Motor Units and Skeletal Muscle Flashcards
What makes the muscle cell unique from the rest of the cells in the body?
Myofibrils
What transmits force from the connective tissue to the muscle tendon?
Fascia layers (endomysium, perimysium, epimysium, deep fascia)
Myofibrils contain what myofilaments?
Actin & Myosin
What is the chemical composition of a muscle fiber?
75% water
20% protein
5% other
What makes up the “other” 5% of a muscle fiber?
sodium, potassium, chloride ATP Urea Lactate Calcium, magnesium, phosphorus amino acids, fats, carbohydrates
Urea is a byproduct of what?
protein metabolism
each muscle fiber is innervated by what?
specific motor neuron
What is the difference between primary motor neurons and secondary or alpha motor neurons?
- Alpha motor neurons are innervated by primary motor neuron from the cortex, sensory neurons, interneurons
- each alpha motor neuron has ONE axon that branches into a number of axon terminals that terminate on muscle fibers
Definition of a motor unit?
the alpha motor neuron and all the muscle fibers it innervates
What concept does the size principle relate to?
activate small to large Motor unit size
What happens when a motor unit fires?
all the muscle fibers that it innervates contract - all or none principle
What allows for multiple alpha motor neurons to activate at one time?
motor neuron pooling - grouping of motor neurons in the ventral horn of the spinal cord
What happens to blood flow when the muscle contracts?
muscle contraction decrease blood flow, relaxation increases the blood flow to the muscle fiber
Power/high intensity contraction (> 80%) sustained for several seconds will use high energy phosphates and what kind of metabolism for the muscle effort (initial movement)?
glycolytic metabolism (lack of oxygen)
Can blood flow to the muscle increase? If so, how?
Yes, vascular growth can happen from stretch and sheer stress
Endurance athletes have how many capillaries around each muscle fiber?
5-7 capillaries (40% higher than untrained individuals)
Fuel source?
glucose
Glucose that goes through glycolysis moves forward into what?
Krebs cycle and electron transport chain
Glycerol moves forward into what?
glycolysis
Fatty acids must go through what cycle before they enter the Krebs cycle?
beta oxidation cycle
what occurs with a greater oxygen demand?
an increase in the number of capillaries needed (training effect)
Fiber number is largely fixed by what trimester of fetal development?
second
what is the cell membrane of the muscle fiber?
sarcolemma
What allows for hypertrophy or enlargement of the muscle fiber itself?
Satellite cells of the basement membrane of the sarcolemma
what are the important components of a muscle fiber? (3)
- glycosomes
- myoglobin
- high energy phosphates
What is another word for the cytoplasm of the skeletal muscle?
sarcoplasm
what is the oxygen binding protein that helps facilitate uptake and utilization of oxygen during metabolic activity?
myoglobin
Function of glycosomes?
allow storage of glycogen for anaerobic activity
Functional significance of a sarcomere?
contains myofilaments (actin and myosin) that contract together
What protein physically binds actin and myosin of the sarcomere?
Titin
What protein keeps passive stiffness of sarcomere and limits its ROM?
Titin
Is the electrical signal from a motor neuron sent directly to the actin and myosin in the muscle cell to achieve a muscle contraction?
No, action potentials get sent down the sarcolemma and the t-tubules that stimulate the release of calcium by the sarcoplasmic reticulum and allow binding of calcium on the actin filaments.
What is the large sac or vesicle called that surrounds each myofibril?
Sarcoplasmic reticulum
What unique structure have special extensions of the sarcolemma or cell membrane of the muscle fiber?
T-tubules
What do t-tubules stimulate the release of to allow for binding of the myosin and actin myofilaments?
Calcium
What conducts nerve-initiated AP deep into fiber to myofibril?
T-tubules
Motor neurons that are selectively activated in prolonged and lower intensity aerobic activities
Slow oxidative
Motor neurons that are activated during fast shortening but also longer duration intense activity
Fast oxidative glycolytic
Motor neurons activated during rapid shortening velocity (typically type II fibers)
Fast glycolytic