Week 10 Muscle Contraction II Flashcards
what is a motor unit
the motor neuron and all muscle fibers it supplies
What are the three phases of muscle twitch
latent period, period of contraction, period of relaxation
what is the latent period
events of excitation-contraction coupling; no muscle tension
what is the period of contraction
cross-bridge formation; tension increases
what is the period of relaxation?
Ca2+ re-enters into the sarcoplasmic reticulum; tension declines to zero
what is a muscle twitch
is a response of a motor unit to a single action potential of its motor neuron
what is a graded muscle response
skeletal muscle can alter the strength of contraction for different demands by changing the frequency or strength of stimulation.
what is graded muscle response 2
Changing the stimulus strength by increasing nerve stimulus to activate more motor units
what is graded muscle response by size principle
- muscle fibers with smallest muscle fibers recruited first
- motor units with larger muscle fibers are recruited as intensity increase
- largest motor units activated for most powerful contractions (50 x contractile force of smaller fibers)
what is an example of graded muscle response by size
the same arm can lightly pick up a pen but deliver a mighty punch to a boxing bag
can motor units be recruited simultaneously
yes. e.g., weightlifting
What are isotonic contractions
muscle changes in length and moves the load
What does the isotonic contraction concentric mean?
that the muscle is shorted
what does the isotonic contraction eccentric mean
that the muscle is lengthened
what are isometric contractions
Tension increases to muscle’s capacity, but muscle neither shortens nor lengthens
what are the types of muscle fibers
speed of contraction and major pathway for ATP generation
What is slow speed contraction
myosin ATPases hydrolyze ATP slowly
what is fast speed contraction
myosin ATPase hydrolyse ATP fast
what is oxidative
use aerobic pathways for making ATP
what is glycolytic
use mainly anaerobic pathways
what are slow oxidative fibers
contract slowly
require oxygen
fatigue resistant
endurance activities
what are fast oxidative fibers
contract quickly
require oxygen
fatigue slowly
intermediate activities walking running
what are fast glycolytic fibers
contract quickly
don’t require oxygen
fatigue quickly
short term, intense movements
are all fibers in one motor unit the same
yes
what is muscle fatigue
physiological inability to contract
what causes muscle fatigue
- Ionic imbalance
- Increased inorganic phosphate
- A potential relative deficit in ATP as muscles use up their stores
- Decrease glycogen
- interference in calcium regulation and release
what is interference in calcium regulation and release?
Potassium is lost from the muscle cells as action potentials keep firing. This causes K+ accumulation in the T-tubules, disturbing the membrane potential of the muscle and halts Ca2+ release from the sarcoplasmic reticulum.
what is oxygen debt
- occurs during anaerobic activity
- extra O2 is needed to replenish glycogen, creatine phosphate stores and to convert lactic acid to pyruvate
what are the smooth muscle organs
blood vessels, gastrointestinal & urinary tract, respiratory tract, and reproductive system
what is the function of blood vessels
regulate blood flow and pressure and regulate filtration in kidneys
what is the function of the gastrointestinal and urinary tracts
regulate movement along internal passages
what is the function of the respiratory tract
alters diameter of airways
what is the function of the reproductive system
movement of sperm , oocytes, and delivery of fetus
What is the structure of smooth muscle
small spindle-shaped cells single central nucleus no striations smaller than skeletal muscle cells less developed sarcoplasmic reticulum no sarcomeres, myofibrils, or T tubules the plasma membrane has alveoli which allow rapid entry of Ca2+ from the extracellular fluid
what are the layers in smooth muscle
Circular muscle layer
Longitudinal muscle layer
what is a circular muscle
- cells run circumferentially around an organ
- contractions reduce diameter if lumen of organ
what is longitudinal muscle
- cells run in the longitudinal axis of an organ
- contractions reduce the length of the organ
what is the nerve supply of smooth muscle
- no neuromuscular junctions
- innervated by autonomic NS
- axons of nerves innervating
smooth muscle have swellings
(varicosities) that contain
neurotransmitters
what are the mechanisms of contraction for smooth muscle
- Ca2+ (mainly from ECF) binds to and activates calmodulin
- Activated calmodulin activates myosin (light chain) kinase (MLCK)
- MLCK phosphorylates and activates myosin
- Cross bridges interact with actin
- When intracellular Ca2+ levels drop - relaxation
what is the regulation of smooth muscle contraction
By nerves, hormones, and local chemical changes
What is neural regulation
- Neurotransmitter binding causes an increase in [Ca2+] in sarcoplasm; either graded potential or action potential
- The response depends on neurotransmitter and type of receptor molecules (G-Protein coupled receptors)
How do hormones regulate smooth muscle contraction
- Some smooth muscle cells have no nerve supply
- Depolarise in response to chemical stimuli that bind to G protein-linked receptors
- Chemical factors include hormones, CO2, pH
what are the special features of smooth muscle contraction
- active relaxation
- stress-relaxation response
- hyperplasia
what is active relaxation
Nerve or chemical stimuli can contract or relax because myosin heads are orientated in one direction on one side and a different on the other side
what is a stress-relaxation response
- Responds to stretch only briefly, then adapts to the new length
- Retains ability to contract on demand
- Enables organs such as the stomach and bladder to temporarily store contents
What is hyperplasia
smooth muscle can divide and increase numbers
