Physiology Block 3 Week 17 19 Exercise Flashcards
Essential aspects in mobilization
communication, energy production, and transportation.
a) the brain must stimulate muscles for coordinated contractions
b) fuel must be made available for the energy needed for muscle contractions
c) oxygen must be provided and waste products must be eliminated.
Where do commands for voluntary movement originate from?
Cortical associate areas
What parts of the brain plan voluntary movements?
The cortex, basal ganglia, and cerebellum work cooperatively to plan movements.
Basal ganglia and cerebellum are part of a feedback circuit concerned with planning and organizing voluntary movement
What feedback does the cerebellum provide in movements?
Feedback to adjust and smooth movements
How are movements from the cortex relayed to muscles?
Executed by the motor cortex thru impulses via corticospinal tracts to spinal motor neurons
Supplementary motor area
involved in organizing or planning particularly complex movement.
Premotor area
setting posture at the start of movement or in control of proximal limb muscles needed to orient the body for movement.
How is the complexity of movement distributed amongst the areas of the cortex?
31% of corticospinal tract neurons are from the primary motor cortex
29% from the premotor and supplementary motor cortex
the remaining 40% from neurons in the primary somatic sensory cortex and posterior parietal cortex
This distribution is indicative of the complexity and multiple muscles that need to be activated for coordinated/smooth movements.
Regions of the human cerebral cortex and other areas concerned with control of voluntary movement
Prefrontal Cortex
Premotor Cortex
Supplementary Motor Area
Motor Cortex
Primary Somatic Sensory Cortex
Posterior Parietal Cortex
Damage to cerebellum leads to?
Ataxia and tremors
Cerebellum provides coordinated muscle activity through input from the contracting muscles and then relaying signals to the primary motor cortex
Basal ganglia are composed of several nuclei and three major biochemical pathways that influence the motor cortex via thalamus
Dopaminergic
Cholinergic
GABAergic
Disease of these pathways lead to hyperkietic (Parkinson’s) or hypokinetic muscle conditions
How can contractile muscle strength be increased?
Contractile muscle strength
can be increased by increasing muscle size through exercise training programs and through the action of anabolic steroids such as testosterone.
Work performed by muscles
Force applied x distance force applied
Power vs strength
Power is work over period of time
Is power output greater during a 100 m dash or running a mile?
100 m dash
Maximal power out declines with duration of muscle contraction
Endurance
time a task can be sustained before exhaustion
Determinant of endurance is glycogen stores in muscle from one’s diet
High carb diet: high glycogen stores (40 g/Kg)
Mixed diet: 20 g/Kg
High fat: 6g/Kg
Why is ATP a good source of energy?
- The last 2 phosphate bonds are high energy
- Only good for 3 seconds of maximal muscle power
- need continuous supply of ATP
Phosphocreatine
Broken down into creatine and phosphate
Muscles have 2-4x more stored than ATP
Phosophagen Energy System
Phosphocreatine and ATP energy storage
Sufficient to provide E for a power event like 100m dash
Glycogen-Lactic Acid System
Anaerobic Metabolism: If oxygen is not available, pyruvic acid is converted to lactic acid which diffuses out of the muscle.
Maximum muscle activity for about 1.5 minutes
Important at work rates greater than about 60% of maximal oxygen consumption
How are high work rates achieved?
Oxygen consumption is proportional to the work load, but there is a maximal capability to provide energy through the oxidative pathway
High work rates are achieved by large increases in contribution from the lactic acid pathway
Aerobic System
oxidation of foodstuffs in mitochondria where glucose, fatty acids, and amino acids are broken down to release energy and form ATP
Supply energy as long as nutrients are available
–provides for endurance of the muscles.
The oxidative pathway provides 32 ATP molecules/molecule of glucose.
Availability of nutrients is enhanced by increased epinephrine during exercise thereby increasing glucose output from the liver and fatty acid output from adipose tissue.
Relative Moles of ATP generated
Phosphagen System
Glycogen-Lactic Acid System
Aerobic System
Phosphagen System: 4
Glycogen-Lactic Acid System: 2.5
Aerobic System: 1
Oxygen Debt
Oxygen consumption remains elevated after exercise to reconstitute (build up) the phosphagen system and convert lactic acid to glucose.
As work rate increases, what happens to:
- VO2
- CO
- HR
- SV
VO2, CO, and HR increase linearly until 60% of maximal exercise due to max SV
Thus, further increases in cardiac output are dependent on increases in heart rate
During exercise, what happens to blood pressure and TPR?
Systolic: Large Increases
Diastolic: very small increase
TPR: Dramatic decrease
The increase in systolic pressure and decrease in TPR is from vasodilation increasing flow to the muscles
Rhythmic due to capillary compression during muscle contraction
How does CO (flow) to change from rest to exercise in:
- muscle
- brain
- abdomen
- kidney
- skin
- heart
Increased: Muscle
Decreased: Brain, Abdomen, Kidney
Unchanged: Skin and Heart
Exercise Centers
In the cerebral cortex
Increase sympathetic/ dec parasympathetic output to the heart and blood vessels
Increase baroreceptor reflex set point via the medullary cardiovascular nuclei
***symp vasoconstriction to non-exercising vascular beds (GI and Kidneys)
***local vasodilation in muscles
During exercise, how does ventilation change at:
- -up to 60% max
- -intense exercise
- -low work rate
60% max: ventilation increases in proportion to metabolic rate
High intensity exercise: hyperventilation–indicates increasing more than metabolic rate
Low work rate: increased ventilation due to increased tidal volume
–more fresh air to lungs with each breath (decreased dead space: tidal volume)
At high TV, lung compliance decreases
–to increase ventilation, increase breathing frequency
Exercise on arterial blood gases
Signal for hypercapnea not from increased stimulation of carotid and intracranial chemoreceptors
Above 60% max: lacacidosis and hyperventilation
Ventilation (atmospheric to alveolar gas exchange) and Diffusion (alveolar to capillary gas exchange) increases with exercise
The increase in diffusion is due to recruitment of alveolar capillary units which increases the surface area for gas exchange.
The increase in the alveolar-capillary PO2 difference at high workloads = hyperventilation and failure of diffusing capacity to increase by the same amount.
The increase in PAO2 provides increased driving pressure for diffusion of oxygen.
Why is pulmonary capillary dilation important in exercise?
The need for gas exchange is greatly increased since arterial-venous (mixed venous) PO2 difference increases
–Exercise MV PO2 «_space;Rest MV PO2
The pulmonary capillaries will dilate so blood remains in lung for longer duration for more extraction
What causes greater extraction of oxygen during exercise to tissues?
This greater extraction of oxygen during exercise is a result of decreased hemoglobin affinity for oxygen
Increases the driving pressure of oxygen from the capillaries to the tissue
Vasodilation in the muscles causes a greater cardiac output delivered to tissues with a high metabolic rate
How much energy released by ATP during exercise is converted to work?
25%, therefore 75% converted into heat
The body will retain some heat and allow the body temp to increase
Ways to lose heat
Vasodilation of arterioles in the skin
Sweating (increased symp innervation to sweat glands)
Temperature controlled by thermoreceptors in skin (environmental temp) and hypothalamus (body temp)
Hydration and electrolyte balance
Neuroendocrine responses to exercise
Increased GH and cortisol after exercise
–tissue repair
Catecholamines (Epi and NE)
–liver release of glucose and adipose release of fatty acid to maintain ATP (glucagon); suppressed insulin
Opiods (endorphins)
–runner’s high
What contributes to increasing maximal oxygen consumption during physical training?
The amount of increase is related to the intensity and duration of the exercise program
Contributing to the increase in maximum oxygen consumption:
-Increased CO secondary to increased in SV and HR
- Enhanced heart performance due to:
- -increase muscle and myocyte site
- -increased vascularization
Increased vascularization of skeletal muscle:
- -enhances delivery of blood
- -reduce the distance for gas diffusion between vasculature and muscle
Training enhances endocrine, thermoregulatory, and metabolic responses
- -enhance mobilization of glucose and fatty acids
- -elimination of heat
Does training enhance the respiratory system?
Other than training of the respiratory muscles, there is little evidence that training enhances the respiratory system.
Limiting Factors to maximal oxygen consumption
Cardiovascular system’s capability to deliver oxygen
Capability of muscle to extract oxygen
Respiratory muscles “steal oxygen” from locomotor muscles
Fatigue
Fatigue limiting work performance is a decrease in work capacity due to work itself.
Also induced by (mental) boredom/staleness, drugs, and illness.
8 hours of office work fatigue is different from 8 hours of heavy construction work
Physical fatigue can be due to:
a) depletion of energy stores
b) accumulation of metabolic waste products
c) breakdown of homeostasis
Potential sites of work induced fatigue include the: a) muscle fiber
b) motor nerve and end plate
c) synapses within ganglia
d) the nerve cell body
e) sensory nerve ending
Motivation–limitations to exercise performance are dependent to some extent on tolerating and/or suppress sensations of fatigue and/or pain
Which of the following statements regarding the signal for limb movement during muscular exercise is INCORRECT?
the cerebral cortex, basal ganglia, and cerebellum collaborate to plan the movement.
the signal for the movement is relayed from the brain to the muscles through the corticospinal tract.
the cerebellum provides feedback to the motor cortex to adjust and smooth movement.
the primary motor cortex is the site from which all movement originates.
dopaminergic, cholinergic, and GABAergic systems in the basal ganglia influence the motor cortex through the thalamus.
the primary motor cortex is the site from which all movement originates
Pre-motor, motor, and intermediate cerebellum
A high carbohydrate diet would be most beneficial to which of the following?
An Olympic sprinter running 100 meters.
A weight lifter competing in the Olympics.
An emphysema patient fishing in a trout stream.
A middle-aged man running the Boston marathon.
A farmer with interstitial lung disease driving a tractor.
A middle-aged man running the Boston marathon.
Which of the following would be expected to decrease as a healthy untrained person undergoes an exercise-training program?
Resting stroke volume Resting cardiac output Resting heart rate Maximal oxygen uptake Maximal alveolar ventilation
Resting heart rate
