FINAL EXAM Flashcards
Define Neuromuscular fatigue
A failure to maintain the required force during a given task;
An exercise-induced decline in maximal muscle force or power production capacity
Perceived vs. performance fatiguability
Fatigue is used to describe a non-specific but debilitating symptom in a range of chronic diseases and disorders such as cancer
Perceived fatiguability
- homeostasis
- psychological state
Performance fatiguability
- contractile function
- muscle activation
Components of the neuromuscular system
Central NS:
- Motor planning
- Motor ‘cortical’ output
- corticospinal conduction
- motoneurone pool output
Peripheral NS:
- motor axon conduction
- Neuromuscular junction
- sarcolemma and T-tubule conduction
- E-C coupling and calcium release/reuptake
- Cross bridge force and ATP hydrolysis
Motor unit
Makes up the functional unit of the movements
Consists of an alpha motoneurone and the specific muscle fibers that it innervates
Difference in muscle fiber-motor unit ratio (e.g. 1:5 or 1:800) contributes to variation in motor skills
All or None principle: All of the muscle fibers innervated in a motor neuron are stimulated to contract
Neuromuscular junction (Motor endplate)
Presynaptic terminal
Synaptic cleft
Postsynaptic terminal
Synaptic vesicles
Acetylcholine
Process of sliding filament theory
- Myosin heads split ATP and become reoriented and energized
- Myosin heads bind to actin, forming cross bridges
- Myosin cross bridges rotate toward centre of the sarcomere (power stroke)
- As myosin heads bind ATP, the cross bridges detach from actin
contraction cycle continues if ATP is available and Ca2+ level in the sarcoplasm is high
Process of muscle contraction
Motor unit sizes and characteristics
Large motor neurones with fast conduction velocity innervate fast-fatigable (FF) and fast fatigue-resistant (FR) muscle fibers.
Smaller motor neurones with slow conduction velocity innervate slow (S) muscle fibers
FF – type IIx muscle fibers
FR – type IIa muscle fibers
S–Type I
Surgically innervating FF muscle fibers with the neurons from a slow-twitch muscle fiber eventually alters the twitch characteristics of FF motor unit.
Central vs Peripheral fatigue
Central fatigue:
With exercise, metabolites activate sensory afferent neurones (group III/IV afferent) which in return convey pain- and fatigue-related sensory signals to the brain
- The brain region related to fatigue and pain sensations will be activated and the brain sends fewer voluntary motor signals to the skeletal muscles
Peripheral fatigue:
- muscle fatigue after exercise
Higher intensity exercises (short duration) result in more peripheral fatigue
Lower intensity exercise (longer duration) result in more central fatigue
Components of maximal voluntary activation (MVC):
SIT (Superimposed twitch)
= relies on the twitch force added by a supramaximal motor nerve stimulus during a voluntary contraction
Resting Twitch
= A first stimulus delivered with the muscle fully relaxed
How do we measure MVC?
Twitch Interpolation technique
The amount (grams) of glycogen and glucose in the liver, muscle and blood
Liver glycogen - 110g
Muscle glycogen - 500g
Glucose in the blood and cell - 15g
The process of oxygen delivery
The respiratory system ensures the delivery of oxygen from the environment into the alveoli and the bloodstream and the elimination of carbon dioxide from the blood into the alveoli and the environment (gas exchange).
The oxygenated arterial blood is pumped by the heart to the mitochondria of the skeletal muscles.
The process of oxygen diffusion
Gas exchange between the alveoli in the lung and the pulmonary capillary blood and the capillary blood and the mitochondria of the skeletal muscles is driven by gas (oxygen and carbon dioxide) pressure differences (diffusion)
The process of oxygen perfusion
Functionally, the heart is two separate pumps:
Right side:
— Atrium receives deoxygenated blood from body
— Ventricle pumps deoxygenated blood to lungs
Left side:
— Atrium receives oxygenated blood from lungs
— Ventricle pumps oxygenated blood to body
The process of oxygen of gas exchange
Exchange of gases (O2 and CO2):
— O2 is moved from the environment to the mitochondria
— CO2 is moved from the mitochondria to the environment
What is the contribution of hemoglobin in oxygen transfer?
Oxygen is carried in two forms
- Dissolved in the fluid of blood
— Very little O2 is transported in solution (Poor solubility)
~4% of O2 consumption at rest
Oxygen transport in blood - Bound to hemoglobin
— Responsible for majority of blood transport
- Each hemoglobin can bind 4 O2 molecules
~96% of O2 consumption at rest
Oxygen-carrying capacity of hemoglobin (mL O2/L blood)
— Hemoglobin concentration (g/L blood)
— Oxygen capacity of hemoglobin (mL O2/g)
- 1.34 mL O2/g
The effect of training on mitochondrial content and volume density
Mitochondria density is increased by training:
1 month of training
— 2 hours/day, every day
— Increased mitochondrial volume density (electron microscopy)
