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96 Cards in this Set
- Front
- Back
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What is a motor unit? |
The alpha motor neuron and the muscle fibres it innervates. |
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The order of motor unit recruitment during a skeletalmuscle contraction of increasing force is:
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Type I, type IIa, type IIx
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Force production by a skeletal muscle can be increased by:
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A. Recruiting more motor units
B. Increasing the frequency of stimulation of amotor unit by the α-motor neuron C. Setting the muscle at its optimal length |
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What are type I, II, and IIx fibres also known as? |
Type I: slow twitch, or oxidative
Type II: fast twitch, or fast oxidative/gylocolytic (FOG) Type IIx: fast glycolytic (FG) |
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What is the name of the neurotransmitter released by the alpha motor neuron? |
ACh, acetylcholine |
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What does ACh bind to? |
Receptors on the sarcolemma |
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What happens if enough ACh is released? |
An action potential is transmitted the full length of the muscle fibre
The action potential triggers Ca2+release from SR Ca2+ binds to troponin on actin filament Troponin pulls tropomyosin, exposing actin binding sites Myosin heads attach to actin binding sites Myosin head undergoes power stroke pulling actin toward centre of sarcomere |
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Explain how carbohydrates are used by the body: |
- Converted to glucose
- Glucose taken up by muscles and liver and converted to glycogen, stored in the cytoplasm of muscle cells available to make ATP - Converted to glucose as needed and released into blood for uptake by other tissues |
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How much glycogen is available for moderate-high intensity exercise? |
About 90 minutes worth |
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What sort of activity level uses fat stores as a primary source of energy, and why? |
Prolonged, low-level activity, as there are a larger number of steps in metabolic pathway which contributes to slow energy yield |
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How is fat stored and then broken down to be used? |
It is stored in triglycerides and then broken down to free fatty acids. |
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What percentage of energy does protein supply during prolonged exercise? |
5-10%
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What are proteins broken down into during metabolism?
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Amino acids. The amino acids enter metabolic pathways at different points depending on which amino acid is being metabolised. |
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What are the 3 energy systems which generate ATP? |
1. ATP-PCr system
2. Glycolytic system 3. Oxidative system |
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How long can the ATP-PCr system fuel activity, and how does it work? |
- 10-15 seconds - There are small amounts of ATP and PCr stored in skeletal muscle fibres. - When ATP is broken down into ADP + P, ATP is regenerated by the breakdown of PCr - This is anaerobic |
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How long can ATP-PCr and glycolysis fuel amximal intensity exercise, and how does glycolysis work? |
ATP-PCr and glycolysis: about 2 minutes
- Requires10-11 enzymatic reactions to break down glucose/glycogen to pyruvate - Occursin the cytoplasm - Glycolysisis anaerobic - Pyruvatecan be converted to lactic acid - Netgain of 2-3 ATP |
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What are the steps in oxidation of fat? |
- Triglycerides are broken down into free fatty acids and glycerol - Free fatty acids are taken up by the muscle fibres and broken down into acetic acid in the mitochondria, which is converted to acetyl CoA through beta-oxidation - Acetyl CoA enters the Krebs cycle & electron transport chain |
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Why does fat oxidation require more oxygen than glucose? |
Free fatty acid molecules are more highly reduced |
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What is the nitrogen in amino acids converted to, and what does this require? |
The nitrogen is converted into amino acids, this requires ATP |
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Steroid hormones and non-steroid hormones are lipid soluble or not lipid soluble? |
Steroid hormones: lipid soluble Non-steroid hormones: not lipid soluble |
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How does a steroid hormone elicit a response? |
Via its effects on gene activation, which increase protein synthesis |
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How does a non-steroid hormone elicit a response? |
Via second messenger systems, as it cannot pass through the cell membrane. This can promote protein synthesis, change cellular metabolism and stimulate cellular secretions. |
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What are 4 hormones involved in regulating glucose metabolism during exercise? |
Glucagon: promotes glycogenolysis in the liver, and gluconeogenesis from amino acids Epinephrine & norepinephrine: promotes glycogenolysis Cortisol: promotes protein catabolism |
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How is the glucose uptake by the muscle maintained during exercise despite insulin levels decreasing? |
- increased plasma glucose concentrations - increased non-insulin mediated glucose uptake - muscle contraction stimulates increased insertion of GLUT4 receptors in the muscle fibre membrane |
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Which hormones trigger lipolysis in exercise: |
- decreased insulin - epinephrine & norepinephrine - cortisol - growth hormone - |
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The peripheral nervous system is divided into: |
Afferent (sensory) and efferent (effector) |
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The efferent nervous system is divided into: |
Autonomic and somatic |
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The autonomic nervous system is divided into: |
Sympathetic (fight or flight) and parasympathetic (rest and digest) |
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What is a nerve impulse? |
The signal which passes from one neuron to another, eventually to an end organ (e.g. group of muscle fibres) or back to the CNS |
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What is the resting membrane potential? |
- Difference between the electrical charges on either side of the cell membrane. - Higher concentration of K+ inside the neuron, higher concentration of Na+ outside the neuron, maintained by sodium-potassium pump. - RMP maintained at -70 mV |
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What is depolarization? |
Inside of cell becomes less negative (>-70 mV) due to change in the membrane's Na+ permeability |
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What is hyperpolarization? |
Inside of cell becomes more negative (<-70 mV) |
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What are graded potentials? |
Localized changes in membrane potential (depolarization or hyperpolarization) |
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What is an action potential? |
Rapid, substantial depolarization of the cell membrane to +30 mV Requires depolarization to -55mV Once this is met or exceeded, all or none principle applies |
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What does the speed of propogation of the action potential depend on? |
Diameter and myelination of the axon
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What are the 5 events of the action potential? |
1. Resting state 2. Depolarization 3. Propagation of action potential 4. Repolarization 5. Return to resting state wit help of sodium-potassium pump |
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What is the synapse, and what occurs at it? |
Site of impulse transmission from one neuron to another - Impulse travels to presynaptic axon terminal - Causesrelease of neurotransmitters into synaptic cleft - Neurotransmittersbind to receptors on postsynaptic neuron |
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Which neurotransmitter is released at the axon terminal at a neuromuscular junction, and what does it do? |
ACh/acetylcholine, • the ACh travels across the synaptic cleft to bindto receptors on a muscle fibre membrane•Neurotransmitterbinding causes depolarization, and once threshold is reached, an action potential occurs |
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What do the primary motor cortex and pre-motor cortex control? |
Primary motor cortex: fine and discrete muscle movement Pre-motor cortex: learned motor skills of a repetitious pattern |
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What does the basal ganglia control: |
Movement of a repetitious and sustained nature (e.g. walking) |
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What does the cerebellum control: |
Facilitates and regulates movement by making postural adjustments and modulating commands based on sensory feedback. |
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Skeletal muscles are the target of which nervous system? |
The somatic nervous system |
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What are direct and indirect calorimetry? |
Direct: measures body's heat production to estimate energy expenditure Indirect: calculates energy expenditure from ratio of CO2 produced to O2 consumed |
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What is the respiratory exchange ratio (RER)? |
The ratio of CO2 produced (VCO2) to O2 consumed (VO2) RER = VCO2/VO2 |
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What is the typical RER at rest? |
0.78-0.8 |
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What is basal metabolic rate? |
Minimum amount of energy required for sustaining basic cellular function. |
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How long does it take to reach a steady state of VO2 during exercise at constant power? |
1-2 minutes |
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What is the oxygen deficit? |
The difference between the oxygen required and the oxygen consumed during the first few minutes of exercise |
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What is EPOC, what can it be used to calculate? |
Excess post-exercise consumption, can be used to calculate anaerobic effort. |
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What factors are responsible for EPOC? |
- Rebuilding depleted ATP and PCr supplies - Clearing lactate from anaerobic metabolism - Replenishing O2 borrowed from hemoglobin & myoglobin - Removing accumulation of CO2 in tissues (extra ventilation required) - Increased metabolic/respiratory rates due to increased body temperature |
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What is VO2 max? |
The maximal capacity for oxygen consumption during maximal exertion Best indication of cardiorespiratory endurance & aerobic fitness |
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What is the lactate threshold? |
- The point at which blood lactate begins to accumulate above resting concentrations during exercise of increasing intensity
- Represents point at which lactate production exceeds lactate clearance |
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Name the main causes of fatigue: |
- Depletion of fuel for energy delivery (ATP-PCr, anaerobic glycolysis, and oxidation)
- Increased temperature - Accumulation of metabolic by-products, suchas lactate and H+ - Failure of muscle fibre's contractile mechanism - Alteration in the nervous system |
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What is an explanation for the increased rate of glycogen depletion during exercise in the heat? |
Increased epinephrine secretion |
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What are the main two metabolic by-products produced in short duration high intensity exercise? |
Lactate and H+ |
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What happens when blood pH reaches: a) <6.9 b) 6.4 |
pH lower than 6.9 slows glycolysis and ATP production At a pH of 6.4, H+ ions inhibit glycolysis and results in exhaustion |
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6 possible causes for neuromuscular fatigue: |
1. Decreased release/synthesis of acetylcholine 2. Hyperactive/hypoactive acetylcholinesterase 3. Potassium leaves intracellular space, decreasing membrane potential below resting values, increases threshold for stimulation of muscle fibre 4. Competition with ACh for receptors on muscle fibre membrane 5. Calcium retention in SR 6. Central nervous system fatigue/cardiac autonomic fatigue |
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During high intensity exercise lastingapproximately 2-3 minutes in duration fatigue is most likely to be caused by:
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Accumulation of metabolic by-products such as lactic acid and H+
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Which ventricle increases in size with exercise training? |
The left ventricle |
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Which 4 structures are involved in the intrinsic control of the heart? |
- Sinoatrial (SA) node
- Atrioventricular (AV) node - AV bundle (bundle of His) - Purkinje fibers |
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How does the parasympathetic nervous system control the heart? |
- Acts through the vagus nerve - Releases ACh which decreases HR and the force of contraction |
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How does the sympathetic nervous system control the heart? |
- Cardio-accelerator nerves release norepinephrine, increases HR and force of contraction - Stimulates release of epinephrine and norepinephrine from medulla, further increases HR/force of contraction |
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What heart rate does the vagus nerve maintain, and what heart rate does the sympathetic nervous system maintain? |
Vagus nerve - below approx. 100 Sympathetic nervous system - above approx. 100 |
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What is stroke volume? |
- Volume of blood pumped per contraction - SV = EDV - ESV EDV = volume of blood in ventricle just before contraction ESV = volume of blood in ventricle just after contraction |
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What is cardiac output (Q)? |
Cardiac output is the volume of blood pumped by the ventricle per minute. Q = HR x SV |
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What is the equation for resistance to blood flow? |
Resistance to blood flow = [ηL / r4], –η= viscosity of the blood –L =length of the vessel –r4 =radius of the vessel to the 4thpower |
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How is blood flow controlled extrinsically? |
- Vasoconstriction caused by increased sympathetic nervous system activity - There is no parasympathetic innervation of blood vessels - Vasodilation caused by decreased sympathetic nervous system activity |
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3 metabolic factors which stimulate intrinsically controlled increased local blood flow? |
- Increased oxygen demand - Increased metabolic by-products - Inflammatory chemicals |
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3 endothelium-released factors which stimulate intrinsically controlled increased local blood flow? |
- Nitric oxide - Prostaglandins - Endothelium-derived hyperpolarization factors (EDHF) |
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Other than metabolic and endothelium-released factors, what else can stimulate intrinsically controlled increased local blood flow? |
Myogenic responses |
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How is blood returned to the heart? |
- Valves in the veins - Muscle pump - Respiratory pump |
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What is haematocrit? |
The ratio of formed elements to total blood volume |
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What does higher haematocrit result in? |
- Increased oxygen carrying capacity - Increased resistance to blood flow due to higher blood viscosity |
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What effect will acute exercise have on hemoconcentration? |
Will increase hemoconcentration |
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How will training effect blood viscosity/oxygen carrying capacity? |
IncreasedRBC and plasma with training results in increased oxygen carrying capacity withlower viscosity |
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4 processes in the respiratory system: |
1. Pulmonary ventilation 2. Pulmonary diffusion 3. Transport of gases via blood 4. Capillary diffusion |
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How does inspiration occur? |
- Diaphragm and external intercostals contract - Increases lung volume, decreases pressure - Air moves down pressure gradient into lungs - Forced inspiration also uses scalenes, sternocleidomastoid, pectorals |
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How does expiration occur? |
- Usually passive - Muscles of inspiration relax - Long volume decreases, pressure increases - In forced expiration, internal intercostals, abdominals, latissimus dorsi, quadratus lumborum contract |
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What is respiratory pump? |
- Changing pressures during inspiration and expiration which assist venous return - increases during exercise |
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What is pulmonary diffusion, and what are its two functions? |
- gases exchanged between the alveoli and capillaries - replenishes blood oxygen supply - removes carbon dioxide from the blood |
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What is the respiratory membrane? |
The surface across which gases are exchanged - approx 300 million alveoli - 0.5-4mm |
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What is the partial pressure gradient? |
Atmospheric pressure x fractional concentration of each gas |
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What determines the rate of diffusion of gases in the alveoli? |
- partial pressure gradient - surface area (smaller at rest, during exercise capillaries are more open and perfusion is increased) - diffusion constant (CO2 has diffusion constant 20x greater than O2, so diffuses faster despite lower partial pressure gradient) |
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How much oxygen can blood carry per 100mL, and what percentage is carried by what? |
20mL of O2 per 100 mL 98% bound to hemoglobin, 2% dissolved in plasma |
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What are 3 factors affecting hemoglobin concentration? |
- partial pressure of O2 - blood pH - blood temperature |
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How is carbon dioxide transported in the blood? |
- 60-70% as bicarbonate ions - 7-10% as plasma - 20-33% bound to Hb (carbaminohemoglobin) |
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What triggers the Bohr effect in carbon dioxide transport? |
The carbonic anhydrase reaction in the RBC converts CO2 to bicarbonate and H+ ions. This lowers the pH and causes the Bohr effect of more oxygen being released |
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What happens when the PCO2 is low in the lungs? |
CO2 comes out of solution and diffuses out in the alveoli |
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What part of hemoglobin do CO2 and O2 bind to? |
O2 binds to 'heme' portion, CO2 binds to protein ('globin') portion |
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Does oxygenated hemoglobin bind CO2 more or less easily? |
Less easily, which promotes release of CO2 in the lungs when O2 binds |
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What causes the (a-v)O2 difference? |
Tissue O2 extraction |
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What is the approximate mixed venous O2 at rest vs. during heavy exercise? |
Rest: 15/16 mL per 100 mL Exercise: 4-5 mL per 100 mL |
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What determines the rate of O2 exchange? |
- local differences in partial pressure - local conditions (pH, temperature) |
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How does CO2 exit the cells in the tissues? |
Diffusion, driven by PCO2 gradient |
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What regulates involuntary pulmonary ventilation? |
- Inspiratory and expiratory centers in medulla/pons - Overriden by cortex if necessary |
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What detects increased levels of CO2? |
- Central chemoreceptors in the cerebrospinal fluid detect increased CO2, and trigger an increased rate and depth of breathing - Peripheral chemoreceptors in aortic/carotid bodies sensitive to blood PO2, PCO2 & H+ - Mechanoreceptors detect excessive stretch in pleurae, bronchioles & alveoli (excessive stretch triggers reduced breathing rate - Hering-Breuer reflex) |
