitation-Contraction Coupling

A

“calcium is the key”
T tubules
Sarcoplasmic reticulum

4
Q

T tubules

A

conduct APs deep into the muscle fiber

DHP receptors function as voltage sensors, activated by the muscle AP (depolarization)

5
Q

Sarcoplasmic reticulum

A
Stores Ca2+ and releases it to myofilaments 
ryanodine receptors (RyR) in the SR membrane are Ca2+
channels
RyR of the SR interact w/ DHP receptors of the T tubule 
Ca2+ released through RyR channels activates muscle contraction 
Ca2+ pumps in the SR membrane actively transport Ca2+ back into the SR
6
Q

Sequence of events in Excitation-Contraction Coupling

1-3

A
  1. Muscle AP travels down the T-tubules
  2. DHP receptors on the T-tubule are activated
  3. Activated DHP receptor opens RyR Ca2+ channels
7
Q

Sequence of events in Excitation-Contraction Coupling

4-6

A
  1. Ca2+ diffuses out of the SR into the cytosol and to the thin filaments
  2. Ca2+ binds to troponin, which moves tropomyosin off the myosin bindin site
  3. Myosin binds to actin -> sarcomere contracts (crossbridge cycle)
    * when APs stop, Ca2+ is pumped back into SR -> sarcomeres relax
8
Q

Motor Unit

A

one motor neuron + all the muscle fibers it stimulates
small motor units (1:10) fine control, less force per unit
large motor units (1:2000) coarse control, greater force per unit

9
Q

recruitment

A

increase in number of active motor units

10
Q

increased CNS stimulation

A

activates more motor neurons with higher thresholds

increased motor unit recruitment -> more muscle fibers activated -> increased force of contraction

11
Q

Twitch

A

single contraction relaxation cycle, evoked by a single muscle AP
latent period, contraction phase, relaxation phase

12
Q

summation

A

two or more closely spaced APs -> increased force

13
Q

tetanus

A

high frequency of APs -> maximum, sustained force

14
Q

Length-tension relationship

A

sarcomere length = 2.0 - 2.2 um (‘resting length)
maximal number of crossbridges -> maximal tension
length >2.2 um - overlap decreases -> tension decreases
length < 2.0 um - interference between filaments -> tension decreases

15
Q

Skeletal muscle mostly operates at

A

the top of the L-T curve

16
Q

Cardiac muscle operates at

A

shorter than optimal length, so increase stretch -> increase force

17
Q

Functions of ATP in muscle contraction

A

detaches the actin-myosin crossbridges
energizes the myosin head
powers the Ca2+ pump in the SR

18
Q

Sources of ATP

A

intracellular ATP stores
phospocreatine + ADP -> creatine + ATP
Glycolytic metabolism
Oxidative metabolism

19
Q

Glycolytic metabolism

A

anaerobic

glycogen -> glucose-6-P -> lactic acid, yields 3 ATP per glucose unit

20
Q

Oxidative metabolism

A

aerobic
glycogen-> gluoce-6-P -> CO2 + H20 yields about 32 ATP per glucose
triglycerides -> fatty acids -> CO2 + H20, yields>100 ATP per fatty acid

21
Q

Muscle fiber types

A

slow-twitch oxidative (SO) (“red muscle”)
fast-twitch oxidative-glycolytic (FOG)
fast-twitch glycolytic (FG) (“white muscle”)

22
Q

Slow-twitch oxidative (SO) (red muscle)

A

slow myosin ATPase, small diameter -> low power
abundant mitochondria and myoglobin
high triglyceride content
highly aerobic -> slow fatiguing

23
Q

fast-twitch oxidative-glycolytic (FOG)

A

fast myosin ATPase, intermediate diameter, intermediate power
can utilize both aerobic and anaerobic metabolism

24
Q

fast-twitch glycolytic (FG) (“white muscle”)

A

fast myosin ATPase, large diameter -> high power
high glycogen content
mostly anaerboic -> fast fatiguing

25
Q

Smooth muscle physiology

General features

A

no sarcomeres, oblique arrangement of thick and thin filaments
contraction results from crossbridge formation between thick and thin filaments
contraction activated by action potentials, graded potentials, or chemical signals
spontaneous contraction (peacemaker activity) in some smooth muscle cells

26
Q

Activation of contraction in smooth muscle 1-3

A
  1. depolarization of smooth muscle cell (AP or GP)
  2. Ca2+ enters cytosol form ECF (through voltage gated Ca2+ channels) and/or from sarcoplasmic reticulum (through RyR Ca2+ channels)
  3. Ca2+ binds to calmodulin -> Ca-calmodulin
27
Q

Activation of contraction in smooth muscle

4-6

A
  1. Ca-calmodulin complex activated myosin light chain kinase (MLCK)
  2. MLCK catalyzes phosphorylation of myosin light chain
  3. phosphorylation of myosin light chain -> crossbridge formation -> contraction
    * when myosin light chain is dephosphorylated, crossbridge activity stops -> relaxation
28
Q

Types of smooth muscle

A

single-unit smooth muscle

multi-unit smooth muscle

29
Q

single-unit smooth muscle

A

extensive connections between cells via gap junctions

fewer innervation points (via varicosities of autonomic motor neurons)

30
Q

multi-unit smooth muscle

A

multiple innervation points, little or no connection between cells